Mesozoic tectonic inversion in the Neuquen Basin of west-central Argentina produced two main fault systems: (1) deep faults that affected basement and syn-rift strata where preexisting faults were selectively reactivated during inversion based on their length and (2) shallow faults that affected post-rift and syn-inversion strata. Normal faults formed at high angle to the reactivated half-graben bounding fault as a result of hangingwall expansion and internal deformation as it accommodated to the shape of the curved footwall during oblique inversion. Contraction during inversion was initially accommodated by folding and internal deformation of syn-rift sedimentary wedges, followed by displacement along half-graben bounding faults. We suspect that late during inversion the weight of the overburden inhibited additional fault displacement and folding became the shortening-accommodating mechanism. A Middle Jurassic inversion event produced synchronous uplift of inversion structures across the central Neuquen Basin. Later inversion events (during Late Jurassic, Early Cretaceous, and Late Cretaceous time) produced an "inversion front" that advanced north of the Huincul Arch. Synchroneity of fault reactivation during the Callovian inversion event may be related to efficient stress transmission north of the Huincul Arch, probably due to easy reactivation of low-dip listric fault segments. This required little strain accumulation along "proximal" inversion structures before shortening was transferred to more distal structures. Later inversion events found harderto- reactivate fault segments, resulting in proximal structures undergoing significant inversion before transferring shortening. The time between the end of rifting and the different inversion events may have affected inversion. Lithosphere was probably thermally weakened at the onset of the initial Callovian inversion phase, allowing stress transmission over a large distance from the Huincul Arch and causing synchronous inversion across the basin. Later inversion affected a colder and more viscous lithosphere. Significant strain needed to accumulate along proximal inversion structures before shortening was transferred to more distal parts of the basin. Timing of inversion events along the central Neuquen Basin suggest a megaregional control by right-lateral displacement motion along the Gastre Fault Zone, an intracontinental megashear zone thought to have been active prior to and during the opening of the South Atlantic Ocean.

Thesis (D. Min.)--New Orleans Baptist Theological Seminary, 1992. / Questionnaires and other appendices are in Spanish and English. Includes abstract and vita. Includes bibliographical references (leaves 147-150).

The seaward end of modern rivers is characterized by the interactions of marine and fluvial processes within a tract known as the fluvial to marine transition zone (FMTZ), which varies between systems due to the relative strength of fluvial, tidal and wave processes. River deltas also show a range of different morphologies and architectures linked to the balance between these depositional processes. However sedimentological interpretations of fluvial to shallow-marine deposits from the rock record commonly relate sedimentary structures to single depositional processes and give greater importance to facies-based observations rather than to architectural style. To better understand how fluvial and tidal process interactions are preserved and distributed in the rock record, deltaic deposits of the Middle Jurassic Lajas Formation (Neuquén Basin, Argentina) have been investigated in large-scale outcrops. The degree of tidal influence has been evaluated using both facies-scale observations and architecture analysis, and critically testing the application of the FMTZ concept in ancient deposits. The characteristics of the reconstructed FMTZ together with the architectural elements described from the Lajas Formation are consistent with an interpretation of a fluvial-dominated, tide-influenced delta, rather than a tide-dominated system, as previously proposed. The results presented herein suggest that highstand systems tract progradational deltas of the Lajas Fm. accumulated largely under microtidal conditions. Comparison of facies and architecture between modern tide dominated deltas and published examples from ancient successions shows a fundamental mismatch; modern systems are mud-dominated with laterally accreting tidal bars while ancient examples are sand-rich and dominated by forward accreting deposits. This thesis argues that the majority of ancient sand-rich successions interpreted as tide-dominated deltas might have formed in large parts in a fluvial-dominated, tide-influenced delta system and that tide-dominated deltas may have not been adequately described from the rock record yet. The improved identification of process interactions presented in this study is crucial to refining classifications of shallow-marine successions and to understanding the recorded spatial and temporal evolution of ancient depositional systems. This can have fundamental implications in refining reservoir models and predicting correct geometries in hydrocarbon-bearing successions.

This study focuses on the facies changes from the lower slope to toe-of-slope to basin floor over a 10 km outcrop belt, in down-dip and oblique-strike directions to the basin margin. The Jurassic Los Molles Formation in Neuquen Basin, Argentina represents the slope and basin floor of basin margin clinoforms, coeval with the shallow water and fluvial deposits named Las Lajas and Challaco formations respectively. The shallow and deep water deposits are diachronously linked in an Early-Mid Jurassic source-to-sink system developed in a back-arc basin during the incipient development of the Andes Mountains. Satellite images, high resolution panorama pictures and measured sections were used to correlate and interpret the spatial variability and overall geometry of the base of slope to basin floor units. The observations of this study refine the model for the channel-to-lobe transition zone with increase recognition and quantification of facies and architecture variability. The Los Molles basin margin was coarse grained and was ideal to observe changes in the geometry and depositional facies of channel-to-lobe deposits from updip to downdip continuous over an 8 km outcrop belt. The described channel-to-lobe transition zone clearly shows a downdip change in bed boundaries from dominantly erosive to non-erosional (bypass) to depositional and with a range of distinct facies changes. In the transition zone the sand to shale ratio is high (N:G: 65-70 %), with gutter casts and deep scours, with a high degree of amalgamation, gravel lags, mud rip-up clasts and laterally migrating beds. Within the same depositional unit (deep water lobe), at the base of the slope, the dominant sandstone beds change from amalgamated structureless and normal graded sandstone beds in the channelized lobe axis to parallel laminated and normally graded in the channelized lobe off-axis areas. Similar facies changes have been observed along proximal to distal direction. The lateral change of the dominant structures in the beds indicates changes in the flow regime and depositional style. / text