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Early Neogene unroofing of the Sierra Nevada de Santa Marta

Early Neogene unroofing of the Sierra Nevada de Santa Marta, as determined from detrital geothermochronology and the petrology of clastic basin sediments Alejandro Piraquive1,2,†, Edna Pinzón2,†, Andreas Kammer2,†, Matthias Bernet1,†, and Albrecht von Quadt3,† 1 Institut des Sciences de la Terre, Université Grenoble Alpes, 1381, rue de la Piscine, 38400 Saint-Martin d’Hères, France 2 Grupo de Investigación en Geologia Estructural y Fracturas, Universidad Nacional de Colombia, Apartado Aéreo, 14490 Bogotá, Colombia 3 Department of Earth Sciences, Institute of Geochemistry and Petrology, ETH Zentrum, Clausiusstrasse 25, 8092 Zurich, Switzerland

ABSTRACT We used geothermochronologic data from sedimentary rocks, coupled with stratigraphic analyses, to unravel the late Paleogene to early Neogene exhumation of the Sierra Nevada de Santa Marta massif. This fault-bounded triangular northernmost promontory of the Northern Andes exposes Precambrian to Paleozoic metamorphic rocks and a Triassic to Jurassic magmatic arc. We examined the Neogene basin fills of two marginal basins, a western one located along the Santa Marta–Bucaramanga fault, and a northern one occupying the southern hanging-wall block of the Oca fault. The western sequence consists of ~1200-m-thick conglomeratic gravity deposits that define a progradational Gilbert-type delta emanating from a scarp coinciding with the present Santa Marta–Bucaramanga fault. By its stratigraphic and structural position, this sequence is similar to the northern sequence, which reveals a retrogradational stacking pattern. In order to reconcile these different architectural styles, we propose a regional-scale tilting of the Sierra Nevada de Santa Marta massif toward the NE during the late Paleogene–early Neogene. This model presumes a concomitant evolution of the two sedimentary sequences. Provenance analyses performed on representative units

† Piraquive—[email protected], [email protected]; Pinzón— [email protected]; Kammer—akammer@ unal.edu.co; Bernet—matthias.bernet@univ-grenoble -alpes.fr; von Quadt—albrecht. [email protected] .ch.

of these sedimentary sections yielded U-Pb age spectra of zircons that correlate with known age data of the underlying basement. Particularly, they lack pre-Grenvillian and Ordovician signals common to Neogene sediments of the wider Miocene Magdalena basin. These marginal basins thus evolved disconnected from the trunk system of the proto–Magdalena River, and they record an initial stage of Oligocene–Miocene segmentation of the South American plate margin. These new findings help to better constrain the paleogeographic setting of the Sierra Nevada de Santa Marta massif and its marginal basins for the late Oligocene–early Neogene during initial breakup of the Caribbean margin. Their sedimentary record depicts an early stage of fault-controlled subsidence of the western margin and a presumably tiltrelated transgression of the northern margin that preceded the Miocene expansion of local depocenters and their merging into a wider embayment of the Neogene Lower Magdalena basin. INTRODUCTION The Northern Andes constitute a distinct tectonic province, characterized by its disintegration into discrete mountain chains and a composite structure of oceanic and continental terranes, commonly referred to as the North Andean block (Pennington, 1981). Contrary to the presence of directional faults that form sharp boundaries (Fig. 1; Motagua fault, Cayman Trough, Puerto Rico Trench) on the northern edge of the Caribbean plate (Keppie and Keppie, 2012), deformation on the southern edge of the Caribbean plate is widely

distributed along crustal heterogeneities of the different mountain chains (Pennington, 1981; Taboada et al., 2000). In its southern part, this North Andean block is subdivided further by mainly margin-parallel faults into minor blocks, a subdivision that underscores the morphological expression of the mountain chains. North of 6°N, on approaching the Caribbean margin, the North Andean block becomes divided by crustal-scale faults oblique to the structural grain of the plate margin, resulting in an apparent loss of a structural continuity of the Andean chains. Major faults have been active at least since the Pliocene to recent E-W–directed plate convergence facilitating relative movements between stable South America and the Caribbean plate (Boconó, Oca; Audemard and Audemard, 2002; Trenkamp et al., 2002), comprising a widely distributed accommodation zone across the North Andean block with still ill-defined velocity gradients, as deduced from regional global positioning data for Central and South America (CASA Project; Trenkamp et al., 2002; Egbue and Kellogg, 2010). Obliquity between convergence and faults increases toward the NW termination of the North Andean block, as the continental margin bends into an E-W direction to the west of the Sierra Nevada de Santa Marta massif. In this characteristic Caribbean position, relative plate motions are increasingly taken up by strike-slip faults (Fig. 1). During the Late Cretaceous to Paleocene, a juvenile Caribbean plateau with an associated island arc collided against northern South America (Ayala et al., 2012; Bayona et al., 2011; Cardona et al., 2011a, 2012; Higgs, 2009; Pindell and Kennan, 2009; Spikings et al., 2015; Villagómez et al., 2011), juxtaposing oceanic crust against a

GSA Bulletin; Month/Month 2017; v. 129; no. X/X; p. 000–000; https://doi.org/10.1130/B31676.1; 15 figures; 5 tables; Data Repository item 2017306.

For permission to copy, contact [email protected] Geological Society of America Bulletin, v. 1XX, no. XX/XX © 2017 Geological Society of America

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Figure 1. Regional tectonic map of the Caribbean realm showing the most relevant geological features intervening in the plate boundary configuration (after Veloza et al., 2012). Elements of the North Andean block (NAB): Maracaibo block, SNSM—Sierra Nevada de Santa Marta, OF—Oca fault, CF—Cuisa fault, SMBF—Santa Marta–Bucaramanga fault, GU—Guajira basin, PSJ—Plato–San Jorge basin MA—Mérida Andes, BF—Boconó fault, FB—Falcon basin, WC—Western Cordillera, CC—Central Cordillera, EC— Eastern Cordillera, MV—Magdalena Valley, PB—Panamá block.

continental Paleozoic basement. This accretion was followed by Eocene collisional shortening, with a concomitant plutonic event that concluded the Cretaceous to Paleogene subduction cycle. Evidence for this shortening is provided by a regional mid-Eocene unconformity with a hiatus comprising Paleogene to Cretaceous platform sediments near the continental margin (Villamil, 1999; Gómez et al., 2005). During the Oligocene and Miocene, convergence became increasingly oblique, and, concomitant with the activation of strike-slip faults, the hitherto continuous and emergent continental margin became disrupted by basin-forming normal faults and the consequent opening of the San Jorge and Plato depocenters to the west of the Sierra Nevada de Santa Marta massif. As a consequence of the breaching of a hitherto continuous plate

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margin, the Lower Magdalena basin formed between the Central Cordillera and the Sierra Nevada de Santa Marta massif. Fault-bounded blocks of this structural depression are confined against the Sierra Nevada de Santa Marta massif by the Santa Marta–Bucaramanga fault, which, in its position as an eastern basin-bounding fault, may have generated much of its present structural relief (>7000 m) by the early Miocene (DuqueCaro, 1979; Mora-Bohórquez et al., 2017; Montes et al., 2010). Considering the junction of the Santa Marta–Bucaramanga fault with the E-W– trending Oca fault at the NW corner of the Sierra Nevada de Santa Marta massif, we investigated the following question: Did this latter fault originate coeval with margin-oblique extension, in concordance with the late Paleogene block tectonics of the Leeward Antilles (Macellari, 1995)?

This geomorphic reorganization of the plate margin was, furthermore, accompanied by an important uplift phase of the Eastern Cordillera of Colombia and the consequent division of the Andean retro-arc basin into the inter-Andean Magdalena and external Llanos basins (Mora et al., 2010; Gómez et al., 2005). The connection between the inter-Andean depression and the corridor at the breached continental margin heralded the modern drainage of the Magdalena River, for which delta sedimentation is interpreted to have begun in the early to middle Miocene (Duque-Caro, 1979; Kolla et al., 1984). In this late Paleogene to early Neogene evolution, an understanding of the timing of exhumation of the Sierra Nevada de Santa Marta massif provides an important key to the disruption of the Caribbean plate margin. Recently elaborated

Geological Society of America Bulletin, v. 1XX, no. XX/XX

Early Neogene unroofing of the Sierra Nevada de Santa Marta bedrock thermochronology evidences exhumation phases spanning the early Eocene to the Miocene, with older age data (50–40 Ma) being preserved within the southeastern flank of the Sierra Nevada de Santa Marta massif and younger ages (25–16 Ma) being concentrated along the western footwall block of the Santa Marta–Bucaramanga fault (Villagómez et al., 2011). The asymmetric Oligocene to Miocene age distribution fits with the stratigraphic constraints of the late Paleogene breaching of the continental margin and highlights the importance of the Santa Marta–Bucaramanga fault as a basin-bounding normal fault since this epoch. In this study, we elucidated the early Cenozoic evolution of the Santa Marta–Bucaramanga fault as a basin-margin fault, examining conglomeratic basin fill in its footwall block. We investigated if its activity could be deciphered by the architectural organization of this clastic sequence. In order to understand better its significance, we compared this sequence with an equally conglomeratic succession in the footwall block of the Oca fault at the northern margin of the Sierra Nevada de Santa Marta massif. Assigning the Santa Marta–Bucaramanga fault and the subsidence of its adjacent basin to an early evolution of the breakup of the continental margin, we further explored if the basin fill documents the denudation of the Sierra Nevada de Santa Marta massif, or if it reveals sourcing from a broader drainage system, as might be inferred from the existence of a proto–Magdalena River. In order to achieve these goals, we present sedimentological logs of the conglomeratic sequences and their stratigraphic significance. With respect to their provenance, we examined their compositional variations by pebble counts and compared them to the bedrock composition of the footwall of the Santa Marta– Bucaramanga fault. We combined these results with U-Pb age spectra measured in detrital zircons, and fission-track cooling ages from apatites and zircons. The integration of these stratigraphic and geochronological data helped us to ascertain the timing of the late Paleogene to early Neogene exhumation of the Sierra Nevada de Santa Marta massif. A comparison of our elaborated U-Pb age with published data of late Paleogene sediments of the Magdalena basin suggests that the examined marginal basin was exclusively sourced from pre-Cretaceous basement rocks of the Sierra Nevada de Santa Marta massif and that it evolved independently from a regional inter-Andean drainage. TECTONIC SETTING The Caribbean continental margin of South America was shaped during a Cretaceous sub-

duction cycle and a subsequent Paleogene collisional event (Audemard and Audemard, 2002; Cardona et al., 2011b, 2012; Van der Lelij et al., 2010; Villagómez et al., 2011). The Cretaceous subduction of the Caribbean plate during convergence occurred at a high angle to the continental margin without strike-slip partitioning (Cortés et al., 2005; Kennan and Pindell, 2009; Vence, 2008). The ensuing Paleogene collisional phase, however, entailed strike-slip reactivation of margin-parallel faults as the North Andean block rotated into its present position (Acosta et al., 2007; Montes et al., 2010; Nova et al., 2013; Vence, 2008). Relative plate movements approximated their present E-W convergence only in the late Miocene to Pliocene with the activation of the Boconó fault of the Merida Andes (Bermúdez et al., 2010; Egbue and Kellogg, 2010; Javadi et al., 2011). The continental margin is dissected by the Santa Marta–Bucaramanga fault, an inherited crustal-scale discontinuity that originated during early Mesozoic continental breakup (Kammer and Sánchez, 2006). Together with the E-W–trending Oca fault, the Santa Marta– Bucaramanga fault ends at the tip of the Sierra Nevada de Santa Marta massif, accommodating northwesterly escape during the late Paleogene to Neogene disruption of the continental margin, as conceptualized by a rootless crustal block that underwent orogenic floating (Audemard and Audemard, 2002; Monod et al., 2010; Oldow et al., 1990). According to its NW-directed escape and the similar vergence of internal reverse faults, the triangular Sierra Nevada de Santa Marta massif displays the structural array of a monocline, with its NW corner exposing an imbricated lowercrustal section that is capped on its southeastern flank by a Jurassic magmatic to volcanic arc sequence. Remnants of Cretaceous cover are conserved below a mid-Eocene unconformity only on the northwestern flank of César-Ranchería basin, which encloses the Sierra Nevada de Santa Marta massif to the SE (Tschanz et al., 1974). At its NW corner, low-grade metavolcanic sequences with subordinate sedimentary intercalations belonging to the Caribbean plate have been obducted (Doolan, 1970). With respect to the basement rocks that contributed to the sedimentary input of the marginal basins, we note the following particularities: The lower-crustal section incorporates low- to high-grade metamorphic units (Fig. 2), the Sierra Nevada Province and the Sevilla metamorphic belt, composed of Precambrian granulites, anorthosites, and gneisses (Cardona et al., 2010a; Cordani et al., 2005; Kroonenberg, 1982; Ordóñez et al., 2002; Restrepo-Pace et al., 1997), the Inner Santa Marta metamorphic belt,

composed of a Permian mylonite suite (Cardona et al., 2010c) of orthogneisses and metasedimentary rocks, and a Triassic to Lower Cretaceous suite of high-amphibolite-facies metasedimentary rocks (Zuluaga and Stowell, 2012). At the NW tip of the Sierra Nevada de Santa Marta massif, obducted oceanic sequences (Doolan, 1970) comprise the Late Cretaceous–Paleogene Outer Santa Marta metamorphic belt, a suite of meta-basites, phyllites, low-grade metamorphic schists, and metaconglomerates (Cardona et al., 2010b; Doolan, 1970; MacDonald et al., 1971). The Cretaceous clastic to calcareous platform sediments at the distal rim of the southeastern flank of the Sierra Nevada de Santa Marta massif form a sequence some 3000 m thick (Sanchez and Mann, 2015). On the northern flank of the Sierra Nevada de Santa Marta massif, Cretaceous limestones are limited to one solitary remnant that outcrops along the Cañas River to the west of the Palomino sequence (Colmenares, 2007). These relations argue for a once-continuous Cretaceous cover. The lack of Cretaceous source material in the examined sequences furthermore supports a denudation phase preceding late Paleogene–early Neogene exhumation. Such a marginwide erosional event can be assigned to the middle Eocene (DuqueCaro, 1979); a hiatus characteristically increases toward the Cretaceous suture, encompassing the Cretaceous and part of the Jurassic magmaticvolcanic arc sequence. STRATIGRAPHY OF THE ARACATACA AND PALOMINO MARGINAL BASINS The Cenozoic Aracataca basin straddles the Santa Marta–Bucaramanga fault in its hanging wall, forms a narrow depositional fill, and is disconnected from the more western Plato depocenter by the Algarrobo high (Mora- Bohórquez et al., 2017; Fig. 2). Previous studies reported sediments deposited in marine to lagoonal and continental conditions (Tschanz et al., 1969; Hernandez et al., 2003). Bedrocks of the eastern footwall block contain the Precambrian Mangos granulite and a Jurassic acid to intermediate plutonic and volcanic suite, which make up the Sierra Nevada Province of Tschanz et al. (1974). The stratigraphic profile consists of a lower shaley to conglomeratic unit with marine fossils, informally designated the Macaraquilla conglomerate (Table 1; Hernandez et al., 2003), and an upper unit of sandstones and conglomerates previously attributed to a fluvial to transitional molasse facies of probable Miocene age (Table 1; Tschanz et al., 1969). This eminently conglomeratic sequence is unconformably overlain by sandstones interbedded with marls and


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OB

CARIBBEAN

FF

AP-50

EMP-35b

Oca Fault

PB

OhF

IB

SEA

EMP-49a AP-45 & 46

SB

AF

SL

SNP

CVI-1302 CVI-13115

AB

EMP-16 CP-088

CRB ta M

San nga

ama car -Bu arta Fault

PR

Quaternary alluvium + +

Paleogene marine and continental strata (Paleogene)

Figure 2. Geological map of the Sierra Nevada de Santa Marta massif (SNSM). Provinces: SNP—Sierra Nevada Province, PR—Perijá Range, SB—Sevilla belt, IB—Inner Santa Marta metamorphic belt, OB—Outer Santa Marta metamorphic belt. Basins: AB—Aracataca basin, PB—Palomino basin, CRB—Cesar-Ranchería basin. Faults: SL— Sevilla Lineament, OhF—Orihueca fault, AF—Aguja fault, FF—Florin fault. Sample locations and basins are in black background, whereas structures and provinces are in white background. Updated from Ingeominas (2007).

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Tschanz et al. (1969)

Neogene

Pliocene

Upper Tertiary sedimentary rocks

Paleogene

TABLE 1. STRATIGRAPHIC NOMENCLATURE FOR THE CENOZOIC SEDIMENTARY ROCKS OF THE ARACATACA BASIN Age Pleistocene

Oligocene

Q.

Miocene

Eocene

Colmenares (2007)

Unidad Arenosa de Fundación

This work Unidad Arenosa de Fundación

Guamachito Conglomerates



Zambrano Formation

Zambrano Formation

Zambrano Formation

Miocene sedimentary rocks

Miocene sedimentary rocks Aracataca Conglomerates

Eocene sedimentary rocks Macaraquilla Conglomerates

Paleocene

mudstones of the Zambrano Formation that yield pollen of early Pliocene age (Hernandez et al., 2003). Upper Pliocene deposits are informally referred to as the Guamachito conglomerate, which, further west, gives rise to the distal “Unidad Arenosa de Fundación” (Table 1). The Palomino sequence unconformably overlies the southern footwall of the Oca fault. These basal strata barely exceed 500 m and consist of a systems tract that comprises, from S to N, pebble conglomerates and an intercalation of sandstones and mudstones of a supposed Miocene age (Tschanz et al., 1969). The Aracataca and Palomino sequences both lack a biostratigraphic frame. Our arguments for an Oligocene to early Miocene age for the Aracataca conglomerate is based on its regional correlation with fault-related Paleogene to early Neogene sedimentary fills of various subbasins of the Lower Magdalena basin, as documented by their subsidence histories (Bernal-Olaya et al., 2015; Flinch and Castillo, 2015). This correlation fits the apatite fission-track (AFT) interval of 29–26 Ma reasonably well, which was obtained within the Jurassic Central Batholith at a distance of some 7 km from the Aracataca basin (Villagómez et al., 2011), if interpreted as exhumation ages. In this correlation, we clearly neglect a major lag time between denudation and sedimentation, which we justify by the relatively high exhumation rate of 0.6–0.7 km/m.y. (Villagómez et al., 2011) and a short transportation distance, supposing a closeness of drainage basin and fault scarp (see later herein). A residence time amounting to just a few million years has been estimated for the gravelly dominated depositional setting of the Ebro Basin (Jones et al., 2004). METHODS Clast Counting Along the two stratigraphic sections, conglomerate clast counts were performed at 13 locations shown in Figures 3 and 4. On average, 100 clasts (range between 60 up to 200 clasts),

Hernandez et al. (2003)

Macaraquilla Conglomerates

with sizes varying from very coarse pebbles (>3 cm) to boulders, were counted using the ribbon method (Howard, 1993). Clasts were classified by their intermediate to felsic plutonic, mafic to ultramafic plutonic, volcanic, metamorphic, and/or sedimentary provenance. U-Pb Geochronology Zircon U-Pb ages were obtained from six samples using laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) analyses. Zircons were extracted from samples using conventional mineral separation techniques, including rock crushing, sieving (250–60 µm fraction), and concentration with heavy liquid and magnetic separation techniques. Detrital zircons (50–200 grains per sample) were randomly picked, selecting clean, crack- and inclusionfree grains. Subsequently polished grain epoxy mounts were coated with graphite and imaged at the Geosciences Department of the Université de Lausanne, Switzerland, using a Vega ©Tescan MV2300VP scanning electron microscope (SEM) to create a detailed set of panchromatic cathodoluminescence images. Laser-ablation spots were selected in both grain cores and rims. LA-ICP-MS analyses and data processing were carried out at the Institute of Geochemistry and Petrology at ETH Zürich, Switzerland. Zircons were ablated with a NewWave UP-193 nm Ar-F excimer ablation system coupled to a PerkinElmer PE SCIEX Elan 6100 ICP-MS to measure Pb/U and Pb isotopic ratios. The following parameters were applied during this process: 30 µm diameter beam size, 10 Hz repetition rate, 30–45 s signal, and a beam intensity of 2.2–2.5 J/cm2. Reproducibility of U/Pb data was monitored by measurements of GEMOC GJ-1, with a chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) 206Pb-238U age of 608.5 ± 0.4 Ma (Jackson et al., 2004), which was used as a primary standard. The external reference standards Plešovice (337.13 ± 0.37 Ma; Sláma et al., 2008) and TEMORA 1 (416.75 ± 0.24 Ma; Black et al., 2003) were used

to calibrate and monitor fractionation and consistency in the measured U-Pb dates. Ages were calculated using LAMTRACE (Jackson, 2008). Additional data reduction details were followed as given by Ulianov et al. (2012). Statistical analyses of zircon data were performed using Isoplot 3.71 (Ludwig, 2003). All discordant (>1%–3%) analyses of magmatic zircons were discarded. Only zircons with concordance greater than 90% were accepted and plotted. Statistical interpretation of the results, regarding to discordance, maximum depositional ages, and selection of the best age, was done considering a threshold of 1.5 Ga, given the change in chronometric power; the details on these proceedings were presented by Spencer et al. (2016). A summary of the isotopic data obtained in this study is presented in Table DR1.1 Detrital Fission-Track Thermochronology Zircons of the 125–250 µm fraction from eight samples were mounted in Teflon® sheets, with at least two mounts per sample. Zircons were polished to expose an internal surface and etched in a NaOH-KOH solution at 228 °C. Etching time varied between 20 and 60 h in order to reveal countable tracks in at least 100 grains per sample. Samples were irradiated together with Fish Canyon Tuff and Buluk Tuff zircon age standards and IRMM541 dosimeter glasses. Apatite crystals of four samples were mounted in epoxy, polished, and etched in 5.5 M HNO3 at 21 °C for 20 s and covered with muscovite detectors. The samples were irradiated together with Fish Canyon Tuff and Durango Tuff age standards and IRMM540R dosimeter glasses. Both apatite and zircon samples were irradiated at the FRM II research reactor at Munich, Germany. A summary of the dated samples and analytical details such as zeta calibration, 1 GSA Data Repository item 2017306, Tables DR1 and DR2, is available at http://www.geosociety. org/datarepository/2017 or by request to editing@ geosociety.org.


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ARACATACA BASIN - WESTERN SNSM Aracataca River M

S

G

COMPOSITION

FACIES

IV

CVI-1302

1000 m

M EP-41 CVI-1302 CVI-13115

Oligocene-Lower - Miocene

Aracataca Conglomerates

III

EP-37

CVI-13115

M

500m

CP-85

II M EP-17

LITHOLOGY M

Conglomerates Sandstones

I EMP-16 EP-08

0m

J

Mudstones

M

Granites

M

Vulcanites

Plant remnants

EP-06

Metamorphic rocks

Bivalve fragments

EP-02

Black Basalts

Gastropods

ARACATACA BATHOLITH

M

Monomictic conglomerates

SAMPLES Clast counts Detrital zircon and apatite samples Paleo-current Vector (clast orientation)

Figure 3. Stratigraphic column of the sedimentary successions at the Aracataca section, western Sierra Nevada de Santa Marta massif (SNSM), with compositional variations of clast counts. Right: Location map of the Aracataca River section. Facies associations are described in detail in Table 2. J—Jurassic; M—mud; S—Sand; G—Gravel.

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PALOMINO BASIN - NORTHERN SNSM Negro River Transect 2 M

S

G

COMPOSITION

FACIES

EMP-35b

500m

Lower Miocene

II EMP-35b

EMP-26

Palomino Sequence

I

AP-45 AP-46 AP-50

P

Muchachitos Gneiss

Negro River Transect 1 M

S

G

EMP-49a COMPOSITION

FACIES

EMP-51

500m

II

EMP-50

EMP-49a

Lower Miocene

EMP-47

LITHOLOGY

I

Conglomerates Sandstones Very fine sandstones (green & black) EMP-43 0m

J

AP-45 AP-46 AP-46 Palomino Pluton

Granites

Vulcanites

Metamorphic rocks SAMPLES

Black Basalts

Clast counts

Detrital zircon and apatite samples

Plant remnants Bivalves fragments Gastropods

Paleo-current Vector (clast orientation)

Figure 4. Stratigraphic column of the sedimentary sequences at the Negro River section, northern Sierra Nevada de Santa Marta massif (SNSM), in the Palomino basin with compositional variations from clast counts. Right: Location map of the Negro River section. Facies associations are described in detail in Table 3. P C—Precambrian; J—Jurassic; M—mud; S—Sand; G—Gravel.


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Piraquive et al. grain number, and U content are presented in Table DR2 (see footnote 1). RESULTS Stratigraphy In this section, we present a lithofacies analysis of the Aracataca and Palomino sequences, each represented by a characteristic section measured along the Aracataca and Negro Rivers (Figs. 3 and 4). Conglomeratic deposits have a deltaic affinity and are mostly polymict, though monomict compositions do occur. We distinguished 19 different facies associated with four different facies associations. For the facies definition, we relied on the fluvial system classification defined by Miall (1978, 2006). Aracataca Conglomerates Along the Aracataca River, we measured a 1200 m composite section of a mainly conglom-

eratic succession, which included fossil-bearing mudstones at its base. Based on lithological criteria and facies analysis, we divided this profile into four sequences, numbered from base to top and labeled by interpretative names for ease of description (Fig. 3; Table 2). Sequence I consists of mudstones to siltstones, alternating with discrete conglomeratic lenses. Sequences II and III are characterized by a predominance of tabular conglomeratic beds, which form amalgamated beds in sequence II and are separated by sandy layers in sequence III. Sequence IV displays conglomeratic beds in discontinuous lenses and channel-like bed forms, which interfinger with sandy units and are separated by muddy beds. The provenance of the gravel fraction delineates a bimodal origin: Monomict conglomerates exclusively consist of the local substratum, which, for the examined column, is the granodioritic Aracataca batholith. Polymict conglomerates, however, include a wider spectrum of acid and basic volcanic clasts of the Jurassic arc assemblage and granulites of Grenvillian age. Monomict conglomerates occur intermittently

throughout the column, while polymict conglomerates tend to be enriched in granitic components at the base and at the transition from sequence II to sequence III, displaying otherwise no distinct variation (Fig. 3). Sequence I starts with a basal polymict pebble-boulder conglomerate, 20 m thick, composed of stacked beds, each distinguished by a characteristic clast size (facies Ia). Up section, muddy to silty beds with calcareous intercalations denote the extent of this unit. They alternate with lenses and mound-like accumulations of debris flows with boulders of granite and micritic limestone (Fig. 5A) and enclose solitary boulders and monomict lenses of angular granitic clasts (facies A-IIb), which are virtually devoid of matrix but are locally intermingled with shell fragments. Overlying laminated siltstones and mudstones smooth out rugged surfaces of these breccia-like conglomerates and mark a steady background sedimentation. The base of sequence II is traced by the appearance of a first thick tabular conglomerate bed that overlies a basal mud layer in sharp

TABLE 2. SUMMARY OF FACIES AND FACIES ASSEMBLAGES IN THE ARACATACA BASIN (WESTERN SIERRA NEVADA DE SANTA MARTA MASSIF) Facies assemblage A-IVc

Code* Fm

Description Massive mudstone to siltstone layer with sand dikes.

Inferred depositional process Overbank deposit

A-IVb

Sm-t

Medium- to coarse-grained sandstone, filling scours or forming planar beds; scoured surfaces are draped by pebbly lag.

Isolated channel fill or crevasse splay on floodplain

Interpreted environment

Gravelly to sandy braid plain constituting the topset of a Gilbert-type delta

A-IVa

Gh-t

Pebble-cobble conglomerate in lenses, 0.8 m to 3 Channelized hyperconcentrated mass flow m thick. Components are well sorted, rounded, and sand to clast supported. Beds tend to be normally graded, displaying a scoured base (Gt), or are interfingered with sandstone (Gh). Cobbles display an a(t)b(i) imbrication.

A-IIIb

Gmt

Pebble-cobble conglomerate in lenses with an erosional base, uniformly dispersed rounded components or angular fragments, sand supported.

A-IIIa

Sh-m

Laminated medium-grained sandstone grading River-generated hyperpycnal flow descending upward into massive coarse-grained sandstone from a delta brink, or: grain flow associated with interspersed pebbles and cobbles. with the turbulent layer of a descending laminar inertia flow of a debris avalanche (Postma et al., 1988)

Foreset domain of a Gilbert-type delta

Channel-fill of a cohesive(?) debris-slide associated with an erosional scar (Postma, 1984; Nemec and Steel,1990)

Slide scar in the foreset domain of a Gilbert-type delta

A-IIb

Gmb

Lenses, pockets, or horizons of outsized boulders Boulders derived from a delta brink zone or from canyon walls of an incised valley by debris-fall with diameters up to 2 m, gravel-supported, composed of granite. avalanches

Boulder accumulation in the foreset to bottomset domain of a Gilbert-type delta

A-IIa

Gms

Pebble-cobble conglomerate in tabular beds, 0.8 m to 1.5 m thick. Clasts are subangular to rounded, sand to gravel supported, poorly to regularly sorted. Beds display a coarse-tail inverse grading in their lower part. Cobbles are oriented parallel to bedding or imbricated, exhibiting an a(p) or a(p)a(i) fabric.

Foreset of a Gilbert-type delta

A-Ia

Laminated mudstone and siltstone with calcareous lenses, containing shells and shell fragments of molluscs and gastropods. Associated with lenses of monomict breccia conglomerates and outsized granite boulders (facies IIb). *Facies code modified from Miall (1978).

8

Fsm

Cohesionless debris flow with sheared basal part. Inverse coarse-tail grading due to the forced upward movement of larger clasts (Lowe, 1982).

Suspension fall-out of turbidity flow or of a homopycnal river outflow (Colella, 1988)


Toeset to bottomset of a Gilberttype delta

Early Neogene unroofing of the Sierra Nevada de Santa Marta contact (facies A-IIa). Large cobble-sized clasts show a bed-parallel orientation and a tendency of a reverse grading in the lower division of this bed (Fig. 5B), displaying characteristics of a noncohesive debris flow (Nemec and Steel, 1984) or a concentrated particle flow (Mulder and Alexander, 2001). Other similar beds contain solitary granitic boulders embedded along their base or floating in cobble conglomerates (facies A-IIb). Where defining closely packed lenses, they display an a(p)a(i) (a—clast axes, p—parallel, i—imbricated) imbrication, with their long axes dipping in a southeastern upflow direction. Other interfaces of debrites contain pockets of polymict cobbles, which are angular and highly disorganized. Occasionally, these conglomeratic layers are superseded by laminated medium-grained and coarse, massive sandstone (facies A-IIIa). Throughout this sequence, conglomeratic beds are intermittently separated by thin beds of siltstones and mudstones, which contain lenses of monomict breccias, as described for sequence I. The presence of these silty to muddy alternations defines the extent of sequence II. Amalgamated debrites prevail in the lower part of sequence III and may be separated into distinct meter-scale flow units, according to particular clast size and a slightly varying content of sandy matrix (Fig. 5C). Further up section, flow units are capped by thin- to medium-sized sandstone beds. These sandy layers are laminar to massive (facies A-IIIa) and display water-escape structures, as evidenced by sheared sandy flames intruded into overlying conglomerates, patchy granular pockets within the sandstone, and conglomeratic pillars or dikes emanating from underlying debris flows (nomenclature adopted from Postma, 1983). These debrites include in their upper part with outsized granite boulders aligned close to or draping the very interface to overlying sandy layers. Where closely packed, they display imbricate arrays (Fig. 5D). Outsized clasts may also be present in the overlying sandy layers, suggesting an emplacement mechanism related to their common interface. Within sequence III, matrix-supported polymict conglomerates compose a distinct facies, as they define channel fills with an abundant sand- to granule-sized matrix (facies A-IIIb). Sequence IV is composed of discontinuous beds of pebble-cobble conglomerate, both clastand matrix-supported, which form channelshaped lenses up to 3 m thick and display no distinct or normal grading (facies A-IVa). Clasts are rounded and display an a(t)b(i) (a,b—clast axes, t—transversal, i—imbricated) imbrication. They alternate and interfinger with trough cross-stratified sand beds that display conglomeratic base lags (facies A-IVb). This assemblage

is subdivided by thin to medium beds of massive mudstone, which are variably scoured by channel-shaped bed forms (facies A-IVc). Interpretation Our facies inventory combines diagnostic characteristics of the three principal architectural elements of a Gilbert-type delta that defines, from base to top, a progradational succession. Sequence I constitutes a bottomset or toeset, sequences II and III represent a lower and upper foreset assemblage of a delta slope, and sequence IV is a topset of a delta plane. We base this interpretation mainly on the facies distribution, as detailed in Table 2. Mudstones and siltstones of facies with embedded conglomerate lenses and outsized boulders (facies A-Ia and A-IIIb) define the bottomset within the reach of debris slides and falls of a nearby delta slope. Our measured section (Fig. 3) illustrates a decrease of muddy lithologies upward, which supports a progradational change from a distal bottomset to a more proximal toeset. By their composition and textural maturity, debris-flow units comprise two distinct classes. Monomict breccias are derived from the local bedrock of the Aracataca granite and are texturally highly immature, as they compose breccias and encompass granule- to boulder-sized rock fragments within the same bed. This lack of sorting and their disordered fabric (akin to an open-work fabric; Gobo et al., 2014) suggest an origin by debris fall from cliffs of a contiguous topographic scarp. Their intermingling with little-fragmented marine fossil shells and boulders of calcareous beds (Fig. 5A) points to the existence of a subaqueous platform or delta plain, which they must have crossed during their avalanching. Considering an elevated sediment supply for the progradational setting of a fan delta, the formation of calcareous beds is atypical and may be restricted to minor transgressional cycles, as documented for a Paleogene clastic fan delta in the Ebro Basin (López-Blanco et al., 2000). Isolated outsized clasts embedded within mudstones attest to the presence of a pronounced delta slope, which contributed to their separation from smallersized clasts, according to the high momentum imparted by their fall or downslope tumbling (Nemec, 1990). Polymict conglomerates, on the other hand, are texturally more mature and represent hyperconcentrated flows. By their inverse grading in basal divisions, they document an incipient sorting of bigger clasts by dispersive pressure (Lowe, 1982; Mulder and Alexander, 2001). In the lower part of sequence II, these beds represent homogeneous units enriched in a sandy matrix, and they lack, as a distinctive

feature, scoured contacts, even overlying soft muddy beds (Fig. 5B). These relations point to a reduced basal drag of relatively impermeable flow units and may have been associated with emplacement by hydroplaning (Mohrig et al., 1998). In contrast to these compact plugs, lenses of polymict cobble-boulder conglomerates, which by their disordered fabric and textural immaturity resemble debris-fall deposits, may have been derived by the extraction of the sandy matrix of a “leaky” debris flow within a gravelrich front of a debris flow (Nemec, 1990), from which gravels may have detached in front of a parental debris flow (Sohn, 2000). Amalgamated conglomeratic units of sequence II may represent multiphase debris flows deposited under different rheological regimes (Sohn, 2000). Basal divisions of inversely graded, thin-bedded pebbly sandstones and conglomerates may be attributed to a traction carpet flow regime, while normally graded, upper conglomeratic divisions may have accumulated by the fall-out of particles initially supported by a turbiditic suspension mechanism (Fig. 6C; Sohn, 1997, 2000). The segregation of conglomeratic and sandy layers becomes distinctly bipartite in sequence III, with a basal conglomeratic traction carpet (or inertia layer; Postma et al., 1988) separated from an overlying sandy turbidite layer by a sharp interface. These debrite-turbidite coup lets contain outsized clasts reaching the fraction of boulders that align close to the top of conglomeratic beds or at the very interface to overlying sandy layers, a situation that relates to the experimental findings of Postma et al. (1988) and their conceptual model of a laminar inertia flow capable of supporting large clasts and a segregating upper turbulent layer. The trapped outsized clasts of Figure 5D may thus have slid close to the interface of a conglomeratic laminar and sandy turbulent flow unit. In contrast to other deltaic foreset sequences (Postma, 1984), secondary reworking of the depositional units is subordinate and can only be inferred from an isolated channel-shaped bed form with the matrix-rich conglomerate that composes facies A-IIIb. Conglomeratic and sandy deposits of sequence IV display channel-like bed forms and may be associated with a distributary delta plain. Intervening muddy layers are likely to represent floodplain deposits. The lack of pedogenic horizons supposes a subaquatic environment and suggests that sea-level rise outpaced depositional aggradation. Summarizing, the depositional environment of a Gilbert-type delta may be constrained by its three basic architectural elements and a progradational setting. The bottomset contains


9


A

B N 10 E

Gms

N 20 W

C

Sh-m

Gmb Calcareous boulder

Gms

Gms

B

Fsm

A2

A con malg glo ama me rati ted cb eds

Sh-m

Gms

Gms

B

Gms

1m

Fsm

Sh-m

A

N 10 E

50 cm

Gmb

A1

S 50 W

1m

C

50 cm

E

F

G N 70 E

B

C

N 10 W

Fm

Fm

fluidized sand

1m

10 1m

D

Fm

St/Sp

St/Sp

lc

A

G ht

Sm

St/Sp

Piraquive et al.

2m


Figure 5. Left: Figures from the Aracataca section (facies refer to Table 2). (A) Facies A-Ia and A-IIb, bottomset of a Gilbert-type delta: Lens of debris flow embedded within mudstone and siltstone. Boulders are concentrated at the head of this mound-like accumulation (termination to the left) and consist of granite and micritic limestone. The boulders are variously tilted with respect to bedding and, according to the muddy matrix, point to a cohesive flow rheology. For scale, refer to the Jacob staff with decimeter-scale divisions. (B) Facies A-IIa, lower foreset of a Gilbert-type delta: Polymict pebble-cobble conglomerate with subrounded clasts, displaying a tendency of coarse-tail inverse grading at its base and normal grading in its upper half. Contact to underlying mudstone is planar. Imbricated and closely packed cobbles may display an a(p)a(i) fabric (basal domain to the right of the Jacob staff). Flow direction is to the right. (C) Facies A-IIa, lower to upper foreset of a Gilbert-type delta: Three amalgamated conglomerate beds may be differentiated by textural criteria, such as clast size and orientation that vary from disordered to bed-parallel and may be imbricated. Despite patchy clast-size variations parallel to bedding, units A to C display some contrasting trends in internal organization: Unit B begins with a sand-supported pebble conglomerate and grades into a coarser, clastsupported cobble-pebble conglomerate. Pebbly sandstones form a topmost division and are loosely stratified, attesting to frictional aggradation. A similar stratified pebbly sandstone forms the top of unit A. The cobble conglomerate of unit C begins with bouldersized clasts and displays a highly disordered fabric. The scale is given by the Jacob staff (1.4 m). Unit labels A, B, and C indicate tendency for normal/reverse grading and flow direction. (D) Facies A-IIa and A-IIIa, upper foreset of a Gilbert-type delta: A thick unit of pebble-cobble conglomeratic (unit A1) is capped by a pebbly sandstone (unit A2; center of figure). Outsized angular granite cobbles and boulders drape or are closely aligned with this lithological boundary. In the central upper part, this interface steps up to a stratigraphically higher horizon and marks the termination of a row of imbricated boulders (center-right of figure). Flow direction is to the left. Right: Figures from the Río Negro section (facies refer to Table 3): (E) Facies P-Ia and P-IIIa, channel fill of braid plain: A crudely stratified conglomeratic unit A is cut by a densely packed unit B, which, in its turn, grades into a stratified pebbly sandstone

(unit C). Units B and C are interpreted to define a channel fill. Outsized boulders mark the erosive base of unit A. (F) Facies P-IIc and P-IId, sandy floodplain: Scoured sandy beds alternate with tabular strata of siltstone and gray mudstone. To the right-hand side of the center, a sandstone forms asymmetric channel fills within a muddy substrate. (G) Facies P-IIIa and P-IIIb, middle to lower shoreface: Sandy cross-stratified units alternate with thin beds of gray mudstone. The coarse- to medium-sized sandstone displays low-angle, tangential foresets, which may abut against underlying muddy beds. Foresets indicate bi- or multidirectional currents. Sandy units are strongly distorted and partially homogenized by fluidization. For facies classification please refer to Tables 2 and 3.

Palomino Conglomerates

This conglomeratic to sandy sequence forms an isolated patch of Cenozoic sediments to the south of the Oca fault. In an internal or southern position, it involves facies associations that comprise hyperconcentrated mass flows of a braid plain. Northward, they grade into sandy sequences associated with floodplain and siliciclastic shoreface deposits. This sequence overlies Precambrian gneisses of the Sevilla metamorphic belt (Tschanz et al., 1974), a quartz monzonite of probable Jurassic age, which has been mapped as the Palomino Stock (Tschanz et al., 1974), and a Late Jurassic volcanic suite. Further toward the hinterland, the basement exposes the Precambrian Mangos granulite and igneous to volcanic suites of the Sierra Nevada Province (Tschanz et al., 1974). We discuss this sequence by means of a southern conglomeratic section and a northern sandy outrunners of outsized clasts and debris-fall de- section, each one resting unconformably on the posits, signaling the proximity of a delta front. Jurassic igneous or Precambrian metamorphic Distal conglomeratic units intercalated with basement (Fig. 4). Their equivalent structural muddy layers of the bottomset to toeset consist position above a pre-Cretaceous basement sugof little-differentiated, matrix-rich debris flows. gests that the facies associations of these two These conglomeratic deposits become increas- sections belong to an equivalent systems tract. ingly differentiated into composite basal con- Correlative sequences are associated with (I) a glomeratic inertia and overlying sandy turbid- gravelly braid plain, (II) a sandy floodplain, and ity flow units. The presence of outsized clasts (III) a shoreface environment. These sequences at clear-cut interfaces attests to elevated grain- are mapped as facies belts (Fig. 4), according to support mechanisms in the proximal foreset set- the predominance of conglomeratic, sandy, and ting of sequence III. Delta plain deposits of se- sandy to muddy alternations. We labeled facies according to the classificaquence IV, finally, may be assigned to a topset. Ubiquitous outsized clasts point to a steep tion of Miall (1978), combining some gravelly foreset gradient and pose the possibility of a and sandy facies of similar bed forms, however, tectonically active catchment area. For poly- into just one category for simplification. Sequence I is composed of pebble-cobble mict conglomerates, the gross compositional trends of sequences I and II record a gradual conglomerates and includes subordinate interincrease in input of the Precambrian granulite calations of sandy and muddy beds (Table 3). suite and gneiss components of the southern Pebble-cobble conglomerates form units up to Sevilla metamorphic belt (Tschanz et al., 1974). 4 m thick (facies P-Ia; Table 3). They display Metasedimentary components of the Santa a sand- to gravel-supported fabric with an illMarta metamorphic belt are, however, conspic- sorted to moderately sorted clast assemblage. uously absent and restrict the catchment area Scoured bases and internal reactivation surfaces to the central and southern parts of the Sierra may be draped by cobbles and outsized boulNevada de Santa Marta massif. Compositional ders (Fig. 5E). Discontinuous sand lenses subvariations of the gravel spectrum are minor, pre- divide conglomeratic beds into individual flow supposing that the drainage system maintained units. Major bed forms with erosive bases grade a similar structural position since its onset, as upward into pebbly sandstones, which display might be expected by the gradual denudation of trough-shaped laminations of channel fills a topographic scarp at an active fault. This rela- (Fig. 5E). Toward the internal part of this braidtively uniform contribution is punctuated by the plain belt (or sequence I), channel-shaped bed monomict input of the of the Aracataca batho- forms comprise stacked units. At the transition lith, which may have constituted the fault scarp to the sandy facies belt (or sequence II), isolated and hillslopes of an incised valley. These find- conglomeratic lenses increasingly interfinger ings support localized uplift of the western flank with sandstones and form thin intercalations of the Sierra Nevada de Santa Marta massif in within sandy beds. Facies P-Ib consists of gravel- to sand- concordance to the AFT data of Villagómez et supported, well-sorted and rounded al. (2011).


11

12

Ba

lt

Ba sa

ite

ac k

sa lt Ba sa lt G ab Vo br lc o an ic Br ec ci a G ne is s Q ua rtz Sa ite nd st on es M ud st on es

Bl

re en

G

ed

R

ite

de s

An

80%

60%

BASE

EP-02 n = 200

40%

20%

0%

Geological Society of America Bulletin, v. 1XX, no. XX/XX 60%

BASE

es

60%

on

80%

st

60%

M ud

80%

es

es on

st

ud

M

ite on

60%

st

80%

ne s

rtz

a

Ba Bl sa ac lt k Ba sa lt G ab Vo br lc o an ic Br ec ci a G ne is s Q ua rtz Sa ite nd st on es M ud st on es

sa lt

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60%

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Ba Ba

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80%

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TOP

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Ba sa lt G ab Vo br lc o an ic Br ec ci a G ne is s Q ua rtz Sa ite nd st on es M ud st on es

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Bl

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G

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An

R

G ra

60%

Sa n

is

ci

br o

Br ec

ne

G

c

ni

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Vo l

lt

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sa

Ba ab

G

Bl ac k

lt

sa

0%

Ba s

20%

0%

n

40%

20%

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40%

G

80%

Ba

100%

de

0%

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R

20%

0%

te

40%

20%

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0%

R

20%

0%

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40%

20%

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40%

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0%

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20%

0%

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40%

20%

An

40%

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0%

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20%

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te

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40%

20%

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EP-06 n = 119

100%

An

100%

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G

sa lt sa lt

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EP-08 n = 73 te

Ba

G ab Vo br lc o an ic Br ec ci a G ne is s Q ua rtz Sa ite nd st on es M ud st on es

Bl ac k

80%

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EP-17 n = 78

ra

100%

G

CP-85 n = 166

te

100%

ni

EP-37 n = 166

ra

G

100%

te

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sa lt

Ba

sa lt

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Ba

de

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G re

R

ni te

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EP-41 n = 134

ra ni

es

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st

ud

M

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sa lt G ab Vo br lc o an ic Br ec ci a G ne is s Q ua rtz Sa ite nd st on es M ud st on es

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G re

R

R

G ra

WESTERN SNSM - ARACATACA RIVER ARACATACA CONGLOMERATES

G

60%

es

60%

on

80%

st

60%

ud

a

80%

es

80%

on

ite

rtz

st

nd

ua

Q Sa

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Br

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Ba

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G

60%

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80%

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40%

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Br

ne

G

c

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br

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lt

lt

sa

sa

Ba

Ba

sa

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si

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Ba

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ed

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R

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TOP

M ud

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80%

R hy ol

te

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G

100%

R hy ol

ite

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G

Piraquive et al.

NORTHERN SNSM - NEGRO RIVER PALOMINO SEQUENCE EMP-26 n = 64

100%

EMP-51 n = 97

100%

EMP-50 n = 75

100%

EMP-47 n = 91

100%

EMP-43 n = 58

AP-46 n = 129

100%

Granite

Black Basalt

Sandstones

Rhyolite

Gabbro

Mudstones

Andesite

Volcanic Breccia

Red Basalt

Gneiss

Green Basalt

Quartzite

Figure 6. Clast counts from the Sierra Nevada de Santa Marta massif (SNSM), Cenozoic Aracataca and Palomino basins, at the Negro and Aracataca Rivers, respectively, where counts were done following the ribbon method (Howard, 1993).

Early Neogene unroofing of the Sierra Nevada de Santa Marta TABLE 3. SUMMARY OF FACIES AND FACIES ASSEMBLAGES FOR THE PALOMINO BASIN (NORTHERN SIERRA NEVADA DE SANTA MARTA MASSIF) Facies Code* Description Inferred depositional process Interpreted environment assemblage P-IIIb Fm Massive mudstone layers. Suspension sedimentation P-IIIa

St/Sp

Well-sorted coarse sand, grouped into low-angle sets of Wave-worked tractional transportation of sand at Middle to lower shoreface, trough or planar cross-stratification constituting units middle to lower shoreface conditions and migration below fair-weather wave 1 m to 4 m thick. Major bed forms and the base of the of predominantly sinuous bed forms or formation of base units are erosive and contain pebbly lags. Foresets rip channels indicate bi- or multidirectional currents. Sand units affected by fluidization.

P-IId

Fm

Massive siltstone to mudstone in tabular beds.

P-IIc

Sm

Medium- to coarse-grained sand in isolated channel fills. Sands emplaced by cut-and-fill processes during flood events

P-IIb

Sh, Sm

Coarse laminar sandstone, grading into massive sandstone.

Flashy overbank floods

P-IIa

Gh, Gm

Pebble conglomerate in tabular beds with scoured bases or thin nonerosive conglomerate layers, clast or sand supported, grading into pebbly sandstone. Disk-shaped clasts tend to be oriented parallel or at high angles to bedding.

Hyperconcentrated gravel or cohesionless debris flow emplaced on floodplain; clasts oriented at a high angle to bedding attest to rapid frictional freezing

P-Ic

Gp, Sp

Pebbly sandstone with moderately inclined foresets ( 150 Ma

Probability density plots

Probability density (%/∆z=0.1)

16

12

AP-046 n= 100

8

4

0 AP-045 n=101

Fission-track grain age (Ma) Figure 9. Detrital zircon fission-track (ZFT) data from Aracataca and Palomino basins, with probability density plots elaborated with Binomfit (Ehlers, 2005; Stewart and Brandon, 2004).

18

The zircon U-Pb maximum relative ages between 1150 and 900 Ma, which can be found in all samples, correspond to inherited Grenvillian zircons (Cordani et al., 2005) from the SunsasPutumayo Province (Ibanez-Mejia et al., 2011). The older populations at 1600–1300 Ma point to a source in the Rondonia San Ignacio Province in the Amazon craton. This composite Proterozoic signature has been detected in Precambrian inliers of the Northern Andes (Cardona et al., 2010a, 2006; Cordani et al., 2005), as well as in post-Permian metamorphic rocks of the Sierra Nevada de Santa Marta massif, the Alta Guajira, and in Cenozoic sediments of the Leeward Antilles (Cardona et al., 2010c; Weber et al., 2010; Zapata et al., 2014). Jurassic and Cretaceous zircons are related to volcaniclastic deposits and arc granodiorites and syenogranites. These zircons indicate the constant erosion of the Central Batholith of the Sierra Nevada de Santa Marta massif, as well as the associated Jurassic plutonic and volcanic units. In the topmost samples, the Precambrian ages became the dominant population. Geochronological data and detailed sedimentology indicate deposition in a Gilbert-type delta system that traversed the Santa Marta– Bucaramanga fault in the western basin, which developed since the late Oligocene. The bottomset segment, with an input of mainly granodiorites, is related to the Aracataca Batholith, part of the Central Batholith suite. The foreset shows a mixture of Precambrian and Late Jurassic to Early Cretaceous ages. Zircons found in Neogene sedimentary rocks of the Aracataca and Palomino sequences are subrounded to subangular, and the presence of unstable heavy minerals indicates a relatively short sediment transport distance from the source area. The presence of rutile is also characteristic of high-grade regionally metamorphosed terrains (Force, 1980), indicating that the conglomerates are highly immature. The provenance information derived from the ZFT maximum relative ages suggests that the main sedimentary source area was the core of the Sierra Nevada de Santa Marta massif. ZFT and AFT ages are younger in the Aracataca sequence in comparison to the Palomino sequence, suggesting that the sediments of the western limb of the Sierra Nevada de Santa Marta massif were derived from a more deeply exhumed lower-crustal source (Fig. 11). Provenance of the Aracataca and Palomino sequences shows that during the Oligocene– Miocene, sediments were sourced from the Sierra Nevada Province, and there is evidence that the Santa Marta Batholith and Buritaca Pluton were not undergoing surface denudation during Oligocene–Miocene times. A drainage system



Probability density (%/∆ z=0.1)

Aracataca Basin

with a NE-SW and N-S trend was controlled by the main structures (i.e., Orihueca fault, Aguja fault, Sevilla lineament). This would explain the early Miocene exhumation of the Eocene batholiths and the absence of Paleocene–Eocene zircons in both basins. The Buritaca Pluton yielded an early Miocene AFT age of 22.3 ± 3.1 Ma (Villagómez et al., 2011) and is cut by N-S drainages, but in the sedimentary rocks of Palomino sequence, there is no record of Paleogene zircons; therefore, it is possible to constrain the deposition of the sediments in this basin to the middle Miocene (ca. 16 Ma), considering a lag time of 5 m.y. constrained from an exhumation rate of 0.8 km/m.y. (Villagómez et al., 2011) and a surface temperature of 30 °C. Sediments deposited after the unroofing of the Buritaca Pluton containing Eocene zircons probably bypassed offshore into the late Miocene–Pliocene deposits (Vence, 2008).

Palomino Basin

CVI-1302 n = 35

EMP-49a n=8

EMP-16 n = 38

AP-045 n = 72

Regional Stratigraphic Correlations

P1 P2 P3 P4

Fission-track grain age (Ma) 19-25 Ma 25-35 Ma Detrital AFT 42-60 Ma Probability density plots > 70 Ma

Figure 10. Detrital apatite fission-track (AFT) data from data from Aracataca and Palomino basins, with probability density plots elaborated with Binomfit (Ehlers, 2005; Stewart and Brandon 2004).

W

E erosion and transport

t3

deposition t2 td

pre-orogenic cooling ages

te

Tilted Isochrons

synorogenic cooling ages

t1

tc 240°C isotherm

P3 P1

P2

Figure 11. Schematic (not to scale) cross section showing the sources for the zircon fissiontrack (ZFT) age populations found in the Aracataca basin. Santa Marta–Bucaramanga fault activity controls exhumation and isochron tilting. Figure is modified from Bernet et al. (2006). td—time of deposition; te—time of erosion; tc—closure time for ZFT system; P1, P2, and P3 correspond to the peaks indentified in Figure 9.

Lower Miocene sedimentary rocks found either in the Aracataca and the Palomino basins correspond to proximal fan delta and estuary systems that developed during the first pulse of surface uplift of the Sierra Nevada de Santa Marta massif during the late Oligocene. The clockwise rotation of the Sierra Nevada de Santa Marta massif toward the east led to the development of an extensional phase defining the Lower Magdalena basin as a rotational basin linked to the advance of the Caribbean plate (Bayona et al., 2010; Montes et al., 2010). The record of the first tectonic pulse of the Santa Marta–Bucaramanga fault is the basal deposits of the Aracataca border basin in the vicinity of the Sierra Nevada de Santa Marta massif. At the western edge of the Plato–San Jorge basin, the Romeral suture separated the continental basement of South America from the Caribbean intra-oceanic crust that hosted volcanic arcs and accreted during the Paleocene. Crustal thickening by terrane accretion evolved into collisional plutonism during the Eocene, transmitting a characteristically mixed oceanic arc–basement zircon U-Pb age signal in the Paleogene sediments from the San Jacinto belt (Cardona et al., 2012). Toward the Sierra Nevada de Santa Marta massif, the Precambrian signature strictly dominates the detrital zircon U-Pb spectra. The sediments in the Aracataca and Palomino sequences record a late Oligocene activation of the Santa Marta–Bucaramanga and Oca faults, as the North Andean block indented against the Caribbean plate. Coarse sediments derived from the Sierra Nevada de Santa Marta massif were deposited as growth strata along the active faults. The coarse facies are typical of


19

Piraquive et al.

Q.

SAN JACINTO LOWER MAGDALENA VALLEY ARACATACA BASIN after Cardona et al., (2012) after Flinch (2003) SNSM W foothills (this study) SW NE SW NE SW (Aracataca) (Tolú) (Luruaco) (Magangué) (El Difícil)

Holocene Pleistocene

Betulia

Neogene

Zambrano/Pajuil

Tubará


Zambrano

Zambrano

Jesus del Monte

Late Porquero

Porquero

Early Porquero Cicuco

Rancho/Alférez

Oligocene

El Difícil

Aracataca Conglomerates

Palomino Sequence

Cienaga de Oro

Arjona

Paleogene

“Unidad Arenosa de Fundación”

Tubará

Miocene

Cenozoic

Corpa

Rotinet

El Descanso/Sincelejo

Pliocene

Phanerozoic

PALOMINO BASIN SNSM N foothills Tschanz et al., (1969) NE (Palomino)

El Carmen

Tolu viejo

Arroyo de Piedra

Chengue Pendales

Eocene San Cayetano/ Arroyo Seco

Mesozoic Cretaceous

Paleocene

Cansona

Upper

Lower

Basement Chert

Limestones

Siltstones

Shale

Sandstones

Conglomerates

Granitoids

Intra Oceanic Arc

discordance

No record

Continental Crust Basement (Precambrian granulites anorthosites and gneisses, Jurassic intermediate to acid plutons, and Triassic-Jurassic volcanics)

Figure 12. Stratigraphic correlation chart from the Plato–San Jorge basin, the adjacent Lower Magdalena basin, and San Jacinto belt, as well as the Guajira basin in the northern foothills of the Sierra Nevada de Santa Marta massif (SNSM). Figure is modified from Cardona et al. (2012); Duque-Caro (1979); Flinch (2003); and Tschanz et al. (1969). Q.—Quaternary.

20


Early Neogene unroofing of the Sierra Nevada de Santa Marta hyperconcentrated flows, being the product of rapid slope instabilities. During the Miocene, in the Plato–San Jorge, the Lower Magdalena, and the San Jacinto basins, distal deposits of mudstones, siltstones, and carbonate facies were deposited in a lowenergy environment, coeval with the conglomerates of the Aracataca and Palomino sequences (Fig. 12). The Santa Marta Batholith, the Palomino Pluton, and Sevilla, Latal, and Buritaca Stocks (Fig. 2) share Paleocene–Eocene zircon U-Pb ages and outcrop close to both the Aracataca and Palomino sequences, but Paleogene zircon U-Pb ages are not found within these sedimentary rocks. In contrast, Paleocene deposits from the Cesar-Ranchería basin (Fig. 2) contain a distinctive population of zircons from this epoch (Bayona et al., 2011). Zircon U-Pb ages from the Lower Eocene Misoa Formation, and the Cerrejón and Tabaco Formations from the Cesar-Ranchería basin, indeed overlap with zircon U-Pb ages of plutons in the Santa Marta metamorphic belt, but erosion of these source rocks during the Paleocene seems unlikely because of the Miocene cooling histories documented for these igneous rocks (Villagómez et al., 2011). Accordingly, the Palomino conglomerates lack corresponding quartz-dioritic and tonalitic components in this intrusive suite. In this context, the Late Cretaceous–Paleogene zircon U-Pb populations in the Cesar-Ranchería basin (56–70 Ma) are probably related to a volcanic source found further to the east, as evidenced by tuffs within the Misoa Formation of the Maracaibo basin, coeval with the Eocene Tabaco Formation (Bayona et al., 2011). Paleocurrent directions measured in the Cerrejón Formation show an E to SE trend (Bayona et al., 2011), given that the Sierra Nevada de Santa Marta massif has rotated clockwise by ~30° after the Eocene, according to Montes et al. (2010), and paleocurrent directions result in E to NE flow directions for the Cerrejón Formation, which in turn are coherent with an E-NE sediment dispersal direction during the early to mid-Paleocene, 65–58 Ma, as documented by Ayala et al. (2012). In this epoch, the Precambrian, Permian–Triassic, and Cretaceous zircons found in the Cerrejón and Tabaco Formations from the Cesar-Ranchería basin may not be exclusively derived from the Sierra Nevada de Santa Marta massif and could also have been supplied by the rocks of the proto–Perijá Range, which yield Permian to Jurassic granitoids as well (Martin, 1968), and the Central Cordillera (Mora-Bohórquez et al., 2017), considering that the Sierra Nevada de Santa Marta massif, Perijá Range, and Central Cordillera were exhumed in

Paleocene times (Ayala et al., 2012; Shagam et al., 1984; Villagómez et al., 2011; Villagómez and Spikings, 2013), with the major exhumation of the Perijá Range during the Oligocene (Shagam et al., 1984). Other sources that supplied Paleocene zircons to the Cesar-Ranchería basin may be related to Paleocene volcanism, and plutons of the Guajira Peninsula (Cardona et al., 2014), and the Central Cordillera. Alternatively, a plutonic source of Paleocene zircons found in the Cerrejón and Tabaco Formations could be related to unrecognized Paleocene plutons (i.e., Atánquez Laccolith; Tschanz et al., 1969) located within the Sierra Nevada Province. This alternative would agree with Paleocene–Eocene exhumation of this province and would correlate with the unstable metamorphic minerals found in the Tabaco and Cerrejón Formations indicative of short sediment transport distance (Bayona et al., 2007). Adjacent to the Cesar-Ranchería basin, the onset of a NE-directed drainage system occurred during the Paleogene, incising the newly formed topography and precluding a connection with the drainage systems in the NW of the Sierra Nevada de Santa Marta massif. The interpretation of a disconnected NW-SE drainage of the Sierra Nevada de Santa Marta massif is validated by the zircon U-Pb ages found in the Sinú San Jacinto belt (Fig. 12), in which Precambrian and Permian– Triassic

source rocks are dominant, along with the youngest arc derived material from the Late Cretaceous, 71.3 ± 1.3 Ma and 68.7 ± 1.4 Ma (Cardona et al., 2012), without record of P aleocene– Eocene zircons in the sediments. Instead of a Paleocene tilting toward the SE, which would have generated an inclined topography toward the Cesar-Ranchería basin and an extensive NW-SE drainage system feeding a clastic wedge, the distribution of U-Pb and detrital thermochronologic ages in Oligocene– Miocene sedimentary rocks in the Aracataca and Palomino sequences indicates that the Sierra Nevada de Santa Marta massif was tilted during Oligocene–Miocene exhumation toward the NE, with increasing relief in the western limb of the Sierra Nevada de Santa Marta massif controlled by the Santa Marta–Bucaramanga fault, the activation of which was contemporaneous with the dextral Oca fault and the onset of transpressive tectonics. The Oligocene–Miocene progradational Aracataca conglomerates coeval with the transgressive Palomino conglomerates during exhumation can be explained by tilting of a block bounded by normal faults (Leeder and Gawthorpe, 1987). For the NE tilting, we presume a fulcrum that separates elevated from subsided segments of a ramp. In this block, two basins are opposed by a drainage divide corresponding to the uplifted crest of the domino block (Fig. 13): a fault scarp

Oligocene-Early Miocene

SW

NE

FOOTWALL SCARP +ve displacement vectors (>Exhumation) -ve displacement vectorsTransgressive Sequence Prograding Sequence

HANGING WALL

fulcrum (zero displacement) FOOTWALL

HANGING WALL Oca Fault

SMBF

Topset

Shoreface

Foreset Bottomset

Sandy braid plain Gravelly braid plain

Figure 13. Conceptual model (not to scale) depicting tectonic slopes associated with a simple tilt block/half graben, involving a fault-bounded synextensional clastic wedge, as the case of the Aracataca basin gravel-rich fan delta, at the Santa Marta–Bucaramanga fault, and its counterpart deposited on a gently inclined slope dominated by estuarine deposits of the Palomino sequence, modified after Henstra et al. (2016); Leeder and Gawthorpe(1987); and Ravnås and Steel (1998).


21

Piraquive et al. SE

NW +

2.5 4

++

2.6

2.8 -2.9 2.8 -2.9

+ +

+ + 2.4 +

2.

+

96

+

+ 2.64 +

+

2.8

+

Late Pliocene

prefiguring a steep slope (drainage basin of Aracataca conglomerates) and ramp with a gentle inclination (Palomino subbasin). The latter is not fault controlled. This mechanism provides a simple kinematic explanation for contemporaneous uplift and subsidence, but it is only valid for a thick crustal block. This block can be delimitated by the Sevilla Lineament and involves the Sierra Nevada Province.

Middle Miocene

Tectonic Implications for the Caribbean Realm

+

+

2.4

+

2.74

+

+

2.8 +

+

+

Mantle Upwelling +

+ +

2.5 4

2.6

++

+

+ + 2.4 +

2.8 -2.9

+

+ + + + +

2.

+

+

96

+

+ 2.64 +

+

2.8

+

2.4

+ +

2.74

2.8 +

+

+

3.4

Slab Flattening

+

+ ++ + + ++ + ++ ++ ++ + ++ + + + + + + + + + +

+

+

+

+ +

+ +

+

+ +

+

+

+

+

+ +

+ +

+

+

+

+

+

+

+

+

Early Eocene Great Caribbean Arc Collision +

+ + + + ++ + ++ + + + + + + + +

+ +

+ +

+

+

+

+

+

+

+

+ + +

Paleocene

+

+

+

+

+

+

+ + +

Late Cretaceous + +

+ + +

+

+ +

+ +

+

+

+

+

+

+

+

+ +

+ +

+

+

+

+ +

+

+ +

+

+

+

+ +

+ +

+ +

MARINE SEDIMENTARY METASEDIMENTARY ROCKS

VOLCANICLASTICS +

GREENSCHISTS

HIGH GRADE GNEISSES AND GRANULITES

+

+

+

+

+

+

+ +

+ +

+

+

PALEOGENE INTRUSIVES

+ +

+

+ +

+ +

+

AMPHIBOLITES & ORTHOGNEISSES

ECLOGITES

+

+ +

CONTINENTAL ARC INTRUSIVES PROTO-CARIBBEAN ARC OCEANIC CRUST

Figure 14. Schematic (not to scale) multistage evolution for the Caribbean–South American margin. During first stages, proto–Caribbean arc approaches South America and obducts the NW tip of the Sierra Nevada de Santa Marta massif; subduction during the Late Cretaceous ca. 75 Ma in this part of the North Andean margin is interpreted from paleogeographic reconstruction of Mora-Bohórquez et al. (2017); in the late Eocene, slab flattening is responsible for the reactivation of crustal structures as the Santa Marta–Bucaramanga fault (SMBF); ve—vertical.

22

Transition in the Caribbean plate subduction angle from 30° to a shallower dipping subduction between 4° and 8° occurred between the late Eocene and middle Miocene (Bernal-Olaya et al., 2015). Since the late Eocene, a relevant change in the subduction regime is evidenced by the gradual cessation of arc plutonism and late cooling, which during the Oligocene–Miocene is defined by a gently inclined slab dipping less than 30°. The establishment of a shallower dipping slab 4°–8° since the middle Miocene was related to the subsequent underthrusting of a thickened Caribbean crust under NW South America, responsible for the Santa Marta– Bucaramanga fault reactivation (Kammer and Sánchez, 2006; Villagómez et al., 2011) and accumulation of left-lateral slip as the Caribbean plate moved to the east during the late Miocene. In response to the rigid coupling of oceanic and continental lithosphere, fault slip on the Santa Marta–Bucaramanga fault was prevented, and in the interior of the Sierra Nevada de Santa Marta massif, early Mesozoic sutures were reactivated as NW-verging thrusts (Fig. 14; Villagómez et al., 2011). The sedimentary rocks of the Sierra Nevada de Santa Marta massif basins attest to basement exhumation, which was controlled mainly by block tectonics at the NW corner of the Sierra Nevada de Santa Marta massif, driven by the normal-sinistral slip of the Santa Marta– Bucaramanga fault (Villagómez et al., 2011). Zircon provenance provides evidence that the fan-delta systems and estuaries sourced by the Sierra Nevada de Santa Marta massif remained isolated from the main trunk system of the proto-Magdalena paleochannel (Fig. 15). The protodelta was controlled by Santa Marta– Bucaramanga fault activity at the southern boundary of the Lower Magdalena basin (Bernal-Olaya et al., 2015). These new findings greatly improve paleogeographic reconstructions for this epoch and allow precise timing between fault activity and the onset of sedimentation in the Lower Magdalena basin and the sourcing of sediments from the Eastern Cordillera, the Central Cordillera, the Santander



Oligocene

lower Miocene

Cratonic sources

SM

Guajira Peninsula (Siamana Formation)

n=105

K-P

CC

n=312

Palomino basin

n=409

Aracataca basin

n=306

MMV (Colorado Formation, Cagui well)

n=201

MMV (Mugrosa Formation, Cagui well) MMV (Colorado Formation, Cocuyo well) MMV (Colorado Formation, Cocuyo & Guane wells)

n=102 n=155

La Salina Footwall (Colorado Formation)

n=85

0

250

500

750

1000

1250

1500

1750

2000

n=170

Nuevo Mundo Syncline (Colorado Formation)

n=208

Nuevo Mundo Syncline (Mugrosa Formation)

n=107

Axial Eastern Cordillera (unnamed unit)

n=192

Llanos basin (Carbonera Formation C3-C1)

n=106

Llanos basin (Carbonera Formation C5)

2250

2500

2750

3000

3250

3500

Zr U-Pb Age (Ma) Figure 15. Comparative plots of detrital zircon U-Pb age spectra for Oligocene–Lower Miocene sedimentary rocks from the Guajira Peninsula (Zapata et al., 2010), the Middle Magdalena Valley (MMV; Caballero et al., 2013; Horton et al., 2015), the axial Eastern Cordillera and Llanos basin (Horton et al., 2010b, 2010a), and the Aracataca and Palomino basins from this study. Diagnostic age populations are delimited by gray shaded zones; SM—Santander Massif, CC—Central Cordillera, K-P—Cretaceous–Paleogene volcanic-plutonic arc.

assif, the Perijá Range, the Sierra Nevada de M Santa Marta massif (Ayala et al., 2012; Caballero et al., 2013; Horton et al., 2010b, 2015; Zapata et al., 2010), and the SNSM (Ayala et al., 2012; Caballero et al., 2013; Horton et al., 2010b, 2015; Zapata et al., 2010). The Miocene activity of the Orihueca fault marks a tectonic pulse driven by a significant variation in convergence rate between the Caribbean and South American plates, and the shift from collision to transpression that produced the increased NW-verging thrusting in the interior of the Sierra Nevada de Santa Marta massif (Fig. 14), culminating in the dis-

placement shift from normal to dextral slip of the Oca fault, which segmented the Guajira basin from the North Andean margin in the Pliocene and displaced it to its current location ~55 km to the east (Kellogg, 1984; Tschanz et al., 1974). Other evidence of this episode can be observed in the Leeward Antilles (Van der Lelij et al., 2010; Zapata et al., 2014), where oblique displacements occurred diachronously, and also in the Venezuelan Andes, when transpression was accommodated by vertical tectonics and caused rapid exhumation through the Boconó fault in the Pliocene (Bermúdez et al., 2010).

CONCLUSIONS (1) Post-Oligocene sedimentary rocks found in the Aracataca basin show a major input from Precambrian source rocks from the Sierra Nevada Province. This major input was the consequence of the unroofing of the basement, which accelerated after the deposition of the Aracataca conglomerates foresets. The shift in composition of the clasts means that the Aracataca conglomerates are growth strata that evidence both extension tectonics along the Santa Marta– Bucaramanga fault since the late Oligocene and exhumation of the massif through NW-verging


23

Piraquive et al. thrusts occurring at least since the early Miocene, supported by AFT and ZFT cooling ages. (2) The Precambrian source material was derived from inherited Grenvillian terranes that passed through the apatite partial annealing zone approximately since 25–20 Ma and were subsequently exhumed and affected by surface erosion. (3) The sudden change from muddy oligomictic conglomerates and siltstones to a coarser facies in the sediments points to a steepening slope in the source areas, which led to debris flow into a Gilbert-type delta environment during the transition from a shallow-marine to a more fluvialdominated environment. The facies change is also related to an increase in erosion and therefore probably also to exhumation rates. (4) Provenance analysis of the basin sediments clearly shows that the clastic material was derived by erosion of Precambrian inliers in the Sierra Nevada de Santa Marta massif, and that Permian–Triassic, and Late Cretaceous accreted terrains at the NW corner of the Sierra Nevada de Santa Marta massif did not contribute to sediments, as these tectonic blocks were not yet exhumed during Oligocene–Miocene times. (5) The major shift in provenance between the bottomset and foresets of the Aracataca conglomerates was related to exhumation of the massif during increasing displacement along the Santa Marta–Bucaramanga fault, which occurred between the late Oligocene and early Miocene. The increase in the variety of source rock lithologies in the stratigraphic record is evidence for unroofing of the Precambrian basement and the Central Batholith suite. (6) Detrital thermochronologic ages from the Aracataca basin are evidence for the Santa Marta–Bucaramanga fault being responsible for the increase in relief of the western flank of the Sierra Nevada de Santa Marta massif, as it acted coeval with NW-verging thrusts. In the Palomino basin, extensional faulting started in the late Eocene–Oligocene with the onset of dextral strike-slip activity of the Oca fault in the Miocene as a consequence of the coupling of South American crust and Caribbean crust. This caused faster exhumation of the western flank of the Sierra Nevada de Santa Marta massif, exhuming lower-crustal levels that acted as sources for the Miocene sequences that yield the oldest zircon U-Pb ages and younger detrital ZFT and AFT ages. ACKNOWLEDGMENTS

This research was funded by COLCIENCIAS (the Colombian Administrative Department of Science, Technology and Innovation), in the framework of the project “Evolución Tectónica del margen Caribeño Colombiano,” which provided the resources for field work and sample analysis. This project was

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also supported by a Bonus Qualité Recherche (BQR) Sud grant from ISTerre, Universite Grenoble Alpes. Mélanie Balvay at ISTerre is thanked for help with fission-track sample preparation. Geochronological analyses were done at the facilities of the ETH Zürich Institute of Petrology and Geochemistry in Zürich; Marcel Guillong carefully explained data reduction procedures. Alejandro Beltran provided his knowledge on the methods for U-Pb sample preparation, and discussions on the significance of geochronological data; Pierre Vonlanthene aided us with cathodoluminescence imagery at Universite of Lausanne, Switzerland. Finally, we want to acknowledge the students of the field courses in geology of the Universidad Nacional de Colombia in the years 2013–2014, who explored with us the different creeks and outcrops inland and on the shores of the Sierra Nevada de Santa Marta massif, and who were involved in the development of a more precise map. Camilo Montes and an anonymous person are thanked for their detailed reviews and comments. REFERENCES CITED Acosta, J., Velandia, F., Osorio, J., Lonergan, L., and Mora, H., 2007, Strike-slip deformation within the Colombian Andes, in Ries, A.C., Butler, R.W.H., and Graham, R.H., eds., Deformation of the Continental Crust: The Legacy of Mike Coward: Geological Society, London, Special Publication 272, p. 303–319, doi:10.1144/ GSL.SP.2007.272.01.16. Audemard, F.E., and Audemard, F.A., 2002, Structure of the Mérida Andes, Venezuela: Relations with the South America–Caribbean geodynamic interaction: Tectonophysics, v. 345, p. 1–26, doi:10.1016/ S0040-1951(01)00218-9. Ayala, R.C., Bayona, G., Cardona, A., Ojeda, C., Montenegro, O.C., Montes, C., Valencia, V., Jaramillo, C., 2012, The Paleogene synorogenic succession in the northwestern Maracaibo block: Tracking intraplate uplifts and changes in sediment delivery systems: Journal of South American Earth Sciences, v. 39, p. 93–111, doi:10.1016/j.jsames.2012.04.005. Bayona, G., Ochoa, F.L., Cardona, A., Jaramillo, C., Montes, C., and Tchegliakova, N., 2007, Procesos orogénicos del Paleoceno para la cuenca de Ranchería (Guajira, Colombia) y áreas adyacentes definidos por análisis de procedencia: Geología Colombiana, v. 32, p. 21–46. Bayona, G., Jiménez, G., Silva, C., Cardona, A., Montes, C., Roncancio, J., and Cordani, U., 2010, Paleomagnetic data and K-Ar ages from Mesozoic units of the Santa Marta massif: A preliminary interpretation for block rotation and translations: Journal of South American Earth Sciences, v. 29, p. 817–831, doi:10.1016/j .jsames.2009.10.005. Bayona, G., Montes, C., Cardona, A., Jaramillo, C., Ojeda, G., Valencia, V., and Ayala-Calvo, C., 2011, Intraplate subsidence and basin filling adjacent to an oceanic arc– continent collision: A case from the southern Caribbean– South America plate margin: Basin Research, v. 23, p. 403–422, doi:10.1111/j.1365-2117.2010.00495.x. Bermúdez, M.A., Kohn, B.P., van der Beek, P.A., Bernet, M., O’Sullivan, P.B., and Shagam, R., 2010, Spatial and temporal patterns of exhumation across the Venezuelan Andes: Implications for Cenozoic Caribbean geodynamics: Tectonics, v. 29, TC5009, doi:10.1029/2009TC002635. Bernal-Olaya, R., Mann, P., and Escalona, A., 2015, Tectonostratigraphic evolution of the Lower Magdalena basin, Colombia: An example of an underfilled to overfilled forearc basin, in Bartolini, C., and Mann, P., eds., Petroleum Geology and Potential of the Colombian Caribbean Margin: American Association of Petroleum Geologists Memoir 108, p. 345–398, doi:10.1306/13531943M1083645. Bernet, M., van der Beek, P., Pik, R., Huyghe, P., Mugnier, J.-L., Labrin, E., and Szulc, A., 2006, Miocene to Recent exhumation of the central Himalaya de-

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Science Editor: Aaron J. Cavosie Associate Editor: Luca Ferrari Manuscript Received 9 October 2016 Revised Manuscript Received 16 June 2017 Manuscript Accepted 29 July 2017

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