EVIDENCE OF HOLOCENE COMPRESSION IN THE VALLE DEL CAUCA, ALONG THE WEST FOOTHILLS OF THE CENTRAL CORDILLERA OF COLOMBIA

In the west foothills of the Central Cordillera of Colombia, east of the town of Tuluá, a series of north-south trending scarps affecting the surface of Quaternary alluvial deposits and a large number and variety of drainage anomalies attest to the recent activity of imbricated north-striking thrust faults that emerge along bedding planes of Miocene units. Some of these faults eventually cut across uncorformably-overlying Quaternary alluviums and overthrust some paleosoils. At the north Tuluá motorway exchanger, these paleosoils have been particularly dated at 12,840 ± 40 and 17,800 ± 660 ka BP; in another scarp sothwest of this place, there are paleosoils in a coluvial wedge with ages of 22.000 ± 160, 21.000 ±140, 17.000 ± 130 and 7.460 ± 330 Ka BP.

West-facing flexural scarps in association with blind thrusting (produced by fault propagation folding), north-south elongated pressure ridges bounded by antithetic and synthetic reverse faults and some anticline emergences in the recent alluvial deposits are clear evidence of the primary west vergence of the fold-thrust belt of these Central Cordillera foothills whose youngest activity used to be thought as Tertiary in age.

Deflections and interruptions of (1) the NNE trend of the Tertiary units by the ENE right-lateral strike-slip system, (2) the trend of the reverse faults, (3) the axial trend of some anticlines, and their spatial configuration suggest that shortening in the western foothills of the Central Cordillera is mechanically and kinematically connected with the ENE RLSS system, at least in this section of the Valle del Cauca.

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Proyect: “Paleseismic Invetigations in the Valle del Cauca – Toward the Seismicity Model in the SouthWest of Colombia” developed by Seismologic Observatory of Southwest Colombia -OSSO- Valle University and EAFIT University with the cooperation of COLCIENCIAS and CORPORACION OSSO.