Methane-derived carbonate cementation of Holocene marine sediments from Kattegat, Denmark

Abstract

Methane-derived carbonate cementation of Holocene marine sediments occurs at several location in Kattegart, Denmark. Generally, the carbonate-cemented sandstone occur at the seafloor as individual slabs or more widely distributed, thinly lithified pavements. Occasionally, the lithified sandstone take the form of large and spectacular, vertical pillar and mushroom-shaped bodies standing up from the seafloor. The carbonate cement consists of aragonite, high-Mg calcite and dolomite. The high-Mg calcite is the most widespread carbonate solid phase found. Aragonite is primarily associated with shell accumulations in the sediments. So far, dolomite has only been recorded as cement in the larger, vertical lithified sanstone bodies. The oxygen isotopic composition and the concentrations of minor elemens indicate that carbonate precipitation took place under relatively constant temperature and salinity conditions in normal marine pore fluids. However, the carbonates are remarkably depleted in 13C, i.e. in the range of −63 to −26% ° 13C and are therefore interpreted as being the result of methane oxidation by sulphate-reducing bacteria in the anaerobic diagenetic zone of the sediments