Sandy fans - from Amazon to Hueneme and beyond

Most submarine fans are supplied with both sand and mud, but these become s egregated during transport, typically with the sand becoming concentrated i n channels and channel-termination lobes. New data from high-resolution sei smic reflection surveys and Deep Sea Drilling Project (DSDP)/Ocean Drilling Program (ODP) wells from a variety of fans allow a synthesis of the archit ecture of those submarine fans that have important sand deposits. By analyz ing architectural elements, we can better understand issues important for p etroleum geology, such as the reservoir properties of the sand bodies and t heir lateral continuity and vertical connectivity. Our analysis of fan arch itecture is based principally on the Amazon and Hueneme fans, generally per ceived to be classic examples of muddy and sandy systems, respectively. We recognize depositional elements, for example, channel deposits, levees, and lobes, from seismic reflection data and document sediment character in dif ferent elements from DSDP/ODP drill cores. We show the utility for petroleu m geology of evaluating sandy and muddy elements rather than characterizing entire fans as sand rich or mud rich. We suggest that fan classification s hould include evaluation of source-sediment volumes and grain size, as well as the probable processes of turbidity-current initiation, because these f actors control the character of fan elements and their response to changes in sea level, sediment supply, and autocyclic changes in channel pattern. B asin morphology, controlled by tectonics, influences overall geometry, as w ell as the balance between aggradation and progradation.