Estudios morfoestructurales recientes han puesto en evidencia la existencia de una serie de superficies elevadas en ambos flancos de la Cordillera de la Costa y en el flanco occidental de la Cordillera Principal de Chile central. Mediante el uso de imágenes satelitales se reconocen doce superficies de erosión de bajo relieve, elevadas, con alturas que van desde los 750-850 m.s.n.m. a los 4150-4300 m.s.n.m. entre los 33°30’S y 34°30’S. Estas poseen una amplia distribución dentro la zona de estudio. Se reconocen en la Cordillera Principal sobre rocas intrusivas, sedimentarías y volcano-sedimentarías de edad Mesozoica. Las superficies que se reconocen en la Cordillera Principal se desarrollan sobre rocas de la Formación Abanico, Farellones, intrusivos Cenozoicos y rocas sedimentarias Mesozoicas en su parte oriental. Por último, las que se reconocen en la Depreseión Central se desarrollan tanto sobre rocas Mesozoicas y rocas Cenozoicas (intrusivas, sedimentarias, volcano-sedimentarias). Se reconocen superficies sobre rocas intrusivas como sobre rocas sedimentarias. Las superficies son dislocadas y limitadas por fallas, sobre todo aquellas ubicadas en la CP. La correlación de las doce superficies descritas se basó en la elevación que posee cada superficie. Esto resultó en un total de cinco peneplanicies relictas. Estas representarían cinco pulsos de alzamiento general de superficie, alzadas diferencialemnte en bloques. La edad de las peneplanicies reconocidas en la CP está acotada una edad máxima de 9,8 Ma (edad del Plutón San Gabriel) y una edad mínima de 4 Ma (3.85 ± 0,18 Ma, edad de un pórfido ubicado en la mina de El Teniente, y 4,2 ± 0,3 Ma edad de unas lavas ubicadas al sur del área de estudio). La edad mínima de las peneplanicies en la Cordillera de la Costa está acotada por la edad Pleistocena de las terrazas marinas (la peneplanicie más baja es mas antigua que las terrazas). Y por una edad de exhumación de 40 Ma tomada del Alto del Cantillana, para la superficie más alta, siendo necesaria nuevas edades para constreñir la edad de formación de las peneplanicies. El modelo explica la existencia de cinco peneplanicies relictas y explica el basculamiento al oeste que exhiben algunas superficies, y a mayor escala, el basculamiento que exhibe el orógeno.

abstract: A fundamental gap in geomorphic scholarship regards fluvial terraces in small desert drainages and those terraces associated with integrating drainages. This dissertation analyzes four field-based case studies within the Sonoran Desert, south-central Arizona, with the overriding purpose of developing a theory to explain the formative processes and spatial distribution of fluvial terraces in the region. Strath terraces are a common form (Chapters 2, 3, 4) and are created at the expense of bounding pediments that occur on the margins of constraining mountainous drainage boundaries (Chapters 1, 2, 3). Base-level fluctuations of the major drainages cause the formation of new straths at lower elevations. Dramatic pediment adjustment and subsequent regrading follows (Chapter 3), where pediments regrade to strath floodplains. This linkage between pediments and their distal straths is termed the pediment-strath relationship. Stability of the base level of the major drainage leads to lateral migration and straths are carved at the expense of bounding pediments through an erosional asymmetry facilitated by differential rock decay between the channel bank and bed. Fill terraces occur within the Salt River drainage basin as a result of the integration processes that connect formerly endorheic basins (Chapter 4). The topographic, spatial, and sedimentologic relationship of the Stewart Mountain terrace (Chapter 4) points to a different genetic origin than the lower terraces in this basin. The high Stewart Mountain fill terrace records the initial integration of this river. The strath terraces inset below the Stewart Mountain terrace are a result of the pediment-strath relationship. These case studies also reveal that the under-addressed drainage processes of piracy and overflow have significant impacts in the evolution of drainages the lead to both strath and fill terrace formation in this region. / Dissertation/Thesis / Ph.D. Geography 2013

Elevation, longitudinal profile, and Schmidt hammer data indicate that strath terraces (specifically the lower elevation terraces) mapped in the Fremont River drainage of Capitol Reef National Park are correlative to the terraces of the smaller Pleasant Creek drainage located approximately ten miles to the south. This correlation suggests that drainage development in this area of the Colorado Plateau was strongly dependent upon a regional-scale forcing mechanism (e.g. climate) rather than strictly independent basin-scale processes. Elevations of mapped strath terraces and their associated black volcanic boulder deposits were calculated from geologic maps, Digital Elevation Models (DEM), and Digital Orthophoto Quadrangles of the Fruita and Golden Throne Quadrangles, Wayne and Garfield Counties, Utah. Terraces in both drainages were placed into twenty foot elevation bins and then gathered into larger terrace levels based upon population breaks and the degree of weathering as seen from Schmidt hammer hardness data. Comparison of the two datasets indicate that the two lowest terrace levels of the Fremont River compare well with the two terrace levels of Pleasant Creek both in elevation above the present stream bed and in Schmidt hammer hardness measurements. Our data demonstrate that the Fremont River drainage is likely much older than the smaller Pleasant Creek drainage. Further, correlative terrace data strongly suggests that glacial-interglacial climate forcing played a dominant role in the landscape evolution of both drainages and by inference, the broader Colorado Plateau. Terrace elevation data were compared with recently published cosmogenic ages for several terrace deposits located within the Fremont River drainage. This comparison provides compelling evidence that highest concentrations of preserved terraces may be time correlative with discrete isotopic stages associated with glacial maximum and/or deglacial conditions. Finally, our data also demonstrate that in this area of the Colorado Plateau incision rates are on the order of ~60 to 85 cm/ka, which is on the high end of reported rates from other researchers.