--> Abstract: Mud Volcanoes of the Louisiana Continental Slope, by T. W. Neurauter and H. H. Roberts; #90987 (1993).

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NEURAUTER, T. W., ARCO Oil and Gas Company, Houston, TX; and HARRY H. ROBERTS, Coastal Studies Institute, Louisiana State University, Baton Rouge, LA

ABSTRACT: Mud Volcanoes of the Louisiana Continental Slope

Remotely sensed acoustic data coupled with direct observation plus sampling using a highly mobile research submersible has provided new insight into the characteristics of both active and inactive mud volcanoes on Louisiana's continental slope. Two seismically similar structures in the Green Canyon (GC) Lease Area, Blocks 53 and 143, were the subject of this investigation. The cone-shaped inactive feature in GC53 is composed of fine-grained sediments, has no central crater, and has a diameter of (approx.) 30 m and relief of 400 m. Although now inactive, furrows on the southern flank of the cone indicate previous downslope sediment transport resulting in erosion. Ridges between furrows are partially lithified. Plate-like carbonate crusts cover the surfaces of these features. Furrow wal s expose alternating lithified and unlithified units suggesting alternating periods of sedimentation and exposure/lithification events. Mg-calcite and aragonite cements in the crusts are extremely C{13}-depleted indicating a link to hydrocarbons.

The active mud volcano in GC143 is also composed of fine-grained sediment, but has a very distinct central crater filled with fluid mud, and is (approx.) 400 m diameter and rises 35 m above the surrounding sea floor. No lithification has been observed in association with this feature. Observation of the GC143 mud volcano in 1989, 1991, and 1992 suggest continuous eruptions of thermogenic gas from the central crater, abundant crude oil in the fluid mud, distinct bacterial mats (Beggiatoa sp) on the crater floor, and impressive changes in mud level within the crater from one dive season to the next. Changes in mud level leaves concentric ridges and abrupt scarps around the crater perimeter. Both mud volcanoes occur at the intersection of several faults which can be traced on high resolu ion seismic data. These features force large volumes of fine-grained sediment and formation fluids onto the surface of the modern slope. Initial analyses of the microfossils carried by the fluid mud of the GC143 feature suggests a Pliocene age for the sediments. These two mud volcanoes are not unique, many similar features occur both in shallower and deeper parts of the slope.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.