Ichnological evidence for bottom water oxygenation during organic rich layer deposition in the westernmost Mediterranean over the Last Glacial Cycle

Abstract

Organic rich layers (ORLs), deposited in the westernmost Mediterranean over the Last Glacial Cycle, have been studied integrating sedimentological and ichnological information from sediment records recovered at Ocean Drilling Program Leg 161 Sites 976 and 977. The conducted study has served to redefine the ORLs initially differentiated in sediment records from Sites 977 and 976, with seven new ORLs recognized, as well as extensions and subtraction of some parts in the ORLs previously defined. In addition, three different ORL types are distinguished according to sedimentological and ichnological features. Type 1 with intermediate thickness is highly bioturbated, mainly consisting of abundant Scolicia and Planolites, frequent Chondrites, and possible Thalassinoides in the base, which are interpreted as supporting dysoxic conditions during deposition. Type 2, corresponding to thicker intervals, shows alternance of highly to moderately bioturbated parts, revealing variable oxygen conditions —from moderate to extreme dysoxic or even suboxic. Type 3 consists of short, laminated intervals characterized by the absence of bioturbation, indicating anoxic or suboxic conditions and determining unfavourable macro benthic habitat. The amended ORLs show a correlation between the Sea Surface Temperatures and established climatic events over the Last Glacial Cycle in the Western Mediterranean.