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This thesis describes the gravity interpretation of Bahia State, Brazil, which comprises the northern Sao Francisco craton, the Upper Proterozoic fold belts and the basins adjacent to the continental margin. The study centres on the isostatic analysis of the region and on the interpretation of large and high amplitude negative anomalies which occur over the Precambrian and the sedimentary basins. The isostatic analysis of the northern Sao Francisco craton was carried out using the isostatic response function technique. Taking into account subsurface loads, an elastic plate with a minimum effective thickness of 20-40 km explains the observed isostatic response function. The subsurface loads are (l) a slight thickening of the crust under the Espinhaco Fold System and (2) five to ten kilometres of low density rocks in the upper crust. A large and high amplitude ( - 50 mGal ) negative anomaly of shallow origin, centred near the western border of the Paramirim complex and parallel to the Espinhaco fold belt, is interpreted as caused by a large and mainly unexposed granite batholith. The granite substantially underlies the fold belt and extends towards the centre of the Paramirim complex. The minimum density contrast between the granite and the country rocks is estimated to be -0.06 g cm(^-3). The thickness of the granite is 8 to 13 km for density contrasts of -0.15 g cm(^-3) to -0.10 g cm(^-3). A series of high amplitude negative anomalies (50 to 100 rrGal), without flanking positive anomalies, characterizes the onshore Reconcavo, Tucano and Jatoba basins, which were ail formed in connection with the South Atlantic opening. The gravity interpretation indicates up to 7 km of sediments infilling these basins and no significant Mo ho upwarp beneath. In contrast, the gravity anomalies over the offshore Jacuipe and Sergipe-Alagoas basins are explained by a thick accumulation of sediments on a strongly attenuated crust. The onshore basins show short-lived subsidence ( < 25 Ma) with little, if any thermal subsidence. Syn-rift and post-rift (thermal) sedimentation is observed only in the continental margin basins. A mechanism in which upper crustal extension in one region (onshore basins) is compensated and balanced against lower extension in another region (offshore basins), through a detachment fault, may explain the way these basins formed.

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Surface and subsurface data indicate that Cretaceous strata in the southern Ventura basin are part of the northward prograding Chatsworth submarine fan. The fan extends westward as far as Trancas Beach in the Santa Monica Mountains and wells in the Oxnard Plain and on Oak Ridge. The eastern edge of the fan is constrained by wells in western San Fernando Valley which contain fine-grained strata which may have been deposited east of the Chatsworth fan. The Nonmarine Simi Conglomerate overlies the Cretaceous and is itself overlain by Paleocene marine beach sandstone and siltstone. These marine strata do not extend eastward into the San Fernando Valley. The lower Paleocene and Cretaceous strata were overlapped by the upper Paleocene Santa Susar1a and middle Eocene Liajas Formations. Sedimentation patterns for the Santa Susana and Llajas may be explained by two models: (1) A northwest-trending submarine ridge on which muds and silts were deposited, was flanked on the northeast and southwest by troughs receiving deep-water sands. (2) Both formations were deposited on a southwest-facing shelf, slope, and turbidite trough. Subsurface data important in basin analysis include 1) bathyal paleo- bathymetry for the entire Santa Susana, 2) sand channels in the Santa Susana which possibly funneled sediment westward down a submarine slope, 3) shelf-facies(?) Eocene strata with neritic to upper bathyal paleobathymetry in Oxnard Plain, and 4) Llajas fades in northern Simi Valley suggesting gradation upward from a shallow marine to outer shelf or slope environment. Facies correlations across the Simi fault indicate no large-scale post- Paleogene strike-slip displacement. If these sequences were rotated, as suggested by paleomagnetic data, the restored Cretaceous fan would come from the east and the restored Paleocene shoreline would face south. Thus paleogeography for the Cretaceous is simplified by the rotation hypothesis, but Paleocene paleogeography is made more complicated. / Graduation date: 1983

Thesis (B.Sc. (Hons.))--University of Adelaide, Dept. of Geology, 1986? / 1 folded chart in back pocket. Includes bibliographical references.

Thesis--Madras University. / Bibliography: p. [149]-157.

Thesis--Wisconsin. / Includes bibliographical references (leaves 89-90).

Thesis (Ph. D.)--Oregon State University, 1995. / Typescript (photocopy). Includes bibliographical references (leaves 176-183). Also available on the World Wide Web.