Do Upper Wilcox Incised Valleys Support Paleogene GOM Isolation?
Imagine Resources, LLC, Corpus Christi, Texas 78401
Four deeply incised valleys (Meyersville, Anna Barre, Hope, and Jennie Bell) of two different Upper Wilcox ages are identified in the onshore mid-Texas Gulf Coast. These shelf valleys have maximum incision depths of 338 m, 201 m, 241 m, and 101 m, respectively. Three of these depths are significantly greater (2–3X) than valleys along the GOM and US Atlantic shelf incised during the last glacial maximum (LGM) of 120 m. These LGM incised valleys range in depth from 20–60 m, except for the Mississippi river which was subjected to glacial mega floods. Recently published Paleogene sea level curves indicate that fluctuations may be driven by glacial/eustatic change; however, none of these is greater than 20–30m. Possible causes of deeply incised Wilcox valleys are: 1) dramatic sea level lowering greater than the LGM (GOM isolation from world ocean); 2) increased discharge or confluence scouring (scale problem); and 3) shelf incised submarine canyons (possible time frame problem; unsupported by valley fill facies). Tectonic separation of the GOM from the world ocean by the Cuban plate, and resultant lowering of GOM sea levels below world ocean levels during Wilcox time have been proposed (Hhypersaline drawdown vs. low salinity hyperpycnite models). The Upper Wilcox incised valley depths support lowered GOM sea levels. Valley fill facies (bayhead deltas, fluvial systems, and barrier/shoreface) do not support shelf incision by submarine canyons. The GOM isolation theory is testable, by searching for other deep circum-Gulf incised valleys of Eocene age.
AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012