Bande, A., B. K. Horton, C. J. Ramirez, A. Mora, M. Parra, and D. F. Stockli, Clastic deposition, provenance, and sequence of Andean thrusting in the frontal Eastern Cordillera and Llanos foreland basin of Colombia, Geol. Soc. Amer. Bull., 124, 59-76, 2012, doi:10.1130/B30412.1, #2446 
Sedimentological, provenance, and detrital thermochronological results for basin fill at the modern deformation front of the northern Andes (6°N latitude) provide a long-term, Eocene to Pliocene record of foreland-basin sedimentation along the Eastern Cordillera-Llanos basin boundary in Colombia. Lithofacies assemblages and paleocurrent orientations in the upward-coarsening, 5-km-thick succession of the Nuncha syncline reveal a systematic shift from craton-derived, shallow-marine distal foreland (back bulge) accumulation in the Mirador Formation, to orogen-sourced, deltaic, and coastal-influenced sedimentation of the distal to medial foreland (foredeep) in the Carbonera and Len Formations, to anastomosing fluvial and distributive braided fluvial megafan systems of the proximal foreland (foredeep to wedge-top) basin in the lower and upper Guayabo Formation. These changes in depositional processes and sediment dispersal are supported by up-section variations in detrital zircon U-Pb and (U-Th)/He ages that record exhumation of evolving, compartmentalized sediment source areas in the Eastern Cordillera. The data are interpreted in terms of a progressive eastward advance in fold-and-thrust deformation, with late Eocene-Oligocene deformation in the axial zone of the Eastern Cordillera along the western edge of Floresta basin (Soapaga thrust), early Miocene reactivation (inversion) of the eastern margin of the Mesozoic rift system (Pajarito and Guaicaramo thrusts), and middle-late Miocene propagation of a footwall shortcut fault (Yopal thrust) that created the Nunca syncline in a wedge-top (piggyback) setting of the eastern foothills along the transition from the Eastern Cordillera to Llanos foreland basin. Collectively, the data presented here for the frontal Eastern Cordillera define a general in-sequence pattern of eastward-advancing fold-and-thrust deformation during Cenozoic east-west shortening in the Colombian Andes.
Horton, B. K., Cenozoic evolution of hinterland basins in the Andes and Tibet, in Tectonics of Sedimentary Basins: Recent Advances, edited by C. Busby and A. Azor, Wiley-Blackwell, Oxford, U.K., 427-444, 2012, #2216
Mackey, G. N., B. K. Horton, and K. L. Milliken, Provenance of the Paleocene-Eocene Wilcox Group, western Gulf of Mexico basin: Evidence for integrated drainage of the southern Laramide Rocky Mountains and Cordilleran arc, Geol. Soc. Amer. Bull., (in press), 2012, doi:10.1130/B30458.1, #2443
Nie, J. S., B. K. Horton, J. E. Saylor, A. Mora, M. Mange, C. N. Garzione, and M. Parra, Integrated provenance analysis of a convergent retroarc foreland system: U-Pb ages, heavy minerals, Nd isotopes, and sandstone compositions of the Middle Magdalena Valley basin, northern Andes, Colombia, Earth Sci. Rev., 110, 111-126, 2012, doi:10.1016/j.earscirev.2011.11.002, #2442
Sediment provenance analysis remains a powerful method for testing hypotheses on the temporal and spatial evolution of uplifted source regions, but issues such as recycling, nonunique sources, and pre- and post-depositional modifications may complicate interpretation of results from individual provenance techniques. Convergent retroarc systems commonly contain sediment sources that are sufficiently diverse (continental magmatic arc, foldââ¬âthrust belt, and stable craton) to enable explicit provenance assessments. In this paper, we combine detrital zircon Uââ¬âPb geochronology, heavy mineral identification, Nd isotopic analyses, conventional sandstone petrography, and paleocurrent measurements to reconstruct the clastic provenance history of a long-lived sedimentary basin now exposed in an intermontane zone of the northern Andean hinterland of Colombia. The Middle Magdalena Valley basin, situated between the Central Cordillera and Eastern Cordillera, contains a 5ââ¬â10 km-thick succession of Upper Cretaceous to Quaternary fill. The integrated techniques show a pronounced change in provenance during the Paleocene transition from the lower to upper Lisama Formation. We interpret this as a shift from an eastern cratonic source to a western Andean source composed of magmatic-arc rocks uplifted during initial shortening of the Central Cordillera. The appearance of detrital chloritoid and a shift to more negative õNd(t=0) values in middle Eocene strata of the middle La Paz Formation are attributed to shortening-related exhumation of a continental basement block (La Ciraââ¬âInfantas paleohigh), now buried, along the axis of the Magdalena Valley. The diverse provenance proxies also show distinct changes during middle to late Eocene deposition of the Esmeraldas Formation that likely reflect initial rock uplift and exhumation of the foldââ¬âthrust belt defining the Eastern Cordillera. Upsection, detrital zircon Uââ¬âPb ages and heavy mineral assemblages for Oligocene and younger clastic deposits indicate that the Mesozoic sedimentary cover of the Eastern Cordillera was recycled during continued Cenozoic shortening. Our multidisciplinary provenance study refines the tectonic history of the Colombian Andes and demonstrates that uncertainties related to sediment recycling, nonunique sources, source heterogeneity, and climate in interpreting provenance data can be minimized via an integrated approach.
Parra, M., A. Mora, C. Lopez, L. E. Rojas, and B. K. Horton, Detecting earliest shortening and deformation advance in thrust belt hinterlands: Example from the Colombian Andes, Geology, 40, 2012, doi:10.1130/G32519.1, #2445
Saylor, J. E., D. F. Stockli, B. K. Horton, J. S. Nie, and A. Mora, Discriminating rapid exhumation from syndepositional volcanism using detrital zircon double dating: Implications for the tectonic history of the Eastern Cordillera, Colombia, Geol. Soc. Amer. Bull., 124, 2012, doi:10.1130/B30534.1, #2444
Taylor, M. T., P. A. Kapp, and B. K. Horton, Basin response to active extension and strike-slip deformation in the hinterland of the Tibetan plateau, in Tectonics of Sedimentary Basins: Recent Advances, edited by C. Busby and A. Azor, Wiley-Blackwell, Oxford, U.K., 445-460, 2012, #2304
DeCelles, P. G., B. Carrapa, B. K. Horton, and G. E. Gehrels, Cenozoic foreland basin system in the central Andes of northwestern Argentina: Implications for Andean geodynamics and modes of deformation, Tectonics, 30, TC6013, 2011, doi:10.1029/2011TC002948, #2448
Cenozoic strata in the central Andes of northwestern Argentina record the development and migration of a regional foreland basin system analogous to the modern Chaco-ParanÃÆá alluvial plain. Paleocene-lower Eocene fluvial and lacustrine deposits are overlain by middle-upper Eocene hypermature paleosols or an erosional disconformity representing 10-15 Myr. This 'supersol/disconformity' zone is traceable over a 200,000 km2 area in the Andean thrust belt, and is overlain by 2-6 km of upward coarsening, eastward thinning, upper Eocene through lower Miocene fluvial and eolian deposits. Middle Miocene-Pliocene fluvial, lacustrine, and alluvial fan deposits occupy local depocenters with contractional growth structures. Paleocurrent and petrographic data demonstrate westerly provenance of quartzolithic and feldspatholithic sediments. Detrital zircon ages from Cenozoic sandstones cluster at 470-491, 522-544, 555-994, and 1024-1096 Ma. Proterozoic-Mesozoic clastic and igneous rocks in the Puna and Cordillera Oriental yield similar age clusters, and served as sources of the zircons in the Cenozoic deposits. Arc-derived zircons become prominent in Oligo-Miocene deposits and provide new chronostratigraphic constraints. Sediment accumulation rate increased from ~20 m/Myr during Paleocene-Eocene time to 200-600 m/Myr during the middle to late Miocene. The new data suggest that a flexural foreland basin formed during Paleocene time and migrated at least 600 km eastward at an unsteady pace dictated by periods of abrupt eastward propagation of the orogenic strain front. Despite differences in deformation style between Bolivia and northwestern Argentina, lithosphere in these two regions flexed similarly in response to eastward encroachment of a comparable orogenic load beginning during late Paleocene time.
Moreno, C. J., B. K. Horton, V. Caballero, M. Parra, and J. Sierra, Depositional and provenance record of the Paleogene transition from foreland to hinterland basin evolution during Andean orogenesis, northern Middle Magdalena Valley Basin, Colombia, J. South American Earth Sci., 32, 246-263, 2011, doi:10.1016/j.jsames.2011.03.018, #2469
The Central Cordillera and Eastern Cordillera of the northern Andes form the topographic flanks of the north-trending Magdalena Valley Basin. Constraining the growth of these ranges and intervening basin has implications for Andean shortening and the transformation from a foreland to hinterland basin configuration. We present sedimentological, paleocurrent, and sandstone petrographic results from Cenozoic type localities to provide insights into the tectonic history of the northern Middle Magdalena Valley Basin of Colombia. In the Nuevo Mundo Syncline, the mid-Paleocene transition from marine to nonmarine deposystems of the Lisama Formation corresponds with a paleocurrent shift from northward to eastward transport. These changes match detrital geochronological evidence for a contemporaneous shift from cratonic (Amazonian) to orogenic (Andean) provenance, suggesting initial shortening-related uplift of the Central Cordillera and foreland basin generation in the Magdalena Valley by mid-Paleocene time. Subsequent establishment of a meandering fluvial system is recorded in lower-middle Eocene strata of the lower La Paz Formation.
Mosolf, J. G., B. K. Horton, M. T. Heizler, and R. Matos, Unroofing the core of the central Andean fold-thrust belt during focused late Miocene exumation: Evidence from the Tipuani-Mapiri wedge-top basin, Bolivia, Basin Res., 23, 346-360, 2011, doi:10.1111/j.1365-2117.2010.00491.x, #2302
As the highest part of the central Andean fold-thrust belt, the Eastern Cordillera defines an orographic barrier dividing the Altiplano hinterland from the South American foreland. Although the Eastern Cordillera influences the climatic and geomorphic evolution of the central Andes, the interplay among tectonics, climate and erosion remains unclear. We investigate these relationships through analyses of the depositional systems, sediment provenance and 40Ar/39Ar geochronology of the upper Miocene Cangalli Formation exposed in the Tipuani-Mapiri basin (15âââ‰â¬Å16ÃâðS) along the boundary of the Eastern Cordillera and Interandean Zone in Bolivia. Results indicate that coarse-grained nonmarine sediments accumulated in a wedge-top basin upon a palaeotopographic surface deeply incised into deformed Palaeozoic rocks. Seven lithofacies and three lithofacies associations reflect deposition by high-energy braided river systems, with stratigraphic relationships revealing significant (âÃâ ü500 m) palaeorelief. Palaeocurrents and compositional provenance data link sediment accumulation to pronounced late Miocene erosion of the deepest levels of the Eastern Cordillera. 40Ar/39Ar ages of interbedded tuffs suggest that sedimentation along the Eastern Cordilleraâââ‰â¬ÅInterandean Zone boundary was ongoing by 9.2 Ma and continued until at least âÃâ ü7.4 Ma. Limited deformation of subhorizontal basin fill, in comparison with folded and faulted rocks of the unconformably underlying Palaeozoic section, implies that the thrust front had advanced into the Subandean Zone by the 11âââ‰â¬Å9 Ma onset of basin filling. Documented rapid exhumation of the Eastern Cordillera from âÃâ ü11 Ma onward was decoupled from upper-crustal shortening and coeval with sedimentation in the Tipuani-Mapiri basin, suggesting climate change (enhanced precipitation) or lower crustal and mantle processes (stacking of basement thrust sheets or removal of mantle lithosphere) as possible controls on late Cenozoic erosion and wedge-top accumulation. Regardless of the precise trigger, we propose that an abruptly increased supply of wedge-top sediment produced an additional sedimentary load that helped promote late Miocene advance of the central Andean thrust front in the Subandean Zone.
Reece, R. S., S. P. S. Gulick, B. K. Horton, G. L. Christeson, and L. L. Worthington, Tectonic and climate influence on the evolution of the Surveyor Fan and Channel system, Gulf of Alaska, Geosphere, 7, 830-844, 2011, doi:10.1130/GES00654.1, #2346
Saylor, J. E., B. K. Horton, J. S. Nie, J. Corredor, and A. Mora, Evaluating foreland basin partitioning in the northern Andes using Cenozoic fill of the Floresta basin, Eastern Cordillera, Colombia, Basin Res., 23, 2011, 1 citation, doi:10.1111/j.1365-2117.2010.00493.x, #2303
This paper addresses foreland basin fragmentation through integrated detrital zircon Uâââ‰â¬ÅPb geochronology, sandstone petrography, facies analysis and palaeocurrent measurements from a Mesozoicâââ‰â¬ÅCenozoic clastic succession preserved in the northern Andean retroarc fold-thrust belt. Situated along the axis of the Eastern Cordillera of Colombia, the Floresta basin first received sediment from the eastern craton (Guyana shield) in the Cretaceousâââ‰â¬Åearly Palaeocene and then from the western magmatic arc (Central Cordillera) starting in the mid-Palaeocene. The upper-crustal magmatic arc was replaced by a metamorphic basement source in the middle Eocene. This, in turn, was replaced by an upper-crustal fold-thrust belt source in the late Eocene which persisted until Oligocene truncation of the Cenozoic section by the eastward advancing thrust front. Sedimentary facies analysis indicates minimal changes in depositional environments from shallow marine to low-gradient fluvial and estuarine deposits. These same environments are recorded in coeval strata across the Eastern Cordillera. Throughout the Palaeogene, palaeocurrent and sediment provenance data point to a uniform western or southwestern sediment source. These data show that the Floresta basin existed as part of a laterally extensive, unbroken foreland basin connected with the proximal western (Magdalena Valley) basin from mid-Paleocene to late Eocene time when it was isolated by uplift of the western flank of the Eastern Cordillera. The Floresta basin was also connected with the distal eastern (Llanos) basin from the Cretaceous until its late Oligocene truncation by the advancing thrust front.
Siks, B. C., and B. K. Horton, Growth and fragmentation of the Andean foreland basin during eastward advance of fold-thrust deformation, Puna plateau and Eastern Cordillera, northern Argentina, Tectonics, 30, TC6017, 2011, doi:10.1029/2011TC002944, #2447
The fault-bounded Cianzo basin represents a Cenozoic depocenter between the Puna plateau and Eastern Cordillera of northern Argentina. Analysis of fold-thrust relationships, nonmarine sedimentation, and detrital provenance at 23-24{degree sign}S helps constrain the origin, interconnectedness, and subsequent uplift and exhumation of the Cianzo basin, a potential analogue for intermontane hinterland basins in the Andes. Structural mapping reveals a plunging syncline within the >6000-m-thick, upward coarsening Cenozoic clastic succession in the shared footwall of the N-striking, E-directed Cianzo thrust fault and transverse, NE-striking Hornocal fault. Growth strata within upper Miocene levels indicate syncontractional accumulation adjacent to the Hornocal fault. Measured stratigraphic sections show upsection changes from (1) paleosol-rich, distal-fluvial sandstones (~400 m Paleocene-Eocene Santa BÃÆÃâÃâárbara Subgroup) to (2) braided fluvial sandstones and mudstones (~1400 m upper EoceneÃÆââ¬Å¡Ãâì-Oligocene Casa Grande Formation) to (3) distributary fluvial megafan sandstones and conglomerates (~3300 m upper Oligocene-Miocene RÃÆÃâÃâÃÂo Grande Formation) to (4) alluvial fan conglomerates (~1600 m upper Miocene Pisungo Formation). 40Ar/39Ar geochronological results for interbedded tuffs indicate continuous RÃÆÃâÃâÃÂo Grande deposition from at least 16.34 {plus minus} 0.71 to 9.69 {plus minus} 0.05 Ma. Sandstone petrographic results define distinct upsection trends in lithic and feldspar content, potentially distinguishing the Western Cordillera magmatic arc from Puna-Eastern Cordillera thrust-belt sources. In addition to growth stratal relationships and 40Ar/39Ar ages, conglomerate clast compositions reflect distinct lithologic differences, constraining activation of the Cianzo thrust and coeval reverse slip on the reactivated (inverted) Hornocal fault. Finally, detrital zircon U-Pb ages, paleocurrents, and facies patterns distinguish local from distal sources, revealing a systematic forelandward (eastward) advance of Eocene through upper Miocene fold-thrust deformation.
Gavillot, Y., G. J. Axen, D. F. Stockli, B. K. Horton, and M. D. Fakhari, Timing of thrust activity in the High Zagros fold-thrust belt, Iran, from (U-Th)/He thermochonometry, Tectonics, 29, TC4025, 2010, 6 citations, doi:10.1029/2009TC002484, #2299
Apatite and zircon (U-Th)/He cooling ages are used to quantify the timing of exhumation associated with thrust faulting in the High Zagros fold-thrust belt. Single-grain cooling age data were collected from (1) Cambrian sandstone in various thrust sheets, (2) sandstone and basement clasts derived from structurally controlled salt plugs or fault-bounded slices, and (3) syntectonic Neogene siliciclastics strata. In the northwestern (Kuhrang) and central (Kuh-e Lajin) High Zagros, apatite (U-Th)/He (AHe) ages range from âÃâ ü26.7 to âÃâ ü0.38 Ma. Most cooling and exhumation occurred in the early to middle Miocene, constrained by AHe ages âÃâ ü19âââ‰â¬Å15 Ma from the High Zagros thrust sheet, localized faults, and reset cooling ages from Bakhtiyari deposits. In the southeastern High Zagros (Kuh-e Dinar), cooling occurred later with AHe ages ranging from âÃâ ü16.5 to âÃâ ü0.79 Ma. Here most cooling and exhumation occurred in the late Miocene, constrained by AHe ages âÃâ ü12âââ‰â¬Å8 Ma from the High Zagros fault, and exhumed Paleozoic clasts in synorogenic strata. Zircon (U-Th)/He (ZHe) ages from bedrock samples across the High Zagros are reflective of the precollisional thermal history. The preservation of precollisional ZHe ages limits the pre-Miocene maximum burial temperature of the exhumed strata to < 180ÃâðC, and indicate < 7âââ‰â¬Å9 km of maximum exhumation in the central Zagros. This study shows that thrust activity in the High Zagros and continental suturing along the Zagros suture was underway by at least 19 Ma, and initiated no later than latest Oligocene to early Miocene time (âÃâ ü23 Ma).
Giovanni, M. K., B. K. Horton, C. N. Garzione, B. McNulty, and M. Grove, Extensional basin evolution in the Cordillera Blanca, Peru: Stratigraphic and isotopic records of detachment faulting and orogenic collapse in the Andean hinterland, Tectonics, 29, TC6007, 2010, doi:10.1029/2010TC002666, #2301
Sedimentologic, provenance, oxygen isotope, and 40Ar/39Ar results provide insights into late Cenozoic evolution of an extensional hinterland basin in the Peruvian Andes. The 5ÃÆââââ¬Å¡Ã¬Ã¢ââ¬Ã
â6.5 km Cordillera Blanca composes the glaciated footwall of a lowÃÆââââ¬Å¡Ã¬ÃâÃÂangle normal fault parallel to active contractional structures in the Andean foldÃÆââââ¬Å¡Ã¬ÃâÃÂthrust belt. The ÃÆâÃâ¹Ã¢â¬Â Ãâü200 km long, WSW dipping (19ÃÆââ¬Å¡ÃâðÃÆââââ¬Å¡Ã¬Ã¢ââ¬Ã
â36ÃÆââ¬Å¡Ãâð) Cordillera Blanca detachment fault accommodated >12ÃÆââââ¬Å¡Ã¬Ã¢ââ¬Ã
â15 km of dipÃÆââââ¬Å¡Ã¬ÃâÃÂslip displacement, inducing subsidence of the hangingÃÆââââ¬Å¡Ã¬ÃâÃÂwall supradetachment basin, which is filled by ÃÆâÃâ¹Ã¢â¬Â Ãâü1300 m of conglomerate, sandstone, siltstone, and limited carbonate of the upper MioceneÃÆââââ¬Å¡Ã¬ÃâÃÂPliocene Lloclla Formation. Lithofacies associations are attributed to lacustrine fanÃÆââââ¬Å¡Ã¬ÃâÃÂdelta to proximal, streamÃÆââââ¬Å¡Ã¬ÃâÃÂdominated alluvial fan sedimentation. Provenance data record footwall unroofing of Jurassic through Miocene volcanic and sedimentary rocks during NW directed, axial dispersal of sediment. Provenance data record the appearance of footwallÃÆââââ¬Å¡Ã¬ÃâÃÂderived granite clasts from the upper Miocene Cordillera Blanca batholith and a change to transverse, WSW directed transport. Variations in the character and preservation of basin fill suggest alongÃÆââââ¬Å¡Ã¬ÃâÃÂstrike propagation of the fault through time. Initial extension and subsidence is constrained to the latest Miocene by an 40Ar/39Ar biotite age of 5.4 ÃÆââ¬Å¡Ãâñ 0.1 Ma for a basal tuff in the Lloclla Formation. Estimation of paleolake water composition shows very negative ÃÆÃ
½Ãâô18O(VSMOW) values (ÃÆâÃâ¹Ã¢â¬Â âââ‰â¢13.6ÃÆââââ¬Å¡Ã¬Ãâð toÃÆâÃâ¹Ã¢â¬Â âââ‰â¢18.2ÃÆââââ¬Å¡Ã¬Ãâð), indicating that high elevations comparable to modern were already attained in the Cordillera Blanca during earliest normal faulting and basin evolution. These results lend support to models suggesting that substantial shortening, crustal thickening, and surface uplift were necessary precursor conditions for the generation of the Cordillera Blanca detachment fault.
Horton, B. K., M. Parra, J. E. Saylor, J. S. Nie, A. Mora, V. Torres, D. F. Stockli, and M. R. Strecker, Resolving uplift of the northern Andes using detrital zircon age signatures, GSA Today, 20 (7), 4-9, 2010, doi:10.1130/GSATG76A.1, #2295
Uplift of the Eastern Cordillera in the northern Andes has been linked to orographic climate change and genesis of South America's largest river systems. The timing of initial uplift remains poorly constrained, with most estimates ranging from ca. 60 to ca. 5 Ma. New detrital zircon U-Pb ages from proximal fill of the Llanos foreland basin in Colombia reveal a pronounced mid-Cenozoic shift in provenance from an Amazonian craton source to an Andean fold-thrust belt source. This shift corresponds with changes in detrital zircon (U-Th)/He ages, a conglomeratic unroofing sequence, and a sharp increase in foredeep accumulation rates. These nearly simultaneous changes in zircon age spectra, clast compositions, and sediment accumulation are attributable to latest Oligocene uplift of the eastern flank of the Eastern Cordillera. The timing relationships suggest an early activation of the frontal thrust system, implying a long-term (up to 25 m.y.) cessation of orogenic wedge advance, potentially driven by structural inheritance and/or climate change.
Horton, B. K., J. E. Saylor, J. S. Nie, A. Mora, M. Parra, A. Reyes-Harker, and D. F. Stockli, Linking sedimentation in the northern Andes to basement configuration, Mesozoic extension, and Cenozoic shortening: Evidence from detrital zircon U-Pb ages, Eastern Cordillern, Colombia, Geol. Soc. Amer. Bull., 122, 1423-1442, 2010, 2 citations, doi:10.1130/B30118.1, #2297
Leier, A. L., N. McQuarrie, B. K. Horton, and G. E. Gehrels, Upper Oligocene conglomerates of the Altiplano, central Andes: The record of deposition and deformation along the margin of a hinterland basin, J. Sedimentary Res., 80, 750-762, 2010, 2 citations, doi:10.2110/jsr.2010.064, #2296
The Altiplano Plateau is a high-elevation, internally drained basin located in the hinterland of the Central Andean fold-thrust belt of Bolivia. Cenozoic strata exposed along the margins of the basin provide a unique record of deposition and deformation in this region and can also be applied to understanding synorogenic sedimentation in other fold-thrust belts. We examined Oligocene conglomerate units deposited along the margin of the nascent Altiplano in an effort to better understand how this large hinterland basin has evolved, and examine the relationship between upper crustal deformation and sedimentation in the interior of the Central Andean fold-thrust belt. Facies associations indicate initial deposition occurred in alluvial-fan and braidplain settings, and growth strata in these units record syndeformational deposition. Facies associations in overlying units contain a greater proportion of fine-grained material and were deposited in isolated fluvial channels surrounded by well drained-floodplain deposits. These units are less deformed relative to the alluvial-fan and braidplain deposits, suggesting that deformation waned as deposition continued. Clast counts and paleocurrents indicate that much of the Oligocene sediment was locally derived from Paleozoic strata and deposited in semi-isolated basins located between major thrusts and folds. Uranium-lead ages of detrital zircons from the conglomerate beds correspond to those from surrounding Paleozoic strata, supporting the hypothesis that most of sediment in the Oligocene conglomerate beds were derived directly from these older units. The youngest population of detrital zircon ages in the conglomerate beds are identical to the inferred ages of the deposits themselves. Collectively, the data indicate that the eastern margin of the Altiplano during Oligocene time was dominated by active upper crustal deformation, with alluvial-fan and braidplain deposition occurring in topographic lows. As deformation waned, deposition shifted from alluvial fans to isolated fluvial channels surrounded by extensive floodplains. In the regional setting, Upper Oligocene sediments exposed along the eastern margin of the Altiplano represent the remnants of a feeder zone to large fluvial distributary systems that occupied and infilled the center of the Altiplano.
Mora, A., B. K. Horton, A. Mesa, J. Rubiano, R. A. Ketcham, M. Parra, V. Blanco, J. Garcia, D. Garcia, and D. F. Stockli, Migration of Cenozoic deformation in the Eastern Cordillera of Colombia interpreted from fission track results and structural relationships: Implications for petroleum systems, AAPG Bull., 94, 1543-1580, 2010, 4 citations, doi:10.1306/01051009111, #2300
Previously unreleased fission-track results and regional structural relationships are used to interpret the migration of deformation during Cenozoic orogenesis in the Eastern Cordillera (Cordillera Oriental) of the Colombian Andes. Low-temperature thermochronological results are based on apatite and zircon fission-track analyses of 41 samples collected along vertical and horizontal transects across the Eastern Cordillera at 4ndash7degN latitude. Inverse modeling of fission-track results helps delimit the most probable cooling histories caused by exhumation linked to upper-crustal deformation. These inverse models are constrained by known structural geometries, chronostratigraphy, biostratigraphy, and vitrinite reflectance data.
Murray, B. P., B. K. Horton, R. Matos, and M. T. Heizler, Oligocene-Miocene basin evolution in the northern Altiplano, Bolivia: implications for evolution of the central Andean backthrust belt and high plateau, Geol. Soc. Amer. Bull., 122, 1443-1462, 2010, 2 citations, doi:10.1130/B30129.1, #2298
Nie, J. S., B. K. Horton, A. Mora, J. E. Saylor, T. B. Housh, J. Rubiano, and J. Naranjo, Tracking exhumation of Andean ranges bounding the Middle Magdalena Valley Basin, Colombia, Geology, 38, 451-454, 2010, 3 citations, doi:10.1130/G30775.1, #2217
Saylor, J. E., A. Mora, B. K. Horton, and J. S. Nie, Controls on the isotopic composition of surface water and precipitation in the northern Andes, Colombian Eastern Cordillera, Geochimica et Cosmochimica Acta, 73, 6999-7018, 2009, doi:10.1016/j.gca.2009.08.030, #2116
Empirical datasets provide the constraints on the variability and causes of variability in stable isotope compositions (δD or δ18O) of surface water and precipitation that are essential not only for models of modern and past climate but also for investigations of paleoelevation. This study presents stable isotope data for 76 samples from four elevation transects and three IAEA GNIP stations in the Eastern Cordillera of Colombia and the northern Andean foreland. These data are largely consistent with theories of stable isotope variability developed based on a global dataset. On a monthly basis, the precipitation-amount effect exerts the dominant control on δDp and δ18Op values at the IAEA GNIP stations. At the Bogotá station (2547 m), the δDp and δ18Op values vary seasonally, with isotopic minima correlating with maxima in precipitation-amount. Although surface water samples from Eastern Cordilleran streams and rivers fall on the Global Meteoric Water Line, samples from three of four lakes (2842ââ¬â3459 m) have evaporatively elevated δDsw and δ18Osw values. The IAEA GNIP station data averaged over multiple years, combined with stream and river water data, define vertical lapse rates of −1.8ââ¬Â° km−1 for Δδ18O and −14.6ââ¬Â° km−1 for ΔδD, and are a close fit to a common thermodynamically based Rayleigh distillation model. Elevation uncertainties for these relationships are also evaluated. Comparison of this Colombian dataset with the elevation uncertainties generated by the thermodynamically based model shows that the model underestimates uncertainty at high Δδ18O and ΔδD values while overestimating it for low Δδ18O and ΔδD values. This study presents an independent, empirical assessment of stable isotope-based elevation uncertainties for the northern Andes based on a dataset of sufficient size to ensure statistical integrity. These vertical lapse rates and associated uncertainties form the basis for stable isotope paleoelevation studies in the northern Andes.
Fakhari, M. D., G. J. Axen, B. K. Horton, J. Hassanzadeh, and A. Amini, Revised age of proximal deposits in the Zagros foreland basin and implications for Cenozoic evolution of the High Zagros, Tectonophysics, 451, 170-185, 2008, 32 citations, doi:10.1016/j.tecto.2007.11.064, #2218
The regionally extensive, coarse-grained Bakhtiyari Formation represents the youngest synorogenic fill in the Zagros foreland basin of Iran. The Bakhtiyari is present throughout the Zagros fold-thrust belt and consists of conglomerate with subordinate sandstone and marl. The formation is up to 3000 m thick and was deposited in foredeep and wedge-top depocenters flanked by fold-thrust structures. Although the Bakhtiyari concordantly overlies Miocene deposits in foreland regions, an angular unconformity above tilted Paleozoic to Miocene rocks is expressed in the hinterland (High Zagros).
The Bakhtiyari Formation has been widely considered to be a regional sheet of PlioceneâPleistocene conglomerate deposited during and after major late MioceneâPliocene shortening. It is further believed that rapid fold growth and Bakhtiyari deposition commenced simultaneously across the fold-thrust belt, with limited migration from hinterland (NE) to foreland (SW). Thus, the Bakhtiyari is generally interpreted as an unmistakable time indicator for shortening and surface uplift across the Zagros. However, new structural and stratigraphic data show that the most-proximal Bakhtiyari exposures, in the High Zagros south of Shahr-kord, were deposited during the early Miocene and probably Oligocene. In this locality, a coarse-grained Bakhtiyari succession several hundred meters thick contains gray marl, limestone, and sandstone with diagnostic marine pelecypod, gastropod, coral, and coralline algae fossils. Foraminiferal and palynological species indicate deposition during early Miocene time. However, the lower Miocene marine interval lies in angular unconformity above ~ 150 m of Bakhtiyari conglomerate that, in turn, unconformably caps an Oligocene marine sequence. These relationships attest to syndepositional deformation and suggest that the oldest Bakhtiyari conglomerate could be Oligocene in age.
The new age information constrains the timing of initial foreland-basin development and proximal Bakhtiyari deposition in the Zagros hinterland. These findings reveal that structural evolution of the High Zagros was underway by early Miocene and probably Oligocene time, earlier than commonly envisioned. The age of the Bakhtiyari Formation in the High Zagros contrasts significantly with the PlioceneâQuaternary Bakhtiyari deposits near the modern deformation front, suggesting a long-term (> 20 Myr) advance of deformation toward the foreland.
Hassanzadeh, J., D. F. Stockli, B. K. Horton, G. J. Axen, L. D. Stockli, M. Grove, A. Schmitt, and J. D. Walker, U-Pb zircon geochronology of late Neoproterozoic-Early Cambrian granitoids in Iran: Implications for paleogeography, magmatism, and exhumation history of Iranian basement, Tectonophysics, 451, 71-96, 2008, 13 citations, doi:10.1016/j.tecto.2007.11.062, #2219
Eurasia has largely grown to its present enormous size through episodic addition of crustal blocks by recurring birth and demise of oceans such as Paleotethys and Neotethys. Excluding the Kopet Dagh Mountains in the northeast, crystalline basement rocks of various dimensions are exposed in all continental tectonic zones of Iran. These rocks have traditionally been viewed as continental fragments with Gondwanan affinity and summarily been assigned Precambrian or younger ages, despite the fact that evidence from isotopic dating has largely been lacking. This study presents new ion microprobe and thermal-ionization zircon U-Pb geochronological data from granitoids and orthogneisses from several locations in central Iran and the Sanandajâââ‰â¬ÅSirjan structural zones to determine crystallization ages and investigate the origin and continental affinity of these various crustal fragments. The resulting U-Pb crystallization ages for the granites and orthogneisses range from late Neoproterozoic to Early Cambrian, matching the mostly juvenile Arabianâââ‰â¬ÅNubian shield and Peri-Gondwanan terranes constructed after the main phase of Pan-African orogenesis. TIMS analyses of zircons with inherited cores from western Iran suggest that the Neoproterozoic crust of Iran might not be entirely juvenile, pointing to the potential presence of inherited older Proterozoic components as is common in the eastern Arabian shield. More importantly, the new zircon U-Pb crystallization ages unequivocally demonstrate that crystalline basement underlying the Sanandajâââ‰â¬ÅSirjan zone, central Iran, and the Alborz Mountains is composed of continental fragments with Gondwanan affiliation, characterized by wide spread late Neoproterozoic subduction-related magmatism. The exposure of these late Neoproterozoicâââ‰â¬ÅEarly Cambrian basement rocks in the Iranian regions north of the Zagros is structurally controlled and linked to both large-scale crustal extension and exhumation during Mesozoic and Tertiary time as well as Tertiary collisional tectonics associated with the closure of Neotethys.
Horton, B. K., J. Hassanzadeh, D. F. Stockli, G. J. Axen, R. J. Gillis, B. Guest, A. Amini, M. D. Fakhari, S. M. Zamanzadeh, and M. Grove, Detrital zircon provenance of Neoproterozoic to Cenozoic deposits in Iran: Implications for chronostratigraphy and collisional tectonics, Tectonophysics, 451, 97-122, 2008, 27 citations, doi:10.1016/j.tecto.2007.11.063, #2150
Ion-microprobe Uââ¬âPb analyses of 589 detrital zircon grains from 14 sandstones of the Alborz mountains, Zagros mountains, and central Iranian plateau provide an initial framework for understanding the Neoproterozoic to Cenozoic provenance history of Iran. The results place improved chronological constraints on the age of earliest sediment accumulation during Neoproterozoicââ¬âCambrian time, the timing of the Mesozoic Iranââ¬âEurasia collision and Cenozoic Arabiaââ¬âEurasia collision, and the contribution of various sediment sources of Gondwanan and Eurasian affinity during opening and closure of the Paleotethys and Neotethys oceans. The zircon age populations suggest that deposition of the extensive ~ 1 km-thick clastic sequence at the base of the cover succession commenced in latest Neoproterozoic and terminated by Middle Cambrian time. Comparison of the geochronological data with detrital zircon ages for northern Gondwana reveals that sediment principally derived from the East African orogen covered a vast region encompassing northern Africa and the Middle East. Although most previous studies propose a simple passive-margin setting for Paleozoic Iran, detrital zircon age spectra indicate Late Devonianââ¬âEarly Permian and Cambrianââ¬âOrdovician magmatism. These data suggest that Iran was affiliated with Eurasian magmatic arcs or that rift-related magmatic activity during opening of Paleotethys and Neotethys was more pronounced than thought along the northern Gondwanan passive-margin. For a Triassicââ¬âJurassic clastic overlap assemblage (Shemshak Formation) in the Alborz mountains, Uââ¬âPb zircon ages provide chronostratigraphic age control requiring collision of Iran with Eurasia by late Carnianââ¬âearly Norian time (220ââ¬â210 Ma). Finally, Cenozoic strata yield abundant zircons of Eocene age, consistent with derivation from arc magmatic rocks related to late-stage subduction and/or breakoff of the Neotethys slab. Together with the timing of foreland basin sedimentation in the Zagros, these detrital zircon ages help bracket the onset of the Arabiaââ¬âEurasia collision in Iran between middle Eocene and late Oligocene time.
Guest, B., B. K. Horton, G. J. Axen, J. Hassanzadeh, and W. C. McIntosh, Middle to late Cenozoic basin evolution in the western Alborz Mountains: Implications for the onset of collisional deformation in northern Iran, Tectonics, 26, TC6011, 2007, 7 citations, doi:10.1029/2006TC002091, #2221
Oligocene-Miocene strata preserved in synclinal outcrop belts of the western Alborz Mountains record the onset of Arabia-Eurasia collision-related deformation in northern Iran. Two stratigraphic intervals, informally named the Gand Ab and Narijan units, represent a former basin system that existed in the Alborz. The Gand Ab unit is composed of marine lagoonal mudstones, fluvial and alluvial-fan clastic rocks, fossiliferous Rupelian to Burdigalian marine carbonates, and basalt flows yielding 40Ar/39Ar ages of 32.7 ñ 0.3 and 32.9 ñ 0.2 Ma. The Gand Ab unit is correlated with the Oligoceneââ¬âlower Miocene Qom Formation of central Iran and is considered a product of thermal subsidence following Eocene extension. The Narijan unit unconformably overlies the Gand Ab unit and is composed of fluvial-lacustrine and alluvial fan sediments exhibiting contractional growth strata. We correlate the Narijan unit with the middle to upper Miocene Upper Red Formation of central Iran on the basis of lithofacies similarities, stratigraphic position, and an 8.74 ñ 0.15 Ma microdiorite dike (40Ar/39Ar) that intruded the basal strata. Deformation timing is constrained by crosscutting relationships and independent thermochronological data. The Parachan thrust system along the eastern edge of the ancestral Taleghan-Alamut basin is cut by dikes dated at 8.74 ñ 0.15 Ma to 6.68 ñ 0.07 Ma (40Ar/39Ar). Subhorizontal gravels that unconformably overlie tightly folded and faulted Narijan strata are capped by 2.86 ñ 0.83 Ma (40Ar/39Ar) andesitic lava flows. These relationships suggest that Alborz deformation had migrated southward into the Taleghan-Alamut basin by late Miocene time and shifted to its present location along the active range front by late Pliocene time. Data presented here demonstrate that shortening in the western Alborz Mountains had started by late middle Miocene time. This estimate is consistent with recent thermochronological results that place the onset of rapid exhumation in the western Alborz at ∼12 Ma. Moreover, nearly synchronous Miocene contraction in the Alborz, Zagros Mountains, Turkish-Iranian plateau, and Anatolia suggests that the Arabia-Eurasia collision affected a large region simultaneously, without a systematic outward progression of mountain building away from the collision zone.
Hampton, B. A., and B. K. Horton, Sheetflow fluvial processes in a rapidly subsiding basin, Altiplano plateau, Bolivia, Sedimentology, 54, 1121-1147, 2007, 19 citations, doi:10.1111/j.1365-3091.2007.00875.x, #2220
Although facies models of braided, meandering and anastomosing rivers have provided the cornerstones of fluvial sedimentology for several decades, the depositional processes and external controls on sheetflow fluvial systems remain poorly understood. Sheetflow fluvial systems represent a volumetrically significant part of the non-marine sedimentary record and documented here are the lithofacies, depositional processes and possible roles of rapid subsidence and arid climate in generating a sheetflow-dominated fluvial system in the Cenozoic hinterland of the central Andes. A 6500 m thick succession comprising the Late EoceneâOligocene Potoco Formation is exposed continuously for >100 km along the eastern limb of the Corque syncline in the high Altiplano plateau of Bolivia. Fluvial sandstone and mudstone units were deposited over an extensive region (>10 000 km2) with remarkably few incised channels or stacked-channel complexes. The Potoco succession provides an exceptional example of rapid production of accommodation sustained over a prolonged period of time in a non-marine setting (>0·45 mm year−1 for 14 Myr). The lower ≈4000 m of the succession coarsens upward and consists of fine-grained to medium-grained sandstone, mudstone and gypsum deposits with palaeocurrent indicators demonstrating eastward transport. The upper 2500 m also coarsens upward, but contains mostly fine-grained to medium-grained sandstone that exhibits westward palaeoflow.
Zhou, J. Y., J. H. Wang, B. K. Horton, A. Yin, and M. S. Spurlin, Sedimentology and chronology of Paleogene coarse clastic rocks in east-central Tibet and their relationship to early tectonic uplift, Acta Geologica Sinica, 81, 398-408, 2007, #2327