AN INTRODUCTION TO GEOSPHERE-BIOSPHERE COUPLING; COLD SEEP RELATED CARBONATE AND MOUND FORMATION AND ECOLOGY

Abstract

A special session ‘Geosphere^biosphere coupling; cold seep related carbonate and mound formation and ecology’ was held at the AGU Fall conference in December 2000, and attracted considerable attention. A total of 17 oral presentations were given and some 30 posters were presented. This session followed up on discussions which have taken place in the scienti¢c community over the past few years, regarding the role and importance of hydrocarbon seepage and hydrate dissociation in the formation of recently discovered, spectacular modern carbonate and mud mounds along the continental margins of the America, Africa, Asia and Europe. These buildups provide an outstanding opportunity to study the processes involved in their formation and provide a challenge in attempting to better understand the coupling between the deep geosphere and the biosphere. Carbonate mounds were prominent reef types during Earth history since Cambrian times and these mounds may form giant host rocks for hydrocarbon accumulation. Carbonate mounds from the geological record provide ample evidence of microbial mediation in mound build-up and stabilisation. Some also suggest an initial control by £uid venting. Advanced models for some Palaeozoic mounds argue for the prominent role which bio¢lms may have played at the interface between the £uid and mineral phases. While up to the early 1990s there was little evidence of mudmound formation from Late Cretaceous times onwards, recent investigations have increasingly reported occurrences of large mound clusters on modern ocean margins, in particular in basins rich in hydrocarbons. We should realise that mound provinces are signi¢cant ocean margin systems, up to now largely overlooked. How do such recent mound provinces relate to the fossil examples, what was and is the role and impact of £uid venting on the genesis of large mounds, and do the modern mound provinces provide a new window on the microbiota that were instrumental in building giant mounds throughout Phanerozoic times? These are burning questions, and the answers will only come through a new and continuous dialogue between experts of the past, explorers of the recent ocean, biologists and microbiologists.