Progressive ventilation of the oceans; an explanation for the distribution of the lower Paleozoic black shales

Geochemical evidence for widespread euxinia in the Later Cambrian ocean

“…Additional oscillations observed in the later Cambrian marine δ 13 C record could reflect environmental perturbations similar to the SPICE. We suggest that anoxic water masses occurred widely in the subsurface of the later Cambrian ocean (i.e., below the wind-mixed surface layer), a view that finds qualitative support in the stratigraphic distribution of organic-rich, pyritic black shales, which peak in abundance in later Cambrian successions 24 . If correct, the high rates of biological turnover 25 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 11 …”

Devonian rise in atmospheric oxygen correlated to the radiations of terrestrial plants and large predatory fish

“…This is because only the deepwater oxic sink imposes a fractionation large enough to allow the δ 98 Mo sw to exceed the river input value by 1.3‰, as observed in the mid-Devonian and younger shales. Extensive black shale deposition (11,27) suggests that the euxinic sink remained substantial in Late Devonian seaways; nonetheless, Mo isotopes in these shales indicate persistent expansion of the deep-water oxic sink.…”

“…Several of these proxies (4,5,8,9) indicate an increase in oceanic O 2 during the Ediacaran Period (635 to 542 million years ago, Ma), roughly synchronous with the emergence of large, motile bilaterian animals and, therefore, suggestive of a physiological link between Ediacaran evolution and environmental change. Despite this, the distribution of organic-rich shales (10,11), the ratio of pyrite sulfur to organic carbon in shales (12), and modeling of the sulfur isotope record (13,14) all indicate that large tracts of subsurface ocean remained anoxic well into the early Phanerozoic Eon (the "age of visible animals," since 542 million years ago). Levels of ocean and atmospheric oxygenation, however, are unquantified from these proxies.…”

Organic geochemical characteristics of black shales across the Ordovician–Silurian boundary in the Holy Cross Mountains, central Poland

“…During the Ordovician-Silurian transition, there were considerable changes in the atmosphere, ocean, biosphere and, hence, in the general marine depositional conditions (Underwood et al, 1997) inextricably linked with the Late Ordovician (End Hirnantian) glacial event (Melchin et al, 2013;Sheehan, 2001). Glaciation events Mustafa, K.A., Sephton M.A., Spathopoulos, F., Watson, J.S., Krzywiec, P. Organic geochemical characteristics of black shales across the Ordovician-Silurian boundary in the Holy Cross Mountains, Central Poland, Marine andPetroleum Geology, doi:10.1016/j.marpetgeo.2015.08.018. 3 have major influence on the productivity and preservation of organic matter due to the changes in oceanic ventilation and circulation that cause oxygenation of the seawater (Berry and Wilde, 1978;Berry, 2010;Wilde, 1987). During the Ordovician-Silurian transitional period, there was a substantial change in organic matter distribution, production, and preservation on the East European Craton, particularly in Poland (Lesniewicz, 2012;Wieclaw et al, 2010).…”