ALBERT

Description: Sedimentological, provenance, and detrital thermochronological results for basin fill at the modern deformation front of the northern Andes (6°N latitude) provide a long-term, Eocene to Pliocene record of foreland-basin sedimentation along the Eastern Cordillera–Llanos basin boundary in Colombia. Lithofacies assemblages and paleocurrent orientations in the upward-coarsening, ~5-km-thick succession of the Nunchía syncline reveal a systematic shift from craton-derived, shallow-marine distal foreland (back-bulge) accumulation in the Mirador Formation, to orogen-sourced, deltaic, and coastal-influenced sedimentation of the distal to medial foreland (foredeep) in the Carbonera and León Formations, to anastomosing fluvial and distributive braided fluvial megafan systems of the proximal foreland (foredeep to wedge-top) basin in the lower and upper Guayabo Formation. These changes in depositional processes and sediment dispersal are supported by up-section variations in detrital zircon U-Pb and (U-Th)/He ages that record exhumation of evolving, compartmentalized sediment source areas in the Eastern Cordillera. The data are interpreted in terms of a progressive eastward advance in fold-and-thrust deformation, with late Eocene–Oligocene deformation in the axial zone of the Eastern Cordillera along the western edge of Floresta basin (Soapaga thrust), early Miocene reactivation (inversion) of the eastern margin of the Mesozoic rift system (Pajarito and Guaicaramo thrusts), and middle–late Miocene propagation of a footwall shortcut fault (Yopal thrust) that created the Nunchía syncline in a wedge-top (piggyback) setting of the eastern foothills along the transition from the Eastern Cordillera to Llanos foreland basin. Collectively, the data presented here for the frontal Eastern Cordillera define a general in-sequence pattern of eastward-advancing fold-and-thrust deformation during Cenozoic east-west shortening in the Colombian Andes.

Description: Low-temperature thermochronometry and crosscutting relationships identified in newly released reflection seismic data reveal a previously unrecognized zone of early Andean shortening in Colombia. Apatite fission-track data and thermal modeling help define a 60–50 Ma onset of rapid exhumation along the present boundary between the Magdalena Valley hinterland basin and Eastern Cordillera thrust belt. Subsurface angular unconformities localized above fold-thrust structures indicate Paleogene deposition in a wedge-top depozone containing doubly vergent reverse faults. Retrodeformation of a cross section based on interpreted seismic profiles and thermochronometric data indicates Paleocene to Early Eocene shortening and exhumation occurred through simultaneous activation of east- and west-directed reverse faults across a broad orogenic front. Subsequent deformation focused along west-directed inversion structures. These relationships reveal that deformation operated in a disparate manner, rather than following a systematic progression from hinterland to foreland. The northern Andes also exemplify the potential effects of hinterland sediment loading and fault strength on deformation advance in contractional orogens.

Description: In order to evaluate the relationship between thrust loading and sedimentary facies evolution, we analyse the progradation of fluvial coarse-grained deposits in the retroarc foreland basin system of the northern Andes of Colombia. We compare the observed sedimentary facies distribution with the calculated one-dimensional (1D) Eocene to Quaternary sediment-accumulation rates in the Medina wedge-top basin and with a three-dimensional (3D) sedimentary budget based on the interpretation of ~1800 km of industry-style seismic reflection profiles and borehole data. Age constraints are derived from a new chronostratigraphic framework based on extensive fossil palynological assemblages. The sedimentological data from the Medina Basin reveal rapid accumulation of fluvial and lacustrine sediments at rates of up to ~500 m my-1 during the Miocene. Provenance data based on gravel petrography and paleocurrents reveal that these Miocene fluvial systems were sourced from Upper Cretaceous and Paleocene sedimentary units exposed to the west in the Eastern Cordillera. Peak sediment-accumulation rates in the upper Carbonera Formation and the Guayabo Group occur during episodes of coarse-grained facies progradation in the early and late Miocene proximal foredeep. We interpret this positive correlation between sediment accumulation and gravel deposition as the direct consequence of thrust activity along the Servitá-Lengupá faults. This contrasts with one class of models relating gravel progradation in more distal portions of foreland basin systems to episodes of tectonic quiescence. © 2010 The Authors. Basin Research © 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.

Description: Lower Cretaceous early syn-rift facies along the eastern flank of the Eastern Cordillera of Colombia, their provenance, and structural context, reveal the complex interactions between Cretaceous extension, spatio-temporal trends in associated sedimentation, and subsequent inversion of the Cretaceous Guatiquía paleo-rift. South of 4°30′N lat, early syn-rift alluvial sequences in former extensional footwall areas were contemporaneous with fan-delta deposits in shallow marine environments in adjacent hanging-wall areas. In general, footwall erosion was more pronounced in the southern part of the paleorift. In contrast, early syn-rift sequences in former footwall areas in the northern rift sectors mainly comprise shallow marine supratidal sabkha to intertidal strata, whereas hanging-wall units display rapid transitions to open-sea shales. In comparison with the southern paleo-rift sector, fan-delta deposits in the north are scarce, and provenance suggests negligible footwall erosion. The southern graben segment had longer, and less numerous normal faults, whereas the northern graben segment was characterized by shorter, rectilinear faults. To the east, the graben system was bounded by major basin-margin faults with protracted activity and greater throw as compared with intrabasinal faults to the west. Intrabasinal structures grew through segment linkage and probably interacted kinematically with basin-margin faults. Basin-margin faults constitute a coherent fault system that was conditioned by pre-existing basement fabrics. Structural mapping, analysis of present-day topography, and balanced cross sections indicate that positive inversion of extensional structures was focused along basin-bounding faults, whereas intrabasinal faults remained unaffected and were passively transported by motion along the basin-bounding faults. Thus, zones of maximum subsidence in extension accommodated maximum elevation in contraction, and former topographic highs remained as elevated areas. This documents the role of basin-bounding faults as multiphased, long-lived features conditioned by basement discontinuities. Inversion of basin-bounding faults was more efficient in the southern than in the northern graben segment, possibly documenting the inheritance and pivotal role of fault-displacement gradients. Our observations highlight similarities between inversion features in orogenic belts and intra-plate basins, emphasizing the importance of the observed phenomena as predictive tools in the spatiotemporal analysis of inversion histories in orogens, as well as in hydrocarbon and mineral deposits exploration. © Journal compilation © 2009 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.

Description: The ability of thermochronometric data to shed light on the geologic history of samples and localities through thermal history inverse modelling is enhanced by the degree to which additional geological information can be incorporated into the modelling process. In this contribution, we describe a new set of methods and processes implemented in the HeFTy modelling software for specifying the stratigraphic relationships between samples down a well or borehole, allowing them to be modelled simultaneously, and demonstrate their use in bringing better definition to both predepositional and burial histories. Data from two wells in the Colombian Andes are examined, one in the Middle Magdalena Valley that experienced not only fast Miocene burial but also features a Mio-Pliocene unconformity, and one in the eastern foothills of the Eastern Cordillera in which burial was accomplished by a combination of sedimentation and overthrusting. Multiple-sample modelling in both wells considerably refines the results that are obtained from single-sample modelling. We also demonstrate how to use these methods to pose and evaluate distinct hypotheses concerning the geologic history. As a general rule, it is best practice to set up thermal history inverse models to pose specific geological questions while ruling out geologically impossible or inconsistent solutions. © 2016 The Authors. Basin Research © 2016 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.