Late Devonian extinction

About: Late Devonian extinction is a research topic. Over the lifetime, 1959 publications have been published within this topic receiving 52570 citations.

A chronology of Paleozoic sea-level changes.

Abstract: Sea levels have been determined for most of the Paleozoic Era (542 to 251 million years ago), but an integrated history of sea levels has remained unrealized. We reconstructed a history of sea-level fluctuations for the entire Paleozoic by using stratigraphic sections from pericratonic and cratonic basins. Evaluation of the timing and amplitude of individual sea-level events reveals that the magnitude of change is the most problematic to estimate accurately. The long-term sea level shows a gradual rise through the Cambrian, reaching a zenith in the Late Ordovician, then a short-lived but prominent withdrawal in response to Hirnantian glaciation. Subsequent but decreasingly substantial eustatic highs occurred in the mid-Silurian, near the Middle/Late Devonian boundary, and in the latest Carboniferous. Eustatic lows are recorded in the early Devonian, near the Mississippian/Pennsylvanian boundary, and in the Late Permian. One hundred and seventy-two eustatic events are documented for the Paleozoic, varying in magnitude from a few tens of meters to ∼125 meters.

A Late Devonian Reef Tract on Northeastern Banks Island, N.W.T.

Abstract: The Upper Devonian Weatherall Formation, outcropping on northeastern Banks Island, N.W.T., contains a 200-ft-thick limestone unit here termed the Mercy Bay Member. The member is Middle to Late Frasnian in age. Gyrfalcon Bluff has been chosen as the type section. Mercy Bay Member outcrops on the extreme northeastern portion of Banks Island, and many excellent exposures permit detailed paleogeographical and paleoecological studies. The member contains numerous organic build-ups and represents a Late Devonian reef tract located in the marine-shelf environment of an exogeosyncline situated between a tectonic highland to the northwest and a stable craton to the southeast. The main facies changes in the Mercy Bay Member occur in an east-west direction. The organic build-ups in the eastern part of the study area are narrow, linear bioherms trending north-south. They are encased in younger terrigenous clastic rocks. To the west the organic build-ups, which are biohermal in the lower part and biostromal in the upper, are more numerous. The lower bioherms trend east-west. Penecontemporaneous interbiohermal strata consist of dark, fine-grained argillaceous limestone. Organic build-ups on the western edge of the outcrop area are bioherms which trend north-south. The lower portion in all organic build-ups consists of corals and tabular stromatoporoids. These are interpreted as biogenetic banks constructed in the quiet and intermediate-energy zones (water depths more than 30 ft). The upper portion is composed of massive stromatoporoids. This facies represents rigid reefs constructed in the high-energy zone (above 30 feet). Successive sea-level rises allowed the reefs to grow upward. Cessation of reef growth was caused by an influx of terrigenous sediment related to the seaward migration of the northern and western shorelines. The outcropping organic build-ups of the Mercy Bay Member are tightly cemented, but frequent bitumen occurrences indicate that they were once oilbearing. Organic build-ups of the Mercy Bay Member probably occur in the subsurface to the west. End_Page 730------------------------

Devonian eustatic fluctuations in Euramerica

Abstract: The Devonian System of Euramerica contains at least 14 transgressive-regressive (T-R) cycles of eustatic origin. These are separated into three groups (or depophases) and from Carboniferous cycles by three prominent regressions. Twelve post-Lochkovian T-R cycles are recognized, and they commonly appear to result from abrupt deepening events followed by prolonged upward shallowing. Deepening events in the western United States (especially Nevada), western Canada, New York, Belgium, and Germany have been dated in the standard conodont zonation and are demonstrably simultaneous in several or all five regions. This synchroneity indicates control by eustatic sea-level fluctuations rather than by local or regional epeirogeny. Facies shifts in shelf sedimentary successions are more reliable indicators of the timing of sea-level fluctuations than are strandline shifts in the cratonic interior, because the latter are more influenced by local epeirogeny. Strandline shifts are most useful in estimating the relative magnitude for sea-level fluctuations. Devonian facies progressions and the three prominent regressions are of a duration and an order of magnitude that could have been caused by episodes of growth and decay of Devonian oceanic ridge systems. The described T-R cycles could have formed in response to mid-plate thermal uplift and submarine volcanism. The latter process may have been a control on small-scale (1–5 m thick), upward-shallowing cycles within the major T-R cycles. Continental glaciation could have been a factor in sea-level fluctuations only in the Famennian and could not have been responsible for the Devonian facies progressions or the numerous T-R cycles. The Frasnian extinctions were apparently cumulative rather than due to a single calamity. Two rapid sea-level rises occurred just before, and one at, the Frasnian-Famennian boundary. It is probable that this series of deepening events reduced the size of shallow-shelf habitats, caused repeated anoxic conditions in basinal areas, and drowned the reef ecosystems that had sustained the immensely diverse Devonian benthos.

Diversification and extinction in the history of life

Abstract: Analysis of the fossil record of microbes, algae, fungi, protists, plants, and animals shows that the diversity of both marine and continental life increased exponentially since the end of the Precambrian. This diversification was interrupted by mass extinctions, the largest of which occurred in the Early Cambrian, Late Ordovician, Late Devonian, Late Permian, Early Triassic, Late Triassic, and end-Cretaceous. Most of these extinctions were experienced by both marine and continental organisms. As for the periodicity of mass extinctions, no support was found: Seven mass extinction peaks in the last 250 million years are spaced 20 to 60 million years apart.

Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events

Abstract: The Devonian Period was characterized by major changes in both the terrestrial biosphere, e.g. the evolution of trees and seed plants and the appearance of multi-storied forests, and in the marine biosphere, e.g. an extended biotic crisis that decimated tropical marine benthos, especially the stromatoporoid-tabulate coral reef community. Teleconnections between these terrestrial and marine events are poorly understood, but a key may lie in the role of soils as a geochemical interface between the lithosphere and atmosphere/hydrosphere, and the role of land plants in mediating weathering processes at this interface. The effectiveness of terrestrial floras in weathering was significantly enhanced as a consequence of increases in the size and geographic extent of vascular land plants during the Devonian. In this regard, the most important palaeobotanical innovations were (1) arborescence (tree stature), which increased maximum depths of root penetration and rhizoturbation, and (2) the seed habit, which freed land plants from reproductive dependence on moist lowland habitats and allowed colonization of drier upland and primary successional areas. These developments resulted in a transient intensification of pedogenesis (soil formation) and to large increases in the thickness and areal extent of soils. Enhanced chemical weathering may have led to increased riverine nutrient fluxes that promoted development of eutrophic conditions in epicontinental seaways, resulting in algal blooms, widespread bottomwater anoxia, and high sedimentary organic carbon fluxes. Long-term effects included drawdown of atmospheric pCO2 and global cooling, leading to a brief Late Devonian glaciation, which set the stage for icehouse conditions during the Permo-Carboniferous. This model provides a framework for understanding links between early land plant evolution and coeval marine anoxic and biotic events, but further testing of Devonian terrestrial-marine teleconnections is needed.