The role of inherited extensional fault segmentation and linkage in contractional orogenesis: a reconstruction of Lower Cretaceous inverted rift basins in the Eastern Cordillera of Colombia Andre?s Mora,n Tatiana Gaona,w Jonas Kley,z Diana Montoya,w Mauricio Parra,n Luis Ignacio Quiroz,? German Reyesw and Manfred R. Streckern nInstitut f?r Geowissenschaften, Universitt Potsdam, Golm, Germany wIngeominas, Bogota? , Colombia zInstitut f?r Geowissenschaften, Universitt Jena, Jena, Germany ?SmithsonianTropical Research Institute, Balboa, Republic of Panama? ABSTRACT Lower Cretaceous early syn-rift facies along the eastern ?ank of the Eastern Cordillera of Colombia, their provenance, and structural context, reveal the complex interactions between Cretaceous extension, spatio-temporal trends in associated sedimentation, and subsequent inversion of the Cretaceous Guatiqu|? a paleo-rift. South of 41300N lat, early syn-rift alluvial sequences in former extensional footwall areas were contemporaneous with fan-delta deposits in shallow marine environments in adjacent hanging-wall areas. In general, footwall erosionwas more pronounced in the southern part of the paleorift. In contrast, early syn-rift sequences in former footwall areas in the northern rift sectors mainly comprise shallow marine supratidal sabkha to intertidal strata, whereas hanging-wall units display rapid transitions to open-sea shales. In comparisonwith the southern paleo-rift sector, fan-delta deposits in the north are scarce, and provenance suggests negligible footwall erosion.The southern graben segment had longer, and less numerous normal faults, whereas the northern graben segment was characterized by shorter, rectilinear faults.To the east, the graben systemwas bounded by major basin-margin faults with protracted activity and greater throw as comparedwith intrabasinal faults to the west. Intrabasinal structures grew through segment linkage and probably interacted kinematically with basin-margin faults. Basin-margin faults constitute a coherent fault system that was conditioned by pre-existing basement fabrics. Structural mapping, analysis of present-day topography, and balanced cross sections indicate that positive inversion of extensional structureswas focused along basin-bounding faults, whereas intrabasinal faults remained una?ected andwere passively transported by motion along the basin-bounding faults.Thus, zones of maximum subsidence in extension accommodated maximum elevation in contraction, and former topographic highs remained as elevated areas.This documents the role of basin-bounding faults as multiphased, long-lived features conditioned by basement discontinuities. Inversion of basin- bounding faults was more e?cient in the southern than in the northern graben segment, possibly documenting the inheritance and pivotal role of fault-displacement gradients. Our observations highlight similarities between inversion features in orogenic belts and intra-plate basins, emphasizing the importance of the observed phenomena as predictive tools in the spatiotemporal analysis of inversion histories in orogens, as well as in hydrocarbon and mineral deposits exploration. INTRODUCTION Abetter understanding of the processes and styles govern- ing the inversion of inherited normal faults in orogenic belts is a fundamental problem in structural geology. For example, in orogens the presence of structural and strati- graphic traps related to former rift tectonics may guide the migration of fossil fuels and the emplacement of mineral resources (e.g. Uliana et al., 1995). In such settings, the origin and evolution of inverted structures are therefore important in improving exploration. Furthermore, if pro- nounced pre-existent anisotropies related to extensional Correspondence: Andre? s Mora, Institut f?r Geowissenschaften. Universitt Potsdam, Karl Liebnecht-Str 24, D14476 Potsdam- Golm,Germany. E-mail: andres.mora@geo.uni-potsdam.de BasinResearch (2009) 21, 111?137, doi: 10.1111/j.1365-2117.2008.00367.x r 2009 The Authors Journal Compilationr Blackwell Publishing Ltd, European Association ofGeoscientists & Engineers and International Association of Sedimentologists 111 tectonics are favorably orientedwith respect to the greatest horizontal stress during a subsequent contractile phase, reactivation of such structures may signi?cantly impact the spatiotemporal evolution of deformation in the entire mountain belt (e.g. Lowell, 1995). Hence the width of an orogen may be a direct consequence of this type of interac- tion and its growth may not be governed by the principles of wedge mechanics (e.g. Davis et al., 1983) documented in regions where such inherited structures do not exist (Hil- ley et al., 2005). In addition, the polarity of normal faults, associated disparities in syntectonic sediment thickness, and existence of extensional transfer structures may exert an important control on orogenic evolution during con- traction (e.g. Hayward &Graham, 1989). Positive basin inversion involves the partial or total re- versal of motion on extensional faults subjected to super- imposed compressional stresses (Williams et al., 1989). The phenomenon of basin inversion has been documen- ted worldwide. For example, mild to moderate inversion in intraplate basins has been observed in numerous North Atlantic basins (Cartwright, 1989; Chapman, 1989; Hay- ward & Graham, 1989; Roberts et al., 1993; Sinclair, 1995; Thomas & Coward, 1995) or in the North German Basin (Kossow et al., 2000; Kossow & Krawczyk, 2002; Gemmer et al., 2003). In addition, strongly shortened half grabens have been documented in the Alps (Gillcrist et al., 1987), with prominent examples found in the Central Andes (Kley&Monaldi, 2002) and Atlas mountains (Beauchamp et al., 1999;Teixell et al., 2003). Huyghe & Mugnier (1995) suggested that the nature of inversion in mildly inverted intraplate basins is di?erent from inversion in orogenic belts where extensional struc- tures are typically fully reversed, creating topography and exposure of former basin strata (e.g. Badley, 2001). The time span between the extensional phase and the onset of subsequent contraction is often larger in orogenic belts compared with intraplate basins (Huyghe & Mugnier, 1995).Therefore, by the time a formerly rifted lithosphere undergoes contraction in an orogenic setting, it may have recovered its pre-extensional strength (Huyghe & Mug- nier, 1995). In this context, it is an important question if di?erent crustal properties in?uence variations in inver- sion styles in fully developed orogenic belts in comparison with intraplate basins. In intraplate basins undergoing mild to moderate inver- sion, high-quality seismic images have improved our 3D understanding of the behavior of individual normal faults and linked graben systems during subsequent compres- sion (Cartwright, 1989; Chapman, 1989). Furthermore, laboratory 3D analog models of inversion have helped visualize the ?rst-order principles and structures asso- ciated with these processes (Eisenstadt & Withjack, 1995; McClay, 1995). In the more severely inverted basins of many orogens, however, detailed ?eld-based accounts regarding the mechanical interaction of segmented former extensional faults, the nature of displacement transfer, and how such structures are incorporated into the orogenic realm are rare (Hayward & Graham, 1989; Garc|? a Senz, 2002; Kley et al., 2005; Monaldi et al., 2008). These problems are of- ten compounded by a general lack of good seismic images with unequivocal extensional features. Furthermore, due to the high degree of superimposed shortening, a precise assessment of extensional features is made di?cult at the outcrop level, as in the case of theWesternAlps (e.g.Gillcr- ist et al., 1987; Coward et al., 1989; Graciansky et al., 1989; Hayward&Graham,1989). In these extreme cases, a palin- spastic reconstruction may help decipher the principal extensional features and original location of ancestral extensional structures (e.g. Nemcok et al., 2001). Finally, prominent along-strike changes in the patterns and styles of deformation have been observed in many inversion oro- gens (Grier et al., 1991; Carrera et al., 2006). However, few studies have unambiguously demonstrated that those changes are indeed determined by along-strike variations in the modes of previous extensional deformation, fault interaction, and linkage. The Eastern Cordillera of Colombia (Fig.1) has experi- enced much less deformation than many other inversion orogens (e.g. Colletta etal.,1990;Mora etal., 2006). It there- fore has the advantage of furnishing valuable information on ancient normal fault arrays, the characteristics of asso- ciated syn-rift depositional settings, and the lateral evolu- tion before contraction. In this study, we document a previously unrecognized pattern of extensional fault interaction, deduced mainly from early syn-rift stratigraphic sequences associatedwith former normal faults. First, we determine the local charac- teristics and lateral extent of syn-rift units in light of the Early Cretaceous paleotopography in order to use the sedimentary facies associations as proxies for past normal fault evolution and linkage. Second, we evaluate the e?ects of the pre-existing extensional fault arrays on Cenozoic contractional deformation. In contrast with the study of Mora et al. (2006), we use sedimentology to document that a pattern of selective fault reactivation is not onlydue to the orientation of the compressive stress ?eld with respect to the pre-existent faults (Mora et al., 2006), but is also relatedwith the pattern of extensional fault growth. GEOLOGIC SETTING OF THE EASTERN CORDILLERA The Colombian Eastern Cordillera is an atypical Andean foreland fold and thrust belt. In stark contrast with other Andean foreland fold and thrust belts it appears to be more in?uenced by inherited structures rather than subduction related orogenesis (e.g. Colletta etal., 1990).The spatial co- incidence between the Eastern Cordillera (Fig. 1) and a Neocomian extensional province was proposed byColletta et al. (1990), although it has also been suggested that this region may represent a simple ramp basin that subsided more than adjacent regions during the Early Cretaceous (Roeder & Chamberlain, 1995), similar to the Cameros Basin in northern Spain (Guimera et al., 1995). Indeed, in r 2009 TheAuthors Journal Compilationr Blackwell Publishing Ltd, EuropeanAssociation of Geoscientists & Engineers and International Association of Sedimentologists 112 A. Moraet al. the Eastern Cordillera it had been impossible to recognize and precisely locate former rift-controlling faults. How- ever, basin-analysis studies of this region favor a rift model (Sarmiento-Rojas et al., 2006). In addition, structural reconstructions (Mora et al., 2006) unambiguously show that the Early Cretaceous basin along the eastern ?ank of the Eastern Cordillera was a rift zone. These authors proposed a reactivation mechanism restricted to an in- verted frontal master fault (Servita? fault), where the entire eastern ?ank of the EC was passively uplifted while the internal structures underwent virtually no contractile reactivation. The main reason for selective fault reactiva- tion in the Cretaceous extensional province was inferred to be related to the orientation of the tectonic stress ?eld with respect to the pre-existing anisotropies (Mora et al., 2006). CD GD SA EF SF SjF NF GF LF TF GT 73?W 4? ECNAZCA PLATE SOUTH AMERICAN PLATE CARIBBEAN PLATE 0? 6? ?73? STRATIGRAPHY Terrace Alluvium Quaternary STRUCTURES Reverse fault Normal fault Anticline Syncline Pre-Devonian Quetame Group Upper Paleozoic sedimentary units Lower Cretaceous basal units Macanal Formation Caqueza Formation F?meque Formation Une Formation Chipaque Formation Guadalupe Group Paleocene-Middle Eocene units Carbonera Formation Le?n Formation Lower Guayabo Formation Upper Guayabo Formation Pre- Cretaceous Lower Cretaceous Upper Cretaceous Paleogene Neogene Alluvial Fan Strike-slip fault CD: Chingaza Dome EF: Esmeralda Fault FA: Farallones Anticline GD: Guavio Dome GF: El Garabato Fault GT: Guaicaramo Thrust LF: Lengup? Fault LMF: Los Medios Fault NF: Naranjal Fault SA: Santa Mar?a Anticline SjF: San Juanito Fault SF: Servit? Fault TF: Tesalia Fault Fig 16c Fig 16b Fig 16a 4?N Fig 17 Villavicencio 20 km 5?N Fig.1. (a) Geodynamic setting and simpli?ed topography of the northern Andes.The study area is indicated by the box. (b) Geological map of the Farallones deMedina area with location of the cross sections in Fig.15.Map depicts areas covered in Figs12, 13, 17, 18 and locations of balanced structural pro?les. r 2009 The Authors Journal Compilationr Blackwell Publishing Ltd, European Association ofGeoscientists & Engineers and International Association of Sedimentologists 113 Role of inherited extensional fault segmentation and linkage The investigated area of this study is located in the Farallones de Medina range of the Eastern Cordillera. This area (Figs1and 2) is located along the eastern foothills of the mountain belt and exposes lower Cretaceous syn-rift facies in di?erent tectonic blocks.Although the structural re- lationships in this region are now well known (e.g. Mora etal., 2006), the lateral distribution of syn-rift facies and their relationship to the structures is not yet fully understood. Phyllites and green schists of the pre-Devonian Que- tame Group constitute the oldest rocks in the area and are overlain by the sedimentary Farallones Group. These units comprise Devonian nonmarine to shallow marine sandstones (Areniscas de Gutierrez Formation); Carboni- ferous continental red-bed sequences (Capas del Valle del Guatiqu|? a Formation), and Permian shallow marine car- bonates (Gachala? Formation). The upper Paleozoic rocks are superseded by ca. 5-km- thick Cretaceous sequence (Fig. 3).The lowermost Berria- sian and Valanginian units overlying the Paleozoic rocks are the main target units of this study, as they represent the early syn-rift strata. However, the Berriasian strata cannot be grouped into one single, basal lithostratigraphic unit as these strata display rapid lateral facies changes. For example, calcareous units overlying the pre-Cretaceous basement have been grouped into the Calizas del Guavio Formation (Ulloa & Rodr|? guez, 1979); coeval strata com- posed of polymictic gravels, breccias, ?uvial sandstones and associated overbank ?nes constitute the Brechas de Buenavista Formation (Dorado, 1992). In other locations, shallow marine terrigenous lithic sandstones, polymictic conglomerates, and subordinate amounts of gray siltstones of Early Cretaceous age that overly Paleozoic rocks belong to the Bata? Formation (B?rgl, 1961; Geyer, 1973; Ulloa & Rodr|? guez, 1979; Etayo-Serna et al., 2003, Fig. 2). All of these units are therefore lateral equivalents and are over- lain by an ammonite-dominated shale unit (Lutitas de Macanal Formation, Fig. 2). METHODS Our study focuses on Berriasian and Valanginian strata re- cording the earliest syn-rift sedimentation in the Farallones de Medina area.We produced a ?eld structural map of the studyareabased on1: 25 000and1:10 000 topographicmaps and aerial photographs (Fig.1). Careful ?eld structural map- ping helped detect and de?ne the best exposures of the early syn-rift units.Where possible, we chose pro?les displaying well exposed contactswith the underlyingPaleozoic substra- tum and used this unconformity as a marker horizon.We measured detailed (1: 200) stratigraphic columns using a Ja- cob sta?. In the gravel intervals, we analyzed clast composi- tions in order to determine provenance (Table1). Additional quantitative petrologic data is mostly abstent in those non- conglomeratic intervals. Paleocurrent measurements of groove castsweremainly taken in turbiditic sandstone strata. However, paleocurrent data is scarce in most of the local- ities. In addition, we integrated our datawith published sec- tions (Stibane, 1968; Dorado, 1992; Parra, 2000; Geostratos, 2005; Rinco? n & Ta? mara, 2005). The measured sections (Fig. 3) were described according to10 di?erent facies asso- ciations. The graphic symbols in the pro?les, representing various lithologic and primary features observed in the ?eld and reported in our stratigraphic pro?les can be seen in Fig. 4. Sections were correlated by following key horizons in the ?eld or on aerial photographs based on prominent topographic features. Using these data, we constructed a map of early syn-rift facieswith the interpreted sedimentary environments in this extensional setting during the Early Cretaceous. To expand our analysis of superimposed con- tractional deformation, we also constructed three balanced cross sections based on outcrop and seismic data. SEDIMENTARYCHARACTERISTICS OF THE EARLYCRETACEOUS RIFT-BASIN FILL Buenavista formation Facies association B1 This facies association constitutes the basal conglomerate at localities 5, 6, 7 (Fig. 6) 11,12 (Fig. 7) and16, and most of the sequence at localities1and 2 (Fig. 5). Its thickness typi- cally ranges from10 to 40m.This association is character- ized by a set of very thick beds, either with lenticular geometry or irregular geometry, occasionally lacking in- ternal strati?cation.The individual beds are composed of poorly sorted cobble-sized, subrounded conglomerates (in localities 5, 11and12 some 25^60 cm boulders are also pre- sent), mostly supported by a sandy to silty matrix. The cobble-size fraction is predominantly monomictic quart- zose. Sorting is commonly poor. Often, there are inter- bedded pebble-conglomerates and pebbly conglomeratic sandstones in well-de?ned beds with variable thickness and inverse grading. We interpret these rocks to have been deposited in an alluvial-fan system. Matrix-supported conglomeratic beds with sandy matrix and irregular geometry may corre- spond to debris- ?ow deposits, whereas conglomeratic beds with well-de?ned geometry re?ect con?ned channel ?ows during stream-dominated deposition (e.g. Rust & Koster, 1984; Nemec & Postma, 1993). At locality 1 (Fig. 5), there is a clear lateral change toward marine facies (i.e. black shales with ammonites) suggesting that in some localities these conglomeratic beds are transitional be- tween ?uvial and coastal environments. Facies association B2 This facies association is characterized by poorly sorted breccias and coarse matrix-supported conglomerates lack- ing internal organization or well de?ned bedding surfaces. This facies association is a lateral equivalent of shallow marine units because it normally outcrops adjacent to ammonite bearing black shales. The thickness is highly r 2009 TheAuthors Journal Compilationr Blackwell Publishing Ltd, EuropeanAssociation of Geoscientists & Engineers and International Association of Sedimentologists 114 A. Moraet al. Fig. 2. (a) Reconstructed distribution of Early Cretaceous faults.The numbers are elevations above sea level in certain localities. (b) Locations of the stratigraphic sections quoted in the text. r 2009 The Authors Journal Compilationr Blackwell Publishing Ltd, European Association ofGeoscientists & Engineers and International Association of Sedimentologists 115 Role of inherited extensional fault segmentation and linkage variable and the lateral continuity is restricted.This facies association overlies the basal Cretaceous unconformity at localities 3 (Fig. 5), 2, 8, 10 and 15 (Fig. 8), and at about 375m above this unconformity, at locality 7 (Fig. 6).Typi- cally, this facies consists of boulders (460 cm in diameter) and cobbles in a pebbly to sandy matrix. Some boulders exceed 2m in diameter; angular to sub-angular clasts dominate. Owing to a general lack of organization and a high fraction of metamorphic basement clasts this facies association di?ers from the basal conglomerates in facies association B1 (Table 1, Quetame Group phyllites), except at outcrop locality 10, where these clasts are virtually absent. Owing to the poor strati?cation and sorting, abundant angular fragments, and limited lateral continuity, the ma- trix-supported conglomerates of facies association B2 are interpreted as debris ?ow deposits (Rust & Koster, 1984; Nemec & Postma, 1993; Blair & McPherson, 1998). The rapid lateral transition into marine facies (e.g. facies Table1. Clast count method Section/m above base Composition of fragments Sedimentary rocks Unstable- basement rocks 1. Puente Quetame 68 100 0 70 100 0 61 100 0 48 100 0 25 100 0 19 100 0 16 100 0 2. Alto del Tigre 437 100 0 426 100 0 415 100 0 405 17 83 387 24 76 363 57 43 354 52 48 263 67 33 137 71 29 24 56 44 13 100 0 3. Paujil Lower segment o30 470 Upper segment 65 35 4. Florida Creek 450 Observed 5. Calvario 2 100 0 6. La Esfondada 6 100 0 5 (n) 45 55 7. San Isidro-Lajitas 525 71 29 523 89 11 515 62 38 503 57 43 497 68 32 484 97 3 447 85 15 422 74 26 1 100 0 8. Carpanta 118 53 47 90 87 13 45 64 34 17 95 5 9. El Tigre Creek 10. La Ardita Creek 248 100 0 224 100 0 195 100 0 164 100 0 142 100 0 118 100 0 102 100 0 Table1. (Continued) Section/m above base Composition of fragments Sedimentary rocks Unstable- basement rocks 72 100 0 29 92 8 24 90 10 18 80 20 11. Palomas 12 100 0 15 100 0 18 100 0 12. Gachaluno River 14 100 0 9 100 0 73 100 0 55 100 0 159 100 0 13. Cascadas 14. Chivor Alto 15. Batatas 59 100 0 43 100 0 18 100 0 10 100 0 16.Malacara 17. Santa Rosa 18.Mina El Porvenir After a general inspection of the outcrop and rough analysis of the clasts present, an arbitrary face was selected in order to count the composition of the clasts in every single gravel size grain (up to boulder size).The frac- tions were separated in clasts of sedimentary rocks, milky quartz from veins, feldespars (never found) and unstable or clearly discernible base- ment lihologies.We took in this table the sedimentary clasts plus the basement rocks as100.Then put in the table the amount of each fraction with respect to the total. Our goal was only to detect the presence or ab- sence of basement rocks. r 2009 TheAuthors Journal Compilationr Blackwell Publishing Ltd, EuropeanAssociation of Geoscientists & Engineers and International Association of Sedimentologists 116 A. Moraet al. associations M1) indicates a fan delta in a shallow marine setting. Facies association B3 These units comprise tabular to lenticular beds, 0.3 to sev- eral meters thick, with medium-to coarse-grained lithic sandstones and laterally equivalent lithic conglomeratic sandstones and conglomerates. Medium to thick beds (up to 1m thick) of siltstones and mudstones are interbedded with the upper sandstones of this facies association. It is well developed at localities 2 (intervals between 30 and 83m and, between 325 and 383m. Fig. 5) and 6 (lower seg- ment of the basal syn-rift unit, Fig. 6).The lower 40m at locality 6 (Fig. 6) have a ratio of sand to mud layers of about 90 : 10. Amalgamated sandstone beds with lenticular geo- metry are abundant, with frequent inverse grading and occasionally with planar cross bedding. However, in the upper 150m at locality 6 the sand to mud layer ratio is 40 : 60. This section contains frequent thin to very thick- bedded (sensu Ingram,1954) red-colored siltstones to sandy siltstones with pervasive mottling.These are interbedded with medium to thick-bedded lithic sandstones (petrogra- phy after Parra, 2000) with normal grading and channel geometry. Amalgamated sandstone beds very often display lateral accretion surfaces and have thin basal conglomera- tic lags. The amalgamated lithic sandstone beds in the lower 40m at locality 6 and 2 are interpreted as bars in a braided river system (e.g.Collinson,1996;Miall,1996). In the upper 150m of locality 6, the channelized sandy ?ning-upward sequences with lateral accretion surfaces suggest a mean- dering river environment. Accordingly, interbedded silt- stones and sandy siltstone beds with pervasive mottling represent ?oodplain deposits and overbank ?nes (Miall, 1985). Calizas Del Guavio formation Facies association C1 Facies association C1 is well developed at localities 18 (between 160 and 215m), 15 (between 95 and 160m) and 14 Stratigraphic interval of interest in this studyBATA` Fig. 3. Meso-Cenozoic stratigraphy of the eastern ?ank of the Eastern Cordillerawith the stratigraphic interval of interest highlighted (Modi?ed fromMora et al., 2006). r 2009 The Authors Journal Compilationr Blackwell Publishing Ltd, European Association ofGeoscientists & Engineers and International Association of Sedimentologists 117 Role of inherited extensional fault segmentation and linkage (discontinuous interval between 35 and135mFigs 2 and 8), and it consists of two distinct inter?ngering cycles with a thickness of 0.5^2m. First, laminated dolomitic mud- stones (at locality 15) or laminated calcareous mudstones (at localities 14 and 18) alternate with thin-to medi- um-bedded nodular calcareous mudstones, often with chicken-wire growths, enterolithic folding, and fenestrae. Desiccation cracks occur on top of some of the beds in this unit.The second unit comprises laminated structures in- terpreted to be stromatolites (Kalkowsky, 1908; Logan et al., 1964; Tucker & Wright, 1990; Riding, 2000). In addition, we found a clothed texture re?ecting syn- depositional processes at locality15, also interpreted to re- ?ect microbial origin (trombolites sensu Riding, 2000). At localities 18 and 15a these associations are also inter- bedded with very thick black shale and black marl hori- zons, occasionally with laminae rich in pyrite. The ?rst unit is characteristic of evaporite pseudo- morphs. For example, nodules and enterolithic structures (Fig. 9) resemble diagenetic structures formed in modern Limestone Dolomites Sandy limestones Stromatolites with hemispheroidal fabric Stromatolites with laminated fabric Marlstones Sandstone Conglomerate Conglomeratic sanstone Claystone Silstones Evaporites pseudomorphs with nodular fabric Pyrite nodules Calcareous concretions Pyrite laminae Breccia SILICICLASTIC SEDIMENTARY ROCKS CARBONATE SEDIMENTARY ROCKS Micrite interlayering Chickenwire structures Sandy mudstone Shale Red mudstones Muddy sanstone Evaporites pseudomorphs with enterolithic structures Muddy limestones Calcareous sandstone Corals Echinoderms Brachiopods Crinoids Bivalves Gasteropods Plant remains Trunk remains Parallel lamination Continuous Wavy bedding Discontinuos wavy bedding Crude bedding Bioturbation Rootlets Organic matter Fault MO GypsumY Synsedimentary folding Ripples Amonites Erosion surface Imbrication Slumps Groove cast Normal grading Inverse grading Angular Unconformity Planar cross bedding with tangential foresets Planar cross bedding Foraminifera Lenticular bedding Trough cross bedding Flaser bedding Fig.4. List of symbols and abbreviations and their meaning.These symbols and abbreviations were used in Figs 5, 6, 7, 8, and10. r 2009 TheAuthors Journal Compilationr Blackwell Publishing Ltd, EuropeanAssociation of Geoscientists & Engineers and International Association of Sedimentologists 118 A. Moraet al. anhydrites (Kendall & Harwood, 1996; Alsharhan & Ken- dall, 2003). Alternations of dolomitic mudstones and an- hydrite are common under hypersaline conditions when calcium sulfate precipitates and residual waters are en- riched in magnesium (Alsharhan & Kendall, 2003). Facies association C1 thus suggests deposition under conditions typical of coastal sabkhas (Warren&Kendall,1985; Alshar- han&Kendall, 2003). In combinationwith the desiccation cracks, these characteristics re?ect arid to hyperarid cli- mate conditions (Tucker &Wright, 1990). The second, stromatolite-bearing unit is interpreted to indicate a temporary changeover from supratidal sabka to intertidal conditions, similar to present-day environ- ments reported inDubai (Tucker &Wright,1990).The pre- sence of black shales and marls interbeddedwith the other units suggests subtidal conditions, possibly associated 2. Alto del Tigre Naranjal Fault Servit? Fault W E 3. Paujil Creek B2 B1 M2 B1 B3 B1 M3 B1 B3 B1 B3 1. Puente Quetame B1 B3 B1 M3 Fig. 5. See locations in Fig. 2. Stratigraphic logs located in the southernmost segment of the study area. Contrasting facies in the di?erent pro?les coincides with di?erent faulted domains. r 2009 The Authors Journal Compilationr Blackwell Publishing Ltd, European Association ofGeoscientists & Engineers and International Association of Sedimentologists 119 Role of inherited extensional fault segmentation and linkage with an euxinic basin.Overall, these deposits appear to in- dicate oscillating sea level in a sustained arid environment. Facies association C2 This facies association is characterized by tabular beds of mudstones, marls, and intraclastic wackestones, well de- veloped at locality 15c (Fig. 8, between 0 and 95m). The beds commonly contain disseminated bivalve shells (bio- clastic wackestones). Locally bivalve packstones are found. In this facies association, well- sorted bioclasts generally do not occur in growth position and are sub-horizontal with respect to bedding. Occasionally, poorly sorted bio- clasts are found in di?erent positions. We interpret this facies association to be related to in- ternal to intermediate parts of a carbonate platform envir- 6.Esfondada 7a. Lajitas San Juanito Fault W E 20 40 60 80 100 120 260 140 160 180 200 220 240 280 300 320 340 360 380 400 420 440 460 480 500 520 B1 C3 M3 M3 B2 Si Sa Gr Md Pc Wc Gr Bd Cl Si Sa Gr Md Pc Wc Gr Bd Cl 280 300 320 340 360 380 400 420 440 460 480 500 20 40 60 80 100 120 140 160 180 200 220 240 260 Cretaceous Paleozoic B1 B3 B3 M1 M1 Si Sa Gr Md Pc Wc Gr Bd Cl Si Sa Gr Md Pc Wc Gr Bd Cl Fig. 6. See locations in Fig. 2. Stratigraphic pro?les in the footwall and hanging wall blocks of the San Juanito fault depicting marked contrasts between early syn-rift facies in both domains. r 2009 TheAuthors Journal Compilationr Blackwell Publishing Ltd, EuropeanAssociation of Geoscientists & Engineers and International Association of Sedimentologists 120 A. Moraet al. onment. Abundantwackestones and some bioclastic pack- stones with horizontal, well- sorted, and often disarticu- lated bivalves may correspond to proximal storm- ?ow shell concentrations (sensu F?rsich, 1995). In contrast, the less frequent wacke- and packstone levels with rarely bro- ken, often articulated bivalve shells in di?erent positions, and poor selection,may indicate storm-wave action (storm wave shell concentration sensu F?rsich, 1995). Overall, we 11. Palomas 12.. Gachaluno River W E 220 240 260 280 300 320 340 360 380 400 420 440 M3 Si Sa Gr Md Pc Wc Gr Bd Cl 20 40 60 80 100 120 140 160 Interval not to scale. Poorly exposed ca.500m shaly interval Paleozoic Cretaceous 180 200 M2 B1 Si Sa Gr Md Pc Wc Gr Bd Cl 20 40 60 80 100 120 140 160 180 200 220 240 260 Paleozoic Cretaceous B1 B3 Bt-1 Si Sa Gr Md Pc Wc Gr Bd Cl 280 300 320 340 360 380 400 420 440 460 480 500 520 Bt-1 Bt-1 Si Sa Gr Md Pc Wc Gr Bd Cl Gachaluno Fault 0 Fig.7. See locations in Fig. 2. Stratigraphic logs east andwest of the Gachaluno fault showing di?erent early syn-rift facies in each domain controlled by the Gachaluno fault. r 2009 The Authors Journal Compilationr Blackwell Publishing Ltd, European Association ofGeoscientists & Engineers and International Association of Sedimentologists 121 Role of inherited extensional fault segmentation and linkage interpret the tabular wacke- and mudstone layers to have been deposited above the basal level of storm in?uence and below the basal level of fair-weather wave in?uence. Facies association C3 Tabular beds of quartzose wackestones, calcarenites, carbonate-cemented sandstones, and minor calcareous mudstones characterize this facies association.The C3 fa- cies association occurs at locality 14 (between 145 and 190m, Fig. 8) and in lower non-conglomeratic segments of locality 7a and 7b (Figs 2 and 6). Interestingly, at both lo- calities there are occasional horizons where the bulk of the rock is composed of calcareous mudstone but most of the sand-size components consisting of quartz or terrigenous fragments (petrography after Parra, 2000). At locality 7a, Parra (2000) observed bioclasts of agglutinated benthic foraminifera (Textularia sp.,Glomospira sp.), aminor amount of planktonic species (Praeglobulina sp.), and ostracods. In addition, gastropods occur in the lowermost calcareous beds at locality 7b. The coarser grain size of this facies association repre- sents a higher-energy version of facies association C2.We interpret theC3 association as internal carbonate platform deposits. In addition, the presence of quartz and other ter- rigenous components indicates an adjacent terrigenous sediment source. Ostracods, agglutinated foraminifera, and gastropods may indicate a restricted, probably high salinity, internal platform environment. San Isidro Fault Paleozoic Cretaceous 20 40 60 80 100 120 140 160 C1 C2 MO MO MO MO Y 20 40 60 80 100 120 140 160 180 200 Paleozoic Cretaceous C1 C3 B2 Si Sa Gr Md Pc Wc Gr Bd Cl 20 40 60 80 B2 Si Sa Gr Md Pc Wc Gr Bd Cl 20 Si Sa Gr Md Pc Wc Gr Bd Cl Si Sa Gr Md Pc Wc Gr Bd Cl Fig. 8. See locations in Fig. 2. Early syn-rift facies controlled by the San Isidro fault, northern segment of the study area. r 2009 TheAuthors Journal Compilationr Blackwell Publishing Ltd, EuropeanAssociation of Geoscientists & Engineers and International Association of Sedimentologists 122 A. Moraet al. Bata? formation Facies association Bt-1 Facies association Bt-1 is well represented at localities 12 and 19. It constitutes a continuously exposed horizon between both localities. The lower section in locality 12 overlying Paleozoic rocks consists of a 30-m-thick con- glomerate included in facies association B1. This unit is overlain by ca. 70m of strata corresponding to facies asso- ciation B3. This interval is superseded by a ca. 400- m-thick sandstone unit that constitutes facies association Bt-1 (Fig. 7). The dominant lithology consists of amalgamated medium to thick beds of medium- to coarse-grained quartz sandstones. These layers are often interbeddedwith thin, ?ne-grained sandstones exhibiting ?aser and lenticular bedding. Occasionally, bioturbation (burrows) characterizes these beds.The medium to thick quartz-sandstone layers are commonly interbedded with upward ?ning, very thick to massive lithic to sub-lithic sandy to conglomeratic layers with erosional bases marked by conglomeratic lags. Large-scale cross bedding with conglomeratic laminae often accompanies layers exhibit- ing erosional bases. These strata are well developed be- tween 30 and190m at locality12 (Fig. 7). At this location, the upper stratigraphic horizons of this fa- cies association are characterizedbydecreasing sandstone,ab- sence of upward?ning conglomeratic sandstone layers, and an increasing proportion of interbedded mud- and siltstones. Between290and360m, transitions betweenmuddyand sandy facies are commonlybioturbated (burrows) and ?aser, lenticu- lar, and wavy laminations are typical. However, these features are less common in the upper portion of the facies association above 360m,which is a dominantly muddy interval. The lower monomineralic sandstones with interbedded thin ?ne-grained sand to siltstone layerswith ?aser bedding are interpreted as shoreline deposits (Galloway & Hobday, 1996; Reading & Collinson, 1996). However, the lithic sand- stones and ?ne-grained conglomerates with sharp basal contacts and ?ning-upward sequences indicate a periodic in?uence of?uvial processes in this near-shore environment (Dalrymple & Choi, 2007). In this context, the large-scale cross bedding with conglomeratic laminae may correspond to ?uvial lateral accretion surfaces.We suggest that this ?u- vial in?uence disappears progressively upsection as lithic sandstones and conglomerates with ?ning upward se- quences disappear. In the upper part of this facies associa- tion, an increasing proportion of shales and siltstones, a decreasing sandstone granulometry, and the presence of bioturbated intervals suggest amiddle to lower shoreface en- vironment (Galloway &Hobday,1996). Macanal formation Facies associationM1 This association is characterized by laminated beds of vari- able thickness with sandy mudstones, siltstones, and ?ne- grained sandstones that are exposed over a ca. 300m interval in the upper section of the pro?le at locality 6 (Fig. 6) and in (a) (b) (c) (d) Fig.9. Photographs of facies association C1at locality15. (a) Enterolithic structures interlayered in a laminated sequence of dolomites and mudstones. (b) Detail of entherolitic structure above interlaminations of dolomites and mudstones. Notice below the laminated beds the presence of calcite nodular growths (anhydrite pseudomorphs?). (c) Interlaminations of dolomites (light layers) and mudstones (dark layers) of interpreted microbial origin. (d) From left to right. Small enterolithic growths; ?rst laminated dolomites; layer with abundant nodular growth; second laminated dolomites. r 2009 The Authors Journal Compilationr Blackwell Publishing Ltd, European Association ofGeoscientists & Engineers and International Association of Sedimentologists 123 Role of inherited extensional fault segmentation and linkage the basal segment at locality13 (Fig.10) where it attains 60m thickness. Sandstones are mostly quartzose. Internally, the beds exhibit ?aser, lenticular, wavy, and planar lamination. The persistent ?aser, lenticular and wavy laminations indicate periodic tidal ?ow in a siliciclastic tidal ?at (Read- ing & Collinson, 1996).These strata are commonly located in the upper part of the described facies associations (e.g. Locality 6, Figs 2 and 6) between transitional to marginal marine environments represented by facies associations B2 and Bt-1, and open-sea shales of facies association M3.Therefore, they re?ect an intermediate part in an up- ward deepening succession. Facies associationM2 Typically, this facies association comprises a cyclic repeti- tion of medium to thin mudstone beds with ?ne-grained to very ?ne-grained sandstones displaying normal grading and erosive to irregular basal contacts. It includes an inter- val of about 150m at locality 11 (Fig. 7).These sandstones commonly have tangential cross bedding and tool marks at the base of individual beds.The top of each sandstone cycle is transitional with thin to medium beds of sandy black shales and shales with abundant plant remnants. The beds with basal erosive contacts, often with tool marks, normal grading, and upper transitional contacts suggest deposition by density currents (e.g. Shanmugam, 1997). A nearby continental source for the turbidites can be inferred from the abundant plant remnants in the inter- bedded shales. Paleocurrent directions measured on the sole marks (Fig. 7) and a westward pinchout of the sand- stones, indicate general ?ow from continental sources in the east.Turbidites in section 11probably represent the lateral equivalents of ?uvial conglomerates and sandstones in locality 12 to the east. Facies associationM3 This facies consists of monotonous, well-laminated, am- monite-bearing shale beds and rare medium-grained sandstones. Occasionally, the shales contain pyritic lami- nae or nodules. In some localities there are abundant plant remains interbedded with the shales (e.g. Locality 11). Facies association M3 occurs on top of all other facies as- sociations or represents their lateral equivalent. Because it constitutes a major part of the up to 3-km-thick Berria- sian-Valanginian Macanal Formation, its most important feature compared with all other facies associations is its thickness of many hundreds of meters. It is also the only unitwith a large lateral extent, covering virtually the entire study area. Based on the predominant ?ne-grained lithologies and ubiquitous ammonites, this facies association is inter- preted to re?ect an open-sea platform environment. The absence of indicators ofwave in?uence or storm beds sug- gest deposition in the deepest portions of the platform. This is compatible with the pyritic laminae, which is an indicator of anoxic conditions. The presence of plant re- mains suggests continental proximity. EARLY CRETACEOUS EXTENSIONAL TECTONICS AND FACIES DISTRIBUTIONS Our facies analysis demonstrates that the Berriasian depositional settings were spatially highly variable and disparate over short distances, emphasizing the important role of tectonism.Thus, to further understand Berriasian paleogeography, it is necessary to view our analysis in a structural context to evaluate fault controls on local and re- gional scales. In the following sections, we ?rst describe the main structures in the study area, group them into re- lated segments, and then compare them with the spatial distribution of facies. MO MO20 40 60 80 100 Paleozoic Cretaceous Poorly exposed shaly interval M3 M1 Cl Si Sa Gr Md Pc Wc Gr Bd Fig.10. See location in Fig. 2. r 2009 TheAuthors Journal Compilationr Blackwell Publishing Ltd, EuropeanAssociation of Geoscientists & Engineers and International Association of Sedimentologists 124 A. Moraet al. The structural pattern shows more segmented and per- vasive faulting in the northern part of the study area. In contrast, in the south faulting is reduced to less numerous and longer structures.Therefore, we de?ned two di?erent segments that constitute the Guatiqu|? a paleo-rift. A northern segment comprising the short and rectilinear Gachaluno, Esmeralda, Garabato, Malacara, Miralindo, San Isidro, and Manizales faults (Fig. 2), and a southern segment with the longer Servita? , San Juanito, Naranjal and LosMedios faults (Fig. 2). Based on the dominant facies association for the ?rst 100m above the basal unconformity at each location (excluding the ubiquitous lowermost basal conglomerates, if they are thinner than 20m) and mapping the lateral ex- tension of the facies associations, we compiled a facies map (Figs 2 and 11), in which we depict the earliest stages of Neocomian sedimentation. We also exclude the very local debris- ?ow deposits in locality 15. We extrapolated the units of interest on the geological map to areas covered by younger strata to the extent admissible from the mapped contacts. In the facies map it is evident that the lateral extent of many depositional systems appears to be bounded by the traces of the main faults (Fig. 11) as discussed below. Structural controls on early Cretaceous sedimentation along the different graben segments In the southern segment shallow marine facies east of the San Juanito fault (facies association C3; localities 5 and 7, Figs 2, 6 and 11) contrast with an up to 300-m-thick basal Cretaceous alluvial sequence west of the same structure (facies association B3; locality 6, Figs 6 and 11). Thus, di?erential subsidence along this fault presumably con- trolled these di?erent depositional systems. In addition, the mean grain size of alluvial sequences west of the San Juanito fault decreases southward until they are replaced by shallow marine deposits almost at the southern tip of the San Juanito fault. Therefore, a paleo-high related to Fig. 8 34 2 1 5 7 6 8 10 12 11 13 19 18 14 15 16 17 9 Tertiary Cretaceous Upper Paleozoic Pre-Devonian metamorphic basement Fluvial sandy facies Fan Delta and gravel facies Carbonate inner platform facies Sabhka and lagoon facies Siliciclastic shallow marine facies Lower Cretaceous facies associations 4?30? 74? 5? 75? 0 10 20 km Fig. 5 Fig. 6 Fig. 7 Fig.11. Map of early syn-rift Cretaceous facies distribution.Notice that the reconstructed distribution of facies does not coincide with the geological map in Fig.1 as the lateral extent of early syn-rift units has been extrapolated to covered areas. However, post-rift shortening has not been removed, but the normal nature of the faults during the early Cretaceous is shown in the ?gure. r 2009 The Authors Journal Compilationr Blackwell Publishing Ltd, European Association ofGeoscientists & Engineers and International Association of Sedimentologists 125 Role of inherited extensional fault segmentation and linkage the San Juanito fault is inferred.We term this paleo-high the Chingaza Dome (Fig. 12). The direction of spatial changes in facies and grain size suggests southward-direc- ted axial drainage west of the San Juanito fault. More sig- ni?cantly, in the southern segment shallow marine facies are restricted to a central area bounded by the Servita? fault to the east and the San Juanito fault to the west (Fig.11). In this area and all other sectors with marine deposition in the southern segment, laterally restricted fan-delta de- posits pinch out (Facies association B2) in a direction per- pendicular to all faults in this segment.This pattern can be interpreted as a transverse drainage from the fault- bounded paleo-topographic highs toward the adjacent subsiding areas with marine deposition. In the northern segment, the Garabato and Malacara faults are associated with an up to 200-m-thick sequence of supratidal evaporites, intertidal stromatolites, and shal- low water carbonates (facies associations C1, C2 and C3), which are restricted to the west of these structures (local- ities14,15,17 and18, Figs 8,11and13). In contrast, a 20-m- thick Lower Cretaceous siliciclastic tidal- ?at unit above Upper Paleozoic rocks is rapidly superseded up section by distal-platform black shales with ammonites in the eastern block of the Garabato fault (facies associationsM1 and M3; Locality 13, Figs 10, 11 and 13). Again, fault con- trolled di?erential subsidence can be inferred from these patterns. Shallow-water to supratidal units to the west pinch out near the tips of the Garabato and Miralindo faults, suggesting that these depositional systems also occupied a fault- controlled paleo-high that we term Rio Guavio Dome (Fig. 13). This assessment is corroborated by emerald-bearing mineralizations which are restricted to facies association C2 in the Rio Guavio Dome. These mineralizations have not been reported east of the Garabato and Malacara faults. Other structures like the Manizales and San Isidro faults can be also reinterpreted ?73.7? 4.5? 4.4? Sa n J ua nit o Fa u lt Ch ing az a D om e Cross section in Figure 12B Metamorphic basement Devonian (?) shales Facies association B3 Facies association M1 Facies association C2 Facies association B2Locality 6 Locality 7 5 km 2000 0 ? 4000 Locality 6 Locality 7 San Juanito Fault (a) (b) Fig.12. Detailed geological map and cross section of the ChingazaDome.Notice that the San Juanito Fault separates a footwall domain to the west where braid and meandering river depositional systems dominate from a domain to the east with fan deltas adjacent to early syn-rit shallow marine systems. See location in Fig.1. r 2009 TheAuthors Journal Compilationr Blackwell Publishing Ltd, EuropeanAssociation of Geoscientists & Engineers and International Association of Sedimentologists 126 A. Moraet al. Sa n Is id ro F a u lt R io G ac ha lu no F a u lt 2000m 0 El G ar a ba to F a u lt Locality 14 Locality 15 Locality 11 Locality 11 Map NW SE El G ara ba to Fa ult Ma lac ar a Fa ult Ma niz ale s F au lt Sa n Isi dr o Fa ul t Shales (Facies Association M3)) Sandy Limestones Facies (Facies association C3) Upper level of estromatolites un evaporites pseudomorphs (Facies Association C1) Upper level of Mudstones and Wackestones (Facies Association C2) Marls and evaporite pseudomorphs (Facies Association C1) Upper Paleozoic Units Locality 15 Locality 14 Locality 16 Locality 13 Locality 17 Locality 18 4? 45` 73?30` Lower level of estromatolites and evaporite pseudomorphs (Facies association C1) Lower Level of Mudstones and Wackestones (Facies Association C2) Conglomerates and limestones interbedded Basal conglomerate (B1) Cross section in Figure 13B (a) (b) 0 5 km Fig.13. Detailed geological map and cross section of theGuavioDome.Notice the map relationships in the area highlighted in the box south of Locality14; the activity of the normal fault near locality15 is contemporaneous or even post-dates the deposition of the level of conglomerates and sandstones but pre-dates the deposition of the lower level of stromatolites and evaporite pseudomorphs (Facies association C1). See location in Fig.1. r 2009 The Authors Journal Compilationr Blackwell Publishing Ltd, European Association ofGeoscientists & Engineers and International Association of Sedimentologists 127 Role of inherited extensional fault segmentation and linkage as Neocomian faults, because they separate di?erent early syn-rift facies in their hanging and footwalls (Figs 8 and 13). Similarly, the Gachaluno and Esmeralda faults restrict the extent of the sandy-shorezone facies (facies association Bt-1, Fig. 6) of the Bata Formation at localities 11 and 19 (Fig. 11), contrasting with the open-sea shaly facies to the west. In general, faults in the northern segments separate marine facies of di?erent bathymetric a?nity. Transverse alluvial to fan-delta depositional systems are only locally present west of the Gachaluno fault. Taken together, the character and extent of the analyzed facies sequences and structures suggest that virtually all faults in both segments are Neocomian in age. Deposition is therefore interpreted to have been determined by fault activity during the initial phase of rifting. In this ex- tensional scenario, the San Juanito fault in the south was kinematically linkedwith theGachaluno fault in the north by an accommodation zone, here called Claraval linea- ment (Fig. 14). However, the Servita? fault and associated faults to the east are di?erent from all other structures. The rectilinear trace of the Servita? fault contrasts with the discontinuous trace of faults farther west. The Servita? fault system along the eastern boundary of the study area also constitutes the depositional boundary of Neocomian strata to the east. We therefore di?erentiate the Servita? fault as a basin-boundary fault contrasting with the intrabasinal faults to the west. In the northern graben segment an equivalent principal Neocomian boundary fault is not discernible from ?eld data, although it should be located along strike of the Servita? fault, as can be inferred from seismic and gravimetry data (e.g. Mora et al., 2006). West of the Servita? fault, irrespective of the structural position, and therefore along all of the intrabasinal struc- tures of the northern and southern segments, there is evidence for a ubiquitous rapid vertical transition from shallow marine and ?uvial facies to more distal marine to deep marine shaly facies. In addition, Berriasian toValan- ginian black shales often attain more than 2 km thickness (e.g. locality 17) whereas underlying alluvial and shallow marine sequences are rarely thicker than 500m. Total accommodation space may apparently have increased after the deposition of shallow-marine and alluvial sequences as intrabasinal footwall blocks were covered by marine sedi- ments, either due to decreased activity or locking of faults. In contrast, pre-Aptian rocks are absent east of the Servita? fault and associated basin boundary structures (e.g. Figs 16 and 17). Therefore, these faults continued to be active until theAptian.Figure13 (see normal fault south of locality 15), 17 and18 show structural relationships doc- umenting some cases where the intrabasinal faults to the west of the basin bounding faults were active only during short periods, as mapped Berriasian horizons clearly post-date the faults. Footwall uplift patterns Structural mapping reveals that in the southern segment of the Guatiqu|? a paleo-rift paleozoic rocks are absent di- rectly to the east of the Servita' fault (Figs1and11, Locality 3). However, at locality 10 west of the Servita' fault, a Ber- riasian debris- ?ow deposit pinches out to the west and evolves into sandy turbiditic facies (Fig. 17), indicating a higher source area to the east. The provenance of these debris- ?ow deposits identi?es a source region in Paleo- zoic sedimentary rocks (Table 1 see Locality 10). Phyllite clasts do not occur, although the faulted contact of the debris- ?ow deposits to the east is against phyllites of the QuetameGroup (Fig.17).The structural and stratigraphic relationships at locality 10 (Fig. 17) thus show that Paleo- zoic rocks were present east of the Servita? fault but eroded before, and during the onset of Cretaceous deposition. Erosion of Paleozoic rocks before, and during the onset of Cretaceous deposition is also documented in the western block of the San Juanito fault by map patterns (Fig. 12; Mora et al., 2006) and sandstone petrography from Parra (2000). Interestingly, except localities 1 and 10, all sites in the southern segment of the graben contain numerous clasts of phyllites coming from the Quetame Group (see Fan Delta and gravel facies Carbonate inner platform facies Fluvial sandy facies Sabkha and lagoon facies Siliciclastic platform facies Exposed areas Transitional to marginal marine facies Fig.14. Idealized con?guration of the Lower Cretaceous graben setting (Guatiqu|? a graben) located in the Farallones deMedina region. Not to scale.Notice alluvial units and erosion in the footwalls to the south (southern graben segment) and fan deltas in the hanging wall areas.The supratidal and intertidal units in the footwalls of the northern segment contrast with siliciclastic platform facies in the hanging walls. r 2009 TheAuthors Journal Compilationr Blackwell Publishing Ltd, EuropeanAssociation of Geoscientists & Engineers and International Association of Sedimentologists 128 A. Moraet al. Table 1 and Fig. 11).This observation, and the presence of debris- ?ow units adjacent to the fault-bounded paleo-to- pographic highs, document that there was footwall uplift along the faults bounding the southern graben.This uplift must have been pronounced, creating high terrain from which basement clasts were eroded and transported to the hanging-wall basins. These processes were ultimately responsible for the removal of ca. 3 km of upper Paleozoic rocks before the onset of Cretaceous deposition on these structural highs (see generalized con?guration in lower part of Fig.14). In contrast, in the northern segment and north of local- ity 10 there are no surface exposures of the Quetame Group phyllites and quartzites immediately below the Cretaceous section (Fig. 11). Underlying units belong to upper Paleozoic sedimentary strata. Interestingly, meta- morphic clasts are absent in the basal conglomerates in sections 10^19 in the northern segment (Table 1). In addi- tion, local debris- ?ow sequences were only observed in the hanging-walls of the San Isidro and Gachaluno faults (Figs 7 and 8).Therefore, the provenance and areal extent of sediments document that footwall upliftwas either neg- ligible or absent in the northern segment (compare lower and upper part of Fig.14). Footwall-uplift patterns are observed along faults dip- ping both west and east (Figs 2, 14 and 16) in both seg- ments. Therefore, we hypothesize that the eastern faults with the footwall to the east, were active at the same time and probably interacted mechanically with the corre- sponding western faults and their footwalls. However, it is not clear whether the southern and northern graben seg- ments were active coevally. Since the work of Jackson & McKenzie (1983), footwall uplift in many extensional provinces has been documented to be proportional to adjacent hanging-wall subsidence. If that is also true for our study area, hanging-wall subsidence in the southern segment should have been higher than in the north. Accordingly, we do not interpret the early deposition of marine sequences in the footwall blocks of the northern segment to re?ect an increase in total tectonic subsidence with respect to the southern segment, but rather reduced local footwall uplift. STYLES OF REACTIVATION Superimposed Cenozoic contraction along the exten- sional structures generated many signi?cant structural features in the Eastern Cordillera. At all scales, former ex- tensional basement highs appear to have con?ned contrac- tional folding structures (Fig. 15). A clear example is the Rio Los Medios syncline, where the former extensional hanging wall of the Los Medios normal fault has been folded in contraction against the former extensional foot- wall uplift (Fig. 18). This behavior, de?ned as basement buttressing, has been identi?ed as a typical form of reacti- vation by Mora et al. (2006) in the Eastern Cordillera.The most representative large-scale examples of basement buttressing are the Farallones and Santa Maria anticlines (Figs 2 and 15). All of the documented Neocomian faults con?ne the areal extent of both structures (Figs 2, 13 and 15). The Farallones anticline coincides with the hanging- wall sectors in front of the normal faults at the southern segment of theGuatiqu|? a graben,whereas theSantaMar|? a anticline coincides with downthrown areas in the north- ern segment, clearly identifying them as inversion anticli- nes. In contraction, the Claraval lineament also forms a transfer zone as the Farallones and SantaMar|? a anticlines are distributed in en-echelon manner along this structure. Therefore, there is a fundamental basement-related pre- disposition of faulting and folding in this part of the northern Andes.This has resulted in di?erences in inver- sion-generated structural relief and reactivation along pre-existent fault planes, which we will discuss for the southern and northern segments.We illustrate these dif- ferences by comparing paleo-topography deduced from the facies map (Fig. 11) with present-day topography (Fig. 2), and by employing serial balanced cross-sections (Fig.15). Reactivation in the southern graben segment In the southern graben segment, the basal Cretaceous un- conformity in the hinge zone of the Farallones anticline lies at ca. 4000m above sea level, the maximum elevation of this horizon in the study area (Figs 2 and 15).The loca- tion of the Farallones anticline coincides with the zone of Metamorphic basement Upper Paleozoic Lower Cretaceous Facies association B2 Lower Creataceous Facies association M2 Lower Cretaceous shale units Upper Cretaceous units Neogene 2 Km 0 1000 2000m Servit? Fault Fig.15. Detailed cross section along the Ardita Creek. Notice the westward granulometric change in the Early Cretaceous facies to the west and the presence of a blockwithout Paleozoic cover below the Early Cretaceous units. See ?Discussion? in the text. r 2009 The Authors Journal Compilationr Blackwell Publishing Ltd, European Association ofGeoscientists & Engineers and International Association of Sedimentologists 129 Role of inherited extensional fault segmentation and linkage 0?4 4 Upper Paleozoic Units 0 4 0 (c) (b) Neogene Molasse Oligocene-Mid-Miocene Paleocene-Eocene Upper Cretaceous Lower Cretaceous Tesalia Fault NW SE NW SE 0 ? 4 4 NW SE 0 4 ?4 (a) San Juanito Fault Servit? Fault Lengup? Fault Tesalia Fault Guaicaramo Thrust Fig.16. Balanced cross sections along the di?erent segments of the study area. (a) Cross section along the northern segment. Note that the present day active foreland deformation front is also included.Below a retrodeformedEocene state is included. (b)Cross-section along the central segment of the study area. (c) Cross section along the southern segment of the study area, in the lower part aMaastrichtian- Paleocene retrodeformed state is included.Notice how fault propagation folding is minor along theServita? fault comparedwith prominent fault propagation folding in the central and northern cross-sections associatedwith theTesalia and Lengupa? thrusts. In contrast, shortening in the central and northern cross-sections is absorbed mostly by the Guaica? ramoThrust. See locations in Fig.1. r 2009 TheAuthors Journal Compilationr Blackwell Publishing Ltd, EuropeanAssociation of Geoscientists & Engineers and International Association of Sedimentologists 130 A. Moraet al. maximum extensional subsidence during the Cretaceous. Despite this, many paleo-topographic highs in extension have retained their character as topographic highs during contraction. For example, the alluvial facies in the footwall of the San Juanito fault (locality 6) or the southernmost exposures of syn-rift rocks in the Farallones anticline (locality 2) coincide with structural and topographic culminations at elevations near 4000m above sea level (compare Figs 2 and11).We therefore posit that maximum inversion-generated structural relief appears to coincide with zones of maximum extensional subsidence, although adjacent paleo-topographic highs have remained as topo- graphic highs in contraction. The contractional reactivation (displacement) in the southern segment along the faults themselves appears to be concentrated along the reactivated basin-boundary faults and associated shortcuts (Figs 2 and 11). For exam- ple, it is evident that reverse displacement along the Servi- ta? fault during contraction is generally limited. However, the Servita? fault was only reactivated in contraction at its southern termination and remained in net extension near its northern termination (Fig. 15). In addition, most of the contractional fault displacement and shortening on the eastern ?ank of the Eastern Cordillera is due to the Mirador shortcut thrust (Fig. 1). This shortcut branches from the Servita? fault, an interpretation supported by seis- mic pro?les and the fact that in map view this structure is always parallel to theServita? fault, except near its tipswhich converge with the trace of the Servita? fault (Figs 1 and 15). Therefore, these map patterns may represent an oblique view of converging thrusts at depth, as has been observed in many thrust systems (e.g., Boyer and Elliot, 1982). The Servita? fault and Mirador shortcut account for ca. 20 km of shortening in the Eastern Cordillera as deduced from line-length balanced cross-sections (Fig. 15). In contrast, intra-basinal faults with their footwalls to the west, such as the San Juanito Fault, only accommodated minor reacti- vation (Mora et al., 2006, Fig. 15). It therefore appears that 10 km MoT LF SjF Ch A AA LMF FA MAT SF MzT BT NF SF NF Villavicencio MAT AA: Apiay Anticline BT: Boa Thrust ChA: Chichimene Anticline FA: Farallones Anticline LMF: Los Medios Fault MAT: Mirador-Agualinda Thrust MoT: Monserrate Thrust MzT: Manzanares Thrust NF: Naranjal Thrust SF: Servit? Fault Reverse fault Normal fault Strike-slip fault Anticline Syncline 4?N 74? W Fig.17. Geological map of the southernmost part of the study area. Symbols are the same as in Fig.1.The Lower Cretaceous Servita? basin bounding fault can be identi?ed as the structure that bounds the area where Upper Paleozoic sequences are preserved above the pre-Devonian metamorphic basement (QuetameGroup). In contrast, east of this structure Lower Cretaceous rocks rest on top of pre- Devonian metamorphic basement.Therefore structures east of the Servita? fault can be interpreted as footwall shortcuts. Symbols are the same as in Fig.1. See location in Fig.1. r 2009 The Authors Journal Compilationr Blackwell Publishing Ltd, European Association ofGeoscientists & Engineers and International Association of Sedimentologists 131 Role of inherited extensional fault segmentation and linkage the intrabasinal Neocomian highs like San Juanito footwall remained in high topographic positions, mainly because they were passively transported by the Servita? fault. Reactivation in the northern graben segment As in the south, in the former northern graben segment, maximum inversion-generated structural relief coincides with areas of maximum Neocomian subsidence, such as the hinge zone of the Santa Maria anticline (Fig. 2). Accordingly, paleo-highs in the northern segment, (e.g. the Rio Guavio paleo-high) have retained their character as structural culminations in contraction with respect to the elevation of the basal Cretaceous unconformity. How- ever, with elevations of about 2200m, structural culmina- tions in the north lie at substantially lower elevations than in the south. Maximum fault displacement in the northern segment is concentrated along structures that lie along strike north of the Servita? fault, including the Lengupa? and Tesalia faults. Neither one of these structures have been unequi- vocally documented as a Lower Cretaceous structures. There is also no evidence that they constitute shortcuts branching out from inherited structures, and the amount of slip is minor comparedwith equivalent reactivated faults along strike in the southern segment (e.g., Servita? fault. Fig. 15). Adjacent normal faults like the Gachaluno fault have not been reactivated in contraction (Fig. 2). In con- trast, it is striking that a vertical to overturned panel of Tertiary and Cretaceous rocks, associated with the Lengupa? andTesalia faults, bounds the entire SantaMaria anticline to the east. No comparable panel exists in the southern segment (Figs 2 and 15). Therefore, most of the basin inversion in the northern segment is due to fault- propagation folding, rather than direct displacement along reactivated faults or footwall shortcuts. Furthermore, shortening accumulated by faulting and fault-propagation folding in the forelimb of theSantaMaria anticline is close to 20 km, similar to the ca. 20 km of shortening to the south in that case almost only due to faulting (Fig.15). Interestingly, if the displacement trends of the paleoto- pographic highs like the Rio Guavio and Chingaza domes Metamorphic basement Devonian (Sandstones) Devonian (Shales) Carboniferous Lower Cretaceous (Pre-Barremian) Barremian to Albian Upper Cretaceous A 0 5 km 74? 500 2000 3000m NW(b) (a) SE Cross section in Figure 18B 4?20? Lo s M ed io s Fa ul t Fig.18. (a)Detailed geological map of theLosMedios fault.Notice the map expression of pronounced footwall uplift before the onset of deposition of Lower Cretaceous strata. On the other hand Barremian units post-date the activity of the LosMedios fault. (b) Reactivation along the plane of the LosMedios fault has been limited but tight folding west of LosMedios fault attests for the Los Medios footwall acting as a stress riser buttressing the folds to the west. r 2009 TheAuthors Journal Compilationr Blackwell Publishing Ltd, EuropeanAssociation of Geoscientists & Engineers and International Association of Sedimentologists 132 A. Moraet al. are compared along strike, a displacement de?cit results in the area between both, in extension as well as in contraction. This is probably related with displacement transfer towards basin bounding structures through the Claraval accommodation zone, both in extension and in contraction. Conversely, reactivated faults bounding the Farallones and Santa Maria anticlines to the east show whatWalsh et al. (2003) called a sympathetic increase and decrease in displacement, without displace- ment gaps. DISCUSSION AND CONCLUSIONS Careful mapping and analysis of Neocomian facies asso- ciations coupled with structural investigations suggest that faults in the Farallones anticline domain originated as extensional faults during the early Cretaceous. Facies and provenance analysis enable us to distiguish former southern and northern rift segments that formed an inte- gral part of the Guatiqu|? a paleo-rift. In the southern seg- ment, during early syn-rift deposition (Facies associations C and B), tectonic subsidence was higher compared with the northern segment. Early syn-rift deposition in the southern segment was associated with adjacent areas of high paleo-topography in footwall areas (Fig. 14). This is true for both intrabasinal and basin boundary faults in this segment where shallow marine facies and fan deltas char- acterize subsiding areas, while alluvial facies were depos- ited in paleo-highs. In contrast, north of about 41300N a more segmented northern rift sector existed during rift initiation (Facies associations C, B, Bt). Here, as deduced from footwall uplift, intrabasinal and basin-boundary faults accrued less displacement than structures in the southern segment. Shallow marine facies dominate in hang- ing-wall areas, whereas sabkha facies characterize footwall sectors. Intrabasinal faults in both the southern and north- ern segments account for a highly variable early syn-rift facies distribution due to isolated depocenters and paleo- highs.This is exempli?ed by the Chingaza and Rio Guavio domes, which restrict the areal extent of Cretaceous deposi- tional systems. Segmented faults, isolated depocenters, and paleo-highs during rift initiation show that intrabasinal fault systems evolved from localized areas of extension and grew along strike through segment linkage (e.g. Cartwright et al., 1995;Dawers&Anders,1995). In the northern part of the rift, individual faults are more numerous, shorter and rectilinear, re?ecting less advanced fault linkage (e.g. Gawthorpe &Lee- der, 2000). Accordingly, a more internally structured north- ern rift, coupled with the spatial patterns of footwall uplift, may have resulted from either rift propagation from south to north or northward extensional displacement gradients (Cowie et al., 2000) (Fig. 2). From the relationships between faulting and sedimentation observed here, we propose that east-dipping intra-basinal faults (e.g., San Juanito andGara- bato faults) interacted mechanically with faults farther east (e.g. Servita? fault) during rift initiation. Subsequently, the rapid overall facies transition from ?rift initiation? (sensu Pr?sser, 1993. Facies associations B, C and Bt) to the ?ne grained ?rift climax? sedimentation (sensu Pr?sser,1993. Facies associationsM)marks the onset of an episode where subsidence was rapid adjacent to the Servita? fault. Footwall uplift along this structure was pro- tracted, contrasting with intrabasinal faults whose footwall areas were already submerged.Thus, footwall uplift of the intrabasinal faults was subdued comparedwith basin sub- sidence associated with the eastern boundary faults.This, and the widespread complete Cretaceous sequence west of the major boundary faults demonstrate that intrabasinal faults remained inactive until their Cenozoic inversion. In contrast, the onset of Cretaceous deposition east of the Servita? fault only occurred during the Albian.Thus, total syn-rift displacement along the basin-boundary faults appears to have been greater than along the intrabasinal faults. If true, the early linkage of the intrabasinal faults was interrupted during the rift climax.Therefore, the fault pattern that we observe in the intrabasinal faults repre- sents the pattern of growth during the rift initiation stage. In this context, it is worth noting that in the southern segment the Servita? fault is rectilinear and displays no evi- dence for earlier coalescing segments that would suggest growth through linkage (Trudgill & Cartwright, 1994; Cartwright et al., 1995; Dawers & Anders, 1995).Therefore, we propose that the facies transition from?rift initiation? to ?rift climax? is not related to enhanced subsidence after linkage (Gupta et al., 1999; Cowie et al., 2000), but rather to an increased displacement along the principal basin- boundary faults.The overall structural evolution suggests that the intrabasinal Neocomian faults may represent antithetic collapse structures associatedwith a major roll- over anticline in the hanging-wall of the eastern boundary faults, analogous to the central Kenya Rift (Roessner & Strecker, 1997), the Viking Graben (Roberts & Yielding, 1991) or the collapse grabens in analog models of listric faults (Mitra, 1993; McClay, 1995; Withjack et al., 1995; Ya- mada &McClay, 2004; Seyferth &Henk, 2006). Cenozoic shortening in the Eastern Cordillera of Colombia is fundamentally in?uenced by the inherited extensional structures. During contraction, the principal bounding faults experienced a higher degree of reactiva- tion, with throw reversing the extensional o?set (Fig. 15). There is more e?cient reactivation along the Servita? fault/Mirador shortcut pair in the southern segment com- paredwith the northernLengupa? andTesalia faults. In the northern segment, fold propagation dominates over direct slip. Interestingly, footwall uplift was absent or negligible during the Neocomian in the northern segment, whereas in the southern segment footwall topography was pro- nounced.Thus, if footwall uplift is a proxy for extensional subsidence in the adjacent hanging wall (Jackson & McKenzie, 1983), areas undergoing maximum extensional displacement also tend to focus reverse displacement along former border faults (Fig. 15). Accordingly, zones of maximum Cenozoic inversion-generated uplift (i.e. reverse fault displacement plus anticlinal fold amplitude) r 2009 The Authors Journal Compilationr Blackwell Publishing Ltd, European Association ofGeoscientists & Engineers and International Association of Sedimentologists 133 Role of inherited extensional fault segmentation and linkage appear to coincide with zones of maximum Neocomian extensional displacement and subsidence, like the Faral- lones anticline in the southern segment. These observa- tions are similar to those of Underhill & Paterson (1998) in the Wessex basin. In addition, we also ?nd similarities with 3D analog inversion models (Yamada & McClay, 2004), suggesting inheritance of along-strike displace- ment gradients in the extensional province. In contrast to the major basin bounding faults, reactiva- tion of the much more segmented intrabasinal faults was less pronounced. As a consequence, syn-extensional paleo-topographic highs were passively uplifted and per- sisted as topographically elevated areas in contraction, with similar segmentation and displacement gaps. It is likely that focused faulting along rectilinear basin-bound- ing structures in both extension and in contraction identi- ?es these structures as long-lived, predisposed zones of weakness in the crust, similar to observations in theGam- toos basin (Paton & Underhill, 2004) of South Africa. In such a scenario, fault length in extension is de?ned early during rifting (Walsh et al., 2002). If fault segments exist, they de?ne a kinematically coherent system that merges into a single structure at depth (Walsh et al., 2003), con- trasting with growth through linkage. Interestingly, in the foreland east of the basin-boundary faults, upper Paleo- zoic rocks were not encountered in exploratory wells, and Andean phyllitic basement rocks are replaced by Guyana shield basement (e.g. Duen as, 2002). In addition, the exis- tence of the basin-bounding faults as pre-Mesozoic mul- ti-phased structures is supported by many studies (e.g. Forero-Suarez, 1990). This could provide a mechanism for the initial rapidMesozoic trace lengthening and subse- quent preferential fault reactivation. In this context, it is clear why intrabasinal faults that grew through linkage are subordinate anisotropies comparedwith the longer basin- bounding structures. These observations raise the question as to which factor de?ned the observed growth mechanisms for the intrabas- inal structures.Walsh et al. (2003) argue that an incidental linkage of otherwise isolated faults is more likely where a pre-existent coherent weakness is absent and faulting has to randomly break through a mechanically heterogeneous multilayer. Interestingly, in contractionwe document either direct reactivation or shortcuts branching from the basin margin faults while intrabasinal faults remained undis- turbed.We interpret this pattern to indicate that, irrespec- tive of long-lived basement fabrics, segmented extensional structures that purely grew through linkage of individual faults may be less prone to inversion than normal faults that propagated upward from a coherent common plane. In summary, our paleogeographic reconstruction of the early syn-rift setting in the northern Andes provides a un- ique comparison between extensional tectonics and subse- quent orogenic contraction.As in other inversion provinces (e.g. Coward et al., 1989; Graciansky et al., 1989; Bailey et al., 2002;Kley etal., 2005; Carrera etal., 2006), the fundamental imprint of pre-existent basement fabrics has generated di- rect reactivation,withbuttresses and shortcuts as typical in- version features. However, our observations show that inheritance of lateral displacement gradients and the me- chanism of extensional fault growth itself are additional, important factors also in?uencing inversion styles in con- tractional orogens. These phenomena may be more com- mon than previously thought. Importantly, only those extensional structures which coincide with basement fea- tures that existed before the extensional phase profoundly determine the width of the contractional orogen. In addi- tion selective fault reactivation in contraction appears to be related to the style of extensional fault growth, and not only to the orientation of the compressional stresseswith respect to the pre-existent normal faults as previously proposed in this region (e.g.Mora et al., 2006). Our observations are useful in the extrapolation of fea- tures observed in analog models and mild to moderately inverted intra-plate basins to the structures of inverted oro- gens. In the latter case, shortening is often more intense and the relationships between ancestral extensional segmenta- tion and superimposed past or ongoing contraction are less clear. However, geometries and patterns of inversion in oro- gens and intra-plate areas are comparable. Our analysis helps understand andpredict the behavior ofmany structur- al and stratigraphic traps of extensional origin incorporated in contractional settings. The documented features are therefore important for fossil fuels or mineral deposits ex- ploration, particularly in frontier intra-plate or orogenic areas that normally rely on limited subsurface data sets. ACKNOWLEDGEMENTS The authors are indebted to Arndt Peterhansel, Estelle Mortimer, Gabriela Marcano, Cornelius Uba and Jessica Zamagni for interesting discussions that improved the ideas in this paper. Cornelius Uba and Jessica Zamagni graciously read an earlier version of this paper. 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