Heidi McDonald

Coastal exposures of the Sydney Mines Formation (Westphalian D) at Morien Bay, Nova Scotia record stacked high-frequency sequences 11-38m thick of fluvial and restricted marine strata with economic coals. The cliffs at Morien Bay are among the world's best continuous Carboniferous coal measure exposures. Sections 75 - 160 m thick at Schooner Pond, Long Beach, and Morien South provide a ~10km downdip direction traverse that encompasses the McRury to Bouthillier coal seam interval. The dominant facies assemblage represents a poorly drained coastal plain and comprises grey sandstone and shale, hydromorphic paleosols, thick coals and distributary channel bodies. The coals are sulphur-rich, suggesting a marine influence, and are up to 2.8 m thick. A second facies assemblage represents a well drained alluvial plain and comprises red mudstone, nodular calcrete, vertic red and grey paleosols, and dryland channel bodies; it predominates at Morien South. Repetition of these facies assemblages represents cycles of relative sea level change, probably linked to glacioeustasy which is inferred to have dominated the formation's stratal architecture.

Applying a sequence stratigraphic framework, marine flooding surfaces are recognized by thick, extensive coal seams or thin coal or coaly shale. Maximum flooding surfaces can be represented by faunal-concentrate limestones rich in bivalves and ostracods and form excellent regional stratigraphic markers. Three main types of sequence boundary are (a) single well-defined calcretes with minimal sedimentation for long periods, (b) sequence boundary zones of vertisol-type paleosols several metres thick in areas of higher sedimentation, and (c) sequence boundary zones of small paleovalley fills or larger dryland channel bodies in association with paleosols. Some calcretes can be correlated between sections and across the basin. The vertisol-type paleosols are also widespread but more difficult to correlate. Within seven stacked sequences, wetland facies and economic coals are well represented within the Transgressive and Highstand Systems Tracts. 'Dry' and 'wet' subdivisions of the Highstand Systems Tract reflect upward passage into red and grey dryland facies which may represent falling sea level prior to the formation of the sequence boundary. Systems tract terminology could not always be applied to the alluvial plain strata.

Stratal packages thicken in Morien Bay when compared to sections in the western part of the Sydney Basin, due to increased subsidence. Particularly at Morien South, increased amount of red floodplain material suggests a more proximal and well-drained region towards the southern limb of the Morien Syncline. Unidirectional paleocurrent data from channel bodies yields an overall paleoflow direction of 347^o (NNW) with vector means of paleocurrent measurements of 029^o (ENE), 001^o (N), and 334^o (NNW) at Schooner Pond, Long Beach and Morien South, respectively. This suggests a local source to the south of Morien Bay, probably the Proterozoic rocks of the Scatarie Ridge and regional sources within the northern Appalachian Mountains. Some channel bodies with NE paleoflow indicate a subsidiary mode sub-parallel to the axis of the Morien Syncline.

An abundant paleobotanical record in grey, coal-bearing strata comprises erect lycopsids, prostrate logs and abundant compression flora. Thirty lycopsid trees in growth position had trunk diameters from 0.25-0.6 m. Lepidodendron sp. and Sigillaria sp. are the two main lycopsids identified. Compression flora consists of pteridosperms (Alethopteris sp. and Neuropteris sp.), marattialean tree-ferns (Pecopteris sp.), sphenophytes (Sphenophyllum sp.), Cordaites, and Calamites. Few plant specimens were recovered from redbed intervals. A rare, well-preserved tetrapod trackway with 18 tracks is provisionally attributed to Baropezia sydnensis, a temnospondyl amphibian.

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Pages: 251
Supervisor: Martin Gibling