683 research outputs found
Evidence for Late Devonian (Kellwasser) anoxic events in the Great Basin, western United States
No full textThe Frasnian-Famennian (Late Devonian) mass extinction has often been related to the development of the Kellwasser anoxic events in Europe and North Africa but the synchronous development of the anoxia has not been reported from the Great Basin of the western United States. An integrated sedimentological, palaeoecological, and pyrite petrographic study has been undertaken on a range of F-F boundary sections from Nevada and Utah spanning a spectrum of carbonate and clastic depositional environments from distal basin, base-of-slope, mid-slope, and intrashelf basin settings. These reveal a range of facies from oxic strata, fully bioturbated and lacking any pyrite, to euxinic strata characterised by fine lamination and pyrite framboid populations of small size and narrow size range. Oxygen-restricted deposition is seen in all sections at various times, but the only interval characterised by basin-wide euxinicity occurs at the end of the Frasnian Stage late in the linguiformis Zone. This is the peak of the F-F mass extinction and it is also contemporaneous with the Upper Kellwasser Horizon of Europe. The study therefore reinforces the claim that the mass extinction coincides with the global development of marine anoxia. Shallow-water sections were not studied but slope and base-of-slope sections record many sediment-gravity flows that transported an allochthonous fauna into deeper water settings. This shallow-water fauna temporarily disappears late in the linguiformis Zone perhaps indicating the development of oxygen-restriction in shallow-water settings. Intriguingly the condensed, deepest water sections from the Woodruff basin record somewhat higher oxygenation levels than the contemporaneous slope sections. The most oxygen-restricted conditions may therefore have occurred in a mid-water oxygen-minimum zone that expanded its vertical range both upwards and downwards and became sulfidic late in the linguiformis Zone
Crafts in the Southern Mountains
No full textThis article appeared in the 1931, November/December issue of "Handicrafter" magazine. It traces author "P.B."'s travels to various craft centers in the southern Appalachian mountains. Mentioned in the article are Allanstand Cottage Industries, The Spinning Wheel, Clementine Douglas, Winogene Redding, Evelyn Bishop, Mrs. Stone, Blue Ridge Weavers, Penland's Weaving Institute, Penland Weavers and Potters, Crossnore School, Mrs. H. N. Johnson, Pi Beta Phi Fraternity School, and Berea College's Fireside Industries. The author only gives a brief impression of his or her visit to each place. It is likely that author P.B. is Paul Bernat, editor of "Handicrafter" magazine
Comment on: Contrasting Deep-water Records from the Upper Permian and Lower Triassic of South Tibet and British Columbia: Evidence for a Diachronous Mass Extinction (Wignall and Newton 2003): Reply
No full textWe are pleased that our paper has generated interest
from Retallack and relish the opportunity to comment further
on the intriguing timing of the end-Permian extinction.
Perhaps not surprisingly, we do not agree with any of
Retallack’s assertions and deal with them here in the order
he presented them
Paleobiology: Anatomy of a mass extinction double whammy
No full textThe Permo-Triassic mass extinction has been resolved into two closely spaced crises that both saw enormous extinction losses. However, food web modelling suggests they were not ecologically equivalent, only the second destabilised communities
Sedimentology of the Triassic–Jurassic boundary beds in Pinhay Bay (Devon, SW England)
No full textSedimentology of the Triassic–Jurassic boundary beds in Pinhay Bay(Devon, SW England). Proceedings of the Geologists’ Association, 112. 349–360. New exposures
in Pinhay Bay (SE Devon) of the White Lias (Langport Member of the Lilstock Formation)and basal Blue Lias reveal rapidly changing palaeoenvironments during the Triassic–Jurassic(T–J) boundary interval. During deposition of the topmost White Lias a soft seafloor of micritic mudstone was lithified and bored. The resultant hardground was locally eroded, probably in a
shallow marine setting, to form a spectacular intraformational conglomerate that was itself lithified. Brief subaerial emergence then followed and produced a fissured and pitted top surface to the White Lias. The regression was short lived and rapid transgression at the base of the Blue Lias established organic-rich shale deposition with a small framboidal pyrite population and
low Th/U ratios indicative of a stable, sulphidic lower water column (euxinic conditions). The White Lias/Blue Lias contact thus records a short duration, high amplitude relative sea-level change. This sea-level oscillation has also been postulated for other T–J boundary sections in
Europe, although the failure to identify it in regional-scale sequence stratigraphic studies is probably due to its brief duration. Deposition of the basal beds of the Blue Lias was marked by a discrete phase of syn-sedimentary folding and small growth fault activity that may record a regional pulse of extensional tectonic activity
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