1,720,985 research outputs found
Evolution of the Western Interior Seaway in west-central Alberta (late Campanian, Canada): Implications for hydrocarbon exploration
Full text linkThis study presents the first integrated, high-resolution stratigraphic analysis of a large area of the Cretaceous
Western Interior Basin in Alberta (western Canada), providing new tools to discriminate sedimentary processes
and stratigraphic patterns of transgressive-regressive (T-R) cycles in correlative marine and non-marine domains.
We integrate gamma ray well-log analysis, measured sections, and paleontological data to determine sediment
accumulation and distribution during the second-order T-R cycle of the late Campanian Western Interior Seaway
over a previously unstudied area encompassing approximately 97,000 km2 of the Alberta foreland basin. The
Bearpaw Formation, historically regarded as the product of a single transgression, is shown to include two T-R
cycles, whose timing is constrained by new chronostratigraphic data that provides an unprecedented resolution
(~200 kyr) for the Cretaceous of western North America. Seven reference stratigraphic markers were mapped
across the study area from the marine deposits into the fluvial domains. 3D-modelled stratigraphic surfaces and
stratigraphic intervals resulted in isopach maps for consecutive systems tracts, allowing detailed interpretations
of their architecture and patterns of sediment accumulation. Our analysis provides paleogeographic maps for the
Western Interior Seaway, focusing primarily on the evidence of the paleo-coastlines during the documented
cycles. The distribution of fine-grained, primarily marine, sediments resulted in an effective seal for hydrocarbon
accumulation in the Belly River Group. Further oil migration upsection, within the Edmonton group, was prevented
by the occurrence of these sealing units. Data support the interpretation that eustasy provided the main
control on the evolution of the Western Interior Seaway during the late Campanian
Discrimination between wave-ravinement surfaces and bedset boundaries in Pliocene shallow-marine deposits, Crotone Basin, southern Italy: An integrated sedimentological, micropalaeontological and mineralogical approach
Full text linkThe lower Pliocene Belvedere Formation, cropping out in the Crotone Basin, southern Italy, exhibits a metre-scale to decametre-scale shallow-marine cyclicity that shares features of both high-frequency sequences linked to shoreline shifts and controlled by minor relative sea-level and/or sediment supply changes, and sedimentological cycles unrelated to shoreline shifts. In order to better understand the high-frequency sequence stratigraphic framework of this succession, an integration of sedimentological, micropalaeontological (microforaminifera assemblages) and mineralogical (heavy mineral abundance) data is used. From a sedimentological/stratigraphic point of view, wave-ravinement surfaces bounding high-frequency sequences, and associated substrate-controlled ichnofacies, are prominent in outcrop and document environmental and water-depth changes, whereas bedset boundaries separating sedimentological cycles have a more subtle field appearance and are only associated with changes of environmental energy. Moreover, condensed deposits are present only above wave-ravinement surfaces, and the high-frequency sequences bounded by these surfaces have a thickness that is an order of magnitude greater than that of the bedsets. Micro-foraminifera assemblages may change, and the content of heavy minerals usually increases, across wave-ravinement surfaces, whereas both parameters do not change significantly across bedset
boundaries. The abundance of heavy minerals is systematically higher, with respect to the underlying and overlying deposits, in the condensed shell beds that overlie wave-ravinement surfaces. An integrated sedimentological, micropalaeontological and mineralogical approach represents a powerful tool to discriminate between wave-ravinement surfaces bounding high-frequency sequences and bedset boundaries, and in general to investigate at the intra high-frequency sequence scale. This integrated approach is expected to be very useful in the study of potentially all shallow-marine successions composed of small-scale cycles, in order to delineate a detailed sequence stratigraphic framework and understand the factors that controlled the cyclicity
Lithostratigraphy, sedimentary petrography and geochemistry of the Upper Karoo Supergroup in the Central Kalahari Karoo Sub-Basin, Botswana
No full textThe Kalahari Karoo Basin of Botswana is an intracratonic basin developed in south-central Gondwana and is filled with Upper Carboniferous-Lower Jurassic Karoo Supergroup volcano-sedimentary units. The Karoo Supergroup units are unconformably covered by the Cretaceous to recent Kalahari Group. The Upper Karoo Supergroup in the Central Kalahari Karoo Sub-Basin of Botswana consists of the lacustrine sediments of the Beaufort Group (Tlhabala Formation), overlaid unconformably by the continental sediments of the Lebung Group, and by the continental basalts of the Stormberg Group. The Late Triassic to Early Jurassic Lebung Group is subdivided into the Mosolotsane Formation and the Ntane Formation. This sedimentary sequence is poorly exposed, and formation boundaries are tentatively identified by lithological changes in boreholes. Here, new sedimentological and geochemical data are used for the refinement of the stratigraphy of the Upper Karoo Supergroup in the Central Kalahari Karoo Sub-Basin of Botswana, new criteria for the identification of unit boundaries are set and provenance of the Lebung Group sediments has been defined. The geochemical investigation of the Upper Karoo Supergroup in the Central Kalahari Karoo Sub-Basin of Botswana revealed clear geochemical markers that have allowed the pinpointing of unit boundaries between the Tlhabala Formation (Beaufort Group), Mosolotsane Formation (lowermost Lebung Group). The sediments from the Tlhabala Formation have a geochemical signature typical of wackes, while the sandstones from the overlying Mosolotsane Formation and the Ntane Formation are dominated by arkose to subarkose. The transition from wacke to subarkose pinpoints the boundary between the Beaufort Group and the base of the Lebung Group. The Tlhabala Formation is characterized by increasing SiO2/Al2O3 ratio, with a maximum at the base of the Lebung Group, and by an upward decrease in the abundance of Na, K and transition metals such as Cr, Mn and Fe. The SiO2/Al2O3 ratio decreases upward in the Lebung Group. Similarly, the abundances of Na, K, Cr, Mn and Fe slightly increase upward only to show a negative peak at the Lebung Group and the Kalahari Group boundary. This contact is marked by a clear increase in the total REE content.The chemical composition of the Lebung Group sandstones also indicates a quartzose sedimentary provenance. The CIA (chemical index of alteration) values for these sandstones ranged from 63 to 73, indicating a high degree of chemical weathering. This type of intense weathering should produce high volumes of clay minerals, which are rather scarce in the studied samples. This indicates that the large amount of quartz in the Lebung Group has been recycled from the Paleoproterozoic sedimentary sequences of the Palapye Group, located southeast from the study area
Traversing the rift: A review of the evolution of the West and Central African Rift System and its economic potential
No full textPaleoenvironmental Context of Microbial Mat-Related Structures in Siliciclastic Rocks
No full textThe role of biological influences in forming carbonate rocks (e.g., Altermann et al., 2006) is almost universally accepted within geology. In contrast, many see clastic sedimentary rocks as being formed primarily through physical and chemical processes, with biological mediation of their genesis being considered as of relatively minor importance (Schieber et al., 2007a). While sedimentologists and most geologists are familiar with the importance of trace fossils within clastic deposits (cf., the seminal work of Seilacher (1964) and many others since), the role of microbial mats in terrigenous sediment accretion, and in the formation and preservation of a whole host of mat-induced (mi) and mat-related structures within clastic sedimentary rocks, is less well known
Stratigraphy and Palaeontology of the Late Cretaceous Wapiti Formation, west-central Alberta, Canada
No full textA complete stratigraphic assessment and revision of the middle Campanian to upper Maastrichtian Wapiti Formation in north-western Alberta and north-eastern British Columbia is the main aim of this research project. The study area encompasses an area of approximately 200X180 km in the Grande Prairie County (west-central Alberta) and easternmost British Columbia, Canada. Results presented here indicate that the 1300m thick succession currently reported in the literature as “undifferentiated lithostratigraphic unit”, consists of five lithostratigraphic units and four unconformity-bounded depositional sequences; their study and description have been documented integrating several geological disciplines, including sequence stratigraphic methods, well-log signatures, facies analysis, and fossil associations. On the whole, particular attention has been given to 1) age and nature of both basal and upper contacts of the Wapiti Formation, 2) effective mappability of lithostratigraphic units and depositional sequences in western Alberta, and 3) the identification of previously undetermined maximum flooding surface of the Bearpaw seaway and Drumheller Marine Tongue, which are reference marine unit in central and southern Alberta. A second, but not less important, guideline for the project has been the rich paleontological record of the Wapiti deposits. Detailed paleoenvironmental and taxonomical information on old and new finds have been the base for correlation with well known associations of Alaska, southern Alberta, and Montana. Newly discovered rich fossil localities documented an extraordinarily diverse fauna during the latest Cretaceous, including dinosaurs, squamates, and fresh-water fishes and reptiles.
Lastly, in order to better characterize the Wapiti Formation, major marker beds were described: these include several bentonites (altered volcanic ash deposits) which have been documented over an area of almost 30.000 km2, as well as four major coal zones, characterized by tabular coal seams with an overall thickness of 2 meters. Such marker beds represent a formidable tool for high-resolution chronology and regional correlations within the Late Cretaceous Alberta foreland basin
Sequence stratigraphy and underlying tectonism of the Northern Richardson Mountains and adjacent Mackenzie Delta related to the formation of the Arctic Ocean
No full textJurassic-Cretaceous rifting within Arctic North America that eventually resulted in the formation of the Arctic Ocean greatly affected deposition within nearshore terrestrial basins in surrounding areas, such as the Brooks-Mackenzie Basin and the Sverdrup Basin. In this thesis, measured stratigraphic sections and detrital U-Pb zircon data from outcrops within the Northern Richardson Mountains are integrated with well-log and core data from the adjacent Mackenzie Delta to establish a model-independent sequence stratigraphic framework for the BrooksMackenzie Basin. This framework is then used to elucidate the underlying tectonic forces responsible for the observed stratigraphy, relating patterns of deposition to various phases of rift development. The proposed interpretation classifies the sub-Jurassic unconformity as a first-order sequence boundary, demarcating a change in tectonic setting from pre-rift to rift, meaning it is also classified as the rift onset unconformity for the Arctic Ocean. The overlying Bug Creek Group is largely progradational, representing a first-order lowstand systems tract corresponding to early syn-rift strata. Detrital zircon data from the Bug Creek Group lacks syn-depositional zircons and resemble the underlying Permian, suggesting a recycled source. A change in the detrital zircon signature is observed within the uppermost Aklavik Formation, representing a new source. This also coincides with a rapid transition to the lower offshore deposits of the Husky Formation caused by normal faulting in the Husky Lakes Fault Zone, which is associated with a dramatic basin expansion. Maximum transgression occurs above the arenaceous member of the Husky Formation, likely near the Jurassic-Cretaceous boundary, representing a first-order maximum flooding surface and rift-climax. Above the rift climax, the overall progradational signature represents a first-order HST and post-rift deposits. The sub-Hauterivian basal Kamik unconformity is observed at the base of the subsequent FSST. This first-order sequence boundary is approximately time equivalent to the breakup unconformity for the Arctic Ocean, with the overlying Kamik Formation resembling the Isachsen Formation in the Sverdrup Basin
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