TY - JOUR
T1 - Late Carboniferous (Bolsovian) macroflora from the Barachois Group, Bay St. George Basin, southwestern Newfoundland, Canada
AU - Bashforth, Arden Roy
PY - 2005
Y1 - 2005
N2 - A well preserved macrofloral assemblage characterized by taxonomically diverse adpressions and large cordaitean tree petrifactions was recovered from the coal-bearing Upper Carboniferous Barachois Group in Bay St. George Basin, southwestern Newfoundland. The collection is dominated by cordaitean and marattialean tree fern foliage, although medullosan pteridosperms, lycopsids and sphenopsids are also represented. 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 Plant Paleokingdom. Recovery of very well preserved cuticles exhibiting fine epidermal cellular details reflects the fact that the strata have experienced very little deformation or burial, and supports previous claims of thermal immaturity. Paleoecological evidence and homotaxial biostratigraphic correlation with other localities in the Europe Paleoarea indicates that the assemblage is late Bolsovian in age, which refines ages determined in previous palynological studies. The fossil-bearing strata record sediment accumulation in a coarse-grained meandering stream system that developed under somewhat seasonal conditions in an intramontane basin distant from marine influence, presumably on the relatively elevated margin of the Variscan Foreland Basin. The locality is characterized by channel sandstones and conglomerates overlain by fining-upwards successions that terminate in clastic swamp deposits preserved as carbonaceous mudstones and thin, laterally discontinuous coal seams. The distribution and relative abundances of plants within each lithofacies, including miospores recorded from coals, have been integrated with previously interpreted habitat preferences for flora represented. The resulting paleoenvironmental model alludes to considerable habitat partitioning between members of different plant groups. In particular, there is evidence for interspecific habitat partitioning within the medullosan pteridosperms occupying the floodplains and levees, whereas arborescent sigillarian lycopsids may have only occupied comparatively drier substrates where medullosan pteridosperms were uncommon or even absent. Forests of towering cordaitean trees probably occupied the topographically raised and well-drained extrabasinal habitats surrounding the catchment basin. Clastic swamps were inhabited by an array of flora, the composition of which depended on the rate of peat buildup versus clastic sediment accumulation that resulted from frequent incursions of sediment-laden floodwaters. During intervals when local subsidence and paleoclimatic conditions were favorable for peat formation, coal-forming vegetation was dominated by arborescent sigillarians and a significant component of Diaphorodendron bretonense (Bell) comb. nov., whereas various tree and ground cover ferns along with calamitean plants probably formed an understory. In the comparatively drier, clastic-substrate phases of swamp development, the arborescent lycopsids Sigillaria, Lepidodendron hickii and D. bretonense comb. nov. coexisted with small cordaitean plants and tree ferns. In the final stages of swamp evolution, swamp-dwelling cordaiteans evidently formed monotaxic or low diversity stands surrounding and possibly within the standing water of anoxic ponds that drowned all other vegetation.
AB - A well preserved macrofloral assemblage characterized by taxonomically diverse adpressions and large cordaitean tree petrifactions was recovered from the coal-bearing Upper Carboniferous Barachois Group in Bay St. George Basin, southwestern Newfoundland. The collection is dominated by cordaitean and marattialean tree fern foliage, although medullosan pteridosperms, lycopsids and sphenopsids are also represented. 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 Plant Paleokingdom. Recovery of very well preserved cuticles exhibiting fine epidermal cellular details reflects the fact that the strata have experienced very little deformation or burial, and supports previous claims of thermal immaturity. Paleoecological evidence and homotaxial biostratigraphic correlation with other localities in the Europe Paleoarea indicates that the assemblage is late Bolsovian in age, which refines ages determined in previous palynological studies. The fossil-bearing strata record sediment accumulation in a coarse-grained meandering stream system that developed under somewhat seasonal conditions in an intramontane basin distant from marine influence, presumably on the relatively elevated margin of the Variscan Foreland Basin. The locality is characterized by channel sandstones and conglomerates overlain by fining-upwards successions that terminate in clastic swamp deposits preserved as carbonaceous mudstones and thin, laterally discontinuous coal seams. The distribution and relative abundances of plants within each lithofacies, including miospores recorded from coals, have been integrated with previously interpreted habitat preferences for flora represented. The resulting paleoenvironmental model alludes to considerable habitat partitioning between members of different plant groups. In particular, there is evidence for interspecific habitat partitioning within the medullosan pteridosperms occupying the floodplains and levees, whereas arborescent sigillarian lycopsids may have only occupied comparatively drier substrates where medullosan pteridosperms were uncommon or even absent. Forests of towering cordaitean trees probably occupied the topographically raised and well-drained extrabasinal habitats surrounding the catchment basin. Clastic swamps were inhabited by an array of flora, the composition of which depended on the rate of peat buildup versus clastic sediment accumulation that resulted from frequent incursions of sediment-laden floodwaters. During intervals when local subsidence and paleoclimatic conditions were favorable for peat formation, coal-forming vegetation was dominated by arborescent sigillarians and a significant component of Diaphorodendron bretonense (Bell) comb. nov., whereas various tree and ground cover ferns along with calamitean plants probably formed an understory. In the comparatively drier, clastic-substrate phases of swamp development, the arborescent lycopsids Sigillaria, Lepidodendron hickii and D. bretonense comb. nov. coexisted with small cordaitean plants and tree ferns. In the final stages of swamp evolution, swamp-dwelling cordaiteans evidently formed monotaxic or low diversity stands surrounding and possibly within the standing water of anoxic ponds that drowned all other vegetation.
M3 - Journal article
SN - 0821-7556
VL - 24
SP - 1
EP - 123
JO - Palaeontographica Canadiana
JF - Palaeontographica Canadiana
ER -
