Maximum Sediment Thickness Research Articles

Sediment Distribution in Western Atlantic Off Northern Brazil--Structural Controls and Evolution

A sediment-isopach map of the western equatorial Atlantic off northern Brazil reveals major structural trends and significant sediment accumulations. The main features of the region beyond the continental slope are: the Amazon Cone, the aseismic Ceara Rise, the Demerara and Ceara Abyssal Plains, the North Brazilian Ridge, and the Fernando de Noronha and Para-Maranhao basins which are semi-isolated basins located on the continental margin seaward of the coastal basins of the Brazilian shelf. The maximum thickness of sediments in the area (> 10 km) exists under the shallowest (upper) part of the Amazon Cone. Sediment thickness in the center of Fernando de Noronha and Para-Maranhao basins exceeds 3 km. Beyond the Amazon Cone and these basins, the sediments are generally about 1 km thick in the abyssal plains and on the higher parts of Ceara Rise. Starting approximately 100 m.y. ago, sediments on the outer margin were derived from segments of the shelf between 37 and 39°W long. and between 43 and 45°W long. The northern Brazilian shelf between 39 and 43°W, and west of 45°W, off the Amazon River, contained shelf-edge structural highs which did not allow sediments to be carried to the outer margin until Cenozoic time. The shelf-edge highs are believed to be landward extensions of the Romanche and St. Paul's fracture zones. Beginning in Miocene time, a major phase of terrigenous transport to the outer margin resulted in the Amazon Cone. At least 2 km of sediment was deposited on the rest of the outer margin during the same interval. Sediments have been carried to the abyssal plains through gaps in the North Bra ilian Ridge only since middle to late Miocene. The Ceara Rise is covered primarily by pelagic sediments. However, its western part has been buried under approximately 3 km of Amazon Cone sediments during the last 6 m.y.

Geophysical studies of the major sedimentary basins of the indian craton, their deep structural features and evolution

The peninsular shield of India is characterized by a number of intra-cratonic sedimentary basins of which the Cuddapah and Vindhyan Basins are conspicuous. The crescent-shaped Cuddapah Basin (~1400 m.y.) covering roughly 35,000 square kilometers in the southern peninsula and enclosing the Cuddapah formations (Precambrian) includes shallow marine shales, limestones, sandstones and quartzites. These sediments are overlain by the younger Kurnool formations of Vindhyan (Upper Precambrian) age in the western and northern marginal portions of the basin and are intruded by basaltic sils and dykes. The eastern margin of the basin is characterized by an overthrust with steeply folded beds, while in the remaining parts, the formations show a gentle eastward dip. Evidence for Recent epeirogenic movements is provided by geomorphic features and current seismicity. The Great Vindhyan Basin of north-central India covering more than 100,000 square kilometers encloses Vindhyan sediments including some marine shales and limestones in the lower parts and shallow-water deposits of red sandstones and shales in the upper parts. The beds are generally horizontal, but are strongly disturbed along the southern margin. There are intrusions of basaltic dykes and kimberlite pipes. The Gondwana basins (Upper Carboniferous to Jurassic) are relatively smaller cratonic units in Archaean faulted troughs. Gravity and magnetic investigations, both regional and detailed, supplemented by deep seismic sounding profiles in the Cuddapah Basin have brought out the deep structural features of the basin, including the Moho, indicating a total thickness of generally 5–8 km with a maximum thickness of sediments of nearly 12 km in the eastern part. The beds show both a layered structure in the horizontal and block structure in the vertical, disturbed by a low-angle thrust fault on the eastern margin. In the Vindhyan Basin, the gravity and magnetic data indicate about 5000 m of sediments in the central portions, with major, roughly faults over the western and southern margins. The deep structural features of these intra-cratonic basins, as indicated by the geophysical results, are discussed in relation to the geological theories proposed for their genesis and development.

RESULTS OF GRAVITY SURVEY OVER RANIGANJ COALFIELD, INDIA*

AbstractResults of a gravity survey conducted over Raniganj coalfield, one of the Gondwana basins of Damodar Valley in north‐eastern part of India, are presented. The gravity field was separated into regional and residual components. The residual Bouguer anomaly map shows that the coalfield is characterized by a gravity low of about—32 mGal associated with Gondwana sediments. The deepest part of basin is found to be located near Asansole (23° 40’N, 86° 55’E), where the maximum thickness of sediments is estimated to be about 1.3 miles (2.08 km). The faults along the northern as well as the southern boundaries are found to be normal. The Gondwana sediments appear to continue eastward beneath alluvium and laterite of Bengal basin as far as 87° 25’E.

GEOLOGY AND PETROLEUM PROSPECTS OF SERAM ISLAND, EASTERN INDONESIA

The Island of Seram is located near the eastern end of the Indonesian Archipelago about 250 km southwest of Irian Jaya and 1000 km north of Darwin.The two main Late Tertiary to Quaternary basins (the Bula and Wahai Basins) totalling approximately 6000 km2 occur both offshore and onshore along the northern and northeastern coasts of the island. Several smaller basins of similar age occur along the eastern, southern and northwestern coasts.Sedimentation in the Bula and Wahai Basins began in the Early Pliocene with a marine transgression which continued into the Early Pleistocene and resulted in the deposition of bathyal facies mudstone and siltstone in the deeper parts of the basins. In the Early Pleistocene uplift occurred resulting in the formation of a regional unconformity in the sedimcn tary sequence. This uplift was followed by further transgression and deposition of neritic sediments during later Pleistocene to Recent times. The estimated maximum thickness of sediments in the Bula and Wahai Basins is 1400 and 2800 m respectively.Although the basement rocks of Seram have been severely folded and faulted, structural deformation within the Plio-Pleistocene basins has been much more subdued, resulting in minor tilting, draping of sediments over basement highs or Pleistocene reefs, and more rarely, small, down-to-the-basin faults near the basin margins.The Bula Basin is a proven petroliferous basin with the small stratigraphie Bula-Lemun Oilfield of Pleistocene age on its northwestern margin. In addition there are abundant surface oil seeps and good free oil shows have been recorded from wells drilled in the Belien-Kola area. Porous beach and bar sands and reefal limestones have been encountered within the onlapping Pleistocene sediments. Future exploration in Seram has good prospects of discovering further oilfields of the Bula-Lemun type.

Hydrocarbon Potential of Offshore California: ABSTRACT

Seaward from the tideline of the California coast to the base of the continental slope is an area of 100,000 sq km (38,600 sq mi) containing 16 sedimentary basins covering 60,000 sq km (23,200 sq mi) with a volume of 166,000 cu km (39,800 sq mi). The shelf is less than 10% explored and the activity has been confined largely to the coastal fringe of the Santa Barbara Channel and near Los Angeles. Nevertheless 1.8 billion bbl of oil and 1,200 billion cu ft of gas have been produced from 4,400 exploration and development wells. Reserves are estimated at 4.5 billion bbl. The region has three distinct tectonic provinces. Clastic sediments with occasional pyroclastic and extrusive igneous rocks are common to all and cherts are abundant in the Santa Maria basin of the northern province. There are no carbonate rocks. The southern province of 46,600 sq km (18,000 sq mi) is a region of tectonic extension with northwesterly trending horst and graben development that clearly reflects the bathymetry. Nine sedimentary basins occupy the deep-water areas; islands and shallow banks are underlain by thin or older sediments and basement rocks. Maximum sedimentary thickness is probably about 4,000 m (13,100 ft) with a volume of about 56,700 cu km (13,600 cu mi). The Santa Barbara Channel province trends eastwest. Compressional forces have formed several lines of sharp folds along the northern edge of the basin. Many large faults on the north and south borders show left-lateral movement. Rocks from Cretaceous to Pleistocene aggregate up to 20,000 m (65,600 ft) in thickness. Basement is estimated at 12,000 m (39,360 ft) at the eastern end rising toward the sea floor at the western end. The basin has an area of 5,200 sq km (2,000 sq mi) and a volume of 41,700 cu km (10,000 cu mi). The northern province has 6 basins covering 31,000 sq km (12,000 sq mi) with a volume of 67,600 cu km (16,200 cu mi). Structural trends are northwest and compression forces are indicated by marginal thrust faulting and folding. Erosional remnants of Upper Cretaceous and lower Cenozoic rocks are common but prospective sediments are of Miocene and Pliocene age. Five of the basins are 3,000 m (10,000 ft) deep or less. The Eel River basin may be as deep as 4,500 m (14,750 ft). Future potential reserves are estimated as 23.3 billion bbl of oil and 16,200 billion cu ft of gas. End_of_Article - Last_Page 1451------------

Synsedimentary tectonics of the Palaeozoic of the Drahany Upland (Sudeticum, Moravia, Czechoslovakia)

Southern parts of the Moravian Palaeozoic afford a good example of the complicated interrelationship between geosynclinal sedimentation and tectonics. The function of transverse deep-seated synsedimentary faults, separating the basin into big transverse blocks, is described in detail. The mobility of the basement of the individual transverse blocks influence sediment development, thickness, and the intensity of their deformation. The flysch and molasse facies complexes display a close relationship with the lifting of intermountain blocks and subsidence of basins. The clastic material was transported transverse to the basin axis. Where transverse axial depressions occur coarse clastic material accumulated as alluvial fans. This material was reworked by lateral currents and distributed parallel to the basin axis, within the limits of the zone of maximum subsidence. This zone of maximum subsidence shifted from the intermountain block toward the foreland (geosynclinal polariry in the sense of Aubouin, 1965). The transverse blocks with maximum sediment thickness (mainly those belonging to pre-flysch and flysch facies complexes) display the most distinct polarity and most intense sediment deformation. By contrast, transverse blocks with sedimentary sequences of small thickness (where carbonate, and eventually molasse facies complexes prevail) lack the pronounced polarity and are less deformed. Our observations lead to the conclusion that dilation stage of geosyncline development did not exist in the course of the deposition of pre-flysch facies complex.

Geology and Future Petroleum Potential, Ventura Basin, California: ABSTRACT

The Ventura basin is the western part of Transverse Ranges geomorphic province. It is a complex, highly folded and faulted synclinorium. Maximum thickness of sediments is 67,000 ft. The ages of formations range from Cretaceous through Holocene. In areal extent--including the onshore, the Santa Barbara Channel and the continental shelf--it is approximately 215 mi long, and averages 30 mi wide. Total volume of sediments is estimated at 40,000 cu mi. Despite its long history as an oil-producing basin, exploration of its ultimate potential is far from complete. Much of the thick sedimentary section has not been penetrated except in limited areas on the basin margins. Large volumes of marine lower Tertiary and Upper Cretaceous rocks are completely unexplored. Evaluation of the known profilic structures has rarely been carried below depths of 15,000 ft. In areas where the upper Tertiary beds are best developed, the obvious surface features have been drilled, and most are productive. Stratigraphic elements of entrapment occur in virtually all accumulations in the Ventura basin. Several primary stratigraphic accumulations are productive. It is believed that the greatest future potential of the basin lies in stratigraphic accumulations, and in the same general areas and measures which have been most productive to date. Estimates of 20-30 billion bbl of remaining oil in place do not appear unreasonable. Exploration for this potential awaits favorable future breakthroughs in economic, technologic, and political developments. End_of_Article - Last_Page 434------------

Geology of Western Canadian Continental Shelf: ABSTRACT

This paper deals primarily with the stratigraphy of the Tertiary sediments in the Tofino and Queen Charlotte basins of Canada's Pacific shelf. Information is included from Mesozoic and Tertiary outcrops along the shoreline margins of the basins; End_Page 1908------------------------------ from the six Richfield Oil Corporation wildcats on the Queen Charlotte Islands; from Shell Canada's aeromagnetic, reflection, and refraction seismic surveys; and from 14 offshore wildcats drilled between May 1967 and May 1969. The pre-Tertiary framework of the shelf consists of a thick and complex sequence of Mesozoic sedimentary, metamorphic, and intrusive and extrusive igneous rocks. Little is known about the early Tertiary history, but data from the Tofino basin suggest widespread early-middle Eocene submarine volcanic activity, initial uplift followed by subsidence in late Eocene time, distinct transgressions of Oligocene-early Miocene seas, followed by a middle Miocene period of crustal deformation, uplift, and regression. There was a major transgression in late Miocene and a lesser one in early Pliocene time, followed by a regressive phase in late Pliocene-Pleistocene time. The early Tertiary volcanism in the Tofino basin spread northward and continued, at least sporadically, in the Queen Charlotte basin into the Miocene. Tertiary sedimentation in the Queen Charlotte basin did not begin until the Miocene and, although interrupted by perhaps two periods of uplift and erosion, continued through the Pliocene into the Pleistocene. The maximum thickness of Tertiary sediments is more than 15,000 ft. Depositional environments range from deep-water, open-marine sequences of shales, siltstones, and sandstones in the Tofino basin, through both deep- and shallow-water marine sediments in the Queen Charlotte basin, to a thick nonmarine sequence of sandstone, shale, siltstone, and coal in Hecate Strait and the Queen Charlotte Islands. The sands in both basins are composed primarily of feldspars and quartz, and those of the Queen Charlotte basin are characterized by high porosity and low permeability. There is a wide variety of structural styles including areas of numerous large anticlines with multiple unconformities and complex growth and fault histories; areas of small, gentle, low-relief anticlines; and areas where the Tertiary sediments onlap older volcanics with little or no folding of the sediments. There are insufficient deep seismic reflections to interpret and understand properly the structural style of the Tofino basin, but at least two basic mechanisms must be considered: (1) simple compressional folding with detachment from the basement, and (2) flowage of the overpressured shales into the cores of the anticlines. At various times in different places in the basin, each of these mechanisms might have been dominant. Both oil and gas shows have been encountered, but no commercial accumulations have yet been found. End_of_Article - Last_Page 1909------------

A gravity survey of a region of the Highland Boundary Fault in Scotland

The results of 1591 gravity measurements made in parts of the Midland Valley and the Grampian Highlands of Scotland, flanking the Highland Boundary Fault-zone between Callander and Cowal are described and density units in the Palaeozoic rocks of the area distinguished on the basis of some 800 laboratory measurements. Steep gravity gradients across the Highland Boundary Fault at Callander and Aberfoyle show that its small hade to the north-west, observed at surface, is maintained to a depth of 2400 ft below sea-level, indicating that the fault behaved as a high-angle reversed fault in mid-Devonian times. West of Loch Lomond, the fault continues in general alignment with its course to the east and is inferred to underlie the Carboniferous cover in the Greenock–Inverkip region. The existence of a deep sedimentary basin bounded to the north-west by three step faults and to the south-east by the Highland Boundary Fault is revealed by a gravity low west of Loch Lomond. The basin is probably partly filled by Lower Old Red Sandstone. The maximum thickness of the Lower Old Red Sandstone sediments in the surveyed area is between 5000 and 6000 ft and the formation thins south-eastwards in the region of the Ochil Fault. On the flanks of the Highland Boundary Fault, the survey has provided information of regional importance: the slate-belt probably occupies a downfolded synform within the Dalradian rocks; the Ochil Fault can have only a small magnitude in the surveyed area; the maximum thickness of the Lower Old Red Sandstone sediments in the area is between 5000 and 6000 ft and the formation thins south-eastwards in the region of the Ochil Fault.

Seismic-Refraction Measurements in Jackson Hole, Wyoming

Three reversed seismic-refraction profiles were recorded in the Jackson Hole, Wyo-ming, area during July 1964. The seismic model which was developed consists of three layers with velocities of 2.4 km/sec for Tertiary and Cretaceous rocks above the Cleverly Formation (Lower Cretaceous), 3.8 km/sec for rocks from Lower Cretaceous down to lower Paleozoic, and 6.1 km/sec for lower Paleozoic (limestones and dolomites) and Precambrian rocks. The maximum thickness of sediments in Jackson Hole is 5 km, and the minimum throw of the Teton fault in the area covered by this survey is about 7 km.

Vermetid Reefs and Coastal Development in the Ten Thousand Islands, Southwest Florida

Sediments which underlie the Ten Thousand Islands have been deposited over the past 5000 years, during a more or less continuous marine transgression. Maximum sediment thickness is approximately 25 feet. Both the macrofauna and microfauna were used to help interpret the depositional environment for these sediments. The clean, slightly peaty basal sand was deposited in a lagoon with very restricted tidal circulation. When more marine waters entered the area about 3000 years ago, a chain of gastropod reefs appeared along the coastline. During the ensuing sea level rise of about six feet, the reefs have grown in size and number to form a reef barrier which has greatly influenced sedimentation throughout the Ten Thousand Islands. Sand from the adjacent shallow shelf has been transported into the reef area by the abnormally high tides and violent wave action accompanying hurricanes. A complex of bay bottom sands and silts, tidal pass sands, oyster bars, and thick mangrove peats has accumulated behind the reef barrier. Reefs were formed by the sessile gastropod Vermetus (Thylaeodus) nigricans Dall. The wave resistant reef core consists of fused vermetid tubes in a matrix of calcareous silt. Talus deposits typically underlie portions of the reef core. Formation of reef rock was confined to the intertidal zone, a vertical distance of less than four feet. Reef cores, as much as nine feet thick, were built up during the period of sea level rise. The vermetid reefs are compared with post-Wisconsin serpulid reefs from Laguna Madre, Texas, and with rudistid reefs from the Edwards Limestone of Texas.

Maranhao Paleozoic Basin and Cretaceous Coastal Basins, North Brazil

The Maranhao intracratonic basin of northern Brazil lies in the states of Maranhao and Piaui, southeast of the mouth of the Amazon River, and is about 600,000 sq. km. in area. Adjacent on the north, are the very much smaller Sao Luis and Barreirinhas coastal basins. The great sedimentary cycles in the Maranhao basin's history deposited a little more than 3,000 meters of sediments, 2,500 meters of which are Paleozoic and the remainder, Mesozoic. Two major erosional unconformities separate the three cycles, the first between Mississippian and Pennsylvanian time, the other during the Jurassic. The lower cycle transgresses folded Cambro-Ordovician and pre-Cambrian rocks and consists of Upper Silurian (?), Lower, Middle, and Upper Devonian marine gray sandstones and dark shales, with continental sediments in the basal part. Marine, deltaic, and finally continental gray Mississippian sandstones form the top of the sequence. A humid and temperate climate prevailed during this deposition. Resting in slight angular unconformity on this sequence is a second cycle deposited during a warm and semi-arid climate, consisting of Pennsylvanian eolian sandstones, anhydrites, red dolomites, thin marine limestones, and continental redbeds; followed by Permian chert beds, anhydrites, dolomites, eolian sandstones, and redbeds; ending with Triassic fluvial and eolian sandstones. Jurassic basalt overlies the Triassic. Diabase of the same age intrudes all rocks of Triassic or older age. A third and final cycle of Cretaceous strata onlaps Paleozoic, Triassic, and Jurassic beds along the north flank of the basin. The Lower Cretaceous sequence begins with lacustrine black shales carrying thin anhydrites and marine limestones, passing to marine sandstones and gray shales, and finally to reddish, continental clastics. Early Cretaceous subsidence in the northern Maranhao basin downwarped the Jurassic unconformity surface, giving the basin an over-all tilt toward the north. The axis of greatest sediment accumulation during the Silurian-Devonian-Mississippian cycle lies along the eastern and southeastern margins of the basin, which is also the area of greatest Jurassic basic igneous intrusive activity. A strong northwestward shift of the focus of subsidence occurred during the Permian and Triassic. The greatest thickness of these younger rocks coincides with the area of basalt extrusion and relatively mild intrusive activity. Fissures to the surface permitting Jurassic extrusion apparently occurred only in areas which had strong subsidence during Late Triassic, whereas the areas of greatest intrusion were those with thick sediments, but no appreciable Triassic subsidence. Only mild pre-Jurassic deformation occurred in most of the Maranhao basin. Jurassic diabase intrusives have created very numerous, large domes that have altered the smaller pre-Jurassic structure and seriously hampered exploration methods. Surface geological, seismic, and gravity methods can not differentiate domes caused by diabase sills and prospective pre-diabase folds. The magnetometer may be able to distinguish the two types. Only in the southwest corner of the Maranhao basin, where moderate compressional folding occurred, are the pre-diabase structures not likely to be masked by diabase domes. The Sao Luis coastal basin has a maximum sedimentary thickness of about 4,500 meters, 2,500 meters of which are Lower-Middle Cretaceous deltaic and continental clastics. The Cretaceous lies unconformably on about 2,000 meters of Devonian-Mississippian (?) dark marine shale. The basin is an ovate graben with bounding normal faults which may have 2,000 meters of displacement. Some of the faulting was contemporaneous with deposition. Although exploration methods function well in this diabase-free basin, source rocks in the Cretaceous and reservoir rocks in the Paleozoic are lacking. In the Barreirinhas basin, maximum sedimentary thickness may exceed 10,000 meters, 8,000 meters of which are probably Lower, Middle, and Upper Cretaceous. More than 3,000 meters of Lower-Middle Cretaceous dark marine shales of the southeastern part of the basin change facies toward the northwestern part to mostly continental and deltaic sandstones. This unit lies deformed and tilted beneath more than 3,500 meters of horizontal Albian marine limestone. Then Turonian marine limestone, shale, End_Page 1475------------------------------ and sandstone overlie the Albian limestones, possibly unconformably. Unconformably overlying Turonian rocks are marine limestone, shale, and sandstone of Late Campanian age. No diabase sills have been found. The Barreirinhas basin is an elongate graben bounded on at least three sides by faults with throws exceeding 3,000, perhaps 4,000 meters. Subsidence occurred along these faults contemporaneously with deposition. The best oil shows in the area of this study were from Lower Cretaceous sandstones and Albian limestones of this basin. Strong facies changes, penecontemporaneous deformation, and thick, interfingering source and reservoir rocks make the Lower Cretaceous Itapecuru-Tutoia Formation the most attractive in the most prospective basin of the three studied.

Gravity survey of Ogden Valley in the Wasatch Mountains, north central Utah

Ogden Valley is a northwest‐trending valley in the Wasatch Mountains of north central Utah. From geologic investigations it is inferred that Ogden Valley is structurally controlled by normal faults along both the northeast and southwest margins. Gravity measurements in the valley indicate a fault with about 2000 ft of vertical displacement along the west margin of the valley. A fault with at least 1000 ft of vertical displacement is postulated along the east margin of the valley, and a smaller, buried fault is postulated within the valley. The maximum thickness of Cenozoic sediments and sedimentary rocks in the valley is estimated to be about 5000 ft.