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Accueil du site → Master → Etats Unis → 1986 → Geology of the Sierra Santa Rosa basin, Baja California, Mexico

San Diego State University (1986)

Geology of the Sierra Santa Rosa basin, Baja California, Mexico

Bryant, Brian Alan

Titre : Geology of the Sierra Santa Rosa basin, Baja California, Mexico

Auteur : Bryant, Brian Alan

Université de soutenance : San Diego State University

Grade : Master of Science in Geology 1986

Three distinct sedimentary sequences are recognized in the Sierra Santa Rosa basin. 1) braided stream gravels lying on basement rocks ; 2) volcanic flows interbedded with alluvial fan and flood-plain deposits ; and 3) above a distinct unconformity alluvial fan and floodplain deposits, without volcanic strata. Five discrete phases of structural deformation are found, 1) deformation in the basement rocks, prior to middle Miocene tec-tonism and local volcanism ; 2) Basin and Range style normal fault-ing ; 3) low-angle normal (detachment) faulting ; 4) prominent sinis-tral strike-slip faulting ; and 5) conjugate shear faulting. During the early Tertiary, the area was tectonically stable, with a gently sloping topography. Sonora, Mexico lay to the east and was the source of exotic clasts, which were eventually de-posited in the Sierra Santa Rosa area in the late-Oligocene or early-Miocene. Local volcanism began approximately 15 Ma. ago, with the onset of "Basin and Range" style deformation and synchronous alluvial fan deposition. A fining-upward trend and the dominance of floodplain deposits suggest that this style of deformation had ceased by late Miocene. In response to crustal dilation southeast of the study area, (early deformation associated with the formation of the Gulf of California) a low-angle normal (detachment) fault formed in the late Miocene or early Pliocene. Following the large scale gravity movement, regional deformation took place, exhibited by high angle nor mal faults and local transform faulting. Cross-cutting rela ti·o ns hips and a faulted soil horizon indicate that a conjugate shear system is active today. with similar characteristics as the San Andreas system. north of the international border.


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