| Abstract: | The Mississippi Trough is divided into two structural and sedimentary provinces: a) the trough axis, b) the trough walls. Interpretation of high-resolution seismic profiling reveals that the trough axis sedimentary reflectors are a combination of chaotic seismic facies, merging laterally into ponded and onlapping fill seismic facies. Acoustically chaotic facies were deposited by low velocity, sediment gravity flows. The chaotic, onlapping, and ponded seismic facies are buried under thick accumulations of recent silts and clays. Sea floor sediments along the trough axis are intensely disturbed by creep and small diapiric intrusions. Trough wall sediments buried a large erosional escarpment and have moved downslope by slump and creep failure. Piston coring along the trough axis recovered olive-grey, silty-clay muds considered to be hemipelagic clays. Abundant terrigenous mineral grains and displaced microfauna in each core suggest considerable sediment transport via low-velocity gravity flows during the late Quaternary. Consolidation tests indicate that Mississippi Trough sediments are very close to a normal consolidation state. Slight overconsolidation may have resulted from dewatering in sediments disturbed by mass failures.. |
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