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An Integrated Analysis of an Orogen An integrated analysis of an orogen–sedimentary basin pair: Latest Cretaceous–Cenozoic evolution of the linked Eastern Cordillera orogen and the Llanos foreland basin of Colombia German Bayona† Smithsonian Tropical Research Institute, Unit 0948, APO AA 34002-0948, USA, and Corporación Geológica ARES, Calle 57 No. 24-11 of 202, Bogotá, Colombia Martin Cortés Corporacón Geológica ARES, Calle 57 No. 24-11 of 202, Bogotá, Colombia Carlos Jaramillo Smithsonian Tropical Research Institute, Unit 0948, APO AA 34002-0948, USA German Ojeda Instituto Colombiano del Petróleo, AA 41815, Km 7 to Piedecuesta, Bucaramanga, Colombia John Jairo Aristizabal§ Ecopetrol S.A., Calle 37 No. 8-43, Bogotá, Colombia Andres Reyes-Harker Instituto Colombiano del Petróleo, AA 41815, Km 7 to Piedecuesta, Bucaramanga, Colombia ABSTRACT identifi ed in two restored cross sections, one Llanos foothills, and synextensional strata on located at a salient and the other in a recess the forebulge of the Llanos Basin constrain The integration of restored basin geome- on the eastern fl ank of the Eastern Cordil- deformation patterns for this time. The try and internal features of syntectonic units lera. The lower two sequences correspond to post–middle Miocene Andean event initiated (e.g., stratal architecture, thickness, sand- late Maastrichtian–Paleocene fl exural events with regional fl ooding of the foreland basin stone composition) with fl exural modeling and record the eastward migration of both in response the widening of tectonic load- of the lithosphere constrains the evolution tectonic loading and depositional zero in ing, after which the foredeep was fi lled with of a basin and its fl exural history related to the Llanos Basin. These sequences consist of coarse-grained alluvial and fl uvial detritus orogenic growth (spatial/temporal load- amalgamated quartzarenites that abruptly derived from the Eastern Cordillera. ing confi guration). Using this approach, we grade upward to organic-rich fi ne-grained The geometry of tectonic loads, con- determined the Maastrichtian-Cenozoic beds and, to the top, light-colored mud- strained by fl exural models, reveals short- polyphase growth of the Eastern Cordillera stones interbedded with litharenites in iso- ening events of greater magnitude for the of Colombia, an inverted Mesozoic exten- lated channels. Amalgamated conglomeratic uppermost two sequences than for pre–mid- sional basin. The record of this growth occurs quartzose sandstones of the third sequence dle Eocene sequences. Tectonic loads for the in an Andean (post–middle Miocene) thrust record ~15 m.y. of slow subsidence in the Lla- late Maastrichtian–middle Eocene phases belt (the Eastern Cordillera) and in adjacent nos Basin and Llanos foothills during early of shortening were less than 3 km high and foreland basins, such as the Llanos Basin to to middle Eocene time, while shortening was 100 km wide. For the late Eocene–middle the east. This approach permitted the identifi - taking place farther west in the Magdalena Miocene phase, tectonic loads changed south- cation of fi ve tectono-stratigraphic sequences Valley. The fourth sequence, of late Eocene– ward from 6 km to less than 4 km, and loads in the foreland basin and fi ve phases of short- middle Miocene age, records a new episode were wider to the north. The strong Andean ening for the Eastern Cordillera. Thermo- of eastward migration of tectonic loads and inversion formed today’s Eastern Cordillera chronological and geochronological data depositional zero in the Llanos Basin. This structural confi guration and had equivalent support the spatial and temporal evolution of sequence begins with deposition of thick tectonic loads of 10–11 km. the orogen–foreland basin pair. fi ne-grained strata to the west, whereas to Integrated analysis is necessary in poly- Tectono-stratigraphic sequences were the east, in the Llanos basin, amalgamated phase orogenic belts to defi ne the spatial and quartzarenites unconformably overlie Cre- temporal variation of tectonic load and fore- †E-mail: [email protected] taceous and older rocks (former forebulge). land basin confi gurations and to serve studies §Present address: REPSOLYP, Calle 71A No. 5-38, Apatite fi ssion tracks in the axial zone of that seek to quantify exhumation and three- Bogotá, Colombia. the Eastern Cordillera, growth strata in the dimensional analyses of thrust belts. For the GSA Bulletin; September/October 2008; v. 120; no. 9/10; p. 1171–1197; doi: 10.1130/B26187.1; 15 fi gures; Data Repository item 2008078. For permission to copy, contact [email protected] 1171 © 2008 Geological Society of America Bayona et al. Eastern Cordillera, thermochronological risen strongly in the late Neogene. Therefore, deformed Llanos foreland basin. Reactivated sampling must span the width of the Eastern studies of shortening in the Eastern Cordillera Mesozoic normal faults, such as the Guaicar- Cordillera rather than be concentrated in a of Colombia, a mountain range of the northern amo fault system in the central Llanos foothills, single range. Andes, must consider temporal and spatial vari- have been considered to be the major boundary ations of crustal shortening that resulted from of those structural styles. Models of inversion Keywords: foreland basin, Cenozoic stratigra- pre-Neogene phases of deformation. tectonics have been created for the southern seg- phy, basin inversion, orogenic belts, Cenozoic This paper presents a kinematic evolution and ment of the Eastern Cordillera and Llanos foot- tectonics, Llanos Basin, Colombia. quantifi cation of tectonic loading of a polyphase- hills (Casero et al., 1997; Rowan and Linares, deformed orogenic belt (Eastern Cordillera) 2000; Branquet et al., 2002; Restrepo-Pace et INTRODUCTION adjacent to a nonmarine foreland basin (Llanos al., 2004; Toro et al., 2004; Cortés et al., 2006a; Basin). We integrate provenance, sedimentol- Mora et al., 2006), in the central segment of the Integrative research on syntectonic sedimen- ogy, stratal patterns, biostratigraphy, subsidence, Eastern Cordillera and Llanos foothills (Colleta tary basins should include different types of data structural, and geodynamic analyses with pub- et al., 1990; Dengo and Covey, 1993; Cooper et sets (sedimentology, stratal architecture, prove- lished thermochronological and geochronologi- al., 1995; Cazier et al., 1995; Roeder and Cham- nance, subsidence) and needs to consider kine- cal data in order to (1) investigate how crustal berlain, 1995; Rathke and Coral, 1997; Fajardo- matic constraints from the adjacent mountain thickening (i.e., tectonic loading) affected the Peña, 1998; Taboada et al., 2000; Sarmiento- belts. Tectonic activity, weathering processes, latest Cretaceous–Paleogene evolution of the Rojas, 2001; Rochat et al., 2003; Toro et al., and isostatic readjustment of the crust delimit Llanos foreland basin, and (2) identify struc- 2004; Martinez, 2006; Mora et al., 2006), and in uplifted blocks and so determine the nature of tures in the Eastern Cordillera that might have the northern segment of the Eastern Cordillera crustal loads adjacent to a basin. On the other been active at each phase of deformation. Our and Llanos foothills (Chigne et al., 1997; Corre- hand, syntectonic sedimentary basins include the results suggest that the present topography of dor, 2003; Villamil et al., 2004). Although struc- most complete record of the evolution of those the Eastern Cordillera does not refl ect the com- tural models differ both in the angle and depth uplifted blocks. Initiation of deformation in a plex earlier evolution of the northern Andes but of detachment of the Guaicaramo fault system formerly tectonically quiet (e.g., passive mar- rather provides a record only of the last phase of and in fault involvement of crystalline base- gin) and nearly fl at (e.g., coastal plain) region deformation. Therefore, integrated analysis of ment to the east, structural restorations from the affects depositional and paleoecological sys- the adjacent Llanos foreland basin is necessary axial zone of the Eastern Cordillera and Llanos tems, provenance, and paleocurrent indicators, to investigate the previous deformation events, Basin are similar (Fig. 1C). Proposed structural as well as climate variables (e.g., precipitation). which are masked by the last phase. models do not show a relationship between the The rearrangement of these variables infl uences amount of shortening and fl exural deformation the tectonic evolution of both mountain ranges TECTONIC FRAMEWORK OF THE in the adjacent basin, and they differ in (1) the (e.g., climatic control of critical wedge in the COLOMBIAN ANDES AND EVIDENCES amount of shortening of the Eastern Cordil- central Andes; Horton, 1999) and adjacent sedi- OF PRE-NEOGENE DEFORMATION lera, mainly from the axial zone to the western mentary basins (e.g., change in fl uvial patterns boundary of the Eastern Cordillera (Fig. 1C), of the Amazon Basin by uplift of the Andes; Regional Tectonic Setting of the Eastern (2) the geometry of fold structures at depth, and e.g., Hoorn et al., 1995). Cordillera (3) the position and confi guration of Mesozoic The kinematic evolution of an orogen affects eastern and western rift shoulders. both the geometry and fi lling patterns of syntec- Three major orogenic belts are the result of As an alternative method to validate the short- tonic sedimentary basins. In orogen and fore- the complex interaction of the Nazca, Carib- ening estimated in our cross sections, we used land basin systems, estimates of spatial and tem- bean,
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