The Basement Fault Block Pattern: Its Importance in Petroleum Exploration, and Its Delineation with Residual Aeromagnetic Techniques

Author(s):  
S. P. Gay
1981 ◽  
Vol 21 (1) ◽  
pp. 91 ◽  
Author(s):  
J. Bein ◽  
M. L. Taylor

The Eyre Sub-basin of the Great Australian Bight Basin comprises a series of half-grabens with a maximum sediment thickness in the order of 6 000 m. It is bounded to the north by high-standing basement with a sedimentary cover about 550 m thick. To the west, sedimentary cover gradually thins and onlaps rising basement. To the south, a high- standing basement ridge separates the sediments within the Eyre Sub-basin from those of the Great Australian Bight Basin proper. The sedimentary pile apparently thickens south of the basement ridge where water depth increases to more than 1 400 m.The high basement trend bounding the sub-basin to the south plunges gradually to the east where it is eventually broken up by faulting. Seismic data from the eastern end of the sub-basin show progressive down-faulting of basement and increasing sediment thickness to the south.Jerboa 1 was drilled on a tilted basement fault block. It penetrated 1 739 m of sedimentary section, which is believed to be a condensed sequence representative of most of the total sedimentary fill of the sub-basin. Middle to Late Jurassic (Callovian-Kimmeridgian) sediments were encountered above basement, and the sequence continued almost unbroken into the Late Cretaceous (Cenomanian). Minor unconformities occur between the non-marine Aptian sequence and the overlying marine Albian, and between the Albian and Cenomanian. A major unconformity separates the Cenomanian from the overlying Tertiary section, interpreted to have been deposited after the separation of Australia from Antarctica.


Introduction. At the inversion stages of continental geostructures evolution, the rocks of the basement acquire significant internal volumetric tectonic mobility due to structural and material transformations and deformations of the tectonic flow. The mechanism and scope of structural changes depend on the characteristics of their primary tectonic structure and geodynamics, the intensity of stress-metamorphic deformations of rocks, the nature and number of inversions of tectonic stress fields. Review of previous publications and studies. Secondary dislocations are important for consideration in geotectonic studies of ancient intra-plate rifts, which include the Dnieper-Donets paleorift (DDP). Studying the systemic organization of its disjunctive tectonics, on the basis of a geometric, kinematic and genetic analysis of structural patterns of faults, it was shown that the rift fault-block structure of the Precambrian basement complicates different-age dislocations of the inversion evolutionary stages. Purpose and objectives of research. The article is the first of a trilogy that continues research into the dynamic geotectonics of paleorift, highlighting the kinematic mechanisms and the geological consequences of the horizontal movements of geomass. It is devoted to the geotectonic study of structural complications of the collisional stages of tectogeneses in the architecture of the Precambrian foundation. Materials and methods of research. The original comprehensive method of regional geotectonic studies is to integrate structural-paragenetic and structure-ne-kinematic methods of tectonophysical research of fault systems. On the cartographic material, with the use of the determinants of kinematic indicators and the principle model of coupled deformation parageneses of the tectonic flow, they were detected at the base of the surface with identification in the local anomalies of geophysical fields and amplitudes of the newest (Holocene) vertical tectonic movements. Presentation of the main material. Territorial distribution and tectonic position of the secondary deformation structures of the tectonic flow of the sub-regional and zonal scales, ranging in the size from first to tens of kilometers complicated by its rift fault-block relief, is studied. They were the result of the deformation mechanism of volumetric tectonic flow of magmatic and metamorphic rocks. Findings. The morphogenetic types, tectonic position and kinematic mechanisms of secondary deformational structures formation of the tectonic flow which complicates its rift’s fault-block pattern, have been studied. Their reflections in the local anomalies of the magnetic and gravitational potential geophysical fields and in the vertical amplitudes of the newest (Holocene) tectonic movements have been analyzed. Their structure-forming role at the collision stage of the continental crust of DDP evolution is shown.


2016 ◽  
Vol 53 (2) ◽  
pp. 93-114
Author(s):  
Jesús Pinto ◽  
John Warme

We interpret a discrete, anomalous ~10-m-thick interval of the shallow-marine Middle to Late Devonian Valentine Member of the Sultan Formation at Frenchman Mountain, southern Nevada, to be a seismite, and that it was generated by the Alamo Impact Event. A suite of deformation structures characterize this unique interval of peritidal carbonate facies at the top of the Valentine Member; no other similar intervals have been discovered in the carbonate beds on Frenchman Mountain or in equivalent Devonian beds exposed in ranges of southern Nevada. The disrupted band extends for 5 km along the Mountain, and onto the adjoining Sunrise Mountain fault block for an additional 4+km. The interval displays a range of brittle, ductile and fluidized structures, and is divided into four informal bed-parallel units based on discrete deformation style and internal features that carry laterally across the study area. Their development is interpreted as the result of intrastratal compressional and contractional forces imposed upon the unconsolidated to fully cemented near-surface carbonate sediments at the top of the Valentine Member. The result is an assemblage of fractured, faulted, and brecciated beds, some of which were dilated, fluidized and injected to form new and complex matrix bands between beds. We interpret that the interval is an unusually thick and well displayed seismite. Because the Sultan Formation correlates northward to the Frasnian (lower Upper Devonian) carbonate rocks of the Guilmette Formation, and the Guilmette contains much thicker and more proximal exposures of the Alamo Impact Breccia, including seismites, we interpret the Frenchman Mountain seismite to be a far-field product of the Alamo Impact Event. Accompanying ground motion and deformation of the inner reaches of the Devonian carbonate platform may have resulted in a fall of relative sea level and abrupt shift to a salt-pan paleoenvironment exhibited by the post-event basal beds of the directly overlying Crystal Pass Member.


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