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Cenozoic Tectonostratigraphy of the Northern San Jacinto Foldbelt, Northwestern Colombia

Mora, Alejandro1; De Freitas, Mario G.; and Velez, Vickye
1[email protected]

The integrated analysis of seismic, well log and outcrop data from the Cenozoic section of the northern San Jacinto Foldbelt (SJFB) in NW Colombia, revealed a complex tectonic evolution from Paleogene extension to Neogene compression and inversion. Interpretation of the first 3D-seismic survey in the SJFB allowed the best imaging and most detailed mapping to date of the pre-Oligocene structure and potential reservoirs. This was complemented by the interpretation of new 2D-seismic in the northernmost portion of the SJFB. Paleocene to Miocene units contain both potential source rocks and main reservoirs, though Cretaceous source rocks may also be active in the area.

Six main second-order sequences of Late Paleocene to Pliocene age were identified in the northern SJFB. The San Cayetano sequence (Late Paleocene-Middle Eocene) was deposited in marine environments and lies unconformably on top of the Cretaceous. In the Middle to Late Eocene, conglomerates and limestones of the Chengue Group were unconformably deposited on top of San Cayetano. 3D-seismic data shows that the Chengue Group was deposited in an extensional fault-controlled regime, as evidenced by planar domino-faulting. After Latest Eocene-Early Oligocene erosion, fine-grained deposits of the Late Oligocene Ciénaga de Oro Sequence onlap the pre-existing paleo-topography, as the area continues subsiding due to sagging. In Early Miocene times, the first compressive event caused initial inversion of pre-existing extensional structures. While pre-Oligocene extensional structures are well preserved in the area of the 3D, inversion is much more intense towards the north, where the pre-Oligocene sequences are affected by more recent WNW-verging thrust faults. The syn-inversion marine, fine-grained Porquero sequences of Middle-Late Miocene age, evidence intense inversion of structures such as the Cibarco Anticline, as they thin and onlap its eastern flank. In the Late Miocene, extensional faulting commonly detaching in Ciénaga de Oro mudstones, affected the Porquero Sequences possibly due to gravitational sliding caused by uplift in other areas. Therefore, the Ciénaga de Oro marks the boundary between two contrasting extensional structural styles. A notorious angular unconformity marks the base of the Tubará Sequence, a Latest Miocene - Pliocene succession of fluvial to shallow marine deposits, that evidences strong inversion pulses which started to shape the present-day topography of the northern SJFB.

 

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013