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Results for “Pacific Section S.E.P.M.”

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6 recordsLinked to original sources
USGS1998

Field trip road log—geology and tectonics of the Gualala block

The Pacific Section, S.E.P.M. 1998 Fall Field Trip will traverse rocks of the Gualala block of northern California. Seven stops (Figure 1) will be made in one and a half days and will examine a variety of geologic features and rock types in this significant area. The field trip is an outgrowth of a symposium held at the 1998 Annual Meeting of the Pacific Section, S.E.P.M. in Ventura, California, where eleven papers were presented. The field trip stops will focus on the effects of the 1906 California earthquake, the nature and significance of the spilite of Black Point, the basement of the region, comparison of different turbidite sequences in the Paleocene/Eocene German Rancho Formation, young tectonics in the northern part of the block, the paleontology and structural significance of the Upper Cretaceous Anchor Bay Member of the Gualala Formation of Wentworth (1966), and the geology of the Miocene Point Arena Formation at Arena Cove. At several stops, the origin of the Gualala block which has traveled progressively northwest as a result of movement along the San Andreas fault system will be discussed.

Book chapter↗
USGS1984

Implications of paleomagnetism for the tectonic history of the Eastern Klamath and related terranes in California and Oregon

Paleomagnetic study of Permian to Jurassic volcanic and sedimentary strata of the Eastern Klamath terrane has shown the remanent magnetism of these rocks to be prefolding and primary. The Permian and Triassic rocks are both indicated to have rotated 100° clockwise, while the Jurassic strata have rotated 60° clockwise. The respective amounts of rotation for Permian and Jurassic strata are similar along two widely-spaced transects of the arcuate Eastern Klamath terrane, which indicates rigid-block rotation rather than oroclinal bending. These results suggest that the Permian and Triassic strata began to rotate during Late Triassic or Early Jurassic time, possibly in response to the beginning of accretion of the Eastern Klamath terrane to the continental margin. Measurements on superjacent Cretaceous strata indicate that the rotation of the Eastern Klamath terrane as well as other parts of the Klamath Mountains province was virtually compete by Early Cretaceous time. The virtual cessation of rotation probably marked the completion of the accretion of the Eastern Klamath terrane to North America. Neither these nor other data currently available show evidence for any significant latitudinal displacement of the Klamath Mountains terranes.

Pacific Section S.E.P.M.↗
USGS1984

Paleomagnetic constraints on the interpretation of early Cenozoic Pacific Northwest paleogeography

Widespread Cenozoic clockwise tectonic rotation in the Pacific Northwest is an established fact; however, the geologic reconstructions based on these rotations are the subject of continuing debate. Three basic mechanisms have been proposed to explain the rotations: (1) simple shear rotation of marginal terranes caught in the dextral shear couple between oceanic plates and North America; (2) rotation during oblique microplate collision and accretion to the continental margin; and (3) rotation of continental margin areas during episodes of intracontinental extension. In areas where detailed structure and stratigraphy are available, distributed shear rotations are amplv demonstrated paleomagnetically. However, rotation due to asymmetric interarc extension must be significant, especially for the Oregon Coast Range, in light of recent estimates of large Tertiary extension across the northern Basin and Range. The relative importance of shear versus extension is difficult to determine, but shear could account for nearly onehalf of the observed rotations. Oblique microplate collision has not contributed significantly to the observed Cenozoic rotations because most of the rotation post-dates collision-related deformation in the Oregon and Washington. Coast Range. The resultant continental reconstructions suggest that about 300 km of extension has occurred at 42°N. latitude (southern Oregon border) since early Eocene time. This reconstruction suggests that Cretaceous sedimentary basins east of the Klamath Mountains have undergone significant Tertiary extension (about f<0%) , but little rotation. Upper Cretaceous sedimentary rocks in the Blue Mountains of Oregon near Mitchell are probably rotated at least 15° and perhaps as much as 60°, which allows considerable latitude in the restoration of that part of the basin.

Pacific Section S.E.P.M.↗