The Devonian and Lower Carboniferous were characterized by a complex sequence of 1st to 5th order global events. These consist of bioevents (extinction and origination pulses, sudden biogeographic spreads, epiboles = short bloom episodes of taxa), short-termed eustatic events, maxima of hypoxic, organic-rich facies, and geochemical anomalies/isotope spikes, which reflect sudden changes of palaeotemperatures, nutrient fluxes, oceanic palaeoproductivity, salinity, and volcanic events. Combined major magmatism and the interference of Milankovitch cyclicity are thought to have triggered repeatedly sudden palaeoclimatic changes resulting in a cascade of palaeoceanographic and biotic processes of different magnitude, duration, intensity, and regional facies expression. This explains the many similarities between smaller-scale events and specific episodes of the two mass extinctions at the Frasnian–Famennian and Devonian-Carboniferous boundaries. The Upper Kellwasser and Hangenberg Crises represent 1st order global environmental perturbations, separated by ca. 12 ma, lasting between 300 and 100 ka, and consisting of discrete event successions. A total of almost forty Devonian and Lower Carboniferous global events can be recognized in several of the distinguished eleven major regions of the Central European Variscides. These are the Ardennes, western Rhenish Massif (Aachen region to southern Hunsrück and Saarland subsurface), eastern Rhenish Massif (east of the Rhine), Harz Mountains (+ Flechtingen Horst), Thuringia/Franconia + Saxonian Vogtland, middle/eastern Saxony, Barrandian, Sudetes + Jested Mountains, Polish eastern Variscan Foreland (Holy Cross Mountains, Lublin Basin, and Kraków region), Moravia, and Vosges Mountains/Black Forest. Event recognition is difficult to impossible in strongly tectonized and metamorphosed massifs but also in some siliciclastic nearshore settings with strongly regional aspects of deposition. Wide event recognition through the Variscides and similar event facies suggest that the effects of intervening plate tectonic sutures and spatial terrain separation were too insignificant in the study interval to cause major barriers for marine faunas or different palaeoceanographic patterns. The high number of recognized events during the ca. 90 ma from the basal Devonian to top Viséan gives one sedimentary/evolutionary perturbation at every ca. 2.3 ma. This suggests that times of predominant greenhouse climate (except for the Devonian-Carboniferous boundary interval) were rather volatile periods of Earth history, with abiotic factors (especially volcanism and climate) leading to recurrent faunal overturns of different magnitude but also stimulating recoveries and evolutionary innovation.

Devonian and Lower Carboniferous Global Events in the Central Variscan Orogen

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2025年

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Ralph Thomas Becker

摘要

The Devonian and Lower Carboniferous were characterized by a complex sequence of 1st to 5th order global events. These consist of bioevents (extinction and origination pulses, sudden biogeographic spreads, epiboles = short bloom episodes of taxa), short-termed eustatic events, maxima of hypoxic, organic-rich facies, and geochemical anomalies/isotope spikes, which reflect sudden changes of palaeotemperatures, nutrient fluxes, oceanic palaeoproductivity, salinity, and volcanic events. Combined major magmatism and the interference of Milankovitch cyclicity are thought to have triggered repeatedly sudden palaeoclimatic changes resulting in a cascade of palaeoceanographic and biotic processes of different magnitude, duration, intensity, and regional facies expression. This explains the many similarities between smaller-scale events and specific episodes of the two mass extinctions at the Frasnian–Famennian and Devonian-Carboniferous boundaries. The Upper Kellwasser and Hangenberg Crises represent 1st order global environmental perturbations, separated by ca. 12 ma, lasting between 300 and 100 ka, and consisting of discrete event successions. A total of almost forty Devonian and Lower Carboniferous global events can be recognized in several of the distinguished eleven major regions of the Central European Variscides. These are the Ardennes, western Rhenish Massif (Aachen region to southern Hunsrück and Saarland subsurface), eastern Rhenish Massif (east of the Rhine), Harz Mountains (+ Flechtingen Horst), Thuringia/Franconia + Saxonian Vogtland, middle/eastern Saxony, Barrandian, Sudetes + Jested Mountains, Polish eastern Variscan Foreland (Holy Cross Mountains, Lublin Basin, and Kraków region), Moravia, and Vosges Mountains/Black Forest. Event recognition is difficult to impossible in strongly tectonized and metamorphosed massifs but also in some siliciclastic nearshore settings with strongly regional aspects of deposition. Wide event recognition through the Variscides and similar event facies suggest that the effects of intervening plate tectonic sutures and spatial terrain separation were too insignificant in the study interval to cause major barriers for marine faunas or different palaeoceanographic patterns. The high number of recognized events during the ca. 90 ma from the basal Devonian to top Viséan gives one sedimentary/evolutionary perturbation at every ca. 2.3 ma. This suggests that times of predominant greenhouse climate (except for the Devonian-Carboniferous boundary interval) were rather volatile periods of Earth history, with abiotic factors (especially volcanism and climate) leading to recurrent faunal overturns of different magnitude but also stimulating recoveries and evolutionary innovation.