Descriptive taxonomy, biostratigraphic correlation and paleoenvironmental reconstruction of an upper carboniferous macrofloral assemblage, Bay St. George Basin, Southwestern Newfoundland

Bashforth, Arden Roy (1999) Descriptive taxonomy, biostratigraphic correlation and paleoenvironmental reconstruction of an upper carboniferous macrofloral assemblage, Bay St. George Basin, Southwestern Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

A diverse, well preserved macrofloral assemblage (herein termed the Blanche Brook Assemblage), which is characterized by large tree petrifactions of cordaitean affinity and an array of adpressed foliage that includes lycopsids, sphenopsids, ferns, pteridosperms and cordaiteans, has been recovered from coal-bearing strata of the Upper Carboniferous Barachois Group of the Bay St. George Basin, southwestern Newfoundland. The locality constitutes part of the northernmost onshore extent of the Maritimes Basin of eastern Canada, which developed on the southern margin of paleoequatorial Laurentia and is included in the Europe Paleoarea of the Euramerian Paleokingdom. Although the fossil site was initially investigated in the late 1800's, the present study comprises the first comprehensive taxonomic description and biostratigraphic correlation of the macrofloral assemblage, and provides an interpretation of the depositional environment and paleoecotogical conditions under which the flora flourished. -- Recovery of very well preserved cuticles exhibiting fine epidermal cellular details from adpressed cordaitean and pteridosperm foliage reflects the fact that fossiliferous strata have experienced very little deformation or burial metamorphism, and supports earlier claims that rocks in the northern part of the Bay St. George Basin and on Port au Port Peninsula are thermally immature. Paleoecological evidence and homotaxial biostratigraphic comparison of selected adpressed macroflora with other localities in the Europe Paleoarea (e.g., Maritimes Basin, western and central Europe, midcontinental North America) indicates that the assemblage is middle to late Bolsovian in age, which corroborates ages determined earlier from palynological studies. -- Fossiliferous and associated rocks in the stratigraphic succession are here subdivided and assigned to one of seven sublithofacies, each of which represents a distinct depositional environment characterized by its sedimentology and stratigraphy, vertical and lateral relationships with other sublithofacies, and plant fossil assemblages. The strata appear to record sediment accumulation in a coarse grained meandering stream system that occupied a narrow alluvial plain and was characterized by poorly developed levee/backlevees that were consequently overtopped or breached during frequent flood events. The distribution and relative abundances of taxa within each sublithofacies, including miospores recorded from associated coal seams, have been integrated with previously interpreted habitat preferences known for flora represented at the fossil site. This has resulted in construction of a working paleoenvironmental model for the Blanche Brook Assemblage, which indicates that there was considerable habitat partitioning and even competition for ecological niches between members of the five main plant groups in response to ecological preferences of each taxa. In particular, there is evidence for interspecific habitat partitioning within the medullosan pteridosperms occupying the floodplains and leveeftacklevees, while competition may also may existed between certain medullosan pteridosperms and sigillarian arborescent lycopsids for drier edaphic substrates in these habitats. Likewise, clastic swamps were inhabited by an array of flora, the composition of which depended on the rate of peat versus clastic sediment accumulation that resulted from frequent incursions of sediment-laden floodwaters.

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