--> Geologic Evolution of Lower Magdalena Valley and the San Jacinto Fold Belt in its Southern Area and the Role of Romeral Fault System

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Geologic Evolution of Lower Magdalena Valley and the San Jacinto Fold Belt in its Southern Area and the Role of Romeral Fault System

Abstract

The Lower Magdalena Valley (LMV) and the adjacent San Jacinto Fold Belt (SJFB), have been considered as two distinct basins separated by the Romeral Fault System (RFS). This fault has been mapped from the Central Cordillera and extended to the North, along the beginning of the deformation of SJFB. However, few sub-surface imaging has been published in order to understand better this structural limit and its relation during the evolution of the northern part of Colombia from the Late Cretaceous to the Oligocene. During the last decade, the Colombia National Hydrocarbons Agency has acquired data wells that add considerable insight on these two important basins. In the Southern part of LMV and SJFB, there are two main stratigraphic packages: Upper Cretaceous – Paleocene and middle Eocene – Oligocene, separated by an early to middle Eocene unconformity. The pre-unconformity sequence includes the Cansona and San Cayetano formations, a very thick sequence deformed by thrust faults. Evidence of compression prior to the unconformity is shown in some areas, related to the accretion of the oceanic crust. The post-unconformity sequence includes the Chengue, Toluviejo, San Jacinto and Ciénaga de Oro formations. This sequence is comprised by several cycles that filled the basin progressively from Northwest to Southeast. The RFS was an active basin edge until early to middle Eocene times; afterwards, the topography was already created and the post-unconformity sequence was deposited with no major influence of the existing fault system. The limit of Oceanic and Continental Crust can be placed further to the East of the SJFB, at least in the area of El Cabano-1 well, as seismic images show that the Cretaceous – Paleocene sequence is still present below and strong reflectors are not the top of the Basement as was previously thought. U-Pb data from El Cabano-1 well, indicates that these reflectors seen below the Unconformity are Paleocene-Eocene in age, which agrees with the seismic correlation. These new data provide important information that shows that the RFS, acted during the formation of the LMV, and that the main activity took place before the Middle-Eocene. Recent tectonic deformation that caused the formation of the SJFB is not related to the activity of the RFS, but the result of the compression between the Caribe and South American deforming all the sequence, using the Cansona shales as a detachment zone.