The Environment of Deposition of Black Shales in the Early Cretaceous an Ongoing Controversy

摘要: During thelast 12 years of the Deep Sea Drilling Project numerous Early Cretaceous black shale horizons have been discovered in all themajor ocean basins Similar organic carbon rich sediments had described earlier from various land outcrops Alps Carribbean region and southern Andes New refined methods sedimen tology geochemistry geophysics applied analysis these which can be classified into four regional groups a central North Atlantic b northern c South Indian Oceans d Pacific Ocean The shales Barremian Albian age Tethys were deposited deep basinal environment under low oxygen or anoxic conditions average content matter theoften laminated is 2070 Terrigenous dominates spectrum western while marine derived material theeastern on passive continental margin depth few hundred to thousand meters are parts turbiditic sequences terrigenous origin These deposits not necessarily connected with Aptian restricted weredeposited waterdepth has mixed rare occurrences submarine rises finding major oceans encouraged authors construct models explaining as result global oceanic events Detailed geochemical sedimentological investigations revealed shortcomings theearly scenarios series alternative spatially wereproposed Models formation pelagic environments such theTethys emphasize importance paleotectonic paleoceanographic situation controlling facies patterns Anoxic bottom water established during periods stratified watermasses underline if conti nental climate input rate terrestrial In future integrate exciting problem possible feedback mechanisms between paleo paleoceanography solved