Browsing by Subject "Andes"
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Item Analysis and correlation of volcanic ash in marine sediments from the Peru Margin, Ocean Drilling Program Leg 201: explosive volcanic cycles of the north-central Andes(Texas A&M University, 2007-04-25) Hart, Shirley DawnA detailed investigation of cores from three Peru Margin sites drilled during Ocean Drilling Program (ODP) Leg 201 has been conducted to determine the occurrence of volcanic ash layers and ash accumulations within marine sediments along the Peru shelf. These sites were previously occupied during ODP Leg 112, which suffered from poor and/or disturbed recovery. Advancements in hydraulic piston coring realized since and employed during ODP Leg 201 resulted in better core recovery and less disturbance of sediment throughout the cored intervals. Since marine sediments potentially undergo less erosion and Leg 201 cores benefited from improved recovery, the tephrachronologic record from Leg 201 has yielded a more complete record of explosive activity for North- Central Andean volcanism than previous studies. The improved recovery of Leg 201 cores has enabled the detailed examination of cores from the above sites needed to test the hypothesis that volcanic ash layers and accumulations are more abundant in the study region than previously reported. Due to the low recovery of Leg 112 cores, Pouclet et al. (1993) document only six-ash layers, one ash pod, and eight ash-bearing layers (for a total of 14 cm of ash) from the three sites (Sites 684, 680, and 681) that were reoccupied during Leg 201 (Sites 1227, 1228, and 1229 respectively). This study reports a total of 332.0 cm of ash deposited into the study region which is approximately 24 times that previously reported. Explosive eruption cycles for the Andean region have been deduced from the documentation of Leg 201 ash layers. Our record of volcanic cycles indicates that explosive activity was less intense during the Miocene, in which one ash layer (1.3 cm) was deposited, compared to that of the Pliocene and Pleistocene which experienced most of the explosive volcanic activity in which 52 ash layers (total thickness equal to 208.6 cm) and 14 ash layers (total thickness equal to 122.1 cm) were deposited respectively (Fig. 14). These data are consistent with the previous study of Pouclet et al. (1990); however these data indicate that explosive activity during the Pliocene and Pleistocene was more intense than previously reported.Item An analysis of forest change : a case study of the Chocó-Andean conservation corridor in the Upper Guayllabamba Watershed, Ecuador(2010-05) Gordon, Jessica Danielle; Young, Kenneth R.; Richardson, Richard H.Deforestation in the tropics is considered to be a primary cause for worldwide loss of biological diversity. Future land use decisions have the potential to escalate or ameliorate this global problem. The goal of this research is to present a case study of an analysis of forest change within the Chocó-Andean Conservation Corridor in the Upper Guayllabamba Watershed in Northwestern Ecuador. Fieldwork, remote sensing, and a Geographic Information System (GIS) were used to analyze land use/land cover changes within the corridor. Change detection from 1986 to 2001 using Landsat imagery confirmed that forests were rapidly being converted to other land covers, but patterns of deforestation rates varied dramatically for different types of forests. The average annual rate of overall loss of forest was 2.7% for lower montane forest, 1.7% for mid-slope cloud forest 2.1% for upper montane forest, and 2.0% for riparian forests. The patterns of deforestation also varied based on scales of analysis. For example, the overall loss of forest within the southern portion of the Chocó-Andean Conservation Corridor occurred at an average rate of 1.3% per year, while the overall annual rate of forest loss within particular sub-watersheds varied from 0.2%-3.1% and the annual average rate of overall forest loss surrounding particular communities ranged from 0.3%-3.3%. Fifty interviews were conducted in 2003 in seven communities within the conservation corridor to determine local perspectives of current land use practices, past land use trends, and future land use goals; regional changes in the forest; and opinions of local conservation projects. An intriguing finding of the study is that remote sensing in isolation of fieldwork would have provided incomplete or misleading results. For example, the community that had the most deforestation between 1986 and 2001 was the community where the conservation projects were actually the most successful, based upon local resident opinion. This report asserts that a holistic approach to conservation is needed to reconcile environmental and socio-cultural needs in order to maintain and improve forest habitat and hydrologic connectivity at multiple spatial scales (including community-level, watershed, and regional) by extending conservation efforts beyond protected areas and utilizing a basin-scale perspective to make land use decisions that maintain biodiversity and promote watershed protection.Item Cenozoic evolution of a fragmented foreland basin, Altiplano plateau, southern Peru(2012-05) Fitch, Justin David; Horton, Brian K., 1970-Debate persists on the timing, magnitude and style of crustal shortening, uplift and basin evolution in the Andes. Many studies suggest that the central Andes, including the Altiplano plateau, were gradually uplifted as a result of protracted Cenozoic retroarc shortening. However, recent isotopic studies conclude that the Andes instead rose in pulses, with the most significant event occurring at 10-6 Ma. Many researchers attribute these rapid pulses of uplift to lower lithosphere delamination events. A better understanding of the history of Cenozoic crustal shortening is essential for determination of the mechanism(s) of Andean uplift. The well-exposed Cenozoic San Jerónimo Group was studied in the Ayaviri basin of the northern Altiplano in southern Peru. The 3-5 km-thick succession is situated at 3900-4800 m elevation, between the Western Cordillera magmatic arc and the Eastern Cordillera fold-thrust-belt. New detrital zircon U-Pb geochronological results from four sandstones and one reworked tuff in the San Jerónimo succession show large age populations indicative of syndepositional volcanism between approximately 38 and 27 Ma. A 1600-m-thick magnetostratigraphic section further constrains the depositional timing and accumulation rate of the upper portion of the succession. Sedimentological observations show a rapid transition from cross-stratified braided-fluvial sandstones to proximal channel-fill and alluvial-fan conglomerates at ~30 Ma. Paleocurrent measurements show important temporal and spatial variations in sediment dispersal patterns while conglomerate clast counts show an upsection transition from almost exclusively volcanic input to increasing contributions of clastic, quartzite, and limestone detritus. The corresponding shifts in depositional environment and sediment provenance are attributed to the activation of new thrust structures in close proximity to the basin, namely the Pucapuca-Sorapata fault system, indicating the presence of an eastward advancing fold-thrust belt dating to at least 38 Ma and reaching the Ayaviri basin within the northern Altiplano plateau at ~30 Ma.Item Cenozoic sedimentation and exhumation of the foreland basin system in the Precordillera fold-thrust belt (31-32°S), southern central Andes, Argentina(2013-05) Levina, Mariya; Horton, Brian K., 1970-; Stockli, Daniel F; Ketcham, Richard AAndean retroarc shortening associated with flattening of the Pampean segment of the subducting Nazca plate has resulted in a thin-skinned, east-directed thrust system that partitioned and uplifted Cenozoic foreland basin fill in the Precordillera of west-central Argentina. The temporal and kinematic evolution of the Precordillera fold-thrust belt can be approached through detailed analyses of the clastic sedimentary deposits now preserved in intermontane regions between major thrust faults. In this project, we focus on the uppermost Oligocene–Miocene basin fill exposed in the axial and eastern Precordillera along the San Juan River (Quebrada Albarracín and Pachaco regions) and western flank of the frontal structure (Sierra Talacasto). The nonmarine successions exposed in these regions record hinterland construction of the Frontal Cordillera, regional arc volcanism, and initial exhumation of the Precordillera thrust sheets. Measured stratigraphic sections and lithofacies analyses of the preserved stratigraphic successions reveal initial development at ~24 Ma of an eolian depositional system influenced by regional volcanism and fluvial interactions, becoming a fully eolian system by 21-19 Ma. This system transitioned to a distributary fluvial system in which regions closer to the deformation front recorded sandy-gravelly braided stream sedimentation and regions farther east recorded more-distal floodplain-dominated deposition of thin-bedded mudstone and sandstone. The youngest sedimentary record is preserved in the Albarracin basin, a zone strongly influenced by explosive volcanism of nearby eruptive centers around 14 Ma, followed by a progradational alluvial-fan succession of pebbly, cross-stratified sandstone and thick, pebble to cobble conglomerate. Provenance changes recorded by detrital zircon U-Pb age populations suggest that initial deformation in the Frontal Cordillera coincided with the early Miocene transition from eolian to fluvial deposition in the adjacent foreland basin. The overall upward coarsening nature of the fluvial succession and increased presence of Paleozoic clasts reflect the eastward progression of thin-skinned deformation in the Precordillera and resultant structural partitioning of the synorogenic foreland successions. Using apatite (U-Th)/He thermochronometry we are able to further constrain the age of uplift-induced exhumation and cooling of several Precordillera thrust sheets to 12-9 Ma. This apparent pulse of exhumation is evident in all three sections, suggesting rapid, large-scale exhumation by synchronous thrusting above a single décollement linking major structures of the eastern Precordillera.Item Cupisnique culture : the development of ideology in the ancient Andes(2010-05) Jones, Kimberly L., 1979-; Bourget, Steve, 1956-; Stuart, David; Leoshko, Janice; Papalexandrou, Athanasio; Knapp, Gregory; Burger, Richard L.Cupisnique culture was first identified by Rafael Larco Hoyle in the 1930s through his encounter with an early ceramic style in the Cupisnique Quebrada on the north coast of Peru. Since that time, the ceramic styles, region and time period to which the term ‘Cupisnique’ pertains have remained loosely defined, associated with northern Peru and the Middle Formative Period (1200-900 BCE). The interpretation of Cupisnique culture has further relied on research at the highland site of Chavín de Huántar and a presumed Chavín style horizon. Cupisnique visual materials, however, provide a rich corpus from which to advance analysis of this cultural tradition. In this dissertation, I group the chapters into two parts – background information and substantive material analyses. In Part I, I begin with a concise history of Cupisnique studies, which review permits to establish the objectives and methodology of the investigation. The latter includes archaeological and visual approaches to Cupisnique culture, as well as the geographic, environmental and ecological conditions pertinent to northern Peru. In Part II, I present the results of archaeological fieldwork at the Cumbemayo Canal, near the city of Cajamarca, Peru. Based on the field research, I examine the impact of coastal Cupisnique culture into this north highland region, and I discuss the symbolic role of monumental water management and the creation of a ritualized landscape. The intricate design of the Cumbemayo Canal segues conceptually to the exploration of a larger visual system. Based on a defined corpus of ‘Classic’ Cupisnique stirrup spout bottles, I venture a comprehensive examination of prominent themes, motifs and scenes in Cupisnique iconography. I argue that the latter comprises a reticular visual program that serves to instantiate a complex and developing ideological system. Given the common visual motifs, the tenets of this ideology consist in concepts of capture, sacrifice and fertility, interwoven through a structure of symbolic dualities. In the conclusion, I demonstrate how this proposed Cupisnique ideology conceptually fits with the development of social complexity in northern Peru through and following the Formative Period in the Andes.Item Foreland basin evolution and exhumation along the deformation front of the Eastern Cordillera, northern Andes, Colombia(2010-08) Bande, Alejandro Ezequiel; Horton, Brian K., 1970-; Ketcham, Richard A.; Steel, Ronald J.Tracking the phases of Cenozoic deformation in the Eastern Cordillera of Colombia has proven to be a challenging task. Clear disagreements remain in interpretations of the timing of uplift of the Eastern Cordillera, possibly based on difficulties in distinguishing first-cycle Central Cordillera grains from recycled Eastern Cordillera clasts. This thesis focuses on the Eocene-Pliocene sedimentary record of the eastern foothills of the Eastern Cordillera at a latitude of 6°N, integrating basin analysis with several provenance techniques in order to date the activation of several thrust systems. Based on assessments of depositional environments and sediment dispersal patterns together with mineralogical and geochronological provenance, the onset of uplift in the axial zone of the Eastern Cordillera is constrained to be Oligocene. Prior to uplift, deposition in the eastern foothills was sourced from the eastern craton. Following the Oligocene episode, a continuous eastward advance of deformation is documented. An early Miocene episode probably reactivated the easternmost Cretaceous rift boundary along the eastern side of the Eastern Cordillera. Subsequent footwall shortcuts of those faults initiated activity in the middle to late Miocene, creating an intermontane (piggyback) basin in the eastern foothills at that time. In the preferred interpretation, this in-sequence history of thrust activation represents the main phases of deformation in the Eastern Cordillera from Eocene to Pliocene time, with neotectonic activity recording continued shortening.Item Genetic diversity of the common vampire bat Desmodus rotundus in Ecuador: Testing cross-Andean gene flow(2009-08) Pinto, Christian Miguel; Baker, Robert J.; Rice, Sean H.; Salazar-Bravo, Jorge; Strauss, Richard E.Without human intervention, species distributions are dictated by suitable environmental conditions and limited by geographic barriers, such as rivers, mountain systems, or other unsuitable habitats. An example of an effective barrier to gene flow is the Andes cordillera. In this study, we investigate whether the effects of human disturbance (e.g., cattle ranching, deforestation) can override the natural isolation of populations of the common vampire bat (Desmodus rotundus) that occur on opposite sides of the Andes. In order to test this hypothesis we explore the genetic constitution of Ecuadorian populations of the common vampire bat, including samples collected in a Trans-Andean transect in southern Ecuador, ranging from 251 m on the western side up to an elevation to 2,142 m in its maximum level, and descending to 875 m on the eastern side. For 136 individuals, we sequenced the entire mitochondrial cytochrome-b gene (1,140 base pairs) and fragments of intron 7 of the nuclear fibrinogen, B beta polypeptide gene (705 base pairs). Analyses revealed high mitochondrial DNA structure between populations from opposite sides of the Andes, and little nuclear DNA structure among populations. This type of distribution of variation in the mitochondrial and nuclear genomes is indicative of an asymmetric dispersal pattern where gene flow between groups is mostly a result of male dispersal events. Results indicate that for some species the high human disturbance in the Andean region may result in sympatry of populations from each side of the Andes and permit contact and potential introgression of divergent populations.Item In Ixtli In Yollotl/A (Wise) Face A (Wise) Heart: Reclaiming Embodied Rhetorical Traditions of Anahuac and Tawantinsuyu(2012-10-19) Ri?os, Gabriela RaquelTheories of writing are one of the fundamental ways by which Indigenous peoples have been labeled as "uncivilized." In these discussions, writing becomes synonymous with history, literacy, and often times Truth. As such, scholars studying Nahua codices and Andean khipu sometimes juxtapose the two because together they present a break in an evolutionary theory of writing systems that links alphabetic script with the construction of "complex civilizations." Contemporary scholars tend to offer an "inclusive" approach to the study of Latin American histories through challenging exclusive definitions of writing. These definitions are always informed and limited by language-the extent to which these "writing" systems represent language. However, recentering discussions of writing and language on what Gregory Cajete has called Native Science shifts the discussion to matters of ecology in a way that intersects with current scholarship in bicocultural diversity studies regarding the link between language, culture, and biodiversity. Because of the ways in which language configures rhetoric and writing studies, a shift in understanding how language emerges bears great impact on how we understand not only the histories tied to codices and khipu but also how they function as epistemologies. In my dissertation, I build a model of relationality using Indigenous and decolonial methodologies alongside the Nahua concept of in ixtli in yollotl (a wise face/a wise heart) and embodied rhetorics. The model I construct here offers a path for understanding "traditional" knowledges as fluid and mobile. I specifically look at the relationship between land, bodies, language, and Native Science functions on the reciprocal relationship between those three components in making meaning. I then extend this argument to show how the complex web of relations that we might call biocultural diversity produces and is produced by "things" like images from codices and khipu that in turn help to (re)produce biocultural diversity. Thing theory, in emerging material culture studies, argues for the agency of cultural artifacts in the making of various realities. These "things" always-already bear a relationship to bodies and "nature." Thing theory, then, can challenge us to see artifacts like khipu and Nahua images as language artifacts and help us connect Nahua images and khipu to language outside of a text-based model. Ultimately, I argue that Native Science asks us to see language as a practice connected to biocultural diversity.Item Paleogene sedimentation patterns and basin evolution during Andean orogenesis, Middle Magdalena Valley basin, Colombia(2010-08) Moreno, Christopher John; Horton, Brian K., 1970-; Steel, Ronald J.; Milliken, Kitty L.The Central Cordillera and Eastern Cordillera of the northern Andes form the western and eastern flanks of the north-trending Middle Magdalena Valley basin. Previous estimates for the timing of initial exhumation of the two cordilleras range from ~100 to ~10 Ma. Accurately constraining the spatial and temporal distribution of deformation in Colombia has implications for the shortening history of the Andean convergent margin and the prediction of rapid lateral facies changes in sedimentary basins in close proximity to sediment sources. This study applies sandstone petrographic point counts, field sedimentological analyses of basin fill, and paleocurrent measurements of trough cross-stratification, clast imbrication, and flute casts to provide new insights into the tectonic history of the flanks of the Middle Magdalena Valley basin. Between the lower and upper Paleocene strata of the Lisama Formation, paleocurrent orientations show a shift from northward to eastward transport. This change in sediment dispersal coincides with a shift from a cratonic (Amazonian) to orogenic (Andean) sediment source, as recorded by published U-Pb detrital zircon geochronological results (Nie et al. 2010), suggesting initial uplift of the Central Cordillera by mid-Paleocene time. Later in the basin’s history, establishment of an alluvial-plain system with meandering-channel deposits is recorded in lower–middle Eocene strata of the lower La Paz Formation. Consistent eastward paleocurrents characterize mid-Paleocene through uppermost Eocene strata, indicating a continuous influence of western sediment source areas. However, within the upper middle Eocene succession (~40 Ma), at the boundary between the lower and upper La Paz Formation, sandstone compositions show a dramatic decrease in lithic content. This compositional change is accompanied by a facies shift to amalgamated fluvial channels, reflecting changes in both the composition and proximity of the western sediment source. We attribute these changes to the growing influence of the exhumed La Cira/Infantas paleohighs off the western flank of the present-day Nuevo Mundo syncline. In the uppermost Eocene strata of the Esmeraldas Formation, paleocurrents show a switch to dominantly westward transport that persisted through the Neogene. In addition, deposits show a contemporaneous decrease in the amount of coarse-grained channel deposits. These changes are interpreted to reflect the onset of exhumation in the Eastern Cordillera. The lack of a significant change in sandstone compositions at this boundary suggests a compositional similarity between strata uplifted by the Lisama structure and the Eastern Cordillera. These data support and further refine previous thermochronologic and provenance studies which suggest that uplift-induced exhumation of the Central Cordillera and Eastern Cordillera commenced by mid-Paleocene and late Eocene–early Miocene time, respectively.Item Responses of plants, pastoralists, and governments to social environmental changes in the Peruvian Southern Andes(2012-05) Postigo Mac Dowall, Julio Cesar; Young, Kenneth R.; Crews, Kelley A.; Doolittle, William E.; Knapp, Gregory W.; Parmesan, CamilleAnthropogenic global changes are altering properties and functions of social and ecological systems at multiple spatial and temporal scales. In addition to climate change, the Peruvian Southern Andes has also experienced dramatic political and social change. This dissertation addresses the responses of plants, humans, communities and sub-national governments to the impacts of these changes. Methods from both the social and natural sciences were used at three levels: 1) on the forelands of the Quelccaya ice cap a chronosequence approach was used and 113 quadrats (1m2) sampled the vegetation covering an altitudinal range from 5113 to 4830 m.a.s.l.; 2) with the households of herders in the Quelcaya community surveys, interviews, participant observation, and archival research were employed; and 3) with the three Regional Governments (Arequipa, Cusco, and Puno) interviews with officials and stakeholders were conducted. The results show an upward displacement of the elevational limit of plants and a trend towards homogenization of vegetation. Warming climate, a shortened rainy season, and longer dry and cold spells are the most relevant impacts of climate change in the study area. Responses to these changes occur within households, supra-household units and communities, through dynamic institutions, traditional knowledge, and flexible polycentric social organization. These responses originate from path dependencies generated by human-environment interactions in the Peruvian Southern Andes. For instance, pastoralists increased livestock mobility within their pastures, created wetlands through irrigation, and introduced agriculture of bitter potatoes. The women agriculturalists modified the productive calendar to adjust agricultural tasks to changes in the rainfall regime; they replaced maize for wheat and fava bean, because these crops are more resistant to cold spells. Agro-pastoralists increase institutional water governance and demand infrastructure to improve efficient water use. Synergies between local and regional adaptive responses to climate change may be led by projects like building irrigation infrastructure and strengthening local resource governance, although there are also disjunctions that limit adaption. Local social ecological systems are adaptive and resilient to multi-scale social environmental disturbances by a malleable forging of former strategies to face change, innovation, polycentric social organization, and a dynamic institutional body that promptly response to change.Item Sedimentary, structural, and provenance record of the Cianzo basin, Puna plateau-Eastern Cordillera boundary, NW Argentina(2011-05) Siks, Benjamin Charles; Horton, Brian K., 1970-; Steel, Ronald J.; Milliken, Kitty L.The fault-bounded Cianzo basin represents a Cenozoic intermontane depocenter between the Puna plateau and Eastern Cordillera of the central Andean fold-thrust belt in northern Argentina. New characterizations of fold-thrust structure, nonmarine sedimentation, and sediment provenance for the shortening-induced Cianzo basin at 23°S help constrain the origin, interconnectedness, and subsequent uplift and exhumation of the basin, which may serve as an analogue for other intermontane hinterland basins in the Andes. Structural mapping of the Cianzo basin reveals SW and NE-plunging synclines within the >6000 m-thick, upsection coarsening Cenozoic clastic succession in the shared footwall of the N-striking, E-directed Cianzo thrust fault and transverse, NE-striking Hornocal fault. Growth stratal relationships within upper Miocene levels of the succession indicate syncontractional sedimentation directly adjacent to the Hornocal fault. Measured stratigraphic sections and clastic sedimentary lithofacies of Cenozoic basin-fill deposits show upsection changes from (1) a distal fluvial system recorded by vi fine-grained, paleosol-rich, heavily bioturbated sandstones and mudstones (Paleocene‒Eocene Santa Bárbara Subgroup, ~400 m), to (2) a braided fluvial system represented by cross-stratified sandstones and interbedded mudstones with 0.3 to 8 m upsection-fining sequences (Upper Eocene–Oligocene Casa Grande Formation, ~1400 m), to (3) a distributary fluvial system in the distal sectors of a distributary fluvial megafan represented by structureless sheetflood sandstones, stratified pebble conglomerates and sandstones, and interbedded overbank mudstones (Miocene Río Grande Formation, ~3300 m), to (4) a proximal alluvial fan system with thick conglomerates interbedded with thin discontinuous sandstone lenses (upper Miocene Pisungo Formation, ~1600 m). New 40Ar/39Ar geochronological results for five interbedded volcanic tuffs indicate distributary fluvial deposition of the uppermost Río Grande Formation from 16.31 ± 0.6 Ma to 9.69 ± 0.05 Ma. Sandstone petrographic results show distinct upsection trends in lithic and feldspar content in the Casa Grande, Río Grande, and Pisungo formations, potentially distinguishing western magmatic arc (Western Cordillera) sediment sources from evolving eastern thrust-belt sources (Puna‒Eastern Cordillera). In addition to growth stratal relationships and 40Ar/39Ar constraints, conglomerate clast compositions reflect distinct lithologic differences, constraining the activation of the Cianzo thrust and coeval movement on the reactivated Hornocal fault. Finally, U-Pb geochronological analyses of sandstone detrital zircon populations in conjunction with paleocurrent data and depositional facies patterns help distinguish localized sources from more distal sources west of the basin, revealing a systematic eastward advance of Eocene to Miocene fold-thrust deformation in the central Andes of northern Argentina.Item Structural and stratigraphic evolution of Shira Mountains, central Ucayali Basin, Peru?(2009-05-15) Sanchez Alvarez, Jaime OrlandoThe Ucayali Basin is a Peruvian sub-Andean basin that initially formed during the extensive tectonics of the Early Paleozoic. Originally, the Ucayali Basin was part of a larger basin that extended east of the current Andean chain along the Peruvian territory. Subsequently, this large basin was divided into many smaller sub-Basins during the Andean Orogeny. Today, the basin covers an area of about 140,000 km2, and it is morphologically defined by two well-differentiated structural features: the sub- Andean fold and thrust belt (SFTB) to the west and the Amazon plain and Brazilian shield to the east. It is limited to the north and south by the Contaya and Fitzcarrald Arches respectively, the Andes to the west and the Brazilian Shield to the east. These structural features acted as favorable elements to add sediments and to contribute to the structural development of this basin. The sedimentary section of the basin varies in thickness from 1 to 10 km, with ages of strata ranging from the Paleozoic to Quaternary. The strata were deposited in deep and shallow marine as well as transitional and fluvial continental environments. The most important phase of marine sedimentation was initiated with the transgression of the Cretaceous sea (Aptian ?Albian) over the irregular paleogeography defined by morphologic highs and peneplains. Tectonic features of the basin show structural deformations parallel to the Andean front, where overturned structures are observed. These are commonly cut by thrusts and laterally displaced by strike-slip faults. To better understand the development of the Shira Mountains in the central part of the Ucayali Basin, the structural and stratigraphic relationships were mapped out using a dense grid of 2D seismic reflection data and well log control. Three regional EW cross sections were constructed and restored to the top of the Cretaceous to determine the nature of deformation and faulting during the Paleozoic and Mesozoic. The reconstructions show that Shira Mountains fault was initially a major normal fault bounding a half graben. The fault was reactivated by later compression as a thick-skinned thrust fault that detaches between 21 and 24 km depth. Reactivation occurred during Upper Miocene between 7.2 and 5.3 Ma, corresponding to the Quechua 3 compressive phase of Andean Orogeny. The shortening of the central Ucayali Basin determined by the reconstructed cross sections ranges between 3 and 5.5%.Item Structure of the Patagonian fold-thrust belt in the Magallanes region of Chile, 53° - 55° S Lat.(2013-12) Betka, Paul Michael; Mosher, Sharon, 1951-; Klepeis, Keith A.The southern Patagonian Andes record the Late Cretaceous closure and inversion of the Late Jurassic – Early Cretaceous Rocas Verdes marginal basin, subsequent development of the Patagonian retroarc fold-thrust belt and the Neogene to present tectonic superposition of a left-lateral strike-slip plate margin defined by the Magallanes- Fagnano fault zone. In this dissertation, I present new geologic maps, cross sections and detailed macro- and microscopic structural analyses that describe the geometry and kinematic evolution of the fold-thrust belt and superposed strike-slip deformation over ~200 km along-strike between 53° and 55° S latitude. Results are discussed in the context of the regional tectonic development of the southernmost Andes and are relevant to the understanding of important tectonic processes including the development of a retroarc fold-thrust belt, the formation of a basal décollement below and toward the hinterland of a fold-thrust belt and the spatial distribution of deformation along a strike-slip plate margin. New maps and balanced cross-sections of the Patagonian fold-thrust belt show that it developed during two main phases of Late Cretaceous to Paleogene shortening that were partly controlled by the antecedent geology and mechanical stratigraphy of the Rocas Verdes basin. During the Late Cretaceous, a thin-skinned thrust belt developed above a décollement that formed first in relatively weak shale deposits of the Rocas Verdes basin and later deepened to <1 km below the basement-cover contact. Ramps that cut mechanically rigid volcanic rocks of the marginal basin link the two décollements. Basement-involved reverse faults that cut the early décollements and probably reactivate Jurassic normal faults reflect Paleogene shortening. Shortening estimates increase northwest to southeast from 26 to 37% over 100 km along-strike and are consistent with regional models of the fold-thrust belt. Structural data, kinematic analyses, and microstructural observations from the lower décollement show that it is defined by transposition of several generations of northeast-vergent noncylindrical folds, shear bands, and a quartz stretching lineation that are kinematically compatible with first-generation structures of the fold-thrust belt. Quartz microstructural data from the décollement are consistent with deformation temperatures that decrease from ~500-650° C to ~400-550° C over ~75 km in the transport direction, indicating that the décollement dipped shallowly (~6°) toward the hinterland. The décollement decoupled the underthrust continental margin from the fold- thrust belt and exemplifies the kinematic relationship between shortening that occurs coevally in a retroarc fold thrust-belt and its polydeformed metamorphic ‘basement’. Fault kinematic data and crosscutting relationships show kinematic and temporal relationships between populations of thrust, strike-slip and normal faults that occur in the study area. Thrust faults form an internally compatible population that shows subhorizontal northeast-trending shortening of the fold-thrust belt and is kinematically distinct from populations of normal and strike-slip faults. Both strike-slip and normal faults crosscut the fold-thrust belt, are localized near segments of the Magallanes- Fagnano fault zone, have mutually compatible kinematic axes and are interpreted to be coeval. Strike-slip faults form Riedel and P-shear geometries that are compatible with left-lateral slip on the Magallanes-Fagnano fault-zone. Strike-slip and normal faults occur in a releasing step-over between two overlapping left-lateral, left-stepping segments of the Magallanes fault zone and record a tectonic event defined by sinistral transtension that probably reflects changing plate dynamics associated with the opening of the Drake Passage during the Early Miocene.Item Systematic studies in Pycnophyllum and Pycnophyllopsis (Caryophyllaceae) of the High Andes(2005-05) Timaná, Martin Enrique; Simpson, Beryl BrintnallThis dissertation examines the taxonomy, morphology, and species relationships of two genera in the family Caryophyllaceae, subfamily Alsinoideae: Pycnophyllum and Pycnophyllopsis. These two genera are restricted to the highest peaks of the South American Andes, from Peru to northern Argentina, above the 3500 m of elevation. Pycnophyllopsis subgen. Coquimbo, a new subgenus and species endemic to northern Chile is proposed based on various morphological characters that confirm its status. A combination of detailed morphological study of herbarium specimens and fieldwork resulted in systematic monographs for these two genera. Eight species of Pycnophyllum are here recognized, with the center of diversity in Peru, where seven species are found. The genus Pycnophyllosis consists of nine species. Pycnophyllopsis smithii a new species from central Peru is described. A molecular phylogeny of the family Caryophyllaceae using nrITS is presented and discussed. All studies species are fully described, illustrated, and mapped. Identification keys are provided for the two larger genera. The systematic relationship with other members of the family is also explored.Item Tectonostratigraphic and subsidence history of the northern Llanos foreland basin of Colombia(2011-08) Campos, Henry Miguel; Mann, Paul, 1956-; Horton, Brian K.; Steel, Ronald J.; Cardozo, NestorThe Llanos foreland basin of Colombia is located along the eastern margin of the northern Andes. The Llanos basin is bounded to the north by the Mérida Andes, to the east by the Guiana shield, to the south by the Serrania de la Macarena, and to the west by the frontal foothills thrust system of the Andes (the Cordillera Oriental). The Llanos foreland basin originated in the Maastrichtian, after a post-rift period during the Mesozoic, and recorded an abrupt pulse of middle Miocene subsidence possibly in response to subduction and collision events along the Pacific margin of northwestern South America. Regional east-west shortening, driven in part by collision of the Panama arc along the Pacific margin of Colombia, has built the widest part of the northern Andes. This wide area (~600 km) includes a prominent arcuate thrust salient, the Cordillera Oriental, which overthrusts the Llanos foreland along a broad V-shaped salient that projects 40 km over the northern Llanos foreland basin. In this study, I interpret 1200 km of 2D seismic data tied to 18 wells and regional potential fields (gravity and magnetic) data. Interpreted seismic data are organized into four regional (300 to 400-km-long) transects spanning the thrust salient area of the northern Llanos basin. I performed 2D flexural modeling on the four transects in order to understand the relative contributions of flexural subsidence due to tectonic and sedimentary loading. Sedimentary backstripping was applied to the observed structure maps of six Eocene to Pleistocene interpreted horizons in the foreland basin in order to remove the effects of sedimentary and water loading. Regional subsidence curves show an increase in the rate of tectonic subsidence in the thrust salient sector of the foreland basin during the middle to late Miocene. The flexural models predict changes in the middle Miocene to recent position of the eastern limit of foreland basin sediments as well as the changing location and vertical relief of the flexurally controlled forebulge. Production areas of light oil in the thrust belt and foreland basin are located either south of the thrust salient (Cusiana, Castilla, Rubiales oilfields) or north of the salient (Guafita-Caño Limon, Arauca oilfields) but not directly adjacent to the salient apex where subsidence, source rock thicknesses, and fracturing were predicted by a previous study to be most favorable for hydrocarbons. There are no reported light oil accumulations focused on the predicted present or past positions of the forebulge, but detailed comparisons of seismic reflection data with model predictions may reveal stratigraphic onlap and/or wedging relationships that could provide possible traps for hydrocarbons.Item Uplift and exhumation of the Eastern Cordillera of Colombia and its interactions with climate(2015-05) Anderson, Veronica Jacqueline; Horton, Brian K., 1970-; Ketcham, Richard A; Stockli, Daniel F; Shanahan, Timothy M; Garzione, Carmala NRecent breakthroughs in assessing past elevation using stable isotopes of sedimentary materials have provided important constraints on the timing and geodynamics of surface uplift in various orogenic systems. These advances in paleoaltimetry have enabled discrimination between competing models of topographic development in the Tibetan plateau, have provided constraints on the longevity of the Sierra Nevada as a major topographic feature in western North America, and have highlighted the possible role of lower lithospheric delamination in the central Andes of South America. However, there remains considerable debate over the geodynamic mechanisms involved in Andean uplift, as most available estimates on the timing and pace of past elevation gain show an irregular spatial and temporal distribution. In particular, uncertainty persists over the timing of surface uplift of the Eastern Cordillera in the tropical northern Andes of Colombia. Although changes in sediment accumulation, provenance, and thermochronometric estimates of bedrock exhumation suggest Andean shortening in the Eastern Cordillera since late Eocene-Oligocene time, the rise of the ~2600-m-high Bogotá plateau (Sabana de Bogotá), a intermontane hinterland basin appears to have significantly lagged the onset of shortening in the fold-thrust belt. In addition, there is dramatic variation in structural style along strike within the Eastern Cordillera, making it unclear whether a major basement-involved topographic high (the Garzón Massif) at the southern end of the range was contemporaneous with the rest of the Eastern Cordillera. Studies of pollen assemblages in clastic sedimentary fill of the Bogotá plateau suggest that it may have risen rapidly from ~6-3 Ma and has maintained the same elevation thereafter. However, this scenario of rapid latest Miocene-Pliocene uplift followed by post-3 Ma stasis appears inconsistent with the structural geologic record, as more than half of the total shortening along the eastern Andean flank has occurred since ~3 Ma. We investigate the elevation history of the Bogotá plateau using novel lipid biomarker proxies for past surface temperature and isotopic composition of precipitation, and update the geochronologic framework of this basin using a refined magnetic polarity stratigraphy. We also utilize a multidisciplinary approach to determine the timing of uplift-induced exhumation of the Garzón Massif, employing U-Pb detrital zircon geochronological and sandstone petrographic results as tracers of sedimentary provenance, apatite fission track (AFT) thermochronometry to constrain exhumation, and the isotopic composition and elemental composition of paleosols and carbonate nodules to track climatic shifts associated with the uplift of the Garzón Massif. These approaches indicate that (1) the Bogotá Plateau had likely been partialy elevated prior to the late Miocene (~7.5 Ma) and has been uplifting continuously since then, (2) and that while the timing onset of exhumation of the Garzón Massif is similar to other parts of the Eastern Cordillera, it did not begin to build substantial topography until ~ 6 Ma. These results imply that the Eastern Cordillera did not become a contiguous topographic barrier, until late Miocene-Pliocene time, providing new constraints on the establishment of the Magdalena River, a northward-draining system that contributes an enormous sediment load to the Caribbean Sea, as a discrete system fully separated from the Amazon basin.