e ATLANTIC GEOSCIENCE SOCIETY

ABSTRACTS

The origin, history and potential of sedimentary basins in eastern and offshore

Symposium 1983

MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 19, 89-103 (1983)

0711-1150/83/020089-14$3.10/0 46 ABSTRACTS

Whether it's known as a symposium or colloquium, the annual A.G.S. gather- ing held this year in Fredericton, N.B. is rapidly becoming the highlight of the local geological scene. This year it was the turn of the symposium with the theme being, "The history, development and economic potential of sedimentary basins in eastern and offshore Canada". The weekend activities started on Friday, 28th January, when the faithful assembled at Keddy's Motor Inn in Fredericton, N.B. About 75 geologists were on hand to hear the two evening presentations, one on offshore geology, the other on the coal basins of Nova Scotia. On Saturday, attendance swelled to 130 and the technical sessions ran from 9 a.m. to 5 p.m. with talks covering all of the Phanerozoic. The onshore was covered in some detail, with the Meguma being a particularly popular topic. By comparison, the offshore received scant attention with only two papers falling into this category. The standard of the presentations was excellent and the accompanying illustrations were generally of a high qua- lity. I was also impressed with the poster exhibits, especially the summa- tion of the remapping program in the Cobequid Highlands. All in all it was a most informative and enjoyable technical program. The Society's annual meeting was sandwiched between the end of the techni- cal sessions and the beginning of the banquet, a procedure recommended to other societies whose business meetings last forever. The President, Laing Ferguson, after dispensing with the preliminaries, introduced the nominees for the new Executive and Council. All were duly elected. There was unani- mous agreement to seek affiliation with C.S.P.G. and to postpone changes to the Bylaws. I appreciated the background information provided for the annual meeting, especially the President's and the Treasurer's reports. The day's activities were brought to a close at the banquet where the in- vited speaker was Hugh Morris, President of G.A.C. He gave an entertain- ing talk on federalism, provincialism and separatism, and showed inspired taste by not digressing for too long. Laing Ferguson thanked the organi- zers of the Symposium, Walter van de Poll, Ron Rickerill and Jim Noble, for a very successful technical and social program. Walter van de Poll in turn thanked all the students and staff of the Department of Geology, University of for their help in running such a trouble-free meeting. The curtain came down on the ABBA II quartet who sang, "All the President's men", a spoof on A.G.S., after which we dispersed to various parties. It was a great meeting; the weather was superb and I am already looking forward to the song entries in the Geolovision song contest at the 1984 reunion. — Graham Williams MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 91 Lower Carboniferous volcanic rocks of the Magdalen Islands: Volcanism in the Fundy Epieugeosyncline Barr, S.M. and MacdonalcL, A.S., Department of Geology Acadia University, Wolfville, N.S. BOP 1X0

Volcanic rocks on the Magdalen Is- led to previous interpretations that lands occur within and overlying Lower the rocks are alkalic based on major Carboniferous clastic, carbonate, and element chemistry. However, the rela- evaporitic sequences which have been tively immobile elements (Ti, Nb, Y, Zr) correlated with the Windsor Group of show clearly that the basalts are con- Nova Scotia and New Brunswick. The vol- tinental tholeiites, probably generated canic units consist mostly of volcani- under moderately thick continental crust. clastic rocks and basaltic flows, in- truded by gabbroic dykes and plugs. The Other volcanic rocks formed in asso- stratigraphy has been widely disrupted ciation with the Fundy Epieugeosyncline by evaporite diapirism which has pro- range in age from Middle Devonian to duced basaltic breccia and melange, the late Carboniferous. They are exposed at latter particularly spectacular where the surface in Nova Scotia and New Bruns- gypsum and volcanic rocks are involved. wick and have been encountered in the Petrological studies of the basaltic subsurface in Prince Edward Island and flows and intrusions show that their the Gulf of St. Lawrence. This wide dis- primary mineralogy included plagioclase tribution of volcanic rocks both geo- (labradorite ?), titaniferous augite, graphically and in time implies a rela- and olivine, but intense alteration has tively high geothermal gradient in the produced abundant chlorite, sericite, Fundy Epieugeosyncline throughout its carbonate, epidote, hematite, and other development. This may have important secondary minerals. The alteration is implications for the formation both of reflected in wide chemical variations, hydrocarbon accumulations and of mineral especially in Ca, Na, and K, which have deposits of submarine-exhalative type.

Marginal molassic basin onlap and mineral deposits, Loch Lomond Basin, Cape Breton Island R. Boehner, Nova Scotia Department of Mines and Energy P.O. Box 1087, Halifax, N.S. B3J 2X1

The Loch Lomond Basin is a small and marine evaporite-carbonate sediments structural basin that presently has the representing molassic deposition. Major form of a northeasterly trending half rock packages recognized are comparable graben. It is fault bound to the north- (with a few exceptions) with those in west and contains up to 800+ m of Visean other parts of Nova Scotia and include to Namurian age rocks. It is bordered in ascending order: Windsor Group eva- on the northwest by Hadrynian Fourchu porite, fine to coarse redbeds and marine Group volcanic-sedimentary rocks and carbonate (middle and upper parts only), plutonic rocks of the East Bay Hills. Enon, Loch Lomond and Uist Formations The major unconformable contact to the (up to 350 m); fine grained Canso Group southwest is with similar rocks of the (up to 200 m); and upper Canso Group East Bay Hills (largely the Loch Lomond (dominantly grey sandstone up to 250+m). Pluton). Progressive onlap and overstep of The Loch Lomond Basin contains a mixed stratigraphic packages with accompany- Carboniferous succession dominated by ing facies changes are well documented marginal continental alluvial-fluvial both parallel and perpendicular to the 92 ABSTRACTS strike of the Loch Lomond Basin. Simi- graphic onlap-overstep). Progressive on- lar changes are also present in the lap-overstep is inferred to be the Salmon River - Glengarry Basin. Details principal factor which produced condi- of these features remain to be fully tions suitable for the concentration documented (1983). and entrapping of contact oriented and Paleotopography and tectonism greatly stratabound celesite, barite, Pb, Zn, influenced sedimentation in the Loch Cu, Mn and abundant, but economically Lomond Basin especially the early strati- unattractive Fe. graphic units. Their importance decreased with time as erosion and deposition of Base metals ± minor celestite ± Fe ± onlapping strata buried the basement Mn occurrences are contact oriented and topography. The stratigraphic section localized at or near unconformity pinch- to the top of the fine grained Canso outs at all stratigraphic levels. Secon- Group displays general fining upward dary redistribution of celestite ± base and basinward trends. Coarse fanglomer- met las ± Fe (supergene ?) is inferred ate facies occur as a marginal facies to have occurred in karst related hydra- of the Windsor Group at all strati- tion zones. Barite and celestite ± Pb ± graphic levels. Zn ± Fe are dominantly stratabound, The numerous mineral occurrences in stratified to nodular deposits (within the area are concluded to be closely marine carbonate, gypsum-anhydrite, red related to paleogeography (topography), siltstone-sandstone) and may represent tectonics and sedimentation history diagenetic replacement during or soon (especially unconformities and strati- after Windsor Group sedimentation.

Fresh-water fauna and flora assemblage from the Devonian La Garde Formation of northern New Brunswick ^W.H. Forbes and ^A.E. Kasper, Jr. *Department of Geology, University of Maine, Presque Isle, Me. 04769 2Department of Botany, Rutgers University, Newark, New Jersey 07102

The oldest recorded fresh-water fossil plexa is known from the Middle Devonian assemblage of animals and plants is Panther Mountain Formation of New York reported from the Campbellton Formation State; the other species are long-rang- of northern New Brunswick, Canada. These ing. The strata have also yielded the continental rocks outcrop along the following fish: Cephalaspis acadica, C. south shore of the Restigouche River at campbelltonensis whiteaves, C. jexi, Campbellton and are of Lower/Middle Phyllctaenaspis acadia. P. atholi. In Devonian age. The unique association of addition this mudstone dike contains the plants and animals occurs within a cal- following invertebrate fossils: ostra- careous mudstone dike cross-cutting a codes, gastropods and occasional seg- rhyolite breccia. The reddish-brown ments of eurypterids. The paleoenviron- slightly calcareous siliceous mudstone ment was probably a pond containing fish, readily weathers to a light buff color snails and ostracodes with vascular accentuating the carbonaceous plant and plants growing along its periphery. The animal material on its surface. The environment of deposition was most plant assemblage contains several well- likely over-bank deposits produced by characterized species, Leclercqia com- periodic flooding. The presence of the plexa, Psilophyton princeps, Drepano- Middle Devonian plant, Leclercqia com- phycus spinaeformis and numerous uniden- plexa, suggests that the age of the for- tified plant remains. Leclercqia corn- mation be restricted to Middle Devonian. MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 93 Preliminary interpretation of gravity and magnetic results from the Epicentral Region of the 1982 Miramichi earthquakes K.B.S. Burke, Department of Geology University of New Brunswick, Fredericton, N.B. E3B 5A3 J.J. Chandra, Geology Surveys Branch Department of Natural Resources, Fredericton, N.B. E3B 5H1

The 1982 Miramichi earthquakes occur- ments show that the diorite unit has a red in a region in central New Bruns- magnetic susceptibility that is gene- wick that is occupied by the North Pole rally two to three times higher than Pluton, an intrusion of Middle Devonian the granitic units, but the phyllite age, that has intruded deformed, Cambro- unit in the country rocks shows a much Ordovician, metamorphic rocks. A 300 wider range in susceptibility. station gravity survey of the epicen- On a regional basis, a large gravity tral region was completed in 1982. In low coincides with the exposed middle addition, samples were collected for portion of the North Pole Pluton and density determinations and in situ mag- also shows its much greater subsurface netic susceptibility measurements were extent. However, in the detailed gravity made on all major outcrops. The results survey results, this large gravity low of this survey, together with previously is also seen to contain smaller posi- flown aeromagnetic data, are being used tive anomalies that suggest that the to construct a subsurface model that higher density diorite unit is more ex- should provide useful constraints in tensive at depth than indicated by sur- earthquake mechanism studies. face exposure of this unit. Initial Density measurements on the samples thickness estimates from the gravity show that the granitic rock units have anomalies suggest that the metamorphic the lowest mean densities (2610-2630 units are generally thin in the region Kgs/m3), whilst the diorite unit.has (0.5-1 km) and that the Miramichi earth- the highest mean density (2780 Kgs/m3). quakes and aftershocks are confined to The metamorphic country rock units have the plutonic body. One explanation for a range of mean densities between 2650 this confinement of the hypocenters is to 2750 Kgs/m3 , with some individual that the brittle rocks of the pluton samples of the phyllite unit yielding are weaker than the surrounding tougher densities as high as 2850Kgs/m3. The metamorphic country rocks when exposed in situ magnetic susceptibility measure- to the same stress system.

Slate belt tectonics in the Bickferton Barrens, N.S.: Horizontal extension and simple shear within the Meguma Basin B.H. O'Brien, Nova Scotia Department of Mines and Energy P.O. Box 1087, Halifax, N.S. B3J 2X1

Greenschist facies sedimentary rocks exceeding 5 km in thickness. Within the underlying the Bickerton Barrens illus- multilayer bedding and stratiform quartz trate a long history of inhomogeneous veins acted as both the principal planes progressive deformation. A discontinuous of shear and anisotropy. Flattening deformation path gave rise to several associated with layer-parallel shear is phases of deformation, each governed by evidenced by the formation of gently a particular type of crustal shortening. dipping, grain alignment cleavage and The earliest event produced a layer- the development of.gently plunging, step parallel shear of variable intensity folds. Localities where bedding is down- throughout a shale-sandstone multilayer folded may mark the site of underlying 94 ABSTRACTS faults, perhaps themselves rooting in wrench movements may have been active the basement to the multilayer. The early during buckling as well as late Meguma slate belt is held to be thin- during the imposition of the upright skinned. LS-fabrics. Layer-parallel shearing was followed After the beds acquired slaty cleav- by a period of layer-parallel shorten- age they ceased to behave as a multi- ing. Where the multilayer remained flat, layer. Gravitational instability fol- gently plunging parallel folds were pro- lowing inhomogeneous layer-parallel duced by buckling. Depending upon the shortening probably caused the vertical ratio of competent to incompetent beds collapse of the slate'belt. An associ- the buckle folds developed by .neither ated flattening produced variably in- flexural slip folding or neutral sur- tense but regionally pervasive subrecum- face folding. At an early stage in the bent folds and gently dipping crenula- buckling of the multilayer pressure tion cleavage. Superimposed coax'ially solution cleavage began to develop with on the major fold structures, they are a characteristic moderate dip. This commonly seen to affect the steep cleav- cleavage together with certain quartz ages but rarely to deform the bedding. veins and the grain alignment cleavage There does not appear to be any prefer- were passively folded and steepened. red direction of translation during this In having done so they provide a record episode of shortening of most of the limb rotation during The slate belt largely acquired its buckling. Newer and successively steeper present configuration in a period of pressure solution stripes were initiated shear folding which most likely suc- as the fold limbs continued to rotate ceeded gravitational collapse. At this and the axial surfaces approached the time the strong, upright foliations were vertical. Subsequent to most but not all the principal planes of anisotropy and of the buckle folding "and late in the so they became the principal planes of episode of layer-parallel shortening shear. The hinges of the major folds the generally upright slaty cleavage was suffered relatively large strains late imposed on all earlier folds. Cleavage- in the layer-parallel shortening event related flattening locally produced and, therefore, they were naturally minor folds, in particular cuspate iso- favoured to be the most active sites of clines of the bedding. Objects in the shear folding. Reclined crossfolds and plane of the steep foliation are typi- crenulations possibly result from shear cally extended subhorizontally parallel related compression; their conjugate to the regional fold axes. Rotation of nature reflecting both dextral and sini- obliquely orientated step folds into stral movements. En echelon boudins ex- the regional E-W grain of the slate tended equally in several directions belt occurred before or during the for- seem to imply a plane strain and an mation of the slaty cleavage. Regional operative simple shear.

Evolution of the Fredericton Trough L.R. Fyffe, New Brunswick Geological Surveys Branch Fredericton, N.B. E3B 5H1

A system of post-Taconian horsts and Uplifted blocks of Taconian basement grabens delimit the tectonostratigraphic on the margins of the Fredericton Trough zones of New Brunswick. The Fredericton are represented by the Miramichi Massif Trough and Matapedia Basin represent in the northwest and Cookson Inlier in graben structures that developed astride the southeast. Shallow-water Silurian the older tectonic grain beginning in sediments (Oak Bay Formation and Waweig the latest Ordovician and earliest Silu- Formation in the southeast, "Canterbury rian. conglomerate and limestone" in the north- MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 95

west) are preserved on these positive shallow-water calcareous sandstone de- areas. posits of Early Devonian age (Flume Small inliers of similar basement are Ridge Formation) representing a mature found in the Becaguimec River area rift stage of sedimentation. (overlain by Upper Ordovician conglo- During the subsequent compressional merate) on the southeastern margin of stage, vergences of second folds indi- the Matapedia Basin and in the centre cate that the sedimentary rocks of the of the Basin at Mars Hill, Maine. Trough were thrust over the uplifted Volcanism initiated during the rift- blocks on its opposite flanks. Syntec- ing is restricted to narrow down-fault- tonic to post-tectonic plutons (St. ed blocks on both margins of the Fred- George and Pokiok batholiths) ranging ericton Trough (Mascarene Group, Long from Early Devonian to Early Carboni- Reach Formation, Jones Creek Formation ferous intruded the faulted margin of in the southeast; Dorrington Hill For- the Trough. Displacement of Early Car- mation, Hartin Formation in the north- boniferous basalt indicates 800 m of west) . The bimodal volcanics varied from down-throw on the southeastern side of submarine in the Early Silurian to sub- the Fredericton Fault. This latest move- aerial in the Early Devonian. ment was related to the development of the Carboniferous Moncton Basin farther Late Ordovician? to Early Silurian to the southeast. sedimentation within the Trough con- The presence of horst and graben sisted of fine-grained, red and green structures trending northeasterly across sandstone and siltstone (Queen Brook the normal east-northeasterly tectonic Formation in the southeast; "Stanley trend of the Appalachians may result beds" " in the northwest). Later thick from New Brunswick's position relative deposits of Silurian greywacke (Digde- to the Saint Lawrence Promontory. Since quash Formation, "Burtts Corner grey- Acadian tectonism in New Brunswick can wacke") reflect more rapid uplift of be related to block faulting, no Devonian the source areas on the flanks of the accretionary terranes will exist here Trough. The greywacke is overlain by north of the Avalonian Platform.

The stromatoporoid fauna of the West Point Formation (Silurian) on the Gaspe Peninsula C.S. Pope, Department of Geology University of New Brunswick, Fredericton, N.B. E3B 5A3 Stromatoporoids are the major con- stromatoporoid morphologies suggestive stituent of most of the facies of the of changing depth and wave energy re- West Point reef complex around Port gimes. Several small stromatoporoid Daniel, Quebec. Variations in the amount patch reefs of bioherms are also pres- and grain-size of siliclastic deposition ent. Progressing analysis of the taxo- seems to have effected the biota coloni- nomy and morphologies of these stromato- zing the facies. The base of the forma- poroids suggest that the West Point For- tion is a relatively shallow, sublittoral mation displays a normal community suc- distal deltaic sequence of siliclastic cession from pioneer stages to climax siltstones colonized by large stromato- and dominance stages but with several poroids and tabulate corals. Other setbacks in the process. These "set- facies include sponge-supported (?J mud- backs" can probably be related to chan- mounds, algal banks and crinoid debris ges in water depth and sediment influx layers. The complex climaxes in a strom- associated with contemporaneous volcanic atoporoid reef and an associated lagoon activity in the area. of mudflat facies with a variety of 96 ABSTRACTS Gold potential of the Meguma Group: New Concepts S.J. Haynes and P.K. Smith, Nova Scotia Department of Mines and Energy P.O. Box 1087, Halifax, N.S. B3J 2X1

Gold in the Meguma Group was tradi- other polytypes, which range from syn- tionally mined from quartz veins pref- to post-Acadian, are apparently barren. erentially located in the slate units (3) In amphibolite facies zones, Acadian of turbidite sequences. Detailed field structures are complicated by intrusion studies at Wine Harbour, Isaac's Har- of late Acadian granitoids, themselves bour, Goldboro, Beaverdam, Cochrane Hill deformed by at least two post-Acadian and Forest Hill have demonstrated the (Hercynian ?) dynamo-met amorphic events. following new information: All quartz vein types common to the (1) At some deposits, gold is present greenschist facies appear to be present. within the host-rock slates as deformed In addition, gold is present in both wisps of free gold and native gold in- deformed andalusite-bearing pegmatoid clusions in garnet prophyroblasts. This veins. Late Acadian static metamorphism implies significant potential for in- incorporated gold as inclusions in gar- creased mining widths of low-grade ore net porphyroblasts. These porphyroblasts comprising both quartz veins and slate. are, in turn, cut by deformed aurifer- (2) In greenschist facies zones, eleven ous, syn-Hercynian (?), stratiform and different quartz vein polytypes have stratafound quartz veins. The final been characterized on the basis of form, stage of gold-quartz deposition appears characteristic mineralogy, wall rock as undeformed, post-Hercynian (?) cross- alteration and crosscutting relation- cutting veinlets. ships to each other and regional struc- tures. However, gold is restricted to A polygenetic model for gold is pro- structurally early (pre-Acadian) cor- posed involving initial deposition from rugated stratiform veins (exhibiting submarine hydrothermal vent systems as cross-laminations and columnar struc- chemical sea-water precipitates, hydro- tures) , boudinaged stratabound veins thermal sills and fault-controlled and associated small side veins. These feeders. Later, polyphase Acadian, Her- are cut by K-feldspar bearing cross- cynian (?) and post-Hercynian (?) dyna- veins, displaying arsenopyritization and mo-thermic solutions remobilized both sericitization of the wall rocks. The gold and quartz; A deformed accretionary terrane in the Newfoundland Appalachians B.A. van der Pluijm, P.F. Williams and K.E. Karlstrom Department of Geology, University of New Brunswick Fredericton, N.B. E3B 5A3

An imbricate stack of three thrust overy olistostrome near Cobbs Arm in sheets is present on New World Island, one of our movement zones, date that northeast Newfoundland. These sheets thrust as U. Llandovery. Since this are separated by movement zones, com- sheet is one of the lowest in the pile, monly marked by melange. Because of the the formation of the accretionary prism, tectonic setting and the geometry the as now exposed, must have started prior area is interpreted as part of an accre- to the U. Llandovery. tionary terrane. Sedimentological work in the area by Our work shows northwest directed a group of workers from Oxford Univer- thrusting indicating southeasterly sub- sity reveals three distinct sequences duction. The presence of an U. Lland- which were interpreted as being deposi- MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 97 ted in three different basins, bounded now. In our model the present distri- by high angle faults which were active bution is a product of thrusting and during sedimentation. More recently it later folding. has been suggested that the faults are Sedimentation occurred on the west northwest dipping thrusts. Either in- margin of the Iapetus during Ordo- terpretation is incompatible with our vician and L. Silurian times. Current structural data. There are no suitable directions and composition of the sedi- high angle faults and they assume the ments show the source to be to the opposite sense of movement on the northwest; where there was an island arc thrusts to that determined in the field. and the North American craton. Starting Furthermore, the youngest basin is as- in L. Silutian times, underplating of sociated with the oldest thrust and the the basin floor took place with subdue- oldest basin with the youngest thrust; tion to the southeast and an accre- this is not normal in accretionary ter- tionary prism was formed. Continued ranes where the piggy-back relation- shortening caused folding of the thrust ship is observed. pile and finally the collision between We present an alternative explanation North America and Europe resulted in which agrees with both the sedimento- modification of these folds. logical and the structural information. This deformation sequence offers an First we assume that the :fault delin- explanation of the observed variation ated basins were parts of a single con- in deformational history in this part tinuous basin and that the pre-deforma- of the Appalachians. In the northwest tional spatial distribution of the the Taconic event represents Ordovician parts was the reverse of that assumed subduction along the edge of the North by the Oxford group for the basins. American continent and the Acadian event Thus the northwest basin, in their in- represents the Silurian/Devonian colli- terpretation, becomes the southeast sion. In the southeast the deformation portion of our continuous basin and so is related to subduction on the south- forth. This we believe, fits the sedi- east side of Iapetus plus the final col- mentological data better than the as- lision. It is continuous from at least sumption that the spacial distribution as early as L. Silurian through to De- was the same, before deformation, as vonian. Basement studies in the Southern Central Carboniferous Basin - New Brunswick J.J. Chandra and T.C. Webb Department of Natural Resources, Fredericton, N.B. E3B 5H1

A geophysical study of the Pre-Car- that the Pokiok Batholith does not ex- boniferous basement in the southern tend into the basin to any degree and Central Carboniferous Basin is present- is perhaps in faulted contact with the ly being undertaken by the Mineral Re- Silurian sedimentary rocks. sources Division. The purpose of the At the northwestern tip of the inter- investigation is two-fold: (1) to deter- preted St. George Batholith extension mine the geothermal potential and (2) is another major gravity low which to aid in the recognition of buried trends northeasterly. It starts at Har- Windsor salt masses. vey Station and terminates as a globu- Filtered gravity data shows a major lar low in the Minto-Meadow Brook area. low underlying the basin in this area. This feature has also been interpreted This major low has been interpreted to to reflect a granite body, however, the reflect an extension of the St. George shape of this granite body and its re- Batholith beneath the Carboniferous lationship to the St. George and Pokiok cover. The filtered data also suggest Batholiths are still not understood. It 98 ABSTRACTS

is possible that this intrusive body is er radioactivity in the soil and water the source of the volcanic units exposed has been confirmed. The other feature in this part of the basin. has been interpreted as a grabben which The residual gravity map of the south- extends from South Oromocto Lake through ern Central Carboniferous Basin also to Fredericton. defines two additional gravity linears. Detailed gravity mapping of this part One linear is coincident with the anom- of the Central Basin has been completed alously radioactive Mt. Pleasant vol- in the summer and fall of 1982. This canic sequence which appears buried coverage has provided adequate data for under the Pennsylvanian cover and ex- three dimensional modelling of these tends as far as French Lake where high- structures. Upper Devonian plant-bearing strata from Cape Breton Island, Nova Scotia lW.H. Forbes, 2A.K. Kasper, 3R.A. Jamieson, M.C. Blanchard-Williamson 1Department of Geology, University of Maine, Presque Isle, Me. 04769 2Department of Botany, Rutgers University, Newark, New Jersey 07102 3Department of Geology, Dalhousie University, Halifax, N.S. B3H 4J1

Plant-bearing sandstones from Cape continental strata in the Escumanic For- Breton Island, Nova Scotia, represent mation of Gaspe Peninsula, in the Perry the first report of Upper Devonian con- Formation of eastern Maine and in Upper tinental strata for the Province. The Devonian beds of the central Appalachians thinly laminated greenish-gray fine- of the U.S. Plants assigned to this grained sandstones are exposed along a taxon were arborescent with large trunks woods road north of Forest Glen Brook, of conifer anatomy. Vegetative foliage east of Cheticamp, Cape Breton Island. consisted of branch systems bearing fan- These sandstones are interbedded with shaped laminar leaves with dichotomous rhyolitic breccias and flows, that in venation. Reproductive foliage consist- turn are overlain by beds of probable ed of non-laminar divided leaves with early Carboniferous age. The igneous numerous sporangia. The specimens as- rocks have yielded a wide range of signed to Archaeopteris consists of both radiometric dates. The plant fossils sterile and fertile foliage. The pres- are assigned to the genus, Archaeopteris ence of this genus in sandstones from of the Division Progymnspermophyta - the Cape Breton Island is the first evidence progymnosperms. Species of Archaeopteris of Upper Devonian continental strata in are characteristic of Upper Devonian Nova Scotia. Polygonal patterns, sedimentary facies and basin analysis H.W. van de Poll and A.M. D'Orsay, Department of Geology University of New Brunswick, Fredericton, N.B. E3B 5A3

Polygonal patterns ranging from ap- tributed to a variety of processes, proximately 15 cm to 300 m in diameter which include: 1) contraction, 2) con- are familiar features in sediments'. Two traction and expansion, 3) sediment pattern types can be recognized: 1) loading and buoyancy displacement and orthogonal polygons with straight and/or 4) sediment intrusion. curved sides and 90° intersection angles Volume reduction (e.g. desiccation, and 2) non-orthogonal (usually hexa- syneresis, frost shrinkage) locally gonal) polygons with tri-radial inter- with secondary infilling (e.g. ice-wedge sections of approximately 120°. The and evaporite polygons) and alternating origin of sediment polygons can be at- periods of contraction and expansion MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 99

(e.g. "patterned" ground in permafrost facies and basin analysis. areas) are examples of the first two Reference will be made to the poly- processes. Polygonal patterns result- gonal patterns occurring in Permo-Car- ing from loading and sediment intrusion boniferous strata of the Maritime Prov- are less well known. They reflect intra- inces, Canada, with particular emphasis stratal transposition of sediments along on those of the West Bay Formation of reverse density gradients that take the Parrsboro area, Nova Scotia. Cur- place with or without the aid of induced rent research suggests that the poly- shear. gonal patterns within this formation Considering the variety of conditions are not desiccation features but are and circumstances that can lead to the polygonally oriented clastic dikes that formation of polygonal patterns it is reflect sediment intrusion in response clear that the correct interpretation to unstable sediment density distribu- of sediment polygons is essential in tions and possibly earthquake motion. Sedimentology of the Halifax Formation, Nova Scotia: Ordovician fine-grained turbidites D.A.V. Stow, M. Alam and D.J.W. Piper, Atlantic Geoscience Centre Geological Survey of Canada, Bedford Institute of Oceanography P.O. Box 1006,Dartmouth, N.S. B2Y 4A2 The Halifax Formation is a several quences have beeen measured that show kilometre thick shale-rich succession thinning-upward, thickening-upward and that forms part of the (?) Cambro-Ordo- irregular patterns of sandstone and vician Meguma Group of Nova Scotia. The siltstone beds on a large-scale (100- Meguma sediments were mostly deposited 200 m). There is also much wedging, by sediment gravity flows on a prograd- subdivision and amalgamation of these ing deep-marine slope-rise complex. coarse lithologies. Erosional features Eight separate facies of the Halifax are locally common at the base of tur- Formation are recognized on a facies bidite beds and still more widespread continuum from very shaley to very sandy. at the top. Slumps and bioturbation are The two most sandy facies show partial less common. The depositional setting Bouma sequences of structures; the of most of the Halifax Formation appears others are best interpreted in terms of to be the mid- or upper-fan area of a a more detailed 'ideal sequence' for muddy deep sea fan, passing upwards fine-grained turbidites. Vertical se- into a prograding continental slope. The Mabou Mines section: Implications of fossil plant collections E.L. Zodrow, Department of Geology The University College of Cape Breton, Sydney, N.S. BlP 6L2 The Mabou Mines section of Cape Bre- of the neuropteris - Linopteris complex ton Island represents the land-based are additionally interesting. Four rea- portion of a supposedly large off-shore sons are cited. First, transitional coalfield (Mabou Coalfield). This sec- phases in the development of Linopteris tion contains an abundant, unoriented mimsteri (loose and meshing venation), phyllocenosis in which the neuropterids i.e., Neuropteris obligua (highly flex- (pteridosperms) predominate. Of the uous venation) and Neuropteris semi re- phytostratigraphically important macro- ticulata (venation between that of L. fossil forms (alethopterids, pecopte- munsteria and N. obligua), are recorded rids, fortopterids and sphenophylls) in the sedimentary rocks; secondly, in that were instrumental in determing a some specimens Linopteris obligua char- Westphalian D plant age, certain forms acteristics (anastomosis, or cross-over 100 ABSTRACTS of veins) are clearly shown; thirdly, cerned with illustrating the transi- much of this material is cutinized al- tional aspects of the Neuropteris-Lino- lowing epidermal investigations; and pteris forms. On evidence collected, it fourthly, this mode of preservation is also interesting to note that both allows a more accurate determination of floras and faunas of the Mabou section mesh formation than it is possible with are of low diversity (as compared with compression/impression material (which the Sydney Coalfield) and that lacus- may eventually contribute in defining trine conditions appear to have .had a natural species). Moreover, the (thick) higher frequency at Mabou than at Sydney. cutin and the vein-mesh formation in Not enough stratigraphic specimens certain pteridosperms of Upper Carboni- have been examined to broach the ques- ferous time can be explained by physio- tion of gradualism versus punctuated logical and paleoecological factors equilibrium as it relates to the evo- (amount of sunshine, height of plant, lution of the Neuropteris obligua - soil moisture, strength of pinnules). Neuropteris semi reticulata - Linopteris The present paper is primarily con- munsteri complex. Cruziana stratigraphy of the ?Cambro-Ordovician Bell Island and Wabana Groups, Conception Bay, eastern Newfoundland R.K. Pickerill and D. Fillion, Department of Geology University of New Brunswick, Fredericton, N.B. E3B 5A3 Unfossiliferous or poorly fossili- this assemblage are spectacularly-pre- ferous sedimentary sequences can poten- served trilobite-produced trace fossils tially be dated and correlated by de- - Cruziana (furrowing traces). Rusophy- tailed examination of contained trace cus (resting traces), Diplichnites (walk- fossils. Such an approach has been wide- ing tracks), Dimorphichnus (sideways ly applied to many such sequences in grazing traces) and Monomorphichnus England, Wales, southwest Europe and (swimming grazing traces). Detailed ex- the Metiterranean region, particularly amination of the distribution of Cruzi- those of Cambro-Ordovician age. In ana species within the sequence has particular, these sequences have been enabled a more accurate definition of dated by perhaps the most useful of all the Tremadoc-Arenig and Lower-Upper trace fossils in stratigraphy, trilo- Tremadoc boundaries than previous paleon- bite-produced species of Rusophycus and tological studies have permitted. The Cruziana. To date, however, the ichno- former is based on the final occurrence stratigraphic paradigm developed in of C. semiplicata,, which is an Upper Europe has not been successfully ap- Cambrian-Tremadoc species, and the lat- plied to any coeval succession in North ter on the initial occurrence of C. America. furcifera and C. goldfussi, previously On Bell Island, Conception Bay, east- only reported from Upper Tremadoc and ern Newfoundland, the ?Cambro-Ordovician younger strata. It is suggested that sequence (Bell Island and Wabana Groups) the Tremadoc-Arenig boundary be placed of shallow subtidal siliclastics, con- at the 1200 m level within the sequence tains a diverse, abundant and well-pre- and the Lower-Upper Tremadoc boundary served trace fossil assemblage. Amongst at 1020 m. Structural evolution of the Quaco Head area, southern New Brunswick A.G. Plint and H.W. van de Poll, Department of Geology University of New Brunswick, Fredericton, N.B. E3B 5A3 Re-mapping of the Quaco Head area of viously recognized. The structure is southern New Brunswick has revealed a dominated by two major thrust slices, more complex structure than was pre- separated by south and southeasterly- MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 101

dipping thrust planes. The lower thrust southeast between 30° and 90°. These eraplaces amygdaloidal basalts and bfed- beds appear to be part of a large re- ded tuffs (?Precambrian, ?Devonian) over cumbent fold which was subsequently sediments of the Tynemouth Creek Forma- thrust over the lower, non-inverted tion (Westphalian A-B). Close to the limb. Folding and thrusting in the Quaco thrust plane, the underlying sediments area was certainly post-Westphalian B have been overturned towards the north. and may be viewed as a local response Resting unconformably on the upper sur- to dextral strike-slip movement on the face of the basalt is a thin layer (<5m) Cobequid Fault which is inferred to lie of Windsor limestone (Visean; probably a few km to the south. Following Alleg- zone A or B) which is disconformably henian/Hercynian deformation, the area overlain by coarse, polymict conglomer- underwent extensive erosion prior to ates of inferred Hopewell/Canso Group deposition of a thick sequence of Trias- age (Namurian). This sequence, which sic alluvial sediments (Quaco Forma- may be a few metres or tens of metres tion) . The upper thrust plane was re- thick dips to the southeast at up to activated as a normal fault during a 50°. It is truncated by a major fault phase of post-Triassic rifting along extending in a northeast-southwest di- the (presumably related to rection and dipping southeast at 45°. early Atlantic rifting). During this To the southeast of the fault, lie period, blocks of the Triassic were thick-bedded Hopewell conglomerates, downfaulted (100s or even 1000s of me- overturned towards the west and north- tres) against rocks ranging in age from west, and dipping towards the east and ?Precambrian to Westphalian. Regional bedrock geology of the Baffin Island Shelf B. MacLean and G.L. Williams, Atlantic Geoscience Centre Geological Survey of Canada, Bedford Institute of Oceanography Dartmouth, N.S. B3J 2X1 During the last decade geophysical those off Cumberland Sound. and geological cruises in Davis Strait On the northeastern Baffin shelf the and BaffiirBay have outlined the regional presence of Paleozoic rocks beneath bedrock geology of the Baffin Island younger sequences shoreward of the con- continental shelf. tinent-ocean transition zone has been On the southeastern Baffin shelf Pre- suggested from seismic refraction re- cambrian metamorphic rocks form the sults, but it has not been possible to bedrock adjacent to the coast. Lower confirm this by sampling. Upper Cre- Paleozoic carbonate rocks underlie much taceous (Senonian) marine sediments of the shelf between Frobisher Bay and sampled at Home Bay and Buchan Trough Cumberland Sound and extend northward occur extensively along the northeastern toward Cape Dyer. These rocks also occur shelf beneath a variable cover of Lower in Hudson Strait and Frobisher Bay and Tertiary sediments. may be present in Cumberland Sound. Post-Ecocene erosion has bevelled much Sedimentary and volcanic rocks mainly of the southeastern Baffin shelf and of Tertiary age occur over much of the developed deep transverse troughs on the central and outer parts of the south- northeastern shelf. eastern shelf. The stratigraphic sec- The presence of an active submarine tion off Cumberland Sound has been dis- oil seep, recovery of samples of pro- turbed by the emplacement of northeast- mising source rocks by seafloor sampl- southwest trending subsurface ridge-like ing and exploratory drilling results structures. Mesozoic strata on the indicate that conditions favourable southeastern Baffin shelf appear to be for the generation of hydrocarbons have confined to the subsurface except where existed in the area. locally involved in structures such as 102 ABSTRACTS Coal rank changes in the Sydney and Pictou coalfields of Nova Scotia: Cause and economic significance P.A. hacquebard, Atlantic Geoscience Centre, Geological Survey of Canada Bedford Institute of Oceanography, Dartmouth, N.S. B2Y 4A2

In eastern Canada the coalification is In addition to the vertical changes essentially post-deformational, result- there are also regional variations in ing in a general increase of rank with rank within one seam at the same depth. depth in individual seams. However, In the Sydney field an easterly increase within the confines of the Sydney Coal- of two V-types in rank over a distance field and between the Sydney and Pictou of 48 km can be related to a difference fields the rate of increase is not con- in the original depth of burial. stant, signifying differences in geo- This eastward shift in rank is econo- thermal gradients and/or thermal con- mically important, because it means ductivity of the sediments. that high quality coking coal of medium In the Sydney Coalfield the Harbour volatile rank is reached at a depth of seam shows variations in the coalifica- 700 m in the eastern part of the field, tion gradient of 0.032 to 0.046% Ro/100 in contrast to a depth of 900 m in the m, which compares with a gradient of central portion. The coal presently 0.052% Ro/100 m for the Acadia seam of mined is high volatile "A" bituminous, the Pictou coalfield. Variable gradients and requires additions of low volatile were also obtained from sequences of American coal to produce coke of metal- separate coal seams cut in twelve bore- lurgical quality. This low volatile holes, which in the Sydney field ranged coal, however, could also be obtained from 0.050 to 0.086% Ro/lOOm. The high- from the Acadia seam in the Pictou est gradient was obtained in the off- field, where it occurs between depths shore Murphy et al. P-05 well, which is of 580 and 990 m. The Acadia reserve located over a pre-depositional high, (comprising 14 million tons) is the where a higher plaeotemperature likely only known low volatile coal deposit in existed. eastern Canada. Fluvial style and its influence on coal deposition in the Carboniferous Sydney Basin of Nova Scotia B.R. Rust, G. Masson, S. Dilles, Department of Geology University of Ottawa, Ont. KIN 6N5 M.R. Gibling, Department of Geology Dalhousie University, Halifax, N.S. B3H 4J1

The abundance, thickness and quality braidplain. The sandstone assemblage of coals in fluvial deposits is strong- contains sandstones (trough cross-bed- ly influenced by the nature of the river bed with some rippled and horizontally channel and floodplain systems. In the stratified units), thin granule-conglo- Morien Group (Westphalian C, D age) of merates, and about 10% mudrocks; thin the Sydney Basin, three fluvial facies coal seams are uncommon, coal logs and assemblages have been reeognized. The lenses are abundant. The assemblage rep- pebbly sandstone assemblage is charac- resents a distal braidplain. The third terized by trough cross-bedded sand- assemblage, about 50% mudrocks alter- stone, thin pebble-conglomerate units, nating with fining-upward sandstone and a paucity of mudrocks; in situ coal sequences, contains trough cross-bedded is absent but carbonized logs and thin and rippled sandstones with large-scale coal lenses are common. The assemblage lateral accretion sets. Significant represents a moderately high energy coal seams are present, and erect trunks MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 103

are common within thin coarsening-up- tent northeastward transport through ward units. The assemblage represents space and time. There is little indi- a meandering alluvial system, with in cation of basement influence at present situ vegetation on levees and flood- basin margins, implying that the basin plains. The alternating assemblage was formerly extended further to the south- initiated earlier in the eastern part west. A basement high along the Bois- of the basin than in the west, but de- dale Anticline apparently influenced veloped fewer, thinner coal seams at paleodrainage in the southern Boular- that time. derie Island area. Paleocurrent studies indicate consis- Geophysical modelling of salt masses and basement structures in the Moncton and Cumberland Basins J.J. Chandra and T.C. Webb Department of Natural Resources, Fredericton, N.B. E3B 5H1 Salt masses are usually characterized gance, Portage Vale, Five Points, and by distinctive gravity lows on Bouguer Pointe de Butte. Gravity coverage in anomaly maps due to their negative den- these areas is considered adequate for sity constrasts with surrounding rocks. the construction of two dimensional Despite this rather unique feature, models. regional gravity variations due to large Model studies indicate that most Wind- scale, deep-seated geologic structures sor salt masses form elongate, semi- as well as density effects caused by diapiric to lensoidal structures. Most intra-basement lithologic variation tend appear to be influenced one way or an- to distort and obscure gravity signa- other by faulting and/or topographic tures of salt masses and other smaller irregularities in the basinal floor. structural features. For this reason, Near Portage Vale, two distinct salt it is necessary to remove these regional masses indicate a bifurcating of the effects from observed gravity values in "Windsor" depositional basin either by order to isolate and more clearly inter- faulting or by the presence of an inter- pret the physical properties of the vening basement high resulting in two structural features in which we are separate, possibly interconnected ba- most interested. sins. The regional gravity field in Several negative gravity anomalies, this area suggests a major upthrusted interpreted to be buried evaporites have basement block which starts just north- been identified throughout parts of the east of Portage Vale and continues Moncton and Cumberland Basins. Although through Middlesex to Moncton. some of these anomalies are no doubt Basal Windsor strata from all con- related to Albert salt masses, gravity structed models from Plumweseep to Port- modelling studies were completed only age Vale indicate a regional paleoslope for those anomalies interpreted to be of approximately 5 degrees to the north- associated with Windsor Group evapori- east. This revelation may be of value tes which locally contain significant in estimating the thickness of post- potash deposits. These included anoma- Windsor sediments in the eastern part lies at Smithtown, Salina, Cassidy Lake, of the Moncton Basin. Millstream, Plumweseep, Penobsquis, Ana-