Brook Formation Research Articles

Discussion: Upper Lower Cambrian depositional sequence in Avalonian New Brunswick

The authors (E. Landing and S.R. Westrop) wish to abandon most of the local stratigraphic nomenclature of the Saint John Group in southern New Brunswick, in order to emphasize the broader tectonic significance of these lower Paleozoic platformal rocks throughout the Avalon terrane. Their approach, based in part on biostratigraphic data, is to use a somewhat arbitrary mixture of stratigraphic terms taken from widely separate type sections in New Brunswick and Newfoundland. Thus, the Ratcliffe Brook Group (a formation defined in New Brunswick), would include the Rencontre and Chapel Island formations (both defined in Newfoundland), whereas the Chamberlain's Brook Formation (defined in Newfoundland) would include the Fossil Brook Member (defined in New Brunswick). The Saint John Group, which clearly has historical precedence (Williams et al. 1985), is left out of their stratigraphic scheme. Since the establishment of a formal lithostratigraphic unit requires that its lower and upper boundaries be explicitly defined, it is difficult to see how this can be accomplished when the supposedly adjacent units are from type sections or reference sections located about 1000 krn apart. Even if separate sections contain similar successions, it is unlikely that lithological boundaries would be identical over large areas in such an episodically high-energy shelf environment. Difficulties in adequately describing formational boundaries are compounded in the case of the Hanford Brook Formation since, as the authors point out, it does not even occur in the Newfoundland type section where the underlying and overlying strata are defined. The two type sections are, therefore, not truly homotaxial, so extrapolation of Newfoundland terminology to New Brunswick may not be justified. The authors insist on placing the upper part of the Glen Falls Formation into the overlying Hanford Brook Formation since they claim a major unconformity exists within the former. Although such a revision is not unreasonable, it is not required. Stratigraphic nomenclature is supposed to be based on empirical lithological changes rather than interpretive depositional history, so the traditional lithological components of the Glen Falls Formation could be retained even if the claimed unconformity were proven to exist. In conclusion, the authors have made a significant contribution to the understanding of tectonic controls on the development of Paleozoic shelf facies covering the Avalon terrane. However, this could have been accomplished without resorting to wholesale name changes, the sole purpose of which is to create a general stratigraphic nomenclature to encompass what is surely a complex depositional setting containing many depocentres. A standard correlation chart retaining local terminology would be a more practical way to convey the reasoning behind the authors' tectono-stratigraphic synthesis. I believe that the composite stratigraphic column proposed by Landing and Westrop creates more problems than it solves and is unlikely to be adopted by others working in this part of the northern Appalachians.

Occurrence and significance of Silurian K-bentonite beds at Arisaig, Nova Scotia, eastern Canada

The most extensive succession of K-bentonite beds known in the Silurian of North America occurs at Arisaig on the northern coast of Nova Scotia. At least 40 ash beds are present in the Llandoverian Ross Brook Formation and at least four in the early Ludlovian McAdam Brook Formation. Most of the beds are thin (< 5 cm), but one bed (the Smith Brook K-bentonite bed) in the late Llandoverian crenulata Zone and another (the McAdam Brook K-bentonite bed) in the early Ludlovian nilssoni Zone each reach a thickness of 20 cm. New graptolite collections provide critical information on the biostratigraphic position of the K-bentonite beds in the Ross Brook Formation. Geochemical data show that the Arisaig ash beds represent calc-alkaline magmas from plate margin, subduction-related volcanic vents. Differences in K-bentonite stratigraphic distribution, combined with paleogeographic considerations, suggest that the volcanoes were located much farther to the south in the Iapetus than the source volcanoes of the British–Baltoscandian Llandoverian K-bentonites.

Formal definition of the Lower Jurassic McCoy Brook Formation, Fundy Rift Basin, eastern Canada

The name McCoy Brook Formation, presently in informal use, is formally proposed to designate outcrops of Lower Jurassic (Hettangian-Pliensbachian) strata overlying the North Mountain Basalt in the structural Minas Subbasin of the Fundy Rift Basin. It is also proposed that this designation be extended to include stratigraphically equivalent strata beneath the Bay of Fundy throughout the entire Fundy Rift Basin. It is further recommended that use of the name Scots Bay Formation, the current designation for post-basalt Jurassic sediments outcropping on the south side of the Minas Subbasin, be discontinued. The name Scots Bay Member of the McCoy Brook Formation is used here to designate distinctive lacustrine strata at the base of the McCoy Brook Formation outcropping on both sides of the Minas Subbasin.
 
 RÉSUMÉ
 On propose officiellement le nom de Formation de McCoy Brook, qui est présentement utilise de manière officieuse, pour désigner les affleurements ou les strates du Jurassique inférieur (Hettangien-Pliensbachien) recouvrant le basalte du mont North dans le sous-bassin structurel Minas du bassin d'effondrement Fundy. Il est en outre proposé que l’on étende ce nom pour qu'il cnglobe les strates stratigraphiquement équivalentes sous la baie de Fundy dans l'ensemble du bassin d'effondrement Fundy. Il est par ailleurs recommandé que l'on cesse d'utiliser le nom de Formation de Scots Bay, nom actuel de l'affleurement de sédiments du Jurassique postérieur au basalte sur la rive sud du sous-bassin Minas. On utilise ici le nom de membre Scots Bay de la Formation de McCoy Brook pour désigner les strates lacustres caractéristiques à la base de l'affleurement de la Formation de McCoy Brook sur les deux rives du sous-basin Minas.
 
 [Traduit par la rédaction]

Continental slope sedimentation in the Sheepbed Formation (Neoproterozoic, Windermere Supergroup), Mackenzie Mountains, N.W.T.

The Sheepbed Formation (Ediacaran) is a 1 km thick, siliciclastic unit that overlies glacial deposits of the Ice Brook Formation and is overlain by carbonates of the Gametrail Formation. Observations in the Mackenzie Mountains indicate that the Sheepbed Formation accumulated in water depths of 1–1.5 km on a passive-margin, continental slope. The lower part of the formation consists predominately of dark mudstone. Fine-grained, turbiditic sandstone becomes more abundant upward, as does the scale and abundance of slope-instability indicators. Mesoscale facies successions (i.e., evidence of channels, lobes, and (or) compensation cycles) are developed in the upper half of the formation. The larger-scale changes are interpreted as reflecting a postglacial sea-level rise, followed by a relative fall and an increase in the rate of deposition. Contourites that may have been formed in response to the circulation of deep, cold water occur in the lowstand deposits. Their presence confirms previous speculation that the proto-Pacific Ocean was initiated at the beginning of Windermere deposition (ca. 780 Ma), not at the start of the Cambrian. The paleoflow direction toward the present-day northwest suggests that this part of Laurentia lay in the northern hemisphere. In situ Ediacaran megafossils are preserved on the soles of sandy turbidites; the deep-water setting indicates that these organisms were not photoautotrophs.

On the cranial structure of a new protosuchid (Archosauria: Crocodyliformes) from the McCoy Brook Formation (Lower Jurassic) of Nova Scotia, Canada

ABSTRACT Well-preserved skull bones referable to a new protosuchid, Protosuchus micmac, are common in the lower portion of the McCoy Brook Formation (Lower Jurassic: Hettangian) of Nova Scotia, Canada. P. micmac is closely related to P. richardsoni (Brown, 1933) from the Moenave Formation (Lower Jurassic) of Arizona and to P. haughtoni (Busbey et Gow, 1984) from the upper Stormberg Group (Lower Jurassic) of southern Africa. It differs from the latter taxa in several craniodental features, most notably in the presence of two large caniniform teeth in the dentary. The geographic range of protosuchid crocodyliforms provides further confirmation of a cosmopolitan distribution of many groups of terrestrial tetrapods during the Early Jurassic.

Sulphur isotope composition of the Brunswick No. 12 massive sulphide deposit, Bathurst Mining Camp, New Brunswick: implications for ambient environment, sulphur source, and ore genesis

The Brunswick No. 12 massive sulphide deposit occurs within a Middle Ordovician bimodal volcanic and sedimentary sequence that is thought to have formed in a continental back-arc rift covered with a thick succession of carbonaceous hemipelagic and turbiditic sedimentary rocks. The deposit consists of three en echelon lenses that are zoned from Vent Complex to Bedded Ore and Bedded pyrite facies. The Bedded Ore facies has the lowest average δ34S values (14.2[Formula: see text]), but are only slightly less positive than laminated pyrite in footwall sedimentary rocks (δ34Smean = 15.1[Formula: see text]). δ34S values for the bedded sulphides show an upward increase from 14.2[Formula: see text] in Bedded Ore to 16.5[Formula: see text] in Bedded Pyrite. Average δ34S values for Vent Complex (15.8[Formula: see text]) and underlying stringer sulphides (16.1[Formula: see text]) are consistently more positive than those for Bedded Ore. In carbonaceous shales and siltstone of the Patrick Brook Formation that underlie the deposit, δ34S values that range between 13.8 and 25.6[Formula: see text], and the similarity of these values to those of the Brunswick No. 12 deposit indicate major bacterial reduction of sulphate to sulphide under closed or partly closed conditions, and that most of the S in the deposit originated from ambient sulphidic bottom waters. Furthermore, the average δ34S value for Brunswick No. 12 bedded ores lies on the Selwyn Basin pyrite evolutionary curve and indicates that anoxic conditions within the Tetagouche back-arc basin reflect a global anoxic episode. The Brunswick No. 12 deposit probably formed, therefore, by the mixing of hydrothermal metals with dissolved sulphide of seawater origin during periods of ocean anoxia. The increase of δ34S values towards the Vent Complex may reflect the addition of isotopically heavy S formed by the inorganic reduction of seawater sulphate.

Upper Lower Cambrian depositional sequence in Avalonian New Brunswick

The Hanford Brook Formation (emended) is a thin (up to 42+ m), upper Lower Cambrian depositional sequence that is unconformably bounded by the lower Lower Cambrian (Random Formation) and the middle Middle Cambrian (Fossil Brook Member of the Chamberlain's Brook Formation). These stratigraphic relationships of the trilobite-bearing Hanford Brook Formation indicate deposition on the Avalonian marginal platform in the Saint John, New Brunswick, region and provide more evidence for a uniform, latest Precambrian–Cambrian epeirogenic history and cover sequence in Avalon. The Hanford Brook Formation is a deepening–shoaling sequence with (i) lower, transgressive sandstone deposited in episodically high-energy environments (St. Martins Member, new); (ii) highstand–regressive, dysaerobic mudstone – fine-grained sandstone with volcanic ashes (Somerset Street Member, new); and (iii) upper, regressive, planar and hummocky cross-stratified sandstone (Long Island Member, new). Trilobites are common in the distal Somerset Street Member, and ostracodes and brachiopods dominate the St. Martins and Long Island members. Condensation of the St. Martins Member and absence of the Long Island Member where the Random Formation and Fossil Brook Member are thinnest suggest onlap of the Hanford Brook and pronounced, sub-Middle Cambrian erosion across epeirogenically active blocks in southern New Brunswick.

Field relations, structure, and geochemistry of the Fisset Brook Formation in the Lake Ainslie - Gillanders Mountain area, central Cape Breton Island, Nova Scotia

Detailed mapping shows that the Fisset Brook Formation in the Lake Ainslie - Gillanders Mountain area consists of a lowermost sedimentary unit overlain by basaltic and rhyolitic units. The sedimentary unit is mainly arkosic pebble conglomerate and siltstone, and unconformably overlies or is in faulted contact with older meta-morphic and plutonic rocks. Scattered gabbroic plutons and dykes in the sedimentary unit are interpreted to represent "feeders" to the overlying basaltic flows. The basaltic unit consists mainly of subaerial flows, locally interlayered and intermixed with red-brown siltstone. The overlying rhyolitic unit consists mainly of eutaxitic to spherulitic flows or welded tuffs, with less abundant lapilli tuff. In the Lake Ainslie area, these rocks occur in a north-south array of rhombic fault blocks, whereas in the Gillanders Mountain area, the dominant structure is a large-scale anticlinal fold closing toward the south, cored largely by rocks of the Fisset Brook Formation. The chemical compositions of the basalt and rhyolite in both areas have been modified by alteration, but discrimination diagrams using relatively immobile elements, including rare-earth elements, indicate that the basalts and gabbros are continental, within-plate tholeiites. The rhyolites also have features indicative of origin in a within-plate setting, but are depleted in Y, Zr, and rare-earth elements compared to A-type granites. A rhyolite sample yielded a U-Pb (zircon) age of 373 ± 4 Ma, thus indicating that the Fisset Brook Formation in the Lake Ainslie - Gillanders Mountain area is Middle to earliest Late Devonian in age, not Late Devonian to Early Carboniferous as previously inferred.
 
 RÉSUMÉ
 Une cartographie detaillée montre que la Formation Fisset Brook dans le secteur du lac Ainslie et du mont Gillanders est constitutée d'une base sédimentaire recouverte d'unités basaltique et rhyolitique. La base sédimentaire est principalement formée d'un conglomcrat de galets arkosiques et de siltstones; elle repose de façon discordante ou par contact faillé sur des roches métamorphiques et plutoniques. Les dykes et les plutons gabbrotques dispersés dans l'unité sédimentaire sont interprétés comme des systèmes d'alimentation » des écoulcments basaltiques sus-jacents. L'unité basaltique est principalement constitutée d'écoulements subécriens, localement interstratifies et entremelés de siltstone brun rougeâtre. L'unité rhyolitique sus-jacente est essentiellement composée d'écoulements eutaxiques à sphérolitiqucs ou de tufs soudés, avec des conglomérats volcaniques à lapilli dans une matrice fine moins abondants. Dans le secteur du lac Ainslie, ces roches se présenters en une rangée nord-sud de blocs faillés rhombiques, tandis que dans le secteur du mont Gillanders, la structure dominante est un plissement anticlinal à grande échelle qui se referme vers le sud et qui abrite en son cocur une quantité substantielle de roches de la Formation Fisset Brook. Les compositions chimiques du basalte et de la rhyolite des deux secteurs ont eété modifiées par alteration, mais des schémas de discrimination utilisant des éléments relativement immobiles, dont des éléments de terres rarcs, révèlent que les basaltes et les gabbros sont des tholéiites intra-plaque continentaux. Les rhyolites possedent en outre des caractéristiques qui témoignent qu'elles proviennent d'un cadre intra-plaque, mais elles sont pauvres en Y, en Zr et en éléments de terres rares comparativement aux granites de type A. Une datation au U-Pb (zircon) d'un échantillon de rhyolite lui a attribue un âge de 373 ± 4 Ma, ce qui révèle que la Formation Fisset Brook du secteur du lac Ainslie et du mont Gillanders remonte a la période du Dévonien moyen au début du Dévonien supérieur, et non à celle du Dévonien supérieur au Carbonifère inférieur comme on L'avait auparavant laisser entendre.
 
 [Traduit par la rédaction]

First record of the early Mesozoic sphenodontianClevosaurus(Lepidosauria: Rhynchocephalia) from the Southern Hemisphere

An incomplete skull of a small sphenodontian lepidosaur from the upper part of the Stormberg Group of southern Africa is referable toClevosaurusSwinton, 1939. It is most closely related toC. bairdifrom the McCoy Brook Formation (Lower Jurassic) of Nova Scotia (Canada) andC. mcgillifrom the Dark Red Beds of the Lower Lufeng Formation (Lower Jurassic) of Yunnan (China). The new specimen is important because it represents the first record ofClevosaurusfrom the Southern Hemisphere. Like many other taxa of Early Jurassic continental tetrapods (crocodylomorph archosaurs, dinosaurs, synapsids),Clevosaurushad an apparently Pangaean distribution.

Late Devonian-Carboniferous detachment faulting and extensional tectonics in western Cape Breton Island, Nova Scotia, Canada

Shallow-dipping detachment faults have played a key role in the evolution of the Late Devonian to Carboniferous Maritimes Basin of western Cape Breton Island. The faults are responsible for large-scale post-orogenic crustal thinning and denudation of mid-crustal levels. Tournaisian and Westphalian clastic sedimentation can be related to detachment faulting along the Margaree Shear Zone (MSZ) and the Ainslie Detachment (AD), respectively. The MSZ consists of thick shallow-dipping retrogressive mylonite overprinted by cataclastic horizons, brittle detachment faults, and chloritic breccia. The shear zone crosscuts and transports low-grade Late Devonian bimodal volcanic rocks and redbeds of the Fisset Brook Formation in its hanging wall towards the west, and juxtaposes them against exhumed medium- to high-grade metamorphic rocks and basement in its footwall. Locally the mylonite is 200–700 m thick and outcrops along strike from north to south for approximately 60 km. Tournaisian coarse clastic units and debris flow deposits of the Horton Group unconformably overlie ductile mylonite of the MSZ due to incision of brittle faults into the MSZ. Regional transgression, and marine flooding of the extensional complex and exhumed units are marked by the thick Visean carbonate and evaporite deposits of the Windsor Group. The carbonates reflect a relatively quiescent tectonic regime, and widespread subsidence was likely due to the cessation of extension-related thermally induced buoyancy in a tectonically thinned crust. The Ainslie Detachment nucleated as a regional flat-lying fault along the carbonate-evaporite contact at the top of the Macumber Formation, forming calc-mylonite near the base of the Windsor Group. Significant stratigraphic omissions in the Windsor Group above the detachment provide clear evidence of an extensional regime during faulting. Clastic deposits of the Westphalian Cumberland Group are bounded by the detachment, and sedimentation is related to listric normal faults which cut down-section towards the west-southwest. The documentation of detachment faults has widespread implications for the interpretation of the post-orogenic evolution of the northern Appalachians. An extensional regime can now be recognized. Deep reflection seismic data are interpreted in light of the new findings and can be related to Late Devonian—Carboniferous basin formation.

A new sphenodontian (Lepidosauria: Rhynchocephalia) from the McCoy Brook Formation (Lower Jurassic) of Nova Scotia, Canada

ABSTRACT A new sphenodontian lepidosaur referable to Clevosaurus Swinton, 1939, C. bairdi, is described from the McCoy Brook Formation (Lower Jurassic: Hettangian) of Nova Scotia, Canada. It is most closely related to C. mcgilli Wu, 1994 from the Dark Red Beds of the Lower Lufeng Formation (Lower Jurassic) of Yunnan, China, and differs from the latter mainly in the absence of the hourglass-shaped constriction of the parietals, the shape of the suborbital fenestra, and in features of the marginal dentition. The new taxon is of considerable interest because it represents the first record of Clevosaurus from North America. Like many other early Mesozoic continental tetrapods, Clevosaurus had an apparently Pangaean geographic distribution.

Distribution and origin of clay minerals in the lower jurassic McCoy brook formation, Minas Basin, Nova Scotia

The distribution of clay minerals in the depositional facies of the McCoy Brook Formation is controlled by the clay-mineral origin (extrabasinal versus intrabasinal). The McCoy Brook Formation was deposited during Early Jurassic (Hettangian-Sinemurian) time in the Minas basin as alluvial-fan, sandflat, playa, lacustrine, fluvial, eolian, debris-flow and talus facies during a period of semiarid to arid climate. The predominant minerals in the clay fraction of the formation are illite, smectite, chlorite, and palygorskite. These minerals are partitioned in the depositional environments in three assemblages. Assemblage one comprises dominantly illite with lesser concentrations of smectite, chlorite and palygorskite. This assemblage characterizes alluvial-fan, sandflat and playa facies. Assemblage two consists predominantly of smectite, with trace concentrations of illite and chlorite. This assemblage is characteristic of fluvial-channel, eolian, debris-flow and talus facies. Assemblage three comprises mainly illite, trace amounts of chlorite, and trace concentrations or no smectite. This assemblage is found in fluvial floodplain and lacustrine facies.Illite and chlorite are mainly of extrabasinal origin, having formed from weathering in the source area. Smectite and palygorskite are of intrabasinal origin. The smectite, identified as Fe-rich saponite, formed from alteration of basalt clasts within eolian, debris-flow and talus facies and of basalt outcrops adjacent to fluvial-channel facies. Palygorskite formed during pedogenesis in facies exposed at the surface for long intervals during deposition under semiarid to arid conditions.

Relationship between the Aspy and Bras d'Or "terranes" in the northeastern. Cape Breton Highlands, Nova Scotia: Discussion

The author, S. Lin, has made major contributions to the understanding of the complex geology in the Cape Breton Highlands through his detailed mapping in the vicinity of the Eastern Highlands shear zone (see also Lin 1992). However, some generalizations made in his paper do not accurately portray the geology, and imply an unrealistic degree of certainty about some interpretations. The purpose of this discussion is to emphasize that many problems remain unresolved in the vicinity of the Eastern Highlands shear zone, contrary to the impression given by him. The author asserted that the late Precambrian rocks of the Bras d'Or terrane are overlain by the Clyburn Brook formation, a volcanic sedimentary sequence of Silurian age. However, the age of the Clyburn Brook formation is uncertain because it is based on a Rb-Sr isochron; such ages have been shown to be unreliable in the Cape Breton Highlands and elsewhere (e.g., Dunning et al. 1990). In addition, the reported isochron (Keppie and Halliday 1986) is based (with one exception) on Rb Sr data for samples from rhyolite on Ingonish Island, not on samples from the Clyburn Brook formation. Unlike rhyolite in the Clyburn Brook formation, the Ingonish Island rhyolite is unmetamorphosed and lacks associated basaltic, volcaniclastic, and sedimentary units (Raeside and Barr 1992); hence, correlation between the Ingonish Island rhyolite and the Clybum Brook formation is speculative. The statement in the abstract of the paper that the Clyburn Brook formation is Silurian is premature. It may be, but that has yet to be demonstrated. The author (p. 1773) implied that amphibolite-facies rocks occur only in the part of the McMillan Flowage Formation within the Eastern Highlands shear zone, with the further implication that there is a connection between the amphibolitefacies metamorphism and the shear zone. Amphibolite-facies metamorphism in the McMiiian Flowage Formation persists for 16 km southeast of (away from) the shear zone. Furthermore, titanite in the McMillan Flowage Formation has yielded ages of Ca. 540 Ma (Raeside and Barr 1992; G.R. Dunning, personal communication, 1990), showing that peak metamorphism was late Precambrian to Early Cambrian, much older than the deformation associated with the Eastern Highlands shear zone as documented by the author. In describing the Aspy terrane, the author (p. 1774) implied that the Cheticamp Lake Gneiss is the only supracrustal rock unit in the Aspy terrane. As documented by Raeside and Barr (1992), as well as numerous other workers (e.g., Currie 1982; Jarnieson et al. 1987, 1990), the Aspy terrane includes various

Geochemistry of Proterozoic (∼ 1.9 Ga) Sedimentary Rocks from the Labrador District, Canada

Weakly metamorphosed metasedimentary rock samples used in this study belong to Ramah group of Proterozoic. The Ramah group, consisting chiefly of sedimentary rocks distribites along north-south trending synclinal axis in northern Labrador. The Ramah group is considered early Proterozoic on the basis of a Rb-Sr whole rock age of 1.89 Ga (Morgan, 1978), obtained from a basalt lava and related feeder dyke near the base of the group. Approximate total thickness of the group is 1700 m, most component of the group are sedimentary rocks. Volcanic rocks are minor component of the lower sequencre, but numerous diabase sills which intruded the group are known. The group is subdivided in to six formations (Morgan, 1975; Knight and Morgan, 1977, 1981), Rosell Harbour, Reddick Bight, Nullataktok, Warspite, Typhoon Peak and Cameron Brook formations in ascending order, the dominant lithologies are quartzite, sandstone, mudstone and carbonate rocks. Samples used in this study are grouped into three categories, black shale, grey shale, and graywacke, from the observation of hand specimens, thin sections as well as from their chemical compositions.

Origin of Authigenic Smectite and Zeolite in the Lower Jurassic McCoy Brook Formation, Fundy Basin, Nova Scotia: ABSTRACT

Origin of Authigenic Smectite and Zeolite in the Lower Jurassic McCoy Brook Formation, Fundy Basin, Nova Scotia: ABSTRACT

Ballast Brook and Beaufort Formations (late Tertiary) on Northern Banks Island, Arctic Canada

Excellent exposures of late Tertiary terrestrial sediments occur in the Ballast Brook region of northwestern Banks Island (Canadian Arctic Archipelago). These sediments contain abundant concentrations of organic detritus as well as autochthonous peats which can be traced for some kilometres. All of these deposits were previously assigned to the Beaufort Formation. In this paper, the deposits formerly grouped as the Beaufort Formation are subdivided into two formations: the newly named Ballast Brook Formation and the Beaufort Formation. The Ballast Brook Formation is characterized by alluvial sand, silt-clay and peat with compressed, altered wood. Paleobotanical evidence indicates an early to mid-Miocene age, with mid-Miocene being the most probable. This formation is believed to overlie the Eureka Sound Group and is in erosional contact with the overlying Beaufort Formation. Plant macrofossils from the Ballast Brook Formation include a number of taxa now found in northern hardwood and southern boreal forests, while the prominent peat which characterizes the formation contains a number of taxa that now grow or could be expected to grow in a cypress swamp type of environment. For example the conifer Glyptostrobus is well represented in the peat. The Beaufort Formation at Ballast Brook consists of alternating sands and gravels, and silt in the lower part. It is characterized by an abundance of unaltered wood and other plant materials. Paleobotanical evidence indicates an early Pliocene to early late Pliocene age (i.e. approx. 5-3 Ma). Like the Ballast Brook Formation, the Beaufort Formation contains an abundance of fossils of conifers, but in contrast with the Ballast Brook Formation nearly all of them belong to Pinaceae, a group well represented in the present boreal forest. The Beaufort Formation also contains insect fossils, which are very rare in the Ballast Brook Formation. Together, the insect and plant macrofossils suggest an environment similar to, but richer in species (some extinet; others now found only in Asia) than present boreal forest and taiga. The Ballast Brook Formation flora resembles the flora from Mary Sachs gravel (formerly Beaufort Formation) on southwestern Banks Island and the flora from the West River beds on the Northwest Territories mainland. It also is similar to a 40 Ar 39 Ar dated mid-Miocene flora from east-central Alaska and to the Mamontova Gora (mid-Miocene) flora from Russia.

Relationship between the Aspy and Bras d'Or "terranes" in the northeastern Cape Breton Highlands, Nova Scotia

According to previous interpretations, the Eastern Highlands shear zone separates Ordovician–Silurian volcano-sedimentary rocks to the west (Cheticamp Lake Gneiss of the Aspy "terrane") from late Precambrian sedimentary rocks and dioritic – tonalitic plutons and Early Ordovician granite to the east (Bras d'Or "terrane"). New mapping discovered a basal conglomerate of the Cheticamp Lake Gneiss that rests on deformed diorite of the Bras d'Or "terrane" and contains clasts similar or identical to rocks of the Bras d'Or "terrane." The late Precambrian rocks of the Bras d'Or "terrane" are also overlain by a volcano-sedimentary sequence of Silurian age (Clyburn Brook formation). These observations suggest that rocks of the Aspy "terrane" lie unconformably on those of the Bras d'Or "terrane." The Eastern Highlands shear zone is therefore not a terrane boundary. The Ordovician–Silurian rocks of the Aspy "terrane" are interpreted to have formed in an arc–back-arc basin system. The back-arc basin is interpreted to have formed by rifting in the Bras d'Or "terrane" and the Eastern Highlands shear zone to have been related to the closure of the basin.

Tectonic significance of the Late Proterozoic Economy River gneiss, Cobequid Highlands, Avalon Composite Terrane, Nova Scotia

A 734 ± 2 Ma U–Pb (zircon) age for the Economy River orthogneiss, Coboquid Highlands, Nova Scotia, is interpreted as being representative of a regionally extensive ca. 820–660 Ma event that is recorded in many parts of the Late Proterozoic – Early Cambrian Avalon Composite Terrane and the Gondwanan margin. The geochemistry of the gneiss is consistent with an arc environment. Although the gneiss may represent part of the sialic basement to the terrane, field relationships indicate that some of the basement is significantly older. The date may provide a minimum age for the platformal sedimentary rocks (Gamble Brook Formation) that the orthogneiss intruded and thus help constrain the Late Proterozoic paleogeographic position of Avalon relative to Gondwanaland.

Depositional facies, paleogeography and palaeoclimatology of the Lower Jurassic McCoy Brook Formation, Fundy rift basin, Nova Scotia

The McCoy Brook Formation is a 230+ m sequence of redbeds of Early Jurassic age that accumulated in the subtropical Fundy rift basin. The basin was asymmetrical, bordered on the northern side by the Cobequid fault system and adjacent highlands. The formation is a mosaic of terrestrial facies. (a) Multi- and single-storey fluvial sandstones were deposited by rivers that collected drainage from the norhern highlands, and flowed southwest across the valley floor. (b) Graded-bed sequences of sandstone → mudstone were deposited by flood events on the fluvial floodplains and the margins of playas. (c) Interbedded sandstones and finely laminated to disrupted red mudstones represent deposits of interfingering sandflats at the toes of alluvial fans and playas, respectively. The fabrics of both lithologies are commonly disrupted by desiccation and intrastratal precipitation of calcite and minor gypsum. (d) Plane-bedded conglomerate and pebbly sandstone record deposition in shallow channels that traversed alluvial fans. (e) Non-bedded breccias of basalt boulders up to 8 m in size in a sand to mud matrix formed as talus against palaeocliffs of the Lower Jurassic North Mountain Basalt. The palaeocliffs resulted from synsedimentary faulting within the basin. (f) Basalt conglomerate beds with matrix- to clast-supported fabrics comprise sequences deposited by debris-flows, probably generated by remobilization of talus. (g) A thin sequence of limestone, siltstone, and muddy sandstone containing fish scales and bones formed in a shallow lake on a basalt flow. (h) Sandstones containing m-scale crossbeds and a three-fold hierarchy of erosional surfaces accumulated as barchans and barchanoid transverse ridges that moved southwest in the valley. All of these facies occur within an area of 18 km 2 located south of the fault-bounded highlands. Synsedimentary faulting within the basin during early deposition of the McCoy Brook Formation created palaeocliffs of North Mountain Basalt. Talus and debris-flow deposits accumulated adjacent to these cliffs, interfingering with eolian, fluvial, and lacustrine sediments. During later deposition of the McCoy Brook Formation, the early fault-controlled topography was buried as alluvial fans prograded southward from the highlands. Broad sandflats extended basinward from the toes of the fans, interfingering with playa mudflats on the valley floor. The palaeoclimate was semi-arid as evidenced by gypsum-bearing playa redbeds, eolian sandstones, and caliche palaeosols.

The Ordovician volcanics of the Elmtree–Belledune inlier and their relationship to volcanics of the northern Miramichi Highlands, New Brunswick

An investigation of the geology and chemistry of the basic igneous rocks in the Elmtree and Belledune inliers in northern New Brunswick shows that the bulk of the Middle Ordovician rocks of the ophiolitic Fournier Group are best interpreted as the products of volcanism and sedimentation in an extensive ensimatic back-arc basin southeast of a volcanic arc. The oceanic back-arc-basin igneous rocks form the basement to renewed arc-related basaltic volcanism in late Middle to Late Ordovician time. The Fournier Group is separated from the structurally-underlying, shale-dominated Elmtree Formation of the Tetagouche Group by an extensive tectonic melange, which incorporates lenses of serpentinite, mafic volcanic rocks, and sedimentary rocks of both the Tetagouche and Fournier groups. The mafic volcanic rocks in the Elmtree Formation correlate best with those intercalated with the lithologically similar sediments of the Llandeilian–Caradocian Boucher Brook Formation in the northern Miramichi Highlands. The melange and the present structural amalgamation of the Tetagouche and Fournier groups result from closure of the marginal basin by northward-directed subduction at the end of the Ordovician. Most mafic suites in the Elmtree and Belledune inliers can be chemically correlated with similar suites in the northern Miramichi Highlands, showing that the two areas are not separated by a terrane boundary.