| Summary: | Black shales, perhaps owing to their seemingly homogeneous nature, are mainly interpreted on the basis of their unusual geochemical characteristics. Their physical record is mostly neglected as a source of information. It has now been amply demonstrated, experimentally and analytically, that many black shales were deposited by physical processes comparable to those that shape coarser grained sediments, i.e. transport and deposition by currents may play a role as well. Black shales are not necessarily the product of sedimentation in quiet, stagnant water and, therefore, the a priori interpretation of such conditions is not valid. These lithologies are more varied than their generic name implies and, in addition to geochemical data, their physical record is an important source of independent information. Black shales are common sedimentary products during periods associated with supercontinent breakup, large-scale volcanic activity and high sea levels. Such periods are associated with greenhouse climates, enhanced nutrient supply to seawater, both a result of volcanism and its byproducts, and extensive shelves. Thus, the overall tendency of marine sediments, in particular in relatively shallow water settings, to become enriched in organic matter during specific periods in Earth’s history, may be ascribed to global forcing mechanisms. These periods are referred to as oceanic anoxic events—not implying, however, global ocean anoxia. It is often asserted that the deposition of black shales during oceanic anoxic events was global and synchronous. The geographical distribution of black shales shows this not to be the case. Storage of organic carbon in geographically definite areas of the seafloor has, nevertheless, led to perturbations in the global carbon cycle, which, in turn, have been recorded in sediments globally as excursions in the carbon isotope record irrespective of lithology. Black shale deposition was regionally favoured in basins with physiographies and hydrological regimes that promoted organic ...
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