Visualizing Seafloor, Seismic, Gravity and Magnetics Data in the Deepwater Gulf of Mexico Improves Understanding of Geohazards, Salt and Seeps

Abstract

Abstract The seafloor of the deepwater Gulf of Mexico represents the composite effects of a wide range of driving forces that include salt, basement faults, fluid and gas migration, depositional lobes and erosional channels. To improve our understanding of the processes that control the seafloor we combine exploration geophysics, remote sensing, and data more commonly associated with site surveys. Multi-channel seismic data (both 2D and 3D) can provide 'big picture' constraints on through-going structures and long-lived depositional/erosional environments. Gravity data, which can be improved by better topographic corrections using seafloor bathymetry, can be used to evaluate the distribution and style of salt migration and basinal features. Magnetics data, in turn, can be used to define the location and orientation of basement lineations and structures. High resolution comprehensive maps of the seafloor provide an accurate geologic 'snapshot', which can be used to evaluate the relative contributions of the various driving mechanisms. In this paper we will present data from the Alaminos Canyon region of the deepwater Gulf of Mexico (Figure 1) that demonstrates the value of this integrated approach. Features that will be illustrated include slope basins where we can interpret the direction of salt withdrawal and movement, amalgamated salt keels created by converging salt tongues, as well as salt extrusion 'bulges' and diapirs. We will show a correlation of seafloor exposed high angle tear faults within the allochthonous section and autocthonous basement lineations, and we will use the character of the tear faults to demonstrate their sense of motion. We will illustrate seep targets and pock marks, and show canyons and slope failures driven by both external (downcutting) and internal (seepage induced) mechanisms. Our objective in this presentation is to demonstrate that an integrated approach to seafloor and subseafloor geology can improve exploration targets and better define geohazards. Working Definition of Geohazards: Any feature or process that could harm, endanger, or affect seafloor facilities, risers, anchors, etc. Facilities can either be designed to avoid or withstand geohazards. Data Details: Gravity and magnetic data were acquired as a part of the same marine survey that collected the high resolution multibeam imagery of the seafloor. Multibeam data consisted of 30kHz Simrad EM-300 data acquired by C+C Technologies (1x2 degree beam geometry; 135 beams, 150 degree maximum sector; Kleiner et al., 1999). The gravity and magnetics data were collected by Fugro-LCT using a ZLS La Coste and Romberg marine gravimeter and GEM Systems Overhauser magnetometer (Kleiner et al., 1999). Line spacing for gravity and magnetic data were 1.9 km for east-west lines and 10.8 km for north-south lines. The resultant Free Air gravity and Total Field Magnetic data provide valuable information on basement fabric and salt dynamics. In addition to the gravity, magnetics, and multibeam data we utilize published multi-channel seismic data for integrating the sub-surface with the seafloor. 3D Data Visualization of "Earth Volumes" One of the challenges facing the earth scientist is the profusion of spatial data sets (data overload) of varying scales, vintages, and qualities. Furthermore, data can come from very different systems (e.g.: gravity, seafloor mapping, and seismic).