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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

500-Kilometer-Long Extension of the Trans-Andean Mega-Regional Seismic Transect Across the Colombian Basin and Implications for Deepwater Hydrocarbon Exploration

Carlos A. Vargas-Jimenez1; Paul Mann2

(1) Department of Geosciences, National University, Bogota, Colomba, Bogota, Colombia, Colombia.

(2) Institute for Geophysics, University of Texas at Austin, Austin, TX.

The Colombian basin beneath the western Caribbean Sea is a vast, unexplored deepwater province with water depths ranging from 4000 m in the central area to depths of 2800 m in the neighboring area of the southern Nicaraguan Rise north of the Hess escarpment and in elevated areas of the South Caribbean deformed belt (SCDB). Acquisition by ANH in 2009 of a 500-km-long seaward extension of the existing 378-km-long, onland Transandean seismic line reveals salient features of the basin including: 1) subduction of late Cretaceous oceanic plateau crust of the CB beneath the SCDB of northern Colombia; 2) subduction-accretion of the Miocene to recent section of the downgoing plate into the SCBD accretionary wedge with subduction of the deeper, pre-Miocene sedimentary rocks and plateau basement; 3) irregular, top basement surface of the late Cretaceous oceanic plateau including seamounts and other relict, volcanic features; 4) late Cretaceous-earliest biogenic, pelagic deposition with thicker deposition of <500 m on oceanic plateau basement highs; 5) overlying terrigenous, basin-filling, deepmarine sedimentary rocks during the period of Eocene through Miocene time reflecting the onset of submarine fan systems in Central and South America; and 6) Late Miocene to recent deposition is controlled by better organized and more voluminous fan systems including the Magdalena and Costa Rica related to topographic elevation and erosion of the northern Andes and Central America. The seismic transect is tied to site 999 of ODP Leg 165 which penetrated a 1066-m-thick continuous and apparently complete upper Maestrichtian-Pleistocene sedimentary section. Previous detailed examination of the δ13C record from site 999 revealed the presence of the well known intervals of high δ13C values between the late early to middle Miocene (~17 and 13.5 Ma), supportive of the so-called Monterey global cooling event characterized by unusually high accumulations of organic matter documented in the Pacific, Atlantic, and Mediterranean. This organic-rich section may serve as a source especially in deeply buried areas of the CB overlain by sand-rich Miocene and younger submarine fans including the Magdalena and Costa Rica. Additional source rocks in the deep CB may include late Cretaceous, pelagic deposits overlying basalt basement that may reflect an oceanic anoxic event linked to the eruption of the late Cretaceous Caribbean mantle plume and oceanic plateau in the late Cretaceous.