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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. / text

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. / text

Sedimentary rocks in the Mecca Hills record a 3-4 Myr history of basin evolution and deformation within the southern San Andreas fault (SAF) zone. Detailed geologic mapping, measured sections, lithofacies analysis, and preliminary paleomagnetic data indicate that sedimentation and deformation in the Mecca Hills resulted from evolution of local fault zone complexities superimposed on regional subsidence and uplift. Sediment was derived from sources northeast of the SAF and transported southeast along the fault zone in large rivers, alluvial fans, and a smaller fault-bounded lake. Inversion of the Painted Canyon fault from oblique SW-side down to SW-side up slip was the main control on local deposition and deformation. Regional controls are suggested by an angular unconformity observed in the Mecca and Indio Hills along ~50 km of the SAF and synchronous post-740 ka uplift northeast of the SAF along ~80 km of the fault zone.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22424号 / 工博第4685号 / 新制||工||1731(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 林 為人, 教授 小池 克明, 准教授 村田 澄彦 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM