Geological Society of America Bulletin Orogenic Wedge Advance in the Northern Andes: Evidence from the Oligocene-Miocene Sedimen
Downloaded from gsabulletin.gsapubs.org on 29 April 2009 Geological Society of America Bulletin Orogenic wedge advance in the northern Andes: Evidence from the Oligocene-Miocene sedimentary record of the Medina Basin, Eastern Cordillera, Colombia Mauricio Parra, Andres Mora, Carlos Jaramillo, Manfred R. Strecker, Edward R. Sobel, Luis Quiroz, Milton Rueda and Vladimir Torres Geological Society of America Bulletin 2009;121 ;780-800 doi:10.1130/B26257.1
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> 2009 Geological Society of America
THE GEOLOGICAL SOCIETY OF AMERICA Orogenic wedge advance in the northern Andes: Evidence from the Oligocene-Miocene sedimentary record of the Medina Basin, Eastern Cordillera, Colombia
Mauricio Parra1 Andres Mora§ Institutfur Geowissenschaften, Universitdt Potsdam, D-14476 Potsdam, Germany Carlos Jaramillo Center for Tropical Paleoecology and Archeology, Smithsonian Tropical Research Institute, Box 0843-03092, Balboa, Panama Manfred R. Strecker Edward R. Sobel Institutfur Geowissenschaften, Universitdt Potsdam, D-14476 Potsdam, Germany Luis Quiroz Center for Tropical Paleoecology and Archeology, Smithsonian Tropical Research Institute, Box 0843-03092, Balboa, Panama Milton Rueda Vladimir Torres Instituto Colombiano del Petroleo, Ecopetrol, AA 4185, Bucaramanga, Colombia
ABSTRACT the Eastern Cordillera to the southwest of the climatic evolution of a mountain belt. A close basin. Zircon fission-track ages and paleo- link among shortening, thrust loading, and the Foreland basin development in the Andes current analysis reveal the location of these flexural response of continental lithosphere, as of central Colombia has been suggested to thrust loads and illustrate a time lag between well as associated changes in topography, is have started in the Late Cretaceous through the sedimentary signal of topographic load- ultimately reflected in the creation of accom- tectonic loading of the Central Cordillera. ing and the timing of exhumation (ca. 18 Ma). modation space for large volumes of sediments Eastward migration of the Cenozoic orogenic This lag may reflect the period between the (Beaumont, 1981; Jordan, 1981; Flemings and front has also been inferred from the foreland onset of range uplift and significant removal Jordan, 1989; DeCelles and Giles, 1996). As basin record west of the Eastern Cordillera. of overburden. Vitrinite reflectance data doc- a result, spatiotemporal variations in the mag- However, farther east, limited data provided ument northward along-strike propagation of nitude of these parameters can be inferred by foreland basin strata and the adjacent the deformation front and folding of the Oli- from trends in the three-dimensional evolu- Eastern Cordillera complicate any correla- gocene syntectonic wedge. This deformation tion of sedimentary facies and the geometry tion among mountain building, exhumation, was coupled with a nonuniform incorpora- (i.e., wavelength) of foreland basins (Flemings and foreland basin sedimentation. In this tion of the basin into the wedge-top depozone. and Jordan, 1990). For example, observations study, we present new data from the Medina Thus, our data set constitutes unique evidence from many mountain belts and deduced con- Basin in the eastern foothills of the Eastern for the early growth and propagation of the ceptual models of orogenic evolution illus- Cordillera of Colombia. We report sedimen- deformation front in the Eastern Cordillera, trate that migration of thrust loading and the tological data and palynological ages that which may also improve our understanding development of characteristic facies belts are link an eastward-thinning early Oligocene to of spatiotemporal patterns of foreland evolu- directed toward the foreland (e.g., Sinclair, early Miocene syntectonic wedge containing tion in other mountain belts. 1997; DeCelles et al, 1998; Ramos et al., rapid fades changes with an episode of fast 2002; DeCelles, 2004; Horton, 2005). How- tectonic subsidence starting at ca. 31 Ma. This Keywords: Andes, Columbia, Cenozoic, in- ever, changes in the sense of propagation of the record may represent the first evidence of version tectonics, foreland basin, fold-and- foreland basin depozones may follow changes topographic loading generated by slip along thrust belts. in the distribution of thrust loading, where out- the principal basement-bounding thrusts in of-sequence faulting (e.g., DeCelles and Giles, INTRODUCTION 1996) and deceleration and thickening of the rE-mail: [email protected] thrust wedge (e.g., Sinclair et al., 1991) pro- ^Current Address: Instituto Colombiano del Petro- The stratigraphic record of a foreland basin mote orogenward migration of the foreland leo, Ecopetrol, AA 4185, Bucaramanga, Colombia yields an important archive of the tectonic and basin depozones. Alternatively, episodic defor-
GSA Bulletin; May/June 2009; v. 121; no. 5/6; p. 780-800; doi: 10.1130/B26257.1; 9 figures; 2 tables; Data Repository item 2008215.
780 For permission to copy, contact editing @ geosociety.org © 2009 Geological Society of America Orogenic wedge advance in the northern Andes, Colombia
mation along a stationary deformation front, reflected in alternating stages of thrust loading and either quiescence or erosional unloading, may account for spatial shifts of the foreland basin depositional environments (Flemings and Jordan, 1990; Catuneanu et al, 1997, 1998). A long-term stagnation of the foreland basin system may also result from lateral variations in Hexural rigidity of the flexed plate (Wasch- busch and Roy den, 1992). Alternatively, its internal structure may be fundamentally influ- enced by inherited basement inhomogeneities, along which deformation is preferentially accommodated during subsequent orogenic processes (e.g., Hilley et al., 2005). Testing such models in natural settings is thus impor- tant and requires a multidisciplinary approach that allows identification of trends in sedimen- tary fades and subsidence rates in the basin, and of the location of thrust loads through time CARIBBEAN (e.g., Jordan, 1995). PLATE / The Cenozoic Andes constitute one of the best suited settings to closely examine these issues. The Andes orogen is the type example of a retro arc foreland basin (e.g., Jordan, 1995; Ramos et al., 2002). Along different sectors of the southern and central Andes of Argentina and 5000 m Bolivia, the onset of mountain building during contractional deformation has been widely docu- mented using the architectural characteristics of depositional foreland sequences and provenance
data (e.g., Damanti, 1993; Jordan et al., 1993; O Zircon fission-track sample Stratigraphic Locations Coutand et al., 2001; Horton et al., 2001; Davila Vitrinite reflectance sample © La India syncline and Astini, 2003; Echavarria et al., 2003; Uba © Southern Middle Magdalena valley et al., 2006). A long-term pattern of cratonward © Girardot fold belt migration of the orogenic wedge leading to the 40 80 km © Usme syncline formation of fold-and thrust belts (e.g., Coutand N © Medina Basin et al., 2001; Ramos et al., 2002; Echavarria et al., 2003) has been explained as the result of Figure 1. A 90 m STRM (Shuttle Radar Topography Mission) digital elevation deformation acting on a relatively mechanically model (DEM) showing that the major thrusts delimit topographic breaks in the homogeneous crust, largely controlled by criti- Eastern Cordillera of Colombia. The black lines mark the boundary of the Flo- cal Coulomb wedge mechanics (e.g., Horton, res ta (F) and Quetame (Q) basement highs and the Macarena Range (M). The 1999; Hilley et al., 2004). However, a nonsys- white line shows the extent of the High Plain of Bogota (B). Locations of vitrinite tematic pattern of lateral orogenic growth or the reflectance and zircon fission-track samples in the area of the Quetame massif absence of typical wedge geometries may occur are indicated. Stratigraphic locations referred to in the text are shown with num- in those settings, where favorably oriented base- bers 1-5. Inset shows the geodynamic setting of the Western (WC), Central (CC), ment anisotropies in front of an orogenic wedge and Eastern (EC) Cordilleras, and the Romeral Suture (RS) within the northern may absorb shortening. This is apparently the Andes. The black frame denotes area covered by Figures 3 and 7. Box in inset case in the Santa Barbara system and the north- indicates the location of the main map. ern Sierras Pampeanas of NW Argentina, where deformation tends to be accommodated along basement inhomogeneities inherited from pre- of the orogen (Fig. 1), such as the Central Cor- gression of the foreland basin system has been vious tectonic events (e.g., Allmendinger et al., dillera and the Magdalena Valley Basin (Cooper identified for the early stages of basin develop- 1983; Ramos et al., 2002; Hilley et al., 2005; et al., 1995; Gomez et al., 2003, 2005; Monies ment during the late Paleocene (Gomez et al., Mortimer et al., 2007). et al., 2005; Ramon and Rosero, 2006). Uplift of 2005). Despite these recent improvements in In contrast to these morphotectonic provinces the Central Cordillera since the Late Cretaceous our understanding of foreland development in of the southern central Andes, in the northern and episodic deformation (Gomez et al., 2005) this part of the Andes, details of the tectonic and Andes of Colombia, a detailed documentation have been inferred to account for the Paleogene stratigraphic expressions of the advance of the of foreland basin evolution has thus far only fades distribution and basin geometry in this orogenic front farther to the east remain ambig- been accomplished in the more internal sectors region. Also, an episode of orogenward pro- uous and largely unidentified. Particularly due
Geological Society of America Bulletin, May/June 2009 781 Parra et al. to a lack of timing constraints for deformation strata occur below a veneer of Quaternary sedi- figuration of an upper Cretaceous to Oligocene in the eastern sectors of the Eastern Cordillera, ments (e.g., Cooper et al., 1995). sedimentary sequence from the eastern flank of the spatiotemporal evolution of thrust systems, East of the Central Cordillera, a foreland the Usme sync line (Julivert, 1963; number 4 the associated creation of topography, and the basin system has evolved in response to shorten- in Fig. 1) has been interpreted as growth strata chronology of denudation and sedimentation ing and uplift of this range since the Late Creta- related to folding and the resultant creation are not very well known in this region. Along ceous (Cooper et al., 1995; Gomez et al., 2003). of subdued topography (Gomez et al., 2005). both flanks of the Eastern Cordillera, the pres- Oblique accretion of oceanic rocks in the West- Finally, along the northeastern margin of the ence of basement inhomogeneities associated ern Cordillera (McCourt et al., 1984) has been Eastern Cordillera, subsurface data have been with Mesozoic normal faults reactivated during suggested as the driving mechanism for the Late used to infer late Eocene to late Oligocene thin- Cenozoic compressional tectonics (e.g., Mora et Cretaceous initiation of uplift, loading, and fore- skinned deformation (Corredor, 2003; Martinez, al., 2006, 2008b) offers the possibility of assess- land basin development (Cooper et al., 1995). In 2006). However, the surhcial sedimentological ing their role in the localization of deformation contrast, the Eastern Cordillera is a north-north- and structural expression of this inferred defor- during erogenic evolution. east-oriented bivergent inversion orogen related mation episode remains ambiguous. Further- In this paper, we unravel the early history of to Cenozoic reactivation of Cretaceous rift struc- more, the exact timing of initial deformation mountain building along the eastern border of the tures during E-W-oriented compression (Col- and spatiotemporal variations along strike is still Eastern Cordillera of Colombia through analy- letta et al., 1990; Cooper et al., 1995; Mora et poorly resolved. sis of the sedimentary record preserved in the al., 2006). The Eastern Cordillera constitutes the Despite these problems and limitations, inte- Medina Basin, along the eastern foothills of the eastern limit of the Colombian Andes, abutting grated regional reconstructions and geodynamic range between 4°20'N and 5°00'N latitude. We the virtually undeformed lowlands of the Llanos modeling have attempted to constrain the onset integrate new detailed geologic mapping of an Basin (Fig. 1). Tectonic inversion has compart- of mountain building in the Eastern Cordillera. -1500 km2 area and structural interpretation of mentalized a once-contiguous foreland prov- Despite evidence for a pre-middle Miocene -50 km of two-dimensional (2D) industry-style ince, including areas east of the Central Cordil- onset of thrust loading, the inferred timing and seismic-reflection profiles with new sedimento- lera, the present-day intermontane Magdalena locus of thrusting differ significantly among logic and biostratigraphic information. We com- Valley Basin, and the Llanos Basin to the east. these models. For instance, at ~4.5°N latitude, bine these results with new thermal maturation The principal phase of tectonic inversion in the tectonic loading in the present-day axial sec- data based on vitrinite reflectance from the fore- Eastern Cordillera is thought to have started in tor of the mountain range has been inferred to land basin sediments, and new zircon fission- the Miocene (Van der Hammen, 1958; Cooper have started in the Late Cretaceous (Bayona et track (ZFT) ages from bedrock in the hinterland et al., 1995) and has been attributed to the colli- al., 2006; Ojeda et al., 2006). Conversely, Sarm- to provide a detailed account of the evolution sion of the Baudo-Panama arc with the western iento-Rojas (2001) suggested initial loading of the northern Andean orogenic front in cen- active margin of South America (Duque-Caro, during the late Paleocene in the eastern foothills tral Colombia. This approach helps document 1990). The appearance of post-middle Miocene region. Here, a minor contribution of remaining the effects of tectonic loading along individual alluvial sediments in the Llanos Basin has been thermal subsidence inherited from Mesozoic thrust sheets, illustrates along-strike propagation linked to the onset of uplift and exhumation in rifting was also suggested for the late Paleocene of faulting, and documents the advance of the the Eastern Cordillera (Van der Hammen, 1958; by this author. Finally, Gomez et al. (2005) mod- orogenic front toward the foreland beginning in Dengo and Covey, 1993; Cooper et al., 1995). eled loading along the axial Eastern Cordillera early Oligocene time. Collectively, our new data Direct indicators of Cenozoic deformation in the as having started in the late Eocene-early Oligo- allow a more robust evaluation of the different Eastern Cordillera are known from the western cene. These temporal disparities in the initiation mechanisms influencing the development of the and, to a lesser extent, central and northeastern of loading along the Eastern Cordillera call for Colombian foreland system through time. parts of the mountain range. To the west, in the a direct assessment of the tectono-sedimentary middle Magdalena Valley Basin (La India syn- evolution of the range and the adjacent basins, TECTONIC SETTING AND cline, number 1 in Fig. 1), middle Eocene strata involving the integration of the uplift history of GEOLOGICAL BACKGROUND rest unconformably over folded early Paleocene the hinterland with an analysis of the response units associated with west-verging thrust sheets. of the basin with respect to crustal thickening The Colombian Andes consist of three prin- This constrains an episode of late Paleocene to and exhumation. cipal, northeast-southwest-oriented geologic early Oligocene deformation (Restrepo-Pace et The record of foreland basin evolution is provinces (Fig. 1): (1) an autochthonous sector al., 2004). Approximately 120 km to the south preserved in the Late Cretaceous to Holocene of accreted oceanic paleo-Pacihc crust west (number 2 in Fig. 1), middle Eocene to Oligo- deposits east of the Central Cordillera. These of the Romeral suture, which constitutes the cene nonmarine growth strata associated with strata consist of an up to 7-km-fhick succession Western Cordillera and the Baudo Range; (2) a west-verging, thrust-related folding (Gomez et evolving from estuarine and coastal-plain to central zone, defined by Proterozoic continental al., 2003) document initial deformation of the proximal fluvial deposits (Gomez et al., 2003). basement covered by upper Paleozoic platfor- Eastern Cordillera. Farther to the south (number Cenozoic uplift of the Eastern Cordillera caused mal sequences, rift-related Mesozoic sediments, 3 in Fig. 1), the local unconformable relation- either erosional removal or nondeposition in and Cenozoic marine and nonmarine sedimen- ship between upper Cretaceous and Oligocene- this part of the succession. Consequently, an tary rocks, which underwent significant Ceno- Miocene deposits in the Girardot fold belt (e.g., incomplete record of foreland basin sedimen- zoic shortening and now constitutes the Central Raasveldt, 1956; Monies et al., 2005) has been tation is preserved in the internal sectors of the and Eastern Cordilleras and the intermontane interpreted to reflect pre-Oligocene to Miocene mountain range and is exposed mainly along Magdalena Valley Basin; and (3) the Guyana erosion as a response to folding along the west- syncline inliers. In the area surrounding the Shield province to the east, where crystalline ern flank of the Eastern Cordillera (Gomez et High Plain of Bogota, for example, upper Mio- Proterozoic basement, lower to upper Paleozoic, al., 2003; Monies et al., 2005). In the axial part cene alluvial deposits (Tilata and Marichuela Mesozoic (post-Cenomanian), and Cenozoic of the Eastern Cordillera, the structural con- Formations; Helmens and Van der Hammen,
782 Geological Society of America Bulletin, May/June 2009 Orogenic wedge advance in the northern Andes, Colombia
1994) rest unconformably on middle Eocene to to the east. Second, -5 km of shallow-marine within laterally equivalent lithostratigraphic lower Oligocene nonmarine sediments (Usme and nonmarine syntectonic sediments (Fig. 2) units across the Medina Basin, we mapped an and Regadera Formations; Hoorn et al., 1987; are well exposed and preserved within the fold- area of -1500 m2 at a scale of 1:10,000. Field Kammer, 2003; Gomez et al., 2005; Fig. 2). In and-thrust belt and thus offer an unrestricted observations were integrated with the interpreta- contrast, a complete record of Cenozoic sedi- view of Cenozoic orogenic processes. tion of two-dimensional industry-style seismic- mentation is exposed in elongated basins along reflection profiles to better document the lateral fold-and-thrust belts on either side of the Eastern METHODS continuity and geometry of sedimentary units. Cordillera (e.g., Cooper et al., 1995). Along the We analyzed stratigraphic sections and fades eastern margin of the range at 4.5-5°N latitude, The apparent discrepancies in the early along three sections to document lithofacies the Medina Basin is particularly well suited for spatiotemporal localization of the leading variations at different positions within the basin. determining the initial stages of orogenesis in edge of deformation in the Eastern Cordillera Approximately 180 measurements of paleocur- this part of the Andes (Fig. 1). First, it is located led us to employ a multidisciplinary approach rent indicators (e.g., DeCelles et al., 1983) were within the present-day wedge-top depozone of aimed at linking the uplift and exhumation carried out to reveal patterns of sediment disper- the foreland basin system between the deeply in the Quetame massif with the creation of sal. To better constrain the depositional history, exhumed basement high of the Quetame massif accommodation space and the depositional his- we provide a new palynological biozonation to the west and the presently deforming moun- tory in the adjacent Medina Basin. In order to based on analysis of 125 samples. We identified tain front demarcated by the Guaicaramo thrust identify variations in thickness and lithology 169 palynomorph species and counted a total of
5 km-,
• VR11
•VR10
•VR9
•VR8
2 - —
•VR21 • VR 14-20 •VR13
\ 1 \ •VR12 •VR7 .VR6 Nonmarine Shallow-marine •VR5 sandstones sandstones •VR4 ] Alluvial fan Shallow-marine Delta and coastal- 0-1 ' conglomerates plain sandstones mudstones ] Nonmarine Delta and coastal- Shallow-marine mudstones plain mudstones carbonates
Figure 2. (A) Generalized stratigraphy of the eastern margin of the Eastern Cordillera and the Llanos Basin showing the spatiotemporal distribution of Cretaceous rift-related and Cenozoic foreland basin sedimentary units. (B) The Upper Eocene-Miocene stratigraphy of the Medina Basin consists of an ~4.5-km-thick, first-order, coarsening-upward succession. Locations of samples for vitrinite reflectance analyses are indicated.
Geological Society of America Bulletin, May/June 2009 783 Parra et al.
16,379 grains (Tables DR1-DR41). All samples neous fission decay of 238U (Wagner and van den Farther east, the Medina Basin constitutes the were collected from unoxidized, organic mud- Haute, 1992). Fission tracks are unstable and are hanging wall of a thin-skinned thrust sheet that stone beds along stratigraphic profiles 1, 2, and progressively erased with time and temperature extends -40 km east of the Tesalia fault. Here, 3 (18, 71, and 36 samples, respectively; Fig. 4). (e.g., Green et al., 1986), and, therefore, they the Guavio anticline is a broad fault-bend fold Sample preparation followed standard proce- are useful for extracting the thermal history of related to the Guaicaramo thrust. In the northern dures (Traverse, 1988), further detailed in the the rocks containing the analyzed mineral. The part of the basin, west of the Guavio anticline, GSA Data Repository (see footnote 1). range of temperatures at which fission tracks are the Nazareth syncline is a highly asymmetric, Our new stratigraphic results were combined partially stable constitutes the partial annealing east-verging fold that forms the westernmost with published data in order to investigate the zone (PAZ; e.g., Tagami and O'Sullivan, 2005). structure in the area; its western limb is over- mechanisms and patterns of subsidence in the The zircon PAZ corresponds to a tempera- turned and constitutes the northern extent of the basin. We performed one-dimensional back- ture range of 250 ± 40 °C (e.g., Tagami et al., western Medina syncline. The steepening of stripping following the procedure described by 1998). Here, we present five ZFT ages obtained the western limb of the Medina syncline occurs Allen and Allen (2005), aimed at estimating the from the western flank of the Quetame massif where the surficial expression of deformation changing depth of the basin floor through time. (Fig. 1). Mineral separation and analytical pro- in the western margin of the Quetame massif Regional changes in accommodation patterns cedures followed conventional methods (e.g., changes. In the south, deformation at the surface were assessed by comparing our results from Bernet and Garver, 2005) and are summarized is mainly accommodated by the Servita fault, the Medina Basin with published data from in Table DR5 (see footnote 1). whereas in the north, deformation has resulted the Magdalena Valley (Gomez et al., 2005), in fault-propagation folding (Fig. 3). -170 km to the west (Fig. 1). STRUCTURAL SETTING AND Finally, southeast of the Guaicaramo thrust, Spatial comparison of the degree of sediment STRATIGRAPHY OF THE EASTERN the Llanos Plain constitutes the modern fore- burial across the Medina Basin was conducted FOOTHILLS REGION deep. Here, deformation is very minor and through vitrinite reflectance (VR) analysis (e.g., mainly results from the southward propagation Guidish et al., 1985). Vitrinite reflectance val- The Medina Basin is an integral part of the of the Yopal thrust and the associated hanging ues (Ro) have been shown to correlate with modern wedge-top depozone (DeCelles and wall, La Florida anticline, a structure corre- the maximum temperature reached by organic Giles, 1996) of the northern Andean foreland sponding to a more frontal depocenter within matter-bearing sediments during heating, basin system. The sedimentary succession the en echelon segments of the eastern fold- allowing for burial assessment in basin analysis of the eastern flank of the Eastern Cordillera and-thrust belt. (e.g., Tissot et al., 1987). We sampled sediments encompasses up to 12 km of Mesozoic rift- rich in organic matter and coal beds at different related and Cenozoic foreland basin deposits Stratigraphy stratigraphic levels within the Cenozoic sedi- that taper eastward onto the pre-Mesozoic mentary units of the Medina Basin and analyzed basement of the Guyana Shield (Fig. 2). In The stratigraphy of the eastern flank of the 26 samples following standard procedures (e.g., the following sections, we provide a general Colombian Eastern Cordillera is composed Barker and Pawlewicz, 1993, and references background on the structural configuration of of three principal subdivisions (Fig. 2): (1) a therein). Ro values were converted to maximum the eastern foothills area and the Mesozoic and Lower Cretaceous, shallow-marine sedimentary paleotemperatures using the kinetic model of Cenozoic stratigraphy. sequence associated with rifting, up to 5 km Burnham and Sweeney (1989) for heating rates thick, is exposed in the internal, elevated areas of 0.5 and 50 °C/m.y. These values represent Structural Configuration of the Eastern Cordillera (Mora et al., 2006). maximum temperatures attained during burial These units unconformably overlie either local- and, when evaluated for lateral equivalent units The Medina Basin separates the northern ized backarc Jurassic volcaniclastic sediments across the basin, allow for spatial comparison of termination of the Quetame massif, west of (Mojica et al., 1996; Rammer and Sanchez, the degree of burial within the basin. the west-dipping reverse Servita fault, from the 2006), an upper Paleozoic shallow-marine In order to obtain information on the initial virtually undeformed Llanos plains east of the sequence, or pre-Devonian phyllites (Campbell exhumation of the Eastern Cordillera in response Guaicaramo thrust (Fig. 1). and Biirgl, 1965; Mora et al., 2006; Sarmiento- to Cenozoic Andean uplift, we performed bed- The Quetame massif is a basement high, Rojas et al., 2006). (2) Up to 3 km of Upper Cre- rock thermochronology using the high-tempera- where pre-Devonian phyllitic basement and taceous platformal deposits register the onset ture zircon fission-track (ZFT) system, targeting upper Paleozoic shallow-marine strata are over- of postrift thermal subsidence (Fabre, 1983; upper structural levels within lower Cretaceous, lain by Cretaceous synrift and postrift depos- Sarmiento-Rojas et al., 2006). (3) Maastrichtian synrift shallow-marine rocks from the Quetame its (Fig. 2). Contractile deformation in the to Recent marginal marine to nonmarine fore- massif area. Fission-track thermochronology Quetame massif is thick-skinned and has been land basin-related units reach a thickness of up is based on the accumulation of linear damage mainly accommodated by reactivation of inher- to -7 km. These foreland basin units comprise zones (i.e., fission tracks) in the crystal lattice of ited Mesozoic normal faults (e.g., Mora et al., three sedimentary sequences bounded by two uranium-bearing minerals caused by the sponta- 2006). In this context, the Farallones anticline major unconformities that merge into a single is a broad hanging-wall fold associated with the composite unconformity toward the east (Fig. 2; tectonic inversion along the Servita and Len- Cooper et al., 1995; Gomez et al., 2005). gupa-Tesalia fault systems (Fig. 3). At ~4°50'N 'GSA Data Repository Item 2008215, analytical latitude, the Farallones anticline plunges north- EARLY SYNOROGENIC STRATA OF methods and detailed reports for palynological, zir- ward and displacement along the Tesalia fault THE MEDINA BASIN con fission-track, geohistory, and vitrinite reflectance analysis; and outcrop pictures of typical lithofacies., decreases. As a result, shortening in the forelimb is available at www.geosociety.org/pubs/ft2008.htm. of the Farallones anticline is accommodated We present a new stratigraphic framework Requests may also be sent to [email protected]. only by folding. for the early Eocene to early Miocene foreland
784 Geological Society of America Bulletin, May/June 2009 Orogenic wedge advance in the northern Andes, Colombia
Stratigraphy
| | Alluvium
| | Alluvial fan
| | Terraces
Upper Guayabo Formation
Lower Guayabo Formation
Wlli'H Leon Formation (Shale Unit)
I••'•'•'. i 1 Leon Formation (Sandstone Unit)
I ] Carbonera Fm. (C5-C1 Members)
[:-K:v'l Carbonera Fm. (C8-C6 Members)
| J Mirador Formation
| | Cuervos Formation
| | Barco Formation
| ]] Guadalupe Formation
| | Chipaque Formation
[ fj Une Formation
XW///A Fomeque Formation
Las Juntas Formation
Macanal Formation
Lower Cretaceous basal units
, o | | Upper Paleozoic sedimentary units | | Pre-Devonian Quetame Group
Structures
Reverse fault ^ \^ Anticline Normal fault X/ Syncline Strike-slip fault
O |J|j£| Vitrinite reflectance sample. West
# |VR2l| Vitrinite reflectance sample. East
• |VR23| Vitrinite reflectance sample Lower Cretaceous units # |MA13| Zircon fission-track sample
(/\\ Stratigraphic profile
10 km \
Figure 3. Geological map and cross section of the Medina Basin and the northern termination of the Quetame massif (location shown in Fig. 1). (A) Map depicting main stratigraphic units and structures. Locations of three stratigraphic profiles and sampling sites for zircon fission-track and vitrinite reflectance analyses are indicated. Abbreviations are as follows: AS—Rio Amarillo syncline; FA—Farallones anticline; F1A—La Florida anticline; GA—Guavio anticline; GT—Guaicaramo thrust; LF—Lengupa fault; MS—Medina syncline; NS— Nazareth syncline; SF—Servita fault; TF—Tesalia fault. (Continued on following page.)
Geological Society of America Bulletin, May/June 2009 785 Parra et al.
NW SE ra 3 ra A Q. « c o .£ £ .E A' ra '> "u < u I K raN c 3 1 ra 3 Z e> ra 51 > ,'". _ ^g i- 0
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^ 5 km
Leon and Guayabo Fm. Barco, Los Cuervos and Mirador Fms. Lower Cretaceous units C1-C5 members Carbonera Fm. C6-C7 members Upper Cretaceous units Pre-Cretaceous basement C8 member
NW
- 0
•4 km
0 - - 0
£ 2 2 £
5 km
Figure 3 (continued). Geological map and cross section of the Medina Basin and the northern termination of the Quetame massif (location shown in Fig. 1). (B) Balanced cross section along structural profile A-A' (location indicated in A) based on detailed surface mapping and interpretation of seismic-reflection profiles. An eastward-thinning sedimentary wedge made up of the Carbonera Formation is shown.
786 Geological Society of America Bulletin, May/June 2009 Orogenic wedge advance in the northern Andes, Colombia
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Geological Society of America Bulletin, May/June 2009 787 Parra et al. basin sediments in the Medina Basin. First, we C7, and C6 members of the Carbonera Forma- Age Constraints describe the spatial distribution of sedimentary tion. A summary of the facies analysis and the units and their major lithological and thickness spatial distribution of the facies associations is Our new chronostratigraphic framework for variations, based on our surface and subsurface presented in Table 2 and Figure 4. the C8-C6 members of the Carbonera Forma- data. Second, we present facies analyses and Our results show a reversal of paleocurrents tion, based on palynomorphs, facilitates the paleocurrent data from the lower members of from initially westward transport directions in evaluation of spatiotemporal trends in basin the Carbonera Formation along three strati- the Mirador Formation, associated with eastern evolution. In our analysis, we follow the bio- graphic profiles across the basin (Fig. 4). Third, sources on the Guyana Shield (Cooper et al., stratigraphic zonal scheme developed by Jara- we present new biostratigraphic data that allow 1995; Cazier et al., 1997), to a northeastward millo and Rueda (2004), Jaramillo et al. (2005), estimation of depositional ages, and finally sediment dispersal pattern. The switch occurs and Jaramillo et al. (2008). Palynological bio- we integrate the stratigraphic results to better in the C7 and C6 members in the northern and zones from northern South America have been assess basin evolution during the initial stages eastern parts of the basin (Fig. 4). This reversal calibrated using foraminifera and nanoplankton of orogenesis in the Eastern Cordillera. thus documents a change in the main sediment from Venezuela (Germeraad et al., 1968; Muller Combined surface mapping and seismic source to the southwest, along the present-day et al., 1987) and stable carbon isotopes (813C) interpretation document the presence of an Eastern Cordillera. Limited paleocurrent indica- from Colombia and Venezuela (Jaramillo et al., eastward-thinning sedimentary wedge consist- tors in the alluvial G4 unit of the western section 2006, 2007). The calibration data provided by ing of the C8-C6 members of the Carbonera suggest a polymodal dispersion pattern (Fig. 4), these authors suggest that uncertainties in the Formation (Figs. 3B and 4). The thickness of interpreted to reflect episodes of avulsion in the time assignments of the individual biozones are the C8 member in the northern axial portion alluvial system. relatively minor, although the published data are of the basin reaches -250 m (profile 1; Fig. 4). Our analysis and lithostratigraphic correla- insufficient to further quantify the uncertainty. Seismic interpretation tied to detailed geologi- tion indicate that the C8-C6 Members consti- Both the eastern and western intervals of the cal mapping suggests rapid thickening of this tute an eastward-thinning syntectonic wedge syntectonic wedge corresponding to the C8-C6 unit to the west (Fig. 3). A varying stratigra- in the Medina Basin. In the western part, the members of the Carbonera Formation were phy within the interval delineated by the base interval equivalent to the C7-C6 members deposited within the palynological zones T-05 of the sandstone-dominated C7 member and a reaches a thickness of 1150 m. It evolves from to Ca-07, corresponding to early Eocene to early bivalve-rich horizon found at the top of the C6 coastal-plain and deltaic deposits in units Miocene time (Fig. 5). Based on the key taxa for member across the basin is illustrated based G1-G3 (facies associations 1 and 2; Table 2) the zonal scheme (Fig. 5), the limits of the bio- on description along profiles 2 and 3, where to braided fluvial deposits in unit G4 (facies zones in the composite section are assigned to the a complete record of the C7 and C6 members associations 3 and 4). Equivalent deposits midpoint between samples belonging to contig- is described (Fig. 4). Due to lithological varia- -20 km to the east are only 455 m thick and uous biozones (Table DR6, see footnote 1). The tions, we subdivided the equivalent interval are exclusively dominated by deltaic facies base of the early Eocene zone T-05 is defined by into units Gl, G2, G3, and G4 in the west- associations 1 and 2. Taken together, the rapid the first appearance datum (FAD) of Tetracolpo- ern profile (Fig. 4). These sections were also facies changes from tidally influenced coastal- rites maculosus. The FAD of Cicatricosisporites sampled for palynology in order to constrain plain to fluvial deposits to the west, and the dorogensis defines the top of the early Eocene depositional ages and environments. In the fol- changeover to northeastward paleocurrent zone T-05. The last appearance datum (LAD) lowing section, we present the facies analysis directions, document the initial existence of of Spinizonocolpites grandis defines the top of for the profiled sections. elevated topography in the area of the present- the middle Eocene zone T-06. The top of the day Eastern Cordillera in early Oligocene time. late Eocene zone T-07 is marked by the LAD Depositional Systems Furthermore, the thickness variations in the of Echitriporites trianguliformis orbicularis. basin clearly illustrate enhanced subsidence The top of the early Oligocene zone T-08 is Based on Ethology and sedimentary struc- in the west, suggesting tectonic loading in the defined by the LAD of Nothofagidites huerta- tures, 15 lithofacies (Table 1) and four facies location of the present-day Eastern Cordillera sii. The FAD of combined acme of Jandufouria associations were recognized within the C8, during the late Eocene-late Oligocene. seamrogiformis, Magnastriatites grandiosus,
TABLE 1. DESCRIPTION AND INTERPRETATION OF LITHOFACIES (AFTER MIALL.1996; EINSELE, 2000) Code Description Interpretation Gcd Disorganized clast-supported conglomerates, cobbles, and pebbles Clast-rich noncohesive debris flow Gco Organized, clast-supported conglomerates, cobbles, and pebbles. Weak imbrication Longitudinal bed forms, lag deposits St Trough cross-stratified sandstone, fine to coarse 3D dunes Sp Planar cross-stratified sandstone, fine to very coarse, often pebbly Transverse and linguoid bed forms (2D dunes) Sr Ripple marks and small-scale cross-stratification Ripples (lower flow regime) Sf Flaser bedded sandstone Alternating suspension settling and lower-flow regime Sw Wavy bedded sandstone Alternating suspension settling and lower-flow regime Sic Lenticular bedded sandstone Alternating suspension settling and lower-flow regime 5c Convoluted bedded sandstone Deformation by differential loading or dewatering 5m Massive sandstone Sediment gravity-flow deposits Fl Laminated mudstone and siltstone Suspension-load deposits Fm Massive mudstone and siltstone Suspension deposits, overbank or abandoned channels Fs Disorganized shell-dominated mudstone Upper flow regime Fb Variegated mudstone and siltstone. Commonly sandy, intense mottling Overbank or abandoned channels Fo Mudstone and siltstone with organic matter-rich laminae Suspension settling deposits C Coal Organic-rich swamp deposits
788 Geological Society of America Bulletin, May/June 2009 Orogenic wedge advance in the northern Andes, Colombia
Mauritiidites franciscoi minutus, and Verruca- CO tosporites usmensis defines the top of the early D) g CO 'Is i C O to middle Oligocene zone T-09. The LAD of the 5-D g- CO To O- E combined acme of Jandufouria seamrogiformis, CD .S „ a. CO O O <= Magnastriatites grandiosus, Mauritiidites fran- E o c i 3 oo 2. c S co III g ciscoi minutus, and Verrucatosporites usmensis 'I defines the top of the middle Oligocene zone - - CD i o c CM 8 '• = c S co o j a, a) o _o T-10. The top of the late Oligocene zone T-ll ! O Qj CM CD g O J2 "§ "a E is defined by the LAD of Cicatricosisporites S To .2 T3.g O) L<=OE dorogensis. Finally, the FAD of Echitricolpo- o c >. co .£ c .2 a .S> : » g o » rites maristellae defines the top of zone Ca-07, u. "B o = s E? CD c ° '^•§ ig^ I CO corresponding to the early Miocene. I 2 r"5 gg 2 » 2 8" lo 2 E 1 GEOHISTORY ANALYSIS E o •| 1 g 1 • CO ?i ffl ro | co -5 c g o CJ m^ 8 The Paleocene-early Miocene tectonic E g co ^ co \ lie? "CO E .S subsidence history of the Medina Basin was ^it^zE g o_ m.S To £a assessed using one-dimensional backstripping of a composite stratigraphic section from the ' < .£ CD g LL ~ Medina Vasin constructed using the strati- cc-o JS S 3 j- .S graphic data presented in this study for the a .2 Li. > lower part of the Carbonera Formation (profiles £ < 1 and 2; Fig. 4), and published data from Paleo- 5= E g-D--
Geological Society of America Bulletin, May/June 2009 789 Parra et al.
Thickness (m)
/ 1 1 1
Age (Ma) 55 60 55 50 45 40 35 30 25 22' i i , i , , , . i . , , , i . , . , i , , S i Paleocene Eocene blic jocene p' Epoch
n n -H -H -H -H -H Q? ~£ -H -H Palynozone 6 £ 4> 4» CT 1 B 1 2 3 1 Reference Figure 5. Palynological biozonation and composite stratigraphic section for the upper Paleocene—lower Miocene strata of the Medina Basin. (A) Photographs of key taxa used in this study. 1—Tetracolporites maculosus; 2—Cicatricosisporites dorogensis; 3—Spinizonocolpites gran- dis; 4—Echitriporites trianguliformis orbicularis; 5—Jandufouria seamrogiformis; 6—Magnastriatites grandiosus; 7—Mauritiidites franciscoi minutus; 8—Verrucatosporites usmensis; 9—Echitricolporites maristellae. See explanation in text. (B). Composite stratigraphic section for the Paleogene strata of the Medina Basin. The composite section is constructed based on thickness, lithology, and biozonation after JaramUlo and Dilcher (2000) for the Los Cuervos and Mirador Formations, and data obtained in this study from profiles 1 and 2 of the Carbonera Forma- tion. The biozonal scheme utilizes the geological time scale of Gradstein et al. (2004). Assignment of biozones is based on Jaramillo and Rueda (2004); and Jaramillo et al. (2005; 2008) (references are coded in zonal scheme with numbers 1,2, and 3, respectively).
790 Geological Society of America Bulletin, May/June 2009 Orogenic wedge advance in the northern Andes, Colombia
Specifically, local (Airy) compensation of the load contribution in the Medina Basin was minor ZIRCON FISSION-TRACK sediment load neglects lateral flexural strength in the early stages of the foreland basin develop- THERMOCHRONOLOGY of the lithosphere and hence results in overes- ment. Since early Oligocene time, sedimentary timation of the contribution of the weight of loads have increased until their contribution to Apatite fission-track (AFT) data from in situ the sediment column to the subsidence of the the total subsidence reached a similar amount bedrock samples from the Quetame massif area basin (Watts et al., 1982). Furthermore, in our (-70%) compared to the backs tripped foreland show rapid cooling below -120 °C since ca. 3 Ma analysis (Fig. 6) we do not extract subsidence strata in the Magdalena Valley. and thus reflect fast rock exhumation of 3-5 km rates, since backs tripping only the Cenozoic Larger amounts of total and normalized sedi- since the late Pliocene (Mora et al., 2008a). These strata implies that underlying units underwent ment-load-driven subsidence during the Paleo- data suggest that any older record of exhuma- no compaction during the Cenozoic. Since the cene-early Oligocene (between 65 and 31 Ma; tion, potentially detectable with AFT, has been pre-Cenozoic substratum in both the Medina Fig. 6C) in the Middle Magdalena Valley Basin erosionally removed from the deeply incised and southern Middle Magdalena Valley Basins relative to the Medina Basin are compatible eastern margin of the mountain range. Thus, in makes up -6-7 km of Mesozoic sedimentary with a basin located closer to the orogenic front. order to obtain information on the earlier stages rocks (Gomez et al., 2005; Mora et al., 2008a), Such a basin would have undergone faster sub- of exhumation, we conducted zircon fission- the total Cenozoic decompacted thickness is sidence and received a greater load of sedi- track (ZFT) analysis. A comprehensive analysis overestimated. Consequently, the decompac- ments from the source areas in the hinterland. of exhumation patterns is beyond the scope of tion curves (Figs. 6A and 6B) are forced to Maastrichtian to Oligocene tectonic subsidence this paper and will be presented elsewhere. How- meet the compacted-thickness curves at our in the Middle Magdalena Valley Basin has been ever, although limited, we present data from five time zero (Angevine et al., 1993). Neverthe- explained by loading of the Central Cordil- samples obtained from the Quetame massif area less, our geohistory analysis is sufficient to lera between the Maastrichtian and late Paleo- (Figs. 3 and 7) in order to document the timing allow for comparisons between the western cene (Cooper et al., 1995; Gomez et al., 2003, of thrust-induced exhumation in this sector of and eastern foothills sections, as we applied 2005) and by loading of the western front of the range. Four samples were collected along a the same procedure to a corresponding time the Eastern Cordillera in the late Eocene-early longitudinal profile running across the pre-Devo- interval in both areas. Oligocene (Gomez et al., 2003, 2005). The nian to Lower Cretaceous section of the western The Paleocene-Miocene subsidence curves increase in accommodation rates in the Medina flank of the Quetame massif. Sampling covered for the Medina and southern Middle Magdalena Basin since the late Oligocene suggests that different structural levels in order to determine Valley Basins (Fig. 6) furnish a means to evalu- the tectonic load, and hence the main source the limits of the ZFT partial annealing zone in ate and compare regional accommodation pat- of sediments, has migrated closer to the east- this part of the mountain range. A fifth sample terns across the entire foreland basin system. ern foothills of the Eastern Cordillera. Despite (MA 13) was collected from a similar structural The total subsidence signal for both areas (low- the limitations of the backs tripping method, the position to that of the uppermost sample (sample est curves in Figs. 6A and 6B) displays a simi- analyzed section in the Medina Basin allows BV 121) in the longitudinal profile. However, lar sigmoidal pattern resulting from a period of us to identify changes in the pattern of tectonic sample MA 13 was located -80 km to the north- reduced subsidence (or even uplift in the case of subsidence rates (Fig. 6D). We conclude that west along strike. Table DR5 (see footnote 1) the southern Middle Magdalena Valley, as sug- the late Paleocene to early Miocene accommo- shows the individual ages for the five analyzed gested by the regional Late Cretaceous-Ceno- dation history in this region is characterized by samples. The three structurally deepest samples zoic unconformity) that separates two episodes a three-stage evolution: an initial late Paleocene pass the %2 test (Galbraith, 1981; Green, 1981) with higher accommodation rates. Importantly, episode of moderate subsidence; limited subsi- with values of P(%2) > 5% (samples BV 151, BV the curve for the Medina Basin suggests (1) dence from Eocene through early Oligocene 192, and MA13), indicating that the single-grain that the onset of faster subsidence occurred at time; and rapid subsidence from early Oligo- age distribution corresponds to a single compo- ca. 31 Ma, at least 30 m.y. after an equivalent cene through early Miocene time. We correlate nent (Fig. 7D). We analyzed the significance of episode in the southern Middle Magdalena the first two stages with a late Paleocene east- the ZFT cooling ages using an approximation Valley, and (2) that this episode, starting in the ward advance, and subsequent Eocene to early to an age-elevation profile. Age-elevation pro- early Oligocene, was responsible for most of Oligocene westward retreat of the foreland files exploit differences in topographic eleva- the basin subsidence, ultimately leading to a basin system. These episodes have also been tion of samples along relatively steep profiles; larger amount of total Cenozoic subsidence in documented in the foreland basin record of if the profile includes part of an exhumed par- the Medina Basin compared to the Magdalena the Magdalena Valley Basin, where they were tial annealing zone, it is possible to derive the Valley (Fig. 6C). The analysis for the Medina interpreted as a response to a phase of tectonic timing of initiation of exhumation (Wagner and and southern Middle Magdalena Valley Basins activity followed by tectonic quiescence in the Reimer, 1972; Huntington et al., 2007). In the shows that the contribution of the sedimentary Central Cordillera (Gomez et al., 2003, 2005). Quetame massif, the absence of deeply incised load to the total subsidence increases through Similarly, we interpret the second episode of canyons cutting through the entire Lower Cre- time (Fig. 6C). Since middle Miocene time faster tectonic subsidence registered in the late taceous to pre-Devonian section prevents such (ca. 12 Ma), sedimentary loads have accounted Oligocene-early Miocene sedimentary record an approach. Instead, we use detailed structural for -70% of the total subsidence in both areas of the Medina Basin to result from the eastward mapping and a structural cross section (Mora et (Fig. 6C). As cautioned earlier, this result is an advance of the deformation front. Rapid subsi- al., 2006) to project the four samples collected overestimation due to the simplification intro- dence in the Medina Basin starting at ca. 31 Ma in the southwestern part of the Quetame massif duced by using local (Airy) isostatic compen- and the concomitant deposition of an eastward- onto a profile. We related the samples to a datum sation. However, the results indicate a different thinning sedimentary wedge are compatible defined by the angular unconformity at the temporal evolution for the sedimentary-load with initial deposition in a foredeep depozone base of the rift-related Cretaceous sedimentary contribution for each area. Mimicking the pat- and, hence, are strong evidence for an eastward sequence (Fig. 7). The stratigraphic elevation tern of the total subsidence curve, the sediment- advance of the orogenic front. of the samples with respect to this datum was
Geological Society of America Bulletin, May/June 2009 791 Parra et al.
Medina Basin B Southern Middle Magdalena Valley Basin
for sediment load Subsidence due to sediment —£}•—Decompacted (total subsidence) —O Tectonic subsidence load
C Tectonic subsidence and sediment load Tectonic subsidence Medina Basin
Age (Ma) 60 40 20 1 1 i Paleocene Eocene Oligocene Miocene Pli. \ \ \ \ T 0.4 \ - 1 ^ ' V, -i 0.8 1 i< " T a. ° 1.2 f 1 - \ 1.6- SMMVB 2.0-
Figure 6. Geohistory analysis for the upper Paleocene-Miocene stratigraphic sections of the Medina and southern Middle Magdalena Valley Basins. (A) Medina Basin. (B) Southern Middle Magdalena Valley Basin (SMMVB) (data from Gomez et al., 2005). Details on parameters used for analyses are shown in Table DR6 (see text footnote 1). (C) Tectonic subsidence curves (black lines) and temporal evolution of the sediment- load contribution to the total (decompacted) subsidence (gray lines) for Medina and southern Middle Magdalena Valley Basins. Rapid subsi- dence in the southern Middle Magdalena Valley Basin during Paleocene time resulted from tectonic loading of the Central Cordillera (Gomez et al., 2005). Enhanced subsidence since ca. 31 Ma (arrow) in the Medina Basin results from initiation of loading along the present-day eastern border of the Eastern Cordillera. See text for discussion. (D) Tectonic subsidence curve of the Medina Basin depicting a sigmoidal, three-stage pattern interpreted as the vertical stacking of distal foredeep, forebulge, and proximal foredeep, resulting from the Eocene retreat and subse- quent Oligocene advance of the foreland basin system. Vertical error bars represent uncertainties in paleoaltitude (water depth) for continental (marine) units. Bars are only visible for the two youngest points representing continental deposits with larger uncertainty in paleoelevation (see Table DR6 [see text footnote 1] and text for discussion).
792 Geological Society of America Bulletin, May/June 2009 Orogenic wedge advance in the northern Andes, Colombia
Area covered in Figure A
BV121 BV65 B 136.5 ±13.4 Ma 61.3 ±3.4 Ma BV 151 BV 192
- 4 (km) •4 (km)
| | Neogene _| Carboniferous ZFT sample and age | | Paleogene | | Devonian Basal Cretaceous unconformity | | Upper Cretaceous | • Andean Basement 5 (km) | | Lower Cretaceous P| Guyana Shield Basement
4 Caqueza Fm BV65 Hr4 1 BV1S1 0 Central age: 64.9 ± 4.0 Ma Pooled age: 18.1 ±1.1 Ma B _-- BV121 3
2 BV65 Partial annealing zone \- f- - Macanal Fm I BV151 1 / / / I 0 I Pre- * BV192 Cretaceous H 20 15 Rel. error [%] Rel. error [%] 50 100 150 200 ZFT age (Ma)
Figure 7. Zircon-fission track (ZFT) data. (A) Geologic map and (B) structural cross section along profile B-B (see location also in Fig. 1) illustrating the location of zircon fission-track samples (red dots) and the unconformity at the base of the Lower Cretaceous sedimentary units (blue line; modified from Mora et al., 2006). (C) Structural elevation vs. age profile for the analyzed samples. The upper part of the Macanal Formation, between samples BV 65 and BV 151, delimits the base of an exhumed partial annealing zone. (D) Radial plots for two samples from the Lower Cretaceous rift-related deposits of the Macanal Formation in the Quetame massif. Sample BV 151 passes the chi- squared test (P[%2] > 5%; see Galbraith, 1981; Green, 1981) and thus represents a single age population. Therefore, the reported pooled age of ca. 18 Ma can be interpreted as reflecting early Miocene, thrust-induced exhumation. Sample BV 65 fails the chi-squared test, reflecting a mixed age population as a result of only partial annealing.
Geological Society of America Bulletin, May/June 2009 793 Parra et al. plotted versus the zircon fission-track age. The and 0.49%, corresponding to maximum paleo- gested by the VR data, constitutes compelling resulting plot illustrates the approximate posi- temperatures of up to -80 °C. Interestingly, evidence for earlier incorporation of the western tion of the base of an exhumed partial anneal- the results cluster at different ranges when sector of the basin into the fold-and-thrust belt. ing zone between sample BV 65 (P[%2] = 0.0; grouped according to basin locality. First, VR This earlier deformation prevented the western central age = 61.3 ± 6.4 Ma) and sample BV values for samples from the western part (sam- Medina Basin from undergoing further burial 151 (?[%-] > 5%; pooled age = 18.5 ± 1.0 Ma; ples VR1-VR11; Table DR7 [see footnote 1]) beneath the stratigraphic thickness as observed Table DR5 [see footnote 1]; Fig. 7C). Further- vary between 0.22% and 0.32%, correspond- farther east, where VR values suggest greater more, the total annealing for the ZFT system of ing to temperatures of up to 60 °C (Burnham burial. Thus, a previously subsiding area in the the Lower Cretaceous section is also supported and Sweeney, 1989). No significant differences western Medina Basin, where the stratigraphic by vitrinite reflectance (VR) data, constraining in maximum paleotemperature were observed thickness of the C8-C6 members reaches a the maximum postdepositional paleotempera- between the lowermost Paleocene and the maximum, became an area of limited accom- ture of the Lower Cretaceous rift-related rocks. youngest Miocene samples. Estimated burial modation space through structural incorporation Regional Ro values for the shales of the Maca- temperatures of up to 60 °C for sedimentary into the eastern Andean fold-and-thrust belt. nal Formation along the Eastern Cordillera vary units as old as early Paleocene have rather low between 3.5% and 5% (e.g., Torn et al., 2004) values considering the maximum overburden DISCUSSION AND CONCLUSIONS and represent maximum paleotemperatures of 4-5 km, equivalent to the full preserved >250 °C, according to the standard correlation stratigraphic thickness of the Oligocene to Late Eocene-Oligocene History of the model (Burnham and Sweeney, 1989). Two VR Miocene units younger than the sampled inter- Eastern Flank of the Eastern Cordillera analyses of samples obtained from the western val. On the other hand, in the eastern part of the flank of the Quetame massif (Mora et al., 2008a; Medina Basin, younger units corresponding to Our data set provides new insights into dif- location in Fig. 3) yielded results similar to the the upper members of the Carbonera Forma- ferent evolutionary stages of a foreland fold- regional trend (Table DR7 [see footnote 1], sam- tion (C6-C3 members; samples VR12-VR21, and-thrust belt, the compartmentalization of the ples VR22 and VR23). Table DR7 [see footnote 1]) yield VR values foreland, and the resulting thermal history of the Sample MA13, from the northern part of the ranging between 0.35% and 0.45%, corre- basin. In particular, we furnish new constraints Quetame massif, adjacent to the Medina Basin, sponding to temperatures of up to 95 °C. The on the propagation of the northern Andes defor- yielded a ZFT age of 17.9 ±1.0 Ma. This age results suggest that strata from the eastern part mation front during the early stages of Cenozoic overlaps within 2a error with the age of the struc- of the Medina Basin were subjected to higher mountain building in this part of the orogen. A turally equivalent sample B V 151 from the south burial paleotemperatures, not only compared to southwesterly sourced lower Oligocene-lower (18.5 ± 1.0 Ma). We interpret these early Mio- their lateral equivalents but also in comparison Miocene eastward-thinning syntectonic wedge cene ZFT ages to represent cooling ages resulting to older units to the west, suggesting nonuni- composed of the C8-C6 members of the Car- from thrust-induced exhumation of the Quetame form burial across the basin. bonera Formation was deposited in the Medina massif. However, these ZFT ages postdate the Considering the maximum overburden, the Basin during an episode of rapid tectonic subsi- onset of thrust-related exhumation, likely by a estimated maximum paleotemperatures sug- dence starting at ca. 31 Ma. Rapidly eastward- small amount, as this information would only be gest a mean paleogeofhermal gradient of only thinning deposits constituting the upper part of provided by the structurally uppermost rocks just -7-9 °C/km for the western area (maximum this sedimentary wedge change their character beneath the zircon partial annealing zone. More paleotemperature = -60 °C; full stratigraphic in an eastward direction from alluvial to tidal- precise identification of this limit requires more thickness = -4-5 km; present surface temper- influenced coastal plain lithofacies. The age at detailed sampling and, ideally, ZFT investiga- ature = 25 °C), a much lower value than the the top of this stratigraphic interval is biostrati- tions along near-vertical profiles. However, our present geofhermal gradient of -22 °C/km, graphically constrained at ca. 22 Ma (Ca7-Ca8 results constrain the stratigraphic interval within obtained from oil wells in the proximal fore- palynozones; Figs. 4 and 5). On the other hand, the upper part of the Macanal Formation along deep of the Llanos Basin (e.g., Bachu et al., our ZFT data reveal ongoing early Miocene which future studies should be focused. 1995). As suggested for similar foreland set- (ca. 18 Ma) exhumation along the northern ter- Early Miocene exhumation and rock uplift tings, such as the southeastern margin of the mination of the Quetame massif, -30 km to the in the Quetame massif area contrast with sub- Puna Plateau in NW Argentina (e.g., Coutand et west of the Medina Basin. ZFT ages determined sidence in the Medina Basin, a few kilometers al., 2006), two possible scenarios may explain from different structural levels on the western to the east. Geohistory analysis of the thick such an extremely low geofhermal gradient. flank of the Quetame massif and burial estimates sedimentary wedge corresponding to the C8-C6 Either it could be related to thermal perturba- from this area based on vitrinite reflectance data members of the Carbonera Formation suggests tions driven by expulsion of pore fluids during suggest that the ca. 18 Ma ZFT ages obtained that enhanced tectonic subsidence in the Medina compaction, caused by rapid syntectonic sedi- from the upper part of the Lower Cretaceous Basin started in the early Oligocene. Combined, mentation (Deming et al., 1990), or the cooling Macanal Formation at least slightly postdate the fhermochronological results help to better effects of groundwater recharge driven by an the onset of exhumation. Roughly simultaneous constrain the position of the deformation front of adjacent orographic barrier intercepting mois- exhumation in the Quetame massif and rapid the orogenic wedge, which by the early Oligo- ture (e.g., Forster and Smith, 1989). However, tectonic subsidence recorded in the upper por- cene, coincided with the inverted Servita fault. the present geothermal gradient of -22 °C in an tion of the syntectonic sedimentary wedge of the analogous foredeep setting of the Llanos Basin Medina Basin thus delineate the position of the VITRINITE REFLECTANCE (Bachu et al., 1995) rules out both of these sce- orogenic front along the fault system separating narios from having significantly affected the the two areas (i.e., the Lengupa-Tesalia fault sys- Observed mean vitrinite reflectance (Ro) maximum paleotemperature. tem) since at least the early Miocene. Further- values in the Paleocene to Miocene sedimen- Conversely, uneven burial between the east- more, the apparent disparity between the onset tary rocks of the basin vary between 0.16% ern and western sectors of the basin, as sug- of rapid subsidence at ca. 31 Ma in the Medina
794 Geological Society of America Bulletin, May/June 2009 Orogenic wedge advance in the northern Andes, Colombia
Basin and the younger initiation of exhumation indicators of deformation (i.e., growth strata the onset of rapid subsidence and the older exhu- during the early Miocene in the Quetame mas- or unconformities) in the forelimbs and back- mation ages may result from a combination of sif can be explained by the following scenarios: limbs of the Farallones anticline (Fig. 3) could (1) an incomplete thermochronologic database, (1) tectonic loads located west of the Quetame be explained by poor seismic imaging in the preventing precise identification of the onset of massif triggered the stage of rapid subsidence steeply dipping, overturned western limb of the exhumation (thus only representing a minimum between ca. 31 Ma and the initial exhumation of Nazareth syncline and/or subsequent erosion age for this process), and (2) a potential tempo- the Quetame massif shortly before 18 Ma; or (2) resulting from protracted exhumation and uplift ral lag between thrust loading and exhumation, the tectonic loads that caused such a rapid subsi- along this structure. reflecting the period between the onset of range dence were located in the area of the present- However, despite the absence of such direct uplift and significant removal of overburden. day Quetame massif, and, hence, a significant indicators, a combination of observed changes More detailed thermochronological investiga- lag time of as much as 13 m.y. occurred between in sedimentary fades, thickness, and subsidence tions in the future might resolve this issue. the emplacement of the thrust loads at ca. 31 Ma patterns in the basin, and the localization of and the onset of significant exhumation of the areas with contemporaneous ongoing exhuma- Migration of the Foreland Basin System Quetame massif. tion enable us to identify the Lengupa-Servita Although geodynamic modeling must be faults as the most likely locus of the orogenic Our plots of Cenozoic sediment accumulation conducted to better define the location of the front since the early Oligocene. Furthermore, and tectonic subsidence display a similar three- tectonic loads, regional structural and strati- the structural configuration of the Lengupa fault stage pattern in the southern Middle Magdalena graphic considerations permit us to hypothesize and our paleocurrent data from the syntectonic Valley and Medina Basins, resulting from two about the most favorable among the two sce- wedge help to place more detailed constraints episodes of rapid subsidence separated by an narios. Along the axial Eastern Cordillera, an on the proposed location of the tectonic loads interval of slower subsidence (Figs. 6A and incomplete Cenozoic sedimentary record (see that triggered the earlier phase of subsidence at 6B). In other foreland basins, such three-stage Fig. 2) and incomplete palynological sampling ca. 31 Ma. The structural cross section across the sigmoidal patterns have been explained by ver- prevent a well-constrained westward extrapola- northern part of the Guavio anticline (Figs. 3B tical superposition of foreland basin depozones tion of sediment accommodation patterns. West and 8) reveals that the overturned western mar- resulting from redistribution of thrust loads and of the Medina basin, the easternmost locality gin of the basin corresponds to the forelimb of progradation of the orogenic wedge (DeCelles where the Paleogene record has been described a fault-propagation anticline associated with the and Currie, 1996; Horton et al., 2001). In such is in the Usme syncline, south of the High Plain northern termination of the Lengupa fault. How- a scenario, a cratonward migration of the oro- of Bogota (Fig. 1). There, the Usme Formation ever, south of the Gazaunta River, deformation genic wedge results in the superposition of the consists of 300 m of deltaic deposits (Hoorn along this thrust sheet has been accommodated foredeep, forebulge, and back-bulge depozones. et al., 1987) unconformably underlying upper by faulting (Fig. 3A). This configuration docu- Alternatively, orogenward retreat of the foreland Miocene strata. The available palynological ments a deformation gradient. Nucleation of this system may lead to vertical stacking of distal data (Hoorn et al., 1987) reveal that the upper- fault system appears to have started first in the (i.e., back-bulge and forebulge) over proximal most 200 m of the Usme Formation correspond south, where the fault has attained maximum foreland basin depozones (i.e., foredeep and to the biozone T-08 (early Oligocene, ca. 34 Ma structural relief. There, pre-Devonian basement wedge-top). This latter scenario may result from to 31 Ma). In the composite stratigraphic sec- rocks have been thrust over upper Cenozoic internal thickening of the orogenic wedge via tion of the Medina Basin, the coeval interval in strata. In contrast, farther north, this fault sys- out-of-sequence reactivation of thrusts in the the C8 member of the Carbonera Formation is tem only causes folding, and the fault has not hinterland (e.g., DeCelles and Giles, 1996), only -70 m thick and corresponds to the upper- yet cut the surface. As illustrated in Figure 8, underplating (e.g., Sinclair et al., 1991), or from most part of the Eocene-early Oligocene inter- we suggest that rapid subsidence and increased a decrease in the wavelength of the Hexural pro- val, which registers limited tectonic subsidence accommodation in the western part of the basin file of the basin. Such a decrease can be related (see Table DR6 [see footnote 1]; Fig. 5). These at ca. 31 Ma would have resulted from load- to episodic deformation associated with alternat- results document faster sediment accumulation ing in the hanging wall of the Servita-Lengupa ing episodes of thrust loading following tectonic and subsidence in the axial part of the Eastern thrust sheet to the southwest of the basin. This quiescence, erosional unloading (Flemings and Cordillera compared to the eastern foothills, is further supported by paleocurrent data from Jordan, 1990; Burbank, 1992; Catuneanu et al., and they support a scenario of tectonic loading the C7-C6 members of the Carbonera Forma- 1998), or lateral variations in the rigidity of the west of the axial part of the Eastern Cordillera tion, which indicate that the main source for flexed plate (Waschbusch and Royden, 1992). prior to 31 Ma. The continuance of this pattern these sediments was located to the southwest Concerning the late Paleocene episode of throughout the Oligocene cannot be evaluated of the basin. Subsequent deformation within rapid subsidence during deposition of the Los due to the incomplete record. However, between this thrust sheet propagated northward via fault- Cuervos Formation in the Medina Basin, accu- the High Plain of Bogota and the Servita-Len- propagation folding, which incorporated the mulation in a back-bulge depozone can be ruled gupa-Tesalia faults, the structural configuration western part of the sedimentary wedge into the out in light of the regional distribution of fore- of the Eastern Cordillera does not involve major thrust belt (Fig. 8). The propagation of the struc- land basin deposits. In particular, late Paleocene faults that could have caused significant tectonic ture is also supported by the northward plunge back-bulge deposition in the Medina Basin loading (Mora et al., 2006; see also Fig. 1). of the Quetame massif. As a result of these pro- would imply that a forebulge would have been Thus, we favor the second scenario, in which cesses, the change from subsidence and burial located to the west of the basin. However, Paleo- tectonic loading at ca. 31 Ma was generated by to folding prevented further thermal maturation gene subsidence patterns in the southern Middle slip along the basement-bounding faults of the of organic matter, as revealed by VR data from Magdalena Valley to the west of the basin do not Quetame massif, which then caused proximal the C8 member of the Carbonera Formation and indicate limited accommodation, such as would foredeep deposition in the Medina Basin. In younger units in the western Medina Basin. In be expected in a forebulge depozone. Instead, this context, the absence of observable direct this context, a difference of -13 m.y. between late Paleocene rapid subsidence in the southern
Geological Society of America Bulletin, May/June 2009 795 Parra et al.
Middle Magdalena Valley Basin (Fig. 6B) and may account for part of the observed rapid tec- in the forebulge) that correlates with diminished a thick upper Paleocene sedimentary section in tonic subsidence in the basin. As pointed out by subsidence or flexural uplift in the foredeep the axial Eastern Cordillera (Cacho Bogota and Gomez et al. (2005), eastward onlapping of the (e.g., Burbank, 1992; Catuneanu et al., 1997, Lower and Upper Socha Formations; Fig. 2) late Paleocene Barco and Los Cuervos Forma- 1998). Although limited, data from the north- result from foredeep deposition related to tec- tions onto the Cenozoic and Mesozoic substra- ern part of the Middle Magdalena Valley Basin tonic loading in the Central Cordillera (Gomez tum of the Llanos Basin suggests an increase in (Pardo-Trujillo et al., 2003) suggest a decrease et al., 2003,2005). We therefore suggest that the the wavelength of the foreland basin (i.e., basin in sediment accumulation rates toward the top rapid accumulation recorded by the Los Cuervos widening; see Figs. 2 and 9C) that may correlate of the upper Paleocene units. This may repre- deposits in the Medina Basin reflects deposition with a diminished load exerted by the Central sent a reduction in subsidence within a proximal in the eastern reaches of this foredeep depo- Cordillera. The adjustment of the flexural pro- foredeep coeval with the increase in subsidence zone. However, as noted by Sarmiento-Rojas file of the basin to such episodes of erosional rates that allowed the accumulation and east- (2001), a minor contribution of remaining ther- unloading is characterized by an increase in sub- ward onlapping of the Barco and Los Cuervos mal subsidence from a Mesozoic rifting event sidence in the distal foreland basin system (i.e., Formations over more distal foredeep areas pre-
NW SE
^=| Leon and Guayabo Fms. NW SE Carbonera Fm. A A' ^Jj Barco, Los Cuervos and Mirador Fms. 4 - 3 Upper Cretaceous units 0- ^ZZ-r^g^. -4- Lower Cretaceous units -6- ^^^^7 Pre-Cretaceous Basement 8 (km) - l (km) •-" i Stratigraphic profiles (projected) Present
Figure 8. Retrodeformed cross section across the Medina Basin during (A) late Eocene, (B) early Miocene, and (C) present time, respectively (location of cross section in Fig. 2). Projected locations of stratigraphic sections and samples for vitrinite reflectance and zircon fission-track analysis are indicated for each time slice. Thrust-induced exhumation along of the Quetame massif during early Miocene incorporated the western part of the syntectonic clastic wedge of the Medina Basin into the fold-and-thrust belt. This resulted in the interruption of the thermal maturation of strata rich in organic matter in the western Medina Basin.
796 Geological Society of America Bulletin, May/June 2009 Orogenic wedge advance in the northern Andes, Colombia viously subjected to erosion in the Llanos Basin cc SMMVB EC Medina Llanos (Gomez et al, 2005) (Fig. 9). We interpreted the intermediate stage of Late Cretaceous reduced accumulation in the Medina Basin dur- A Initial uplift CC ing the Eocene-early Oligocene (ca. 56-31 Ma) using a regional comparison of accommoda- tion patterns across the foreland basin system. This stage of moderate subsidence rates in the Medina Basin was coeval with late Paleocene to middle Eocene unconformity development in the Middle Magdalena Valley Basin (Restrepo-Pace et al., 2004; Gomez et al., 2005). In the southern part of the southern Middle Magdalena Valley Basin, such an episode is represented by the flat early Paleocene segment in the subsidence curve (Fig. 6B). Sub- B Increase of tectonic loading sequent uplift in the western part of the Eastern Cordillera documented by AFT modeling and middle Eocene-Oligocene growth strata in the southern part of the basin also overlaps in time with the episode of limited accommodation recorded by the Eocene-lower Oligocene depos- Distal foredeep \ its of the Medina Basin. We suggest that such Forebulge limited accommodation, subsequent to a late Paleocene episode of rapid subsidence, which we interpret to have occurred in a foredeep late Paleocene depozone, is compatible with a distal foredeep C Erosional unloading setting. In this context, we invoke a reduction in tectonic subsidence, which reveals an episode of basin narrowing and westward retreat of the foreland basin system (Fig. 9D). Moreover, in the east, the development of an unconformity with an eastward-increasing chronostratigraphic gap Forebulge beneath the middle Eocene Mirador Formation (Jaramillo et al., 2008) suggests the existence of a forebulge in the Llanos Basin at that time. Following the late Paleocene episode of faster Dearly-middle Renewed loading subsidence in the course of erosional unloading, E (eastward advance of CC + Initial uplift western EC) limited Eocene accumulation in the eastern foot- hills can be interpreted as a flexural response of the basin to a renewed episode of thrust load- ing. This may have resulted from the eastward migration of the Central Cordillera thrust front Distal foredeep - \ as well as the onset of thrusting along the west- // forebulge Forebulge ern flanks of the Eastern Cordillera (Fig. 9D). Interestingly, available palynological data from the northern Magdalena Valley Basin (Pardo- late Eocene- Trujillo et al., 2003) show a coeval, yet opposite C. Eastward advance pattern of increased sediment accommodation early Oligocene (inversion of EC eastern margin) between the Paleocene and Eocene, which is in line with asymmetric subsidence as a response to renewed thrust loading and basin narrowing. This long-lasting (ca. 25 m.y.) episode of slower subsidence and narrowing of the Medina Basin / may also suggest protracted stationary foredeep Proximal foredeep Forebulge and forebulge depozones. Such stagnation of the foreland system may have been the consequence of tectonic loading acting over a less rigid part Figure 9. Cartoon illustrating the Maastrichtian-early Oligocene evolution of the of the foreland lithosphere (e.g., Waschbusch foreland basin system in response to uplift of the Central (CC) and Eastern (EC) and Royden, 1992). In this case, the weakened Cordilleras of the Colombian Andes. SMMVB—southern Middle Magdalena Valley lithosphere could correspond to a prestrained Basin. See text for discussion.
Geological Society of America Bulletin, May/June 2009 797 Parra et al.
area affected by Mesozoic rifting, which now the principal mechanism controlling foreland chemistry, v. 20, no. 6, p. 643-651, doi: 10.1016/0146- delimits the extent of the Eastern Cordillera dynamics up to late Paleocene time. Likewise, 6380(93)90050-L. Bayona, G., Reyes-Harker, A., Jaramillo, C.A., Rueda, (Fabre, 1983; Sarmiento-Rojas et al., 2006). we suggest that this mechanism was gradually M., Aristizabal, J., Cortes, M., and Gamba, N., 2006, However, a comprehensive regional documenta- replaced by a combination of renewed loading Distinguishing tectonic versus eustatic surfaces in tion of Cenozoic exhumation patterns and geo- in the Central Cordillera and eastward migration the Llanos Basin of Colombia, and implications for stratigraphic correlations, in Asociacion Colombiana dynamical modeling are required to further test of the deformation front to the western foothills de Geologos y Geofisicos del Petroleo ed., Extended the validity of these hypotheses. of the Eastern Cordillera during Eocene-early Abstracts, IX Simposio Bolivariano de Exploracion Finally, the second stage of rapid subsidence Oligocene time. Finally, ~31 m.y. ago, the oro- Petrolera en las Cuencas Subandinas: Cartagena de Indias, Colombia, 13 p. in the Medina Basin, starting in the early Oligo- genic front would have shifted eastward, and Beaumont, C, 1981, Foreland basins: Geophysical Journal cene, documents proximal foredeep deposition deformation would have been accommodated of the Royal Astronomical Society, v. 65, p. 291-329. Bemet, M., and Garver, J.I., 2005, Fission-track analysis of due to loading through initial inversion of the along an inherited Mesozoic extensional struc- detrital zircon: Reviews in Mineralogy and Geochem- Servita fault (Figs. 8 and 9E). This episode thus ture. The behavior of the foreland basin of the istry, v. 58, p. 205-238, doi: 10.2138/rmg.2005.58.8. reveals a stage of basinward migration of the Colombian Andes thus resembles other foreland Burbank, D.W., 1992, Causes of recent Himalayan uplift deduced from depositional patterns in the Ganges basin: foreland basin system that involved the reactiva- regions of the Andean orogen (Mon and Salfity, Nature, v. 357, p. 680-682, doi: 10.1038/357680a0. tion of inherited Cretaceous extensional faults. 1995; Hilley et al., 2005; Carrera et al., 2006; Burnham, A.K., and Sweeney, J.J., 1989, A chemical kinetic Moreover, this early initiation of thrusting along Hain and Strecker, 2008), where predicted pat- model of vitrinite maturation and reflectance: Geo- chimica et Cosmochimica Acta, v. 53, no. 10, p. 2649- the Servita-Lengupa fault in the early Oligo- terns of gradual, foreland-directed migration of 2657, doi: 10.1016/0016-7037(89)90136-1. cene documents protracted deformation located deformation are modified by the effects of load- Campbell, C.J., and Biirgl, H., 1965, Section through the Eastern Cordillera of Colombia, South America: along this reactivated fault. This is in line with ing of inherited crustal weak zones, the activa- Geological Society of America Bulletin, v. 76, no. 5, active thrust-induced exhumation throughout the tion of which generates a much more complex p. 567-590, doi: 10.1130/0016-7606(1965)76[567:ST Miocene, suggested by the ZFT data, and rapid pattern of thrust-belt evolution. TECO]2.0.CO;2. Carrera, N., Munoz, J.A., Sabat, F, Mon, R., and Roca, E., exhumation during the last ~3 m.y., as indicated 2006, The role of inversion tectonics in the structure of by apatite fission-track data in the Quetame ACKNOWLEDGMENTS the Cordillera Oriental (NW Argentinean Andes): Jour- massif (Mora et al., 2008a). Our data thus pro- nal of Structural Geology, v. 28, no. 11, p. 1921-1932, doi: 10.1016/j.jsg.2006.07.006. vide compelling evidence for the fundamental This research was supported by grants and schol- arships from the German Academic Exchange Ser- Catuneanu, O., Beaumont, C, and Waschbusch, P., 1997, Interplay of static loads and subduction dynamics in role exerted by inherited basement anisotropies vice (scholarships A/02/11325 and A/01/12054 foreland basins: Reciprocal stratigraphies and the in accommodating contractional deformation to M. Parra and A. Mora, respectively), Deutsche "missing" peripheral bulge: Geology, v. 25, no. 12, during Cenozoic orogenesis in the northern Forschungsgemeinschaft (DFG; Str 373/19-1 to M. p. 1087-1090, doi: 10.1130/0091-7613(1997)025<10 Andes. The Eastern Cordillera of the Colombian Strecker), funds from the DFG-Leibniz Center for 87:IOSLAS>2.3.CO;2. Earth Surface and Climate Studies at Potsdam Uni- Catuneanu, O., Hancox, P.J., and Rubidge, B.S., 1998, Andes hence constitutes a natural testing ground versity, and the Universidad Nacional de Colombia Reciprocal flexural behaviour and contrasting stratig- for numerical models predicting the locus of (Beca de Honor to M. Parra). We also thank the Insti- raphies: A new basin development model for the active deformation in an orogen as determined tute Colombiano del Petroleo and the Smithsonian Karoo retroarc foreland system, South Africa: Basin Research, v. 10, no. 4, p. 417-439, doi: 10.1046/J.1365- Tropical Research Institute for financial support. to a great extent by weak zones in the crust that 2117.1998.00078.x. accommodate shortening. However, as predicted Seismic profiles were kindly provided by the ANH Cazier, E.C., Cooper, M.A., Eaton, S.G., and Pulham, (Agenda Nacional de Hidrocarburos) of Colombia. A.J., 1997, Basin development and tectonic history by Allmendinger et al. (1983), more straightfor- We thank B. Horton, G. Bayona, and C. Uba for of the Llanos Basin, Eastern Cordillera, and Middle ward time-space patterns of deformation asso- discussions that helped improve the paper. We also Magdalena Valley, Colombia: The American Asso- ciated with an orogenic wedge may develop in greatly appreciate discussions with A. Kammer and ciation of Petroleum Geologists Bulletin, v. 81, no. 8, p. 1332-1338. those areas where the role of such anisotropies E. Lopez on the Cenozoic stratigraphy of the area. N. Cardozo generously provided us with his program Coleman, J.M., Roberts, H.H., and Stone, G.W., 1998, Mis- sissippi River delta: An overview: Journal of Coastal is reduced or where pre-existing basin fills pro- OSXBackstrip for one-dimensional backs tripping. vide a much more homogeneous material to Research, v. 14, no. 3, p. 698-716. A. Gomez kindly identified fossils. G Veloza and R. 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REVISED MANUSCRIPT RECEIVED 12 MAY 2008 Raasveldt, H.C., 1956, Mapa Geologico de la Republica de Tissot, B.P, Pelet, R., and Ungerer, P., 1987, Thermal his- MANUSCRIPT ACCEPTED 6 JULY 2008 Colombia, Plancha L9 (Girardot): Bogota, Institute tory of sedimentary basins, maturation indices, and Geologico Nacional, scale 1:200,000. kinetics of oil and gas generations: American Asso- PR I NTH) IN THE USA
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