AAPG Bulletin; June 2004; v. 88; no. 6;
p. 825-840; DOI: 10.1306/01260403104
© 2004 American Association of Petroleum Geologists (AAPG)
Depositional processes of uniform mud deposits (unifites), Hedberg Basin, northwest Gulf of Mexico: New perspectives
Efthymios K. Tripsanas1,
William R. Bryant2 and
Brett A. Phaneuf3
1 Texas A&M University, Department of Oceanography, College Station, Texas 77843-3146; thymios{at}ocean.tamu.edu
2 Texas A&M University, Department of Oceanography, College Station, Texas 77843-3146; wbryant{at}ocean.tamu.edu
3 Texas A&M University, Department of Oceanography, College Station, Texas 77843-3146
Efthymios Tripsanas is currently working as a postdoc at Bedford Institute of Oceanography in Dartmouth, Nova Scotia, with David Piper, Dave Mosher, and Kimberley Jenner. He is originally from Delphi, Greece, where he received his bachelor's degree in geology. He obtained his Ph.D. at Texas A&M University, College Station, Texas, with William Bryant. Efthymios has worked on sediment facies and slope instability associated with active salt tectonics on the Gulf of Mexico slope. His current research is focused on the understanding of sediment instability on the continental margin cast of Newfoundland, particularly Orphan basin.William Bryant is a professor of oceanography. He received an M.S. degree and a Ph.D. at the University of Chicago. He has spent the last 40 years at TAMU teaching and doing research in marine geology, high-resolution marine geophysics, and marine geotechnology. He was head of the Department of Oceanography from 1998 to 2000. He has worked in the Gulf of Mexico, Caribbean, west Africa, the Arctic and Antarctic, and sailed all five of the Russian polar seas. Author of more than 300 papers, co-editor of 1 book, and advisor of more than 100 M.S. and Ph.D. graduates. He was co-chief scientist on Deep-Sea Drilling Program Leg 10, and scientist on Leg 96 and Oil Drilling Program Legs 113 and 121.
Brett Phaneuf is a graduate student in the Department of Oceanography. His research focuses primarily on high-resolution applications to deep-sea imaging. Phaneuf works extensively with the U.S. Navy, particularly aboard the U.S. Nuclear Research Submarine, NR-1, and also has been working with the Deep-Tow Research Group at Texas A&M for eight years.
Structureless mud deposits (unifites) are a common depositional phenomenon in the intraslope basins of the continental slope of the northwest Gulf of Mexico. High-resolution acoustic data and long sediment cores from Hedberg Basin (middle slope) were used to provide a better insight into the origin of these enigmatic depositional units. The unifite, occurring in Hedberg Basin, is structureless under visual observations, but x-ray radiographs reveal that it consists of three divisions: (1) "U1 division," representing waning sequences of fine-grained (mud) turbidites, (2) "U2 division," characterized by faint, normally graded mud layers with occasionally wispy, silty interlaminae, and (3) "U3 division," characterized by a uniform appearance with no obvious sedimentological structures other than a faint banding of slightly siltier and slightly more clayey layers. High-resolution geophysical data reveal that there is no connection between intrabasinal sediment failures and the occurrence of unifites. We suggest that unifites have resulted from the deposition of a long-lasting (1.5–3 months), pulsating (showing internal surges), fine-grained turbidity current (dated at 28.6–29 ka) that originated from the flow transformation of a series of massive sediment failures on the shelf edge and/or upper continental slope. The fine-grained nature of the turbidity current is probably caused by the depositional segregation of the flow by depositing its coarsest material in intraslope basins in more proximal locations. We propose that the uniform texture of the unifite is attributed to the development of a stratification interface (lower stratified layer) generated by the continuous introduction of a turbulent sediment cloud in the intraslope basins. The lowest two unifite divisions are considered to develop prior to and during the development of the stratified layer.
Copyright © 2009 by American Association of Petroleum Geologists (AAPG)
