Diversity of Large-Scale, Deepwater Bed Forms in Mexico Offshore Areas: Neogene to Modern

Abstract

Large scale (>10-20m height, 1000m wavelength) bed forms are common in early Neogene to modern sediments of offshore areas in Mexico. Their occurrence was apparent in early reflection seismic surveys of the southern Gulf of Mexico, shot before law of the sea restricted global seismic acquisition. New reflection seismic data and multi-beam surveys in Mexico now document their widespread occurrence ranging from the Perdido Fold belt, Mexican Ridges, Campeche Salt Province and other areas. The bed forms are found in near surface sediments seaward of the modern shelf margin and in older strata also basinward of the paleo-shelf margin. These are particularly common in Miocene strata eastward of the Mexican Ridges but also in Quaternary to Pleistocene sediments of the Rio Grande Fan. Orientations of bed form crests vary considerably from north-south to east-west aligned, depending on location. Accretion sets that encompass the bed forms can be as thick as 30m and the overall stratal packages can exceed 150m. In some areas, there is a distinct association of these bed forms with submarine mounds that have clearly been modified from their original form. In other areas, distributive depositional axes are unaltered and maintain a distinct fan-like geometry. The diversity of bed form types and orientations implies a variety of genetic processes responsible, including ocean current bottom flow, contour currents, hyperpycnal flows, cyclic steps, and turbidity flow stripping. These processes are considered with regard to bed form architecture, orientation, and depositional and tectonic history of the area. Analogous reservoir potential of the bed form dominated successions may be significant, given the abundant traction type bedding, apparent on back-scatter images, which is often associated with a sand-size grain caliber. High amplitude seismic reflection response in many locations hints at alternating sand and shale. Entrapment of hydrocarbons in shallow strata may be challenging in some locations but in other areas, these bed form dominated Miocene intervals are buried below a thicker cover to provide appropriate top seal.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017