ABSTRACT We describe local structural controls on deposition above contractional fault-related folds that yield patterns of stratigraphic onlaps, pinch-outs, and facies transitions that are diagnostic of folding mechanism. In folds that grow by kink-band migration, stratigraphic onlaps and pinch-outs that formed at emergent fold scarps are incorporated into fold limbs and aligned along growth axial surfaces. In contrast, the positions of these same features in structures that grow primarily by limb rotation are more variable and are controlled directly by sedimentation-to-uplift ratio. We present kinematic models and natural examples that integrate seismic reflection data and well control to describe these structural influences on growth stratigraphy. An understanding of this interplay between local deformation and deposition helps us infer the positions of subtle pinch-outs that may provide hydrocarbon traps and can yield a detailed history of structural development.

Abstract Integrated studies of the hydrocarbon system in frontier areas are important to assess exploration risk. The Rubio block located in the Táchira Depression has been the focus of various geological studies, yet very few studies of its petroleum system have been published. Based on seismic, surface geologic, and geochemical data, a study of the petroleum system has been developed. We have identified, based on quality limited seismic and surface data, at least three major periods of deformation in the study area, ranging from the Upper Cretaceous to the present. The first event is of Late Cretaceous age and is characterized by compression. The second period is characterized by extension and took place at least during the Paleocene. Both events may be related to the development of the Colombian Central Cordillera and the flexure caused by its tectonic load, which affected western Venezuela from the Upper Cretaceous to the Paleocene. The third event is characterized by compression that has occurred quite recently, and it may be associated with the development of the Mérida Andes. This last event is responsible for the development of the major structures in the Rubio block. It is worth noting that western Venezuela also was affected by a Jurassic extensional event that is not illuminated by the seismic data of the study area but has been amply shown in both surface and seismic data in the surrounding areas. According to the 1-D and 2-D geochemical modeling results, we propose that maturity of the source rock (the La Luna Formation) is greater to the west than to the east. Hydrocarbon expulsion from the source rock started in the western portion of the area 25 m.y. This local kitchen stopped expelling because of its uplift, which was caused by the latest compression. On the other hand, the La Luna Formation in the eastern portion started to expel hydrocarbon very recently, which is still ongoing. This active oil kitchen may be feeding the oil seeps in the eastern part of the study area.

ABSTRACT The Santa Barbara Channel basin, located in southern California, is undergoing significant shortening. We use contour and axial surface maps of several horizons and balance regional cross sections through the eastern and western Santa Barbara Channel, as well as structural profiles and surface restoration techniques, to analyze how the subsurface structures in this basin accommodate the deformation. Reflection seismic profiles show that some of the mapped structures are active (e.g. the Oak Ridge, the Blue Bottle, the Pitas Point, the Dos Cuadras, the Carpinteria and the Santa Rosa trends) and accommodate a large part of the shortening, whereas others are completely inactive (e.g. the Western Deep trend). Restoration of seismic profiles shows that structures in the basin grow by kink-band migration. In cross sections, we interpret that to the east, there are mainly two levels of faulting. The Oak Ridge trend develops above the deeper one, whereas the Dos Cuadras, the Pitas Point, the Carpinteria and the Blue Bottle trends develop on the shallow one. To the west, we interpret the existence of three levels of faulting. A mid-crustal detachment is the deepest one, the Blue Bottle and the Western Deep trends are developed above the shallowest one. The Santa Rosa trend is growing above an intermediate one. The axial surface and contour maps suggest that the Blue Bottle and Pitas Point trends end progressively to the west, accommodating an average of 2 to 4 km of shortening. The Oak Ridge trend terminates at a tear fault south of the Santa Barbara city. This fold accommodates about 11 km of slip. We show, using map view restoration, that slip involved in this trend is transferred to the west through a mid-crustal bedding parallel detachment fault. The Dos Cuadras trend extends beyond the mapped area both to the east, where it becomes the Ventura anticline, and to the west. We determine that the Dos Cuadras and Carpinteria trends accommodate about 11 km of shortening. The Santa Rosa trend is a new mapped trend in the southwestern area of the basin.