Sequence Stratigraphy of the Alaminos Fan (Upper Miocene-Pleistocene), Northwestern Deep Gulf of Mexico

Morton, C.H. and Paul Weimer, Energy and Minerals Applied Research Center, Department of Geological Sciences, University of Colorado, Boulder, CO 80309-0399

Abstract

The Alaminos fan (uppermost Miocene to lower Pleistocene) is a moderate sized, mud-dominated submarine fan in the northwestern deep Gulf of Mexico. Located in the southern portion of the Alaminos protraction area, the fan is bounded to the north by the salt tongues of the Sigsbee Escarpment and overlies and extends southeast of the northern portion of the Perdido fold belt.

Interpretation of 1500 km of 2D multifold seismic data has defined four depositional sequences, each consisting of channel-fill, levee/overbank, and areas of mass transport complex (MTCes) and/or localized slides. Channel-fill deposits are characterized by high-amplitude subparallel reflections having poor to good continuity. Levee/overbank deposits are characterized by low-moderate amplitude, parallel to subparallel reflections with good continuity. MTCes and/or slides are characterized by a series of hummocky to chaotic reflections with variable amplitude and poor continuity.

Channels in the two oldest sequences have been derived from the lower slope east of the modern Alaminos Submarine Canyon. Channels in the two youngest sequences have been derived derived from the Alaminos Submarine Canyon, and extend across the "Baha" fold of the Perdidio Foldbelt, to the unconfined setting to the southeast. All channels have a low to relatively high degree of sinuosity, from 0 to 5.5 km lateral migration, and widths of up to 1.5 km. MTCes and/or localized slides exhibit varying degrees of geometry as well. Two sequences have MTC's having an elongated distribution, mimicked by overlying channels, whereas one MTC is areally widespread. Localized slides exhibit varying degrees of width and length but are not as areally e xtensive as the MTCes.

Typical evolution of an Alaminos fan sequence consists of an erosional base, which is overlain by a MTC. This, in turn, is overlain by a relatively thin zone of distributary channels (high amplitude reflections) that is areally widepread (16 km wide). This zone evolves upward into one main aggradational channel that has low to high sinosity, shows lateral migration, and bifurcates downfan.

Sediments deposited in the Alaminos fan are tentatively interpreted as being sourced from deltas derived from Texas and the Mississippi Delta during the latest Miocene to early Pleistocene (about 6.6 to 1.9 Ma).