Earth deformation initially delineates basins and, together with climate and provenance, guides the distribution of sediments. In geosynclines and mobile belts the rise and fall of welts and troughs influence the facies sharply. Even in cratonic regions, tectonic control of sedimentation is clear. Crustal deformation also occurs after deposition, and the positionings and geometric details of structures are controlled by the mechanical properties and inhomogeneities of the strata. In such cases stratigraphy clearly has guided structure. In many regions, however, deformation and deposition have occurred together, and an interplay continues intermittently for long periods of time. As a result, deformation guides deposition which in turn guides deformation et cetera. Such an nterrelated continuum regulates the movements of fluids, including oil and gas, within the strata.

Modern analysis of basin history requires a careful reconstruction of the interplay between deformation and deposition. The analysis is most effective if one begins with the present and works backward in time, sorting out the geological events and their effects one by one. Knowledge gained recently of modern depositional environments and the geometry and distribution of sedimentary facies within them provides the geologist with reference models of the appearance of his study area in the past. It is not sufficient to visualize static strata as having been deformed suddenly after deposition and lithification. Instead the geologist must find techniques which permit him to reconstruct the panorama of continuous changes not only of the stratigraphy through time, but also the folding, fault ng, and movements of fluids within the strata. (Crowell)

The sediments of the Ventura basin are more severely deformed than those of most oil-producing provinces. This circumstance, in combination with the narrow linear aspect of the basin and the abundance of outcrops, yields more conspicuous examples of structural-stratigraphic relations than usually are encountered.

The basin's early history reveals a characteristic common to all depositional areas, i.e., the manner in which basin and basin-margin structure affected sedimentation. A second feature of basin history that is not so conspicuous elsewhere is the manner in which stratigraphy affected later deformation of the basinal sediments, as well as oil accumulation in them.

Major high-angle reverse faults now exist locally along the north and south boundaries of the main Pliocene basin. The very thick (world-record) Pliocene section not only thins toward these faults, but also typically has a notable decrease in permeable sandstone percentage.

The fault zones contain fine-grained terrigenous clastic rocks and siliceous shale, which served as a lubricant for fault movements. The fault zones probably

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also served as intermittent avenues for migration of sub-fault oil into producing structures above the fault. (Paschall)

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