Late Carboniferous and Early Permian drainage patterns in Atlantic Canada

MARTIN R. GIBLING Department of Geology, Dalhousie University, Hal*, N.S., Canada B3H 3J5

JOHN H. CALDER AND ROBERT RYAN Nova Scotia Department of Mines and Energy, P. 0. Box 1087, Halifax, N.S., Canada B3J 2x1

H. WALTER VAN DE POLL Department of Geology, University of New Brunswick, P. 0. Box 400, Fredericton, N. B. , Canada E3B 5A3

AND

GARY M. YEO Department of Geology, Acadia University, Wolfville, N.S., Canada BOP 1x0

Received April 27, 1991 Revision accepted September 9, 1991

Paleoflow data have been compiled for Late Carboniferous (late Westphalian A) to Early Permian alluvial deposits over a large area of Atlantic Canada. The data, which include more than 36 000 measurements of large-scale trough cross-strata, indicate a predominantly northeasterly paleoflow, and suggest that a major source area lay to the southwest of the region throughout the 30 Ma period represented. Uplands within the basin deflected paleoflow and probably formed important local drainage and sediment sources. Tectonostratigraphic analysis suggests that the drainage originated in the fold-and-thrust belt of the central Appalachians and parts of the northern Appalachians. Rivers probably followed northeast-oriented structural lineaments through the older Acadian mountains of the northern Appalachians. A considerable proportion of the rising oro- gen's drainage, and probably detritus, may have traversed basins along the strike of the mountain belt, a situation analogous to that of the modern Himalayas.

Les directions de palCocourants ont CtC compilCes pour les dCpBts alluviaux, datant du Carbonifkre tardif (Westphalien tardif A) jusqu'au Permien prkcoce, d'une grande aire de 1'Atlantique canadien. Les donnCes, incluant plus de 36 000 mesures des strates obliques de structures synclinales de grande Cchelle rCv2lent des pal6ocourants allant principalement vers le nord-est, et suggkrent que une importante aire nourricikre occupait le sud-ouest de la rCgion durant les 30 millions d'ann&es de la g r i - ode reprCsentCe. Les hautes-terres de I'intCrieur du bassin orlt d h i e les pal&ocourants, el il s'est probablement dCveloppt un drainage local majeur arrachant des sCdiments. Les analyses tectonostratigraphiques suggtrent que. initialement, le drainage a commencC 2 se dtvelopper dans la zone plisste et faillee des Appalaches du centre et partiellement dans les Appalaches du Nord. Les rivikres suivaient probablement les lineaments structuraux orient& vcrs le nord-est et traversPrent les montagnes acadiennes plus anciennes des Appalaches du Nord. Une part importante du drainage crCC par le soulbvement orogCnique, et probablement aussi des sediments, a pu traverser les bassins le long de la direction de la zone montagneuse, une situation analogue 2i celle qui existe actuellement dans les Himalayas.

[Traduit par la rkdaction] Can. J . Earth Scr. 29, 338-352 (1992)

Introduction

The Maritimes Basin of Atlantic Canada (Fig. 1) is a com- plex of depocentres that extends from western New Brunswick to offshore southeastern Newfoundland (1000 km) and from northern Newfoundland and the Gasp6 to southern Nova Scotia (500 krn). The basin, a structural and erosional remnant of a larger depocentre of unknown original extent, originated in the mid-Devonian following the Acadian orogeny. The Devonian and Early Carboniferous basin fill comprises allu- vial and lacustrine deposits of the Horton and Canso groups and marine deposits of the Windsor Group (other names are used for these groups locally). However, alluvial sedimenta- tion dominated virtually the entire basinal area from the Namurian or Westphalian A (Gussow 1953; Fralick and Schenk 1981; Knight 1983) to the Early Permian, a period of about 30 Ma. The strata form the Riversdale, Cumberland and Pictou groups (Fig. 2), typically several kilometres thick.

What was the source of this extensive and long-lived drainage system? van de Poll (1966, 1968, 1973) documented an easterly to northeasterly paleoflow for Late Carboniferous alluvial strata in New Brunswick, and suggested that the drain- age originated in the Appalachian mountain belt southwest of the Maritimes Basin. We here evaluate van de Poll's hypothe- Printed In Canada 1 lrnpr~me au Canada

sis using our own newly available paleocurrent data, published and unpublished, for Late Carboniferous and Early Permian rocks over most of the Maritimes Basin onshore. Important questions include, (1) Were intrabasinal and marginal uplands important drainage sources for the Maritimes Basin during the Late Carboniferous and Early Permian? (2) Were distant, extrabasinnl drainage sources important, and if so, where were they located and how were drainage networks disposed?

The approach employed here concerns drainnge systems but does not necessarily indicate the sediment source: drainage may have originated in a distant mountainous area but much sediment could have been derived from local, tributary sources.

Geological database

Stratigraphic units In the present study, local depocentres within the Maritimes

Basin are termed "basins" in their own right, following tradi- tion. Biostratigraphic units have been delineated in accord with western European zonation.

Our data were obtained from early Silesian (Westphalian A) to Early Permian units, the Cumberland and Pictou groups of northern Nova Scotia, and their correlatives elsewhere in

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GIBLING ET AL. 339

48"-

46'-

Corbontterous-Perm~on rocks:

Onrhore - Pmoable n i f~hotn ertcni

- Mojor Ioullr

Q 100 2mY I 1

KILOMETRES

FIG. 1. Distribution of Carboniferous and Permian rocks and major faults in the Maritimes Basin of Atlantic Canada. Modified from Williams (1978) and McCutcheon and Robinson (1987).

Nova Scotia, New Brunswick, and Prince Edward Island (Fig. 2). We refer also to published data for units in southern New Brunswick, GaspC, Newfoundland, and the Magdalen Islands. The Riversdale Group (Namurian to Westphalian A, locally Westphalian B) was not included because our data for this unit are few. All the units studied consist predominantly of alluvial sandstones, mudstones, and conglomerates, with minor lacustrine and eolian strata, and with local marine influ- ence in the Sydney Basin.

Paleojlow analysis Because the paleoflow data compiled here were obtained by

several workers over a 20 year period, four criteria were used in data selection to ensure consistency (Table I).

Table 2 documents the paleoflow indicators measured, using Miall's (1974) rank categories. Large-scale trough cross-strat- ification (rank 5) forms our major data source (n = 36 691). It is attributed to the downstream migration of three-dimen- sional dunes (Harms and Fahnestock 1965), and is a good indi- cator of both modern and ancient channel trend (Cant and Walker 1976, 1978). Rank 6 structures, mainly small-scale cross-stratification and primary current lineation, were used only as supporting evidence because they commonly form

under conditions of shallow and (or) low-velocity flow (Harms and Fahnestock 1965). Erosional structures (flute and groove casts and tool marks) and imbrication of gravel-sized clasts may have great directional significance (Bluck 1974), and were used locally.

A single sedimentation unit (that thickness of sediment deposited under essentially constant physical conditions: Otto 1938) was assigned a mean paleocurrent value where possible. However, sedimentation units are lensoid and difficult to dis- tinguish in many of the channel deposits, especially where exposure is limited. In such cases, all measurements were given equal weight.

Vector mean, vector magnitude and significance level of the directional data (Curray 1956) were calculated for most data groups. Other data were plotted as rose diagrams in 30" class intervals.

Paleoflow data

New Brunswick Platform The New Brunswick Platform (Fig. 1) extends from the

Rocky Brook - Millstream Fault in the north to the Belleisle Fault in the south (Fig. 3). Dinantian strata are thin or absent,

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340 CAN. 1. EARTH SCI. VOL. 29, 1992

FIG. 2. Stratigraphic units in the Maritimes Basin from which paleoflow data were obtained. The Riversdale Group underlies the analysed strata in many areas, but was not included in the present study. See Fig. 1 for locations. Age and stratigraphic information based on Barss et al. (1963), Barss and Hacquebard (1967), Hacquebard (1972) and for columns 1, 2: Gussow (1953), Ball et al. (1981); 3: van de Poll and Forbes (1984), Mossman and Place (1989); 4: Hacquebard and Donaldson (1964), Dolby (1984, 1987); 5, 6: Bell (1925, 1940), Fralick and Schenk (1981), Yeo (1985), Dolby (1987); 7: Bell (1938), Boehner and Giles (1986), Dolby (1988); 8: Hesse et al. (1982), Rust (1984), forma- tions indicated as probably mid-Carboniferous; 9: Stopes (1914), Plint and van de Poll (1982, 1984), Nance (1987); 10: Knight (1983); 11: Hyde (1984), Hyde et al. (1988); 12: Brisebois (1981). Vertical lines indicate ages of strata not represented in the area. Contacts shown as broken lines indicate unproven lower boundaries (columns 3 and 6) and areas where overlying strata are under water (columns 1-5 and 7). Time scale from Hess and Lippolt (1986).

and the Pictou Group (less than 1000 m thick) commonly rests with angular unconformity on pre-Carboniferous rocks. The Pictou Group is virtually undeformed, except near faults, and the region formed a stable "platform" that was not covered by fluvial systems until the mid-Silesian, after which it sub- sided slowly. The strata are cut by the northeast-trending Catamaran and Fredericton faults. Northeast of Fredericton, the Minto High (a buried basement high: Ball et al. 1981) is overstepped by Pictou strata. Anastomosed and braided river deposits have been identified locally (Rust and Legun 1983).

Paleoflow was northeasterly to easterly throughout deposi- tion of the Pictou Group over this large area (Fig. 3), based on 2 1 405 measurements of trough cross-strata. The paleoflow arrows represent vector means of grouped data, and the accompanying values for vector magnitude (in percent) sug- gest that the calculated directions are significant. Easterly paleoflow characterizes the coast east of ~a thur s t . Between the Fredericton and Belleisle faults, paleoflow shows a distinctive centripetal pattern with respect to the margin of the present- day outcrop, with a well-marked northerly paleoflow along the southern outcrop limit. The interfault region probably formed a depositional trough bordered to the south by uplands, but the absence of alluvial-fan deposits suggests that the paleomargin of the basin lay to the south or southwest and (or) that relief was gentle. Paleoflow appears to have been deflected slightly by the Minto High, which may have exhibited minor relief.

Moncton Basin The Moncton Basin (Fig. 1) is bounded by the Caledonia

Highlands Massif to the south and the Kingston Upland to the northwest (Fig. 3). The Westmoreland Uplift, a buried base- ment high, underlies the northeastern part of the basin. Along the Northumberland Strait, the basin is taken arbitrarily to span the area between Renouard Point and Cape Tormentine.

The Moncton Basin differs from the New Brunswick Platform

in containing a thick, deformed Dinantian succession and probably a thicker sequence of the Boss Point Formation. The latter formation is transitional upward into the Pictou Group, which is more than 750 m thick locally. As Boss Point and Pictou strata are lithologically similar in this region, the paleo- flow data may include a few measurements from the Boss Point. The basin appears to have subsided actively during the Dinantian but experienced a reduced subsidence rate, more akin to that of the adjacent New Brunswick Platform, during the Late Carboniferous.

Pictou Group paleoflow, based on 1558 measurements of trough cross-strata (van de Poll 1966), was northeasterly (vector mean 038") in the central part of the basin, but more easterly (vector mean 062") beyond the northeastern limit of the Caledonia Highlands Massif (Fig. 3). Vector magnitudes are generally high. Locally, paleoflow was more northerly along the southern basin margin adjacent to the massif, which may have influenced drainage by subsiding more slowly than the adjacent basinal area. No paleoflow deflection is evident adja- cent to the Kingston Upland or Westmoreland Uplift.

Prince Edward Island Prince Edward Island (Fig. 1) is underlain by Pictou Group

strata contiguous with those of New Brunswick and northern Nova Scotia across the Northumberland Strait. The exposed strata are estimated to be 1650 m thick (Frankel 1966), with an additional 2400 m proven by drilling (Hacquebard 1972; van de Poll 1983). The youngest strata onshore are late Early Permian (late Autunian) in age (Mossman and Place 1989).

Paleoflow inference is based on 9963 measurements of trough cross-strata from coastal exposures. Vector means and magni- tudes were calculated for data groups (Fig. 4). A grand vector mean of 047" with a vector magnitude of 53% was obtained (van de Poll and Forbes 1984). The orientation of parting line- ation (n = 1507) supports a northeasterly flow trend. The

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GIBLlNG ET AL.

TABLE 1. Criteria used in selection of paleoflow data

Criterion Rationale

1. Alluvial channel and fan deposits Reflect regional paleoslopes; floodplain, lacustrine, and eolian deposits not considered

2. Rank of paleoflow Directional variance decreases with increasing scale of flow indicator (Allen 1966; Miall 1974); high-rank indicators emphasized

3. Three-dimensional outcrop Important for accurate measurement of trough cross- strata (Dott 1973); majority of data collected from wave-cut surfaces; where exposure is limited, data were grouped and analysed statistically (van de Poll 1966)

4. Correction for tectonic dip Linear data corrected during measurement or with a steronet, where dips exceed 30" (Potter and Pettijohn 1977)

TABLE 2. Paleocurrent database for the Late Carboniferous and Permian strata of the Maritimes Basin

Rank No. of category Landforms Structures measured measurements

2 Alluvial fans Basin-margin fans (bajada) mapped at surface and in subsurface 1

3 Major channel reaches Channel bodies mapped in subsurface and outcrop 18

4 Minor channels and bar Small-scale hollow fills; lateral forms accretion surfaces 3 1

5 Structures within channels and bars Trough cross-beds

NOTE: Rank subdivision based on Miall (1974).

northeasterly paleoflow in the western part of the island accords with paleoflow patterns in the adjacent New Brunswick Plat- form and Moncton Basin. A more northerly flow direction prevailed in the southeast (Fig. 4). One conglomerate interval in this region, in contrast to overlying units and those else- where in the island, shows relatively high contents of igneous and metamorphic clasts, low contents of quartz and quartzite clasts, and low values of mean roundness (van de Poll and Forbes 1984). A relatively short-lived, proximal source area is indicated, possibly involving the Cobequid Highlands of Nova Scotia to the south (Frankel 1966; van de Poll 1983) and (or) an unknown upland farther south.

Cumberland Basin Paleoflow inference for the Cumberland Basin (Fig. 1) is

based largely on 1095 measurements of trough cross-strata (mainly one measurement per sedimentation unit), from which a grand vector mean of 062" was obtained (Fig. 5) , vector strength 72 %. Vector means for data groups are also shown. Channel-body orientation (rank 3) was deduced from closely spaced drill holes and mine workings, and an abandoned- channel fill (rank 3) and hollow-fills (rank 4) were measured in open pits. Paleoflow on alluvial fans that bordered the Cobequid Highlands Massif (rank 2) is inferred from facies distribution (surface and subsurface data) and imbrication.

In the western Cumberland Basin, paleoflow data from the Cumberland and Pictou groups (about 5000 m thick) show a well-defined easterly trend with a vector mean of 095" (n =

548 trough cross-beds) (Fig. 5). This trend is consistent throughout the Cumberland and Pictou groups, with minor variations adjacent to diapirs (which may have developed syn- depositionally) and near basin margins, and accords with earlier studies (Duff and Walton 1973; Rust et al. 1984; Salas 1986). Dispersal trends are generally southeasterly on the northern limb and northeasterly on the southern limb of the Athol Syncline, which probably formed a depositional trough coaxial with the present structure.

In the south-central Cumberland Basin, data were derived from alluvial-fan conglomerates of the basal Cumberland Group (Polly Brook Formation, 600 m thick) and coeval coal- bearing fluvial strata (Springhill Mines Formation, 1300 m thick). Mapping of alluvial-fan deposits indicates northerly, transverse drainage from the Cobequid Highlands (Fig. 5). Cross-bed trough axes, measured as trends in poor outcrops, suggest northwesterly paleoflow across the fans. Channel bodies in the Springhill Mines Formation trend northeasterly, indicating axial paleoflow parallel to the southern basin mar- gin formed by the Cobequid Highlands. At Salt Springs, northeasterly (axial) paleoflow is also indicated from orienta- tions of hollow fills and a few trough cross-beds.

In the eastern Cumberland Basin, trough cross-beds (n =

503) in the Cumberland and Pictou groups show two distinct trends. Paleoflow was north-northwesterly (349") in the Tata- magouche Syncline adjacent to the southern basin margin (Cobequid Highlands). Paleoflow was northeasterly (045 ") along the Northumberland Strait, in accord with Pictou paleo-

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342 CAN. J. EARTH SCI. VOL. 29, 19W

. . . _ . . . . . . . . . . . . _ . . . .

n.22 963

GULF OF ST LLTWRENCE

0 Olher pndom~nanlly older rocks

Pokcdlow veclor B slrcnglh

FIG. 3. Paleoflow map for Late Carboniferous strata of the New Brunswick Platform and Moncton Basin. Arrows show local vector means for trough cross-strata, with vector magnitude in percent. Summary rose diagram represents all data (22 963 measurements). Note the generally northeasterly paleoflow (see text for discussion). Minto High and Westmoreland Uplift from Gussow (1953) and Ball et al. (1981).

flow in the contiguous Moncton Basin and western Prince Edward Island.

Stellarton Gap The Stellarton Gap forms the physiographic lowland between

the Cobequid and Antigonish highlands of northern Nova Scotia, at the eastern end of the Cumberland Basin (Fig. I). Two outcrop areas, the Stellarton Graben and North Stellarton Gap (Figs. 2, 6), are distinguished based on strong facies con-

trast in coeval strata. Most paleoflow data (Fig. 6) were derived from trough cross-strata (n = 2313), with some measurements of imbrication in conglomerates. Lower rank indicators, including parting lineation, ripple crests, ripple cross-lamination, and oriented plant fragments, generally show good agreement with the higher rank data (Yeo and Ruixiang 1987, Fig. 3).

The Cumberland Group comprises two formations. The Middle River Formation (about 1150 m thick) shows locally

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GIBLING ET AL. 343

I I

63000' Vector f7lean (azimuth) 62200'

- 47'00' / for trough cross-strato based on 31- 346 obsavations-

,' Vector mean based on less than 20 observations I

Locolion Mop

9963 GULF OF

ST L A W R E N C E

- 46'00' 46'00'

.............. ............... .............. I I ............... 1 I 1 0 111 2 0 30 4 0 k m

.............. ............... Pictou Group ............... ..............

64O00' 63O00' 62'00' 1 I i

FIG. 4. Paleoflow map for Stephanian and Permian strata of Prince Edward Island. Arrows show local vector means for trough cross-strata (9963 measurements), with indications of vector magnitude (in percent). Summary rose diagram shows vector mean of 047" and vector magni- tude of 53%. Note the northeasterly paleoflow with a more northerly trend in the eastern part of the island. Modified from van de Poll and Forbes (1984).

unimodal but regionally polymodal paleoflow, with north- easterly to southeasterly flow away from the eastern end of the Cobequid Highlands and northwesterly flow away from the western end of the Antigonish Highlands (Figs. 1, 6). Imbrica- tion at four localities in the New Glasgow Conglomerate (> 700 m thick) was northerly, away from the Cobequid Fault (Fig. 6).

The Stellarton Formation (>2700 m thick) is restricted to the Stellarton Graben between the Cobequid and Hollow faults. The formation is interpreted as a lacustrine and deltaic deposit with fluvial components (Bell 1940; Fralick and Schenk 1981). Polymodal paleoflow (Fig. 6) supports the stratigraphic evidence for a small, restricted basin.

Pictou Group paleoflow was predominantly north-northeast- erly (Fig. 6), in accord with paleoflow in the contiguous east- ern Cumberland Basin. Northerly paleoflow in the area north of the Stellarton Graben suggests that a regionally important river system periodically flowed northward through the Stel- larton Gap.

Sydney Basin In the Sydney Basin (Fig. l), the Morien Group, about

2000 m thick, is divided into the South Bar and Sydney Mines formations with a local facies equivalent, the Waddens Cove

Formation, in the southeast part of the basin. The Pictou Group underlies much of the offshore area. Agglutinated for- aminifera, suggesting marine influence, have been identified in the Morien Group (Thibaudeau and Medioli 1986).

Both the South Bar and Sydney Mines formations (Fig. 7) show northeasterly paleoflow, based on 357 measurements of trough cross-strata on wave-cut platforms (generally one mea- surement per sedimentation unit). The South Bar Formation shows a relatively low overall paleoflow variability, consistent with its braided-fluvial origin (Rust et al. 1987; Rust and Gibling 1990). The basal strata show strong paleoflow deflec- tion adiacent to basement blocks that border the Morien Group; paleoflow fanned around the northeastern end of the Coxheath Hills and was directed eastward at the western out- crop limit (Fig. 7). Paleoflow was deflected near outcrop mar- gins of the Boularderie and Sydney Harbour synclines (Giles 1983). The higher strata show consistent northeasterly paleoflow.

The Sydney Mines Formation shows a relatively high over- all paleoflow variability, consistent with its meandering- fluvial origin (Gibling and Rust 1987; Rust et al. 1987). The trough cross-strata represent 28 channel-sandstone bodies, the paleoflow variability of some of which is almost as great as that of the entire formation. Linear to slightly sinuous belts of thinned coal beneath channel-sandstone bodies offshore (Duff

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344 CAN, J , EARTH SCI. VOL. 29, 1992

FIG. 5. Paleoflow map for Late Carboniferous strata (Cumberland and Pictou Groups) of the Cumberland Basin. Arrows show local vector means for trough cross-strata (1095 measurements). Channel-body trends are from mine and drill-core data at Springhill. Fan trends indicate directions of basinward fining adjacent to the Cobequid Highlands Massif. Note the overall northeasterly paleoflow for the basin, with strong local variation adjacent to pre-Carboniferous rocks of the Cobequid and Caledonia massifs.

et al. 1982; Calder et al. 1987) (Fig. 7) probably correspond to thalweg positions (rank 3). Four channel bodies (rank 3) in the Waddens Cove Formation show northerly paleoflow (Gibling and Rust 1990).

The progressively reduced influence of adjoining basement areas on Morien paleoflow patterns suggests that a preexisting topography was progressively buried under the alluvial plain (Giles 1983; Rust et al. 1987). The relatively fine grained strata and the absence of alluvial-fan facies strongly suggest a distant source area (Gibling et al. 1987).

Minas Basin In the Minas Basin area south of the Cobequid Fault (Fig. I),

the Scotch Village Formation, in part of Westphalian D age (Barss 1965), has yielded a vector mean of 020" based on 10 trough cross-bed measurements.

Other areas In the GaspC, a Silesian, but possibly Visean, age was sug-

gested for the Cannes de Roche Formation (Hacquebard 1972; Rust 1984) (Fig. 1, Table 2). The Bonaventure Formation of Chaleur Bay is undated but is probably mid-Carboniferous in age (Hesse et al. 1982). Paleoflow data (150 measurements, chiefly imbrication) from the Bonaventure suggest deposition in a Carboniferous valley with transverse marginal drainage and eastward axial paleoflow (Zaitlin and Rust 1983). A simi- lar pattern of marginal and southeastward axial flow was inferred for the Cannes de Roche (95 measurements), for which the composition of some detritus was matched with local sources to the west (Rust 1984).

In southwestern New Brunswick (Fig. 3, Table 2), the fluvial Boss Point Formation is overlain conformably by alluvial-fan deposits of the Tynemouth Creek Formation, both Westphalian A-B in age, at Quaco Head (Plint and van de Poll 1982, 1984). Paleoflow was northeasterly for the Boss Point but northwesterly for the Tynemouth Creek Formation (98 cross-bed measurements). Near St. John, the Lancaster Formation (Westphalian A -C) overlies, is laterally equiva- lent to, and locally underlies the Balls Lake Formation (Stopes 1914; Nance 1987). Westerly paleoflow was recorded for the Balls Lake Formation. The westerly and northwesterly paleo- flow in these areas suggests a rising upland to the southeast, associated with northwest-directed thrusting at a restraining bend in the Cobequid-Chedabucto fault system (Plint and van de Poll 1984; Nance 1987).

In western Newfoundland (Fig. 1, Table 2), the Barachois Group of the Bay St. George Basin is early Namurian to West- phalian C in age (Hacquebard et al. 1960; Knight 1983; Solomon 1986). Namurian strata (Searston Formation) show southwesterly paleoflow in the basal 500 m, with sparser, bimodal (southwesterly and northeasterly) directions in younger strata (125 measurements: Knight 1983). Strata of probable Westphalian A age show both southerly and north -northeast- erly directions (91 cross-bed measurements: Solomon 1986). No paleoflow data were recorded for a small outcrop of West- phalian C age near Stephenville. In the Deer Lake Basin, the Howley Formation (Westphalian A or possibly in part late Namurian: Hacquebard et al. 1960; Belt 1969; Hyde 1984) has yielded few paleoflow data, but clast composition suggests

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CIBLINC ET AL. -345

FIG. 6. Paleoflow map for Late Carboniferous strata of the Stellarton Gap. Trough cross-strata are represented by 2313 measurements. Note the overall northeasterly paleoflow for the area, but the high degree of paleoflow variability within the Stellarton Graben, which was interpreted as a pull-apart basin by Fralick and Schenk (1981) and Yeo and Ruixiang (1987).

.. ".. ' . ' . .. . . . . . . . . . . . ' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................ \ Trough emam-bods (n r15)

\ Trough cmsa-beds (n c 15) . . . . . . . . . . F elart hnbrlcatlon In * 15)

vector strannth

\ \ k b

100% 75% 50% 25%

new Glasgow C6nglomerste

Middle River Fm. In r 207) kr~omat ra r

a source area to the east (Belt 1969; Hyde 1984). The fluvial Humber Falls Formation, the lower part of which is Visean, shows southwesterly paleoflow (1 17 trough cross-bed mea- surements, vector mean 229" : Hyde 1984). Thus, paleoflow was southwesterly but locally variable in several Visean to mid-Silesian formations in western Newfoundland. Variable paleoflow would be expected for such small depocentres, which developed in association with the transcurrent Cabot fault system (Knight 1983; Hyde 1984; Hyde et al. 1988).

The Magdalen Islands (Fig. 1) provide the only potential source of paleoflow information near the centre of the Mari- times Basin. The Cap-aux-Meules Formation (Stephanian or younger) is correlated with the Pictou Group, but the ubiqui- tous large-scale cross-bedding is probably eolian (Brisebois 1981). Paleoflow was predominantly southwesterly.

I Paleoflow summary (I) Northeasterly to easterly paleoflow characterized all

western and southern parts of the Maritimes Basin (Fig. 8) from the late Westphalian A to the Early Permian. Drainage

1 was southeasterly, at least in the early Silesian, in northern- most New Brunswick and GaspC. A major source of drainage, and probably of sediment, is inferred to have lain to the south- west and west of the basin. Southwesterly paleoflow may have 1 characterized northeastern parts of the basin early in the Silesian.

I

(2) Local uplands caused paleoflow diversion in many parts of the basin, but few alluvial-fan deposits are present. The influence of local uplands was progressively reduced by onlap through the Late carboniferous, except in the Stellarton GG and possibly eastern Prince Edward Island.

(3) Paleoflow within the basin was generally parallel to regional structural lines, including fault traces.

Tectonic reconstruction

Location of mountainous regions The northeasterly paleoflow documented for much of the

Maritimes Basin suggests that most drainage originated in the Appalachian Orogen (Fig. 9), as inferred by van de Poll (1973). Structural and stratigraphic data from the central and southern Appalachians indicates that northwest-directed Alleghanian thrusting was associated with the progradation of clastic wedges across the Appalachian foreland basin during the late Mississippian to Permian (Cook et al. 1979, 1981; Donaldson and Shumaker 198 1). Tankard (1986) correlated the onset of extensive fluvial sedimentation (Lee Formation and equivalents) with the initiation of Alleghanian overthrust- ing. Thick Alleghanian sediments and (or) thrust masses for- merly covered southeastern Pennsylvania and parts of New York State (Friedman and Sanders 1982; Johnsson 1986; Levine 1986).

Geodynamic modelling of the orogen has enabled its topo- graphic elevation to be assessed. Modelling of Alleghanian thrust-load distribution in the central and southern Appa- lachians (Quinlan and Beaumont 1984; Beaumont et al. 1987, 1988) suggests Pennsylvanian loads of up to 7 km and Permian loads of up to 12 km. Models based on comparison of calcu- lated load distribution with Bouguer gravity gradients (Stock- ma1 et al. 1984) suggest that mountainous areas existed locally in the southern and central Appalachians by the early Pennsyl- vanian and throughout the area by the Permian (Beaumont

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346 CAN. J . EARTH SCI. VOL. 29, 1992 I

FIG. 7. Paleoflow map for Late Carboniferous strata (Morien Group) of the Sydney Basin. Trough cross-strata are represented by 357 mea- surements. Linear belts of thinned coal (channel-body trends) are from offshore mine data (see text). Note the overall northeasterly paleoflow, subparallel to fault and fold trends.

et al. 1987; Fig. 9). Pressure - temperature - time data allow constructive (relief increasing), destructive (relief decreas- ing), and steady-state conditions of the orogen to be distin- guished for some areas (Jamieson and Beaumont 1988, 1989). A steady-state orogen may yield large amounts of detritus, despite remaining at a relatively constant elevation. Results suggest that the central Appalachians formed a steady-state orogen during most of the Pennsylvanian, with constructive or steady-state conditions from Maryland southward, and that all areas were constructive during the Permian. Slingerland and Furlong (1989) suggested that the Early Permian central Appalachians possessed a central Andean topography with average relief of 3.5-4.5 km and width of 250-300 km.

In the northern Appalachians, widespread Devonian allu- vium attests to the existence of mountainous areas. Late Car- boniferous and Early Permian thermal and structural events and intrusions have been documented in eastern New England, the Gulf of Maine and southwestern Nova Scotia (Skehan et al. 1986; Reynolds et al. 1987; Cormier et al. 1988; Hutch- inson et al. 1988; Pe-Piper and Loncarevic 1989; Dallmeyer et al. 1990). The ~ a r r a ~ a n s e t t Basin and adjacent smaller depocentres contain 3-6 km of coarse-gained alluvium, including thick conglomerates, which are dated as West- phalian A to Stephanian C (Skehan et al. 1979, 1986). Paleo- flow directions within the basins are variable. consistent with deposition in small, tectonically active depocentres (Skehan et al. 1986). The Narragansett Basin continues southward off- shore (McMaster et al. 1980) and may extend to the edge of the present continental margin (Klitgord and Behrendt 1979;

Fig. 9), while a linear trough, probably containing Carbonifer- ous strata, extends northeastward from the adjacent Boston Basin into the Bay of Fundy (Ballard and Uchupi 1975; Fig. 9). Small Carboniferous outliers are found along the Norumbega fault zone in Maine (Skehan et al. 1979).

The southern part of the Maritimes Basin lay within a Late Paleozoic strike-slip zone that extended from the Appalachians to the Urals (Arthaud and Matte 1977). Late Carboniferous strike-slip faulting has been widely documented (Webb 1969; Yeo and Ruixiang 1987), and probably generated relief locally through thrusting associated with local transpression (e.g., Plint and van de Poll 1984; Nance 1987).

The above review indicates that active tectonism, alluvial sedimentation, and probably considerable relief characterized the southern, central, and parts of the northern Appalachians during the Late Carboniferous and Permian. We suggest that drainage entering the Maritimes Basin from the southwest originated primarily in this region. The petrography and source of sediment deposited within the Maritimes Basin has received little systematic study to date.

Extrapolation of paleoflow directions suggests that the Mauritanide fold-and-thrust belt (LCcorcht and Sougy 1978; LtcorchC 1983) was a possible, although less obvious, source of drainage for the Maritimes Basin (Fig. 9). Rocks of the belt 1 are thrust eastward over the West African Craton (Fig. 9), with widespread Narnurian to Stephanian thrusting (Ltcorche 1983; Villeneuve and Dallmeyer 1987). Mylonitized zones in the southern Mauritanides indicate a major Early Permian tec- tonothermal event (Villeneuve and Dallmeyer 1987). The

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GIBLING ET AL. 347

E WFOUNULAND

Carbonlleroul - Pcrmlon rocks :

Onshore

- Prokb ia oilshore crtent

- Major laults

4 RoDresenlallve Paleoflow directions

Ross doaqrnml tor basinol regions * (trough cross- stratal

FIG. 8. Summary paleoflow map for Late Carboniferous (late Westphalian A) to Early Permian strata of the Maritimes Basin. Solid arrows show representative paleoflow directions selected from Figs. 3-7, with a few data points from other studies (see text). Rose diagrams show all measurements of trough cross-strata within local areas of the basin. Note the predominantly northeasterly paleoflow, subparallel to the line of major faults.

Reguibat Spur, a cratonic extension that transects the Mauri- tanide Belt (Fig. 9), may have acted as an "indentor" into the southern and central Appalachian region during late stages of continental convergence (Lefort 1987; Villeneuve 1987).

Drainage paths Drainage paths from the inferred central-northern Appa-

lachian source area to the Maritimes Basin are speculative. Drainage is presumed to have followed structural lines, espe- cially those associated with faults active during the Allegha- nian orogenic phase, and to have connected known Late Paleozoic depocentres .

We suggest that rivers flowed northeastward through the northern Appalachians to cross the New Brunswick Platform. The Norumbega Basin, situated on the Norumbega Fault, may have been an intermontane basin on one such drainage line. Drainage may have entered the northern Maritimes Basin through the Chaleur Bay paleovalley and possibly along Aca- dian faults in the Gasp6 (Bourque et al. 1986), at least in the early Late Carboniferous.

Drainage to the Cumberland (and Moncton?) Basin may have traversed the Narragansett Basin and a structural trough in the Bay of Fundy (Fig. 9). The southward, offshore con- tinuation of the Narragansett Basin suggests the possibility of through drainage from more southerly parts of the Appa- lachians. Topography in the Cumberland Basin approaches probably was complicated by uplands east of southern New Brunswick in the Westphalian B (Nance 1987) and probably through to the Permian.

The Stellarton Gap probably received drainage along the Cobequid Fault, although drainage from local uplands was an important component of the small Stellarton Graben. In the early Permian, a more proximal source area south of the Mari- times Basin may have been responsible for the influx of coarse clastics into eastern Prince Edward Island. Local uplift in the Cobequid Highland Massif is possible also.

All these alluvial areas would have drained across Prince Edward Island towards the central (presently offshore) part of the Maritimes Basin.

The Sydney Basin received drainage through central Cape

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34 8 CAN. J . EARTH SCI. VOL. 29, 1992

NORTH AMERICAN

BOSTON BAS/!/

Corbonlferous- Perrnlon rocks

WEST AFRICAN generol~zed poleoflow

Major faults / Major thrusts <

FIG. 9. Late Carboniferous paleogeographic reconstruction for eastern North America and adjacent areas. Continental disposition from Scotese and McKerrow (1990). Reconstruction shows no translocation along faults in the Maritimes Basin. Disposition of mountainous areas in the Appalachians from Jamieson and Beaumont (1988, Fig. 1). The Appalachians are divided at the New York - Pennsylvania and Kentucky-Tennessee state boundaries into "northern," "central," and "southern" regions (Osberg 1983). West African geology from LCcorchk and Sougy (1978). Late Carboniferous to Permian paleoflow in the Appalachian Basin from Donaldson and Shumaker (1981) and in the Tindouf Basin of Morocco from Padgett and Ehrlich (1976).

Breton Island. Maritimes Basin drainage probably traversed Ingersoll 1985) suggest that this drainage pattern has been the Sydney Basin, where periodic marine influence is indi- long-lived and that an unknown but probably large proportion cated, and continued eastward to western Europe where Late of available detritus was transported longitudinally from the Carboniferous marine strata are widely distributed. Early orogen. Jurassic uplift of Nova Scotia (Ravenhurst et al. 1990) mav have marked the end of the drainage pattern documented here. Conclusions

The central Appalachians may have formed a major drain- Using a database of more than 36000 measurements of age divide if the Reguibat Spur acted as an indentor into the

mid-Appalachians during continental collision. trough cross-strata in alluvial-channel deposits over a wide area, we have evaluated van de Poll's (1973) hypothesis that

A modern analogue Late Carboniferous and Early Permian drainage in the Mari- Large amounts of sediment were transported southward into times Basin of Atlantic Canada was derived from the Appa-

the foreland basin of northern India from the rising Himalayas lachian Orogen to the southwest. Our compilation indicates during the late Cenozoic. However, some of the world's larg- that northeastward paleoflow prevailed in most of the exposed est rivers rise behind the main thrust front and drain longitudi- part of the basin for at least 30 Ma (late Westphalian A to early nally for long distances to receiving basins such as the Bay of Permian), and supports the identification of the Appalachian Bengal and the South China Sea (Fig. 10). Thick Tertiary sedi- Orogen as a major drainage source for the Maritimes Basin. ments in some of these basins (Paul and Lian 1975; Suczek and Local uplands within the basin significantly influenced paleo-

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GlBLING ET AL. 349

FIG. 10. Regional structure and drainage of eastern Asia. Heavy solid and broken lines indicate major faults, some of them strike-slip, and solid triangles indicate thrusts (or subduction west of Malaysia); data from Molnar and Tapponnier (1975) and Tapponnier et al. (1982). Note that many large rivers follow structural lineaments and run laterally into receiving basins (compare with Fig. 9 for the Late Paleozoic Appa- lachians).

flow patterns, especially early in the Late Carboniferous, and contributed both drainage and sediment to the basin locally. The Maritimes Basin in turn probably drained eastward to western Europe.

Consequent drainage that links rising fold-and-thrust belts to subsiding foreland basins is currently receiving considerable attention. The present study suggests that longitudinal drainage was an important part of the Appalachian Orogen, as it is of the modern Himalayas, and hence large volumes of fluid and probably of sediment were transported from the orogen to basins other than the foreland basin and located in diverse tec- tonic settings. Rising thrust belts may form a barrier that pre- vents drainage from reaching the adjacent foreland basin, at least locally (Hirst and Nichols 1986), and thus contribute to the development of persistent longitudinal drainage.

Acknowledgments We thank David Piper and Guy Plint for their thoughtful

reviews of an earlier draft, and John Clague for editorial assistance. Financial and technical assistance was provided by the Nova Scotia Department of Mines and Energy, in part under the Canada - Nova Scotia Mineral Development

Agreement. A Natural Sciences and Engineering Research Council of Canada operating grant (A8437) to M.R.G. is gratefully acknowledged.

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