Pore-water in marine sediments associated to gas hydrate dissociation offshore Lebu, Chile

Abstract

Abstract. Gas hydrate occurrences along the Chilean margin has been documented, but the processes associated to fluid escapes originated by gas hydrate dissociation yet are unknown. Here, we report morphologies growing related to fluid migration in the continental shelf offshore western Lebu (37 °S) by analysing mainly geochemical features. In this study oxygen and deuterium stable water isotopes in pore water were measured. Knowledge was completed by analysing bathymetric data, biological and sedimentological data. From bathymetric interpretation a positive relief at 127 m below sea level was recognised; it is oriented N55 °E and characterised by five peaks. Moreover, enrichment values for δ18O (from 0.0 to 1.8 ‰) and δD (from 0.0 to 5.6 ‰) were obtained. These are typical values related to hydrate melting during coring and post-sampling. The evident orientation of positive relief could be associated with faults and fractures reported by others authors, in which these structures constitute pathways for fluid migration from deep to shallow zones. Finally, benthic foraminifera observed in the core sample can be associated to seep areas. On the basis of theoretical modelling, we conclude that the positive relief correspond to mud growing processes related to gas hydrates dissociation and represent a key area to investigate fluid migration processes.