Showing papers on "Pull apart basin published in 1976"

Late Cenozoic fault patterns and stress fields in the Great Basin and westward displacement of the Sierra Nevada block

Abstract: The patterns of late Cenozoic faulting in the Great Basin apparently delimit two deformational fields, each extensional but contrasting in magnitude and style of extension. The field of smaller magnitude, which shows about 10 percent extension, occupies the northern and most of the central part of the Great Basin. It is characterized by steeply dipping normal faults and gently tilted blocks, with a preferred north to northeast trend. Evidence of greater extension occurs in the other deformational field, which lies between Walker Lane and the Sierra Nevada and extends across the narrow southern end of the Great Basin. This field contains most of the complementary strike-slip faults (northwest-striking right-lateral and northeast-striking left-lateral faults), long recognized as major components of the structural framework. It also contains abundant normal faults, most of which strike north to northeast. In certain areas, extension of 50 percent or more is indicated in the association of strike-slip and normal faults and in the palinspastic restoration of fault blocks that have been steeply tilted along gently dipping normal faults. These contrasts in structural pattern and apparent percentage of extension may be related to westward movement of the Sierra Nevada block and southward narrowing of the Great Basin. The faults along which strike-slip displacement occurred in late Cenozoic time appear to have functioned as conjugate shears, the shears and associated normal faults being first-order extensional features. The fault pattern also invites a simplistic interpretation that is based on the orientation of three mutually perpendicular directions of stress. The major normal faults, which strike north-northeast in most parts of the Great Basin, suggest a pervasive horizontal minimum compressive (maximum tensional) stress that is oriented west-northwest. Maximum compressive stress would be oriented perpendicularly where the horst and graben structure predominates and horizontally to the east-northeast where the strike-slip faults are abundant.

A new look at the otway basin

Abstract: The Otway Basin in western Victoria and eastern South Australia is a primarily offshore, Upper Cretaceous to Recent basin overlying a Lower Cretaceous basin. The major stratigraphic break developed after the deposition of the Upper Cretaceous Sherbrook Group. The offshore part of the basin in Victorian and Tasmanian waters has been explored since 1960 with a series of seismic surveys which improved in quality after 1971. Further offshore seismic data has been provided by the Bureau of Mineral Resources (BMR) Continental Margins Survey and by Shell Petrel lines. Seven wells have been drilled in Victorian/Tasmanian waters and six in South Australian waters. Stricter control of recording noise levels and continuous velocity analyses in processing, plus the use of refraction in seismic surveys since 1971 has enabled an improved interpretation of the Victorian/Tasmanian part of the basin. The Upper Cretaceous clastic sediments were deposited in an intracratonic basin with a maximum thickness of approximately 20 000 feet. The northeast flank is formed by a series of down-to-basin faults and increased movement on these faults and overall tilting gave a marginal basin in Tertiary time so that the section comprises a series of outbuilding sedimentary wedges. A major basin started to form across southern Australia in Lower Cretaceous times. In the Upper Cretaceous the three discrete Bass Strait basins developed from the major basin with Australia and Antarctica still in close relationship. Plate separation was associated with the change from an intracratonic basin to a marginal basin. Further separation produced no major change in the nature of deposition in the marginal basin.