ABSTRACT Utilizing a basin-wide data set of three-dimensional seismic volumes and the application of principles of seismic stratigraphy and seismic geomorphology allowed identifying numerous depositional elements within the Vaca Muerta–Quintuco system, a set of clinoforms whose topsets belong to the Quintuco Formation, whereas the bottomsets and foresets belong to the Vaca Muerta Formation. Within the topsets, small circular geobodies clustered near the prograding shelf margin, averaging 200–800 m (656–2625 ft) in diameter and up to 75 m (246 ft) in height. These features comprise small carbonate buildups defining carbonate factories trending strike parallel. Identification of intervals where these geobodies are abundant is important because wells drilled through them have experienced either drilling mud admission or gas influx. In addition to these biogenic carbonate mounds, the topsets show elongated oolitic grainstone shoals oriented orthogonal to coeval shelf margins, in some cases measuring up to 22 km (14 mi) long and 5 km (3 mi) wide. The foresets (slope deposits) become progressively enriched in total organic carbon (TOC) and porosity downdip—key variables for a self-sourced unconventional reservoir. These deposits commonly comprise mudstone and marlstone, interbedded with limestones. In the lower foresets to toesets, strike-parallel, high–seismic-amplitude, and high-energy calcareous deposits are embedded in organic-rich mudstones. In some instances, these amplitude anomalies, drilled and cored by a few wells, show both well-defined linear geobodies along the toeset and evidence of bottom currents in cores (thicker limestone beds, ripples, bioturbation, and occasional centimeter-scale soft-sediment deformation). Identification of such geobodies is critical, as there is evidence from ongoing development drilling that these may act as hydraulic-fracture barriers and can also affect well performance as evidenced by increased water production. The bottomsets consist of low–amplitude-parallel, “railroad track” reflections that extend for tens of kilometers, characterizing the classic basin center Vaca Muerta play. Within these deposits, no major mappable geobodies are observed other than localized compressional ridges of mass-transport deposits (MTD) near the toesets. In some areas of the basin, the Vaca Muerta Formation was deposited directly on top of a preexisting non-marine paleo-aeolian dune topography which had a direct impact on the stratal geometries and the bottomset facies of the Vaca Muerta Formation. Acoustic impedance (AI) from seismic inversion show well-defined Vaca Muerta low-impedance seismic facies, which relate to the presence of predominantly fine-grained, organic-rich (~5%), porous (~11%) mudstones and marlstones. Within the high-TOC Vaca Muerta interval, most AI three-dimensional (3-D) volumes throughout the basin show an average of five to six seismic facies with discrete AI values that can be directly correlated to rock types, depending on their position within the clinoform (i.e., topset, foreset, bottomset). These seismic facies correlate to facies associations with distinct petrophysical and geomechanical properties at core/outcrop scale, as measured by lab studies. Understanding this relationship and its distribution in space is critical to predicting optimum horizontal well landing zones and sweet spots.

ABSTRACT The Vaca Muerta Formation consist of outer ramp to basinal facies in a mixed siliciclastic–carbonate creating an organic-rich section up to 500 m thick. This chapter documents stratal terminations, main bounding surfaces, and stacking patterns of the Vaca Muerta–Quintuco system as a means to establish a new sequence stratigraphic framework. The data set comprises more than 500 wells and a basin-scale seismic coverage that spans 30,000 km 2 Regional seismic interpretations and well correlations were calibrated with well geochemical data and acoustic impedance seismic sections. Twelve high-frequency depositional sequences (HFS) with variable combinations of systems tracts were defined and grouped in three low-frequency depositional sequences (LFS). Within this sequence stratigraphic framework, the Vaca Muerta Formation includes organic-rich (total organic carbon, TOC > 2wt. %) and organic-poor intervals (TOC < 2wt. %) At a high-frequency scale, the organic-rich intervals with the highest concentration of TOC belong to transgressive systems tracts and the lower sections within clinoform bottomset and foreset of highstand systems tracts. These condensed sections usually show the best reservoir properties in the self-sourced unconventional play. Conversely, organic-poor intervals are found in the foresets of falling-stage systems tracts and lowstand systems tracts. Condensed sections of each sequence allow subdivide the unconventional play in a stacking of 12 organic-rich Vaca Muerta units (OVM, TOC ≥ 2wt. %). The lowermost eight OVM units correspond to the main tested landing zones. Moreover, a detailed map of shelf breaks reveals a strong three-dimensional (3-D) spatial variability, which is summarized in four groups of plan-view geometries. The 3-D spatial variability of the organic-rich intervals is analyzed at local scale in two cases with different plan-view geometries. At regional scale, thickness maps of the main OVM units allow infer stratigraphic controls (e.g., systems tracts, previous clinoform paleo-topography) and tectonic controls, both regional (morphostructural domains) and local (subsidence axes and paleo-highs), active during the deposition of the Vaca Muerta Formation. The proposed sequence stratigraphic framework provides a predictive understanding of 3-D spatial distribution of the organic-rich intervals in subsurface assessments for the Vaca Muerta play and is applicable to the exploration of other analogous (mixed siliciclastic-carbonate systems) self-sourced unconventional resources.

Abstract The geology, inferred evolution and classification according to widely accepted schemes of 22 basins from the Indian Precambrian record on the Arravali–Bundelkhand, Singhbhum, Bastar and Dharwar cratons are discussed in this volume. Although their classification is biased owing to all depositories having continental lithospheric substrates, most of the basins reflect divergent plate motion and thus lithospheric stretching and cooling. Convergent plate motion and concomitant lithospheric flexure owing to loading are postulated for the Kurnool Basin and the Eastern Dharwar Craton supracrustals. Transcurrent plate motion is interpreted for the Bhima and Kaladgi–Badami basins. The Cuddapah Basin suggests a complex polyhistory influenced by both mantle circulation/dynamic topography and loading-related flexure of the lithosphere. Mantle circulation and dynamic topography may have played a role in the evolution of the Dhalbhum and Dalma–Chandil basins. Examination of possible time trends indicates that pre- c. 2.0 Ga basins were mostly continental rifts, followed by some intracratonic basins and lesser rift-sag and back-arc basins; post- c. 2.0 Ga basins exhibit a much larger range of basin types. While this Memoir offers a broad sample of the application of plate-tectonic principles to the Precambrian basins of the large Indian shield, it also underscores that Phanerozoic-style plate tectonics and basin evolution histories are widely identified within the Precambrian sedimentary rock record. Analogously, the case studies in this book support the essential similarity between the features observed within the Precambrian basins of India and the norms that describe Phanerozoic successions in terms of sequence stratigraphic architecture. The Indian Precambrian basin-fill record shows that all types of sequence, systems tract and sequence stratigraphic surface that are known from the Phanerozoic record also occur within Precambrian successions. Differences between the stratigraphic architecture of Precambrian and Phanerozoic basin-fill successions can be ascribed to variable rates and intensities of the controls on accommodation and sediment supply, the changes inherent in the evolution of the hydrosphere–atmosphere system and related physical processes, and the evolution of the biosphere system and associated biogenic processes.

Abstract The conventional Wheeler diagram aids the construction of a spatiotemporal framework of strata. The diagrams are created manually by studying outcrops, wells, or seismic data. For the latter case, automated methods now exist, which support the construction of 2D, as well as 3D Wheeler diagrams. Seismic data contains information in three dimensions, X , Y and Z , where ‘ Z ’ is either two-way time or depth. Seismic horizons are correlated surfaces that often follow geological time lines. In this case, a set of interpreted seismic horizons contains information in four dimensions ( X , Y , Z , and Geological Time). In the mapping from the structural domain to Wheeler space, information about Z (thickness) is lost. This means that one dimension is missing in the conventional Wheeler diagram. This paper describes a method to add information from the Z dimension to the Wheeler domain. It is done by computing stratigraphic thicknesses per sequence stratigraphic unit and displaying these as colour-coded overlays in the Wheeler domain. Thus displayed, thickness variations help in understanding changes in accommodation, sedimentation rate, and depositional trends. 3D Wheeler displays with colour-coded thickness information are referred to as 4D Wheeler diagrams. In this article, the method is described and applied to a case study from the southern North Sea.

Pennsylvanian and Permian glacigenic deposits of the Dwyka Group occur within Karoo basins throughout southern Africa. The largest, the main Karoo Basin, evolved into a foreland basin during Dwyka accumulation. Tectonism along the convergent margin of Gondwana resulted in the formation of a foreland basin bounded by southern (Cape fold belt) and northern (Cargonian Highlands) uplands. Glaciers carved deep paleovalleys into the northern highlands that were later filled by glacigenic and post-glacial strata. Within this basin, a platform facies association composed of four deglaciation sequences occurs. These sequences, which are hundreds of meters thick, consist of thick, massive, basal diamictite lithofacies that grade upward into stratified lithofacies (stratified diamictites, dropstone-bearing mudrocks, and rhythmites). Interpretations depict grounded ice advancing into the basin followed by gradual retreat of the ice front resulting in ice-proximal followed by ice-distal glaciomarine sedimentation. Sensitive high-resolution ion microprobe (SHRIMP) dates of juvenile zircons obtained from tuff beds indicate that the deglaciation cycles were 3.6–8.2 m.y. in duration. Such cycles were likely the result of tectonic development of the foreland basin. Paleocurrent and provenance studies indicate that Dwyka glaciation asynchronously emanated from multiple glacial centers in upland areas, and in Antarctica. Therefore, southern Africa was not covered by a single ice sheet, but instead, smaller ice sheets, ice caps, and alpine glaciers waxed and waned along basin margins during the late Paleozoic. Despite a long history of study, many questions concerning Dwyka glaciation remain.