SS: Multibeam Backscatter - Insights into Marine Geological Processes and Hydrocarbon Seepage

Abstract

Abstract By combining multibeam bathymetry and backscatter with accurately placed piston cores, and integrating these data with 2D multi-channel seismic and high-resolution sub-bottom profiling, we can gain a better understanding of the processes active in a marine basin. In addition on mass transport complexes, basin floor fans, slumps, and faults, we can identify and sample potential hydrocarbon seeps that provide direct samples of a petroleum system. This paper will examine features imaged during a large (400,000 sq. km.) survey carried out in Indonesia in 2006-2008. Using hull-mounted systems, an average 1000 sq. km. of high resolution (25m bathymetric bin, 5m backscatter pixel) data were acquired per day in water depths from 100 to 3500m. Piston cores accurately placed on seafloor targets using USBL navigation were described visually on the coring vessel, sub-sampled for geochemical analyses, with the remainder of the core preserved for later analysis. Approximately 35% of the cores have been CT scanned, highlighting density differences related to seepage (such as authigenic carbonate and shell fragments), or related to sedimentological features (where higher density sand grains can be distinguished from lower density mud). The cores, and the targets they analyzed, provide a catalog of anomalous backscatter features that have been ground-truthed to constrain the processes that created the features. Features such as basin floor fans, overbank deposits, upslope climbing mud-rich mega-dunes, sand-rich channel axes, drowned carbonate reefs, mud volcanoes, and chemosynthetic seeps have been sampled throughout the program. This catalog demonstrates that backscatter can be calibrated by cores to specific processes, and thus that multibeam backscatter is a robust tool for constraining geologic processes active in a basin including present-day sediment distribution on the seafloor. Piston cores accurately placed on zones of potential hydrocarbon seepage interpreted based on multibeam backscatter can significantly impact exploration. Specifically, the presence of oil and gas in a basin, and the composition of the hydrocarbons, can dramatically reduce the exploration risk by providing information on source, migration, and maturity. Introduction Human beings have been gathering information about the seafloor since they first took to boats. Until the development of acoustic techniques, soundings were taken by lowering a weight to the seafloor (lead line), and marking the length. Acoustic techniques involving a " ping?? of energy sent out, and then received, by a transducer, only became commonplace after World War II (for an excellent discussion on the evolution of seafloor mapping, see Mayer, 2006). The next big leap in seafloor mapping capabilities came in the 1960s.