Classic Carboniferous Sections of the Minas and Cumberland Basins inNova Scotia
With Special Reference to Organic Deposits

The Society for Organic Petrology Annual Meeting Field Trip, 29-30 July, 1998

Nova Scotia Department of Natural Resources
Mineral Resources Branch
Open File Report ME 1998-5

Table of Contents

• Safety Measures for Coastal Sections and Quarries
• Acknowledgments
• Itinerary
• Introduction
• Geological Setting: the Maritimes Basin inEuramerica
• Late Paleozoic Stratigraphy of the Maritimes Basin in NovaScotia
• Stop 1: Falls Brook Quarry
• Stop 2: Horton Bluffs Coastal Section
• Stop 3: Cheverie Coastal Section
• Stop 4: Avonport Coastal Section
• Stop 5: Joggins Coastal Section
• Stop 6: West Bay Coastal Section
• References
• List of Figures

Safety Measures for Coastal Sections

The coastal exposures of Nova Scotian geology offer spectacular views but also somevery real hazards. Please read on.

TIDES:These geological sites witness the highest tides in the world.Consult tide tables or tide times published daily in most provincial newspapers before visitingthem. If none are available, you can gauge the time of the high tide approximately with thephase of the moon: at full (and new) moon, the tide is high roughly at noon.For mostcoastal sections, you should plan to depart two hours before high tide.Plan yourdeparture on the basis of how many hours after low tide the site became accessible. Low andhigh tides are separated by approximately 6.5 hours, with the high tide time advancing (later)by about an hour each day.

INTERTIDAL AREAS:Avoid muddy areas, especially in the lowerintertidal zone, where you can become stuck during a rising tide. Always be vigilant of therising tide behind you.

FOOTING:Intertidal rocks can be exceedingly slippery, resulting in aswift and unforgiving fall. Avoid damp rocks and in particular those with green algal growth(veryslippery).

CLIFFS:Never climb the cliffs:they are unstable and a fallcan be fatal.Stay back from the cliffsas much as possible: rock falls occur withoutwarning and can be fatal.

.... and wear a hard hat!

Acknowledgments

We would like to acknowledge the work of our various colleagues who are not authors ofthis guide, but who contributed to the ideas presented here through ongoing debate andexchange of thoughts. We are especially grateful to Doug MacDonald, who in two weeksperformed the tasks of editing the text, overseeing the drafting of figures, and printing thefield guide. Thanks to Barb MacDonald for desktop publishing under pressure. Robert Naylorkindly reviewed the field guide. Thanks to the Cartographic Section of the Nova ScotiaDepartment of Natural Resources and to Tanya Costain for their work on the figures.

TSOP '98 Field Trip Itinerary

Introduction

The Maritimes Basin of Nova Scotia offers a nearly complete stratal record of theCarboniferous Period, spectacularly exposed along continually eroding coastal sections. Onthis field trip, we will visit some of these classic exposures ( Fig. 1 ), with stops to examine each of the lithostratigraphic groups ( Fig. 2 ), with the exception of the redbeds of the uppermostPictou Group.

As we approach the end of the Twentieth Century, it is invigorating to see that theseclassic sections, long ago made famous by the likes of Sir William Dawson, Sir CharlesLyell, Sir William Logan, and Walter Bell, still can surprise and stimulate debate. It is safe tosay that as this field guide is being written, geologists are re-evaluating long-standing ideas,'facts' and models, with the fresh thinking that marked the work of our predecessors. One ofthese ideas involves reconsideration of the aquatic fossil record and its implications for ourinterpretations of the pre- and post-Viséan/Windsor basin fill. This fossil record hasbeen long held, perhaps dogmatically, to be strictly continental and devoid of marineinfluence (see Calder, 1998 and recent research cited therein). Accompanying and perhapsspurring this open mindedness has come a resurgence of hydrocarbon exploration. At each ofthe field stops, coal-bearing strata and hydrocarbon source and reservoir rocks areprominent.

In this field guide, stop descriptions have been contributed by the various stop leaders,with a concerted attempt at minimal editing, except where necessary for the continuity of theguide and a modicum of consistency. In this way, the various points of view of individualgeological colleagues hopefully remain. For any personal perspectives that may have crept into your stories, the first author offers his apologies! Much of the introductory geology in thefield guide has been borrowed liberally from the recent review of the Carboniferous evolutionof Nova Scotia by Calder (1998).

Summary of the Carboniferous of Nova Scotia (after Calder, 1998)

During the Carboniferous Nova Scotia lay at the heart of paleo-equatorial Euramerica in abroadly intermontane paleo-equatorial setting, the Maritimes-West European province; to thewest rose the orographic barrier imposed by the Appalachian Mountains and to the south andeast, the Mauritanide-Hercynide belt. The geological affinity of Nova Scotia for Europe,reflected in elements of the Carboniferous flora and fauna, was mirrored in the evolution ofgeological thought even before the epochal visits of Sir Charles Lyell.

The Maritimes Basin of eastern Canada, born of the Acadian-Caledonian orogeny thatwitnessed the suture of Iapetus in the Devonian, and shaped thereafter by the inexorableclosing of Gondwana and Laurasia, comprises a nearly complete stratal sequence as great as12 km thick that spans the Middle Devonian through Lower Permian. Across thesouthern Maritimes Basin, in northern Nova Scotia, deep depocentres developed en echelonadjacent to a transform platelet boundary between terranes of Avalon and Gondwananaffinity. The subsequent history of the basins can be summarized as distension and riftingattended by bimodal volcanism waning through the Dinantian, with marked transpression inthe Namurian and subsequent persistence of transcurrent movement linking Variscandeformation with Mauritanide-Appalachian convergence and Alleghenian thrusting. ThisMid-Carboniferous event is pivotal in the Carboniferous evolution of Nova Scotia. Rapidsubsidence adjacent to transcurrent faults in the early Westphalian was succeeded by thermalsag in the later Westphalian and ultimately by basin inversion andunroofing after the earlyPermian as equatorial Pangea finally assembled and subsequently rifted again in theTriassic.

The component Carboniferous basins have provided Nova Scotia with its most importantsource of mineral and energy resources for three centuries. Their combined basin fill sequencepreserves an exceptional record of the Carboniferous terrestrial ecosystems of paleo-equatorialEuramerica, interrupted only in the mid-late Viséan by the widespread marine depositsof the hypersaline Windsor gulf. Stratal cycles in the marine Windsor, schizohaline Mabou,and coastal plain to piedmont coal measures 'cyclothems' record Nova Scotia'spaleogeographic evolution and progressively waning marine influence. The semi-aridpaleoclimate of the late Dinantian grew abruptly more seasonally humid after the Namurianand gradually recurred by the Early Permian, mimicing a general Euramerican trend.Generally more continental and seasonal conditions prevailed than in contemporary basins tothe west of the Appalachians and, until the mid-Westphalian, to the east in Europe.Paleogeographic, paleoflow and faunal trends point to the existence of a Mid-Euramerican Seabetween the Maritimes and Europe that persisted throughthe Carboniferous. The faunal recordsuggests that cryptic expressions of its most landward transgressions can be recognized withinthe predominantly continental strata of Nova Scotia. The recognition of marine influence hasparticular implications for interpreting and predicting the composition and stratigraphicoccurrence of coal and hydrocarbon source rocks.

Geological Setting: The Maritimes Basin in Euramerica

The Carboniferous strata of Nova Scotia record most of the history of the larger, latePaleozoic Maritimes Basin (Williams, 1974) of New Brunswick, Nova Scotia, Prince EdwardIsland and Newfoundland ( Fig. 3 ). Late Paleozoic strata ofthe Maritimes Basin span the Middle Devonian (Dawson, 1862; McGregor, 1977;Forbeset al.,1979) through Early Permian (Dawson, 1891 and earlier;Barsset al.,1963) with remarkably few gaps. The Maritimes Basin is a complex ofpredominantly northeasterly trending intermontane basins, once variously interconnected andnow, as then, defined by intervening massifs of the Avalon, Grenville and Meguma terranes.The basin was born of the Devonian (Emsian) Acadian orogeny (Poole, 1967), contemporaryof the latest stage of the Caledonian orogeny, both of which record final closure of theIapetus Ocean (McKerrow, 1988). The Carboniferous evolution of the Maritimes Basin bearswitness to the nativity of Pangea as Gondwana and numerous platelets of suspect terranecollided with Laurasia and the Old Red Continent,manifested in the Hercynian andAlleghenian orogenies (Rast, 1988). Evolution of the Maritimes Basin during the lateDevonian and Dinantian records extension (McCutcheon and Robinson, 1987; Bradley, 1982;Hamblin and Rust, 1989), most pronounced between the Lubec-Belleisle, Cobequid andHollow faults, an area which has been termed the Maritimes Rift (Belt, 1969; van dePollet al.,1995). This was succeeded in the Silesian by transpression andtranstension in a renewed orogenic phase (Plint and van de Poll, 1984; Nance, 1987;Waldronet al.,1989; Yeo and Ruixiang, 1987) and broadly across the basin bythermal sag (Bradley, 1982) and ultimately in the Permo-Triassic, by inversion (Ryan andZentilli, 1993).

The late Paleozoic to Mesozoic rocks in Atlantic Canada record a complex history ofsedimentation, tectonics and volcanism in the northeast Appalachians. The strata within thesesuccessor basins reach a maximum thickness of 12 km in the central Gulf of St.Lawrence (Magdalen Basin). They are a complex molassic succession dominated bycontinental deposition. Sediments were derived both locally (especially in the Late Devonianand Early Carboniferous) and regionally (Late Carboniferous) from the Appalachian Orogen.These transient depocentres represent the waning stages of the Devonian Acadian orogeny andthe subsequent uplift of the orogen following the mid-Devonian docking of the AvalonComposite Terrane (Avalonia) and the Meguma Terrane. The early Mesozoic records theinitial rifting phase of the Proto-Atlantic Ocean and the late Mesozoic to Cenozoic itssubsequent opening.

The Late Devonian to Early Viséan was characterized by crustal instability withinitial molassic deposition of coarse- to fine-grained alluvial, fluvial, lacustrine and locallyrift-related volcanic deposition in intermontane basins (Fountain Lake Group and HortonGroup). Deposition occurred initially under dry (seasonal?) conditions (Late Devonian) thenhumid lateritic conditions. Extensive alluvial to fluvial-lacustrine deposition in the Tournaisianevolved through semi-arid dry conditions with local evaporitic lacustrine deposition andredbeds in the late Tournaisian to early Viséan (Horton Group).

Nova Scotia and the Maritimes Basin in the Carboniferous lay within paleo-equatorialEuramerica, drifting northward from a paleolatitude of South 12 degrees to cross the equatorby the beginning of the Permian (Scotese and McKerrow, 1990). Generally considered anorthern part of the Appalachian orogenic belt, the Maritimes Basin lay situated at thepaleosoutheastern margin of the Appalachians in a paleogeographic region distinct from theAppalachian Basin to the west ( Fig. 4 ). The mountain rangeposed an orographic climate barrier, drainage divide and phytogeographic barrier to bioticexchange between these two areas. No suchlandbarrier existed to the east,however, and Nova Scotia can be included with Britain and western Europe in a broadlyintermontane paleogeographic region of tropical paleolatitude lying to the east of theAppalachians, north of the Mauritanides, and west of the Urals, and traversed by theAcadian-Hercynide upland belt ( Fig. 4 ). This region wascalled the Maritime-West European Province by Calder (1998),modified after Leeder (1987),analogous to the Equatorial Low Latitude-Acadia phytogeographic unit of Rowleyetal.(1985). Even before the concept of continental drift, the close affinity of Nova Scotiafor western Europe and Britain in particular has been long known (Dawson, 1888; Bell, 1929,1944 among others).

Depocentres of the Maritimes Basin in Nova Scotia

The major basinal depocentres of the southern Maritimes Basin in Nova Scotia ( Fig. 3 ); after Calder, 1998, modified from Gibling, 1995, from westto east, are: (1) Cumberland Basin, (2) Minas Basin (including Windsor-Shubenacadie,Musquodoboit-Mahone Bay and depocentres along the southern Cobequids), (3) StellartonGap and Stellarton Basin, (4) Antigonish Basin, (5) Western Cape Breton, at the margin ofthe submarine Gulf of St. Lawrence, (6) Central Cape Breton, including Glengarry, LochLomond, Salmon River, and (7) Sydney Basin. Each of these component basins in turncomprises smaller depocentres, in part reflecting the anastomosing fault configurationgenerated by the transcurrent fault systems of the Maritimes Basin. The accruedCarboniferous fill of these component basins may reach 12 km in thickness (Belt,1968b). The reader is referred to Bell (1929, 1940, 1944; 1960), Belt (1965), Ryanetal.(1991), Williamset al.(1985) and to Gibling (1995) for comprehensivedetails of their stratigraphy. The component formations of the sixmain lithostratigraphicgroups are given in Table 1. This field trip examines classicsections in the first two of these component depocentres, the Cumberland and Minasbasins.

Late Paleozoic Stratigraphy of the Maritimes Basin in Nova Scotia

The first comprehensive account of the Carboniferous geology and mineral resources ofNova Scotia is that of Richard Brown (1829). Brown was employed by the London-basedGeneral Mining Association as manager of coal mining operations in the Sydney coalfield,Cape Breton County, from 1827 to 1864. An "experienced observer", as he wasrespectfully described by Sir Charles Lyell (1845, p. 206), Brown (1829) applied to theCarboniferous strata of Nova Scotia the then recently published stratigraphic nomenclature forBritain of Coneybeare and Phillips (1822). The early stratigraphic interpretation of Brown isstriking in its similarity to current subdivisions ( Table 1 ). Currentstratigraphic nomenclature has been adopted largely from Dawson (1878), who drew upon thework in the coalfields of his contemporaries McOuat and Robb at the Geological Survey ofCanada, and from the subsequently evolved nomenclature of Walter A. Bell (1929,1944) and Edward Belt (1964).

Bell (1929, 1940, 1944) established series for the Carboniferous strata of Nova Scotialargely on the basis of the macroflora (Calder, 1998, appendix A) and bivalve fauna (Calder,ibid., appendix B), which he correlated with equivalent European stages. The series of Bell,which established the age relationship of coal-bearing strata within the disjunct Carboniferousbasins, were subsequently adopted as the lithostratigraphic groups ( Fig. 2 and Table 1 ) shown below.

The diachronous nature of lithostratigraphic units in the Maritimes Basin was illustratedby the application of miospore biostratigraphy (Belt, 1964; Hacquebardet al.,1960;Barsset al.,1963). Problems inherent with the adoption of a lithostratigraphy bornof biostratigraphy have dogged virtually all subsequent stratigraphers. This inherentstratigraphic problem has been accommodated in part by the growing practice of assigningdiachronous coal measures within the disjunct coal basins to the Cumberland Group andsucceeding redbeds to the Pictou Group, as proposed by Ryanet al.(1991).

Because the biostratigraphy of the Carboniferous of the Maritimes Basin is rooted in theterrestrial fossil record, except during the mid to late Viséan ( Fig. 2 ), the effects of provincialism and paleogeography can beparticularly problematic in achieving precise correlations with stage boundaries based onmarine fauna elsewhere in Euramerica. The scarcity of recognized tonsteins (Lyonsetal.,1994) further stymies the use of absolute radiometric dates, which otherwise couldbe employed to assist in the resolution of chronostratigraphy.

Organic Deposits

Coal Deposits

With the exception of a few restricted beds in the Middle Devonian McAdam LakeFormation and Lower Carboniferous Horton Group, coal-bearing strata are assigned to thePennsylvanian Cumberland Group ( Fig. 2 ). Coal deposits ( Fig. 5 ) of (?late Namurian-) Westphalian A-C age developedas areally restricted rheotrophic mires, nourished through the dry season by supplementalgroundwater flow (Calder, 1994), were generated at piedmont margins (Springhill coalfield:Calder, 1994), in distributary (Joggins coalfield: Calder, ibid.) and lacustrine (Stellarton Basin:Calder, 1979; Hacquebard and Donaldson, 1969; Nayloret al.,1989; Waldron,1996) settings during regional transpression and transtension. The coal-bearing strata of theStellarton Basin in particular include sapropelic ('oil shale') deposits (Smith and Naylor,1992). Areally extensive mires developed in the Westphalian D-Cantabrian on upper coastalplains (Hacquebard and Donaldson, 1969; Gibling and Bird, 1994) during thermal sag. Theresulting coal deposits constitute the maineconomic seams of Nova Scotia, mined in collieriesof the Sydney Basin. These coal beds, in the past assigned either to the Morien or Pictougroups, may have attained a mesotrophic status if only through the increased, hence insular,area of the peatlands (Marchioniet al.,1994; Calderet al.,1996).

Table 1
Lithostratigraphic formations of late Paleozoic fill in the Maritimes Basin, Nova Scotia(after Calder, 1998).

Kinematic research into coal bed methane generation indicates that gas desorption in coalbeds of less than R_o0.9 may be impeded by microporeblockage by earlier-generated oil, but enhanced above that maturity by cracking of the oil(Mukhopadhyayet al.,1993). In all basins, rank increases within the bituminousrange with depth of burial (Hacquebard and Donaldson, 1970). Near the juncture of theHollow and Cobequid faults in the eastern Debert-Kemptown coalfield, rank attains a high ofsemi-anthracite.

Hydrocarbons

Hydrocarbon source rocks in of the Maritimes Basin in Nova Scotia ( Fig. 5 ) include sapropelic shales of the Horton Group, widespreadorganic-rich carbonate laminites of the Windsor Group, and sapropelic shales, sapropelic andhumic coals, and basin-wide, organic-rich bivalve-bearing limestones and shales, all of theCumberland Group.

With few exceptions (see Utting and Hamblin, 1991), the strata of the Maritimes Basin atsurface lie everywhere within the oil or gas windows, with an R_oat surface ranging from 0.4 where suppressed by liquidhydrocarbons (Mukhopadhyayet al.,1991) to >2 (Hacquebard and Donaldson,1970; Ryan and Boehner, 1994). Oil seeps occur presently (Bell, 1958; Short, 1986), eventhough the apatite fission track record indicates that the oil window had been attained early inthe basin history, prior to 250 Ma (Gristet al.,1995). New models of hydrocarbongeneration in Nova Scotia should incorporate the different thermal and structural histories ofHorton, Windsor and Mabou strata before the Mid-Carboniferous event and Cumberland andPictou strata thereafter, and should consider possible cryptic marine transgressions withingroups traditionally described as "non-marine" (Calder, 1998).

Although the organic-rich shales of the Horton Group traditionally have been consideredto hold the greatest potential as a hydrocarbon source (Bell, 1958), current research isfocusing elsewhere. The potential of organic-rich carbonates of the Windsor Group has beenlargely overlooked, and perhaps even more so, the thick and areally extensive black shales ofthe Mabou Group and organic-rich limestones of the coal measures.

Horton Group Sections (Stops 1 & 2)

General Stratigraphy of the Horton Group

Bell (1929) defined the Horton Series and divided it into a lower Horton Bluff Formationand an upper Cheverie Formation. The type area is near Hantsport ( Fig. 6 ), including the Horton Bluff section (Stop 2). Bell (1960)subsequently defined the strata as the Horton Group ( Fig. 2 ), and divided the Horton Bluff Formation into four informal units: basal member, lower andupper parts of the middle member, and the upper member. Martel (1990) and Martel andGibling (1996) presented detailed coastal and stream sections and formally named fourmembers ( Fig. 7 ) that correspond closely with those ofBell.

The formation is at least 525 m thick in the type area (Stop 2), where it restsunconformably on metasedimentary rocks of the Meguma Group and granitic rocks of theSouth Mountain Batholith. It thins southwestward to continental alluvial redbeds (1650 to3000 m) approximately 350 m in the Upper Falmouth area and Falls BrookQuarry (Stop 1), pinching out completely in the Five Mile Plains area. A Horton Bluff section1015 m thick was penetrated in the 1975 Soquip Noel #1 well at Kennetcook ( Fig. 6 ), and lithological sections and seismic data indicate that theHorton Group thickens substantially northward towards the Cobequid Fault (Martel andGibling, 1996). The Horton Bluff and Cheverie formations are dated, using palynomorphs, asUpper Devonian to Tournaisian (see summaries in Uttinget al.,1989;Martelet al.,1993; Martel and Gibling, 1996).

The Falls Brook Quarry near Three Mile Plains (Stop No. 1)

Stop leader: Robert J. Ryan, Nova Scotia Department of NaturalResources

Location and Access

The Falls Brook section is located approximately 1.7 km due south of Three MilePlains ( Figs. 1 and 8a ). From theHighway 14 turnoff on the 101 Highway proceed south for 0.9 km to the junction withHighway 1. Proceed 3.4 km west on Highway 1 to the turnoff for theWindsor Back Road, and from this junction proceed along the Windsor Back Road towardMartock approximately 1.4 km (past the T junction in the road) to a small gatedlane (Windsor Water Supply) that heads almost due south. The quarries are just east of thisroad 1 km south of the Windsor Back Road.

Geological Units Exposed

The Falls Brook Quarry section ( Fig. 8b ), describedpreviously by von Bitter and Moore (1992), is unique in exposing over a short distance all ofthe lithotypes that characterize the Horton Group of the Maritimes Basin. The progressiveonlap of Horton Group strata onto a Cambro-Ordovician basement high in this area hasresulted in deposition of a sequence wherein the lithology of the entire Horton Group isrepresented. The result is that the lower units are thin when compared to their basinalequivalents exposed, for example, at Horton Bluffs (Stop No. 2). Diamond-drilling inthe area confirms the nature of the facies and unit correlations. Units above the middleHorton Bluff are consistent in thickness but the lower and middle Horton Bluff members varyconsiderably with paleotopography.

Starting at the south end of the South Quarry and working up-section from the vicinity ofthe Falls, the following units are exposed ( Fig. 4 ). Thebasal exposure is the Goldenville Formation (Steves Road Unit), a thick metamorphosedsuccession of metagreywackes, meta-quartzarenites and slates of Cambro-Ordovician age.These strata are overlapped unconformably by a compressed section of the lower (HardingBrook), middle (Blue Beach) and upper (Hurd Creek) members of the Horton Bluff Formation(Mississippian: Tournaisian). Our interpretation of the stratigraphy differs from that of VonBitter and Moore (1992), who considered the Meguma and Horton groups to be in faultcontact. The Horton Bluff Formation is a succession of interbedded quartzarenites,subarkoses, siltstones, and shales with variable thicknesses of interbedded coaly shales andpebble conglomerates. The Horton Bluff Formation is in turn overlain unconformably byarkosic conglomerates and sandstones with subordinate interbedded fine-grained siltstones andshales which constitute the Cheverie Formation oftheHorton Group. To the north of thequarry, the gypsum cliffs of the overlying White Quarry Formation of the marine WindsorGroup (Viséan) can be seen.

Meguma Group: Goldenville Formation

The Goldenville Formation of the Meguma Group (Unit 1, Fig. 8 ) was the principal rock quarried from the South Quarry ( Fig. 8 ) and at this locality are predominantly metasandstones,metasiltstones and thin slates cut by a few thin quartz veins. There are well preserved primarysedimentary structures in these beds even though they have been metamorphosed togreenschist facies and folded. The Meguma Group strata are approximately 9 km thickand are interpreted to have been deposited in submarine delta fans by turbidity currents. TheMeguma Group strata at this locality have been folded into a broad anticline with the foldaxis striking east-west approximately 200 m south of the quarry ( Fig. 8 ). Meguma Group rocks are the primary hosts of gold deposits inNova Scotia with the gold usually occurring within bedding-parallel quartz veins nearanticlinal hinges. It is interesting to note that this locality is the site of an abandoned goldmine that recovered gold from the basal quartz pebble conglomerate oftheHorton Group. Thequartz in the conglomerate was probably locally derived from gold-bearing quartz veinsassociated with the adjacent anticline. Although these rocks are Cambro-Ordovician in ageand metamorphosed, it is often difficult to distinguish them from some of the overlyingMississippian terrestrial strata of the Horton Group. The most reliable methods are to look forthe spotted nature (small metamorphic minerals) of the silty horizons in Meguma Group rocksand the presence of plant fossils in the Horton Group strata.

Horton Group: Horton Bluff Formation

Lower Member of the Horton Bluff Formation

The lower, Harding Brook/?Curry Brook Member of the Horton Bluff Formation (Unit 2, Fig. 8 ) at this locality comprises a succession of interbeddedquartz pebble-rich polymictic paraconglomerate, coarse-grained subarkose, and greyfine-grained carbon-rich siltstones and thin shales. The sequence is sand dominated with theconglomerates inter-cross-stratified with the sandstones. The organic-rich shales contain type2 to 3 kerogen with R_oof 0.7-0.8% and area potential petroleum source rock, although not as impressive as the upper units of the HortonBluff Formation. This is only a thin wedge of the member; however, the rock types presentare characteristic of the thicker basinward facies of this unit. The strata are interpreted to havebeen deposited as locally derived alluvial fans as well as low sinuosity streams along thebasin margin. Lacustrine influence in the unit is more evident toward the top of the sequence.The conglomerates at the base of the unit have been mined for paleoplacer gold in the past.Any gold you find is yours tokeep!

Middle Member of the Horton Bluff Formation

The middle, Blue Beach Member of the Horton Bluff Formation (Units3 and 4, Fig. 8 ) is made up predominantly ofblack to grey shale, coaly shale, siltstone and nodular carbonate beds. There are a few thinsandstone beds but they usually do not exceed 1.2 m in thickness. An exposure oforganic-rich, coaly shale within this unit is of type 3 kerogen and is within the oilwindow, with R_oof 0.7-0.8%. This unit is thin at thislocality but can exceed 300 m in thickness elsewhere in the Maritimes Basin. The unitfills in the paleotopography inherited from the basement structure and the unit thickensconsiderably in areas underlain by basement synclines (inferred from diamond-drilling in thearea). Top of formation maps in the area show a marked flattening of topography at the topof the Middle Horton Bluff member when compared to the lower unit. These rocks are thestratigraphic equivalents of the black albertite-bearing shales of the Albert Formation of theHorton Group in southern New Brunswick. AlbertFormationrocks in the Stoney Creek area ofNew Brunswick are the source and reservoir rocks for that small but long-producing oil andgas field. Concretions are common within these beds and are interpreted as paleosol horizons.The unit is fossiliferous with abundant plant debris, ostracods, and fish scales present in theshale. Plant stems of the early lycopsidLepidodendropsisare present in some ofthe coarser interbeds. The middle member of the Horton Bluff Formation is interpreted torepresent lacustrine deposition in a large shallow inland lake that covered much of theMaritimes Basin during the time of deposition. The presence of soil horizons and theabundance of plant detritus are interpreted as evidence that there were periodic regressions ofthe shoreline in this lake environment. Local sandstone interbeds with distributary channelconfigurations indicate that there were lacustrine deltas developed along the shores of thelake, and these may have also contributed to the terrestrial plant detritus found in the shalesand siltstones. This thick lacustrine shale unit can be correlated throughout the entireAtlanticregion of Canada.

Upper Member of the Horton Bluff Formation

The upper, Hurd Creek Member of the Horton Bluff Formation can be divided into twounits: the lower, Glass Sand (Units 5 and 6, Fig. 8 ) and the upper, Multi-Coloured Shale beds (Unit 7, Fig. 8 ).

Glass Sand Unit

The Glass Sand is an easily distinguishable unit in the upper member of the Horton BluffFormation. The unit is characterized by thick quartz-rich sandstones, which at some localitiesare pure enough to be used for the manufacture of glass (past production of Depression-eraglass, now a collectible Nova Scotian antique, gave rise to the name). The unit is dominated(90% or more) by quartzarenites ranging from quartz-pebble conglomerates to fine-grainedquartz sandstones. The Glass Sand unit varies in thickness from 25-35 m. Thesandstones are generally fining-upward cycles approximately 50 cm in thickness. Thereis a paucity of large-scale cross stratification and an absence of lateral accretion beds. Minorkaolinite, lithic fragments, traces of pyrite, and ubiquitous (although not volumetricallysignificant) plant detritus are the only components of the rock other than quartz. The unit isvery consistent and can be traced in subsurface and outcrop for more than 30 km alongstrike with no visible variation in lithotypes present. The fining-upward cycles usuallyculminate with fine-grainedmedium-greysiltstone with abundant fossil debris. Fossils includeboth plants and aquatic fauna (ostracods and fish scales). Paleocurrent determinations fromthe unit are very consistent, indicating deposition in low sinuosity streams. The interveninggrey lacustrine fine-grained beds, the unimodal paleocurrent trends, the absence of large-scalecross stratification, and the lateral consistency of the beds suggest that they were deposited ina beach or low gradient delta fan environment along the lake margin in the waning stages ofdeposition of this large inland lake or embayment. The consistent quartz-rich nature of theunit may be a reflection of a monomineralic source area, the Goldenville Formation, ratherthan a mineralogically mature environment caused by long transport.

Multi-Coloured Shale Unit

This unit can be distinguished by the fine-grained nature and variegated coloration of thebeds. The unit varies in colour from maroon red, grey, grey-green to light yellow. The coloursare more easily distinguished in drill core from the area, but some of the colour variations canbe observed in outcrop at the quarry. The rock types present are multicoloured silty shale andsiltstone interbedded with grey shale. There are a few thin sandstone interbeds. Theabundance and thickness of the grey shales and the abundance of plant debris decrease upsection. At the base of the unit the grey shales still have a significant TOC content; however,upper beds generally have less than 0.5% TOC. The thickness of the unit rarely exceeds20 m, although locally it may be very thin, probably as a result of erosion along theoverlying unconformity with the Cheverie Formation.

Horton Group: Cheverie Formation

The Cheverie Formation of the Horton Group (Unit 8, Fig. 8 ) is composed primarily of a thick succession of arkosic pebbleconglomerate and coarse-grained sandstone. The multilateral, multistoried sandstone bodiesare interbedded with thin siltstone and shale that are usually red-brown. In the central parts ofthe basin the upper part of the formation is siltstone dominated; however, thick sandstoneinterbeds are common. The sandstone units are trough cross-stratified and there are usuallyseveral stacked channels within each sandstone bed. The sandstones form large sheet-likeblankets which extend for many kilometres. This unit is essentially a "granitewash" and the arkosic nature of the beds indicates a major shift in the source area(bedrock sediment supply) in the Horton Group. The arkosic strata are clearly derived fromthe Devono-Carboniferous granitoid rocks of the South Mountain Batholith. The inference canbe made that there was a major uplift and denudation event just prior to the onset ofdeposition of the Cheverie Formation in the middle to upper Tournaisian.Theunconformitybetween the Horton Bluff Formation and the Cheverie Formation representsa significant change in the composition of the detrital material entering the basin and a shiftto deposition in a large alluvial fan braidplain environment. Although grey fine-grained bedsoccur within the formation, they are rare. The usual non-red siltstones and shales are green incolour. The abundance of plant debris and TOC is significantly lower in the CheverieFormation compared to the underlying Horton Bluff Formation. Although there is a paucity ofsuitable source rocks in the Cheverie Formation, permeabilities and porosities in the sandstoneunits indicate that the arkosic sandstones have excellent potential as reservoir rocks.

Horton Bluffs Coastal Section (Stop 2)

Stop leader: Martin R. Gibling, Dalhousie University

Location and Access

The Horton Group crops out widely in the Windsor Subbasin where the Blue Beachsection at Horton Bluff ( Fig. 1 ) provides what is probablythe most continuous exposure of the dark shales in Atlantic Canada. The Blue Beach sectionis approached by driving north on Highway 101 and taking Exit 9 to Avonport. Shortlyafter leaving the highway, turn left at a T-junction and drive north roughly parallel to themain highway. Turn right toward Oak Island Road at the next T-junction, in the small villageof Avonport, and proceed past the school (on your right) and up the hill, bearing right onBluff Road. Continue downhill and cross the railroad trackonceNote: Ifyou have crossed the railway tracks twice, you have proceeded too far.You are nowvery close to the shore of the Avon River on your left. One hundred metres beyond thetracks, turn left on a grassy lane that terminates immediately at the beach and provides accessto the Blue Beach North section (Access N: Fig. 9 ). Parkthere or along the nearby road. Turnright on the beach and proceed south to the lowermostbed of the section. The Blue Beach North section extends from the access point for about1 km to the high cliffs below the lighthouse, where it is separated from the Blue BeachSouth section by a fault. (For alternative access to the Blue Beach South section, continuesouth along the Hantsport road, and turn left on a dirt road that takes you downhill to thebeach (Access S: Fig. 9 ). Parking is available just beyondthe railroad bridge).

The Fundy tides reach their maximum range (approximately 17 m) along this coast,and it is possible for the unwary adventurer to be cut off. Make sure that you know the timesof low and high tide before examining the section. A small, rough path ascends the cliff inthe cove just south of the lighthouse, and can be used in an emergency. However, it is steepand slippery, and is not recommended for normal use. The cliffs are loose, and should beapproached with care.

The Blue Beach and Hurd Creek Members are exposed in the Blue Beach South section,but only the Hurd Creek Member is seen in the Blue Beach North section ( Fig. 9 ), the locality of this field stop. A detailed bed-by-bed column ofthe northern section is shown in Figure 10.

Cycles and Depositional Setting

The most prominent aspect of the cliff section is the well developed cyclicity (Hesse andReading, 1978; Martel and Gibling, 1991). A detailed log for five cycles is shown in Figure 11, with a general interpretation in Figure 12. The cycles are typically approximately 6 m thick andshoal upward, with three components: a basal grey shale; a medial sandstone and shale; andan upper green mudstone with dolomite sheets and nodules.

The basal shale is medium to dark grey, and has an abrupt, planar contact with theunderlying cycle, locally overlain by a single-grain layer of coarse quartz, fish debris, andreworked paleosol fragments. The shales contain fossils of paleoniscid fish, ostracods,conchostracans, fish, amphibians and plants (Bell, 1960; Bless and Jordan, 1971;Carrollet al.,1972). Trace fossils (Planolites) are uncommon, and theshales are mostly platy weathering, indicative of only limited bioturbation. Dolomiticseptarian nodules are prominent in places. The shales are interpreted as an offshore facies,deposited under quiet and variably aerobic to anaerobic conditions.

The shales are overlain, usually abruptly, by interbedded sandstone, siltstone and shale,which form bedsets that project from the cliff face. The lowermost beds contain regularlyspaced sandstone lenses that are isolated within shale. Where seen in three dimensions, theselenses are up to 40 cm thick and 3 m wide, and most are linear and up to6 m long. They contain low-angle truncation surfaces and antiformal sedimentaccumulations that are typical of hummocky cross-stratification (HCS), and many are cappedby wave-rippled sandstones. The lenses and associated sandstones have excellent suites ofsedimentary structures that include gutter casts, prod marks, and well developed groove castson their lower surfaces. Some groove casts are recurved, with parabolic shapes, indicating thatthey and other grooves were formed under oscillatory waves with an associated unidirectionalflow component (combined flow, possibly due to longshore drift)(Martel and Gibling, 1994).Planar beds with horizontal and graded laminae are also present. A variety of features indicateshallow and locally subaerialconditions:rhizoliths, mudcracks, rain prints, ladder andplaned-off ripples, double-crested ripples, scratch circles (formed when the leaves of rootedvegetation are rotated by the wind), and tetrapod trackways. The tracefossilsIsopodichnus, Pelecypodichnus, ?Margaritichnus,PalaeophycusandPlanolitesare present on some basal bed surfaces. Verticalcasts and associated rhizoliths ofArchaeocalamitesare also present. The sandy,medial part of the cycles is interpreted as a wave-dominated nearshore facies. The HCS lenseswith basal sole structures and capping wave ripples represent individual storm events. Theupper beds were deposited under very shallow water and were periodically subaeriallyexposed.

The upper parts of the cycles comprise poorly stratified, rooted green mudstone with thinsandstones. Vertical trees include probableLepidodendropsis(Bell, 1960)andArchaeocalamites.Dolomite is present as sheets and nodules, with sucrosictexture in thin section. The facies is interpreted as a poorly drained paleosol, with pedogenic(nodular) and groundwater-generated (sheet) carbonates. The tough, well-cemented sandy bedsare a distinctive feature of the wave-cut platform, and show prominent circular hollows andsurrounding ridges concretionary growths formed around the former positions of trees that areno longer preserved.

The Horton Bluff Formation has generally been interpreted as lacustrine, based on itssedimentological features and the apparent absence of marine biota. However, Tibert (1996)re-examined the ostracods from the Blue Beach and Hurd Creek Members (originally reportedby Bell, 1929, 1960). He identified the generaCopelandella, Shemonaella, Chamishaella,Cavellina, Carbonita, Bairdia, GeisinaandYoungiella,and noted that severalspecies are well documented in coeval marine assemblages elsewhere in the world.Additionally, Tibert identified agglutinated foraminifera (Trochammina sp.) andglaucony (confirmed by microprobe analysis) in the formation. Tibert's work implies a marineconnection during Horton Bluff deposition, although the source ocean remains uncertain.Calder (1998) hypothesized that this and other marine connections in the Carboniferous ofNova Scotia derived from he called a Mid-Euramerican Sea that waxed and waned from adeep basin between the Maritimes Basin east of Newfoundland and the Western EuropeanBasin, west of Ireland.

Clastic Dykes and Collapse Structures

Clastic dykes and collapse structures both are spectacular features of the cycles. They arevirtually confined to the base of HCS lenses that overlie thick shales, and are especially wellrepresented in five consecutive cycles in 13 m of the Blue Beach North section ( Fig. 10 ). The dykes project from the base of the lenses ( Fig. 13 ), and their quasi-regular spacing in cliff sections is afunction of the regular distribution of the HCS mounds. They range from 1 cm wideand 5 cm deep to 40 cm wide and 40 cm deep (measured vertically),narrowing downwards, and some are at least 5 m long below the linear mounds. Mostdykes show ptygmatic folding due to the higher degree of compaction experienced by thesurrounding muds. From the total unfolded length of the (presently folded) dykes, themaximum original penetration depth is estimated at 110 cm. Seventeen measurementsof unfolded dyke length to present thickness of shale penetrated by the dyke average 2.3,which is a measure of the compaction ratio oftheshale. Dykes in a single cycle are alignedsub-parallel to one another and mean dyke orientation is similar from one cycle to the next.Dyke orientation is also parallel to wave-ripple crest orientation both in the same cycle andregionally, as well as to the orientation of linear HCS accumulations.

Hesse and Reading (1978) suggested that the dykes and overlying sediment lenses weregenerated by upward transposition of liquified sediment from underlying feeder beds as aresult of earthquake shocks, with sediment extrusion at the sediment surface to form themounds (essentially sand volcanoes). However, the recognition that the mounds arewave-formed structures, as well as good evidence for downward movement of sediment intothe dykes, suggests a different origin (Martel and Gibling, 1993). The dykes were probablyinitiated in shallow water during or shortly after the storms that laid down the HCS-bearinglenses. The lenses loaded down into surficial, fluid muds, and the dykes were injecteddownward where underlying, more compacted muds failed in a brittle manner. Cyclic waveloading and microseisms may have promoted sediment failure. Although the prior orientationof HCS lenses would seem to have been a primary control on dyke orientation, the fracturedirection probably also reflects a tensional stress controlled by a gentle, basinward slope.

Five bowl-shaped features, 2-15 m in diameter, are striking features on thewave-cut platform of the Blue Beach North section. They show slight to intense deformationof the sediment fill, with evidence of downward motion along planar slip surfaces, and manyhave an underlying, linear clastic dyke ( Fig. 14 ). Theywere interpreted by Hesse and Reading (1978) as collapse structures, associated with sedimentextrusion of liquified (and possibly gas-rich) sediment. However, the evidence points tosubsidence without extrusion. Similar collapse depressions have been described frominterdistributary bays of the Mississippi Delta (Coleman and Prior, 1980).

Tectonic Setting and Sequence Stratigraphy

The Horton Group is well exposed along the southern shore of the Minas Basin but is notexposed on the northern shore ( Fig. 6 ) apart from smalloutcrops of coeval formations in the Cobequid Hills to the north. This uneven outcropdistribution limits detailed tectono-stratigraphic interpretation. The northward thickening ofthe Blue Beach and Hurd Creek Members from Blue Beach northwards to Tennycape ( Fig. 6 ), as well as the northward thickening across the MinasBasin apparent in seismic, suggests that the Horton Bluff Formation occupies a half-grabenwith a master fault near the present line of the Cobequid Fault. Following this interpretation,the outcrop belt that includes Horton Bluff developed on the hanging-wall margin of thebasin. In accord with this interpretation are paleoflow patterns in other members of theHorton Group, which suggest that the coastal plain prograded northward above the basalunconformity with the Meguma Group. At both Blue Beach and Tennycape, cycles thinupwards and are progressively dominated by subaerialfaciesand biota (Martel and Gibling,1991; Tibert, 1996), with a decreased proportion of the offshore shale facies. This implies aprogressively decreasing rate of tectonic subsidence, following a major subsidence andtransgressive event early in Blue Beach times that can be identified in Horton outcrop beltsacross Atlantic Canada.

Horton half-graben fills are present onshore and offshore elsewhere in Atlantic Canada(e.g. Hamblin and Rust, 1989), and reflect a regional phase of extension following themid-Devonian Acadian Orogeny. The Horton Group in the Minas Basin is the lowermostPaleozoic unit to overstep the boundary of the Meguma and Avalon terranes, brought togetherduring the Orogeny. Age dates from the South Mountain Batholith near Wolfville(approximately 370 Ma) suggest that the Meguma Terrane underwent rapid exhumation priorto Horton subsidence and accumulation (approximately 355 Ma for the basal strata in thisarea).

The stacked shoaling up cycles ( Fig. 11 ) can bedescribed in sequence stratigraphic terms as parasequences, separated by flooding surfaces.The upward trend to more subaerial conditions implies that they are part of a progradingparasequence set. Exxon sequence boundaries are not apparent in the section. One possibleexplanation for the 'parasequence world' of Horton Bluff is that the basin subsidedepisodically along the northern boundary fault, causing repeated transgression in coastal zonesin the Blue Beach area, with subsequent progradation to form shoaling-up cycles. Underconditions of rapid subsidence, base-level falls were probably insufficient to cause majorincision and generate sequence boundaries.

Several major faults are evident in the Blue Beach section, and strata farther east atWalton are intensively deformed, and locally overturned. The timing and significance of thedeformation is not well understood, but it may reflect a major mid-Carboniferous tectonicevent that is well documented elsewhere in mainland Nova Scotia, especially adjacent to theCobequid Fault.

Hydrocarbon Potential of Organic Material

Black, organic-rich shales are present in the Horton Group at many localities acrossAtlantic Canada, and the Horton Group historically has been considered the most prospectiveupper Paleozoic unit for hydrocarbon generation (Bell, 1958). Hydrocarbons of the StoneyCreek oil and gas field in the Moncton Subbasin have been linked to Horton shales. Smithand Naylor (1990) summarised available information and obtained new analyses for theHorton Bluff shales at Blue Beach and in drill core at Upper Falmouth to the south; to thesewe add new data obtained for this study. The Blue Beach shales contain <1 to 3.5% TOCbut are thermally over mature, with Tmax values of 436-460°C and hydrocarbon yieldsof <5 l/t on distillation. The shales at Falmouth are of substantially better grade. Theycontain 2.7-31.6% TOC, with hydrocarbon yields of up to 28.3 l/t. Tmax values were433-439°C. Rather low hydrogen indices (81-180) suggest a humic, rather than an algal,source for the organic matter. Kerogen type 2 and types 2 to 3 arerepresented. As noted above, vascular plantmaterial iscommon at the Blue Beach section.

The maturity profile of Horton Group source rocks indicates that they have been renderedover mature by fluid migration adjacent the Cobequid Fault where R_ovalues exceed 1.5%. At distances 2 to 3 kmaway from the fault, however, they fall within the oil window (Mukhopadhyay, 1991).

Horton-Windsor Group Contact at Cheverie (Stop No. 3)

Stop leader: Robert C. Boehner, Nova Scotia Department of NaturalResources

Location and Access

From Exit 5A ramp on Highway 101, turn left. Below the overpass, take a second left onthe gypsum mine road, passing Fundy Gypsum on the right. Turn left on Highway 214, thenleft on Highway 236, crossing the bridge over the St. Croix River. At the stop sign, turn righttowards Union Corner. Proceed left on Highway 215 (Glooscap Trail) for 2.8 km. Onthe left, the Kennetcook Limestone of the Windsor Group is exposed. At Cheverie ( Fig. 1 ), turn left on Ross Road and continue to the shore. [Pleaserespect the wishes of the landowners with respect to parking your vehicle.]

Background

The Maritimes Basin complex ( Fig. 3 ) was breached inthe Viséan by a major evaporitic marine incursion of the sub-sealevel landscape.Deposits of this marine incursion are assigned to the Windsor Group ( Fig. 2 ). The Windsor Group evaporitic basin system continued to infilland expand, arguably with relatively little coincident tectonic activity. The middle to lateViséan was a time of regionally extensive, restricted marine to evaporitic marine andcontinental redbed deposition. Numerous minor and major cycles were accumulated inshallow shelf to interconnected intermontane basins. Deposition occurred under hot semi-aridto arid stressed environmental conditions.

The structural geology of the Kennetcook Basin is complex (Boehner, 1991) and iscompatible with restraining-convergence tectonics on subsidiary faults related to dextraleast-west strike slip motion on the Cobequid Chedabucto Fault System (e.g. KennetcookThrust Fault). Superposition of the Triassic rift basin in a later extensional environment hasfurther complicated the interpretation of the structural history. Well documented thrusting hasbeen previously restricted to small scale thrust faults near the western extremity of the basin(e.g. Cheverie). A complex gravity slide/decollement has been identified by Moore andFerguson (1986) in the Windsor area. The relationship of this structure with the highlydeformed Horton Group and the Kennetcook Thrust on the northern side of the basin remainto be determined. It is not clear if there is a genetic relationship with similar complexstructure near Kennetcook and along the north part of the Shubenacadie Basin. Thetranspressive-thrusting model is compatible with gravity slide tectonics. The Windsor Groupevaporites and especially the lower salt section, are apreferredlocus for ductile deformationand decollement in the Carboniferous Basin fill (e.g. Boehner, 1992). Giles and Lynch (1994)have recognized a regional detachment within the Windsor Group in east-central NovaScotia.

Late Paleozoic to early Mesozoic basins in Nova Scotia, especially in the north-centralpart of the province, have complicated and interesting stratigraphy, sedimentology, structureand very significant mineral and energy resource potential. The Cheverie Stop ( Fig. 15 ) is located in the northwestern part of the Kennetcook(Windsor) structural basin. The Musquodoboit, Shubenacadie and Kennetcook (Windsor)structural basins are the main components of this area, referred to as the Minas Sub-basin ofBell (1958) which includes the Carboniferous outcrop area on the north central part of theMeguma Platform. The area occurs along the extreme northern boundary of the MegumaZone and, consequently, the geology of the Carboniferous basin fill is complicated by theproximity to the Cobequid-Chedabucto Fault System and superimposed Mesozoic rift basinoccurring in the area of the Bay of Fundy and Minas Basin ( Fig. 1 ).

This tectonically complicated setting is important in the localization and deformation ofsignificant mineral deposits (Boehner and Ryan, 1989; Fig. 5 ) including base metals, silver and barite (e.g. Walton, past producer), manganese, siderite,gypsum and anhydrite (e.g. Wentworth and Miller Creek Operations of Fundy GypsumCompany Limited and the Domtar Gypsum, Maynard Quarry near McKay Section), sulphur,salt and limestone (e.g. Miller Creek Quarry). In addition, interest in hydrocarbon exploration(including exploration well-drilling) began in the early part of the century near Cheverie andFalmouth (Windsor). Interest continued to recent times, including several programs operatedfrom the mid 1940s to the early 1980s with several wells drilled the Kennetcook area. Mostof this hydrocarbon exploration focused on plays in the Horton Group and the lowermost partof the Windsor Group. The rocks in this interval are noted for hydrocarbon shows andoccurrences (e.g. Cheverie, Walton Barite Mine, Soquipet al.Noel No. 1);however, commercial discovery anddevelopment have yet to occur.

Previous geological mapping in the area includes: Boyle (1972), Crosby (1962), Weeks(1948), Ferguson (1983) and Moore and Ferguson (1986). The founding work on the detailedstratigraphy and biostratigraphy of the Windsor and Horton groups in this region, their typeareas, was produced by Bell (1929 and 1958).

Cheverie Stop

The Cheverie Stop ( Figs. 1 and 15 ) is located on the eastern shore of the Avon River estuary near the transition to the MinasBasin. It is very easy to access via paved roads (Routes 14 and 215) north from Windsor andBrooklyn. Cheverie Point is accessed by a short road northwest off Route 215 at a location750 m south of the New Cheverie Road intersection in the community of Cheverie.Most maps identify White Head as a shoreline feature. This is located at the northeastern endof the Cheverie Stop.

The Cheverie Stop area is part of the Bay of Fundy tidal system, with tidal rangeapproaching 15 m. This coincidence of extreme tidal action, erosion and geologicalstructure has resulted in an excellent locality to view the upper part of the Horton Group andthe contact with the overlying Windsor Group in the shoreline cliffs and wave cut platforms.Although this is a relatively benign shore section, due care must be exercised to avoidunnecessary exposure to rock falls along the high cliffs, and especially in traversing theintertidal zone to avoid soft mud areas. The tide level must always be considered to avoidgetting cut off at points (see Safety Considerations for Coastal Sections).

The Cheverie Stop provides a small window into the complex and interesting latePaleozoic basin geology near the Cobequid-Chedabucto Fault System and coincidentMesozoic rift. The general geology, sedimentology and stratigraphy of the Horton Group hasbeen outlined in previous field stop descriptions. Outcrop sections of the Horton Group,Horton Bluff Formation and Cheverie Formation are present at the Cheverie section; however,only the uppermost portion of the Cheverie Formation will be examined. The lower units ofthe Windsor Group, especially the Macumber Formation (the basal carbonate), Pembrokebreccia, and the White Quarry Formation (basal anhydrite), are well represented and easilyaccessible at low tide.

Macumber Formation

The Macumber Formation lectostratotype and type area is identified in the Cheverie areabased on units b and c of Section 1 described by Bell (1929). The namewas introduced by Weeks (1948) and this basal carbonate unit of the Windsor Group probablyhas the most voluminous research literature of any formation of the group (e.g. Schenketal.,1994, and references therein).

The Macumber Formation comprises buff to light grey-brown to dark grey pelletallimestone to dolostone, variably argillaceous and arenaceous. Well developed laminations arecharacteristic. The Macumber Formation in the Maritimes Basin varies widely in thickness inthe region from 1-18 m. At Cheverie it is quite thin (only a few metres) due in part tothe presence of thick Pembroke breccia. Although it is relatively thin, it is a key correlationunit because of the wide distribution as the basal Windsor Group carbonate in AtlanticCanada. The Macumber Formation, also known as the A₁or Ribbon limestone, or Ship Cove Formation and other names,overlies concordantly, conformably? to unconformably older Carboniferous rocks includingHorton Group or older Devonian to Carboniferous rocks. In the Cheverie section it overlies athin, distinctive, locally developed quartzose sandstone withabundantSchizodousbivalves on the upper surface (included in the Windsor Groupby Bell). Locally and regionally it is conformably overlain by, and often transitional withathick anhydrite sequence informally referred to as the basal anhydrite (local name WhiteQuarry or Carrolls Corner Formation).

Macumber-Basal Anhydrite Contact - Paleokarst and Pembroke Breccia

In some present-day outcrop areas the contact between the Macumber Formation and theoverlying basal anhydrite is marked by the presence of a complex carbonate breccia (a few totens of metres thick), referred to as the Pembroke breccia. This contact is a common locationfor karst-related solution features, including solution trenches that may extend down dip for100 m or more and be filled with Carboniferous or Cretaceous sediments and/orQuaternary to recent material. Multiple generations of paleo-karst features are evident. Ingeneral, undisturbed (structurally or by karst processes) contacts are rarely exposed and suchis the case at Cheverie.

White Quarry or Carrolls Corner Formation (basal anhydrite)

The basal anhydrite of the Windsor Group is dominated by thick, massive, nodular topoorly stratified anhydrite with minor thin (locally petroliferous) carbonate, halitic ormudstone interbeds. It is approximately 80-90% anhydrite and typically is variably hydratedto gypsum in near-surface environments where karst features are well developed. Thethickness varies from 100-300 m and the unit is regionally distributed throughoutAtlantic Canada. It is especially well developed in the Cheverie region and exceptionally wellexposed and accessible at the Cheverie section. It conformably and transitionally overlies theMacumber Formation. The basal anhydrite unit is commonly overlain by a very thick saltsequence, which for obvious reasons does not occur as outcrops.

The basal anhydrite is well exposed in the area of White Head in the Cheverie Sectionand is not complicated by extensive hydration. Rapid erosion is a factor in allowing theoccurrence of the anhydrite in outcrop. Irregular cliffs and superb wave-cut platform outcropsof the gently dipping beds expose the various textures and inter-relationships of the anhydriteand carbonate/mudrock. The carbonate/mudrock interbeds are exceptionally petroliferouswhich probably attracted interest in hydrocarbon exploration (including exploration welldrilling) in the early part of the century near Cheverie. These anhydrite/carbonaterelationships include discrete and distinctive interbeds and lamination through interstitialnodular progressions to massive mosaic anhydrite textures. These transitions can be observedalong strike as well as vertical facies changes over a few centimetres (bed boundaries) to tensof metres from relatively pure carbonate/mudrock to nodular mosaic anhydrite.

Two variants of tectonic breccia in the anhydrite section are also well exposed atCheverie. The south exposure of mud and gypsum occurs near the abandoned gypsum quarryand adjacent to a concealed interval in the inferred contact area with the Pembroke brecciaand Macumber Formation. The northerly exposure of gypsum and mudrock near White Headis more clearly a fault contact with Horton Bluff Formation mudrocks.

Pembroke Breccia

Breccia rocks of the Macumber Formation are a problematic and important geological unitin the Kennetcook Basin and are similar to those described by Boehner and Giles (1993).Weeks (1948) introduced the term 'Pembroke Formation'; however, the term was laterabandoned and the term 'Pembroke breccia' is applied to a variety of carbonate brecciaspatially associated with the Macumber Formation. The Pembroke breccia at the Cheveriesection is exceptionally well developed and accessible in outcrop along a strike length ofseveral hundred metres in low shoreline cliffs and wave-cut platforms in the intertidalzone.

The age, origin and development history of these breccias has generally not been welldefined. Lavoieet al.(1995) have made substantial advances in documenting thecharacter and genesis of these complex rocks. Their work identified three breccia types atvarious localities in the province, including Cheverie: (1) synsedimentary, (2) tectonic orkarst-related, or (3) multigeneration. Understanding their relationship in space and time tometallic mineralization and potentially hydrocarbon reservoirs near the base of the WindsorGroup will be important in establishing mineral and energy exploration models. Two factorsare very significant. The carbonate breccia is dominated by, and most likely derived from,laminated and recrystallized carbonate typical of the Macumber Formation and carbonateinterbeds within the White Quarry Formation (basal anhydrite). The breccia forms asubstantial thickness of host rock for mineralization, and may be tens of metres thicker thanthe Macumber Formation. The breccias appear to have a spatial association with the dissolvedand eroded solution trench typically formed at thecontact between the Macumber and WhiteQuarry formations. The breccia is also often associated with faults,but in many areasdisappears rapidly downdip beneath the basal anhydrite. Alternative hypothesis for formationinclude: synsedimentary breccia, growth fault origin, and karst or residual accumulation inpaleo-solution trench features with or without faults.

Hydrocarbon Occurrences

Organic-rich and carbonate interbeds in the White Quarry Formation (basal anhydrite)exposed near Cheverie reek of hydrocarbons. They yield type 2 to 3 kerogen,within the oil window, with R_oof 0.8-0.9%. Productionindex (PI) values, however, suggest early hydrocarbon generation. The Macumber limestonehas favourable potential as a hydrocarbon source, lying within the oil window withR_oof 0.9%, type 2 kerogen, and TOC in the 1-2%range. Windsor Group source rocks everywhere fall within the oil window, with the exceptionof areas immediately adjacent the Cobequid Fault (Mukhopadhyay, 1991).

Recent natural gas exploration interest in the Alton area in the Shubenacadie Basin couldexpand into the geologically similar Kennetcook Basin. Minor liquid oil and natural gasoccurrences have been documented in the Kennetcook Basin (e.g. Walton Mine). Potentialtraps and source rocks similar to the Alton occurrence could exist in the west-central parts ofthe Kennetcook Basin. The only seismic surveys available were run in the eastern part of thebasin where the Soquipet al.Noel No. 1 well was drilled (Boehner, 1991).Unfortunately, the base of the Windsor Group was intersected at a very shallow depth withouta significantly thick salt seal. Interesting occurrences of natural gas were reported in the upperpart of this well (near base of Windsor Group).

Upper Windsor Limestone - Avondale Section (Stop 4)

Stop leader: David E. Brown, Canada-Nova Scotia Offshore Petroleum Board,Halifax, Nova Scotia

Location and Access

The exposure is accessible, with their permission, via a farm track on the property of Mr.and Mrs. William D. Siler, Avondale, which passes to the left of their farmhouse. Theroad passes through an apple orchard beyond which it is best negotiated on foot or by fourwheel drive vehicle. At the shore, turn to the right and proceed to the first outcrop.

Introduction

The easily accessible limestone succession exposed here on the south bank of the AvonRiver ( Fig. 16 ) is an excellent example of the thin, butlaterally continuous carbonate sheets representative of the Upper Windsor Group. However,this 10 m thick exposure is unique in containing a well preserved calcrete paleosolhorizon developed at the top of the sequence, significant oil staining within the same interval,several other excellent potential reservoir zones, and a black lacustrine shale (possible sourcerock) in the clastic strata immediately below the carbonates.

The Avondale sequence was first described by Bell (1929) in his seminal work on theWindsor Group, though he incorrectly assigned it to the underlying Avon Limestone. Crowell(1967) recognized that these rocks were equivalent to one of Bell's unnamed units, and sosubdivided the subzone into the Avon (D-1) and Meander River (D-2) limestones, with theAvondale exposure designated as the reference section for the unit. Waring (1967) and Moore(1967) also studied this section and agreed with Crowell's interpretation that the limestonesrepresented a transgressive unit with capping breccias the result of evaporite dissolution. Thiswriter's work (Brown, 1979) described in detail the sedimentary environments of thecarbonate sheet's lithozones and determined that it represented a pair of incomplete,asymmetrical transgressive and regressive cycles ( Fig. 17 ).Most important was the recognition of the well developed but complex calcrete soil horizoncapping the sequence, and a detailed description of its various textures which provided anunderstanding of its evolution, and paleoclimaticandpaleogeographic significance. Laterrevision of Windsor Group stratigraphy in the central Nova Scotia subbasins by Giles andBoehner (1979) grouped the Meander River and other related Upper Windsor limestones (C,D and E subzones) into a single large depositional cycle and in the Minassubbasin Giles (1981) assigned them to the Murphy Road Formation.

Description of the Succession

As noted above, the Meander River sequence represents a textbook example of a shallowmarine transgressive carbonate succession ( Fig. 18 ). Thesequence transgressed a basically featureless clastic fluvial plain, similar to those whichseparate each of the Upper Windsor limestones. These clastics are tens of metres thick andare composed of red calcareous fluvial sandstones, siltstones and mudstones. Minor lacustrineintervals can be recognized and exposed at Avondale is a 10-50 cm thick black shale(with fine-grained sand laminations at the base) overlain by a thin buff-colouredunconsolidated siltstone to fine-grained sandstone with oscillation ripples. Overlying this areabout 2 m of green fluvial/lacustrine deposits becoming limonitic at the base of thecarbonates.

The contact between the clastics and overlying carbonates displays little relief and isessentially flat-lying. A thin (10-20 cm) transgressive ostracodal and oolitic grainstonemarks the initiation of carbonate deposition and likely represents a coastal marsh setting. Thislithology grades rapidly into an extremely well sorted brown ooid grainstone about1.1 m in total thickness. This open marine (tidal?) shoal sequence is vaguely laminatedwith low angle cross-stratification, and reveals evidence of both early syndepositional andlater calcite spar cementation, although significant intergrain porosity is visible in handspecimens. The 20 cm thick transition to the overlying open marine lime sands iscomposed of a dark grey to black, shaly fetid ooid to bioclastic grainstone. The ooids here arenoteworthy due to their colour and large size when compared to the underlying strata. Thelight grey, poorly consolidated marine lime sands to silts (about 1.8 m thick) are rich inbioclastic debris (crinoids, echinoids, brachiopods, pelycepods and dascycladacean algaefragments) and are heavily bioturbated. Toward thetopof the interval the rocks shows moredistinct rippled bedding and progressively less evidence of bioturbation and fauna in lifepositions, inferring deeper water conditions.

Overlying the shoal lime sands are about 2.7 m of platy, laminated grey to brownpelleted micritic limestones with rare fossils. A deep water, inner shelf environment isinterpreted for this unit. Individual beds increase in thickness upward and are separated bythin, soft, shaly yet highly fossiliferous light grey lime siltstones. Interestingly, towards thetop of the unit the micrites, black algal laminations with associated laminoid fenestrae,calcite-lined open voids, small 0.8 mm gypsum crystals, and a mottled texture becomeincreasingly common. These features reveal evidence of a much more shallow waterenvironment, possibly a lagoonal setting. Although no physical evidence is observed, it isbelieved that a rapid regression took place such that the lagoonal strata were superimposedconformably upon the deeper water, inner shelf micrites. Indeed, the top of this unit ismarked by a thin (35 cm) leached, limonitic brown limestone displaying abundant algalmats, gas and gypsum blisters, and buckle cracks, all indicative of a subaerially-exposedsurface, here interpreted as a supratidal lagoonalfringeenvironment.

Immediately overlying the supratidal setting are 2 m of brown, pelleted, highlyburrowed micritic rocks very similar in appearance to the deeper water lithologies. However,this lithology is characterized by repetitious (cyclic?) 5-10 cm thick undulatory beds(interference ripples) separated by thin (2-5 mm thick) black calcareous shales. Prismcracks are observed on planar surfaces and small 0.8 mm gypsum crystals are common.A lagoonal intertidal flat environment is interpreted for these rocks. Again, like the previousfacies, fossils are rare and calcite-lined open voids become increasing common.

Superimposed upon the tidal facies is a 1.6 m thick, mature calcrete paleosolhorizon. The outstanding exposure of this early post-depositional lithozone reveals the fullprogression of subaerial diagenesis on the underlying micritic sediments, from slightlymottled, cracked and pitted textures at the base, intermediate solution and collapse brecciasand pseudobreccias, to an upper silt-rich saccharoidal calcite spar grainstone (heavilyoil-stained). Classic paleosol features recognized in this lithozone include solution pipes, rootsand root traces, solution vugs, dissolution and collapse breccias, slump features, bucklecracks, meniscus cementation, laminated beds, coated clasts, limonite staining, siltstoneintraclasts, and laminated 'saucer' pebbles.

Capping the entire carbonate sequence are intraclast-rich sandstones and siltstones,interpreted to represent distal debris flow and sheetflood deposits sourced from nearby basinmargin alluvial fans overlain by clastic fluvial strata. About half a metre above the top of thepaleosol is a very thin (6 cm) flat-pebble algal-laminated micrite which are believedremnants of playa lake deposition.

Hydrocarbon Systems and Features

There is only a limited understanding of the hydrocarbon system(s) for the WindsorGroup, and indeed, the entire Carboniferous succession in Atlantic Canada. Numerous oilshows, as well as possible source and reservoir rocks have been identified and encounteredboth on and offshore. However, over the past century exploration activity has been sporadicand with the exception of the Stoney Creek oil and gas field in New Brunswick, discovered inthe early 1900s, there have been no significant discoveries nor sustained commercialproduction of hydrocarbons from the rocks of this age in the region.

Based on the above example, most of the hydrocarbon potential was (and to a certaindegree is still) believed to exist in various fluvial-lacustrine facies of the basal Horton Group(Tournaisian). Oil and gas shows and staining have also been encountered in overlyingWindsor Group (Viséan) carbonates and evaporites, though mostly in Lower Windsorrocks. Interestingly, Bell's (1958) speculations on the potential of the Lower Windsor pointedto possible significant biohermal reservoirs being developed in the Sydney Basin (i.e. GaysRiver-type carbonate banks). These would make attractive reservoirs as they are known tooccur on structural highs, are variably dolomitized (enhanced porosity and permeability), andcould be sourced from basinal evaporites and shales, and also sealed by the former(Gileset al.,1979; Boehneret al.,1989). However, migration pathwayswithin the evaporites to such build-ups could be problematic and would appear to require theassistance of later faulting and fracturing.

Bell (1958) suggested that although fair to good potential source rock facies were to befound in the Horton and Lower Windsor strata, the better reservoir zones existed in thebiohermal limestone beds of the Upper Windsor. Within the Upper Windsor, severalbiohermal-biostromal reef mounds have been documented (Boehner, 1988; Boehneretal.,1989). Potential reservoirs in the Upper Windsor would have better potential toreceive upward-migrating hydrocarbons generated from deeper, more mature basinal LowerWindsor source rocks. Again, suitable migration pathways are required. Seals in this intervalare also problematic as they are composed mostly of variably-grained fluvial clastics of theCanso Group.

At the Upper Windsor Avondale section, several potential reservoir facies are represented,and they, or their lateral equivalents, may be encountered throughout the basin ( Fig. 18 ). The basal limestone has observable interoolitic porosityvisible to the naked eye, though to date, no porosity/permeability analyses have beenconducted to quantify these rock attributes. When freshly broken, these rocks occasionallygive off a weakly petroliferous odour indicating possible passage of hydrocarbons at one time.However, at the unit's top is a 10 cm interval of poorly sorted, dark grey to black shalyoolitic bed, which although it has no visible porosity, gives off a strong petroliferous odouron fresh samples.

A more important, and perhaps overlooked reservoir facies, is the calcrete paleosoldeveloped at the top of the carbonate succession. Indeed, a number of hydrocarbon showsencountered in petroleum wells and drillholes were from intervals described as"breccias" of various types, though their stratigraphic position is not known orpoorly understood (see examples in McMahonet al.,1986). Due to subaerialexposure and diagenesis, excellent vuggy and intercrystalline porosity has developed inotherwise tight tidal and lagoonal micritic mudstones. To date, the unit's porosity andpermeability have yet to be properly quantified. Whereas here reservoir development isfacies-dependent within the oolitic grainstones, the development of the calcrete is not anddepending on the time and extent of exposure, regression or basin drawdown may besuperimposed on any of the Meander River facies. This has significant explorationimplications. Although the proclivity and effects of calcretization are greater toward the basinmargins (Crowell, 1967), it is possible that minor basinal warping and faulting within thebasincentre, perhaps related to movement of deeper Lower Windsor evaporites, could expose thecarbonates to subaerial diagenesis.

In addition to creating an excellent reservoir facies, any later structural activity could tapinto and/or juxtapose source and reservoir facies, thus facilitating either vertical or lateralmigration of hydrocarbons generated from older or time-equivalent strata. Indeed, therecognition of a major thrust fault in the adjacent Kennetcook basin to the east of theWindsor Subbasin (Boehner, 1990) and similar faults in other subbasins (Smith and Collins,1985) would provide the necessary conduits for the large scale migration of hydrocarbons andmineralizing fluids. Evidence for this mechanism has been observed at the Walton baritedeposit adjacent to the Kennetcook Trust (Boehner, ibid.) where petroleum was pervasive atthe deposit in the form of liquids, staining, and fluid inclusions (Boyle, 1972).

Such a scenario could explain the presence of the well developed and pervasive oilstaining present in the calcrete's uppermost sucrosic spar grainstone ( Fig. 18 ). Freshly broken samples from this black, 30 cm thickzone give off an intense petroliferous odour, and display an orange fluorescence oil stainingsuggestive of a mature oil which might be biodegraded. Intriguingly, the stained interval has avery sharp basal contact which is horizontal with original bedding. This infers that liquidhydrocarbons were likely generated very early and must have migrated from a distal sourceup-dip toward the basin margins perhaps driven by tectonic activity in the source area prior toany tectonism and formation of traps in this area. If correct, then reservoirs within this andother Upper Windsor limestone members in the Minas Subbasin may have received liquidhydrocarbons and, where nor breached by erosion or penetrated by later faults remainpreserved as untapped accumulations.

Although it appears to have been overlooked, there may be potential for source rocksexisting in Upper Windsor Group rocks. About 2 m below the carbonate at Avondalestrata is a variably thick (10-50 cm) black lacustrine shale overlain by a thinbuff-coloured unconsolidated siltstone to fine-grained sandstone with oscillation ripples ( Fig. 18 ). An incomplete analysis of this rock has recently beencompleted though more detailed work is required. Fluorescence observation on unpolishedwhole rock suggests the presence of oil-prone mixed algal and terrestrial organic matter ofkerogen Type 2-3 or 2 and that the sample is within the oil window (thecalculated vitrinite reflectance would be between 0.8 to 1.1% R_o(Mukhopadhyay, personal communication, 1998). Although modestat this site, it is speculated that this interval, and related ones, likely thicken basinward andhave potential to become volumetrically significant and under the right conditions to generateappreciable quantities of hydrocarbons.

The Joggins Carboniferous Section (Stop No. 5)

Location and Access

To reach Joggins ( Fig. 1 ) by road, leave Route 302 atMaccan, turning west (right if travelling south from Amherst via Nappan) on Route 242.Proceed 20 km, crossing bridges spanning the Maccan River and the River Hebert,continuing through the village of River Hebert to Joggins. Proceed along the main street,turning right toward Lower Cove; park at the bridge crossing Little River and proceed to theleft (southward) along the shore. Alternatively, follow the signs from Main Street leading tothe designated parking area and descend the steps at Bell's Brook.

Background

The Joggins Section is arguably the world's best exposed section of Carboniferous coalmeasures. The "classic" section from Lower Cove south to MacCarrons River ( Fig. 19 ) comprises cliffs 20 m high that run for3 km, bordered by a wave-cut platform about 500 m wide that is completelyexposed at low tide. Since the first visit to this coastal section by Sir Charles Lyell in 1842,Joggins has been one of the most celebrated geological sites in the world. The fossil recordfrom whence its claim to fame largely derives, we owe largely to the half century labour oflove by Nova Scotian Sir William Dawson. In recognition of its pre-eminent place in thehistory of geology, the community of Joggins and surrounding area currently are developing asubmission to the United Nations for the designation of the fossil cliffs as a World HeritageSite.

In spite of its fame, advances in our understanding of the Joggins section have beenpainfully elusive since the pioneering, and to date most exhaustive, research of the section bySir William Dawson in the Nineteenth Century [summarized in his highly recommended,seminal workAcadian Geology(editions of 1855, 1868, 1878 and 1891)]. Arevised sedimentological description of the section by Davies, Gibling, Calder and othersprovides an important new framework for research of the fossil record and its paleo-ecology.Recent paleontological research of the fossil lycopsid forests by Andrew Scott (RoyalHolloway, University of London) and Calder in concert with the sedimentology of Giblingand Davies, and an appraisal of the marine affinities of the aquatic realm by Skilliter andCalder, are two lines of current research that offer promise in increasing our understanding ofthis most marvellous but enigmatic of Carboniferous sections.

Recent Work

Many papers have been published about the Joggins section, although surprisingly few inthis century. The works of Dawson are the most prolific and important. Logan (1845)presented a bed-by-bed section that includes cm-scale measurements of the coal beds, whichhe numbered, and has remained the cornerstone of stratigraphic study ever since. More recentsedimentological studies of parts of the section were carried out by Duff and Walton (1972)and Rustet al.(1984). Selected paleosols were studied by Smith (1992). A detailedanalysis of floral occurrences and associated tetrapod remains was carried out by Scott andCalder from 1993-96, and several papers are completed or in preparation. A study of tracefossils and foraminifera was published by Archeret al.(1996), and studies of fossilcharcoal and sedimentological response to wildfire were carried out by Falcon-Lang (RoyalHolloway) in 1996 and 1997.

In the summers of 1996 and 1997, a comprehensive remeasurement of the section fromLower Cove to Bell's Brook was completed by Sarah Davies (University of Edinburgh),Gibling and Calder. The overlying strata exposed between Bell's Brook and McCarron's Creekwere measured by Ténière and Tonelli (Dalhousie) in 1997. This is the firsttime that the entire 2 km thick "classic" section has been systematicallymeasured since the 1840s. This measured section now provides a comprehensive stratigraphicand sedimentological framework for the section, especially for the remarkable fossiloccurrences ( Fig. 20 ).

Stratigraphy

The classic Joggins section lies within the Cumberland Basin ( Fig. 3 ). It comprises the Joggins and Springhill Mines formations(Westphalian A to early B) of the Cumberland Group (Ryanet al.,1992), exposedbetween Lower Cove and McCarron's Creek in a near-continuous section nearly 2 kmthick. Underlying these strata are 400 m of less completely exposed Joggins Formationstrata in Lower Cove, and an additional approximately 1500 m of continuous exposurearound Boss Point of the Mabou Group and overlying Boss Point Formation (lateViséan to Namurian or Westphalian A). An additional 650 m of strata of theSpringhill Mines Formation, differentiated from the Joggins Formation by its absence offossiliferous limestones, is exposed from McCarron's Creek to the Ragged Reef. These stratadevelop inland to include 4 m thick piedmont coals of the Springhill Coalfield (Calder,1993; 1994). South of Ragged Reef, the cliffs continue for many kilometres along ChignectoBay with a near-continuous strike section. Thus, theJoggins section forms part of anear-continuous, mid-Carboniferous section >4 km thick. The remarkably thicksection reflects the rapid subsidence of the fault-bounded Cumberland Basin under atranstensional to transpressional regime near a micro-plate and terrane boundary; basinalsubsidence at this time was linked to the Alleghanian Orogeny and the final stage of assemblyof Pangea.

The Fossil Record

The fossil record of Joggins and its paleo-ecology has been the subject of research byCalder over the past few years and a comprehensive summary is forthcoming (Calder,submitted). The complete flora and fauna are included in the appendices of Calder (1998).The fossil fauna of Joggins can be grouped into two categories each for the terrestrial andaquatic realms: invertebrates and vertebrates. The terrestrial record by far has received thegreatest attention, with comparatively little work on the aquatic invertebrates and even less onthe vertebrates (fishes).

The aquatic record derives exclusively from the limestone and 'clam coal' beds thatoverlie certain of the seams, in particular the Forty Brine (Coal 20) and overlying 'clam coal'(Coal 19) (Stop 5.3) and the Joggins Seam (Coal 7). Their paleo-ecological significance withrespect to marine incursions, hence, has remained largely unevaluated; however, not allaquatic fauna are unequivocally freshwater. Taxa of dubious affinity include agglutinatedforaminifera, spirorbids, bivalves, limulids, eocarid crustaceans, elasmobranch sharks andcoelacanths (Calder, 1998).

Many of these fossils can be found in fallen material on the beach, and some of the bestmaterial is on display in the Fossil Centre at Joggins. Joggins is a protected site under theSpecial Places Act of the Province of Nova Scotia and excavation of fossil material from thecliffs is prohibited. Common fossils found in beach stones, however, are collectible. Thatsaid, virtually all of the important paleontological discoveries over the years have been madefrom material fallen from the cliffs, so be on the lookout! Should you find a vertebrate orother unusual fossil, please bring it to the attention of the trip leader, Nova Scotia Museum(902-424-6451), Fundy Geological Museum (902-254-3814), or Joggins Fossil Centrestaff.

Sedimentology

The cliff and platform exposures allow an unrivalled 3D perspective of the strata, whichcan be grouped into several facies types:

Alluvial redbed facies(Stop 5.1) include narrow (width: depth approximately10:1) channel bodies, typically a few metres thick with numerous abandoned hollow fillsinternally, isolated within red floodplain strata (immature, humid paleosols). Thin sheetsandstones represent crevasse splays and levees. Where they have been studied higher in thesection, these deposits have been interpreted as anastomosing river deposits.

Alluvial grey facies(Stop 5.4) larger channel bodies are well exposed wherethey form resistant headlands. They are up to 10 m thick, contain scroll bar deposits(exhumed on the wave-cut platforms) and lateral accretion surfaces, indicative of meanderingrivers. Some channel bodies have erect trees exposed on their margins (as in many modernrivers).

Bay-fill and poorly drained floodplain facies(Stop 5.2) comprise stacked,progradational coarsening-up units. They represent the fills of shallow standing water bodies,and are commonly associated with distributary channel bodies. Abundant rooted andtransported vegetation is present, including the many erect trunks, and coals up to 2 mthick are present. Some fills are capped by ganisters (silica-cemented paleosols) or byhydromorphic paleosols.

Shallow nearshore facies(Stop 5.3) are largely wave-dominated shales andsandstones, with hummocky cross-stratification (HCS) and wave ripples. Large-scale(50-100 m across) domal forms can be observed in the cliff and wave-cut platformexposures. They include stacked HCS units and delicate exposure features (planed-off ripples,backwash drainage structures), and are interpreted as the deposits of nearshore bars. Dark,organic-rich limestones up to 1 m thick contain an abundant shelled fauna. Brackishmarine (?estuarine) conditions are indicated by the trace fossil suite, foraminifera, and recentSr isotope data on fish fragments (see Calder, 1998).

Coal Beds and Hydrocarbon Source Rocks

The coal beds of this famous section have received surprisingly little study, and the bulkof what has been done is largely unpublished as yet. Coal beds of the Joggins Formationtypically are thin (less than 1 m) although they can form seams interstratified withclastic partings that comprise zones exceeding 2 m, as for example, the Fundy Seamand overlying Coal 28. Typically the coals are bright, clarain-rich and pyritic; calcareouspermineralization of lycopsid periderm occurs locally within the coal beds. Discrete breaks(plies) in a bed invariably occur on fusain horizons. R_oatsurface ranges from 0.67 to 0.70% and may be suppressed to lower values by liquidhydrocarbon expulsion (Mukhopadhyayet al.,1991).

The coal beds typically are dominated by the arboreous lycopsidsincludingLepidodendron,with the miosporeLycosporapellucida,produced byLepidophloios,particularly abundant within the FortyBrine and Queen seams (Dolby, 1998). Conspicuously rare are miosporesofSigillaria,whose compression fossil is commonly found associated with fossilforests in the section. This may reflect its weak output of miospores or its ecologicalpreference for ecotonal clastic-rich substrates.

Analysis of the hydrocarbon-generating potential of basin wide organic-rich limestonesand 'clam coal' beds from the Joggins section reveals that they contain 1.41 to 13.10% TOC.The Joggins Formation source rocks are thermally immature to slightly mature, with Tmaxvalues of 414-434°C and R_oof 0.6%. Hydrogenindices in the range of 316-978 suggest derivation from algal and vascular plant sources, withkerogen types 1, 2 and 2 to 3 represented. These data are consistent withwidespread flooding events, possibly from a marine source, of lowland plantcommunities.

Sequence Stratigraphy

The Joggins section is a coastal to alluvial succession, and should be a good candidate forrecognition of high-resolution Exxon sequences, sequence boundaries and systems tracts.However, our detailed analysis has failed to identify sequence boundaries in the section,despite the very complete exposure. Paleosols are apparently immature throughout, andchannel bodies are meandering or anastomosing in style, in accord with the associatedfloodplain facies. There are no indications of major basinward shifts of facies (for example,proximal braidplain sandstones) that might indicate major lowstand events or be candidatesfor valley fills. Instead, the section is dominated by a hierarchy of flooding surfaces, andthese define parasequences that are stacked in progradational and retrogradational sets. Theflooding surfaces are marked by bivalve-ostracod limestones, coals and carbonaceous shales,grey mudstones in predominantly red successions, and ostracod (freshwater) limestones insome redbeds. The parasequence sets form large-scale cycles (approximately 50-200 mthick) that reflect major transgressive-regressive events.The cyclestypically show a gradualpassage from shallow subtidal through lagoonal to alluvial facies as the coastal plainprograded, followed by a return through lagoonal to subtidal facies. The cycles vary fromnear-symmetric to strongly asymmetric in their facies organization. The sharp-based nature ofmost subtidal sandstone sheets suggests that many progradational events were associated withbase-level fall (forced regression), although the falling levels were apparently insufficient tocause incision and valley formation at this locality.

It is probable that rapid subsidence in the Cumberland Basin, with an abundant sedimentsupply, allowed sedimentation to be virtually continuous. Under these conditions, majorhiatuses that would be represented by valley fills or mature paleosols would not be generated.Such a style of basinal filling through a thick succession is unusual, and forms an interestingcontrast to the better known Exxon model.

Alluvial Redbeds of the Lower Joggins Formation (Stop No. 5.1)

Stop leader: Martin R. Gibling, Dalhousie University

The lower strata of the Joggins Formation provide an opportunity to examine the alluvialredbed facies. Channel bodies typically occupy narrow incisions, manifested as isolated bodiesin the intertidal zone in contrast to the more laterally continuous sheets of the grey bedshigher in the section. Internal bed geometry of the sandstone bodies is characterized bysuccessive cross-cutting hollow fills evocative of intermittent flashy flow.

These strata contrast in their sedimentary style with those associated with coal beds andwith fossil forests higher in the section, indicating that they were deposited under different,presumably more seasonal conditions.

Fundy Seam Fossil Forests (Stop No. 5.2)

Stop lader: John H. Calder, Nova Scotia Department of NaturalResources

At this locality, spanning the 37 m thick interval ( Fig. 21 ) from Coal 32 of Logan (1845) to Coal 29 (theFundy Seam), occurs one of the finest examples of the fossil lepidodendrid forests for whichthe Joggins cliffs are noted. The forests are coincidental with the first 'thick' coal bed of theJoggins Formation, Coal 32, atop a thick succession of redbeds. This interval serves toillustrate the sedimentological association of the lepidodendrid-calamitean forests that recursthroughout the section.

Erect Lycopsid and Calamite Trees, and Their Effects on Sedimentation

The section contains 49 recorded horizons containing erect trees ( Fig. 20 ), and new finds are constantly being made as the cliffs recedeand the thin sediment cover on the wave-cut platform shifts. The most spectacular preservedtrees are up to 3 m tall and nearly 1 m in diameter near the base, but many arealso visible truncated shortly above the base of the trunk. (Fallen logs up to 13 m longhave been found in former coal mines in the area). Virtually all lepidodendrid trees (lycopsidsbearing the rootstockStigmaria) are rooted in coal beds, however thin. The treesare easily visible in the cliff faces, and numerous occurrences with tens of trunks in a singlelayer can be examined in resistant sandstone 'reefs' that run across the wave-cut platform.

How the trees were entombed before they