Journal Article•
Endemism and dispersal of Devonian conodonts
About: This article is published in Journal of Paleontology.The article was published on 1980-03-01 and is currently open access. It has received 167 citations till now. The article focuses on the topics: Devonian & Biological dispersal.
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TL;DR: The Devonian System of Euramerica contains at least 14 transgressive-regressive (T-R) cycles of eustatic origin this paper, which are separated into three groups (or depophases) and from Carboniferous cycles by three prominent regressions.
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.
879 citations
TL;DR: In this paper, the authors used U-Pb zircon ages of volcanic ashes closely tied to biostratigraphic zones to revise the Devonian time-scale.
289 citations
01 Jan 2002
223 citations
TL;DR: In this article, an integrated lithologic, paleontologic, and multi-proxy geochemical study of the Middle Devonian Oatka Creek Formation, a black shale in the northern Appalachian Basin, indicates that a number of different factors contributed to organic carbon-rich black shale deposition.
Abstract: An integrated lithologic, paleontologic, and multi-proxy geochemical study of the Middle Devonian Oatka Creek Formation, a black shale in the northern Appalachian Basin, indicates that a number of different factors contributed to organic carbon-rich black shale deposition. Conditions leading to this organic-rich sedimentary deposit were ultimately controlled by a relative sealevel rise, dominantly eustatic but with possible contributions from local tectonics, which cut off the supply of carbonate to the basin. Geochemical proxy evidence –such as Mo/Ti, Fe/Ti, Corg, Spy, and δ34Spy –suggests that as sealevel continued to rise after the carbonate supply was cut off, a threshold was crossed at which point conditions in the basin shifted from dominantly anoxic to dominantly euxinic (anoxic-sulfidic bottom waters). Concurrent with the shift to dominantly euxinic conditions, the supply of siliciclastic sediments was cut off, resulting in a condensed horizon, as evidenced by the elemental ratios of Si/Al and K/(Fe+Mg) and the relative concentration of eolian silt as determined petrographically and from scanning electron microscopy. Sediment starvation in the basin appears to have facilitated the biogeochemical (re)cycling of C, N, and P. Specifically, the elemental ratios of C, N, and P and the stable carbon isotope composition of organic matter suggest that the preferential regeneration of P under anoxic conditions (and of N during the oxic phase of oxic/anoxic oscillation) led to enhanced primary production in surface waters, thereby maintaining euxinic conditions in the bottom waters through respiration of settling organic matter. Finally, it is observed that, though conditions in the basin seem to have remained consistently anoxic-sulfidic for some time after the initial shift to euxinic conditions, a progressive increase in siliciclastic sedimentation led to a corresponding decrease in the enrichment of various redox-related elements, illustrating the overriding control that sedimentation can have on geochemical proxy records.
214 citations
TL;DR: In this article, a strong relation is shown between times of global or regional sea-level change inferred from stratigraphic analysis, and times of high turnover of Phanerozoic marine invertebrates, involving both extinction and radiation; this is valid on a small and large scale.
Abstract: A correlation between global marine regressions and mass extinctions has been recognized since the last century and received explicit formulation, in a model involving habitat-area restriction, by Newell in the 1960s. Since that time attempts to apply the species-area relation to the subject have proved somewhat controversial and promoters of other extinction models have called the generality of the regression-extinction relation into question. Here, a strong relation is shown to exist between times of global or regional sea-level change inferred from stratigraphic analysis, and times of high turnover of Phanerozoic marine invertebrates, involving both extinction and radiation; this is valid on a small and large scale. In many cases the most significant factor promoting extinction was apparently not regression but spreads of anoxic bottom water associated with the subsequent transgression. The sea-level-extinction relation cannot be properly understood without an adequate ecological model, and an attempt is made to formulate one in outline.
182 citations