Series Of Horsts Research Articles

Far–field tectonic controls on deposition in the Appalachian Basin – A case study of Late Cambrian–Late Ordovician strata in Morrow County, Ohio

Far–field tectonics can often be overlooked when studying orogens, particularly when much of the deformation occurs near the loading loci. As stresses are propagated further from the loading into the craton, whether compressional, extensional, or shear, faults and fractures within the basement often act as pathways for stress transmission, traveling along these pre-existing planes of weakness, or creating new. The Appalachian Basin in the eastern United States is a classic foreland basin example that showcases far-field tectonic influence on deposition and structure. This study characterizes the structural architecture of the basement along the western Appalachian Basin margin by analyzing well log data from 2,662 wells to create structure, isopach, trend surface, and residual maps of Late Cambrian through Upper Ordovician strata (Knox through Black River). Fourteen lineaments interpreted as faults were delineated, creating two series of horsts and grabens. The northeast–southwest faults are related to structures that formed during Keweenawan extension, and the northwest–southeast faults are related to structures that formed during the Grenville Orogeny. Both sets of faults stem from the Precambrian basement and are shown to have been reactivated during the Blountian Tectophase of the Taconian Orogeny (Black Riverian deposition), creating localized thinning and thinning adjacent to the lineaments. Furthermore, these faults appear to have undergone additional reactivation since the deposition of these strata in a transtensional regime to create the observed horst and graben structures. Overall, far–field tectonics plays an important role in understanding the geologic history of a basin.

Automatic characterization and quantitative analysis of seismic facies in naturally fractured reservoir: Case study of Amguid Messaoud field, Algeria

Purpose. Natural fractured reservoirs are a special category of reservoirs due to the effects of porosity and permeability. Optimizing the exploitation of hydrocarbon reserves in this type of reservoir requires a specific study compared to other conventional reservoirs. Methods. We have focused on the quantitative analysis of seismic traces for the purpose of an automatic seismic facies recognition strategy. The study area, the Amguid-Messaoud Basin, is formed by a series of horsts and grabens bounded by submeridional “North-East and South-West” faults, as well as perpendicular “North-West and South-East” faults with-out outcrops of fractures, which have a great influence on reservoir fracturing. A set of statistical data analysis methods, such as principal component analysis, discriminant factor analysis, and automatic classification, have been tested on real data from geophysical seismic data interpretation, in particular the stratigraphic interpretation. Findings. The results obtained show a better use of data, which, however, are of a different nature, leading to a reliable interpretation of the geological environment. Originality. The methodology proved to be useful for constructing a reservoir model and predicting the geological properties of the reservoir along a field. Practical implications. The results obtained clearly demonstrate the best use of data, which, however, are of a different nature, which leads to a reliable interpretation of the geological environment. These methods have proved to be very useful for constructing a reservoir model and predicting the geological properties of the latter along a field.

Oil and gas bearing in Norwegian Sea basins

The Norwegian passive continental margin is represented by an extensive gentle shelf and continental slope. On the continental slope, there are the isolated Voring, More and Ras basins, the Halten Terrace is situated to the east of them at the shelf, then the Nordland submarine ridge and the Trondelag Platform at the seaboard. There are Paleozoic, Mesozoic and Cenozoic sediments in its sections. Two complex structures are clearly distinguished in the sedimentary section: the lower stage (up to the Upper Cretaceous), reflecting the rifting structure of the basins, broken by a system of dislocations to a series of horsts, grabens, and separated blocks; and the upper stage, poorly dislocated, like a mantle covering the lower stage, with erosion and sharp unconformity. The Halten Terrace is the principal oil and gas production basin. At present, there are more than 50 oil, gas, and condensate fields in it. The following particularities have been discovered: than the field lays in the deepwater, than the age of the hydrocarbon pay is younger. It is also interesting that all gas fields are situated in the Voring and More basins and western part of the Halten Terrace; the oil and gas fields, mainly at the center of the Halten Terrace; but pure oil fields, in the north of the terrace. In conformity with discovering the particularities, it is possible to say that the prospects of oil and gas bearing in the Norwegian Sea are primarilyt related to the Halten Terrace and the Voring and More basins, especially the territories situated at the boundary of the two basins, where it is possible to discover large hydrocarbon accumulations like the Ormen-Lange field, because the Paleocene-Upper Cretaceous productive turbidite thick at the boundary of these basins is on the continental slope, which is considered promising a priori.

Remote Sensing and GIS Tool to Detect Hydrocarbon Prospect in Nagapattinam Sub Basin, India

Cauvery Basin is one of the pericratonic rift basins located in the east coast of Tamilnadu. The rifting has resulted in a series of horsts and grabens. The present study uses a new technique which was devised with the help of GIS by analyzing the surface lineaments and subsurface linearities effectively. In this present study, a satellite image based analysis was conducted for extracting surface lineaments, and for the subsurface linearities, the basement linearities were extracted from seismic, magnetic, and gravity data. An orientation analysis of these surface and subsurface linear features was performed to detect the basic structural grains of the study area. The correlation between these structural grains and subsurface oil and gas traps was performed to understand the connectivity to the reservoirs. This article discusses in detail about the same and the importance of using surface and subsurface lineament analyses for delineating hydrocarbon reservoirs in the Nagapattinam Sub-Basin of Cauvery Basin.

Subsurface structural mapping of the area lying between Gabal Elgalala Elqibliya and Elgalala Elbahariya, Northern Eastern Desert, Egypt

The area lying between Gabal Elgalala Elqibliya and Elgalala Elbahariya is located in the Northern Eastern Desert of Egypt, between 28° 49' N and 29° 10' N and 31° 50' E and 32° 30' E. The exposed rock units in the study area are represented by various lithologic associations ranging in age from Late Paleozoic to Quaternary. I applied gradient interpretation techniques (analytic signal and Euler deconvolution) as well as magnetic modelling to the aeromagnetic data, to delineate the subsurface structural features and estimate depths to basement. The results of all methods of depth determination suggest a fault-controlled region, especially in its eastern part. Moreover, moving from its western side towards its eastern side, the study area could be represented by a series of horsts (domes or anticlines) and grabens (troughs, basins or synclines) ranging in depth between 0.1 and 4.0 km. The study area is intruded by two nearly parallel systems of more basic and more recent dykes than the surrounding rocks, at depths varying from 0.2 km and 2.0 km.

Sediment thickness and crustal structure of offshore western New Zealand from 3D gravity modelling

3D modelling of satellite gravity data covering the offshore area west of New Zealand has been used to predict the depth to the seafloor, basement, and Moho. The models assume constant densities for each layer, with no lateral changes of rock properties. The modelling was done on a 2.5 km grid. Depths to the seafloor, basement, and Moho were interpreted from seismic data or taken from published sources, and were used to constrain the solutions. Where control points are available, the models generally match the interpreted depths to within the expected level of accuracy. Basement depth is underestimated in the deeper parts of the basin. This is due to the assumption of constant density layers. Use of a more appropriate density/depth function would have resulted in a better match with the interpreted depths. The modelling highlights Cretaceous rift structures along the margins of the Challenger Plateau, Lord Howe Rise, and West Norfolk Ridge. Horsts and graben oriented parallel to the Challenger Plateau and Lord Howe Rise margin formed prior to seafloor spreading in the Tasman Sea. They are typically 10–20 km across and 1–2 km deep. The northwest‐southeast trend is interrupted by north‐south‐trending faults associated with a later phase of subsidence in the Bellona Trough. The basement structure of the West Norfolk Ridge extends to the southwest as a buried series of horsts and graben which separate sedimentary basins in Northland and the New Caledonia Basin. The sediment thickness predicted by the models in the New Caledonia Basin is thinner than that interpreted on seismic sections, emphasising the importance of using density gradients in models of deep sedimentary basins. The modelled depth to Moho is c. 13 km in the Tasman Sea and 25 km beneath the Challenger Plateau. Crustal thinning of c. 30% is predicted for the Bellona Trough, New Caledonia Basin, and Lord Howe Basin.

A new tectonic model for the Cameroon Line, Central Africa

The Cameroon Line, a major geological feature in Central Africa, has been considered successively as a series of horsts and grabens, a continental rift and a mega-shear zone. It is marked out by about 60 anorogenic complexes and a dozen volcanic centres, all of which have alkaline affinity. Remote sensing allows us recognition of the main lineament trends: N70°, N-S, N135° and E-W, while autocorrelation analysis reveals a major fault zone striking N30° in western Cameroon and N15° in the northern region. A mega left-lateral shear zone is the model that best accounts for the fracture pattern and associated features such as linear and circular structures alignment of subvolcanic complexes, syntectonic leucogranites marking out older shear zones and vein dykes. The N70° Adamawa fault zone, a Pan-African fracture reworked during Albian-Aptian times, is the only shear zone of continental scale that could have initiated “en echelon” mega-tension gashes within the Cameroon Line during a Cainozoic left-lateral transcurrent movement.

Triassic/Jurassic Faulting Patterns of Conecuh Ridge, Southwest Alabama: ABSTRACT

Two major fault systems influenced Jurassic structure and deposition on the Conecuh Ridge, southwest Alabama. Identification and dating of these fault systems are based on seismic-stratigraphic interpretation of a 7-township grid in Monroe and Conecuh Counties. Relative time of faulting is determined by fault geometry and by formation isopachs and isochrons. Smackover and Norphlet Formations, both Late Jurassic in age, are mappable seismic reflectors and are thus reliable for seismic-stratigraphic dating. The earlier of the 2 fault systems is a series of horsts and grabens that trends northeast-southwest and is Late Triassic to Early Jurassic in age. The system formed in response to tensional stress associated with the opening of the Atlantic Ocean. The resulting topography was a series of northeast-southwest-trending ridges. Upper Triassic Eagle Mills and Jurassic Werner Formations were deposited in the grabens. The later fault system is also a series of horsts and grabens trending perpendicular to the first. This system was caused by tensional stress related to a pulse in the opening of the Gulf of Mexico. Faulting began in Early Jurassic and continued into Late Jurassic, becoming progressively younger basinward. At the basin margin, faulting produced a very irregular shoreline. Submerged horst blocks became centers for shoaling or carbonate End_Page 268------------------------------ buildups. Today, these blocks are exploration targets in southwest Alabama. End_of_Article - Last_Page 269------------

Provenance et modèle de dépôt de la Formation de la Rivière Nicolet : flysch taconique du Domaine autochtone et du Domaine externe des Appalaches du Québec

The composition of the detrital fraction of the Nicolet River Formation suggests that the rocks of the Autochtonous and the External Domains of the Quebec Appalachians were mostly derived from the sedimentary nappes of the External Domain. The contribution from the metamorphic nappes and ophiolites of the Internal Domain was minor but it indicates that the dynamothermal metamorphism had been completed by the end of the Middle Ordovician (C. spiniferus Zone). Piling up of the nappes, each one progressively richer in feldspar, produced a source of high relief subject to subaerial erosion. The vertical evolution observed in the flysch probably results from tectonic activity at the source area rather than from deep-sea fan progradation. The stratigraphic relationships evince that the deposit accumulated in basins controlled by a series of horsts and grabens.

Étude géologique du socle ante-mésozoique au nord du Massif Armoricain: limites et structures de la Domnonée

The study of samples taken on the bottom of the sea north of the Massif Armoricain, and the geological, magnetic, gravimetric and seismic data collected on land and at sea, confirms that this region is characterized by: (1) a series of horsts where fragments of Pentevrian and Cadomian orogenies outcrops; (2) gullies, or synclines, of Palaeozoic terrain. The separation of the horsts is the result of tectonic shearing which developed during the Ordovician, Carboniferous and Triassic ages. The Cadomian chain, which constituted the fundamental structure of the region, was broken up very early and is no longer recognizable. In the west, traces of this chain seem to have lasted until the Llanvirnian. In the east, the uplands, which were probably less harsh, were levelled before the start of the lower Cambrian age. A general upwarp of the eastern part between the middle Cambrian and the middle Ordovician could correspond to a reaction to the Caledonian orogeny. The northern part of the Alassif Armoricain had little part in the Hercynian paroxysm, however, this period witnessed an important tangential tectonism, the horsts riding over the edges of the synclines. The western formations show more marked structures than the eastern formations. The area which has been studied largely corresponds to the Domnonean domain, a puzzle of horsts and grabens. The Domnonea is itself a large horst, limited to the north by thick Palaeozoic sequences and to the south by the central Armorican zone and the Mancellian domain.

Geological and Geophysical Studies at Railroad Valley, Nevada: ABSTRACT

In Paleozoic time 20,000 feet of sediments accumulated in the Railroad Valley area. Limestone and dolomite make up about 85 per cent of these sediments, with 5-10 per cent sandstone and the rest shale. Fossils and lithologic characteristics indicate most or all of these sediments were deposited in shallow water, but subsidence of the area was nearly continuous, and all of the Paleozoic systems are represented in the sequence of beds. In late Paleozoic or early Mesozoic time the area was uplifted and no seas are known to have covered it since that time. Erosion produced a surface with slight to moderate relief, and beds ranging in age from Devonian to Permian were exposed. On these upper Paleozoic strata Tertiary lake and stream sediments and volcanic materials were deposited in thicknesses ranging up to 15,000 feet. These Tertiary beds can be subdivided into four groups which can be recognized in wells in Railroad Valley and in several nearby mountain ranges. Some diastrophism occurred in early and middle Tertiary time, resulting in several widespread unconformities, but the diastrophism which produced the present basin-and-range topography occurred after deposition of all of these Tertiary beds. Seismic and gravity surveys were used to delineate structural features in the sediments beneath the valley. Both methods show that Railroad Valley is an asymmetrical basin with the greatest depths on the east. The gravity survey shows a major border fault probably is present on the east flank of the basin, and a series of horsts and grabens parallel the mountain on the west side of the valley. Seismic reflections outlined several structural highs which were tested; one of these produced oil in the Eagle Springs field. Seismic reflections are not of the best quality in the valley, but the most numerous, reliable, and continuous reflections originate from within Tertiary and Quaternary clastic deposits. Reflections from greater depths are fragmentary, but often are useful. In some instances, the unconformity at the top of the Tertiary volcanics could be mapped. Reflections could not be obtained on the fan deposits at the edge of the valleys, where major border faults probably occur. In these regions gravity data were used to trace the faults, obtain estimates of their dips, and to outline the structure of the Paleozoic surface. Estimates of depth to Paleozoic rock in several basins along the axis of the valley could also be made from gravity data; these depths range from 7,000 to 15,000 feet. End_of_Article - Last_Page 215------------