Clastic Sand Research Articles

Marine to fluvial transition: Proterozoic Upper Rewa Sandstone, Maihar, India

The Proterozoic Upper Rewa Sandstone in central India, is generally interpreted as entirely marine. A detailed study in Maihar, Madhya Pradesh, however, reveals upward transition from marine to fluvial through a mixed facies association also bearing eolian imprints. Facies associations differ in stratal geometry and arrangement, palaeocurrent direction and pattern as well as in grain size and sorting. The fine-grained marine association is dominated by tidal sheet deposits with characteristic rhythmic changes in thickness and style of cross-stratification and their packages, as well as local evidence of current reversals. Subordinate beach deposits are also present. The major palaeocurrent direction is highly consistent and westward. The coarse-grained, often granule-rich, sandstones of the fluvial association are embodied by four facies correlatable with flow stages and relative bed shear. These braided stream deposits are preserved in vertical stacks of tabular sandbodies in response mainly to basin subsidence. The palaeocurrent pattern is unimodal and northwestward, but its dispersion covers 180°. The rocks are poorly sorted and at places incorporate sand clasts, although they are virtually mud-free and mineralogically mature as in two other associations. The medium- to fine-grained sandstones at the intermediate interval between the marine and fluvial associations are of distinct lensoid geometry. They incorporate representatives from the previous two associations as well as translatent strata, interdune erg deposits and possibly aeolian cross-strata. Consequently the palaeocurrent pattern is polymodal with a spread over 270°. An overall coarsening-up trend in the fluvial part and thinning-up trend in the tidal part imply progradation in spite of evidence of basin subsidence. A high rate of sediment discharge from a perennial river system in a humid climate is suggested.

Mixed Carbonate and Clastic Sedimentation: North Insular Shelf of Puerto Rico: ABSTRACT

Light-colored carbonate sands and dark-colored muddy clastic sands are deposited in distinct and sharply defined bands across the narrow (less than 3 km, 1.9 mi) and steep insular shelf of northern Puerto Rico. The narrow bands of clastic sands are found adjacent to the mouths of each of the rivers. These bands are in textural equilibrium with the present-day physical conditions on the shelf and are deposited as a result of successive hurricane-related flooding events. Dominant sand-sized components are quartz, feldspar, and rock fragments. The rate of sedimentation in the intervening cross-shelf strips of carbonate sediment is much lower, and the shelf sediment cover here is not in textural equilibrium with the physical environment. Dominant sand-sized components are mol usk, algae, coral, and bryozoan fragments. The boundary between carbonate and clastic bands is very sharp, often occurring within 100 m (330 ft). The small carbonate fraction of the rapidly deposited clastic sediment and the particles making up the slowly deposited carbonate sediment exhibit strong differences in physical condition. The clastic calcareous fraction is fresh in appearance, highly angular if fragmented, and has original coloration. The relict calcareous material is old appearing, commonly stained and rounded, and has a dull luster. Polished surfaces and highly rounded grains characterize adjacent calcareous beach sands. The striking difference in the physical condition of the carbonate grains in clastic and carbonate sediments is a function of differing lengths of sea-floor exposure. End_of_Article - Last_Page 535------------

Paleotectonic Implications of Arkose Beds in Park Shale (Middle Cambrian), Bridger Range, South-Central Montana: ABSTRACT

The Cambrian System in the Bridger Range, south-central Montana, is represented by the Sauk sequence, a transgressive-regressive package of fine-grained clastic sand carbonates. In ascending order, the sequence consists of the Flathead Sandstone, Wolsey Shale, Meagher Limestone, Park Shale, Pilgrim Limestone, and Snowy Range Formation. Regionally, the Park is a green, micaceous shale with interbedded siltstone at the base and intercalated limestone at the top. However, in the northern Bridger Range, the lower 30 m (98 ft) is a prominent interval of interbedded arkosic sandstone and shale. A quartz- and/or orthoclase-rich facies and a biomicritic, arkosic, glauconite-rich facies comprise this interval. Individual sandstone beds, 5-17 cm (2-7 in.) thick, are characterized by sharp contacts, scoured surfaces, load structures, and weakly developed cross-stratification. Gneissic, quartzofeldspathic pebbles and biomicritic cobbles occur in sharp contrast to adjacent shales. The arkosic sandstones were deposited in a nearshore island environment adjacent to an areally restricted source of clastic detritus. Variations in en ironmental energy regime and tectonic stability resulted in the two facies. The abundance of basement-generated grains in the basal Park Shale, their absence in the upper Wolsey Shale and Meagher Limestone, and the localized occurrence of arkose indicate late Middle Cambrian tectonism and exposure of Precambrian crystalline basement. Subsequent weathering resulted in an easily erodable source of coarse-grained clastics. Due to its unique mineralogy and stratigraphic setting, the Park arkosic interval may provide a key stratigraphic marker for refining estimates of displacement along Laramide structures within the study area. End_of_Article - Last_Page 848------------

Supraglacial Diamictons at Continental Ice Margins: Pleistocene Alluvial Fan-Flow Till Deposition in Southeastern Michigan: ABSTRACT

Glacial sediments more than 50 m (165 ft) thick were laid down over southeastern Michigan during retreat of the late Wisconsinan continental ice sheet. As a result, the topography of the region is now dominated by recessional moraines composed of thick sequences of outwash sand and gravel, which are in turn capped by up to 7 m (23 ft) of glacial diamicton. Sedimentary structures exposed in many gravel pits in the Fort Wayne moraine suggest that outwash sequences were deposited as proglacial alluvial fan systems which were partially overridden during short periods of ice readvance. Several features, including abruptly truncated trough cross-bedding in gravels and truncated large clasts of previously ice-cemented sand at outwash-till contacts, require shearing at outwash su faces either prior to or during till emplacement. Such outwash till contacts suggest that some of the diamicton was deposited in subglacial settings as lodgement till. Other exposures, however, exhibit gradational outwash till contacts, fluidized mixtures of thin outwash and till layers, and till draped over large sand clasts. Such features require that much of the diamicton was emplaced without truncation at the outwash surface, and suggest that deposition occurred in supraglacial settings as flow till. The distribution of lodgement till and flow till in this region indicates that lodgement tills predominate on proximal (iceward) portions of moraine slopes and that flow tills predominate on distal slopes. This distribution suggests that during outwash till deposition, the front of the continental ice sheet had readvanced only to the moraine crest, and that a single depositional episode gave rise to the entire outwash till sequence. Similar features are typical of other moraines in the region and suggest that, in general, the crests of gravel-cored Pleistocene moraines coincide with the maximum limits of ice readvance and delineate areas of lodgement till deposition on proximal slopes and areas of flow till deposition on distal slopes. End_of_Article - Last_Page 563------------

Preservation of Ice-formed Features in a Subarctic Sandy Beach Sequence: Geologic Implications

ABSTRACT The barrier-beach shoreline near Michael River, Labrador, is ice-bound for more than 6 months each year. The contemporary beachface deposits record a complete yearly cycle as follows. The lowermost unit (d), a well-laminated fine- to medium-grained sand, and the overlying unit (a), a graded sequence of well-mixed and gravel near the bottom and medium-grained laminated at the top, represent foreshore accretion during summer and fall. Unit a is overlain by unit b, a laminated, fine- to medium-grained deposit, containing contorted and disrupted laminae and intrabedded sand clasts, features which characterize middle to upper foreshore deposits that have accreted under freezing conditions. The cycle is completed by unit c, a mixed gravel and that resembles ice rafted and ice-push deposits which form on cold-climate beaches during spring of nearshore ice. Unit b is considered to be the deposit formed during early winter, and unit c the subsequent break-up deposit which accumulated during spring. Unit c is overlain by unit d, a well-laminated foreshore which marks the beginning of the next cycle. The fact that freeze-up and events are recorded in a yearly cycle of beachface accretion indicates that such deposits could have been preserved in the rock record. If the cyclic sequence, recorded in the beachface near Michael River, were encountered in ancient rocks it could be a good indicator of paleo-climatic summer-winter seasonal conditions.

Micropaleontologic Analysis of Navarin Basin, Bering Sea, Alaska: ABSTRACT

Navarin basin, a large structural basin filled in places with more than 12,000 m of sediment, underlies the Bering Sea continental shelf about 100 km from the Koryak coast, U.S.S.R. The shelf in this region is relatively flat with a pronounced shelf-slope break at about 200 m. In contrast, the continental slope is incised by three large canyons. Little is known about the sediment and microbiota in the Navarin basin province because preveious work in the Bering Sea has been concentrated in the eastern and southern areas. More than 100 gravity cores and grab samples were collected during the summer of 1980 from the basin, adjacent slope, and nearby canyons in water depths ranging from about 80 to 3,300 m. Cores as long as 6 m contain predominantly clastic mud and sand. This preliminary U.S. Geological Survey sampling program is the first attempt in the Navarin province in which the three microorganism groups--diatoms, radiolarians, and foraminifers--are used to obtain paleogeographic information and to establish age-datum planes. Diatoms, the most abundant micro-organisms in the cores, are useful for defining glacial events and sea level fluctuations, and for establishing depth of deposition. Radiolarians are more abundant in the deeper shelf area, and are used to delineate paleogeographical boundaries and biostratigraphic events in the Navarin province. Calcareous foraminifers are abundant in the cores from even the deepest stations, but diversity is low. Shallow-water benthic foraminifers recovered in deep water indicate downslope movement of sediment. Study of these three micro-organism groups provides a more complete picture of the benthic and planktonic communities and thereby leads to a more accurate paleoecologic interpretation of Navarin basin. End_of_Article - Last_Page 975------------

Sediments of the Mississippi, Alabama, and Florida (MAFLA) Continental Shelf

ABSTRACT The eastern Gulf (MAFLA) continental margin may be conveniently divided into two parts of opposing history and character. West of Cape San Blas lies the eastern limb of the Gulf Coast Geosyncline whose surface expression is a clastic sand body, called the MAFLA Sand Sheet, grading westward into the muds of the Mississippi pro-delta. These sediments have a clay mineral suite dominated by smectite. East of Cape San Bias lies the West Florida Margin, a sequence of carbonate and evaporitic rocks which has been cut off from a major clastic source since Jurassic time. The surface expression of this sequence is the West Florida Sand Sheet, predominantly a patchy veneer of shell hash and foraminiferal, algal, and even oolitic sands which is subjected to periodic reworking by frontal system st rms and hurricanes. Kaolinite dominates its clay mineralogy. Seaward of the carbonate sands lies the West Florida Lime Mud facies, slope sediments composed of planktonic foraminifera and coccoliths. Inshore of the carbonate sands and separated from them by a zone of mixed composition lies a mature quartz fine sand, which also makes up the beaches of Southwest Florida. West Florida shelf quartz sands appear to have been deposited at lower sea level stands and to have been transported back and forth with no net drift in a longshore current system which changes seasonally from north to south. Clay mineralogy in portions of the MAFLA region shows distinct changes in composition over a period of a year in the benthos and over periods as short as a few hours in the water column. These changes reflect contribution from two distinct provenances. Benthie variation probably results from occasional intrusion of smectite laden Mississippi River or Loop Current water into the eastern zone. Water column variation may be the result of seiching of the Gulf or the pulsing movement of kaolinite laden eastern shelf water to the west.

Smackover Formation of Gulf Coast Region: ABSTRACT

The Smackover Formation in the United States Gulf Coast region has been the target of continuing, and indeed renewed, exploratory interest of the oil industry. It is important that geologists understand the depositional and diagenetic realms that affected the Smackover, because of the influence they have on reservoir development. The Smackover was deposited during a major transgressive-regressive cycle. High-energy fossiliferous, pelletal, and oolitic grainstones deposited during the regressive End_Page 534------------------------------ phase form carbonate reservoirs that are widespread in Texas, Arkansas, Louisiana, Mississippi, Alabama, and Florida. Although much of the upper Smackover displays packstone and grainstone textures, there are variations in the type of allochems, percentage of micrite, and clastic sand content. For example, there are oolitic grainstones in the upper Smackover of east Texas, Arkansas, Louisiana, and southeastern Mississippi; micritic, pellet packstones are most common in parts of Alabama and the Florida panhandle; and deltaic, beach, and offshore-bar clastic sands are intermixed with carbonate beds in much of Mississippi. Of greater significance to the exploration geologist are variations in the amount and type of porosity within similar Smackover lithologies. These variations result from differences in diagenetic regimes. In Arkansas, Louisiana, and eastern Mississippi, the best reservoirs display incompletely cemented primary porosity. The preservation of porosity may be the result of early freshwater cementation, which occurred in areas that were uplifted and exposed during salt movement. Most of the updip Smackover carbonate grainstones contain leached moldic porosity, developed as extensive freshwater flushing occurred near the regional shoreline. Combinations of dolomitized intercrystalline and leached moldic porosity are prevalent in east Texas and Alabama-Florida. Dolomite porosity is less depe dent on early salt tectonics, although salt structures may still affect the shape of the productive reservoir. End_of_Article - Last_Page 535------------

The Deformed Nature of Various Size Fractions in Some Clastic Sands

ABSTRACT The degree of development of undulatory extinction and fractures as measures of the deformed condition of quartz grains in clastic sands was in terms of grain-size. Four samples from the Oligocene clastic deposits and separate sand-dunes from four different localities around Cairo were used in this work. On the basis of close similarity in their physical constitution and textural composition, the microscopic studies were carried out on quartz of three size fractions from each sand, representing the coarse, moderate, and fine fractions. The frequency of occurrence of secondary enlargements on detrital sand grains was also studied in terms of grain-size. It was found that the degree of development of the undulatory extinction phenomenon, the frequency of occurrence of fractures and seco dary enlargements, and roundness all decrease with the decrease in grain-size. The frequency of occurrence of fractures as well as secondary enlargements was also found to decrease with the decrease in the degree of development of undulatory extinction. The mechanical means of size reduction, as fracturing processes, are discussed in terms of the deformed condition of the structure of clastic quartz.

Abyssal Basin Sedimentation: ABSTRACT

Clastic sands and silts transported and deposited by turbidity currents have created the vast abyssal plains of the ocean basins and have constructed the abyssal cones and natural levee systems of the continental rise. Clastic silts and lutites, largely transported by ocean currents, have created much of the continental rise and the outer ridges which parallel the continental margins. Biogenous sediment, resulting from near-surface productivity, more or less redistributed by currents, has created the rolling abyssal swales of productive mid-oceanic areas and has contributed to the continental rise and marginal trench sediments. Although turbidity currents are responsible for the leveling of the abyssal plains, turbidites constitute less than one-third of the sediments beneath the plains. Horizontal size grading in turbidites away from source areas is detectable but small. Apparently a much more important control on size is imposed by the lower courses of the major rivers. Turbidity currents originate near the mouths of several major rivers at the rate of 50 per century but in many other likely areas none have occurred for thousands of years. End_of_Article - Last_Page 344------------

Grains of Detrital, Secondary, and Primary Dolomite from Cretaceous Strata of the Western Interior

Three genetic types of dolomite grains occur in Cretaceous sandstones of the Western Interior and Alaska. They are: (1) Detrital—clastic fragments eroded from dolomite rocks in the sediment-source terrain. These are well-rounded polycrystalline aggregates with relict internal textures inherited from the source rocks. (2) Secondary—formed after deposition of the enclosing sediment. These are small euhedral rhombs that replaced calcite cement in lenticular marine sandstones. (3) Primary—formed within the depositional basin prior to final settling-down and burial of the sediment. These are single rhombic crystals abraded to various degrees of roundness and sorted to the size of associated clastic sand grains. The fabric relationships are of the depositional type, with no evidence of relict internal structures. This ––––eliminates a possible secondary origin. A detrital origin is eliminated by the absence of inherited textures and by the distribution patterns, for primary-dolomite grains are restricted to marine sandstones. Within these sandstones, the primary-dolomite grains are most abundant in the basinward portions. The grains are widely distributed in marine Cretaceous sandstones throughout the Western Interior, regardless of variations in lithology of sediment-source terrains. The recognition and interpretation of primary-dolomite grains is the major contribution of this paper.

Relationship of the Insular Shelf Sediments to the Sedimentary Environments and Geology of Anacapa Island, California

ABSTRACT Anacapa Island comprises three small islands which lie approximately 12 miles off the southern California coast along longitude 34°0030 N. They rise above a submerged westward-trending anti-clinal ridge which extends seaward from the western terminus of the Santa Monica Mountains. The island is barely 5 miles long and includes an area of about 1 square mile. Gentle north-dipping Middle Miocene andesitic lavas and pyroclastic rocks of the Conejo Volcanics form the bulk of the island. Two strata of the San Onofre Breccia, each a maximum of 35-40 ft thick, occur as interbeds near the base of the exposed volcanic rocks which are about 1700 ft thick. Fossiliferous marine sands 2-3 ft thick of Early Pleistocene(?) age and alluvial sands 25-30 ft thick of Late Pleistocene age overlie a summit terrace atop the central of the three islands. The Conejo Volcanics crop out over much of the insular shelf east, west, and south of the island. Siliceous and calcareous shale and gray mudstone of the Monterey Formation of Middle Miocene age crop out about one mile west of the island beneath Anacapa Passage. Two contrasting sedimentary environments, the geology of the island and the surrounding shelf, and the submarine topography control the character and distribution of the unconsolidated shelf sediments. East and west of the island relatively strong currents prevent the accumulation of detrital clasts and the sediment blanket is thin and mainly composed of calcareous animal and plant fragments. In areas of submarine outcrops relict and residual detrital sand and gravel have formed. North and south of the island detrital sedimentation is dominant; the deposits decrease in grain size with distance from shore and are composed mainly of sand size rock and mineral fragments derived from the Conejo Volcanics and to a lesser extent from the San Onofre Breccia. Detrital clasts finer than about .125 mm are able to by-pass the rather steeply sloping (1°30) and narrow southern shelf. A much wider and more gently sloping northern shelf largely prevents by-passing of the finer sand clasts north of the island. Sedimentation has been fastest on the northern shelf during Recent time, and the sediment blanket is here thickest and most uniform.

Geology of Keyes Field, Cimarron County, Oklahoma: ABSTRACT

The development of the Keyes field as a major gas reservoir in the lower Morrow sand has done much toward instigating the current wildcat play throughout the Hugoton Embayment, and Dalhart and Anadarko basins. This field, although discovered in 1943 by the Pure Oil Company, produced gas with a low 825 BTU, and development stagnated until a subsequent Coltexo discovery of high BTU gas in the upper Morrow (Purdy sand) incited major companies to exploit their leases. The exploitation of the Purdy sand for high BTU gas failed to develop substantial reserves; however, it did succeed in delineating the Keyes sand, although low BTU gas, as a major gas field. The Keyes is considered to be a blanket clastic sand of Lower Pennsylvanian age, deposited on an erosional surface of late Mississippian time. Pre-Pennsylvanian structure and some later rejuvenation apparently are responsible for the accumulation, with porosity and permeability controlling local production. Stratigraphic conditions vary markedly throughout the columnar section, indicating numerous alternating shallow marine and continental environments of sedimentation. These abrupt facies changes may offer additional zones of production. Though the Keyes sand is the major producer in the field, the Purdy (upper Morrow) and the Cherokee (lower Des Moines) have been proved for production in parts of the field. To date, 107 wells have been completed in the Keyes sand, having a calculated reserve of 514,120,000,000 cubic feet of gas. End_of_Article - Last_Page 428------------