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High-Resolution Multibeam Backscatter Reveals Dramatic Basin-Floor Fans of Varying Character in the Deep Water Mexican Gulf of Mexico


High-resolution multibeam data acquired in 100% of the Mexican Gulf of Mexico (MGOM) deeper than 750m water depth as part of the TGS “Gigante” multi-client program (total area surveyed = 477,000 km2) reveal strikingly different basin floor fan geometries. Some fans show subtle positive relief, whereas others show no bathymetric relief (bathymetric data binned at 15m independent of water depth). Although the fans would be difficult to identify in bathymetric data alone, the backscatter shows exceptional detail that can be tied to sedimentary processes (backscatter data mosaicked at 5m independent of water depth). Sub-bottom profiler (SBP) data acquired on all multibeam lines provide depth information for the fans in the sub-surface (including buried fans; approximate depth of SBP penetration ~50m), and USBL positioned piston cores provide ground truth material from identified features. East of the Mexican Perdido fold belt we identify at least 3 generations of the Rio Grande fan. The fan emanates from a canyon ~50km SE of the previously identified fan termination. The fan then extends an additional ~230 km SSE across the lower slope basin floor to the seaward-most lobe identified on backscatter. The total distance from the mouth of the present-day Rio Grande River to the most distal mapped lobe is 480km. Two younger progressively backstepping fans are visible in the backscatter and SBP data. On the uppermost fan, the largest axial channel is up to a kilometer wide and 20 to 40m deep. Sands from Jumbo Piston Cores are moderately well sorted, fine grained, quartzose with potassium feldspar, plagioclase, and granitic rock fragments. Multiple basin floor fans have been imaged north of the Yucatan Peninsula in the central to eastern MGOM. These fans appear to have been deposited by west moving currents. They have a distinctive dendritic pattern, with abrupt change from the high backscatter fan to low backscatter beyond the fan terminus. SBP data indicate that the dendritic backscatter pattern may be related to the base-of-fan channeling ~14m below the seafloor. In the NE MGOM, the likely distal extent of the Mississippi delta has been imaged with multibeam backscatter as a southerly radiating distributary channel network.