William R. Bryant¹, Tim Dellapenna², Armand Silva³, Dan Bean², Wayne Dunlap²
(1) Texas A&M University, College Station, TX
(2) Texas A&M University
(3) University of Rhode Island

Abstract: Mega-Furrows on the Continental Rise South of the Sigsbee Escarpment, Northwest Gulf of Mexico

While conducting a deep-tow survey, which consisted of a 3.5 kHz subbottom profiler and a 100 kHz side-scan-sonar, of the northern Gulf of Mexico continental slope and rise around Bryant Canyon in the spring of 1999 it was observed that a series of longitudinal mega-bed-forms were found in ~3000 m of water along strike at the base of the Sigsbee Escarpment. The mega-bedforms surveyed included a field of sedimentary furrows ~10 m deep and ~30 m wide, spaced ~100 m apart in a field 10-25 km wide south of the escarpment. Sedimentary furrows are longitudinal bed-forms which occur in fine-grained sediment, and have been observed in a wide variety of settings. The existence of furrows in deep sea settings suggest that bottom currents exist in the range of 1 to 100 cm/sec and higher and are inferred to be formed due to helical secondary circulation. Sedimentary furrows were first produced in the lab by Allen (1969). Allen found a hierarchy of bed-forms ranging from uniform furrows at low flow conditions, to meandering furrows and flute casts, at the highest flow conditions he found sheet flow. All the conditions described by Allen are present in the area due south of Bryant Canyon on the continental rise. The significance of these features is the high water velocities necessary for their formation and the large amount of erosion occurring at the base of the Sigsbee Escarpment. Indication are that the erosional process are active at the present time and may impact on seafloor structures.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana