An Integrated Analysis of an Orogen

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An integrated analysis of an orogen–sedimentary basin pair: Latest Cretaceous–Cenozoic evolution of the linked Eastern Cordillera orogen and the Llanos foreland basin of Colombia

German Bayona† Smithsonian Tropical Research Institute, Unit 0948, APO AA 34002-0948, USA, and Corporación Geológica ARES, Calle 57 No. 24-11 of 202, Bogotá, Colombia Martin Cortés Corporacón Geológica ARES, Calle 57 No. 24-11 of 202, Bogotá, Colombia Carlos Jaramillo Smithsonian Tropical Research Institute, Unit 0948, APO AA 34002-0948, USA German Ojeda Instituto Colombiano del Petróleo, AA 41815, Km 7 to Piedecuesta, Bucaramanga, Colombia John Jairo Aristizabal§ Ecopetrol S.A., Calle 37 No. 8-43, Bogotá, Colombia Andres Reyes-Harker Instituto Colombiano del Petróleo, AA 41815, Km 7 to Piedecuesta, Bucaramanga, Colombia

ABSTRACT identifi ed in two restored cross sections, one Llanos foothills, and synextensional strata on located at a salient and the other in a recess the forebulge of the Llanos Basin constrain The integration of restored basin geome- on the eastern fl ank of the Eastern Cordil- deformation patterns for this time. The try and internal features of syntectonic units lera. The lower two sequences correspond to post–middle Miocene Andean event initiated (e.g., stratal architecture, thickness, sand- late Maastrichtian–Paleocene fl exural events with regional fl ooding of the foreland basin stone composition) with fl exural modeling and record the eastward migration of both in response the widening of tectonic load- of the lithosphere constrains the evolution tectonic loading and depositional zero in ing, after which the foredeep was fi lled with of a basin and its fl exural history related to the Llanos Basin. These sequences consist of coarse-grained alluvial and fl uvial detritus orogenic growth (spatial/temporal load- amalgamated quartzarenites that abruptly derived from the Eastern Cordillera. ing confi guration). Using this approach, we grade upward to organic-rich fi ne-grained The geometry of tectonic loads, con- determined the Maastrichtian-Cenozoic beds and, to the top, light-colored mud- strained by fl exural models, reveals short- polyphase growth of the Eastern Cordillera stones interbedded with litharenites in iso- ening events of greater magnitude for the of Colombia, an inverted Mesozoic exten- lated channels. Amalgamated conglomeratic uppermost two sequences than for pre–mid- sional basin. The record of this growth occurs quartzose sandstones of the third sequence dle Eocene sequences. Tectonic loads for the in an Andean (post–middle Miocene) thrust record ~15 m.y. of slow subsidence in the Lla- late Maastrichtian–middle Eocene phases belt (the Eastern Cordillera) and in adjacent nos Basin and Llanos foothills during early of shortening were less than 3 km high and foreland basins, such as the Llanos Basin to to middle Eocene time, while shortening was 100 km wide. For the late Eocene–middle the east. This approach permitted the identifi - taking place farther west in the Magdalena Miocene phase, tectonic loads changed south- cation of fi ve tectono-stratigraphic sequences Valley. The fourth sequence, of late Eocene– ward from 6 km to less than 4 km, and loads in the foreland basin and fi ve phases of short- middle Miocene age, records a new episode were wider to the north. The strong Andean ening for the Eastern Cordillera. Thermo- of eastward migration of tectonic loads and inversion formed today’s Eastern Cordillera chronological and geochronological data depositional zero in the Llanos Basin. This structural confi guration and had equivalent support the spatial and temporal evolution of sequence begins with deposition of thick tectonic loads of 10–11 km. the orogen–foreland basin pair. fi ne-grained strata to the west, whereas to Integrated analysis is necessary in poly- Tectono-stratigraphic sequences were the east, in the Llanos basin, amalgamated phase orogenic belts to defi ne the spatial and quartzarenites unconformably overlie Cre- temporal variation of tectonic load and fore- †E-mail: [email protected] taceous and older rocks (former forebulge). land basin confi gurations and to serve studies §Present address: REPSOLYP, Calle 71A No. 5-38, Apatite fi ssion tracks in the axial zone of that seek to quantify exhumation and three- Bogotá, Colombia. the Eastern Cordillera, growth strata in the dimensional analyses of thrust belts. For the

GSA Bulletin; September/October 2008; v. 120; no. 9/10; p. 1171–1197; doi: 10.1130/B26187.1; 15 ﬁ gures; Data Repository item 2008078.

Eastern Cordillera, thermochronological risen strongly in the late Neogene. Therefore, deformed Llanos foreland basin. Reactivated sampling must span the width of the Eastern studies of shortening in the Eastern Cordillera Mesozoic normal faults, such as the Guaicar- Cordillera rather than be concentrated in a of Colombia, a mountain range of the northern amo fault system in the central Llanos foothills, single range. Andes, must consider temporal and spatial vari- have been considered to be the major boundary ations of crustal shortening that resulted from of those structural styles. Models of inversion Keywords: foreland basin, Cenozoic stratigra- pre-Neogene phases of deformation. tectonics have been created for the southern seg- phy, basin inversion, orogenic belts, Cenozoic This paper presents a kinematic evolution and ment of the Eastern Cordillera and Llanos foot- tectonics, Llanos Basin, Colombia. quantifi cation of tectonic loading of a polyphase- hills (Casero et al., 1997; Rowan and Linares, deformed orogenic belt (Eastern Cordillera) 2000; Branquet et al., 2002; Restrepo-Pace et INTRODUCTION adjacent to a nonmarine foreland basin (Llanos al., 2004; Toro et al., 2004; Cortés et al., 2006a; Basin). We integrate provenance, sedimentol- Mora et al., 2006), in the central segment of the Integrative research on syntectonic sedimen- ogy, stratal patterns, biostratigraphy, subsidence, Eastern Cordillera and Llanos foothills (Colleta tary basins should include different types of data structural, and geodynamic analyses with pub- et al., 1990; Dengo and Covey, 1993; Cooper et sets (sedimentology, stratal architecture, prove- lished thermochronological and geochronologi- al., 1995; Cazier et al., 1995; Roeder and Cham- nance, subsidence) and needs to consider kine- cal data in order to (1) investigate how crustal berlain, 1995; Rathke and Coral, 1997; Fajardo- matic constraints from the adjacent mountain thickening (i.e., tectonic loading) affected the Peña, 1998; Taboada et al., 2000; Sarmiento- belts. Tectonic activity, weathering processes, latest Cretaceous–Paleogene evolution of the Rojas, 2001; Rochat et al., 2003; Toro et al., and isostatic readjustment of the crust delimit Llanos foreland basin, and (2) identify struc- 2004; Martinez, 2006; Mora et al., 2006), and in uplifted blocks and so determine the nature of tures in the Eastern Cordillera that might have the northern segment of the Eastern Cordillera crustal loads adjacent to a basin. On the other been active at each phase of deformation. Our and Llanos foothills (Chigne et al., 1997; Corre- hand, syntectonic sedimentary basins include the results suggest that the present topography of dor, 2003; Villamil et al., 2004). Although struc- most complete record of the evolution of those the Eastern Cordillera does not refl ect the com- tural models differ both in the angle and depth uplifted blocks. Initiation of deformation in a plex earlier evolution of the northern Andes but of detachment of the Guaicaramo fault system formerly tectonically quiet (e.g., passive mar- rather provides a record only of the last phase of and in fault involvement of crystalline base- gin) and nearly fl at (e.g., coastal plain) region deformation. Therefore, integrated analysis of ment to the east, structural restorations from the affects depositional and paleoecological sys- the adjacent Llanos foreland basin is necessary axial zone of the Eastern Cordillera and Llanos tems, provenance, and paleocurrent indicators, to investigate the previous deformation events, Basin are similar (Fig. 1C). Proposed structural as well as climate variables (e.g., precipitation). which are masked by the last phase. models do not show a relationship between the The rearrangement of these variables infl uences amount of shortening and fl exural deformation the tectonic evolution of both mountain ranges TECTONIC FRAMEWORK OF THE in the adjacent basin, and they differ in (1) the (e.g., climatic control of critical wedge in the COLOMBIAN ANDES AND EVIDENCES amount of shortening of the Eastern Cordil- central Andes; Horton, 1999) and adjacent sedi- OF PRE-NEOGENE DEFORMATION lera, mainly from the axial zone to the western mentary basins (e.g., change in fl uvial patterns boundary of the Eastern Cordillera (Fig. 1C), of the Amazon Basin by uplift of the Andes; Regional Tectonic Setting of the Eastern (2) the geometry of fold structures at depth, and e.g., Hoorn et al., 1995). Cordillera (3) the position and confi guration of Mesozoic The kinematic evolution of an orogen affects eastern and western rift shoulders. both the geometry and fi lling patterns of syntec- Three major orogenic belts are the result of As an alternative method to validate the short- tonic sedimentary basins. In orogen and fore- the complex interaction of the Nazca, Carib- ening estimated in our cross sections, we used land basin systems, estimates of spatial and tem- bean, and South America plates since the Late the fl exural geometry of synorogenic Paleogene poral variations of crustal thickening commonly Cretaceous: the Western Cordillera, the Central to Neogene foreland basins, growth-strata pat- rely on studies of orogenic belt deformation in Cordillera, and the Eastern Cordillera. The East- terns, and crosscutting relationships of hanging- conjunction with proximal-to-distal synoro- ern Cordillera bifurcates to the north into the wall and footwall structures on the eastern fl ank genic stratigraphic and compositional analyses Santander massif–Perija Range (MS-PR) and of the Eastern Cordillera and Llanos foothills to (e.g., Horton et al., 2001; Liu et al., 2005) of the Merida Andes (MA) (Fig. 1). The Eastern better constrain the kinematic evolution of the the foreland basin. Geodynamic models of fore- Cordillera is interpreted as a wide Cretaceous eastern fl ank of the Eastern Cordillera. land basins have been essential in defi ning the extensional basin that was formed during at spatial and temporal variation of tectonic load least two stretching events (Sarmiento-Rojas et Evidence of Pre-Neogene Deformation geometries, since there is a primary relationship al., 2006) and that was tectonically inverted dur- among tectonic loading, strength of the litho- ing the Cenozoic (Colleta et al., 1990; Dengo Paleobotanical, thermochronological, and sphere, and basin geometry (e.g., Jordan, 1981; and Covey, 1993; Cooper et al., 1995; Mora et geochronological data indicate that surface Cardozo and Jordan, 2001). al., 2006). However, basement and sedimentary and rock uplift, as well as rock deformation, Integrated orogen and foreland basin analy- rocks exposed in the Eastern Cordillera and have occurred at different times but primarily sis of the type presented here is an essential adjacent basins indicate that this complex region in the late Neogene. Paleobotanical data indi- approach to understanding of polyphase thrust- has been the scene of polyphase tectonics since cate a change in fl ora from lowland associa- belt systems and deciphering deformation Precambrian time (see Etayo-Serna et al. [1983] tions to Andean-type forests (Helmens, 1990) phases. Investigations in the central (e.g., Horton and Cediel et al. [2003] for details). in the last 5 m.y., but the timing of this change et al., 2001) and northern Andes (e.g., Gómez et The eastern fl ank of the Eastern Cordillera of ranges between 3 and 6 Ma (Helmens and Van al., 2005a) indicate that pre-Neogene deforma- Colombia (Fig. 1) exposes contrasting structural der Hammen, 1994; Hooghiemstra and Van tion played an important role in the tectonic evo- styles between highly deformed rocks along an der Hammen, 1998). Zircon fi ssion-track ages lution of the Andes, which are believed to have east-verging fold-and-thrust belt and the less- support earlier uplift in the Central Cordillera

1172 Geological Society of America Bulletin, September/October 2008 An integrated analysis of an orogen–sedimentary basin pair

74ºW 72ºW

Bucaramanga Fa Mountain ranges and B Thrust fault massifs Anticline AM= Andes of Merida Syncline CC= Central Cordillera ult MV EC= Eastern Cordillera AM 8ºN FM= Floresta massif Quaternary GM= Garzon massif Cenozoic sedimentary rocks MV= Magdalena Valley 5 MM= Macarena massif Cenozoic volcanic rocks SM PR= Perija range QM= Quetame massif Upper Cretaceous sedimentary rocks NORTHERN LLANOS SM= Santander massif Lower Cretaceous sedimentary rocks NORTHERN CROSS SECTI SMM= Santa Marta massif CC WC= Western Cordillera 3 Lower Cretaceous intrusive rocks 4 2 ON (Fig. 3A ) Triassic-Jurassic intrusive rocks 1 CHUCARIMA Faults Triassic-Jurassic volcanic and MV sedimentary rocks TRANSVERSE ZONE A Romeral F. System (RFS) Cocuy Paleozoic 12 Northern Llanos foothills and SM Precambrian basement 1 Chucarima F.

8 2 Cobugon F. A 7 6ºN EC FM 3 Labateca F. 66ºW69ºW 72ºW 75ºW 78ºW 11 4 Chinacota F. Caribbean Plate 10 CENTRAL LLANOS 20 mm/yr 12º Bocono F. Tu n j a 5 6 M Central Llanos foothills and axial SM CENTRA PR A 9 zone of the EC L CROSS SECTION (Fig. 3B) 6 Cusiana-Cupiagua F. 9º S RF Guicaramo F. System (GFS) SM AM 7 MV Bogota 14 15 SA 8 Pajarito F. TRAN BANAL CC 12 13 SVERSE ZONEARGA 9 Chameza F. 6º Restored cross 7 sections Guyana QM 10 Soapaga-Pesca F. Nazca WC shown in C Shield Plate EC 54 11 Boyaca F. mm/yr 4ºN RFS NAZARET 3º Western flank of the EC Llanos basin TRANSV A GM 12 Salinas F. MM H ERSE SOUTHERN LLANOS enlarged map ZO Southern Llanos foothills NE 250 km shown in B QM 13 Medina-Guavio F. 0º SOUTHE RN STR Tesalia-Lengupa F. AT I 14 GRAPHIC (Bay SE ona et CTION Servita-Santa Maria F. al., 2006) 15 MM

RESTORED WIDTH OF THE PRESENT EASTERN CORDILLERA = 287.5 km regional pin line 333 km C 125 km restored MV CC eroded 12 TOP OF CRETACEOUS 11 10 7

Dengo and Covey, 1993

Restored trace of thrust faults RESTORED WIDTH OF THE PRESENT EASTERN CORDILLERA = 218.2 km

Present erosion profile 264 km 131 km restored MV Sedimentary Mesozoic rocks CC eroded 12 11 10 7 6 TOP OF CRETACEOUS Basement and Paleozoic rocks 9

100 km

Cooper et al., 1995 Figure 1. (A) Regional tectonic setting of the northern Andes of Colombia. (B) Geologic map of the Eastern Cordillera of Colombia (modi- ﬁ ed from Cediel and Cáceres, 1988) showing the location of the northern and central cross sections (see Fig. 3) and stratigraphic control along the southern stratigraphic cross section (for details, see Bayona et al., 2006). (C) Restored cross sections showing different interpretations of the restored position and geometry of major structures of the Eastern Cordillera. The restored distance between a regional pin line in the Llanos Basin and the Soapaga-Pesca fault (western boundary of our study area) is similar between these two interpretations (differ- ence = 6 km). In contrast, the restored width of the western ﬂ ank of the Eastern Cordillera differs by 75 km.

Geological Society of America Bulletin, September/October 2008 1173 Bayona et al.

(around the Campanian-Maastrichtian bound- identify the location of loads that affected the confi rm and provide control on the lateral conti- ary; Toro, 1999; Gómez et al., 2005a) than geometry of the Paleocene foreland basin in the nuity and consistency of the regional structural in the Santander massif–Perija Range and Llanos foothills and Llanos Basin. models. Surface mapping, seismic-refl ection Merida Andes (near the Cretaceous-Tertiary Angular unconformities and growth-strata pat- profi les, gravity data, and well data constrain the [KT] boundary; Shagam et al., 1984; Kohn et terns of Paleogene beds place constraints on our construction of balanced cross sections. Strati- al., 1984). Apatite fi ssion-track ages (AFTA) ability to defi ne phases of deformation. A highly graphic thickness and units for each thrust sheet indicate a northward exhumation that began variable angular unconformity between lower- were provided from the tectono-stratigraphic in the Oligocene in the Floresta (22.3 ± 4 Ma) to-middle Eocene strata resting upon Paleocene analysis carried out along these regional cross and southern Santander (30.8 ± 5.8 Ma) mas- or older units has been well documented in sections (see next section). sifs (Toro, 1990), then moved to the central and the subsurface of the Magdalena Valley (Vil- northern Santander massif in the Miocene and lamil et al., 1995; George et al., 1997; Pindell Structure of the Northern Cross Section Miocene-Pliocene, respectively (Shagam et al., et al., 1998; Gómez et al., 2003, 2005b) and in 1984). AFTA ages on the western fl ank of the outcrops (Restrepo-Pace et al., 2004). In the This cross section (Fig. 3A) traverses a base- Eastern Cordillera (Gómez et al., 2003) support Magdalena Valley, structures beneath the uncon- ment structural high, named the Pamplona two phases of cooling, the fi rst between 65 and formity have been interpreted as high-angle indenter by Boinet et al. (1985), which is bor- 30 Ma, which involved the removal of 3–4 km strike-slip faults (Pindell et al., 1998; Gómez et dered by the northwest-striking Chucarima of overlying sedimentary cover, and the second al., 2005b). Strata overlying this unconformity fault, north-striking Labateca and Chinacota between 10 and 5 Ma, which involved denuda- show a wedge of divergent growth strata of mid- reverse faults, and northeast-striking right-lat- tion of 3 km of sedimentary cover. AFTA results dle Eocene–lower Miocene age in the southern eral Bocono fault. This cross section, located at on the eastern fl ank of the Eastern Cordillera middle Magdalena Valley (Gómez et al., 2003) the recess of the Guaicaramo fault system (the (Hossack et al., 1999) require exhumation along and upper Oligocene–middle Miocene age in Guaicaramo fault system is displaced to the the Chameza fault at 25 Ma and exhumation in the northern Magdalena Valley (Gómez et al., west to become the Cobugon fault), starts at the the foothills between 3 and 15 Ma. AFTA data 2005b). In the axial zone of the Eastern Cor- western fl ank of the Santander massif, passes from the Garzon and Quetame massifs indicate dillera, the structure of the eastern fl ank of the through the northern Llanos foothills, and ends younger phases of deformation, ranging from Usme syncline (south of Bogotá in Fig. 1B) has at the Caño Limon oil fi eld in the northern Lla- 12 to 3 Ma (Van der Wiel, 1991). The genera- been interpreted as a progressive unconformity nos Basin (Figs. 1 and 3A). The trace of this tion of an orographic barrier at ca. 6–3 Ma trig- that has been growing since the late Paleocene cross section is far from the transverse bound- gered rapid denudation and shortening rates of (Julivert, 1963). In the northern Llanos foothills aries of the Pamplona indenter and at the place the eastern fl ank of the Eastern Cordillera (Mora and Llanos Basin, Corredor (2003) and Cortés where deformation is mostly plane strain. et al., 2005). Reported geochronological data et al. (2006b) reported growth-strata patterns in Structural domains in the Eastern Cordillera from green muscovite crystallized on emerald- Oligocene-Miocene strata. In the central Llanos and Llanos foothills of the northern cross sec- bearing vein wall rocks (Ar/Ar and K/Ar) indi- foothills, Rathke and Coral (1997) and Martinez tion involve basement rocks. These domains cate a fi rst extensional event at 65 ± 3 Ma on the (2006) suggested the incipient development of end southward at the northwest-striking Chu- eastern fl ank and a compressional event on the broad fault-related anticlines and synorogenic carima fault system. The latter structure places western fl ank between 32 and 38 Ma (Branquet deposition during the Oligocene. Adjacent to a >3-km-thick succession of lower Cretaceous et al., 1999). leading structures of the Llanos foothills (e.g., rocks (Fabre, 1987) in the upthrown block over A regional shift from marine to continental Cusiana fault in Fig. 1), however, seismic refl ec- NNW-striking folds involving upper Cretaceous depositional environments at the end of the Cre- tors of Oligocene and Miocene strata are paral- and Paleogene strata in the downthrown block. taceous was coeval with accretion of oceanic lel and generally isopachous (Toro et al., 2004). In the latter block, the maximum thickness of the terranes west of the Romeral fault system (e.g., Parra et al. (2005) interpreted the westward lower Cretaceous rocks is 1.2 km (Fig. 2). South Etayo-Serna et al., 1983; McCourt et al., 1984). coarsening and thickening of the Oligocene of the Chucarima fault, structural domains are Mechanisms driving this shift have been inter- clastic wedge across a 20-km-wide syncline as more similar to those described for the central preted as eustasy and tectonism (Villamil, 1999) the result of fl exural subsidence related to the cross section. or increasing rate of sediment supply associated uplift of the Quetame massif. Structural balance of the northern cross sec- with exhumation and denudation of the Central tion indicates a total shortening of 30.5 km Cordillera (Gómez et al., 2005a). Interpreted STRUCTURE OF THE EASTERN FLANK (Fig. 3A). Major basement-involved faults form Paleocene basin geometry varies from a single OF THE EASTERN CORDILLERA the boundaries between structural domains. The and continuous foreland basin (Cooper et al., west-dipping basement-involved faults trans- 1995; Villamil, 1999; Gómez et al., 2005a) to In order to better understand the regional lated displacement and strain eastward through a continuous negative fl exural basin with appar- geometry and lateral variations along the eastern an imbricated fold-and-thrust belt. The major ent absence of bounding thrusts (Pindell et al., fold-and-thrust belt of the Eastern Cordillera, displacements occurred along faults exposed 2005) to a foreland basin disrupted by uplifts two regional balanced cross sections extending toward the hinterland, where the Santander mas- along the axial zone of the basin (Fabre 1981, from the axial zone of the Eastern Cordillera sif is exposed (domains DN1&2, Fig. 3A). Out- 1987; Sarmiento-Rojas, 2001; Pardo, 2004), to the Llanos Basin were constructed in areas of-sequence deformation along the Cobugon the western border of the basin (Bayona et al., where the geometry of the Guaicaramo fault sys- and Samore faults is inferred from the crosscut- 2003; Restrepo-Pace et al., 2004, Cortés et al., tem, the internal structural confi guration of the ting relation between fault surfaces and footwall 2006a), or at both borders of the basin (Fajardo- Eastern Cordillera, and the Cretaceous-Ceno- structures (domain DN3). A late Oligocene– Peña, 1998; Villamil, 1999). The integration of zoic stratigraphy differ (Figs. 1 and 2). Local early Miocene phase of east-verging deforma- basin geometry, provenance, paleocurrent, sub- cross sections were studied to the north and tion is constrained by growth-strata patterns sidence, and geodynamics analyses allows us to south of these regional cross sections in order to identifi ed in the syncline bounded by the Samore

1174 Geological Society of America Bulletin, September/October 2008 An integrated analysis of an orogen–sedimentary basin pair

coal shale - mudstone sandstone conglomerate A Northern cross section limestone chert low-grade metamorphic rocks high-grade metamorphic rocks detachment level AGE UNIT (thickness in m) Mechanical units in sections cross Llanos foothills Llanos Llanos basin Llanos B Central cross section Pliocene Guayabo - 3300 Guayabo AGE Mechanical units in sections cross Llanos foothills Llanos Llanos basin Llanos NEOGENE

Leon Pliocene >1250 Miocene

450 Guayabo

Leon NEOGENE Axial zone of the EC Santander massif Santander 350-400 Miocene

Oligocene Carbonera - 2000 Carbonera 1400-2100 Oligocene

Mirador Eocene Mirador 140-240 Eocene 290 Cuervos Cuervos PALEOGENE Paleo- 180-480 Upper PALEOGENE 460 Upper

L Barco Barco 200 50-200 Guaduas Paleocene L Colon- Maastrichtian 0-50 Guada- Maastrichtian Mito Juan lupe 400 500-530 Campanian Luna Campanian Santonian 50-200 Coniacian Chipaque Turonian Gacheta Santonian 400-620

380 Upper Coniacian Cenomanian Turonian Cenomanian

Albian Une 900-1400 1300

Albian Aptian Aguardiente

Tibu- CRETACEOUS

CRETACEOUS Mercedes 700-900 Aptian 300 Fomeque Lower Upper Barremian Lower Juntas Hauterivian 500-700 Aptian 0-1330 Rio Negro Valanginian- Valanginian Giron JURASSIC 250 PERMIAN- Diamante Caqueza Gr. and Gr. Caqueza Berriasian units >1500 other DEVONIAN Floresta

F. El Aji F. pre-Cretaceous ?? CAMBRIAN Silgara Bucara-

PRECAMBRIAN LabatecaF.

Figure 2. Generalized stratigraphic columns showing the lateral distribution of units along the (A) northern and (B) central cross sections. Regional detachment levels and mechanical units used for construction of cross sections are indicated.

Geological Society of America Bulletin, September/October 2008 1175 Bayona et al. E ank SE Gu1 CL1 Fig. 4C 20 km 20 km LP Gu1 LP pre-Mesozoic Lower Cretaceous - Lower Jurassic-Triassic Al Al Aq1 Ce e amount of restoration for the eastern ﬂ for e amount of restoration ed from Geoconsult-Pangea (2003). A complete A Geoconsult-Pangea (2003). ed from owever, the structural geometry is more similar similar the structural geometry is more owever, 5 iﬁ 4 C N D D middle Eocene - Paleocene LG1&2 lower Paleocene - Upper Cretaceous Regional pin line (for comparison with Fig. 1C) Regional Regional pin line Regional Regional pin line Regional

LM LC LG1&2 Ce LM LC

Fig. 4B Cusiana-

A1&3 Ju1

Cusiana- Bojaba F. Bojaba 4 C-BA C middle Miocene - upper Eocene Pliocene- middle Miocene D C-BA

TN Yopal F. Yopal Guaicaramo F. Guaicaramo 3 Yopal F. Yopal 3 N C D

D Chameza F. Chameza

TN Guaicaramo F. Guaicaramo 2 G1&2 C D Fig. 4A

G1&2 Samore F. Samore

Cobugon F. Cobugon

Chameza F. Chameza Samore F. Samore 1 C 2 D Contact (dashed when inferred) Fault Restored fault trace N D

Central cross section

Cobugon F. Cobugon La Northern cross section Pesca F. Pesca

Va Labateca F. Labateca 87.1 km L1= Deformed length, L1 = 90.4 km 1 N D Outcrop section Well Structural domains 1 Va C D

Original length, L0 = 120.9 km

; Labateca F. Labateca 1 W NW N

D Pesca F. Pesca 129 km L0 = 130.1 km L0 of the Eastern Cordillera along the central cross section (Fig. 3B) has similar results to those shown in Figure 1C (129 km); h to those shown in Figure results section (Fig. 3B) has similar of the Eastern Cordillera along central cross section was mod the central cross of the basement in Llanos Basin for Structure et al. (1995) interpretation. to the Cooper surface and subsurface data is in Cortes et al. (2006). for list of references Figure 3. (A) Northern and (B) central balanced and restored cross sections showing major structures and structural domains. Th and structural domains. structures sections showing major cross 3. (A) Northern and (B) central balanced restored Figure A B

1176 Geological Society of America Bulletin, September/October 2008 An integrated analysis of an orogen–sedimentary basin pair

fault (Cortés et al., 2006b) (Fig. 4A). Two con- of thickness of lower Cretaceous strata. The lat- through the Llanos foothills with no exposures trasting structural styles are well defi ned in both eral changes in structural and stratigraphic pat- of basement blocks and reaches the Llanos extremes of the northern Llanos Basin (domain terns across the Chucarima fault, as described Basin (Fig. 3B). Farther south along the Llanos DN4). In the western extreme, strata are folded here, defi ne the Chucarima transverse zone. foothills, the Quetame massif plunges north- in a compressive anticline structure (well A1&3 Similar relationships between curved geometry ward at the same latitude where other folds in Fig. 3A), and upper Oligocene–lower Mio- of orogenic belts and basin geometry bounded plunge, and the Guaicaramo fault system is dis- cene strata thin at the crest of the fold, suggest- by transverse structures have been documented placed to the west to become the Servita fault. ing a growth structure (Fig. 4B). At the eastern in other regions (Macedo and Marshak, 1999). The alignment of these elements corresponds side (well CL1 in Fig. 3A), synfaulting upper to the Sabanalarga transverse zone; structures Oligocene–lower Miocene strata document Structure of the Central Cross Section that strike parallel to this transverse zone show normal faulting (Fig. 4C). This is interpreted as evidence of reactivation (Mora et al., 2006). We fl exural deformation associated with a forebulge This section traverses the area where the interpret this transverse zone as a buried E-W (Cortés et al., 2006b). Guaicaramo fault system has its easternmost transfer fault system composed of Mesozoic The recess geometry of the frontal thrust belt advance into the foreland basin, defi ning a normal faults, as suggested by Sarmiento-Rojas north of the transversal Chucarima fault sug- salient geometry of the thrust belt. At this lati- et al. (2006) in this area and farther south in a gests that: (1) the Chucarima fault, a transverse tude, the Eastern Cordillera reaches its maxi- system named the Nazareth transfer zone. fault, was an E-W transfer fault system in a N-S mum width in a NW-SE direction. This cross Although basement rocks are not exposed system of normal faults during Mesozoic rifting section starts at the hanging-wall block of the along the eastern fl ank of the Eastern Cordil- phases; and (2) the recess and salient geometries east-verging Pesca fault, the southern equivalent lera between the Chucarima and Sabanalarga of the frontal thrust belt across the Chucarima to the basement-rooted Soapaga fault system transverse zones, we interpret basement-rooted transverse fault are controlled by a lateral change to the north (Fig. 1). This cross section passes faults as the boundaries of structural domains in

A NW SE C NNE SSW Samore F. Top Carbonera Fm.

Top Cretaceous

2 km 1 s

upper Oligocene-lower Miocene B strata (middle Carbonera Fm.) SWW NEE

Top Carbonera Fm. Well A1 Well Top Carbonera Fm. Top Paleocene Top Paleocene Top Cretaceous Top Cretaceous 1 s 1 s

5 km 5 km

Figure 4. Evidence of faulting during deposition of upper Oligocene–lower Miocene Carbonera strata (thick black line) in the northern cross section (see Fig. 3A for location of seismic lines). From west to east: (A) Depth-migrated seismic line across the western ﬂ ank of a hanging-wall syncline showing growth-strata patterns; arrows indicate the onlap relation of strata. (B) Left: time-migrated seismic line showing lateral thickness change across an anticline structure in the western Llanos Basin. Right: line ﬂ attened to the top of the Carbonera Formation showing the thinning of strata at the axial zone of the anticline. (C) Time-migrated seismic line showing thickening of the Car- bonera Formation across extensional structures in the Llanos Basin.

Geological Society of America Bulletin, September/October 2008 1177 Bayona et al. the Eastern Cordillera and Llanos foothills. Pre- fold broke along the major fault system, and is the equivalent record of foredeep strata. As Mesozoic metamorphic and sedimentary rocks the hanging wall overrode the overturned fl ank the paired load (sedimentary and tectonic) and exposed in the Floresta massif in the axial zone of the asymmetrical syncline. Seismic refl ec- fl exural wave advance cratonward, dark-col- of the Eastern Cordillera and the Quetame mas- tors of upper Oligocene and Miocene strata ored mudstones of the axial foredeep migrate sif to the south of the Sabanalarga transverse do not show growth-strata patterns above the cratonward, while deposition of amalgamated zone support this assumption. These basement- uppermost detachment level (Toro et al., 2004); sandstones takes place on the former forebulge. rooted faults (domains DC1&2, Fig. 3B) are however, this detachment level cut off structures If new tectonic loading breaks back within the interpreted as reactivated normal faults because involving Paleogene strata, suggesting incipi- hinterland or the tectonic loading confi gura- of the contrasting stratigraphic thickness ent deformation beginning in the Oligocene in tion changes abruptly, the foreland geometry variations of Paleozoic-Mesozoic successions the Llanos foothills (Rathke and Coral, 1997; will change, and a new tectono-stratigraphic between structural blocks (Mora et al., 2006; Martinez, 2006). In addition, out-of-sequence sequence will be formed. Kammer and Sanchez, 2006). The Llanos foot- reactivation is inferred from offset of fold axes The Maastrichtian-Pliocene stratigraphic suc- hills area includes the east-verging Guaicaramo across the east-verging Chameza fault and from cession can be divided into fi ve tectono-strati- fault system, overturned Neogene beds in the the irregular hanging-wall and footwall cutoff graphic sequences (Figs. 5 and 6), the chrono- adjacent syncline, and low-angle thrust faults at patterns of the Guaicaramo fault system. logical intervals of which are constrained by the leading edge of the deformation front. The Two other styles of deformation are inter- palynological data (see methods in Jaramillo et Guaicaramo fault system includes a symmetri- preted for the Llanos foothills (domain DC4, al., 2006a, 2006b). Palynological age determina- cal syncline in the hanging wall and offsets an Fig. 3B). The fi rst style is observed on the west- tions have the following resolution: 1–2 m.y. for asymmetrical overturned anticline-syncline pair ern segment, where fold geometry is related to the Maastrichtian-Paleocene, 5–10 m.y. for the (domain DC3). To the east, Ordovician, upper a ramp-fl at geometry of the basement-rooted Eocene, 3 m.y. for the Oligocene, and 1–2 m.y. Cretaceous, and Cenozoic strata are involved Yopal fault and where there is an upper décol- for the early and middle Miocene. In this sec- in east-verging low-angle thrust fault systems lement surface in upper Eocene rocks. The tion, we focus on lateral and vertical changes (domain DC4; Martinez, 2006). These faults other style is interpreted on the eastern seg- of lithofacies associations and key sedimento- deform the eastern fl ank of wide and laterally ment, where fold geometry is associated with logical data for Maastrichtian–middle Miocene continuous synclines; both frontal faults and the propagation of the east-verging Cusiana tectono-stratigraphic sequences, and we present synclines form an en echelon array along the fault system, which has a décollement surface in a brief description of the middle Miocene–Plio- eastern boundary of the Llanos foothills. In Ordovician sedimentary rocks and breaks to the cene sequence. Lithostratigraphic units of the the Llanos Basin (domain DC5), upper Creta- surface along the frontal limb of the syncline. Llanos foothills area are indicated in the head- ceous and Cenozoic rocks dip gently westward The latter style is complex at depth due to (1) an ers for each tectono-stratigraphic sequence, and and overlie Paleozoic and basement crystalline out-of-sequence west-verging fault system that equivalent lithostratigraphic units are indicated rocks. Basement structures locally offset the offset the east-verging fold-and-thrust system in Figures 5 and 6. sedimentary wedge. (Martinez, 2006), and (2) the subsequent trun- The total shortening estimated for this cross cation of footwall structures by the east-verging Tectono-Stratigraphic Sequence One (Upper section is 43 km (Fig. 3B). Basement-involved Yopal fault. Maastrichtian to Lower Lower Paleocene; structures transfer displacement at shallow Upper Guadalupe-Guaduas Formations and depths into a dominantly east-verging fold-and- MAASTRICHTIAN–PLIOCENE Equivalent Strata) thrust belt with décollement surfaces at several TECTONO-STRATIGRAPHIC levels within Cretaceous and Oligocene rocks SEQUENCES A regional shift from marginal to coastal (Figs. 2 and 3B). West-verging fault systems fl uvial depositional environments is recorded in the axial zone of the Eastern Cordillera are A tectono-stratigraphic sequence in a foreland in this sequence. A brief description of this interpreted as back thrusts that deform the foot- basin is a rock unit genetically related to one tec- shift is presented from east to west. In the cen- wall block of the Pesca fault (domain DC1). The tonic loading event, and it may be constrained tral Llanos foothills, Guerrero and Sarmiento east-verging basement-cored anticline-syncline by the internal architecture of foredeep strata (1996) reported a 150-m-thick coarsening- pair in the Llanos foothills is interpreted as an (Flemings and Jordan, 1990) and lateral migra- upward succession from medium-grained to overturned and displaced fault-propagation fold tion of foreland basin depozones (DeCelles conglomeratic sandstones with cross-beds and because: (1) beds in the hanging wall and foot- and Giles, 1996). In a nonmarine siliciclastic reworked bivalves, oysters, and corals (Fig. 5). wall blocks of the Guaicaramo fault system are tropical foreland basin (i.e., the Llanos Basin), Bioturbation is observed both in sandstone and overturned and have high-angle dip, and (2) the a tectono-stratigraphic sequence is bounded at black mudstone beds. These Maastrichtian con- Guaicaramo fault system displaced overturned the base by fi ne-grained strata in the axial fore- glomeratic sandstones have been reported up to beds of the eastern fl ank of the anticline. Kine- deep (high tectonic subsidence and low infl ux 200 km farther north along the Llanos foothills matic modeling of similar structures (Narr and of detritus from the forebulge or orogen) and (e.g., Colmenares, 1993; Arango, 1996), and Suppe, 1994) indicates that basement-involved amalgamated sandstones in the distal foredeep fi ne-grained interbeds show recovery of pollen structures within the anticline forelimb contrib- (subsidence decreasing toward the forebulge). and dinofl agellate cysts that indicate a Maas- ute to the formation of asymmetrical overturned In the proximal and axial zone of the foredeep, trichtian age (Bayona et al., 2006). In the north- synclines in the front. As the anticline devel- the tectono-stratigraphic sequence consists of ern Llanos foothills, fi ne-grained siliciclastic oped, deformation played a more important muddy sandstones, sandstones, and conglom- successions and thin carbonate interbeds domi- role in controlling the location and architecture erates showing an upsection increase of lithic nate (Royero, 2001; Geoestratos-Dunia, 2003). of synorogenic Cenozoic deposition eastward content supplied from the orogen coincident A 30–40-m-thick succession of Maastrichtian of the Guaicaramo fault system. As shortening with decreasing accommodation space. If the carbonaceous mudstones overlies the conglom- increased, the asymmetrical fault-propagation forebulge is exposed, a correlative unconformity eratic sandstones (Fig. 5, section TN).

1178 Geological Society of America Bulletin, September/October 2008 An integrated analysis of an orogen–sedimentary basin pair Ce 50% basal sandstone 0 ank of the Eastern LG 50% Llanos Llanos units No record No record No record Fm. Barco No record Cuervos to the west). (only Fm Cuervos 0 10 km 200 m LC 50% 0

ANIAN

PALEOCENE

CAMP shows the westward thickening of tectono- gure

Carbonera Fm. Carbonera Fm. Carbonera upper Mirador Fm. Mirador lower Fm. Fm. Cuervos Fm. Barco Fm. Guaduas Upper Guadalupe Fm. UPPER units Foothills 50% LOWER OLIGOCENE 0 Interval with palynological sampling. Percentage of marine influ- Interval depthence is indicated with bars at each specific sequence boundary inferred sequence boundary C-BA 50% 0 Tectono-stratigraphic foreland sequences Tectono-stratigraphic Concentracion Fm. Concentracion Fm. Concentracion Fm. Concentracion Fm. Picacho Fm. Upper Socha Fm. Socha Lower Fm. Guaduas Upper Guadalupe Fm. Upper Guadalupe Fm. Llanos foothillsLlanos Basin Llanos Cordillera (EC) units 3b 3a 2 1 4a axial zone of the Eastern 50% les of sections and gamma-ray curves of wells are plotted twice by reversing the plotted twice by reversing les of sections and gamma-ray curves wells are 2 1 4a 3b 3a 0

ANIAN

EOCENE

EOCENE LEOCENE CAMP R

UPPER

MIDDLE

PPE

PALEOCENE

MAASTRICHTIAN

LOWER-

LOWER PA LOWER CENE

ING THE EOCENE THE ING

DURING THE LATE PALEO- LATE THE DURING

THICKENING (1 km) DUR- km) (1 THICKENING

THICKENING (2.5 km) (2.5 THICKENING

AREA OF CRUSTAL OF AREA AREA OF CRUSTAL OF AREA 80 km 50% 1 2 4a 0 3a 3b Cordillera (section NM) is shown to illustrate the westward coarsening of Eocene strata. Palinspastic distances for TN. Sources sections eastward of TN; the horizontal scale is for sections west of section indicated for are et al., 2003; NM (Jaramillo, 1999; Pardo-Trujillo construction of composite stratigraphic sections and ages are: and Sarmiento, 1996; Jaramillo, TN (Guerrero 2001; Pardo, 2004; this study); Gómez et al., 2005b); La (Yepes, cited in Bayona et al., 2006). 2001; and references 1999; Jaramillo and Dilcher, Figure 5. Stratigraphic correlation of Maastrichtian to uppermost Eocene strata among the axial zone 5. Stratigraphic correlation Figure TN, well C-BA), and the Llanos Basin (wells LM, Eastern Cordillera (section La), Llanos foothills LC, LG, Ce). Grain-size profi This fi scale, giving a uniform display of grain-size patterns. (named 4a; see part of tectono-stratigraphic sequence four and the lower stratigraphic sequences one to three partial section of the western fl A description of each tectono-stratigraphic sequence). text for La

axial EC

CAMP ANIAN

N Paleo- MAASTRICHTIA

Lower cene?

EOCENE

UPPER

LEOCENE

Lower

UPPER EOCENE UPPER LOWER-MIDDLE EOCENE LOWER-MIDDLE LOWE

LOWER OLIGOCENE PALEOCENE DURING THE EOCENE EOCENE THE DURING

ZONE OF CRUSTAL ZONE (3 km) THICKENING THE DURING MAASTRICHTIAN

THICKENING (1.5 km) (1.5 THICKENING

160 km

ZONE OF CRUSTAL OF ZONE

UPPER UPPER PALEOCENE LOWER-MIDDLE EOCENE LOWER-MIDDLE UPPER EOCENE UPPER 2 4a LOWER PALEO- CENE ? 3a 3b

Western flank EC. Western NM

LOWER OLIGOCENE Fm.

P Lisama upper La Paz Fm. Esmeraldas Fm. Esmeraldas Fm. Paz La upper az Fm. az La lower

THE LATE PALEOCENE LATE THE

THICKENING DURING THICKENING AREA OF CRUSTAL OF AREA Madgalena Valley

Geological Society of America Bulletin, September/October 2008 1179 Bayona et al. 50% total thickness of sequence 5 (from et al., Fajardo 2000) 0 LP 4b 5 4c

of composite stratigraphic

-OLIGOCENE d

La), Llanos foothills (section

Mi CAMPANIAN Bayona et al., 2006). LOWER MIOCENE UPPER OLIGOCENE MIDDLE MIOCENE 50% 0 Llanos units No record No record No record Leon Fm. Fm. Carbonera Fm. Carbonera Carbonera Fm. (basal sandstone) m). Palinspastic ve in well LC (3811 Ce 50% sequence boundary inferred sequence boundary 0 LG 3110 m 2515 m 1997 m Carbonera Fm. Carbonera Fm. Carbonera Fm. upper Mirador Mirador lower Fm. Foothills units Foothills Fm.Guayabo Fm. Guayabo Leon Fm. Fm. Carbonera Carbonera Fm. Carbonera 50% Interval with palynological sampling. Percentage of marine influ- Interval depth ence is indicated with bars at each specific 0 50% LC 3811 m 3811 50% 0 0 LM

3735 m

CEN CENE

plotted twice by revers- les of sections and gamma-ray curves wells are PALEO 5 Tectono-stratigraphic foreland sequences Tectono-stratigraphic 4b 4c

No record No record Fm. Concentracion Fm. Concentracion Fm. Concentracion Fm. Picacho partial record of Fm. Concentracion

UPPER UPPER ER OLIGO ER Cordillera (EC) units 50%

axial zone of the Eastern LOW 0 5 4c 4a 3a 4b 3b gure illustrates tectono-stratigraphic sequences three and four and the lower part of and the lower and four illustrates tectono-stratigraphic sequences three gure

C-BA

2835 m PER PALEOCENE PER

LOWER MIOCENE

UPPER OLIGOCENE UP 3b 3a 4a

MIDDLE MIOCENE 50% Llanos foothills Llanos Basin 0 10 km TN

200 m

1400 m

EOCENE

MIDDLE

LOWER-

MIOCENE MIOCENE

OLIGOCENE OLIGOCENE

OLIGOCENE-LOWER ING THE EOCENE THE ING

THICKENING (3 km) (3 THICKENING

THICKENING (4 km) (4 THICKENING

THICKENING (1 km) DUR- km) (1 THICKENING

EOCENE ZONE OF CRUSTAL OF ZONE

ZONE OF CRUSTAL OF ZONE

AREA OF CRUSTAL OF AREA OLIGOCEN

PPER

80 km U LOWER 50% 0

Oligocene biozone biozone Oligocene no record of upper of record no

LOWER

EOCEN La

the thickest succession of sequence ﬁ The abrupt thickening of these sequences migrates eastward, reaching ve.

axial EC

LOWER-MIDDLE EOCENE LOWER-MIDDLE UPPER EOCENE UPPER ZONE OF CRUSTAL THICKENNING (10 km)- post MIDDL ZONE OF CRUSTAL E MIOCENE 4a 3a 4b 3b Figure 6. Stratigraphic correlation of Eocene to middle Miocene strata among the axial zone Eastern Cordillera (section 6. Stratigraphic correlation Figure TN, well C-BA), and the Llanos basin (wells LM, LC, LG, Ce, LP). Grain-size profi This fi ing the scale, giving a uniform display of grain-size patterns. sequence fi distance between sections La and TN is indicated; the horizontal scale is for sections eastward of TN. Sources for construction for TN. Sources sections eastward of TN is indicated; the horizontal scale for distance between sections La and cited in 2001; and references TN (Jaramillo, 1999; Jaramillo and Dilcher, La (Pardo, 2004; this study); sections and ages are:

1180 Geological Society of America Bulletin, September/October 2008 An integrated analysis of an orogen–sedimentary basin pair

Along the axial zone of the Eastern Cordil- Geoestratos-Dunia, 2003), in the Llanos foot- The lower and upper intervals are also pres- lera, strata of this sequence are represented hills, it ranges between 0.6 and 0.2 km, and in ent in the axial zone of the Eastern Cordillera by fi ne- to medium-grained sandstones with the Llanos Basin, it ranges from 0 to 0.2 km (section La in Fig. 5). The lower interval (3a cross-beds and abundant ichnofossils (Perez (Figs. 1 and 5). in Fig. 5) includes cross-bedded, medium- to and Salazar, 1978; Fabre, 1981). These beds The vertical arrangement of lithofacies and coarse-grained sandstone and conglomeratic are overlain by a unit that consists in the lower palynofacies has been interpreted as a product sandstone, which changes upsection to inter- half of fi ne-grained strata with abundant coal of deposition, from base to top, in fl uvial, fl u- beds of tabular-bedded fi ne-grained sandstone seams and in the upper half of laminated mud- vial-estuarine, and coastal-plain systems. Sand- and discontinuous mudstone interbeds (Cés- stones and massive light-colored mudstones stones indicate fl uvial infl uence in the axial zone pedes and Peña, 1995; Pardo, 2004). The upper (Sarmiento, 1992). The thickness of this unit of the Eastern Cordillera (Pardo, 2004), whereas interval (3b in Fig. 5) includes laminated gray is variable; there is a 1100 m depocenter near they are more tidally infl uenced in the Llanos mudstone with some interbeds of sandstone and Bogotá, and it thins eastward to less than foothills (Cazier et al., 1995; Reyes, 1996). The oolithic sandstone (Reyes and Valentino, 1976). 450 m and northward to less than 300 m near fi ne-grained strata accumulated in fl oodplains The thickness of this sequence in section La is the Santander massif (Fabre, 1981; Royero, with increasing estuarine infl uence toward the twice as thick as in the Llanos foothills (Fig. 5). 2001). Maastrichtian–lower Paleocene units in Llanos foothills. The change from excellent to Farther west in the Magdalena Valley, coeval the Magdalena Valley include conglomeratic poor pollen recovery in fi ne-grained units sug- lower and middle Eocene strata are as much as units derived from the Central Cordillera to gests that deposition of upper strata took place 1 km thick and consist of conglomeratic sand- the south (Gómez et al., 2003), whereas to the above the water table (Pardo, 2004). Equivalent stone, multistoried cross-bedded sandstone and north, carbonate silt and mudstones dominate strata in the Magdalena Valley consist of 1.2-km- mudstone (Restrepo-Pace et al., 2004; Pardo- (Gómez et al., 2005b). Maastrichtian strata are thick organic-rich mudstone interbedded with Trujillo et al., 2003; Gómez et al., 2005b). absent in the southern Llanos Basin (Bayona et ripple-laminated and cross-bedded lithic sand- Sandstones of the lower interval have been al., 2006), in the frontal thrust sheets of the cen- stone that accumulated in fl uvial-deltaic plain interpreted as amalgamated fl uvial channels, tral Llanos foothills and Llanos Basin (Cooper environments (Gómez et al., 2005b; section NM whereas sandstones of the upper interval record et al., 1995), as well as along the frontal thrust in Fig. 5). a stronger infl uence of brackish and marine con- sheets of the western fl ank of the Eastern Cor- ditions. In the central Llanos foothills, these beds dillera (Bayona et al., 2003). Tectono-Stratigraphic Sequence Three accumulated in mouth-bar and coastal-plain set- (Lower to Middle Eocene; Mirador–Basal tings (Cazier et al., 1995; Fajardo, 1995; Warren Tectono-Stratigraphic Sequence Two Carbonera Formations and Equivalent and Pulham, 2001), whereas in the northern Lla- (Upper Lower Paleocene to Upper Paleocene; Strata) nos foothills and axial zone of the Eastern Cor- Barco-Cuervos Formations and Equivalent dillera, they accumulated in a more continental Strata) Lithological units of this age are reported setting (Fajardo-Peña, 1998; Reyes, 2004). only west of the Llanos foothills and consist Biostratigraphic data indicate that fi ne-grained of two intervals. The lower interval (named 3a Tectono-Stratigraphic Sequence Four strata of this tectono-stratigraphic sequence in in Fig. 5) rests in abrupt contact with strata of (Upper Eocene to Middle Miocene; the axial zone of the Eastern Cordillera corre- sequence two (Fig. 7D) and includes fi ne- to Carbonera Formation and Equivalent Strata) late with aggradational, fi ne-to-coarse-grained medium-grained and locally conglomeratic quartzarenites in the Llanos Basin (Fig. 5). This quartzarenites beds that internally are mas- Lowermost strata of tectono-stratigraphic succession changes upsection from: (1) cross- sive, cross-bedded, and wavy-laminated to the sequence four vary laterally from fi ne-grained bedded, fi ne- to coarse-grained upward-fi ning top (Fig. 7E). The upper interval (named 3b in deposits in the axial zone of the Eastern Cordil- quartzarenites (Fig. 7A), locally conglomeratic Fig. 5) has upward-fi ning successions and coal lera, Llanos foothills, and northern Llanos Basin in Cocuy (Fabre, 1981) and section La (Pardo, interbeds in the northern Llanos foothills (Reyes, to amalgamated sandstones in the central Llanos 2004) (this unit pinches out west of Bogotá; 2004), whereas in the central Llanos foothills, Basin (intervals 4a and 4b in Fig. 6). Fine-grained Hoorn, 1988); to (2) interbeds of upward-fi n- sandstones show a diverse ichnofacies associa- strata include laminated dark-gray mudstone ing sandstone and mudstone with bidirectional tion (Ophiomorpha, Thalassinoides, Psilonich- with thin seams of coal and bioturbated fi ne- cross-bedded and bioturbated heterolithic lami- nus, and Diplocraterion; Pulham et al., 1997), grained sandstone (Mora and Parra, 2004) in the nated sandstone; (3) locally bioturbated dark- couplets in foreset laminations, and wavy and Llanos foothills and dark-colored mudstone rest- gray organic-rich claystone and mudstone with fl aser lamination in upper mudstone interbeds ing upon the unconformity in the northern Lla- thin coal seams and excellent pollen recovery; (Parra et al., 2005). Dark-colored mudstones nos Basin. Amalgamated to upward-fi ning suc- and (4) at the top, massive light-colored sandy with thin coal seams rest conformably on the cessions of fi ne- to coarse-grained sandstone and mudstone with very poor pollen recovery. This bioturbated sandstones (Jaramillo, 1999; Jara- conglomeratic sandstone show an onlap relation uppermost lithology contains isolated sand- millo and Dilcher, 2001). These two intervals are with the unconformity in the central and south- stones with upward-fi ning and coarsening separated by light-gray massive sandy mudstone ern Llanos Basin (Bayona et al., 2006). grain-size trends with cross-beds, wavy lamina- and locally laminated, organic mudstone with Strata overlying these lowermost beds have tion, and ripple cross-lamination (Figs. 7B and plant remains (Fig. 5); this level is characterized a more uniform upward-coarsening grain-size 7C). The thickness of this tectono-stratigraphic by moderate abundance of marine indicators, trend in the axial Eastern Cordillera, Llanos foot- sequence decreases eastward and northward: including foraminiferal test lining and several hills, and Llanos Basin (interval 4b in Fig. 6). in the Bogotá area, it varies from 0.9 to 1.2 km dinofl agellate cysts, such as Polysphaeridium An upward-coarsening succession includes (Hoorn, 1988), in sections La-Cocuy-Va (west- subtile, Achomos phaera sp., Spiniferites sp. laminated mudstone with mollusks (Parra et al., ern end of cross sections in Fig. 1), it ranges Cordosphaeridium inodes, and Nematosphae- 2005) and marine- to brackish-water indicators from 0.4 to 0.8 km (Fabre, 1981; Pardo, 2004; ropsis (Jaramillo and Dilcher, 2001). at the base (Fig. 6), which grade to tabular

Geological Society of America Bulletin, September/October 2008 1181 Bayona et al.

A E Qm

Qpf Qm— monocrystalline quartz Qp— polycrystalline quartz Qpf— foliated polycrystalline quartz Qc— cryptocrystalline quartz (chert) Lm— metamorphic lithic fragment 0.5 mm Pgl— plagioclase fragment B Qm Lm Pgl F

Qc Qp

0.25 mm

G D

Figure 7. (A–B) Abrupt change in sandstone composition within tectono-stratigraphic sequence two in Cocuy area (northern area, Fig. 1). (A) Quartzarenite of the lower upper Paleocene Barco Formation. (B) Sublitharenite of the middle upper Paleocene Cuervos Formation. (C–G) Outcrops around section TN (central cross section). (C) Sets of planar cross-bedding in the upper Paleocene Cuervos Formation; lithic fragments are concentrated along the cross-beds. (D) Topographic contrast at the contact between Cuervos (valley) and Mirador Forma- tions (scarp). (E) Amalgamated channels of the Mirador Formation with thin mudstones interbeds (tectono-stratigraphic sequence three). (F) Coarsening-upward succession at the top of the Carbonera Formation (tectono-stratigraphic sequence four), which is coeval with deposition of shale of the Leon Formation in the Llanos Basin (Parra et al., 2005). (G) Mottled reddish mudstones (paleosols) interbedded with sandstones of the Guayabo Formation (tectono-stratigraphic sequence ﬁ ve).

1182 Geological Society of America Bulletin, September/October 2008 An integrated analysis of an orogen–sedimentary basin pair and wavy laminated, locally bioturbated, fi ne- foothills and Llanos Basin. The lower unit doc- Sandstones of sublitharenite and litharenite grained sandstone. In the central Llanos foot- uments westward fl ooding of a broad fl uvial- composition in tectono-stratigraphic sequence hills, these successions include coal seams, feld- deltaic system followed by regional onset and two contain polycrystalline quartz and unstable spar-bearing fi ne-grained muddy sandstone, and establishment of lacustrine-lagoonal environ- lithic fragments (Fig. 7B), which constitute up locally conglomeratic cross-bedded sandstone ments (Hoorn, 1994), but with less brackish- to 33% of the framework grains, and some feld- (Parra et al., 2005). Upward-coarsening suc- water infl uence than that reported in Eocene spars. Reported lithic grain types include silt- cessions dominate in the Llanos foothills, with strata. In contrast, the upper unit represents stone, chert, gneiss, schist, phyllite and igneous some incursions of brackish waters (Figs. 6 and the eastward advance of a coarse clastic wedge rock fragments. In addition, paleocurrent data 7F), whereas in the Llanos Basin, upward-fi ning accumulated in fl uvial and alluvial-fan systems. indicate a shift to northward directions and an trends are more common toward the top of this increasing variability of paleocurrent directions sequence (interval 4c in Fig. 6). PROVENANCE AND PALEOCURRENTS at the end of the Paleocene (Figs. 8B and 8C). The northward and eastward lateral change Provenance and paleocurrent data suggest expo- of depositional patterns supports an interpreta- Sandstone composition in a tropical nonma- sure of basement rocks, such as the Floresta and tion of an eastward-prograding fl uvial-deltaic rine foreland basin, such as the Llanos Basin Santander massifs (Vasquez, 1983; Mesa, 1997), plain developing into a coastal plain (or savan- and restored eastern fl ank of the Eastern Cor- that controlled drainage patterns within the axial nas) and a coeval lacustrine-lagoonal deposi- dillera since the latest Cretaceous, is controlled zone of the Eastern Cordillera during deposition tional system to the east (Mora and Parra, 2004; mainly by chemical weathering and compo- of tectono-stratigraphic sequence two. Bayona et al., 2006). In the Llanos Basin, the sition of source areas. Late Paleocene paleo- The abrupt change from upper Paleocene abrupt change in lithological associations of the climate conditions (mean annual temperature litharenites (tectono-stratigraphic sequence lowermost beds has been interpreted as a change = 23.8 ± 2.1 ºC, mean annual precipitation = two) to lower-middle Eocene quartzarenites and from channel-fi ll processes in fl uvial systems 3.4 m/yr; Herrera, 2004) and number of mor- sublitharenites (tectono-stratigraphic sequence to transgressive tidal fl ats and delta bays with phospecies (Jaramillo et al., 2006a) were simi- three) with feldspars in the clay fraction (Bena- minor brackish-water infl uence changing upsec- lar to the present tropical rain forest. Changes in vides, 2004) coincides with a change in stacking tion to a lacustrine environment (Fajardo et al., composition of modern fl uvial sands in the Ven- pattern of sandstone beds from isolated chan- 2000). The lacustrine system interfi ngers on the ezuela Llanos Basin indicate that unstable lithic nel beds within mudstone at the top of tectono- east with a fl uvial system draining the Guyana fragments are not preserved more than 200 km stratigraphic sequence two to multistoried chan- craton and on the west with prograding del- from the Andes of Merida (the source area), and nel beds in tectono-stratigraphic sequence three taic systems. Strata at the top of this sequence sands with more than 25% of lithic fragments lie (Fig. 5). Paleocurrent data indicate a high dis- record fl uvial systems across the Llanos Basin mostly within 100 km of the Andes (Johnsson persion pattern, as would be expected in mature (interval 4c in Fig. 6). et al., 1991). We consider these distances to be (>10 m.y.) fl uvial systems located in areas of the maximum possible for source areas for the slow subsidence. Supply of detritus from nearby Tectono-Stratigraphic Sequence Five Paleocene basin, bearing in mind that tropical uplifted blocks is supported by the presence of (Middle Miocene to Pliocene; Leon and climatic conditions controlled chemical weath- Cretaceous foraminifera fragments in the matrix Guayabo Formations) ering processes in source and basin areas. of conglomerates (Céspedes and Peña, 1995) Integration of paleocurrent indicators and and lithic clasts composed of chert, claystone, The uppermost tectono-stratigraphic sequence sandstone composition from Paleogene rocks siltstone, gneiss, schist, and igneous rock frag- consists of two lithological units that are recorded in the axial zone of the Eastern Cordillera, Lla- ments (Mesa, 1997, 2004). partly in the Llanos foothills and occupy most nos foothills, and Llanos Basin indicates a shift The dominance of quartzose sandstones of the Llanos Basin. The lower unit consists of in provenance since the Paleocene (Fig. 8; see persists in tectono-stratigraphic sequence four. dark-colored laminated mudstone and shale with Data Repository for a complete list of references However, the presence of sublitharenite and an isolated record of mollusks and foraminifera and evaluation of data1). Maastrichtian to lower subarkose, as well as conglomerate beds con- (Bayona et al., 2006; Fig. 6). This unit is slightly Paleocene sandstones of tectono-stratigraphic taining clasts of chert and Cretaceous fossilifer- younger westward, as shown in the southern Lla- sequence one contain predominantly quartz ous limestones, documents the preservation of nos Basin (Bayona et al., 2006), and sandstone fragments and minor feldspars (Fig. 8A) in the unstable lithic fragments supplied from uplifted interbeds increase northward and westward Llanos Basin, indicating sediment supply from blocks within the Eastern Cordillera. (Cooper et al., 1995; Fajardo et al., 2000). In the Guyana craton. Supply of detritus from the The dominance of quartzose sandstone com- the Llanos foothills, this unit consists of wavy craton is additionally supported by the regional position in Paleogene sandstones in the Llanos laminated, bioturbated, and varicolored mud- westward migration of the Maastrichtian clastic Basin suggests that the continuing supply of stone interbedded with tabular-bedded, biotur- wedge (Diaz, 1994). In the Bogotá region, sand- detritus from the Guyana craton was mixed with bated quartzarenite (Geoestratos-Dunia, 2003). stone of the upper Guaduas Formation (lower chemically stable fragments derived from the The upper unit includes varicolored mudstone, Paleocene) contains unstable siltstone, mud- Eastern Cordillera. However, this pre-Miocene lithic-bearing sandstone, and conglomerate, and stone (10%), and chert (7%) grains, along with pattern in the Llanos Basin contrasts with sub- the coarser lithologies dominate toward the top phyllite and trace amounts of feldspar grains, litharenites and litharenites in tectono-strati- (Fig. 7G). The maximum recorded thickness is in suggesting uplift of nearby blocks (Sarmiento, graphic sequence fi ve (Moreno and Velasquez, the Llanos Basin (in well LC in Fig. 6), and not 1992; Torres, 2003). 1993), which were derived from the Eastern in the Llanos foothills, as in sequence four. The Cordillera. Palynological samples from fi ne- stratigraphic position of the upper unit indicates a grained strata of tectono-stratigraphic sequence 1GSA Data Repository item 2008078, references post–middle Miocene age. and evaluation of petrographic and provenance data, fi ve contain pollen, as well as dinofl agellate and These units represent the onset of coarse- is available at www.geosociety.org/pubs/ft2008.htm. foraminifera fragments, of Paleocene and older grained fl uvial systems covering the Llanos Requests may also be sent to [email protected]. age (Milton Rueda and Vladimir Torres, 2006,

Geological Society of America Bulletin, September/October 2008 1183 Bayona et al.

Maastrichtian-early early Paleocene (upper Guadalupe Group - Late early Paleocene-early late Paleocene (upper Guaduas, Cacho, A lower Guaduas Formation; Sequence One) B Lower Socha and Barco formations; lower Sequence Two)

a r e l l 1300000 i 1300000 d r C G1&2 o C C l e a r h A1&3 t en of t Cocuy f the CC C n e

h itio t

s f o po r e 1200000 d 1200000 position o r LERA o

estored r

e t

a CENTRAL

CENTRAL e

La t n CORDIL

CORDILLERA

se e

m range of r

r Tunja 1100000 p 1100000 ximu

Ma UNDEFORMED Minimum range of restored LLANOS BASIN C-BA LM C-5 LP-1 1000000 1000000

Bogota

100 km 100 km 900000 900000 11000001200000 1300000 11000001200000 1300000

Late late Paleocene (Bogota, Upper Socha and Cuervos Early-middle Eocene (Regadera, Picacho and Mirador C formations; upper Sequence Two) D formations; Sequence Three)

a a r r e e l l l l i i 1300000 d 1300000 d r r o o C C

l l a a r r t

en ent C C

e e h h t t f f o o

r r e e d rd r o o 1200000 1200000 b b RAL n n r r

e e t t s s

a scatter paleocurrents

ea e

t t

n n

CENTRAL CENT

e r

CORDILLERA re CORDILLERA

p p

Tu 1100000 1100000

1000000 1000000

100 km 100 km 900000 900000 11000001200000 1300000 11000001200000 1300000

Late Eocene-early Miocene (Usme, Concentracion and Reference localities Bogota; Cocuy; La; Tunja; E Carbonera formations; Sequence Four) Reference wells A1&3; C-BA; LM; LP-1

a r e l l i d 1300000 r trace of regional profiles (northern and central cross sections) o C l a r restored trace of major thrust fault systems ent C

e h

t f o

r e

rd o 1200000 b Qt

e t s Quartzarenite

CENTRAL n

s e

CORDILLERA r Subarkose Sublitharenite p mean direction and range

Fel 1100000 of directions dsp. li L itha range of paleocurrent re

thareni nite directions

Arkose 1000000

Lithic arkose

F L 100 km 900000 11000001200000 1300000

Figure 8. Paleogene palinspastic maps of the inverted Eastern Cordillera (EC) and adjacent Llanos Basin (see details in Fig. 10) showing changes in sandstone composition and paleocurrents for tectono-stratigraphic sequences one to four (see Data Repository for complete list of references [see text footnote 1]). (A) Palinspastic distance between Central Cordillera (CC) and Llanos foothills ranges from 335 to 355 km (Colleta et al., 1990; Cooper et al., 1995; Taboada et al., 2000) to 440–460 km (Dengo and Covey, 1993; Roeder and Chamberlain, 1995); the shorter distance is shown for parts B to E. Source areas in the restored Eastern Cordillera need to be considered to explain the presence of litharenites. See discussion in the text about provenance and paleocurrent data for evidence that supports the interpretation of block uplifts within the Eastern Cordillera.

1184 Geological Society of America Bulletin, September/October 2008 An integrated analysis of an orogen–sedimentary basin pair personal commun.) and document unroofi ng of related to increasing subsidence rates in tectono- lera. The purpose of fl exural modeling was to the Eastern Cordillera. stratigraphic sequences one and two, the second test whether fl exure of the lithosphere resulting corresponds to the time interval of tectono- from the weight of the Central Cordillera could ONE-DIMENSIONAL BACKSTRIPPING stratigraphic sequence three, and the last regime reproduce the geometry of the Maastrichtian- AND TWO-DIMENSIONAL FLEXURAL shows an abrupt increase in subsidence rates in Paleocene foreland as far east as the Llanos SUBSIDENCE ANALYSIS tectono-stratigraphic sequences four and fi ve. Basin. Gómez et al. (2005a) were able to obtain The ages of the breaks in the slope of the curve a reasonable fi t between the observed and the A comparison of one-dimensional (1D) tec- do not overlap for all sections, suggesting that calculated basin geometry for the Colombian tonic subsidence profi les from sections in the the onset of each event that caused the increase foreland basin using an infi nite plate model, axial Eastern Cordillera, Llanos foothills, and of tectonic subsidence differed across sections a discrete load confi guration, and a horizontal Llanos Basin guided selection of time intervals in the study area. However, minor differences density contrast between tectonic loads and of comparable tectonic subsidence signatures in the age of those breaks may be due to lack adjacent sediment fi ll. All model runs reported (Fig. 9). Additionally, 1D backstripping tech- of resolution of biostratigraphic determinations by Gómez et al. (2005a) were performed on a niques were used to decompact the measured (see bar error for different intervals in Fig. 9). 35 km Te plate using a thermochronologically stratigraphic thickness of each section, follow- We interpret all the breaks in the slope of the constrained history of uplift for the Central Cor- ing the methods and assumptions specifi ed in tectonic subsidence curve as a result of fl exural dillera and western fl ank of the Eastern Cordil- Watts and Ryan (1976) and Allen and Allen subsidence related to tectonic and sedimentary lera. We used a tectonic load confi guration simi- (1992). The Late Cretaceous–Cenozoic fi rst- loading. Signifi cant differences in the ages of lar to the one proposed by Gómez et al. (2005a), order sea-level curve of Haq et al. (1987) was the infl ection points between the northern and but the width of our basin was 40 km narrower used for eustasy correction of 1D tectonic sub- central cross sections may record diachronous (see Figs. 1C and 8A). Our model only consid- sidence. along-strike tectonic loading. The age differ- ered sections/wells close to the cross sections in Two-dimensional (2D) backstripping of ences of infl ection points on curves for the axial order to avoid important changes of thickness the two cross sections was carried out follow- zone of the Eastern Cordillera and the Llanos of Cenozoic synorogenic strata across these ing the procedures detailed in Watts (2001) to Basin may represent a fl exural response of the traverse structures, as reported by Parra et al. better quantify the subsidence history of the lithosphere to foreland-directed migration of (2005) and this study. Llanos foothills and Llanos Basin. In order to tectonic loads. Model runs using these confi gurations were properly represent the original basin geometry, not able to match the “observed” (i.e., recon- the positions of each section were plotted in the Results of Two-Dimensional Flexural structed) fl exural tectonic subsidence profi le Paleogene palinspastic map of Sarmiento-Rojas Backstripping (Fig. 11). One cause of the discrepancy between (2001; Fig. 10), which depicts shortening esti- our results and those of Gómez et al. (2005a) mates for the eastern fl ank of the Eastern Cor- In this study, we tested two hypotheses of is the restored width of the Eastern Cordillera. dillera that agree with restorations of our two foreland evolution for an 800-km-wide plate. Because the basin geometry of Gómez et al. balanced cross sections. This palinspastic map Our fi rst model used a spatially continuous (2005a) is 40 km wider than ours, the additional constrains (1) the most probable position of foreland basin with a laterally constant plate sedimentary load, 40 km wide and ~1.5 km tectonic loads (areas with no Cenozoic record), fl exural rigidity (Te) for late Maastrichtian, thick to the west of the axial zone of the Eastern (2) areas with growth strata, and (3) areas with early Paleocene, and late Paleocene time. Our Cordillera, contributed to fl exural subsidence in intra-Cenozoic angular unconformities. Next, second model considered uplifts of blocks that the Llanos Basin. Because we used a narrower the minimum and maximum 2D basin depths separated the foreland basin into two main restored basin, both tectonic and sedimentary were defi ned for each time interval using the depocenters, the Magdalena and Llanos Basins, loading within the restored Eastern Cordillera compacted and decompacted thickness, respec- on a plate of laterally variable fl exural rigidity were required to match the fl exural tectonic sub- tively, of each section or well. The effect of (Te). We used data from the Magdalena Valley sidence in the Llanos Basin (see next section). fl exural subsidence due to sediment loading was presented in Pardo-Trujillo et al. (2003) and calculated after basin geometry was defi ned. Gómez et al. (2005a) for section NM, and from Model 2: Interrupted Foreland Basin and The latter exercise permitted calculation of the Restrepo-Pace et al. (2004) for section RM. Variable Elastic Thickness “observed minimum” and “observed maxi- Geodynamic modeling of these profi les was The other hypothesis tested in this study was mum” tectonic fl exural subsidence of the basin extended to include the restored position of the a foreland basin interrupted by tectonic loads in for each time interval. In this study, the numeri- axial Central Cordillera and wells in the distal the middle of the basin, which developed on a cal implementation of Bodine (1981), which Llanos Basin (Fig. 10). We focused on the area lithosphere of laterally variable Te. The fl exural allows plates of laterally variable elastic thick- between the axial zone of the Eastern Cordil- strength of the northern Andean lithosphere is ness to be considered, was applied to model the lera and Llanos Basin because the uncertainty known to vary laterally from low values near the Llanos foreland basin. of palinspastic restoration increases as we move axis of the east Andean topography to high val- westward from the axial zone of the Eastern ues over the Guyana craton, as supported by two- Results of One-Dimensional Backstripping Cordillera to the Magdalena Valley and Central dimensional fl exural models (Ojeda, 2000; Sarm- Cordillera (Figs. 1C and 8A). iento-Rojas, 2001), gravity modeling (Stewart Breaks between periods of constant sub- and Watts, 1997), and topography/gravity coher- sidence rate allow the discrimination of three Model 1: One Basin and Uniform Elastic ence studies (Ojeda and Whitman, 2002). subsidence events in the Llanos foothills and Thickness For each profi le, we applied an estimated Te Llanos foreland basin (Fig. 9); these closely In this hypothesis, the Maastrichtian-Paleo- confi guration that refl ected the lateral variabil- follow the fi ve tectono-stratigraphic sequences cene foreland basin was a fl exural response of ity in fl exural strength of the lithosphere inher- defi ned previously. The fi rst subsidence event is the lithosphere to loading of the Central Cordil- ited from the complex Phanerozoic tectonics of

Geological Society of America Bulletin, September/October 2008 1185 Bayona et al.

Age (Ma) Northern cross section 80 70 60 50 40 30 20 10 0 CL1 0 Ju1

A1&3

Sequence 1 Seq. 2 Sequence 3 Sequence 4 Sequence 5 1

Va poor palynological record G1&2 2

Cocuy

Llanos basin wells Llanos foothills wells sections in the axial zone of the Eastern Cordillera resolution of palynological age determinations 4

Age (Ma) Central cross section 80 70 60 50 40 30 20 10 0 0

C-BA LP LM LG 1 LA Sequence 1 Seq. 2 Sequence 3 Sequence 4 Sequence 5

poor palynological record 2 One-dimensional tectonic subsidence (km)

3 Llanos basin wells Llanos foothills wells sections in the axial zone of the Eastern Cordillera resolution of palynological age determinations Figure 9. One-dimensional tectonic subsidence curves for selected sections and wells along the northern and central cross sections. Time intervals of the fi ve tectono-stratigraphic sequences are also shown. Cocuy section was modifi ed from Gómez et al. (2005a). Tectono-stratigraphic sequence three records a time interval of very low tectonic subsidence rates, in contrast to Maastrichtian-Paleocene and late Eocene–Pliocene breaks in the slope of the curve. The shape and diachronism of those breaks are interpreted as episodes of fl exural subsidence. See Figure 3 for locations of sections and wells.

1186 Geological Society of America Bulletin, September/October 2008 An integrated analysis of an orogen–sedimentary basin pair Profile for 2D geodynamic analysis Profile (see Fig. 1) restored trace of major faults possible location of tectonic loads (no record of Cenozoic strata) zone transverse pre-Eocene angular unconformity and strata Eocene-Miocene growth strata Miocene growth Oligocene-lower well in the distal Llanos basin projected to the cross section (only for Oligocene and et from Fajardo younger strata; modified al., 2000) LT- 1 LT- 1 e is similar to the restored width proposed by width proposed to the restored e is similar ntral Cordillera) used for two-dimensional (2D) ntral Cordillera) used for PR-1 dicated.

Northern cross section ells are shown in Figure 3, and present traces of major traces of major 3, and present shown in Figure ells are STO-2 1100000 1300000 1000000 ST-15 CL1 Pl-1 Ju1

Chucarima transverse zone

Central S-1 cross section A1&3

UNDEFORMED LLANOS BASIN LP a

GUA-1 rg

G1&2

LG1&2 LLANOS F. Ce FOOTHILS

RESTORED RESTORED 1200000

ugon F. ugon erse zone

Cob LM F. LC

Cusiana- Cupiagua Cupiagua Cusiana-

Labateca Labateca A Guicaramo F. Guicaramo Sabanala C-BA

Va transv

Chinacota Chinacota F. Cocuy La

1100000 1300000 Chameza F. Chameza F.

Soapaga Soapaga

Medina-Guavio Medina-Guavio

F. esalia-Lengupa esalia-Lengupa

F. T Pesca Pesca

Bucaramanga Tunja ORED EASTERN CORDILLER

REST NM F. Salinas 100 km Bogota

LLEY

A V Salinas Salinas

A A

LLEY

A V

A A

GDALEN

ALEN

Restored boundary of the Central Cordillera Central the of boundary Restored UNDEFORMED

CENTRAL CORDILLER CENTRAL

Romeral paleosutur Romeral BROKEN PLATE BROKEN Figure 10. Palinspastic position of sections and wells and trace of the northern and central cross sections (extended to the Ce 10. Palinspastic position of sections and wells trace the northern central cross Figure Eastern Cordillera her geodynamic modeling, plotted on the palinspastic map of Sarmiento-Rojas (2001).The width restored Colleta et al. (1990), Cooper et al. (1995), and our restored cross sections shown in Figure 3. Present positions of sections/w 3. Present sections shown in Figure cross restored et al. (1995), and our Colleta et al. (1990), Cooper also in of Cenozoic strata are with no record unconformities, and areas angular strata, reported 1. Growth in Figure faults are

Geological Society of America Bulletin, September/October 2008 1187 Bayona et al.

Observed decompacted thickness Tectonic subsidence (maximum total subsidence) Figure 12. Two-dimensional fl exural model observed minimum using variable elastic thickness of the litho- Equivalent tectonic load observed maximum computed sphere (A), interrupted basin geometry since Maastrichtian, and an 800-km-wide plate forebulge produced by tectonic loading with a broken boundary at the restored Densities position of the Romeral fault system (see Elastic thickness = 35 km Mantle = 3300 kg/m3 Fig. 1A). Effects of fl exural subsidence by E = 70 GPa; v = 0.25; Tectonic loads = 2700 kg/m3 sediment loads have been removed to cal- gravity = 9.78 m/s Sediments = 2400 kg/m3 culate observed fl exural tectonic subsidence in two regional cross sections with different Lower Paleocene (60-65 Ma) geometry of the Guaicaramo fault system (km) 4 (GFS). CC—Central Cordillera; MV— Magdalena Valley; EC—Eastern Cordillera; CC MV EC Ft Llanos Ft—Llanos foothills; SM—Santander massif. 2 See Figures 3 and 10 for actual and restored positions of sections and wells, respectively. NM Cocuy Va G1&2 Ar1&3 Ju1 CL1 Note that tectonic loading in the Central Cor- 0 dillera does not contribute to tectonic subsidence in the Llanos Basin (B and C, see also

Northern cross section -2 Fig. 11). For simplicity, we only show tectonic 0 200 400 600 800 (km) subsidence proﬁ les from the axial zone of the (km) Eastern Cordillera to the Llanos Basin. See 4 text for discussion of models. CC MV EC Ft Llanos

0 RM La TN C-BA LP consistent with early uplift of segments of the axial zone of the Eastern Cordillera. Equivalent tectonic loads (i.e., crustal thickening), rang- Central cross sectio n -2 ing from 0.5 to 3 km, and synorogenic depo- 0 200 400 600 800 (km) sition explain the fl exural wavelength and the Figure 11. Two-dimensional model for fl exural tectonic sub- eastward migration of the fl exural wave, as sidence using a constant elastic thickness of the lithosphere suggested by the Llanos foreland stratigraphy (35 km), continuous basin geometry for lower Paleocene strata (Figs. 5, 12B, 12C, and 12D). Tectonic loads (60–65 Ma), and an 800-km-wide plate with a broken bound- on the Santander massif in the northern cross ary at the restored position of the Romeral paleosuture (see section and west of the Pesca fault on the cen- Fig. 1A). Effects of fl exural subsidence by sediment loads have tral cross section (west of section La) resulted been removed to calculate observed fl exural tectonic subsidence. in development of three distinct depocenters, CC—Central Cordillera; MV—Magdalena Valley; EC—East- matching the observed tectonic subsidence. For ern Cordillera; Ft—Llanos foothills. See Figures 3 and 10 for the late Paleocene, a new foreland-breaking actual and restored positions of sections and wells, respectively. deformation front advanced eastward to create This model indicates that tectonic loading is required within the widening accommodation space in the Llanos restored Eastern Cordillera in order to match the observed tec- Basin (Fig. 12D). As the basin stratigraphy and tonic subsidence in the Llanos Basin as modeled in Figure 12. geometry indicate, tectonic loads in the northern cross section (Santander massif) were wider than in the central cross section. northern South America (Fig. 12A). The Guy- of Romeral fault system to be the western edge In the early and middle Eocene, the tectonic ana craton is relatively thick, thermally relaxed, of our broken plate. An older Paleozoic paleo- load–fl exural wave pair migrated westward and rigid (Te > 50 km; Stewart and Watts, 1997). suture underlying the southern and central Lla- (Fig. 12E), explaining the very low subsidence We assigned a Te in the range of 15–25 km for nos foothills (see Cediel et al., 2003) was rep- regime in the study area for tectono-stratigraphic the lithosphere that underlies the locus of Meso- resented as a laterally variable Te confi guration sequence three (Fig. 9). Equivalent tectonic zoic extension (Sarmiento-Rojas et al., 2006). under the central Llanos foothills. loads on the western fl ank of the Eastern Cordil- We regarded the lithosphere under the Central Results of our second set of models were lera and Magdalena Valley were less than 3 km Cordillera as tectonically stable and assigned a capable of reproducing the tectonic fl exural high on the northern section and less than 2 km Te value of 55 km for the western end of our subsidence observed in the Llanos foothills and high on the central section, with minor loading profi les. Paleosuture zones, such as the Romeral Llanos Basin, and they honor the paleogeogra- (<1 km) along the axial zone of the Eastern Cor- fault system, are zones of plate rupture (zero phy suggested by stratigraphic and provenance dillera and Llanos foothills. In the late Eocene, fl exural strength), or areas of very low fl exural data of our tectono-stratigraphic analyses. loads remained largely unchanged except for rigidity. We considered the palinspastic position Models for the latest Cretaceous–Paleocene are minor increases in equivalent tectonic loading.

1188 Geological Society of America Bulletin, September/October 2008 An integrated analysis of an orogen–sedimentary basin pair

Mesozoic rift mar- Mesozoic rift Paleozoic (km) gins A (km) margins suture A Lateral variation of elastic thick- 40 40 ness

0 0 0 200 400 600 800 (km) 0 200 400 600 800 (km)

4 CC MV EC Ft Llanos ObservedO decompacted thickness Tectonic subsidence (km) (maximum( total subsidence) Tectono-stratigraphic sequence one observed minimum B B 2 (late Maastrichtian–early Paleo- Equivalent tectonic load observed maximum computed cene, 65-70 Ma)

forebulge (only by tectonic load) RM La TN C-BA LP Pl-1 STO-2 Densities 0 Elastic thickness = Variable Mantle = 3300 kg/m3 E = 70 GPa; v = 0.25; Tectonic loads = 2700 kg/m3 -2 gravity = 9.78 m/s2 Sediments = 2400 kg/m3 0 200 400 600 800 (km)

4 CC MV EC Ft Llanos 4 CC MV EC Ft Llanos (km) (km) Tectono-stratigraphic sequence two SM C C 2 2 (lower segment) (early to middle Paleocene, 60–65 Ma) NM Cocuy Va G1&2 Ar1&3 Ju1 CL1 LT - 1 La RM 0 0 TN C-BA LP Pl-1 STO-2

-2 -2 0 200 400 600 800 (km) 0 200 400 600 800 (km) EC Ft Llanos EC Ft Llanos (km) SM (km) 2 2 Tectono-stratigraphic sequence two D D (upper segment) (middle to late Cocuy Va G1&2 Ar1&3 Ju1 CL1 LT - 1 La LP-1 TN C-BA Pl-1 STO-2 Paleocene, 55–60 Ma) 0 0 -1 -1 200 400 600 800 (km) 200 400 600 800 (km)

(km) EC Ft Llanos (km) EC Ft Llanos 2 2 Tectono-stratigraphic sequence E E three (early to middle Eocene, 44– Cocuy Va G1&2 Ar1&3 Ju1 CL1 LT - 1 La 0 0 TN C-BA LP Pl-1 STO-2 55 Ma) -1 -1 200 400 600 800 (km) 200 400 600 800 (km)

(km) SM 4 EC Ft Llanos F EC Ft Llanos F Tectono-stratigraphic sequence four (Oligocene, 24–34 Ma) 2 2 (km) Cocuy Va G1&2 Ar1&3 Ju1 CL1 LT - 1 La 0 0 TN C-BA LP Pl-1 STO-2 -1 -2 200 400 600 800 (km)

200 400 600 800 (km) Central cross section (salient of the GFS) Central cross

Northern cross section (recess of the GFS) section (recess Northern cross (km) (km) Llanos EC Ft Llanos 10 10

Tectono-stratigraphic sequence five 8 G 8 G (upper Miocene-Pliocene, 0–10 Ma) 6 6

4 4

2 2 Cocuy Va G1&2 Ar1&3 Ju1 CL1 LT - 1 La 0 0 TN C-BA LP Pl-1 STO-2

-2 -2

-4 -4

-6 -6 200 400 600 800 (km) 200 400 600 800 (km)

-8 -8

Geological Society of America Bulletin, September/October 2008 1189 Bayona et al.

In Oligocene to early middle Miocene time, mation section) provide evidence for at least be conducted in order to test this hypothesis tectonic loads consisted of uplift of the Santander four shortening events in the axial zone and (Andres Mora, 2007, personal commun.). massif, the eastern fl ank of the Eastern Cordil- eastern fl ank of the Eastern Cordillera prior to Out-of-sequence deformation along the lera, and incipient uplifts in the Llanos foothills. the strong post–middle Miocene Andean defor- Cobugon and Samore faults in the Llanos foot- The foreland-breaking advance of tectonic load- mation. These tectonic phases of deformation hills is indicated by the truncation of tight anti- ing controlled migration of the fl exural wave as advanced dominantly eastward from the hinter- clines involving Paleogene units by both the recorded by tectono-stratigraphic sequence four land (Figs. 13, 14, and 15), but changes in fl ex- east-verging Cobugon fault to the west and the (Figs. 6 and 12F). For the Oligocene, equiva- ural subsidence rates and in the relation between west-verging Samore fault to the east (Figs. 3A, lent tectonic loads on the northern cross sec- hanging-wall and footwall structures document 13C, and 13D). East-verging thrust faults tion ranged between 3 and 5 km and were over periods of westward migration of deformation bounding eastern structures of the Llanos foot- 150 km wide, whereas for the central cross sec- and out-of-sequence reactivation, respectively. hills involve upper Miocene–Pliocene strata and tion, the effective tectonic load, 2 km high and In our forward kinematic models for the north- locally offset Pliocene strata, suggesting post- less than 100 km wide, was located in structures ern and central cross sections, we translated Pliocene activity for the last phase (Fig. 13D). between the axial zone of the Eastern Cordillera the positions of tectonic loads into areas where and central Llanos foothills sections (Fig. 12F). active basement-involved deformation was tak- Kinematics of the Central Cross Section In the early-middle Miocene, tectonic loads ing place. advanced eastward toward the present western The fi rst shortening recorded in this area Llanos Basin and appeared to be the dominant Kinematics of the Northern Cross Section occurred during latest Cretaceous to late Paleo- loads (equivalent tectonic loads of 4–6 km) in cene time, earlier than in the northern cross sec- foreland basin formation. As discussed later, The earliest phase of foreland development tion (Figs. 14A, 14B, and 15A). Loads were differential loading along the Eastern Cordil- is recorded in Paleocene strata. Flexural defor- less than 3 km high and were located west of lera imparted differences in stratal architecture mation may explain: (1) erosion or nondepo- the Pesca-Soapaga fault system; they subse- of Oligocene–middle Miocene strata between sition of lower Paleocene rocks in the Llanos quently advanced eastward to involve rocks of the central and northern Llanos foothills. For Basin and erosion of uppermost Cretaceous the eastern fl ank of the Eastern Cordillera dur- the central cross section, any loads located west rocks farther east, (2) eastward migration of ing the late Paleocene (Figs. 12B, 12C, and of the axial zone of the Eastern Cordillera dur- the depositional zero in tectono-stratigraphic 15B). These pulses explain the eastward thin- ing this time resulted in subtle subsidence of the sequence two (Barco-Cuervos Formations, ning of Maastrichtian-Paleocene sequences Llanos Basin, as demonstrated by Figures 11 Figs. 12C, 12D, and 15B), and (3) increased one and two, which are bounded at the base by and 12C. Therefore, we considered only the supply of chemically unstable lithic fragments sandstones and conglomerates and, at the top, effects of tectonic loading to the east of the axial coincident with increased tectonic subsidence by fi ne-grained strata (Fig. 5). Flexural uplift zone of the Eastern Cordillera. rates (Figs. 8, 11, and 15B). Our geodynamic related to the Maastrichtian phase of deforma- For the middle-late Miocene to Pliocene, the models indicate that uplifted areas were located tion explains the presence of quartzose sand- model predicts fi rst a period of considerable mainly at the Santander massif (Figs. 12C, 12D, stone and conglomerate beds in the Llanos foot- decrease of effective tectonic loading followed and 15B), a source area for litharenites in the hills (Fig. 15A), which were supplied mainly by a strong uplift of the Andes. Accumulation of Cocuy and Va sections less than 100 km away. from uplifted cratonic sources. Flexural exten- the Leon Formation occurred in a basin created Although reported zircon fi ssion-track ages in sion at the border of the forebulge in the Llanos by 2 km of equivalent tectonic load west of well the Santander massif suggest exhumation at this foothills explains the presence of faults in the Ar1–3 in the northern cross section and west of time, the data set of Shagam et al. (1984) needs Paleocene (65 Ma), as indicated by micas fi lling well C-BA in the central cross section. The load to be reevaluated with new analyses that con- vein-wall rocks (Fig. 14A). During the Paleo- confi guration in the late Miocene and Pliocene sider analytical and conceptual advances of this cene, upper Cretaceous strata were eroded in the is consistent with the modern load distribution technique (Andres Mora, 2007, personal com- eastern Llanos foothills and Llanos Basin, and (Fig. 12G). The coarse-grained Guayabo For- mun.). Subsequent, westward migration of tec- synorogenic deposition of the Barco-Cuervos mation was deposited in the Llanos Basin as tonic loads to the Magdalena Valley in the early succession migrated eastward (Figs. 14B and the Eastern Cordillera (equivalent tectonic load Eocene resulted in deposition of amalgamated 15B). Unstable lithic fragments indicate that of 10–11 km) was emplaced over the adjacent sandstones of the thin Mirador Formation and uplifted areas were less than 100 km from the foreland, loaded the lithosphere, and generated basal shale beds of the Carbonera Formation. Llanos foothills, Bogotá, and Tunja areas, and a broad fl exural sag east of the Cordilleran fron- (Figs. 12E and 13A). those uplifts controlled the northward dispersal tal fault. The uplift of the Eastern Cordillera pro- Field evidence supporting shortening during of detritus, as indicated by paleocurrent data vided much of the sediment for infi ll of the sag. the Oligocene consists of growth strata in broad (Fig. 15B). synclines in the Llanos foothills and adjacent During the early and middle Eocene, tectonic DISCUSSION: LINKAGE BETWEEN to a fault-related anticline that formed west of loads were located in the Magdalena Valley, as THRUSTING AND BASIN EVOLUTION the Llanos Basin (Figs. 4, 12F, 13B, and 15C). indicated by the angular unconformity underly- Localized normal faulting in the eastern Llanos ing Eocene strata and strike-slip deformation. The integrative approach used in this work Basin at this time can be explained as fl exural Farther to the east, a period of westward-increas- predicts the geometry and position of the tec- extension at the forebulge, as indicated in our ing subsidence took place in the axial zone of tonic loads necessary to produce the observed early Oligocene fl exural model (Figs. 12F and the Eastern Cordillera (Figs. 11 and 12E). The basin geometry at different time intervals. Our 15C). Ages of apatite fi ssion tracks in rocks amalgamation of fl uvial channels of the Mira- results and published thermochronological- from the Santander massif (Shagam et al., 1984; dor Formation indicates low rates of subsidence geochronological and paleobotanical data (see Toro, 1990) support this interpretation. New during this episode of deformation (Figs. 4 and references in Evidence of Pre-Neogene Defor- zircon and apatite fi ssion-track analyses should 14C). The presence of lithic fragments and

1190 Geological Society of America Bulletin, September/October 2008 An integrated analysis of an orogen–sedimentary basin pair

WE Kinematics of the northern cross section . . Va G1&2 A1&3 Labateca F. Labateca Cobugon F Samore F Outcrop section Well Contact 20 km Fault A. Late Eocene - Tectono-stratigraphic sequence 4 Restored fault trace (Deposition of lower Carbonera Fm., 36 Ma) Holocene- Middle Miocene Oligocene growth strata Fig. 4A Fig. 4B Middle Miocene - Upper Eocene Middle Eocene - Paleocene Apatite FT ages (Toro, 1990) 20 km Lower Paleocene- Upper Cretaceous B. Middle Miocene - Tectono-stratigraphic sequence 4 Lower Cretaceous - (Deposition of upper Carbonera Fm., 14 Ma) Jurassic-Triassic

pre-Mesozoic

Apatite FT ages (Shagam et al., 1984) 20 km C. Latest Miocene - Tectono-stratigraphic sequence 5 (Deposition of Guayabo Fm., 5 Ma) . . Va G1&2 A1&3 Labateca F. Samore F Cobugon F

20 km

D. Present day

Figure 13. Kinematic forward model for the northern cross section since the middle Eocene. Basin geometry and position of structural activity are constrained by geodynamic modeling, thermochronology, growth structures, and provenance and paleocurrent data. FT—ﬁ ssion track.

Geological Society of America Bulletin, September/October 2008 1191 Bayona et al. SE ssion track. ssion Gu1 Gu1 20 km 20 km 20 km 20 km 20 km LP LP symbols in Figure 13. FT—ﬁ symbols in Figure Ce Ce tructural activity are constrained by geodynamic tructural activity are LC LG1&2 LC LG1&2

LM LM

Cupiagua F. Cupiagua

Cusiana- Cupiagua F. Cupiagua Cusiana- C-BA

C-BA

TN F. Guaicaramo

A. Latest Cretaceous - Tectono-stratigraphic sequence 1 A. Latest Cretaceous - Tectono-stratigraphic (Deposition of lower 65 Ma) Guaduas Fm., sequence 2 - Tectono-stratigraphic B. Latest Paleocene (Deposition of upper Cuervos 55 Ma) Fm., sequence 3 C. Middle Eocene - Tectono-stratigraphic (Deposition of upper Mirador 39 Ma) Fm., sequence 4 D. Middle Miocene - Tectono-stratigraphic (Deposition of upper Carbonera 14 Ma) Fm., E. Present day - Tectono-stratigraphic sequence 5

Chameza F. Chameza Guaicaramo F. TN Guaicaramo sandstones Flexural subsidence causes abrupt change of thickness, incipient development structures

Apatite FT ages (Mora et al., 2005)

Conglomeratic Micas filling normal Micas filling faults (Branquet et al., 1999) - Forebulge Chameza F. Chameza Kinematics of the central cross sectionKinematics (Hossack et al., (Hossack Apatite FT ages 1999) Andean-type paleoflora paleoflora Andean-type

La Pesca F. Pesca Litharenites; source areas less than 100 km Litharenites; Paleorelief controlled northward dispersion of detritus Amalgamated sandstones = very low subsidence Amalgamated sandstones = very

La Pesca F. Pesca (Toro, 1990) (Toro, Apatite FT ages NW Zircon FT ages Zircon et al. , (Shagam 1984) Figure 14. Kinematic forward model for the central cross section since the late Maastrichtian. Basin geometry and position of s the central cross 14. Kinematic forward model for Figure data. See explanation of and paleocurrent and provenance structures, data, growth and geochronology modeling, thermochronology

1192 Geological Society of America Bulletin, September/October 2008 An integrated analysis of an orogen–sedimentary basin pair LT- 1 LOWER CARBONERA STO-2 CL1 Pl-1 MIDDLE CARBONERA LP ank of the Central Cordillera from Diaz ank of the Central Cordillera from C-BA Va TN astern ﬂ Cocuy La Oligocene eastward exural wave migration during (A) late Maastrichtian, migration of flexural wave wave migration of flexural FM studied sections and wells studied sections and wells 2D geodynamic and structural sections (dashed when inactive) restored trace of major faults easternmost sedimentary record by tectonic loading (see Fig. 12) forebulge direction of dispersal detritus (see Fig. 8) CONCENTRACION CONCENTRACION a SM j n QM u Latest Oligocene - middle Tectono-stratigraphic sequence 3 sequence 3 Tectono-stratigraphic Latest Oligocene - middle Tunja T siliciclastic shoreface; quartzarenites quartzarenites shoreface; siliciclastic topography and associated alluvial fans topography and associated alluvial fans topography with no record of alluvial fans marine; shale, carbonates shallow conglomerate and lithic sandstones alluvial fan; braided fluvial system; quartzose sandstones fluvial-deltaic system; quartzose and sublithic sandstones alluvial plain (oxic); lithic-bearing sandstones in fluvial fine-grained channels, mottled mudstones (paleosols) coastal plain and tidal flats (anoxic); coals, sandstones in locally meandering channels; shales and mudstones in isolated lakes, estuarine C USME 100 km Tectonic loads and source areas (see Fig. 12) loads and source areas (see Fig. 12) Tectonic Sedimentary basin LT - 1 Bogotá = Quetame massif = Floresta massif = Santander massif CL1 CL1 Pl-1 FM QM SM UPPER GUADALUPE GUADALUPE LP LP COLON BARCO BARCO LOWER CUERVOS CUERVOS C-BA C-BA Va Va y LOWER TN u TN GUADUAS GUADUAS c o Cocuy La Cocuy C La UPPER PINOS CUERVOS CUERVOS SM a j FM n TIERNA TIERNA u Tunja T Tunja of flexural wave wave of flexural á á t t UMIR NM o BOGOTÁ BOGOTÁ NM o flexural wave wave flexural g g o o UPPER UPPER Late Paleocene eastward migration eastward Late Paleocene LISAMA M B Bogotá Bogotá Bogotá B RM RM R GUADUAS GUADUAS LOWER

GUADUAS GUADUAS

late Maastrichtian migration of

i illera illera

a LOWER

t LISAMA

SECA

t s

Restored boundary of the Central Cord Cord Central Central the the of of boundary boundary Restored R Restored Restored boundary of the Central Cordillera Central the of boundary Restored A

HOYON HOYON A

100 km

100 km CORDILLER CENTRAL CENTRAL CORDILLER CENTRAL

Latest Cretaceous - upper Tectono-stratigraphic sequence 1 sequence 1 Tectono-stratigraphic - upper Latest Cretaceous

Latest Paleocene - upper Tectono-stratigraphic sequence 2 Tectono-stratigraphic Latest Paleocene - upper

Romeral paleosuture Romeral Romeral paleosuture Romeral CIMARRONA A B Figure 15. Paleogeographic maps (palinspastic map is from Sarmiento-Rojas, 2001) illustrating three phases of eastward ﬂ Sarmiento-Rojas, 2001) illustrating three 15. Paleogeographic maps (palinspastic map is from Figure and e Valley the Magdalena and B include data for A discussion. Panels (B) late Paleocene, and (C) Oligocene. See text for (1994) and Gómez et al. (2005a).

Geological Society of America Bulletin, September/October 2008 1193 Bayona et al.

fragments of Cretaceous foraminifera in the composition, etc.), fl exural modeling, and kine- basement-rooted structures, whereas in the cen- axial zone of the Eastern Cordillera indicates matic constraints of the orogenic belt permits tral Llanos foothills, it is mainly constrained by that minor uplifts continued to supply detritus to identifi cation of phases of deformation in an the increasing fl exural subsidence toward the the adjacent basin. orogen–foreland basin system. The current con- Eastern Cordillera and subtle deformation of Late Eocene to middle Miocene shortening fi guration of the Eastern Cordillera and adjacent tectono-stratigraphic sequence four. The fourth emplaced loads less than 4 km high in the area Llanos Basin of Colombia is the result of the tectonic phase was also characterized by east- between the axial zone of the Eastern Cordillera polyphase growth of basement-rooted structures ward reactivation of tectonic loads and genera- and the eastern Llanos foothills (Figs. 12F, 14D, and ensuing foreland basin development. There- tion of the salient-recess geometry of the thrust and 15C). Exhumation of this area, bounded fore, a comprehensive analysis of the adjacent belt (Fig. 15C). In the hinterland, this phase is by the Chameza fault to the east, is supported foreland basin can be used to defi ne the spatial identifi ed by published apatite fi ssion tracks by AFTA data. At this time, a fold-and-thrust and temporal patterns of deformation of former (Shagam et al., 1984; Toro, 1990; Hossack et belt advanced eastward to the present position events in the evolving Eastern Cordillera. al., 1999). Geodynamic analyses indicate that of the western Llanos foothills (Fig. 15C), and Five episodes of deformation have been tectonic loads were 3–6 km high, 50–100 km the salient-recess geometry of the thrust belt documented from analysis of the sedimentary wide, and wider in the northern than in the cen- began to form. Deposition in the eastern Lla- record in the axial zone and eastern fl ank of the tral cross section. nos foothills was mostly accommodated by Eastern Cordillera, Llanos foothills, and Llanos The last tectonic episode identifi ed in this increasing fl exural subsidence toward the East- Basin. The fi rst three episodes of deformation study encompassed the width of the entire East- ern Cordillera (Fig. 12F), as indicated by the include shortening during latest Cretaceous to ern Cordillera, involved reactivation of basement abrupt change in thickness of Oligocene and middle Eocene time. During this period, the structures during middle Miocene to Pliocene lower Miocene strata, and it was less affected by deformation front fi rst moved eastward from time, and ultimately defi ned the current confi gu- growth of incipient structures. The dominance the axial zone to the eastern fl ank of the East- ration of major structures that bound the Eastern of sublitharenite and subarkose supports the ern Cordillera (tectono-stratigraphic sequences Cordillera, as well as the fl exural geometry of the interpretation that nearby structures in the east- one and two, Figs. 15A and 15B), and then it Llanos Basin. Tectonic loads advanced eastward ern Llanos foothills were not exposed to supply shifted to the western fl ank of the Eastern Cor- during at least two periods of out-of-sequence detritus to the basin. dillera and Magdalena Valley (tectono-strati- reactivation, as inferred from relations between Strong basin inversion took place during graphic sequence three). Flexural deformation hanging-wall and footwall structures of the Cha- middle Miocene to Pliocene time and gave rise induced: (1) erosion of Paleocene–upper Creta- meza and Guaicaramo faults in the central cross to today’s Eastern Cordillera structural confi gu- ceous strata in the Llanos foothills and Llanos section, and of the Cobugon and Samore faults ration (Figs. 12G and 14E). Equivalent tectonic Basin, (2) westward thickening of unconfor- in the northern cross section. These phases of loads along the eastern fl ank of the Eastern Cor- mity-bounded Maastrichtian- Paleocene syn- deformation are further constrained by rock- dillera were 10–11 km high, and they advanced tectonic sequences, (3) increased input of lithic exhumation (Van der Wiel, 1991; Mora et al., eastward to the eastern boundary of the Llanos fragments in upper Paleocene strata and north- 2005) and surface-uplift (Hooghiemstra and foothills. The onset of Andean-scale deforma- ward dispersal of detritus, (4) amalgamation Van der Hammen, 1998) evidence. However, the tion created a regional and nearly simultane- of fl uvial-to-estuarine channel structures dur- lack of biostratigraphic constraints in the associ- ous fl ooding event that is recorded in most of ing the early and middle Eocene, (5) change of ated alluvial and fl uvial deposits precludes rec- the sub-Andean foreland basins in the middle subsidence rates in the latest Cretaceous and ognition of individual phases of deformation, Miocene. The rapid uplift and consequent basin late Paleocene, and (6) slow tectonic subsid- similar to those uncovered here for the upper fi lling caused abrupt eastward migration of the ence regimes during the early-middle Eocene Cretaceous–middle Miocene succession. forebulge and fl uvial-alluvial depositional sys- in the axial Eastern Cordillera and Llanos The integrative approach used for this research tems originating from the Eastern Cordillera. foothills. These phases of deformation are con- permits identifi cation of the timing of activity The most active fault during this latter tec- strained in the hinterland by: (1) zircon fi ssion- on the different structures within the Eastern tonic phase was the Guaicaramo fault system, track data from the Santander massif (Shagam Cordillera and their effect on the adjacent sedi- which allowed exhumation of the Quetame et al., 1984); (2) geochronological data from mentary basin. This two-dimensional approach massif and basal Cretaceous strata. It was only micas fi lling normal faults associated with should be considered prior to a three-dimen- at this time that strong surface uplift took place fl exural extension during the latest Cretaceous sional analysis of a thrust belt system in order between 6 and 3 Ma, as documented by the (Branquet et al., 1999); and (3) angular uncon- to constrain the effects of a particular phase of change of paleobotanical associations and the formities in the Magdalena Valley (Gómez et deformation on location of source areas, dis- generation of an orographic barrier that accel- al., 2003, 2005b). Geodynamic analysis allows persal of synorogenic detritus, distribution of erated deformation on the eastern fl ank of the us to infer that equivalent tectonic loads for depositional systems, and stratal architecture in Eastern Cordillera. Out-of-sequence deforma- these phases were less that 3 km high, less than the basin. In addition, future thermochronologi- tion along the Guaicaramo fault system was 100 km wide, and wider in the northern than in cal studies designed to quantify the exhumation coeval with the different phases of exhumation the central part of the study area. of the Eastern Cordillera must encompass the documented by AFTA data for the Garzon and Tectonic loads in the late Eocene–middle width of the Eastern Cordillera rather than sam- Quetame massifs. Miocene fl exural phase were higher than former pling a single range. episodes of deformation, and they were concen- CONCLUSIONS trated in the axial zone of the Eastern Cordillera, ACKNOWLEDGMENTS eastern fl ank of the Eastern Cordillera, and to a This research was supported by the Colombian The integration of palinspastically restored lesser extent in the Llanos foothills. In the north- Petroleum Institute, Ecopetrol S.A., the Smithso- basin geometry and internal features of syntec- ern Llanos foothills, this phase is constrained nian Paleobiology Endowment Fund, and the Unre- tonic units (e.g., stratal architecture, sandstone by the presence of growth strata that bound stricted Endowments SI Grants. Thanks are due to

1194 Geological Society of America Bulletin, September/October 2008 An integrated analysis of an orogen–sedimentary basin pair

the Biostratigraphic Team at the Colombian Petro- The American Association of Petroleum Geologists Bul- Fajardo, A., Rojas, E., Cristancho, J., and Consorcio G&G leum Institute, Nestor Gamba, and Johana Pinilla for letin, v. 79, p. 1444–1463. Going System, 2000, Defi nición del Modelo estratigra- their collaboration at different stages of this project. Cediel, F., and Cáceres, C., 1988, Geologic Map of Colombia: fi co en el Intervalo Cretaceo Tardio a Mioceno Medio We thank Timothy Lawton for a careful review of the Bogotá, Geotec Ltd., scale 1:1,200,000. en la Cuenca Llanos Orientales y Piedemonte Llanero: Cediel, F., Shaw, R., and Cáceres, C., 2003, Tectonic assembly Informe Final: Bucaramanga, Ecopetrol S.A. y Instituto manuscript, which, together with the comments of of the Northern Andean block, in Bartolini, C., Buffl er, Colombiano del Petroleo, 181 p. an anonymous reviewer and Associate Editor James R., and Blickwede, J., eds., The Circum-Gulf of Mexico Fajardo-Peña, G., 1998, Structural Analysis and Basin Inver- Schmitt, improved the content of this paper. Natasha and the Caribbean: Hydrocarbon Habitats, Basin Forma- sion Evolutionary Model of the Arcabuco, Tunja and Atkins reviewed the last revised version of the sub- tion and Plate Tectonics: American Association of Petro- Sogamoso Regions, Eastern Cordillera, Colombia mitted manuscript to improve the fl ow of the English. leum Geologists Memoir 79, p. 815–848. [M.Sc. thesis]: Boulder, University of Colorado, 114 p. Bayona acknowledges discussions with Elias Gómez Céspedes, S., and Peña, L., 1995, Relaciones Estratigráfi cas y Flemings, P.B., and Jordan, T.E., 1990, Stratigraphic modelling concerning foreland evolution of the Magdalena Val- Ambientes de Depósito de las Formaciones del Tercia- of foreland basins: Interpreting thrust deformation and ley and Llanos Basin, Andres Mora concerning the rio Inferior Afl orante entre Tunja y Paz del Rio, Boyacá. lithosphere rheology: Geology, v. 18, p. 430–434, doi: 10. 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