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Tectonic Controls on the Spatial and Temporal Migration of Depocenters in Forearc Basins: A Comparison of Modern and Ancient Caribbean Examples

Bernal-Olaya, Rocio D.*1; Mann, Paul 2; Escalona, Alejandro 3
(1) Jackson School of Geosciences, University of Texas at Austin, Austin, TX.
(2) Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX.
(3) Department of Petroleum Engineering, University of Stavanger, Stavanger, Norway.

Forearc basins form behind a submarine or emergent forearc high built by the accumulation of accreted sedimentary or igneous rocks on the overriding plate. Knowledge of the migration patterns of forearc depocenters is important for understanding their tectonic controls, subsidence and thermal maturation history for petroleum exploration. We use ~3000 km of regional seismic reflection lines tied to 3 wells showing the actively forming Eocene to recent, forearc basins formed in the South Caribbean deformed belt (SCDB), between the partially submerged Great Arc of the Caribbean and a submerged forearc high in the offshore area of northern Venezuela to illustrate a landward depocenter migration. In this area and many other well-studied forearc basins, common features are noted: 1) uplift and landward rotation of the forearc high creates an asymmetrical forearc basin, deeper adjacent to the forearc high; 2) as more sedimentary and igneous rocks are accreted in front of or beneath the prism, the forearc high is progressively uplifted and rotated in the landward direction; 3) the rotation and uplift of the forearc high results in a onlap surface separating accreted rocks below from onlapping forearc rocks above; and 4) low sediment supply and/or gaps in the barrier of the forearc high have led to an underfilled forearc basin along SCDB. We contrast the characteristics of the little deformed SCDB with the complexly deformed and overfilled Lower Magdalena forearc basin (LMB) onland area of Colombia. In this example, we see the opposite migration of depocenters seen in the SCDB case. In LMB, we use 5000 km of seismic reflection data tied to 13 wells to define three depocenters of shallow marine to continental rocks ranging in thickness from 650 to 2000 m. In the Oligocene, the main depocenter is located to the southeast; by late Miocene time, it has migrated 110 km to the northeast. In cross section, onlap of late Oligocene, forearc basin sediments shows that the forearc high formed at this time and progressively migrated seaward though time. Our possible explanation for this direction of migration in LMB is that the great thickness of continentally-derived sediments delivered by the Magdalena River, which is presently the ninth largest river in the Caribbean, was sufficient to depress the forearc basin and shift the depocenter in the seaward direction. Eventually the basin was filled with the delta of the Magdalena River now overspilling the forearc high.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California