EAGE

Basin Research (2010) 22, 874–903, doi: 10.1111/j.1365-2117.2009.00459.x Tectonic controls on Cenozoic development in the north-eastern , Mauricio Parra,n Andre´ s Mora,n,w Carlos Jaramillo,z Vladimir Torres,w Gerold Zeilingern and Manfred R. Streckern nInstitut fˇr Geowissenschaften, Universitt Potsdam, Potsdam, Germany wInstituto Colombiano del Petro¤leo, Ecopetrol Bucaramanga, Colombia zSmithsonianTropical Research Institute, Balboa, Ancon, Republic of Panama

ABSTRACT In order to evaluate the relationship between thrust loading and sedimentary facies evolution, we analyse the progradation of £uvial 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) to Quaternary sediment-accumulation rates in the Medina wedge-top basin andwith a three-dimensional (3D) sedimentary budget based on the interpretation of 1800km of industry-style seismic re£ection pro¢les 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 £uvial and lacustrine sediments at rates of up to 500 m my 1 during the . Provenance data based on gravel petrography and paleocurrents reveal that theseMiocene £uvial systemswere sourced from Upper and Paleocene sedimentary units exposed to the west in the Eastern Cordillera. Peak sediment-accumulation rates in the upper Carbonera Formation and the Guayabo occur during episodes of coarse-grained facies progradation in the early and late Miocene proximal foredeep.Weinterpret this positive correlation between sediment accumulation and gravel deposition as the direct consequence of thrust activityalong theServita¤ ^Lengupa¤ faults.This contrasts with one class of models relating gravel progradation in more distal portions of foreland basin systems to episodes of tectonic quiescence.

INTRODUCTION (e.g., Burbank, 1992); (2) an increase in the e⁄ciency of erosion triggered byglobal climatic oscillations(e.g., Mol- Grain-size trends and the basinwide distribution of nar, 2004) or by orographic e¡ects (Ho¡man & Grotzinger, coarse-grained strata in foreland basins have been used to 1993; Masek etal.,1994); (3) tectonic quiescence favouring a interpret the tectonic and climate-related controls on fore- decrease in subsidence and progradation of coarse- land basin accumulation (e.g., Flemings & Jordan, 1990; grained sediments to the distal part of the basin(e.g.,Hel- Heller & Paola, 1992; Paola et al., 1992). In general, the ba- ler et al., 1988; Flemings & Jordan, 1990; Burbank, 1992; sin’s stratigraphic architecture is a function of the relative Heller & Paola, 1992); and (4) increase of erosion rates and importance between sediment discharge and the rate of sediment discharge due to a decrease in the resistance to creation of accommodation space (e.g., Schlunegger et al., erosion of the source areas, (e.g., DeCelles et al., 1991; Car- 2007). Multiple mechanisms have been proposed to ac- roll et al., 2006). Numerical modelling has been used to count for the progradation of coarse-grained sediments evaluate the role of each of these controlling factors on in foreland basins: (1) uplift of the source areas by either the overall distribution of coarse-grained facies in basins increased tectonic activity in the fold-and-thrust belt with di¡erent £exural rigidities (e.g., Flemings & Jordan, (e.g., Burbank et al., 1988; Schlunegger et al., 1997a, b; Hor- 1989; Flemings & Jordan, 1990; Sinclair et al., 1991; Paola ton et al., 2004) or erosionally driven isostatic rebound etal.,1992). A critical factor determining a basin’s sedimen- tary response to the aforementioned changes, however, in- Correspondence: Mauricio Parra, Institut fˇr Geowissenschaf- volves an improved knowledge of the time scales over ten, Universitt Potsdam, Karl-Liebknecht-Strasse 24, Haus 27, which variations in the external forcings occur compared 14476 Potsdam, Germany. E-mail: [email protected] with an inherent background level of erosional and deposi- potsdam.de tional processes in the basin. While considerable debate Present address: Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, has existed on the role of each of these factors in the distal TX 7871-0254, USA portion of foreland basins (Burbanketal.,1988; Helleretal.,

r 2010 The Authors 874 Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Controls on foreland-basin sedimentation, Colombia

1988), combined ¢eld evidence and numerical models have Medina Basin with a three-dimensional (3D) sedimentary demonstrated that coarse-grained sediments accumulate budget for an area of 5000 km2, based on the interpreta- in the proximal part of foreland basins, irrespective of pre- tion of 1800 km of industry-style depth-migrated, mul- cise tectonic and climatic regimes (e.g., Flemings & Jordan, tichannel seismicre£ectionpro¢les andborehole datatied 1990; Jones et al., 2004). These inherent characteristics to a new biostratigraphic framework. Importantly,our data complicate a rigorous assessment of the role exerted by show that episodes of coarse-grained sedimentation are each of these competing factors on the accumulation of coeval with rapid subsidence throughout the basin history, coarse-grained sediments in proximal sectors of foreland illustrating that increased tectonic activity in the Eastern basins. Provided su⁄cient temporal control, tectonically Cordillera has exerted a dominant control on the geome- and climatically controlled forcing factors re£ected in de- try and pattern of sediment distribution. Our work has im- positional characteristics may be deconvolved for an im- plications for the understanding of the response time of proved understanding of the spatiotemporal trends in surface processes to tectonic forcing. tectonic and sedimentary processes of convergent oro- genic belts. Such is the case in the northern Andes, where contractional deformation and orogenic growth have been linked with reactivated long-lived anisotropies GEOLOGIC BACKGROUND (Mora et al., 2008; Parra et al., 2009b) that have fundamen- Geodynamic and structural setting tally in£uenced the loci of tectonic deformation, erosion and sediment dispersal. TheMedinaBasinisa90 25 km wedge-top depocentre In the eastern Andes of central Colombia, the sedimen- located atop the most external east-verging thrust- tary record of subduction-related orogenesis is preserved sheet along the eastern margin of the Eastern Cordillera in to Cenozoic basins that extend east of of the Colombian Andes (Fig.1).The Eastern Cordillera is the Central Cordillera, the present-day magmatic arc the easternmost branch of a retroarc fold-and-thrust belt (Fig.1).Mesozoic rifting occurredin the areapresentlyoc- related to Late Cretaceous to Cenozoic shortening, result- cupied by the Eastern Cordillera north of 21N(e.g., ing from the interaction between the Nazca, Caribbean Campbell & Bˇrgl,1965; Mora et al., 2006; Sarmiento-Ro- and South American plates (e.g., Cooperet al.,1995;Taboa- jas etal., 2006). In the course of Cenozoic contraction, ma- da et al., 2000; Go¤ mez et al., 2005; Parra et al., 2009a). Late jor inherited extensional faults became the locus for Cretaceous ( 80 Ma) oblique accretion of relicts of a Pa- preferential accommodation of thrust loading and defor- ci¢c oceanic plateau (e.g., Kerr & Tarney,2005;Vallejo etal., mation (Mora et al., 2006, 2008; Parra et al., 2009a, b), and 2006) constituted the Western Cordillera and triggered therefore prevented a signi¢cant eastward advance of the crustal shortening and thickening and initial mountain orogenic front.This con¢guration has led to the unroo¢ng building within the present-day Central Cordillera (e.g., of progressively older structural levels from the eastern Cooper et al., 1995). The tectonic loading exerted by this £ank of the Eastern Cordillera and resulted in the coeval range created a foreland-basin system, east of the Central accumulation of sediments in the to the east. Cordillera (Cooper et al., 1995; Go¤ mez et al., 2005). Subse- Plio^ eastward advance of the foreland fold- quent deformation compartmentalized the foreland basin and-thrust system to the present-day frontal structure in a nonsystematic manner due to the selective reactivation (Mora, 2007) has incorporated only the proximal part of of crustal anisotropies inherited from Proterozoic and Pa- this Mio^ foredeep into the orogen in the form laeozoic collision and subduction episodes (e.g., Restrepo- of the Medina wedge-top basin. This exhumed foredeep Pace et al., 1997; Cediel et al., 2003, and references therein), o¡ers a unique,yet areallylimited locationwhere the sedi- and more importantly extensional structures generated mentary record of the late stages of Andean uplift and ex- during Mesozoic rifting (e.g., Cooper et al., 1995; Mora humation are well exposed. However, because of the et al., 2006; Sarmiento-Rojas et al., 2006). In this context, absence of radiometrically datable minerals and the pau- initial middle Eocene tectonic inversion of Mesozoic city of published biostratigraphic markers, the sedimen- basins in the area of the present-day Eastern Cordillera tary evolution and its relation with Andean tectonic and disrupted the once contiguous foreland basin and formed climatic evolution are still unclear. two principal Cenozoic basins: the MagdalenaValley Basin In this study,we present re£ection data unreleased pre- to the west, and the Llanos basin to the east (e.g., Go¤ mez viouslythat re¢ne earlierestimates on the age ofthrust in- et al., 2003; Parra et al., 2009a). During inversion, signi¢ - itiation and help unravel the tectono-sedimentary cant rockuplift in the Eastern Cordillera occurred through evolution along the eastern margin of the Eastern Cordil- the reverse slip along the formerly rift-bounding faults. lera. We also present new ¢eld-based sedimentological These major faults include the east-dipping Bituima^La and provenance data and the ¢rst systematically acquired Salina faults to the west, and the west-dipping Servita¤ ^ biostratigraphic dataset, based on detailed palynology, for Lengupa¤ faults to the east (Fig. 1a). This process has re- the proximal foredeep deposits in this area. In order to dis- sulted in the formation of a bivergent, thick-skinned criminate among multiple potential forcing factors on the fold-and-thrust belt with the loci of maximum exhuma- basin architecture, we compare one-dimensional (1D) Eo- tion coinciding with the proximal hanging-wall blocks of cene to Pliocene sediment-accumulation rates in the inverted Mesozoic normal faults whose orientation was r 2010 The Authors Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 875 M. Parra et al.

Fig. 1. (a)Geologic map of theEasternCordillera(Mora etal., 2008; Parra etal., 2009a) showing main structures in the northern sector of the Quetame Massif and the adjacent Medina (black box) and Llanos basins. Locations of seismic lines (white lines) and wells are indicated. Inset map denotes the location of the Western (WC), Central (CC) and Eastern (EC) cordilleras within the Colombian Andes. White box in inset indicates the location of the main map. (b) Structural cross section (Location in a) showing the main structures across the double-vergent Eastern Cordillera and the adjacent Magdalena and Llanos basins. (c) Geological map of the Medina Basin (location shown in a). Locations of growth strata (Fig. 3) and measured stratigraphic sections are shown.

r 2010 The Authors 876 Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Controls on foreland-basin sedimentation, Colombia

Fig. 1. Continued favourable for the accommodation of compressional stres- basement massifs in the axial and eastern sectors. Outside ses during the (Mora et al., 2006). Promi- of the Mesozoic rift domain, e¤ n-echelon, northeastward nent examples of the more deeply exhumed sectors in the stepping, thin-skinnedCenozoic thrust sheetswith oppo- Eastern Cordillera are the Villeta Anticlinorium on the site vergence are thrust over the Magdalena and Llanos ba- western £ank of the range, and the Floresta and Quetame sins above detachment levels within mechanically weak r 2010 The Authors Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 877 M. Parra et al.

EPOCH AXIAL EASTERN CORD. MEDINA BASIN LLANOS BASIN

TILATÁ GUAYABO

LEÓN

CARBONERA

USME MIRADOR

REGADERA FORELAND BASIN BOGOTÁ LOS CUERVOS

GUADALUPE GROUP

CHIPAQUE

UNE POST-RIFT

FÓMEQUE Glauconite-bearing units LAS JUNTAS

MACANAL

BUENAVISTA GUAVIO SYN-RIFT Fig. 2. Chronostratigraphic diagram of the Late ^Cenozoic strata in the eastern £ank of the Eastern Cordillera Nonmarine Shallow-marine Lacustrine siltstone (after Go¤ mez, E. et al., 2005; Mora, A. et al., sandstones Angular 2008b; Parra et al., 2009a). Grey shading unconformity Alluvial-fan Delta and coastal- Shallow-marine conglomerates plain sandstones mudstones represents lithostratigraphic units with Facies change Nonmarine Delta and coastal- Shallow-marine glauconitic sandstones used to evaluate mudstones plain mudstones carbonates the unroo¢ng of the source areas (see text).

Cretaceous and Palaeogene strata (e.g., Butler & Schamel, limits of the rift, including areas of the Llanos and Magda- 1988; Cooper et al., 1995; Go¤ mez et al., 2005; Mora et al., lena basins (e.g., Cooper et al., 1995; Mora et al., 2006; Sar- 2008). miento-Rojas et al., 2006). In the Eastern Cordillera, these units include decimetric layers of glauconitic sandstones Stratigraphy of the Eastern Cordillera in the Une, Chipaque and Guadalupe formations (Guer- rero & Sarmiento, 1996; Vergara & Rodr|¤ guez, 1996), fora- Pre- low-to medium-grade phyllites, quartzites minifera-bearing siliceous siltstones and phosphatic and schists, and sparse Palaeozoic intermediate to acid in- sandstones (Guadalupe Group, e.g., F˛llmi et al., 1992; Ver- trusives comprise the basement of the Eastern Cordillera gara & Rodr|¤ guez, 1996), which constitute important (Segovia, 1965; Ulloa & Rodr|¤ guez, 1979; Ulloa & Rodr|¤- lithologic markers that help constrain the provenance of guez, 1982; Jime¤ nez, 2000).These basement rocks are un- Cenozoic sedimentary units. conformably overlain by up to 4 km of Devonian The onset of nonmarine sedimentation in the Eastern marginal marine mudstones and sandstones and Carboni- Cordillera is recorded by the up to 1100-m-thick coastal ferous nonmarine red beds (e.g., Ulloa & Rodr|¤ guez,1979). plain, estuarine and £uvial sedimentary rocks of the upper These units are in turn superseded by Mesozoic rift-re- ^lower Palaeocene Formation lated units including: (1) up to 2 km of Lower to Upper Jur- (Sarmiento, 1992). This unit is interpreted as the distal assic lacustrine andvolcanoclastic rocks, locally deposited equivalent of coarse-grained, westerly sourced synoro- in narrow half-graben basins in the western half of the genic deposits of the Magdalena Valley (Go¤ mez et al., range (e.g., Kammer & Sa¤ nchez, 2006; Sarmiento-Rojas 2005). In the Medina Basin, only 60m of the Guaduas et al., 2006); (2) up to 5 km of (Berria- Formation (Guerrero & Sarmiento, 1996) are preserved sian to ) synrift platformal units, deposited in a below a regional unconformity associated with forebulge wider rift basin whose limits approximately coincide with erosion (Go¤ mez et al., 2005; Fig. 2). Here, the overlying the margins of the present-day mountain range (Mora Cenozoic units comprise two megasequences of late Pa- et al., 2006, 2009a); and (3) up to 2 km of postrift, shallow laeocene and Eocene^Pliocene age, respectively,that pro- marine rocks, deposited within and beyond the structural gressively onlap eastward to the Mesozoic substratum of

r 2010 The Authors 878 Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Controls on foreland-basin sedimentation, Colombia the Llanos Basin (Cooper et al., 1995; Fig. 2). The ¢rst se- westernmost structure in the area. The western limb is quence consists of up to 700 m of estuarine and coastal overturned and constitutes the northern extent of the wes- plain deposits of the Barco and Los Cuervos formations tern Medina syncline.The steepening of the western limb (Cooper et al., 1995; Guerrero & Sarmiento, 1996; Cazier of the Medina syncline occurs where the deformation style et al., 1997; Jaramillo & Dilcher, 2000). The second se- changes at the eastern margin of the Quetame massif; in quence comprises a 5-km-thick lower Eocene to Neo- the south, it is primarily accommodated by thrusting gene strata that thins eastward and rests unconformably along the Servita¤ fault, whereas in the north deformation upon progressively older Palaeocene and Cretaceous units has resulted in fault-propagation folding (Fig. 1c). Farther toward the east in the Llanos Basin. This sequence com- east, in the footwall of the Guaicaramo thrust, follows the prises up to 250 m of estuarine valley- ¢ll and coastal- Llanos Plain in the modern foredeep depozone. Here, de- plain deposits (Cazier et al., 1997) of the lower to middle formation is minor and results primarily from the south- Eocene Mirador Formation that are superseded by up to ward propagation of the Cusiana fault and the associated 3 km of estuarine and locally marine deposits of the late hanging-wall La Florida anticline (Fig.1c), a structure cor- Eocene^ Carbonera Formation (Cazieretal., responding to a more frontal depocentre within the e¤ n- 1995, 1997; Cooper et al., 1995; Bayona et al., 2008; Parra echelon segments of the eastern fold-and-thrust belt.To et al., 2009a).The Carbonera Formation consists of eight a lesser degree, deformation is associated with minor nor- members (the C1^C8 members) of interlayered - mal faulting within the Cenozoic deposits, imaged in seis- and mudstone-dominated deposits (e.g., Cooper et al., mic re£ection pro¢les and interpreted to be related to 1995). Rapid sediment accumulation within an eastward- forebulge extensional faulting (Bayona et al., 2008). thinning sedimentary wedge with pronounced facies changes in the upper Eocene^Oligocene lower part of the Chronology of foreland-basin deformation Carbonera Formation can be inferred for the western part of the Medina Basin and has been related to the initial up- Crustal thickening in the Central Cordillera since the Late lift of the axial Eastern Cordillera (Parra et al., 2009a, b). Cretaceous time ( 75^80 Ma) led to initial foreland-ba- These strata are overlain by the approximately 500-m- sin development in central Colombia (e.g., Cooper et al., thick Leo¤ n Formation (Cooper et al., 1995), which records 1995; Go¤ mez etal., 2005). Eastward advance of the orogenic lacustrine deposition with short-lived marine incursions front has occurred episodically,with stages of fast advance (Bayona et al., 2008). Overlying the Leo¤ n Formation, pro- associated with the disruption of the basin through an in- tracted nonmarine sedimentation is represented by distal itial bivergent inversion of the Eastern Cordillera. Subse- to proximal alluvial deposits of the Lower Guayabo and quently, stagnation of the deformation front has resulted Upper Guayabo formations (Cooper et al., 1995). The from contractional deformation being preferentially ac- Upper Guayabo Formation intersects the present-day commodated along crustal inhomogeneities inherited erosion surface and has an exposed minimum thickness from previous tectonic events (Mora et al., 2008; Parra of 700m. Our ¢eld observations and geologic mapping etal., 2009a).In particular,this pattern has been documen- show that the spatial distribution of the upper Carbonera ted for the contractionally reactivated Servita¤ ^Lengupa¤ Formation and younger units displays numerous facies faults along the eastern limit of the Quetame basement changes, leading to a signi¢cantly di¡erent stratigraphic high. There, zircon ¢ssion-track data constrain the mini- column for the eastern and western sectors of the Medina mum age of initial deformation-related exhumation asso- Basin. In this study, we focus on the Miocene^Pliocene ciated with the slip along this fault at 20^25 Ma (Parra stratigraphy of this foreland basin. et al., 2009b). Subsequent deformation and erosion of the Cenozoic strata in the vicinity of the trace of the Lengupa¤ Structure fault have prevented the determination of tighter age con- straints on the initial deformation. However, despite these The Medina Basin constitutes the hanging wall of a thin- limitations, growth-strata relations in lower Miocene skinned thrust sheet that extends 40km east of theTesa- units of the lower Carbonera Formation (described below) lia fault (Fig. 1c). Here, the Guavio anticline is a broad support previous interpretations of an early Oligocene to fault-bend fold related to the Guaicaramo thrust. Subsur- early Miocene onset of thrusting along this fault (Parra face data and structural interpretations suggest that this et al., 2009b). Protracted deformation and tectonic loading thrust splays at depth from the Tesalia fault (Mora et al., along this structure is inferred from a Miocene increase in 2006) and propagates along two decollement levels within the tectonic subsidence of the Medina (Parra et al., 2009a) the Lower Cretaceous and the Upper and Llanos (Bayona et al., 2008) basins. Moreover, the sub- Cretaceous Chipaque Formation (Rowan & Linares, horizontal strati¢cation (i.e. the absence of growth strata) 2000). The thrust propagates to a higher decollement in Miocene^Pliocene strata in the footwall of the Guaicar- above an underlying normal fault and, farther east has gen- amo thrust, as deduced from the analysis of industry seis- erated a fault-propagation fold (Limones anticline) in its mic lines (Mora, 2007), provides a maximum age of hanging wall (Fig.1c). In the northern part of the Medina 5 Ma for the initial thrusting along this fault.This pat- Basin, west of the Guavio anticline, the Nazareth syncline tern thus demonstrates Miocene^Pliocene stagnation of is a highly asymmetric, east-verging fold that forms the the deformation front along the long-lived crustal aniso- r 2010 The Authors Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 879 M. Parra et al. tropy of the Servita¤ ^Lengupa¤ faults and subsequent post- Basin. In addition, seismic re£ectors were tied to the stra- Pliocene migration of the deformation front to its present tigraphy with data from seven hydrocarbon-exploration location along the Guaicaramo thrust (Mora, 2007; Parra boreholes, especially in areas with no surface exposure et al., 2009b). within the footwall of the Guaicaramo thrust.The accu- mulated (compacted) volume of rock was estimated from the seismic data by converting the vertical time axis into METHODS depth. We used check-shot surveys from seven boreholes across the Medina and Llanos basins to evaluate the seis- Detailed mapping of an area of 1500 km2 provides the micvelocities in theCenozoic strata.The near-surfaceve- basis for stratigraphic pro¢ling of Neogene foreland basin locity gradient decreases eastward from 3770 m s 1 in strata. We conducted sedimentary facies interpretation, theMedinaBasin(Coporo-1Well)to 2840 m s 1 in the and palaeocurrent and provenance determinations on easternmost part of the study area in the Llanos Basin nine measured sections totalling 5.3 km of the Carbo - (Upia-1 Well; see Fig. S1). We therefore derived di¡erent nera Formation and the Guayabo Group exposed in the depth^time relations for the hanging and footwalls of the Medina Basin (Fig.1). Correlations between measured sec- Guicaramo thrust by combining information from avail- tions are based either on the tracing of laterally continuous able wells in each fault block. For the hanging-wall block, lithostratigrahic units over distances of a few kilometres combined data from the Coporo-1 and Medina-1wells re- within individual limbs of folds or on subsurface extrapo- sult in an average velocity of 3650 m s 1, whereas data from lation of outcrop exposures in seismic re£ection pro¢les the Guacavia-1, San Pedro-1, Chaparral-1and Upia-1wells where surface correlation is precluded by erosion. Such yield a value of 3050 m s 1. We thus estimate that maxi- an extrapolation was carried out by correlating seismic re- mum errors in depth conversion due to averaging data £ectors with the surface geology, as derived from our de- from various wells are up to 4% in the Medina Basin tailed mapping. A new chronological framework of and up to 7% in the Llanos Basin. sediment accumulation is provided on the basis of a paly- nological study performed on 500 samples. Palaeocurrent directions were derived from imbricated RESULTS clasts, channel-axis orientations and trough cross-bed- ding. Sixteen conglomerate clast counts were conducted Growth strata and growth unconformities to reveal the unroo¢ng history of the source areas. A mini- First, growth-strata relationships and unconformities are mum of 100 clasts were counted in individual, clast-sup- well preserved in di¡erent stratigraphic levels along the ported conglomerate layers, using a 10-cm grid. western margin of the Medina Basin. In the seismic line Conglomerate petrography data are reported inTable1. MVI-1020, a package of divergent re£ectors in the strata We evaluate the spatial and temporal patterns of sedi- equivalent to the lower part of the C5^C2 members of the ment accumulation in the Medina and Llanos basins by Carbonera Formation occurs within the western limb of assessing both 1D and volumetric sedimentary budgets. the Medina syncline (Fig. 3). Awestward decrease in stratal First, we reconstruct1D,decompacted sediment-accumu- thickness and onlap geometries suggests contempora- lation rates along a composite stratigraphic section in the neous sedimentation and tilting of the forelimb of the Medina wedge-top basin. A composite stratigraphic sec- fault-propagation Farallones anticline (e.g., Riba, 1976). tion of the Upper Cretaceous^Pliocene units of the Medi- These geometries constrain a minimum, early Miocene na Basin was constructed by combining the measured age for the initiation of folding associated with slip along pro¢les of Mio^Pliocene units presented in this study the Lengupa¤ fault. Second, in the northwestern part of and sections for older units presented by Parra et al. the basin, growth strata and growth unconformities in (2009a) and Jaramillo & Dilcher (2000). Sediment-accu- the strata of the upperMiocene^PlioceneGuayaboGroup mulation rates are estimated using thickness and age con- exist on the western £ank of the Nazareth syncline at straints based on the palynological biozonation. In order 41400N (Mora, 2007).This geometry reveals continued to account for anomalies in measured stratigraphic thick- deformation through the tilting of the Farallones anticline nesses derived from the progressive loss of porosity with forelimb. Overall, these syncontractional stratal geome- burial depth and inhomogeneous compaction of mechani- tries in di¡erent stratigraphic intervals of the Mio^Plio- cally di¡erent lithologies, we used a porosity-depth rela- cene units of the western Medina Basin document tion to estimate decompacted thicknesses (Sclater & inversion, protracted reverse faulting and fault-related Christie,1980).Decompaction parameters anddetailed re- folding associated with the long-lived Lengupa¤ fault. sults are presented in Table S1. Second, we estimate the volume of sedimentary strata accumulated for speci¢c in- Sedimentary facies architecture of the tervals in the Medina Basin and the proximal, western sec- Medina Basin tor of the Llanos Basin by interpreting an extensive grid of 1800 km of 2D industry seismic re£ection data (Fig.1a). The upperEocene^Pliocene basin ¢ll of theMedinaBasin Mapped units were identi¢ed in the grid of seismic lines is reconstructed on the basis of 13 stratigraphic sections by a direct extrapolation of surface outcrops in the Medina totalling 7.4 km of strata, which constitute the Carbo-

r 2010 The Authors 880 Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists ai Research Basin r 00TeAuthors The 2010 Table 1. Gravel petrography data for Eocene-Pliocene units of medina basin

Ve i n Siliceous Glauconitic Phosphatic r 1 1 n 00BakelPbihn t,Erpa soito fGocetss&EgnesadItrainlAscaino Sedimentologists of Association International and Engineers & Geoscientists of Association European Ltd, Publishing Blackwell 2010 Sample Long ( W) Lat ( N) Thickness (m) Unit quartz Chert Mud-stone Sand-stone siltstone sandstone sandstone Shale Total

MP 603 73.22359 4.80948 1840 C7 64 36 0 0 0 0 0 0 100 64% 36% 0% 0% 0% 0% 0% 0% 100% MP 605 73.22125 4.80544 2538 C7^C5 61 36 3 0 0 0 0 0 100 61% 36% 3% 0% 0% 0% 0% 0% 100% MP 607 73.21739 4.80495 2658 C7^C5 70 27 2 1 0 0 0 0 100 70% 27% 2% 1% 0% 0% 0% 0% 100% MP 608 73.21604 4.80566 2687 C7^C5 65 25 8 0 2 0 0 0 100 65% 25% 8% 0% 2% 0% 0% 0% 100% MP 610 73.19455 4.81072 3743 C1 37 13 14 32 0 1 0 0 97 38% 13% 14% 33% 0% 1% 0% 0% 100% MP 642 73.36852 4.58595 3925 C1 20 12 4 60 2 0 2 0 100 20% 12% 4% 60% 2% 0% 2% 0% 100% MP 611 73.19678 4.80565 4008 C1 39 15 5 32 11 2 0 0 104 38% 14% 5% 31% 11% 2% 0% 0% 100% MP 612 73.19920 4.79959 4353 C1 11 8 2 19 19 15 2 0 76 14% 11% 3% 25% 25% 20% 3% 0% 100% MP 613 73.19947 4.79635 4615 C1 15 4 3 64 10 4 0 0 100 Colombia sedimentation, foreland-basin on Controls 15% 4% 3% 64% 10% 4% 0% 0% 100% MP615 73.19999 4.79340 4816 LowerGuayabo 13 8 10 65 4 4 0 0 104 13% 8% 10% 63% 4% 4% 0% 0% 100% MP 641 73.34744 4.57738 4905 Lower Guayabo 0 0 0 100 0 0 0 0 100 0% 0% 0% 100% 0% 0% 0% 0% 100% MP 616 73.19732 4.78996 4995 Lower Guayabo 0 2 4 102 0 0 0 0 108 0% 2% 4% 94% 0% 0% 0% 0% 100% MP626 73.17091 4.78835 5136 LowerGuayabo 5 2 14 53 2 26 0 0 102 5% 2% 14% 52% 2% 25% 0% 0% 100% MP618 73.19704 4.78743 5246 LowerGuayabo 0 0 0 70 0 30 0 0 100 0% 0% 0% 70% 0% 30% 0% 0% 100% MP 623 73.19790 4.78494 5380 Lower Guayabo 0 2 4 86 0 8 0 0 100 0% 2% 4% 86% 0% 8% 0% 0% 100% MP 627 73.17641 4.79269 5507 Upper Guayabo 3 1 4 69 3 20 0 2 102 3% 1% 4% 68% 3% 20% 0% 2% 100% MP 630 73.18339 4.79121 6188 Upper Guayabo 0 0 2 56 0 42 0 0 100 0% 0% 2% 56% 0% 42% 0% 0% 100%

n

881 Stratal thickness in Composite Section (Figs 8 and 9) M. Parra et al.

CDP 313 424 535 646 758 869 980 1091 1202 1313 1424 1535 1647 1758 SP 156 212 267 323 379 434 490 545 601 656 712 767 823 879

Medina Syncline Limones Anticline

–1000

Tesalia fault hrust

León –2000 C1 Guaicaramo t C2 (Huesser) traveltime (ms)

Gacenera y –3000 C6 (Guaicarama)

Mirador Two-wa

–4000

1 km

–5000

CDP 341 369 396 424 452 480 507 535 563 591 619 646 674 SP 170 184 198 212 226 240 253 267 281 295 309 323 337 B

–2500

Gacenera traveltime (ms) C5-C2 members y Two-wa

–3000 C6 (Guaicarama)

250 m

Fig. 3. (a) Time-migrated seismic line MVI-1997-1020 across the southern sector of the Medina Basin (see Fig.1), depicting the tops of interpretedCenozoic units(seeFigs5,6and8).For an approximatevertical scale bar,thevertical axis is based on avelocitycorrection of 4kms1.The vertical exaggeration is1.7X. (b) Detail of growth-strata geometries in the lower Miocene C5^C2 members of the Carbonera Formation in the Medina syncline. nera (C8^C1 members), Leo¤ n, Lower Guayabo and Upper was presented by Parra et al. (2009a) based on four strati- Guayabo formations. The characteristics of the lower graphic pro¢les with facies associations that represent tid- 2.1km of this record, comprising the C8^C5 members, ally in£uenced deltaic, lacustrine, alluvial plain and

r 2010 The Authors 882 Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Controls on foreland-basin sedimentation, Colombia braided £uvial sedimentary environments. These four fa- lingh et al., 2002; Anderson et al., 2006; Wesselingh & Mac- cies associations(FA1^FA4;Table2)are also present in the sotay, 2006), as well as the occurrence of gastropods upper members of the Carbonera Formation and overlying Sheppardiconcha (Go¤ mez et al., 2009; see also Fig. 6a). The units that are the subject of this work. Here, we build upon fragmentation, corrosion and abrasion of gasteropoda our previous work by complementing the description of and disarticulated bivalve shells re£ect reworking in an en- facies associations FA1^FA4 with new data from the upper vironment with moderate energy.Finally,the sporadic oc- Carbonera and Leo¤ n formations. In addition, we add the currence of mudstone with negligible bioturbation is description and interpretation of facies associations FA5 indicative of rapid accumulation (e.g., Dalrymple & Choi, and FA6, which occur in the Upper Guayabo Formation. 2007). Collectively, these observations suggest deposition Facies associations are described on the basis of the recog- in a transitional environment between freshwater lakes nition of 16 lithofacies, following Parra et al.(2009a).These and estuaries. descriptions are included in the supplementary material (TableS2). In the following section, we focus on the inter- Facies association 3 (channelized sandstones and conglomerates). pretation of the spatial distribution of the six identi¢ed fa- Laterally restrictedsandstone bodieswithbasal scours are cies associations based on the measured stratigraphic characteristic of stream-£ow deposition (e.g., Bridge, pro¢les(Figs4and5),and the associated depositonal pro- 2003).The lenticular morphology of the sandstone beds cesses and sedimentary environments. and the presence of erosive basal scour marks and muddy intraclasts suggest transport by traction (e.g., Collinson et al., 2006). The poorly de¢ned large-scale, low-angle Interpretation of lithofacies associations planar cross-strati¢cation, absence of well-de¢ned nor- Facies association 1 (coarsening-upward laminated sandsto- mal grading and ubiquituous £oating pebble clasts may nes). Thin interbedded sandstone^mudstone couplets represent deposition in braided £uvial channels (e.g., with lenticular and £aser lamination suggest tidal in£u- Miall, 1985; Bridge, 2003). ence (Reineck & Wunderlich,1968).The extensive areal ex- tent of laterally continuous sandstone bodies with a variety Facies association 4 (overbank mudstones and siltstones).Later- of wavy, lenticular, £aser and cross lamination, as well as ally continuous variegated mudstone and siltstone units associated coal laminae and coal seams, suggests deposi- represent deposition by suspended load in overbank areas. tion in a transition zone between £uvial^marine and tide- Pervasive mottling and root traces (Fig. 6b) indicate dominated estuarine systems (e.g., Dalrymple et al., 1992; palaeosoil development in a £uvial £oodplain environ- Dalrymple & Choi, 2007). The thickening- and coarsen- ment (e.g., Bridge, 1984). Dessication cracks (Fig. 6c) and ing-upward sequences evolve from laminated dark mud- sporadic ferruginous nodules (Fig. 6d) re£ect pedogenesis stones to wavy, lenticular and ¢nally to cross-strati¢ed during intermittent £ooding and subaerial exposure and sandstones, suggesting an increase in current velocity £uctuating wet^dry soil conditions (e.g., McCarthy et al., (Collinson et al., 2006) and possibly indicating a decrease 1997; Kraus, 1999). In this scenario, the thin, wedge- in water depth through time. This is compatible either shaped, ¢ning-upward sandstone bodies may have been with eustatically controlled parasequences (e.g., Mitchum deposited as crevasse channel ¢lls (e.g., Bridge, 1984). & VanWagoner,1991) or, alternatively autogenic prograda- tional successions, such as those observed in delta-front Facies association 5 (granule to pebble conglomerates and con- deposits (e.g., Tye & Coleman, 1989; Coleman et al., 1998). glomeratic sandstones). Clast-supported, granule and peb- Although dewatering structures, soft-sediment deforma- ble conglomerates with horizontal strati¢cation or, rarely tion and growth faults indicate a rapid deposition (Lowe, 1975; Owen, 1996) typical for deltaic environments (Cole- low-angle through cross-strati¢cation, lack of muddy ma- trix and dominantly sharp, non-erosive basal contacts man et al., 1998; Dalrymple et al., 2003), some allogenic (Fig. 6e) indicate waterlaid deposition by uncon¢ned control cannot be ruled out. stream £ows (e.g., Blair, 1999b).These features may repre- sent deposition by sheet£oods (e.g. Hogg,1982).The inter- Facies association 2 (massive and laminated mudstones).Amar- bedding of this facies with facies association FA3 likely ine in£uence is indicated by discrete thin levels with abun- indicate deposition in the distal sectors of waterlaid allu- dant microforaminiferal linings and dino£agellates, vial-fans (e.g., Blair,1999b). including Homotryblium £oripes, Cordosphaeridium inodes, Polysphaeridium subtile, Achomosphaera and Spiniferites.The Facies association 6 (cobble and boulder conglomerates).Clast- laterally continuous, dark-grey mudstone-dominated fa- supported, crudely strati¢ed, pebble-to-boulder con- cies associated with thin, £aser-laminated sandstones and glomerates (Fig. 6e) with a ribbon-like geometry represent coal beds suggest deposition in a mud £at environment. deposition by high-energy stream£ows in moderately to This interpretation is supported by the presence of the bi- well-con¢ned channels (e.g., Blair, 1999b). Occasional, valves Pachydon, Anondondites and Mytilopsis (Go¤ mez et al., very poorly sorted, matrix-supported conglomerates or- 2009; Parra et al., 2009a), which have been associated with ganized in subtabular beds are diagnostic of debris- £ow fresh-water lacustrine systems (e.g., Nuttall, 1990; Wesse- deposits (Nemec & Postma, 1993; Blair, 1999a). Taken to- r 2010 The Authors Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 883 884 Parra M. Table 2. Summary of facies associations ai Research Basin Facies Association Description Stratigraphic occurrence Interpretation tal et FA1 (coarsening-upward Up to 8 m thick thickening- and coarsening- Predominant lithofacies in C7,C5 and C3 Tidally in£uenced deltaic environment. laminated sandstone) upwards intervals of tabular sandstone with members in the eastern margin of the basin. Growth faults, convolute bedding and water- . r minor thin interbeds of mudstone. Sandstone Common in lower part of C1 escape structures suggest rapid 00BakelPbihn t,Erpa soito fGocetss&EgnesadItrainlAscaino Sedimentologists of Association International and Engineers & Geoscientists of Association European Ltd, Publishing Blackwell 2010 beds present nonerosive basal contacts and are accummulation. Possible allogenic control frequently bioturbated. Laminae rich in organic-matter, plant remains.Thin pebble conglomerate commonly cap intervals at top. Typical lithofacies pattern includes, from base to top, Fm, Fl, Sw, Sf, Slc, Sr and Gco. Dewatering structures, convolute bedding and growth faults occur. Sandstone-mudstone couplets with wavy (Sw), lenticular (Slc), £aser (Sf) and oscilltory current ripple lamination (Sr) FA2 (massive and laminated Thick intervals (up to100 m) of dark-gray to In the eastern margin of the basin dominant Mud £at in a deltaic plain. Coal indicates humid dark mudstone) greenish mudstone. Occasional minor facies in C8, C6, C4 and C2 members and in climate. Fragmented freshwater mollusks bioturbation. Limited interbeds of trough Leon Formation suggest a high-energy environment. cross-laminated sandstone, and up to 30-cm- Dino£agellates and microforaminiferal linings thick coal seams. Occasional thin, disorganized indicate local marine in£uence bivalve-bearing shell-beds. Local microforaminiferal linings and dino£agellates. Fragmented and disarticulated bivalves belonging to the genus Pachydon, Anondondites and Mytylopsis, and gastropods Sheppardioncha (Fig.6a). Discrete levels with microforaminiferal linings and dino£agellates including Homotryblium £oripes, Cordosphaeridium inodes, Polysphaeridium subtile, Achomosphaera,and Spiniferites FA3 (channelized sandstones Medium- to thick-bedded, medium-to coarse Interbedded with FA4 in Upper Carbonera Stream £ow deposits. Loosely de¢ned large- and conglomerates) grained, and pebbly sandstone. Gravel lags and (C5^C2 members) to the west, and in C1and scale, low-angle planar cross-strati¢cation, mudstone intraclasts common at base of Lower Guayabo everywhere. Interbedded with absence of well de¢ned normal grading and individual beds. Beds have erosive bases above FA5 and FA6 in Upper Guayabo Formation frequent £oating pebbles suggest deposition in

r mottled sandy mudstones and siltstones, and braided £uvial channels

00TeAuthors The 2010 extend laterally up to few tens of meters. Commonly £oating pebble clasts occur. Granule and pebble stringers loosely de¢ning large-scale planar cross strati¢cation occur ai Research Basin r 00TeAuthors The 2010 r 00BakelPbihn t,Erpa soito fGocetss&EgnesadItrainlAscaino Sedimentologists of Association International and Engineers & Geoscientists of Association European Ltd, Publishing Blackwell 2010

Table 2. (Continued)

Facies Association Description Stratigraphic occurrence Interpretation

rarely.Frequently,strata grade upward into variegated mudstone (FA4) FA4 (overbank ¢nes) Reddish to brown, massive to crudely strati¢ed Dominant facies in C5^C2 members to the west Fluvial £oodplain environment. Dissecation sandy mudstone and siltstone. Ubiquitous and in C1and Lower Guayabo to the east. Less cracks, pervasive mottling and ferruginous mottling and root traces (Fig. 6b). Sporadic frequent in Upper Guayabo nodules indicate pedogenesis during mudcracks (Fig. 6c) and iron nodules (Fig. 6d). £uctuating wet^dry conditions Lenticular, normally graded, thin sandstone interbeds FA5 (granule to pebble Medium- to thick-bedded, clast-supported Occasionally in C1member; Frequent in upper Stream £ow deposits in subaerial alluvial fans conglomerates and granule and pebble conglomerates. Individual part of Lower Guayabo, and Upper Guayabo sandstones) beds have sheet-like and lenticular geometry,

poor developed subhorizontal strati¢cation and Colombia sedimentation, foreland-basin on Controls rarely low-angle through cross-strati¢cation and clast imbrication. Moderate sorting. Flat, non erosional bases are common (Fig. 6e). Interbedded with FA4 and FA3 FA6 (massive, coarse Up to10 m-thick, dominantly clast-supported Exclusively in upper part of Lower Guayabo, Gravel bars in £uvial channels on alluvial fan conglomerates and cobble and pebble conglomerate (Fig. 6f). and Upper Guayabo sandstones) Subangular to well rounded clasts. Individual beds have ribbon-like geometry,latterally continuous for tens of metes and display basal scours. Moderate to poor sorting, ungraded to reverse grading and crude imbrication. Lenticular sandstone interbeds. Lithofacies Gcd, Gco, Sm. Interbedded with FA3 and FA 885 M. Parra et al.

500

400

300 León 200

300 100 200

200 C1 0 C2 100 10. Gazatavena-Gazamumo 100 C2 0 7. Bellavista 0 400 9. Gazaunta north C3 700 300

600 200 C4 500 C4 500 100 C5 400 C1 0 C5 6. Humea 300 200

200 100 C6 100 0 5. Maya

0 8. Gazaunta south

Fig. 4. Measured straigraphic pro¢les of the Carbonera (C6^C1members) and Leo¤ n formations in the southeastern sector of the Medina Basin (locations in Fig.1b), including lithostratigrahic correlation based on ¢eld-based and remote-sensing observations, interpreted facies associations and palaeocurrent measurements. Locations of facies photographs of Fig. 6 are shown. gether,these features representdeposition in the proximal sively coarser grained braided stream and sheet£ood sector of alluvial fans. deposits become more abundant upsection. Finally,coarse alluvial-fan conglomerates prograded eastward and be- yond the eastern margin of the basin toward the Llanos Facies distribution plains. A coeval increase in tectonic deformation rates in Both ¢ne- and coarse-grained strata constitute the sedi- the Eastern Cordillera is suggested by the ¢rst occurrence mentary ¢ll of the Medina Basin. Coarse-grained £uvial of growth unconformities within the coarse conglomerates deposits are commonly con¢ned to the western border of of the Upper Guayabo Formation (Mora, 2007). the basin and appear in units as old as laterally equivalent Palaeocurrent indicators re£ect a predominant easterly strata to the C6^C5 units of the eastern margin (Parra etal., transport, locally varying from NE to SE directions (Figs 4 2009a; Pro¢les1^4; Fig.7). Conversely,¢ne grained lacus- and 5).This palaeo£ow pattern, the trend toward an east- trine and marginal marine deposits are almost exclusively ward change of facies from alluvial to estuarine strata, and restricted to the eastern margin of the basin.There, the ba- the presence of growth strata within the early lower Mio- sin ¢ll can be subdivided into two coarsening-upwards cy- cene to Pliocene strata clearly indicate syntectonic sedi- cles, largely delineated by the eastward progradation of mentation related to the uplift and denudation of braided stream deposits that constitute the C1 member of mountainous terrain to the west of the basin. the Carbonera Formation over areas dominated previously by estuarine systems (C5^C2 members; Fig. 7). Spatially Age constraints extensive freshwater-lake deposition punctuated by short- lived marine incursions (facies association FA 2) of the We build upon our chronostratigraphic framework re- Carbonera and Leo¤ n formations exclusively occur in the leased previously for the Late Cretaceous ^ Oligocene easternmostdistalpartofthebasin.This facies association fromtheMedinaarea(seeJaramillo&Dilcher,2000;Parra in the Leo¤ n Formatio¤ n is 450 m thick and marks the begin- et al., 2009a, and references therein) by providing a new ning of the uppermost coarsening-upward cycle. Progres- biozonation based on palynomorphs for the Carbonera

r 2010 The Authors 886 Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Controls on foreland-basin sedimentation, Colombia

1000

900

800

700

400 Upper Guayabo 600 300

500 200

400 100

300 0 1200

12. Tontogüe 3 200 1100

100 Lower Guayabo 1000

900 0 Carbonera (C1) + León 13. Portones 800

11. Tontogüe 2 700

600

500

400 Carbonera C1 300

200

100

0

11. Tontogüe 1

Fig. 5. Measured straigraphic pro¢les of the Carbonera Formation and the Guayabo Group in the northwestern sector of the Medina Basin (locations in Fig.1b), including lithostratigrahic correlation based on ¢eld-based and remote-sensing observations, interpreted facies associations and palaeocurrent measurements. Locations of facies photographs of Fig. 6 are shown.

r 2010 The Authors Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 887 M. Parra et al.

Fig. 6. Photographs of representative sedimentary facies from the Mio^Pliocene sedimentary units of the Medina Basin. Locations are indicated in Figs 5 and 6. (a) Mollusc-rich horizon at the top of the C2 member (Huesser Horizon) in Pro¢le 7 (Bellavista). Approximately 1.5 m-thick shell bed formed by densely packed specimens of the gasteropod Sheppardiconcha (shown in inset) and molds of thin-shelled bivalve Anondonites (Go¤ mez, A. et al., 2009) embedded in muddy matrix (facies association FA1). Dip direction is to the left. (b) Well- developed mudcracks and root traces in pedogenically altered £oodplain deposits (facies association FA4) of the C1member in Pro¢le11 (Tontogˇe 2). See pencil for scale. Dessication cracks (c) and ferruginous nodules (d) in massive, pedogenically altered £oodplain siltstones and silty sanstones of the C1member in Pro¢le11(Tontogˇe1). (e) 2 m-thick, subtabular, granule-to-pebble conglomerate bed with nonerosive basal contact (facies association FA5) overlying £oodplain siltstones in the Lower Guayabo Formation along Pro¢le12 (Tontogˇe3).(f)View towardtheNof massive cobble and blockconglomerates of theUpperGuayaboFormation inPro¢le13(Portones). Bedding dip is 121 toward the SW (left).

r 2010 The Authors 888 Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Controls on foreland-basin sedimentation, Colombia

NW SE Alluvial-fan deposits

? Upper Guayabo

Braided fluvial deposits 12. Tontogüe 3 10. Gazatavena-Gazamumo 13. Portones

Estuarine deposits 12. Tontogüe 2 León L. Guayabo L.

11. Tontogüe 1 C1 + León 8. Gazaunta sur

9. Gazaunta norte Carbonera (C1) Carbonera Carbonera (C1) Carbonera 7. Bellavista Huesser horizon

Gacenera horizon ~ 300 m 6. Humea estimated in C6-C5 seismic lines

3. Gacenera Guaicarama horizon 5. Maya C7-C6

Base C7 4. Guaicarama

Base C7

2. Guadualera 1. Piñalerita ~5 km

Fig. 7. Scheme of facies distribution in the Medina Basin based on a simpli¢ed representation of measured stratigraphic pro¢les 5^13 (this study)and1^4 (Parra, M et al., 2009a). Locations of pro¢les are shown in Fig.1. Easterly sourced coarse-grained £uvial strata in the Carbonera Formation occur mainly along the western sector of the basin and grade eastward to temporarily marine-in£uenced lacustrine deposits.The distribution of facies delineate two main coarsening upward cycles. See text for discussion.

(C5^C1 members), Leo¤ n, Lower Guayabo and Upper is de¢ned by the FAD of Grimsdalea magnaclavata and cor- Guayabo Group, which follows standard biostratigraphic responds to the upper part of the early Miocene.The FAD methods (Traverse, 1988). Palynological zones were cali- of Crassoretitriletes vanraadshooveni de¢nes the top of Zone brated with foraminiferal (Diaz de Gamero, 1977a, b, 1985, T-14, which is dated as the upper part of the early Miocene 1988, 1989, 1997; Wozniak & Wozniak, 1987; Diaz de Ga- to middle Miocene.The top of middle Miocene ZoneT-15 mero & Linares, 1989; Rey, 1990), vertebrates (Linares, is marked by the FAD of Fenestrites spinosus.TheFADofCy - 2004) and magnetic stratigraphic information (Herrera, atheacidites annulatus marks the top of ZoneT-16, which cor- 2008) from the Urumaco Basin inwesternVenezuela. responds to the upper part of the middle Miocene to late Our main results are summarized in Fig. 8. Units C5 to Miocene.The ZoneT-17 is de¢ned at the top by the LAD Upper Guayabo were deposited within palynological of Lanagiopollis crassa, and is dated as late Miocene to ear- zones T-12 to T-18 (biozones after Jaramillo & Rueda, liestPliocene.Finally,the ZoneT-18encompasses the Plio- 2004), corresponding to early Miocene to Pliocene time cene to modern times. (Fig. 4).The pollen zone ZoneT-12 is de¢ned at the base by the last appearance datum (LAD) of Cicatricosisporites Unroofing of Eastern Cordillera source areas dorogensis, and at the top by the ¢rst appearance datum (FAD) of Echitricolporites maristellae.Thiszoneisdatedas We evaluate the unroo¢ng history of the basement-cored the lower part of the early Miocene.The top of ZoneT-13 uplift of the Quetame Massif by tracking the occurrence r 2010 The Authors Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 889 890 Jaramillo (2004), Rueda & Jaramillo Jaram by sections stratigraphic on based 8. Fig. Parra M. epciey.h lp ftecreidctssdmn-cuuainrts ae ae ndcmatdtikesaeidctd(see indicated are thickness decompacted on based Gradstein Rates rates. from scale S1).Time Table sediment-accumulation and indicates text curve the of slope respectively).The Age (Ma) ai Research Basin ayooia iznto n opst tairpi eto fteLt rtcosPicn taao h eiaBasin Medina the of strata Cretaceous^Pliocene Late the of section stratigraphic composite and biozonation Palynological tal et Late Cretaceous 07 02 55 15 20 70 75 80 . 119 r 00BakelPbihn t,Erpa soito fGocetss&EgnesadItrainlAscaino Sedimentologists of Association International and Engineers & Geoscientists of Association European Ltd, Publishing Blackwell 2010 25 56 55 54 25 40 45 50 55 60 65 94 aecn oeeOligocene Eocene Paleocene 163 tal et 20)adJaramillo and (2005) . lo&Dlhr(00,Parra (2000), Dilcher & illo Channelized sandstone Conglomerate Mudstone Sandstone Interlayered sandstoneandmudstone Variegated mudstone tal et 29 ,2004). ., 27 tal et 66 20)(eeecscddi oa ceewt ubr1 n 3, and 2 numbers1, with scheme zonal in coded (references (2009) . 35 etal 72 34 ,(09) n hssuyTeasgmn fbooe sbsdon based is biozones of assignment study.The this and (2009a), ., 207 30 96 462 502 Miocene. 104 89 10 207 Thickness 4000 5000 6000 (km) 1000 2000 3000 Plio. Reference Palynozone Epoch Sub-epoch /Stage Biozone Guadalupe Barco Los Cuervos C8 C7 - C5 C3 C2 C1 León Upper Guayabo Unit r 00TeAuthors The 2010 Controls on foreland-basin sedimentation, Colombia of distinct conglomeratic clasts in the Oligo^Miocene strata. Such a scenario limits the maximum value of strata of the Medina Basin. Conglomerate clasts are com- eroded thickness to that of the overlying Cretaceous sec- posed of two main lithologies: vein quartz and sedimen- tion (6.5 km). We, therefore, estimate an apparent long- tary lithic fragments, with an increasing abundance of the term 1D denudation rate of as much as 0.3 mmyr 1 for latter upsection (Fig.9). Conglomerate petrography docu- the area of the Quetame massif in the interval between ments a ¢rst appearance of diagnostic Upper Cretaceous 23 and 2 Ma. Similar apparent exhumation rates have glauconitic sandstone fragments in the lower Miocene C1 been inferred from thermochronological data in the East- Member of the Carbonera Formation (Fig.9). Glauconitic ern Cordillera (Parra et al., 2009b). sandstone gravel is present throughout the Miocene sedi- ments and constitutes as much as 40% of the bulk sedi- mentarycomposition.However,withintheMiocene Sediment-accumulation rates units, we identi¢ed two peak intervals in the occurrence 1D analysis of glauconitic sandstone clasts. The ¢rst peak occurs in the upper part of the C1 Member, and the second peak in Sediment accumulation in the Medina Basin re£ects a the Guayabo Group. These zones are separated by inter- three-stage history characterised by an Eocene^early vals with o 4% of glauconitic sandstone clasts. In addi- Oligocene episode of slow sediment accumulation with tion, a small amount of phosphatic sandstones (up to 3%), rates of 30^70 m my 1 that separates two periods of and as much as 25% of siliceous siltstones are associated faster accumulation during Late Cretaceous^Paleocene with the ¢rst peak of glauconitic sandstones in the upper ( 100 m my 1) and late Oligocene^Pliocene time sections of the C1Member.Finally,redbed clasts indicative ( 220 m my 1), respectively. In agreement with the dis- of the Upper Palaeozoic sedimentary units are absent in tribution of Cenozoic sedimentary facies and unconfor- the Oligocene^Miocene sedimentary record of the basin. mities in the southern Basin The ¢rst appearance of Palaeozoic red sandstone clasts is (Go¤ mez et al., 2005), plausible explanations for these sedi- observed in the undated lower alluvial terrace levels of the ment accumulation trends and tectonic subsidence rates Humea and Gazaunta rivers of the inferred Quaternary have been explored by Parra et al.(2009a).Theyinterpret age (see Fig.1for location). this pattern as the result of alternating episodes of craton- In the source area, the Upper Cretaceous glauconitic ward and orogenward migration of the orogen-basin pair. sandstone-bearing units (the Une, Chipaque and Guada- Here, we particularly consider the signi¢cance of the lupe formations) have been completely eroded from the late Oligocene^Pliocene episode of rapid accumulation. basement-cored Farallones anticline and only crop out A ¢rst increase in the rate of sediment accumulation oc- along its £anks (Fig. 1). From the gravel petrography data, curs at the base of BiozoneT-10, at 30 Ma, which corre- we interpret a normal unroo¢ng sequence that can be sponds to the base of the C7 member of the Carbonera summarized as follows (Fig.9): (1) an absence of glauconi- Formation in the Guadualera pro¢le (Fig. 8). On the basis tic sandstone clasts in the conglomerates below the C1 of a comprehensive examination of exhumation patterns Member suggests a source dominated by Palaeogene derived from thermochronology and of other indicators rocks; (2) during early Miocene accumulation of the upper of deformation in the Eastern Cordillera, such an episode portion of the C1 Member, an important fraction of the was likelyassociatedwith an eastward migration of the tec- source area included glauconitic and phosphatic sand- tonic loads to the present-day axial sector of the Eastern stones, and siliceous siltstones indicative of erosion of the Cordillera, toward the Soapaga fault (Parra et al., 2009b). Upper Cretaceous Guadalupe Group; (3) conglomerates Our new data reveal a second, more pronounced increase in the uppermost portion of the C1 Member and the in rates of sediment accumulation at the beginning of the coarse-grained strata laterally equivalent to the lower part earlyMioceneBiozone31(23 Ma). During the early of the Leo¤ n Formation are devoid of glauconitic sand- Miocene, spanning 7 my, accumulation of 3350m of stones and siliceous siltstones, suggesting an exposure of sediments implies peak mean accumulation rates of the mudstone-rich Cretaceous Chipaque Formation 480 m my 1. Our data further suggest that middle rather than the Guadalupe Group; and (4) the renewed oc- Miocene accumulation rates decline to values of 100 m currence of glauconitic sandstone likely re£ects unroo¢ng my 1during accumulation of the Leo¤ n and Lower Guaya- of the Cretaceous during the late Mio- bo formations. However, we interpret this result with ex- cene^Pliocene accumulation of the Guayabo Group. treme caution, as this part of the composite section is Wethus deriveapproximate denudationrates on theba- based on lithostratigraphic correlation of £uvial deposits sis of the thickness of the reconstructed erosion window in theTontogˇe section, in the northwest of the basin, with (e.g., DeCelles et al., 1991) and the time of denudation as their distal, laterally equivalent lacustrine units in the constrained by the statigraphic age of the appearance of southeast, spanning a distance of 35 km along the struc- particular clasts. Upper Cretaceous glauconite-bearing tural termination of the Guavio anticline (Figs 1 and 7). units typically have a thickness of 1.5 to 2 km in the East- Despite these unavoidable di⁄culties imposed by the ern Cordillera (Mora et al., 2006). An upper limit for the location of the best-exposed sections in the densely vege- thickness of the eroded rock is provided by the absence of tated area, our correlation suggests that rapid sediment ac- Palaeozoic clasts in the investigated Oligocene^Miocene cumulation prevailed throughout the Miocene^Pliocene. r 2010 The Authors Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 891 M. Parra et al.

Thickness Unit DETRITAL MODES EROSION WINDOW (km) Biozone 630

6000 Pliocene

Upper Guayabo

m

F

627 e n

623 U 618 626

5000 616 .

- m

641 a

F

p

i

615 e h

Middle-Late Miocene

u

C q 613

612 Upper Cretaceous, glauconite-bearing units C1

4000 611 Guadalupe Group 642

610 C2 Early Miocene C3

3000

608 607 Paleocene-Eocene units

605 C7 - C5

2000

Oligocene 603 0 10 20 30 40 50 60 70 80 90 100

C8 % of gravel clasts Eocene Shale Sandstone Phosph. sandstone Mudstone Glauc. sandstone Chert 1000 Siliceous siltstone Vein quartz Los Cuervos Paleocene Conglomerate Barco Channelized sandstone Variegated mudstone Interlayered sandstone and mudstone Sandstone Guadalupe 5 Mudstone

Fig. 9. Compositional trends in Eocene^Pliocene conglomerates of the Medina Basin. Black circles denote the stratigraphic position of conglomeratic samples. Clasts of Upper Cretaceous glauconitic sandstone, phosphatic sandstone and siliceous siltstone occur in Miocene strata of the Carbonera Formation and Guayabo Group, documenting progressive unroo¢ng of the Eastern Cordillera (right panel). Rawdata and recalculated modes are reported inTable1. See text for discussion.

r 2010 The Authors 892 Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Controls on foreland-basin sedimentation, Colombia

3D sedimentary budget early Oligocene accumulation, rapid sediment deposition at rates of100^350 m my 1 (compacted thickness) have oc- In order to account for potential lateral thickness variations curred since the Miocene, with an absolute minimum dur- and to provide a more regionally meaningful assessment of ing accumulation of the middle Miocene Leo¤ n Formation. the sedimentary budget, we interpreted an extensive grid The more regionally meaningful, 3D reconstruction of se- of 70 2D industry multichannel seismic re£ection pro- diment accumulation reveals patterns not captured in the ¢les totalling 1800 km.We translated six mapped lithos- 1D reconstruction. First, as a result of the lower resolution, tratigraphic limits into the seismic pro¢les intersecting the the onset of rapid sediment accumulation at 30 Ma is outcrop exposures close to the measured sections. We not portrayed in the 3D sedimentary budget. Second, the chose horizons that constitute clearly traceable markers absolute maxima in mean sediment-accumulation rates either exposed in the basin or in the seismic pro¢les.We occur during the youngest history of the basin, repre- trace stratigraphic limits southward along the hanging wall sented here as late-Miocene to . This pattern is of the Guaicaramo thrust toward the area where the thrust independently captured in the sedimentary budget of each loses displacement and ¢nally terminates, allowing the in- block of the Guaicaramo fault (Fig.10).Third, higher sedi- terpreted horizons to be extended eastward toward the ment-accumulation rates occur in the western, hanging- footwall.We further tied seismic re£ectors with the strati- wall block of the thrust throughout the basin history. Fi- graphy based on interpreted depths of well-de¢ned hori- nally, a local maximum in sedimentation rates restricted zons from borehole reports. We interpret ¢ve rock units to the hanging-wall block of the thrust occurs during de- bounded by the following horizons (Table 3): (1) the top of position of the C1member. the Eocene Mirador Formation sandstones; (2) the top of The spatial distribution of sediment-accumulation the C6 member, de¢ned by the appearance of the fossilifer- rates for the ¢ve time windows analysed displays a consis- ous Guaicarama horizon; (3) the top of the C2 member, de- tent pattern of eastward-decreasing rates without major ¢ned by the outcrop of the fossiliferous Huesser horizon; north^southvariations along the strike (Fig.11). Our ana- (4) the top of the C1 member, de¢ned by the change of £u- lysis also portrays widespread increases in sedimentation vial overbank deposits and channelized sandstones to rates during the accumulation of the lower Miocene C5^ monotonously bedded, organic-rich mudstones of the C2 members of the Carbonera Formation and enhanced Leo¤ n Formatio¤ n; and (5) the top of the Leo¤ n Formation the accumulation in the proximal, western part of the ba- mudstones. Stratigraphic ages for these horizons are inter- sin during deposition of the C1member.Likewise, an over- polated from the palynological zonation. all increase in sedimentation rates is a characteristic since Based on interpolations between seismic re£ectors for the late Miocene, but is slightly more pronounced in the each of these horizons, we constructed surfaces in a two- northern part of the basin. way travel time for the hanging- and footwall blocks of the Guaicaramo thrust. In order to avoid errors in areas of poor seismic-re£ection coverage, we exclude the area in the footwall beneath the thrust sheet. Depth conversion DISCUSSION was carried out for surfaces of each block using seismic ve- Early Miocene basin evolution locities obtained from check-shots surveys from the Co- poro-1 and Medina-1 wells in the hanging-wall block of Integration of the multiple datasets presented in this the Guaicaramo fault, and from the Guacav|¤ a-1, Chapar- study allows a correlation of tectonic episodes in the oro- ral-1, San Pedro-1 and Up|¤ a-1 wells in the footwall (see gen with the distribution and rates of sediment accumula- depth^time relations in Fig. S1). Finally, to reveal spatio- tion in the adjacent basin.The early Miocene represents a temporal variations in sediment-accumulation rates, we minimum age for folding associated with the initial mo- calculated an average sediment-accumulation rate (com- tion on the Lengupa¤ fault west of the basin, as supported pacted) for each of the ¢ve interpreted rock-units, com- by growth^strata relationships in rocks equivalent to the puted by dividing the volume of rock between successive C5^C2 members. An independent assessment of the tim- depth-converted surfaces (evaluatedwithin the 2D projec- ing of thrust-related exhumation in the Eastern Cordillera tion area of the smaller, usually upper surface of each rock is available from the mineral cooling ages derived from package), by the area of that 3D surface. In addition, we apatite and zircon ¢ssion-track data from the eastern £ank generated maps of sediment-accumulation rates, obtained of the Eastern Cordillera.This thermochronological infor- by dividing isopach thicknesses by the geologic time re- mation documents the initial exhumation and uplift dur- presented by each unit. Parameters for volumetric calcula- ing the middle-Eocene to Oligocene (40^30 Ma) in its axial tions and results are reported inTable 3. sector (Floresta Massif) and during the late Oligocene^ Figure10 shows the middle Eocene^Holocene history of early Miocene (25^20 Ma) along its eastern £ank (Toro, variation in sediment-accumulation rates.The sediment- 1990; Parra et al., 2009b). budget pattern for the entire area resembles that of the1D An abrupt two- to four-fold increase in sediment-accu- reconstructed basin history, albeit with a broader resolu- mulation rates is observed at the base of the lower Mio- tion resulting from the larger time windows into which cene lower Carbonera Formation (C6^C5 member) in the the thickness data are binned. After limited late Eocene^ Medina Basin (Figs 8, 10 and 11), which followed a period r 2010 The Authors Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 893 M. Parra et al. C1 C8 Barco Guaduas Guadalupe León Cuervos Mirador Upper Guayabo C2-C5 C6-C7 Guayabo Lower WE

400

3D compacted, hanging wall 200 3D compacted, footwall 1D decompacted

1D compacted Sediment accumulation rate (m/my)

0 Pli. Miocene Oligocene Eocene Paleocene Late Cretaceous

04020 60 Fig. 10. Reconstructed one-dimensional sediment-accumulation rates for the Medina Basin (green and black dotted lines), and three- dimensional (3D) sedimentary budgets for the Medina and proximal Llanos basins (blue and red lines, respectively). Errors in 3D accumulation rates are indicated by the shaded areas. Episodes of faster accumulation are coeval to deposition of coarse-grained facies in both the western and eastern sectors of the basin, as indicated by lithologies in the upper panel (colour shading as in Fig. 5). Pliocene eastward progradation of coarse conglomerates is contemporaneous with faster shortening rates in the eastern £ank of the Eastern Cordillera. See text for discussion. of rapid accumulation that commenced in the late Oligo- that an upsection increase in tectonic subsidence re£ects cene ( 30 Ma). Sediment-accumulation rates are primar- the relative shift of the depositional site toward a more ily a¡ected by tectonic subsidence in foreland basins where proximal sector within the foredeep depozone, in response accommodation space provided by lithospheric £exure is to the migration of the £exural pro¢le accompanying nearly ¢lled or over¢lled with sediments (Burbank et al., growth and forward propagation of the orogenic wedge. 1988; Jordan, 1995). In the foreland of the Colombian An- However, the e¡ect of this tectonically enhanced accom- des, a dominant orogen-perpendicular, eastward palaeo- modation space is attenuated toward the distal part of the current direction observed in Miocene units and the lack basin. As a result, farther away from the deformation front, of evidence of Miocene forebulge erosion (e.g., Bayona such an increase in sedimentation rates may be delayed etal., 2008) point toward a ¢lled-to-over¢lled foreland ba- with respect to thrusting (e.g., Flemings & Jordan, 1990; sin. However, nonmarine basins do have a topographic Jones et al., 2004). Alternatively, other £exural models gradient and the fan apex might be as high as several hun- (Quinlan & Beaumont,1984; Beaumont et al.,1988) predict dreds of metres (e.g., Blair & McPherson, 1994). In such a that, under the presence of static loads or even tectonic case, sediment accumulation rates may overstimate subsi- quiescence, such deepening and narrowing of the basin dence rates. For the Medina basin, we infer that maximum may result from stress relaxation on long-time scales in a elevation at the fan apex never exceeds the present-day viscoelastic plate. In the eastern £ank of the eastern Cor- elevation of 300 m at the outlets of main rivers toward dillera, synchroneity between independently constrained the Llanos basin alluvial plain (e.g., the Humea River, Fig. early Miocene ages of thrustbelt advance toward the Len- 1c). This represents only a minor overestimation, and gupa¤ fault (Parra et al., 2009b) and an increase of tectonic hence permits using sediment-accumulation rates as a subsidence in the Medina Basin suggest a causal relation- proxy for tectonic subsidence. Foreland basin models that ship between these phenomena. Although our data cannot consider crustal accommodation on a elastic plate (e.g., completely rule out viscoelastic relaxation of the South Flemings & Jordan, 1989; DeCelles & Giles, 1996) suggest American plate, such synchroneity can be explained with

r 2010 The Authors 894 Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Controls on foreland-basin sedimentation, Colombia N

° ′ ° ′ ° ′ ° ′ N ′

73 30 W 73 0 W 73 30 W 73 0 W ′ 0 0 °

Guayabo León ° 5 5

t s u t r s h u t r h o t o am N N r ′ ′ a ram c a ai c 30 30 Medina u ai ° ° G Medina u 4 4 basin G basin Llanos Llanos basin basin

0 to 11.6 ± 1 Ma 11.6 ± 1 to 16.0 ± 1 Ma

mean sediment accumulation rate: mean sediment accumulation rate:

N hanging wall: 195 m/my hanging wall: 104 m/my ′

0 footwall: 77.5 m/my ° footwall: 173 m/my 4 N N ′ ′ 0 0 C1 C2 - C5 ° ° 5 5

t s u r h t o N N ram ′ ′ a c ai 30 30 u ° ° Medina Medina G 4 4 basin basin Llanos Llanos basin basin

16.0 ± 1 to 19.0 ± 1.5 Ma 19.0 ± 1.5 to 25.3 ± 1.5 Ma

mean sediment accumulation rate: mean sediment accumulation rate:

N hanging wall: 188 m/my hanging wall: 156 m/my ′ 0

° footwall: 98 m/my footwall: 114 m/my 4 73°30′W 73°0′W

N Sediment accumulation rates in m/my ′

0 C6 - C8 ° 5 hanging wall footwall

300 t s u r h t o

N am ′ r a c

30 ai

° u Medina G 4 basin m/my Llanos basin

25.3 ± 1.5 to 42.0 ± 2 Ma

mean sediment accumulation rate:

N hanging wall: 38 m/my 0 ′ 0

° footwall: 15 m/my

4 010203040505 73°30′W 73°0′W Kilometers

Fig. 11. Spatial distribution of sediment-accumulation rates (compacted thickness) for ¢ve interpreted Eocene to Holocene stratigraphic units in the hanging wall (Medina Basin) and footwall (Llanos Basin) of the Guaicaramo thrust.Towns and the present-day sur¢cial trace of the thrust and indicated for reference. Inset shows the location of the mapped area.

r 2010 The Authors Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 895 M. Parra et al. a purely elastic plate. Furthermore, in-phase thrusting facies distribution and the reconstructed early Miocene ac- and rapid sediment accumulation 20 km away of the de- cumulation history of the Medina Basin support those formation front suggest an almost immediate response foreland-basin models that predict coeval thrusting and time between crustal loading and the increase of sediment accumulation of coarser grained facies in the proximal part £ux, which ultimately results in coeval thrusting in the of the foredeep depozone (e.g., Burbank et al., 1988; Schlu- hinterland and gravel progradation into the basin. Such a negger et al., 1997a). Our data suggest that this mechanism scenario is di¡erent from the predictions of numerical may have been active at multiple time scales. First, coarse- models (e.g., Flemings & Jordan, 1990; Sinclair et al., 1991), grained facies of the C6^C1members of the Carbonera For- and from the results of case studies (e.g., Schluneggeretal., mation were deposited in the proximal foredeep during an 2007) that document a response time of several million episode of fast subsidence lasting 7 m.y.during the early years between crustal thickening and enhanced sediment Miocene. Second, peak eastward progradation of these transfer.We suggest that the close proximity of the Medina coarse-grained sediments towards the easternmost sector basin to the location of the Early Miocene deformation of the present-day Medina wedge-top basin (C1 member) front in the Quetame Massif may have conditioned such a appears to have occurred during episodes of maximum lo- rapid response, which is di¡erent from the larger response cal subsidence associated with active thrusting. time of sediment transport from a sediment source lo- cated beyond the wavelength of the orogen/basin interac- Middle-Miocene basin evolution tion. In addition, such a shorter response time than that predicted by numerical models that consider di¡usion as A second coarsening-upward cycle corresponds to the ac- the mechanism governing sediment transfer suggests that cumulation of the middle Miocene Leo¤ n Formation and it can rather be dictated by advection, as recent models the late Miocene^Pliocene Guayabo Group (Fig.7). Similar suggest. to the underlying coarsening-upward cycle of the upper In the Medina Basin, the C6^C1 members of the members of the Carbonera Formation, this coarsening-up- Carbonera Formation comprise a lower Miocene ward pattern is more pronounced in the eastern sector of coarsening upward cycle approximately 2500 m thick. We the basin, where the Leo¤ n Formation comprises tidally in- calculate an average 1D decompacted accumulation rate £uenced lacustrine deposits punctuated by short-lived of 480 m my 1 over a span of 7 Myr (Figs 8 and 10), marine incursions. This mud-dominated sequence pro- which is within the upper limit of long-term accumulation gressively changes westward to laterally equivalent £uvial rates determined for most nonmarine foreland basins deposits in the eastern limb of the Nazareth syncline (Fig. (Burbank et al., 1988; Meigs et al., 1995; Schlunegger et al., 7). Such a lateral facies change caused the lower portion of 1997b; Echavarria et al., 2003; Uba et al., 2007). Sedimen- this cycle to directly overlie similar £uvial deposits of the tary facies and provenance analysis of the Carbonera For- C1 member, thus partially obscuring the coarsening-up- mation document the accumulation of westerly sourced ward pattern (Fig. 7). A similar pattern of a westward in- sediments derived from Mesozoic and Palaeogene sedi- crease in the sand-to-mud ratio in the Leo¤ n Formation mentary rocks from the Eastern Cordillera along an east- occurs approximately 100 km to the north along the wes- ward-sloping alluvial plain that transitioned to a low- tern margin of the Llanos basin (Cooperet al., 1995). Poten- energy, tidally in£uenced estuarine system. The distribu- tial causes of such an anomalous widespread accumulation tion of sedimentary facies reveals an earlier accumulation of ¢ne-grained sediments in temporarily marine-in£u- of £uvial deposits along the western margin of the basin enced, primarily lacustrine environments in proximal sec- (upper part of C7^C5 members; Guadualera^Gacenera tors of the foredeep may have included several factors. pro¢le;seeFig.7and alsoParraetal., 2009a) comparedwith These entail eustatic sea level change (e.g., Van Wagoner, the east (Guaicaramo and Maya sections; Figs 4 and 7). 1995), reduced erosion rates in the source area due to an Subsequent forelandward migration of coarser-grained, arid (e.g., Paola et al., 1992; Schlunegger & Simpson, 2002) £uvial deposits resulted in the accumulation of the C1 or stable (Molnar, 2004) climate, and an exposure of ero- member at the eastern margin of the basin (Gazaunta sec- sion-resistant lithologies in the source area causing a gen- tion; Figs 4 and 7). Our volumetric sedimentary budget re- eral decrease in erosion rate and sediment supplyleading to veals that such a progradation of coarser-grained facies under¢lling or sediment starvation in the basin (e.g., likely occurred during a period of peak accumulation and Schlunegger & Simpson, 2002; Carroll et al., 2006). Alter- subsidence rates, whichwas restricted to the Medina Basin natively,accumulation of ¢ne-grained sediments may have in the latest early Miocene ( 19^16Ma). Farther east, in resulted from waning tectonics (e.g., Jordan et al., 2001) or the footwall of the Guaicaramo fault, accumulation rates from the exposure of nonresistant, ¢ne-grained lithologies during deposition of the C1 member are slightly lower that are less likely to generate coarser sediments (DeCelles compared with those of the underlying lower Miocene et al., 1991). Below,we explore each of these scenarios. units (Figs10 and11). First, recently published sea-level curves (e.g., Kominz In light of the reconstructed position of the orogenic et al., 2008; and references therein) do not show any signif- front, we interpret such a pattern as the result of an episode icant increase in eustatic level between early and middle of tectonic thickening along a stationary deformation front Miocene time, arguing against a causal link between mid- located immediately to the west of the basin. Overall, the dle Miocene deposition of marine-in£uenced ¢ne-

r 2010 The Authors 896 Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Controls on foreland-basin sedimentation, Colombia grained sediments in the foreland of the Colombian Andes Flemings & Jordan, 1990). Geologic evidence supports and eustatic sea-level changes (Cooper et al., 1995; Go¤ mez the notion that both mechanisms are not mutually exclu- et al., 2003). Second, whether regional climatic change sive and may have operated virtually synchronously.Back- drove the accumulation of ¢ne-grained sediments in the ward stepping of the tectonic loads by out-of-sequence middle Miocene is unclear due to the paucity of detailed thrusting in the interior of the orogen is supported by the reconstructions of pre-middle Miocene climate condi- cross-cutting relationships of the Soapaga and Pesca faults tions. However, high-resolution palaeoclimate proxies in in the axial sector of the Eastern Cordillera (Fig.1a).There, northern South America for the last 13 m.y. suggest that a the Oligocene Concentacio¤ n Formation east of the Flores- wetter-than-present-day climate punctuated by intermit- ta Massif is truncated to the west by the east-verging Soa- tent aridity promoted rapid erosion during the middle paga Fault. Early and Middle Miocene apatite ¢ssion-track Miocene andPliocene times(Harris&Mix, 2002).In con- ages in the hanging-wall block (Parra et al., 2009b) most trast, an opposite climatic pattern (i.e., a relatively wet and likely re£ect a synchronous slip along this fault. Similar stable climate) prevailed during late Miocene time, which out-of-sequence reactivation in the interior of the Eastern may have resulted in low erosion rates (Harris & Mix, Cordillera has been documented 200 km farther north 2002).It is hard to envision that this post-middleMiocene (Bayona et al., 2008). On the other hand, Flemings & Jor- climatic pattern of diminishing wetness and increasing dan (1990) and Sinclairetal. (1991) demonstrated that wan- stability could have controlled the observed late Miocene ing tectonic activity in the thrust wedge generates foreland coarsening-upward trend in the deposits of the Medina basin accumulations with lens-shaped geometries, as op- Basin. If climate had played an important role, such a pat- posed to wedge-like geometries developed during active tern would have resulted in diminished rates of sediment thrusting. Based on subsurface data in the Llanos basin, supply,and thus would have prompted a contradictory ¢n- Cooper et al. (1995) show that middle Miocene mudstones ing-upward trend in the middle to upper Miocene strata. (their sequence T80) extend farther eastward to the Guya- Third, our unroo¢ng estimates document an early Mio- na shield than any of the older foreland basin strata. In cene to Pliocene erosion window in the Eastern Cordillera addition, our sedimentary budget shows that mean accu- encompassing up to 2 km of Upper Cretaceous glauco- mulation rates between the hanging and footwall blocks nitic-bearing units (Fig. 9). Clast composition suggests of the Guaicaramo fault were more similar during the that, within this unroo¢ng sequence, a relatively higher accumulation of the Leo¤ n Formation (104 vs. 78 m my1, contribution from the mud-rich, glauconitic-poor Chipa- respectively) than previously, during accumulation of the que Formation characterised the accumulation of most of C5^C1 members (207 vs.108 m my 1, respectively; seeTa- the ¢ne-grained middle Miocene Leon Formation. Over- ble 3 and Figs 10 and 11). Such patterns re£ect a more uni- all, gravel petrography data do support a correlation be- form distribution of tectonic subsidence along the tween the erodability of source-area lithologies and foreland basin during accumulation of the Leo¤ n Forma- grain-size trends. However, had a high erodability of the tion than before, and thus are compatible with the lens- source areas exherted the dominant role on sedimenta- shaped foreland strata.Taken together with the decline in tion, accumulation of ¢ne-grained sediments of the Leon rates of sediment accumulation, this suggests an episode Formation should have accompanied an increase in sedi- of diminishing tectonic loading in the Eastern Cordillera. ment accumulation rates as a consequence of an increase in sediment supply to the basin (e.g., Carroll et al., 2006; Late Miocene to Pliocene basin evolution Korup & Schlunegger, 2009). On the contrary, both 1D and 3D reconstructions of the post-early Miocene sedi- A major increase in grain size characterises the second ment accumulation history suggest that sedimentation coarsening-upwards cycle at the base of the upper Mio- rates declined during middle Miocene deposition of ¢ne- cene Lower Guayabo Formation. There, sediment accu- grained sediments of the Leo¤ n Formation. Subsequently, mulation in braided £uvial and alluvial-fan settings above an increase in sediment accumulation accompanied the estuarine and bayhead deposits of the Leon Formation progradation of coarse-grained facies of the middle Mio- documents an event of sediment progradation. East of cene to Pliocene Guayabo Group (Figs 7 and10).This pat- Medina,theLeon^Guayabo transition in theLlanos basin tern resembles the syntectonic origin of coarse-grained corresponds to a major change in the seismic character facies progradation in the proximal foredeep observed in from a seismic sequence exhibiting continuous re£ectors, other areas (e.g., Burbank et al., 1988; Paola et al., 1992; which include the Carbonera and Leon formations, to a Schlunegger et al., 1997b; Horton et al., 2004), and hence unit with irregular discontinuous subparallel re£ectors suggests that variability in tectonics, rather than climate, (Fig. 12). In contrast to the facies progradation episode erodability or eustasy exerted the de¢ning control on sedi- that occurs at the transition between the Early Miocene ment accumulation trends. C2^C1 members in the Medina basin, susburface data in- Plausible tectonic scenarios that explain the decrease in dicate that the late Miocene progradational event was accumulation (and subsidence) rates accompanying the much more regionally extensive. Upper Miocene^Plio- deposition of ¢ne-grained strata of the Leo¤ n Formation cene coarse-grained £uvial and alluvial-fan conglomerates include either backward stepping of thrust loads (e.g., De- were primarilysourcedfromUpperCretaceous units from Celles & Giles, 1996) or waning tectonic activity (e.g., the Eastern Cordillera and accumulated in the Medina r 2010 The Authors Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 897 M. Parra et al.

Table 3. Results from three-dimensional sedimentary budget of Eocene-Holocene units in the Medina and Llanos basins

Volume 2D Area at 3D Area at Age at Acc. rate Acc. rate Acc. rate Unit (km3) top (km2) top (km2) top (Ma) min (m my1) mean (m my1) max (m my 1)

Guaicaramo hanging wall (Medina Basin) Guayabo 1177 744 755 3.6 1.8 144 195 300 Leon 347 734 759 11.6 1.0 71 104 190 C1 522 876 924 16.0 1.0 103 188 1129 C2^C5 1102 1165 1284 19.0 1.5 101 156 344 C6^ C8 1020 1462 1526 24.5 1.5 32 38 48 Mirador 42.0 2.0 C1^C5 1624 876 924 16.0 1.0 160 207 293 Guaicaramo footwall (western Llanos Basin) Guayabo 6793 3382 3386 0 159 173 189 Leon 1153 3291 3380 11.6 1.0 53 78 142 C1 949 3351 3339 16.0 1.0 52 95 569 C2^C5 2118 3376 3387 19.0 1.5 74 114 250 C6^C8 939 3472 3628 24.5 1.5 12 15 18 Mirador 42.0 2.0 C1^C5 3067 3351 3339 16.0 1.0 84 108 153

CDP 4005 4129 4254 4379 4504 4629 4754 4879 5004 5129 5254 5379 5504 5629 5754 5879 6004 SP 2 64 126 189 251 314 376 439 501 564 626 689 751 814 876 939 1001

–1000

–2000

–3000

–4000

–5000 Two-way traveltime (ms) 1 kkmm –6000

CDP 4005 4129 4254 4379 4504 4629 4754 4879 5004 5129 5254 5379 5504 5629 5754 5879 6004 SP 2 64 126 189 251 314 376 439 501 564 626 689 751 814 876 939 1001 Upía 1

–1000

LLaa FFlolorridaida aanticlnticliinene t –2000 s u r hhrust t

a n –3000 ia s u CCusiana t –4000

–5000 Two-way traveltime (ms) 1 kkmm –6000

Fig. 12. Seismic re£ection pro¢le CO-1995-10 across the western sector of the Llanos Basin (see Location in Fig.1a).Tops of lithostratigraphic units are indicated. A major change in seismic facies occurs at the top of the Leon Formation, where a seismic sequence characterised by continuous re£ectors is superseded by a unit with discontinuous re£ectors.This change represents the regional eastward progradation of alluvial deposits of the upper Miocene Guayabo Group to deltaic and estuarine deposits of the Leon formation. See text for discussion.

r 2010 The Authors 898 Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Controls on foreland-basin sedimentation, Colombia

Basin during an episode of increasing sediment-accumu- border of the Eastern Cordillera provides an outstanding lation rates (Figs 7, 10 and 11). As in the underlying coar- scenario for directly linking a long-lived history of exhu- sening-upward cycle of the Carbonera Formation, such a mation of the Eastern Cordillera with the sedimentary re- coupled increase in both grain size and tectonic subsi- cord of the adjacent proximal foredeep. 1D and 3D dence indicates a syntectonic origin for gravel prograda- reconstructions of sediment accumulation reveal that tion (e.g., Burbank et al., 1988; Heller & Paola, 1992; coarsening-upward trends in sedimentary facies occur Schlunegger et al., 1997b). primarily as a result of increased tectonic activity in the The reconstructed kinematic history of the Eastern Eastern Cordillera. Climate, eustasy and di¡erential erod- Cordillera reveals stagnation of the orogenic wedge tip ability of the source areas have played a minor role in deter- along the Servita and Lengupa¤ faults, west of Medina, mining the large-scale trends of facies distribution in the since late Oligocene (Mora et al., 2008; Parra et al., 2009b). proximal sector foreland basin system of the Colombian Wethus hypothesize that a renewed increase in the thrust- Andes during most of the Neogene. ing rates following proposed tectonic quiecense along this front triggered the increase in accomodation space in the proximal foredeep. Indeed, the development of growth ACKNOWLEDGEMENTS unconformities in the Upper Miocene^Pliocene strata of the Upper Guayabo Formation in the Nazareth syncline This study was supported by grants and fellowships from suggests that the uplift rates associated with fault-related the German Academic Exchange Service (DAAD) to M folding of the Farallones anticline were greater than local Parra and A. Mora, the German Research Foundation sediment-accumulation rates (Mora, 2007). In addition, (DFG), Str 373/19-1 to M. Strecker, funds from the Leib- regional eastward progradation of £uvial systems to the niz Center for Earth Surface and Climate Studies at Pots- Llanos Basin, in the course of stagnation of the deforma- dam University,the project ‘Cronolog|¤ a de la Deformacio¤ n tion front, also suggests that sediment supplyfrom the up- en las Cuencas Subandinas’ at the Instituto Colombiano lifting Eastern Cordillera must have increased in the lower del Petro¤ leo (Ecopetrol/ICP), and Universidad Nacional late Miocene (e.g., Schlunegger et al., 1997a). Plausible me- de Colombia (Beca de Honor to M. Parra). Additional sup- chanisms for the enhancement of sediment supply may port was provided by the Smithsonian Tropical Research have included an increase of exhumation rates, an increase Institute (STRI). The seismic data used in this work were in the topographic gradient induced by surface uplift in released by an agreement with the Colombian National the source area or encroachment of the catchments. En- Hydrocarbons Agency (ANH).We are grateful to J. Cardo- hanced exhumation associated with orographically fo- na at ANH for his help in providing data for this study. cused erosion in the Quetame Massif area is documented Seismic interpretation was carried out using the PET- for Pliocene times (Mora et al., 2008). However, available RELt software package through an academic license thermochronometric data do not support a similar pattern kindly provided by Schlumberger.J. Sayago at the Potsdam of increase in exhumation rates for the lower early Mio- University is thanked for her help and advice during seis- cene (Parra et al., 2009b). On the contrary,widespread late mic interpretation. C. Caldana is greatly acknowledged for Miocene cooling ages in the Eastern Cordillera (Mora her help with the graphic work. The ideas presented here et al., 2009b; Parra et al., 2009b) suggest ubiquitous exhu- bene¢ted from informative discussions with B. Horton, mation through the widening of the actively deforming P. Ballato and T. Gaona. We thank S. Moro¤ n, L. Quiroz, areas. A coeval increase in sediment-accumulation rates A. Rodr|¤ guez and O. Romero for their help during ¢eld in a ¢lled-to-over¢lled basin re£ects an increase in tec- work.The manuscript was improved by the very construc- tonic subsidence, and hence suggests that tectonics must tive reviews of Paul Heller, Jaume Verge' s and Fritz Schlu- have exerted a major control on the distribution of negger, and the Editor, Peter van der Beek. coarse-grained strata. Finally, rapid subsidence during the accumulation of the late Miocene^Pliocene Upper Guayabo Formation, besides re£ecting faster tectonic SUPPORTING INFORMATION rates, may also have been favoured by enhanced sediment loading. Models predict that widening and deepening of Additional Supporting Information may be found in the the basin may occur when su⁄cient sediment £ux from online version of this article: the orogen is coupledwith e⁄cient mass transport in the basin, which produces signi¢cant sediment loading and Tabl e S1. Input parameters for decompaction of the generates additional subsidence, even beyond the £exural Cenozoic Strata of the Medina Basin. wave (Flemings & Jordan, 1989). Tabl e S2 . Description and interpretation of Lithofacies (after Miall,1996; Einsele, 2000). Fig. S1.Velocity models for seven boreholes in the Med- SUMMARYAND CONCLUSIONS ina and Llanos basins. Locations ofwells are shown in Fig. 1a. Models are based on check-short surveys measuring The stationary condition of the orogen-basin pair im- the seismic travel-time from the surface to known depths. posed by the inherited structural fabrics of the eastern Since velocity gradient decreases eastward toward the r 2010 The Authors Basin Research r 2010 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 899 M. Parra et al.

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