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Contourite Terraces: Sedimentary and Conceptual Implications

Abstract

Over the last few decades, bathymetric data and multichannel 2D and 3D seismic reflection profiles have revealed that features generated by bottom currents are ubiquitous on continental margins. They are characterized by large erosive (moats, channels), depositional (drifts) and mixed (terraces) contourite features. Contourite terraces have been described at varying water depths along the continental slope and rise. They are sub-horizontal, morphologic elements identified both on the present sea-floor and in the sedimentary record, which have developed over geological time in fluctuating constructional and erosive phases. Their location can be correlated with the main interfaces of regional water masses, conditioning a remarkable change in the morphological profile of continental slopes, different to that defined in the conceptual models for passive continental margins. The present work has three main objectives: (1) to summarise the main depositional and erosive elements associated with bottom-currents on buried contourite terraces on the Uruguayan, Brazilian, Gulf of Mexico, Canadian and Northern European margins; (2) to evaluate their roles in determining the morphology and sedimentary stacking pattern; and (3) to propose some implications on hydrocarbon exploration. Deep-water sands have come a long way. Usually, deep-water sand deposits are interpreted as a product of submarine gravity flows, whose facies model is derived primarily from the ancient record. While most of contourite features are mud-rich, extensive sand-rich deposits have been observed, predominantly in higher velocity bottom currents settings. Deep-water sandy deposits generated or reworked by bottom currents are still poorly understood, but new perspectives should be studied and evaluated. These deposits are of great scientific significance and might represent potential hydrocarbon reservoirs, thereby being of potential interest to petroleum explorers.