FACIES DISLOCATION ON TOP OF THE CRETACEOUS SEQUENCE OF THE NEIVA SUB-BASIN, UPPER MAGDALENA VALLEY, IMPLICATIONS IN THE SEQUENTIAL STRATIGRAPHIC MODEL OF COLOMBIA

The identification of an abrupt facies change between the Monserrate and San Francisco formations allows us to identify a Facies Dislocation on top of the Cretaceous marine sequence of the Neiva sub-basin, due to the uplift of the Central Cordillera and the accretion of tectonic blocks, west of the Romeral Fault Zone. With an integrated detailed stratigraphic analysis in surface sections and wells, marine environments were identified for the Monserrate Formations, ranging from near offshore to middle shoreface. For the San Francisco Formation, continental environments were identified, ranging from coastal to fluvial plain, swamps and paleosoils. The lack of all the regression of facies, from deep marine environments to the continental realm is the principal evidence of the paraconformity between those units, implying that sediments from proximal environments were eroded or bypassed. This surface and their correlative surfaces have to be interpreted as the boundary of the marine sequence of the Cretaceous of Colombia in this area, and gives an evidence of the first pre-Andean uplift.