ABSTRACT: Yarbuh and Contreras

Usama Yarbuh L. and Juan Contreras
Centro de Investigacion Cientifica y de Ensenada, Baja California (CICESE), Ensenada, B.C., Mexico

The Interplay between Deformation, Erosion, and Sedimentation in the Deepwater Mexican Ridges Fold Belt, Western Gulf of Mexico Basin

Oral Presentation: Mexico Exploration and Opportunities (GRBCC, Ballroom C)
Monday, September 21, 2015, 3:20 pm
Poster Presentation: Mexico and Caribbean Plays (Third Floor Exhibit Hall)
Sunday, September 20, 2015, 6:00 pm until Tuesday, September 22, 2015, Noon

In this study we constructed excess-area diagrams for each of the folds comprising the Mexican Ridges Fold Belt (MRFB).  From them, we estimated the degradation of the seafloor deformed by folding.  By assuming denudation is in steady state, we were able to differentiate sediments derived locally from sediments transported from distant sources.  From the chronostratigraphy of the growth strata, we derived rates of tectonic and superficial mass transport and illustrated how they changed spatially across the fold belt.  We estimated that the constant of mass diffusivity, which controls the rate of degradation, has a mean value of 0.27 m2/yr.  This value is characteristic of rapid, episodic superficial mass movements.  Finally, the combined supply of both local and distal sediment is ~0.2 mm/yr.  However, the structures proximal to the continental shelf are being degraded more intensely than those in the distal part of the fold belt.  By contrast, sedimentation in the east section of the fold belt outweighs tectonic uplift.  Our results show that the response of sedimentation to folding is not instantaneous.  Our analysis indicates that stacking geometries underestimate the beginning of deformation by as much as ~3 Myr.  Moreover, we found that deformation started synchronously during the Late Miocene throughout the MRFB, and not in two episodes as stacking relations suggest.  Both phenomena can be understood in terms of a delay in the sedimentary response to tectonic forcing.  Additionally, the discrepancy in the onset of folding across the MRFB is due to the copious sedimentation and low degradation rate in the eastern section of the fold belt; which further hindered the development of onlap and thinning upward patterns, commonly signaling the beginning of fold growth.  This delay, in turn, led to erroneous interpretations regarding correlation of growth strata and the timing of fold development.