39 research outputs found
The SPICE carbon isotope excursion in Siberia: A combined study of the upper Middle Cambrianlowermost Ordovician Kulyumbe River section, northwestern Siberian Platform
(Re)proposal of Three Cambrian Subsystems and Their Geochronology
The Cambrian is anomalous among geological systems as many reports divide it into three divisions of indeterminate rank. This use of âlowerâ, âmiddleâ, and âupperâ has been a convenient way to subdivide the Cambrian despite agreement it consists of four global series. Traditional divisions of the system into regional series (Lower, Middle, Upper) reflected local biotic developments not interprovincially correlatable with any precision. However, use of âlowerâ, âmiddleâ, and âupperâ is unsatisfactory. These adjectives lack standard definition, evoke the regional series, and are misused. Notably, there is an almost 50 year use of three Cambrian subsystems and a 1997 proposal to divide the Avalonian and global Cambrian into four series and three subsystems. The global series allow proposal of three formal subsystems: a ca. 32.6 Ma Lower Cambrian Subsystem (Terreneuvian and Series 2/proposed Lenaldanian Series), a ca. 9.8 Ma Middle, and a ca. 10 Ma Upper Cambrian Subsystem (=Furongian Series). Designations as âLower Cambrian Subsystemâ or âglobal Lower Cambrianâ distinguish the new units from such earlier units as âLower Cambrian Seriesâ and substitute for the de facto subsystem terms âlowerâ, âmiddleâ, and âupperâ. Cambrian subsystems are comparable to the Carboniferousâ Lower (Mississippian) and Upper (Pennsylvanian) Subsystems
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Atmosphere-ocean oxygen and productivity dynamics during early animal radiations
The proliferation of large, motile animals 540 to 520 Ma has been linked to both rising and declining O2 levels on Earth. To explore this conundrum, we reconstruct the global extent of seafloor oxygenation at approximately submillion-year resolution based on uranium isotope compositions of 187 marine carbonates samples from China, Siberia, and Morocco, and simulate O2 levels in the atmosphere and surface oceans using a mass balance model constrained by carbon, sulfur, and strontium isotopes in the same sedimentary successions. Our results point to a dynamically viable and highly variable state of atmosphereâocean oxygenation with 2 massive expansions of seafloor anoxia in the aftermath of a prolonged interval of declining atmospheric pO2 levels. Although animals began diversifying beforehand, there were relatively few new appearances during these dramatic fluctuations in seafloor oxygenation. When O2 levels again rose, it occurred in concert with predicted high rates of photosynthetic production, both of which may have fueled more energy to predators and their armored prey in the evolving marine ecosystem
The SPICE carbon isotope excursion in Siberia: a combined study of the upper Middle Cambrianâlowermost Ordovician Kulyumbe River section, northwestern Siberian Platform
Editorial note - Corrigendum
The following specimen/sample accession numbers and accompanying information are update