Abstract: This paper provides an overview of the role that geochemistry plays in petroleum systems analysis, and how this can be used to derive constraints on the key elements and processes that give rise to a successful petroleum system. We discuss the history of petroleum geochemistry before reflecting on the next frontier in geochemical applications in hydrocarbon systems. We then review the individual contributions to this Special Publication. These papers present new geochemical techniques that allow us to develop a more systematic understanding of critical petroleum system elements; including the temperature and timing of source-rock deposition and maturation, the mechanisms and timescales associated with hydrocarbon migration, trapping, storage and alteration, and the impact of fluid flow on reservoir properties. Finally, we provide a practical example of how these different geochemical techniques can be integrated to constrain and generate a robust understanding of the prolific Paleozoic petroleum system of the Bighorn Basin.

The Puna Plateau, a high-elevation portion of the central Andean Plateau, possesses some of the thickest crust on Earth, and its structural growth should be reflected in the adjacent foreland basin (present-day Eastern Cordillera and Santa Bárbara system) as a flexural response to crustal thickening via contractional deformation. The Cretaceous–Cenozoic stratigraphy preserved within the Eastern Cordillera and Santa Bárbara system also records the influence of the Cretaceous Salta Rift system, which heavily influenced depositional patterns in the region, particularly during postrift thermal subsidence. The Eastern Cordillera and Santa Bárbara system were significantly modified by Neogene inversion of Salta Rift basins, which subdivide the foreland basin and localize depocenters. Here, we examine results of two-dimensional kinematic models of basin formation and fill that proxy the thermal and mechanical behavior of the Salta rifting, and superimpose upon this rifting event two different scenarios for the temporal growth of the Puna Plateau—one with crustal thickening predominantly in the Eocene, and another with progressive crustal thickening beginning in the early Miocene. The two models attempt to forecast the combined effects of inherited rift history and growth of the Puna Plateau on the development of accommodation within the adjacent foreland basin. A Neogene (Miocene-age) Puna Plateau scenario creates a coeval foredeep within the Salta Rift system, but its magnitude and wavelength are influenced by crustal thickening in the Eastern Cordillera and Santa Bárbara system. In contrast, a Paleogene (Eocene-age) growth scenario for the Puna Plateau results in a substantial amount of coeval flexural accommodation in the adjacent Eastern Cordillera that extends across most of the Salta Rift system, which is broken up by subsequent loading in the Eastern Cordillera and Santa Bárbara system. Thermal subsidence associated with thinned or delaminated mantle lithosphere in the Late Cretaceous also contributes to accommodation and is most prominent during periods of tectonic quiescence. Our modeling results show that: (1) Neogene topographic growth of the Puna Plateau produces a basin subsidence history that is consistent with the geologic record, (2) the Salta Rift system was not buried deeply prior to Neogene exhumation, (3) the eastward advance of the flexural foreland can be related to crustal thickening and elevation gain of the Puna Plateau and Eastern Cordillera at ca. 15 Ma, and (4) interpretations of foreland subsidence history across the Eastern Cordillera may need to consider the influence of thinned mantle lithosphere during Late Cretaceous Salta rifting, which continues to create some accommodation in the region through subtle thermal subsidence.

Convergent orogenic systems pose challenges for the prospector seeking to predict oil and gas reservoirs, as these regions are often data poor. Explorationists, therefore, must often rely on conceptual models to predict the occurrence of oil and gas, and to choose the most favorable exploration areas. This paper examines how different conceptual models of hinterland evolution can influence predictions of hydrocarbon systems in an adjacent foreland. A one-dimensional (1-D) method was developed for assessing incremental hydrocarbon yield during progressive fold-belt deformation and source rock burial and maturation. This method was employed to evaluate the way in which hydrocarbon yield is affected by two different scenarios for the timing of uplift of the Puna Plateau and subsequent burial of the adjacent Metán region of northwestern Argentina. In the first scenario, plateau growth and burial of the Metán region begin in the early Miocene and progress to the present day. In the second scenario, plateau growth and basin formation occur predominantly in the Eocene, with minor deformation from middle Miocene to present. The later load timing decreases the relative volume of liquid hydrocarbons available to fill structural traps. The differences in charge volume and timing between the two scenarios are enhanced in this region as a result of thinned crust and relatively high heat flow that linger from a Cretaceous rifting event. The results of the study provide an example of how boundary conditions obtained from studies of an orogenic hinterland can be used to calculate risk for exploring a potential play within a basin where data are incomplete or inconclusive. They also yield general insights on the use of regional genetic concepts to predict thermal history and source rock maturation and yield in data-poor areas.

Abstract We have been studying the effects of diagenesis on the paleomagnetic signal of lacustrine sediments by examining tephra layers found in unaltered and altered states in the same diagenetic environment. In this paper, we report rock magnetic data from seven such layers in six diagenetic environments ranging from saline-alkaline to mildly alkaline. The effects of diagenesis can be complicated and varied but certain patterns are evident. These patterns indicate that both the physical state of the magnetic grains and the geochemistry of the porewaters are important in determining the effects of diagenesis. In some cases, diagenesis simply reduces the intensity of the original magnetization, but in others it produces a new magnetization that completely overwhelms the original one. Measurements of various rock magnetic parameters have allowed us to relate the changes in intensity to changes in the particle-size distribution of the magnetic carriers. In particular, decreases in intensity appear to be associated with selective dissolution of the fine-grained magnetic carriers or with a general reduction in the quantity of magnetic carriers of all grain sizes; increases in intensity seem to result from a reduction in the numbers of coarse-grained magnetic carriers. Plots of the demagnetization behavior of natural and saturation isothermal remanent magnetizations may be useful in discriminating between unaltered and altered material, especially when used in conjunction with other rock magnetic information.