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Showing papers in "Journal of Sedimentary Research in 1970"


Journal ArticleDOI
TL;DR: In this paper, the determination of detrital modes in graywackes and arkoses, here grouped as subquartzose sandstones, requires special attention to the identification of detribal grain types, as defined operationally.
Abstract: The determination of detrital modes in graywackes and arkoses, here grouped as subquartzose sandstones, requires special attention to the identification of detrital grain types, as defined operationally, and to the recognition of detrital textures, as opposed to textural elements of diagenetic origin. Accurate detrital modes can yield specific information on provenance that can be gained in no other way. Reserving the terms graywacke and arkose for imprecise field descriptions and abandoning the proportion of matrix as a prime means of classification, subquartzose sandstones can be described adequately using six numerical grain parameters. Three primary parameters summing to 100 permit quantitative serial designation of rock types in the form QxFyLz, w ere Q is total quartzose grains, F is total feldspar grains, and L is total unstable lithic fragments in the framework. Three secondary parameters in the form of ratios permit desirable refinement within each primary parameter: C/Q where C is total polycrystalline quartzose grains, P/F where P is total plagioclase grains, and V/L where V is total volcanic lithic grains. Stable grains, whose sum is the parameter Q, are essentially pure silica in mineralogy, and include both monacrystalline quartz and polycrystalline lithic fragments. The latter are gradational to less quartzose types and difficult to distinguish from felsite grains, which display relict textures of volcanic origin and internal relief owing to their polyminerallic nature. Lithic fragments are subdivided at two levels into our main categories within which are various subcategories: (a) volcanic fragments include felsitic, microlitic, lathwork, and vitric types; (b) clastic fragments include silty-sandy and argillaceous types; (c) tectonite fragments include metasedimentary quartzose types and metavolcanic feldspathic or ferromagnesian types; and (d) microgranular fragments include hypabyssal, hornfelsic, and indurated sedimentary types. Interstitial materials include (a) exotic cements like calcite or zeolite; (b) homogeneous, monominerallic phyllosilicate cement displaying textures indicative of porefilling; (c) clayey detrital lutum called protomatrix; (d) recrystallized lutum or protomatrix called orthomatrix with relict detrital texture| (e) murky, polyminerallic, diagenetic pore-filling called epimatr x, whose growth is accompanied by alteration of framework grains; and (f) deformed and recrystallized lithic fragments called pseudomatrix. Extensive albitization and other alterations complicate the interpretation of detrital modes in many rocks, but potential errors commonly can be avoided by close attention to mineralogy and relict texture except where tectonite fabrics disrupt or transpose the original detrital framework. Most subquartzose sandstones were derived from one. or a mixture, of three salient provenance types: (a) volcanic terranes, yielding feldspatholithic rocks nearly free of quartz, (b) plutonic terranes, yielding feldspathic rocks with few lithic fragments, and (c) uplifted sedimentary and metasedimentary "tectonic" terranes, yielding "chert-grain" lithic rocks with f w quartz and feldspar grains except where recycled volcanic or plutonic detritus is abundant. Many voluminous accumulations of subquartzose sandstones near continental margins had as their provenance complex volcano-plutonic orogens representing ancient magmatic arcs analogous to modern arcs associated with trenches.

1,073 citations


Journal ArticleDOI
TL;DR: In the shallow water lagoon of Bimini, Bahamas, the following plants are sufficiently abundant to influence sedimentation locally: Mangroves (Rhizophora mangle), marine grass (Thalassia testudinum), macroscopic green algae (Penicillus, Batophora, Halimeda, Rhipocephalus and Udotea) and microscopic red, green and blue-green algae forming surface mats of intertwining filaments as discussed by the authors.
Abstract: In the shallow water lagoon of Bimini, Bahamas, the following plants are sufficiently abundant to influence sedimentation locally.--mangroves (Rhizophora mangle), marine grass (Thalassia testudinum), macroscopic green algae (Penicillus, Batophora, Halimeda, Rhipocephalus and Udotea) and microscopic red, green and blue-green algae forming surface mats of intertwining filaments (Laurencia, Enteromorpha, Lyngbya and (?)Schizothrix). Plants were observed under conditions of natural tidal currents and artificial unidirectional currents produced in an underwater flume and measurements were made of the abilities of the plants to trap and bind the carbonate sediment. The density of plant growth is crucial in the redu tion of current strength at the sediment-water interface. The most effective baffles are Rhizophora roots exposed above the sediment, dense Thalassia blades and Thalassia blades with dense epiphytic algae, Laurencia intricata and Polysiphonia havanensis. All three types can reduce the velocity of water from a speed sufficiently high to transport loose sand grains along the bottom in clear areas (30 cm/sec) to zero at the sediment-water interface in the vegetated areas. The strongest binders of sediment are the roots of Rhizophora and Thalassia. These two hardy plants trap and bind sediment for a sufficient time to produce an accumulation higher than in nearby areas without dense mangroves or grass. Macroscopic green algae growth is not suf iciently dense and the holdfasts too weak to appreciably affect the accumulation of sediment although they provide a degree of stabilization to the substrate. Algal mats trap sediment chiefly by adhesion of grains to the sticky filaments. Their ability to resist erosion by unidirectional currents varies considerably depending on mat type, smoothness of surface and continuity of the cover. The intact areas of dense Enteromorpha mat can withstand currents five times stronger than those that erode loose unbound sand grains. Premature erosion of mats by currents occurs at breaks in the mat surface caused by the burrowing or browsing action of animals. Algal mats were found to be ephemeral features and consequently do not build up thick accumulations of sediment as do dense grass and m ngroves. The thickest accumulations of sediment in the lagoon correlate with deepest bedrock surfaces. The distribution of many plants in the lagoon is directly or indirectly controlled by the depth to bedrock; for example, mangroves on bedrock highs, marine grass in sediment-filled depressions.

322 citations


Journal ArticleDOI
TL;DR: In this article, a quantitative physical model is proposed to understand the facies transitions in the fining-upwards cyclothems of the Old Red Sandstone (Devonian) of Britain and the Appalachian region of North America.
Abstract: The fining-upwards cyclothems repeated through thick stratigraphic sections in the Old Red Sandstone (Devonian) of Britain and the Appalachian region of North America comprise a maximum of six major facies. The cyclothems when complete consist each of a lower coarse member and an upper fine member, between which the facies are distributed. An analysis of facies transitions is made to arrive at an understanding of the composition and variability of these cyclical deposits. The coarse members, which as regards the variety of facies and numbers of facies representatives are more variable than the fine members of the cyclothems, are shown to have been formed through processes of lateral deposition in streams with sinuous talwegs. A quantitative physical model, partly based on general hydr ulic principles and partly empirical, is advanced to show how the different facies sequences observed in the coarse members can be understood in terms of the chief variables involved in river flow. Specifically, the model reproduces the vertical patterns of grain size and sedimentary structure observed in the coarse members. The model also shows how the coarse members may be interpreted in terms of stream power and channel sinuosity.

291 citations


Journal ArticleDOI
TL;DR: Grain shape can be described as precisely as needed by Fourier series expansion of the radius about the center of mass utilizing coordinates of peripheral points as mentioned in this paper, which can easily discriminate grain differences arising from geographic, stratigraphic, and process factors.
Abstract: Grain shape may be described as precisely as needed by Fourier series expansion of the radius about the center of mass utilizing coordinates of peripheral points. Empirical results of grains from typical samples indicate that the series contains, in partitioned form, a large amount of geologically interesting information. Consequently, previous subjective evaluations of the worth of shape variations in the solution of geologic problems are justified. The shape variable is amenable to semiquantitative graphical evaluation or may be used as data for multivariate analytical schemes. Illustrative examples show that the shape variables easily discriminate grain differences arising from geographic, stratigraphic, and process factors.

271 citations


Journal ArticleDOI
TL;DR: A causal connection between time-velocity asymmetry of tidal currents and bar topography is demonstrated in this article, where the intertidal sand bars of the Minas Basin, Nova Scotia, are asymmetrical in cross-section and linear in plan.
Abstract: The intertidal sand bars of the Minas Basin, Nova Scotia, are asymmetrical in cross-section and linear in plan. They are formed and reworked by tidal currents which are characterized by an asymmetric time-velocity profile. A causal connection between time-velocity asymmetry of tidal currents and bar topography is demonstrated. Average bottom ebb current velocities (90 cm/sec) were found to exceed average bottom flood current velocities (65 cm/sec) over gently-sloping (2 to 3 degree) bar surfaces, whereas over steep-sloping (8 degree) bar surfaces, average bottom flood current velocities (90 cm/sec) were found to exceed average bottom ebb current velocities (65 cm/sec). Both bar topography and zones of flood- or ebb-dominated bottom tidal currents control the distribution of sediment texture and sedimentary structures. On steeper bar slopes, the sediment is fine-grained sand and is characterized by airholes, planar lamination, and surface dunes and ripples. On the gentler bar slopes, the texture of the sediment is medium-grained and coarse-grained sand which has been fashioned into current ripples, simple dunes, complex dunes, simple sand waves and complex sand waves. The internal organization of some dunes and sand waves is extremely complex, inasmuch as thickness of internal sets of cross-stratification is considerably less than dune and sand wave height. A total of 14 sedimentary bar facies are defined from combinations of texture, internal cross-stratification and surface bedforms. Both topography and zones of ebb- and flood-dominated bottom tidal currents control the orientation of directional current structures. Over steep faces of bars, the slip faces of sand waves are oriented in the same direction as flow directions of bottom flood tidal currents, although they do show evidence of reworking by ebb currents. Over gently sloping bar surfaces, slip faces of both dunes and sandwaves are oriented parallel to the direction of flow of bottom ebb current systems. Because dunes and sand waves migrate only during a single phase (ebb or flood) of a tidal cycle, their orientation is generally unimodal. Current ripples are formed in depths of water less than 0.6 meters, during late-stage sheet-like runoff that is controlled by local slope changes on the bar. Indi idual tracer grains are dispersed in a radial-elliptical pattern form a point source. The size of directional properties is hierarchically sensitive to dispersal history. Tracer grains (modeling mineral indicator grains) are dispersed in a radial-elliptical pattern from a point source. Trimodal, highly variant, current ripple slip face orientation develops during late stage sheet runoff at low water depths; this flow is controlled by local bar slope. Unimodal, low variant dune slip faces, sand wave slip faces and associated maximum dip direction of cross-stratification are aligned parallel to tidal current flow and basinal topographic trend. The sand bars are aligned parallel to basinal topographic trend and in turn segregate zones of flood- and ebb-dominated bottom current systems. The tidal sand bars of the Minas Basin are equilibrium forms. Sand is dispersed alternately around the bar through zones of ebb- and flood-dominated bottom tidal currents. As a consequence, the sedimentary facies distribution on the bars has remained essentially unchanged since 1938. Comparison of low-tide airphotos taken in 1938, 1947 and 1963 in one of the study areas shows a slight erosional regime. This erosional regime controls the extreme reworking of sediments, and the formation of an erosional sand wave bedform by wave processes. Physical criteria characteristic of tide-dominated sand bodies include: sharp erosional contacts between sets of cross-stratification; rounded upper set boundaries of cross-stratification; unimodal and bimodal distributions of orientation of cross-stratification; bimodal distributions of set thickness and dip angles of cross-stratification; orientation of dunes, sand waves and cross-stratification in the dominant direction of flood or ebb tidal flow, basinal topographic trend and sand body axis; trimodal orientation of current ripples; oblique or 90° superposition of smaller current ripples on larger current ripples; double-crested current ripples; superposition of current ripples at 90° or 180° on slip faces and crests of dunes and sand waves; complex organization of inte nal cross-stratification in sand waves; etch marks on slip faces of dunes and sand waves; and alignment of the long axis of sand bodies parallel to tidal current flow, basinal topographic trend and basin axis.

241 citations


Journal ArticleDOI
TL;DR: A survey of clay mineral distribution shows that any major-group clay mineral may occur (be found though not necessarily formed) in any major sedimentational environment as discussed by the authors, and it is suggested that the greatest utility of indicator minerals will be achieved if they are defined first by geochemical parameters which are then translated into geologic environments.
Abstract: Clay minerals are reactive responses of geologic materials to energies characterizing certain environments during time. They may therefore be indicators of the reacting environments. Conversely, after a clay mineral has formed, it becomes a reactive and characteristic part of the environment--whereupon the environment acts also as an indicator of the clay mineral in it. A mineral used as an indicator is not only geologic, but also is psychologic in import because it must be recognized, and likewise is conceptual because its use includes interpretation. Environments are described in geologic jargon from a geologic viewpoint, and alternatively in geochemical parameters which permit higher precision in description in relation to stabilities of specific minerals. It is suggested that greatest utility of indicator minerals will be achieved if they are defined first by geochemical parameters which are then translated into geologic environments. Environments may be micro-, macro-, and mega- in scale; they may radically differ among themselves in geochemical characteristics although one may constitute a scale part of another. Clay minerals found here may not have formed here. Therefore, maximum caution must be used when environmental interpretations are drawn from clay mineral occurrences. Primary-stage clay minerals are those formed as clay minerals for the first time; they are formed here. Other clay minerals that are altered or deposited in an environment different from their primary genesis are termed N + 1 stage clay minerals. Examples are cited in the paper of primary-stage clay minerals deposited from solution, by replacement, by crystallization from a colloidal gel, and alteration of non-layer silicates. The geochemical environments in which these geneses occurred are taken to be described or defined by stability-diagram models such as those which have been prepared for systems of H2O-SiO2-Al2O3 and Na2O or K2O. It is suggested that the solubility of Al and its complexes is less well understood than of the other components of clay minerals, and probably is a more important variable in clay mineral genesis than has been documented. In clay-mineral forming systems, kaolin tends to be produced when [H+] is high relative to Metal ions, and End_Page 788------------------------ Al concentration is high. The 3-layer clay minerals tend to be formed where concentrations of Ca2+, Mg2+ Fe2+, and SiO2 are high in relation to others. Illite requires [K+] high relative to other Metal ions. N + 1 stage clay minerals transformed during deposition in marine environments include chlorite. and illite from antecedent "open illite." Maximum diagenetic illitization and probably chloritization occur, however, upon deep burial and/or contact of clay minerals with relatively high concentrations of K+ and Mg2+. Designation of an indicator mineral of marine environment must be accompanied or preceded by a clear cut, geochemical definition of what is meant by "marineness" in a marine environment, a definition that is apparently still lacking. A survey of clay mineral distribution shows that any major-group clay mineral may occur (be found though not necessarily formed) in any major sedimentational environment. Hydrothermal clay minerals are best recognized from their geologic occurrences. Metamorphic and igneous clay minerals, i.e.. clay mineral formed in metamorphic and igneous environments, have been reported as saponite in limestones (Dalradian) in sillimanite grade zones, and smectite in andesite.

184 citations


Journal ArticleDOI
TL;DR: In this article, the composition and microstructure of widespread subtidal biological mats binding sandy carbonate sediments in the Rock Harbour Cays vicinity of Little Bahama Bank were examined in detail; these mats were subjected to in situ flume experiments.
Abstract: The composition and microstructure of widespread subtidal biological mats binding sandy carbonate sediments in the Rock Harbour Cays vicinity of Little Bahama Bank were examined in detail; these mats were subjected to in situ flume experiments. The mats consist of various assemblages of green algae, red algae, blue-green algae, diatoms and animal-built sand grain tubes. Green algae, red algae and/or sand grain tubes provide a rigid open network into which grains infiltrate and are trapped. The mucilaginous secretions of both blue-green algae and diatoms in association with the fine filaments of blue-green algae bind the grains to each other and to the mat network. On the basis of composition and microstructure, three basic mat types were recognized: a fibrous, rigid, Cladoph ropsis mat; a thin, gelatinous, Lyngbya mat; a cohesive, aggregated, Schizothrix mat. The erosion by artificial currents of initially undisturbed mats was studied in the field using an underwater flume, and the complex manner in which the mats disintegrated was recorded. The surface sediment from each mat area was then treated with NaOCl to remove the organic matter and erosion tests repeated in a tank in the laboratory with the same apparatus. The natural, in situ, mat-bound sediment could withstand current velocities at least twice as high and, in some cases, as much as five times as high as those that eroded the treated, unbound sediment. The intact mat surface could withstand direct current velocities three to nine times as high as the maximum tidal currents 13 cm/sec) recorded in the mat environment. Each mat type eroded in a characteristic manner and sequence dependent upon the mat composition and microstructure. This breakdown process differed markedly from the erosion behavior of loose sediment. Observations indicate that grain size, sorting, packing, structure and sediment surface morphology are influenced by mat formation. This study demonstrates the need for close consideration of interfacial biological communities when examining depositional and erosional processes at the sediment-water interface, or when making interpretations from the products of these processes in ancient rocks.

181 citations


Journal ArticleDOI
TL;DR: Basalt pebble morphology was studied in nine rivers and on fourteen high and low-wave-energy beaches around Tahiti-Nui as mentioned in this paper, where the maximum projection sphericity averaged.68 for rivers,.64 for low wave energy beaches, and.58 for high wave energy ones.
Abstract: Basalt pebble morphology was studied in nine rivers and on fourteen high- and low-wave-energy beaches around Tahiti-Nui. The study included about 15,000 measurements on 961 pebbles in the 16-256 mm size range. Tahiti was chosen because it consists predominantly of isotropically-wearing basalt, has many rivers, and numerous beaches with different sand-pebble ratios and different wave energy characteristics. The maximum projection sphericity averaged .68 for rivers, .64 for low-wave-energy beaches, and .58 for high-wave-energy beaches. Roundness averaged .38 for rivers, .47 for low-wave-energy beaches, and .55 for high-wave-energy beaches. The oblate-prolate index averaged +0.18 (prolate, rod-like) for rivers, -0.81 for low-wave-energy beaches, and -2.13 (oblate, disc-like) for high-wave-energy beaches. It appears that a sphericity value of under .66 and oblate-prolate index more negative than -1.5 distinguish beach from river pebbles. On sandy, low-wave-energy beaches the smallest pebbles are flattest, while on gravelling, high-wave-energy beaches the largest pebbles are flattest. Thus the optimum sliding size of pebble is a measure of surf vigor. A selective trapping effect causes discs to be more abundant on sandy than on gravelly beaches. Abrasion is the chief cause for the abundance of discs on the beaches; evidence is that as roundness increases from rivers to beaches, sphericity decreases and oblate-prolate index becomes more negative (disc-like). The production of discs on the beaches is predominantly a result of abrasion caused by pebbles sliding back and forth over sand or smaller pebbles in the surf zone. This change in shape is accomplished within distances of a few feet to a few hundred feet of the river mouth. Selective shape sorting is also important on some beaches with waves 1-3 feet high, and sandy beaches tend to selectively trap discs.

181 citations



Journal ArticleDOI
TL;DR: Porphyroblastic and alabastrine secondary gypsum is divided into two main petrographic groups, porphyro-blastic (PBP) and alABastrine (ABG) as mentioned in this paper.
Abstract: Secondary gypsum rocks, formed from anhydrite by the action of ground waters and/or surface weathering and unmodified by tectonic influences, are divided into two main petrographic groups, porphyroblastic and alabastrine secondary gypsum. The two groups though often occurring together, are thought to be essentially distinct. Porphyroblastic gypsum is the first to form and sometimes dates from early diagenesis. Alabastrine gypsum includes a wide variety of related textures. Hydration fabrics vary from indefinite grains with irregular extinction to more perfectly defined granoblastic gypsum. Recrystallization of hydration gypsum leads to unequigranular granoblastic gypsum, in unstrained and perfectly oriented grains. Prophyroblastic gypsum may also recrystallize in conjunction with the labastrine variety. In most cases of gypsification there is no evidence for any volume increase or associated crushing, and there may often be a net volume reduction due to solution. Excess amounts of certain trace-elements, notably strontium and boron, are released from some anhydrite rocks during hydration and occur in the form of such minerals as celestite and probertite. Three reaction mechanisms appear to be possible, all of which may occur naturally to a greater or lesser extent. Late stage displacive gypsum veins possibly form from the excess sulfate removed in solution during gypsification, or alternatively may precipitate from sulfate-rich connate waters.

105 citations



Journal ArticleDOI
TL;DR: In this article, the authors examined the paleoecologic implications of differential shell burial and destruction in a shallow, low energy, sublittoral environment and found that shells with less surface area per unit weight were buried more rapidly than thinner and lighter valves, which were maintained above the ediment-water interface.
Abstract: Eighty four single valves, equally divided between the bivalve species M. mercenaria, Argopecten i. irradians and Mya arenaria, were submerged for three years in a shallow, low energy, sublittoral environment. Weight changes, modifications in shell characteristics, the growth of attached epifauna, and the effects of boring algae were recorded on a yearly basis. Valves with greater surface area per unit weight suffer a greater weight change, are more subject to breakage, and are more heavily encrusted with attached epifauna than those with less surface area per unit weight. These differences are explained in terms of differential burial; shells with less surface area per unit weight being buried more rapidly than thinner and lighter valves, which are maintained above the ediment-water interface. Solution appears to be the chief destructive agent below the sediment-water interface whereas boring marine organisms are the dominant agent in shell destruction above the interface. Comparison with other environments indicates that shell destruction is 150 to 1000 times more rapid in surf zones when abrasion is the principal destructive agent, than it is in low energy sublittoral environments. The paleoecologic implications of differential shell burial and destruction are examined.

Journal ArticleDOI
TL;DR: Using an area of recent lacustrine sedimentation as a reference model, several methods of treating grain-size distribution of sands were evaluated for their ability to discriminate between, or identify, depositional environments as mentioned in this paper.
Abstract: Using an area of recent lacustrine sedimentation as a reference model, several methods of treating grain-size distribution of sands were evaluated for their ability to discriminate between, or identify, depositional environments. The techniques of Passega (1957), Mason and Folk (1958), Friedman (1961), Sahu (1964), and Klovan (1966) were applied to sediment samples from known depositional settings. When analyzed as though from unknown environments, none of the methods could reliably identify the true depositional environment of the samples as established on the basis of hydrographic, topographic, geographic and sedimentologic criteria. Of the methods, only factor analysis (Klovan, 1966) produced mappable results consistent with known energy conditions at the depositional sites. Differences in energy conditions which may exist between lacustrine and marine environments may be such that the techniques might not be expected to be environmentally sensitive. However, the ultimate goal of all such "grain-size-environment" studies is to predict depositional environments of ancient sand bodies for which little or no information concerning the depositional setting is available. Because factor analysis was able to produce useable results even under the restricting conditions of a lacustrine setting it may be expected that it will perform even better in the marine realm. The lack of success of the methods may result from any or all of the following factors: (1) Standard bivariate plots cannot adequately express the complex processes producing particular grain-size distributions. (2) Grain-size parameters are merely descriptors of grain-size distributions. As such they may not contain all available information, nor perhaps of the right kind, to enable environmental determination. (3) Combinations of amount and type of kinetic energy (which may be primarily responsible for the grain-size distribution of a sand) may produce similar distributions in different environments. The hypothesis that grain-size distributions can identify depositional environments is probably not universally valid. It is concluded that grain-size distributions reflect depositional processes rather than environment and that the two need not be the same.

Journal ArticleDOI
TL;DR: Epibiotic growth of coralline red algae and serpulid worms on the marine turtle grass Thalassia testudinum is sufficient to produce carbonate mud at rates comparable to the rates of accumulation of ancient platform carbonates.
Abstract: Epibiotic growth of coralline red algae and serpulid worms on the marine turtle grass Thalassia testudinum is sufficient to produce carbonate mud at rates comparable to the rates of accumulation of ancient platform carbonates

Journal ArticleDOI
TL;DR: In this paper, Deepstar 4000 observations from Block and Corsair Canyons indicate that erosion is pre predominantly biological, and no evidence for large mass movements in the axis area or recent turbidity current activity was observed in either canyon.
Abstract: Observations from Deepstar 4000 in Block and Corsair Canyons indicate that, at present, erosion is pre predominantly biological. No evidence for large mass movements in the axis area or recent turbidity current activity was observed in either canyon.

Journal ArticleDOI
TL;DR: The Penrith Sandstone (Lower Permian) of north west England is a continental red bed sandstone, deposited as barchan sand dunes in a hot, arid desert environment.
Abstract: The Penrith Sandstone (Lower Permian) of north west England is a continental red bed sandstone, deposited as barchan sand dunes in a hot, arid desert environment. The rock displays a high degree of mineralogical and textural maturity, being a coarse, well sorted orthoquartzite, composed of rounded unstrained, strained and polycrystalline quartz grains, with subordinate feldspar and rock fragments. Distinct petrographic features of the detrital grains suggest derivation from the Millstone Grit (Upper Carboniferous) sandstones of Yorkshire, and perhaps County Durham. In the southern part of the area non-silicified sandstones are interbedded with calcite cemented alluvial fan breccias (brockrams). This contrasts markedly with northern areas where brockrams are absent, in that the sandstones are tightly cemented with secondary quartz, occurring as overgrowths of optically continuous, bipyramidal quartz crystals around detrital grains. Many varieties of overgrowth are present, their structure being pre-determined by the internal structure of the detrital grains. Thus, unicrystaline unstrained and strained, and polycrystalline overgrowths can be recognised. Overgrowths of secondary feldspar occur occasionally on detrital orthoclase and microcline. It is suggested that the source of the secondary quartz is due to the solution of the siliceous dusts produced during aeolian abrasion of the quartz grains. Alkaline desert groundwaters are considered to be responsible for taking the siliceous dust into solution, which, upon evaporation, precipitated the silica as optically continuous quartz overgrowths around the detrital grains. The inverse relationship between silicification of the Penrith Sandstones and brockram distribution is attributed to differences in compositon of the groundwaters in the two facies.


Journal ArticleDOI
TL;DR: The difference in color between the Upper Ordovician red Juniata and underlying drab (gray-green) Bald Eagle Formations in central Pennsylvania is of secondary, diagenetic origin this paper.
Abstract: Diverse geochemical data on mineral compositions and abundances, coupled with stratigraphic data on mineral distributions, indicate that the difference in color between the Upper Ordovician red Juniata and underlying drab (gray-green) Bald Eagle Formations in central Pennsylvania is of secondary, diagenetic origin. The color boundary separating the two sandstone units cuts across lithofacies boundaries, and varies more than 700 feet in vertical position. Red hematite pigment consistently occurs between grains at points of grain contact in red rocks, whereas drab clay-mineral pigment does not consistently occupy this textural site in drab rocks. At least some of both pigments has been secondarily generated; drab-pigment generation occurred later than red-pigment generation. Opaque-oxid grains are of identical composition in both drab and red rocks, but are much less abundant in drab rocks. Chlorite is more abundant and more iron-rich in matrices of drab sandstones than in those of red sandstones. Drab rocks contain less total iron and less ferric iron than red rocks. These and other data suggest that red pigment was diagenetically removed from the lower portions of an initially all-red sequence by aqueous reduction and dissolution, with generation of iron-rich clay-mineral phases stable in a saturated environment.

Journal ArticleDOI
TL;DR: Pore casts provide information on the distribution and shape of pores and interconnecting passageways that influence permeability and control the flow of fluids as mentioned in this paper, and are useful for the study of pore geometry can be prepared from rocks impregnated with plastic.
Abstract: Various types of pore casts, replicas of void space, useful for the study of pore geometry can be prepared from rocks impregnated with plastic. Conventional light microscopes are suitable for examination of most pore casts, however the scanning electron microscope is definitely superior and is essential for good photographic illustrations. Study of pore casts provides information on the distribution and shape of pores and interconnecting passageways that influence permeability and control the flow of fluids.

Journal ArticleDOI
TL;DR: In this paper, an idealised standard sedimentary cycle is proposed which, in the vertically upward sequence, comprises the following lithologic types: (A) pebbly very coarse sandstone, (B) coarse to medium sandstone and fine sandstone (C) fine sandstones, (D) interbedded assemblage of fine to medium siltstones, siltstone and shale, (E) carbonaceous silt stone and shale (F) coal, shaly coal), and (G) coal seam.
Abstract: This study corroborates the earlier view that the Barakar coal measures (Lower Permian), as examined in 14 "Lower" Gondwana coalfields, is largely of cyclic nature. An idealised standard sedimentary cycle is proposed which, in the vertically upward sequence, comprises the following lithologic types: (A) pebbly very coarse sandstone, (B) coarse to medium sandstone, (C) fine sandstone, (D) interbedded assemblage of fine to medium sandstone, siltstone and shale, (E) carbonaceous siltstone and shale, (F) coal, shaly coal. Most cycles are, however, truncated, nonetheless each shows a fining upward character. Bedding types, like texture, show systematic variation within each cycle. Largescale cross-bedding which occurs profusely in the lower two units is steadily replaced by smallscale cros -bedding, wavy or parallel lamination in the succeeding units above. The associated sedimentary characters suggest that as the deposition of a cyclothem proceeded, the flow intensity progressively decreased, and was perhaps considerably reduced during the deposition of the carbonaceous unit (E). Significantly, the next unit above is a coal seam in many cyclothems, which may suggest stagnation of the depositional area allowing mainly vegetal accumulation. Sedimentation inevitably took place in the alluvial basin(s), and, for each cyclothem, the lower coarse grade member apparently represents a variety of lateral accretion deposits and the upper fine grade member largely overbank and lake/swamp deposition. It is suggested that the development of cycles was in all probability controlled by (1) channel or sediment wandering, and (2) intermittent tectonism in the basin which tended to convert the alluvial flood plain into coal-forming environment.

Journal ArticleDOI
TL;DR: In this article, a technique utilizing a petrographic microscope with a flat stage for analysis of provenance has been developed, which concentrates feldspar in the medium or coarser sand range by flotation techniques, and then separates this concentrate by means of heavy liquids into potash, albite, oligoclase-andesine, and calcic plagioclase.
Abstract: A technique utilizing a petrographic microscope with a flat stage for analysis of provenance has been developed. Procedure is to concentrate feldspar in the medium or coarser sand range by flotation techniques, then to separate this concentrate by means of heavy liquids into potash feldspar, albite, oligoclase-andesine, and calcic plagioclase. Thin sections of these plagioclase separations are examined for twin characteristics (C-twins, A-twins, and untwinned), and zoning characteristics (progressive, oscillatory, and unzoned). This leads to inferences about the presence of metamorphic, plutonic igneous, or volcanic-hypabyssal rocks in the source area. Only the predominant rock type usually can be detected. An exception to this is volcanic and hypabyssal rocks, which commonly yield pl gioclase with diagnostic properties.

Journal ArticleDOI
TL;DR: Pleistocene and recent Mississippi sediments possess a distinctive heavy mineral assemblage which retains its identity between Cairo, Illinois and the Gulf of Mexico Abyssal Plain this article, which is used to trace the Mississippi contribution from fluvial, through deltaic, neritic and bathyal, to abyssal environments.
Abstract: Pleistocene and Recent Mississippi sediments possess a distinctive heavy mineral assemblage which retains its identity between Cairo, Illinois and the Gulf of Mexico Abyssal Plain. Thus this assemblage may be used to trace the Mississippi contribution to the Gulf of Mexico from fluvial, through deltaic, neritic and bathyal, to abyssal environments. Significant changes in the heavy mineral assemblage of sediments in the Gulf are related to source changes and not to the reworking or selective sorting of Mississippi sediments. As a result, three distinct sediment input sources may be recognized for detrital sediments in the Gulf of Mexico Abyssal Plain, 1) The Mississippi, 2) the Rio Grande, and 3) the rivers of north-east Mexico. The Mississippi contribution is dominant and is only repl ced by other inputs in the northwest and southwest corners of the abyssal plain. On the Louisiana-Texas Inner Continental Shelf, Mississippi sediment forms a veneer which extends between the present delta and the Sabine River. Dredge samples reveal that underlying sediments were derived from the central Texas rivers to the west, probably during a period of regression which occurred between 10,000 and 7,000 B.P. The interaction of a high zircon content and intense selective sorting in the Inner Continental Shelf sediments has resulted in two areas of zircon enrichment which may be of economic significance. Because of the insensitivity of the heavy mineral assemblage of the Mississippi contribution to processes of selective sorting and reworking, only 200 non-opaque grains from one size fraction of one sample are needed to characterize this contribution.

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TL;DR: In this paper, the authors studied the Permian and Triassic Gondwana deposits around Bheemaram and found that pebble sizes in the Upper Kamthi decrease to the west-southwest, possibly due to a local swing in t e size trends.
Abstract: The Permian and Triassic Gondwana deposits around Bheemaram belong to six mapable rock units ("formations"): Barakar, Ironstone Shale, Kamthi, Yerrapalli, Bhimaram and Maleri. Of these, the Barakar, Middle and Upper Kamthi and Bhimaram formation are composed of profusely cross-bedded, prismatic or lenticular bodies of coarse, argillaceous sandstones. The other formations are made of structureless, thin sheets of clay stone (or shale) and silty sandstones with inter-bedded lenses of calcareous sandstones and sandy limestones. The sandy and clayey formation juxtapose, often, with interfingering contacts. Lithology, sand, body geometry, primary structures and patterns of grain-size distribution of these Gondwana rocks are comparable to those of fluvial sediments. The coarser fractions of the rocks which were transported mainly by tractive currents, constituted point-bars and channel-bars of the Gondwana river and the finer fractions were deposited from suspension in the interchannel floodplain areas. Cross-bedding dip directions indicate a northerly paleocurrent. In the Lower Kamtha, the measurements show large dispersion due to arcuate directions of flow at the river meanders. With time, the direction of sediment transport shifted gradually, but statistically significantly, to the west. The flow was essentially unidirectional during the later phase of Kamthi sedimentaion. Orientation of long-axes of elongate pebbles and ripple mark lee-slopes are in conformity with the local foreset dip directions. Within the limited area studied, only slight suggestion of a northerly decrease in cross-bedding thickness, indicating a northerly paleocurrent, is noted. Contrary to these observations, pebble sizes in the Upper Kamthi decrease to the west-southwest, possibly due to a local swing in t e size trends. Variations in pebble size seem to yield useful paleocurrent clues only when studied on a regional scale with the observations restricted to the same depositional plane. Pebble roundness is found to vary only as a function of pebble size, and provide no clue to the paleocurrent direction. The study reveals an uninterrupted fluvial sedimentation during the Upper Paleozoic and Mesozoic, during which time, a number of dissimilar sedimentological units were contemporaneously deposited in the varied environs of the same fluvial system. On the other hand, several similar units were also deposited in similar environmental conditions at different times. An appropriate scheme of Gondwana classification should be developed to depict the complex relationship between the various lithological, chronological and biological units which have developed in this process.

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TL;DR: An analysis of the mineralogy and geochemistry of continental shelf sediments offshore of the Washington-Oregon Coast indicates that three depositional areas are present on the continental shelf; these consist of a nearshore area including the lower portion of the Columbia River estuary and a main shelf area, both characterized by poorly sorted sediments, and a third area seaward of 80 fm which is characterized by glauconitic sediments.
Abstract: An analysis of the mineralogy and geochemistry of continental shelf sediments offshore of the Washington-Oregon Coast indicates that three depositional areas are present on the continental shelf; these consist of a nearshore area including the lower portion of the Columbia River estuary and a main shelf area, both characterized by poorly sorted sediments, and a third area seaward of 80 fm which is characterized by glauconitic sediments. Within each area the mineral and chemical compositions of the sediments appear distinctive and characteristic for the area. The glauconite in the continental shelf sediments is generally found in the deeper shelf areas. It is derived from glauconitic-bearing Tertiary sedimentary rock units exposed in the area, some may be transported north from shelf areas off central and southern Oregon and some may be forming in place. Boron is associated with the glauconite and may be indicative of the presence of glauconite or as an indicator of the marine environment.

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TL;DR: In this paper, the authors examined the evolution of carbonate mounds in the McKelligon Canyon Formation (Cloud and Barnes subunit B1, interval 15) and the largest mound found, Lechuguilla Mound, in detail.
Abstract: Relatively small-scaled carbonate mounds are a conspicuous sedimentary feature within various stratigraphic horizons of lite Lower Ordovician El Paso Group, southern Franklin Mountains, west Texas. Mounds are best developed within the McKelligon Canyon Formation (Cloud and Barnes subunit B1, interval 15) and the largest mound found, Lechuguilla Mound, has been examined in detail in order to shed some light on the factors controlling and determining the morphology, petrology, and biotic sequence of the mound interval. Three distinctive growth stages can be recognized: (1) establishment of a pioneer colony, (2) the development into a mature biotic entity, and (3) development of a climax community. This sequential growth series may reflect a simple response to organism require ents with increasingly shallower depositional environments. Many of the McKelligon Canyon mounds are cut by channels filled with rather coarse calcarenites. It is believed that the channels are erosional features formed during repetitive intervals when mounds were subaerially exposed, eroded, and subsequently filled in with available skeletal debris. These erosional intervals are probably related to shifts in sea level stages occurring within a shallow intertidal to subtidal depositional environment. The Lower Ordovician mounds present in the southern Franklin Mountains of west Texas closely resemble the Middle Ordovician (Chazyan) mounds of northeastern New York and western Vermont in gross morphology, petrology, and basic biotic composition and sequence, although there are important temporal biotic differences when evolutionarily more advanced organisms occupied similar mound niches.

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TL;DR: Carbon and oxygen isotopes were analyzed in carbonate apatite CO2 and in coexisting calcite as discussed by the authors, and the results confirmed the proposition that carbonate is part of the apatitic structure.
Abstract: Carbon and oxygen isotopes were analyzed in carbonate apatite CO2 and in co-existing calcite Both C and O in apatite CO2 are enriched in the respective light isotopes relative to calcite These results confirm the proposition that carbonate is part of the apatite structure

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TL;DR: The detailed nature of relict sediments resulting from and related to the Holocene transgression has been revealed through a sedimentological study of a densely sampled segment of the Long Island, New York, continental shelf as mentioned in this paper.
Abstract: The detailed nature of relict sediments resulting from and related to the Holocene transgression has been revealed through a sedimentological study of a densely sampled segment of the Long Island, New York, continental shelf. Bathymetry of the Long Island shelf reflects the relict patterns of subaerial coastal-plain fluvial drainage systems from lower stands of sea level. The shelf sediments can he divided into an inner (0 to 25 fathoms) and middle (25 to 35 fathoms) shelf clean sand facies and an outer (>35 fathoms) shelf muddy sand facies. Locally on the middle shelf, the outer muddy sand facies is preserved as erosional remnants and also within the interiors of shells that are buried in the clean sand. This evidence supports the view that the outer muddy sediment is relict (Garrison and McMaster, 1966); the sharp "mud line" at about 35 fathoms results not from modern deposition but from the winnowing of the formerly more extensive muddy sediment. Standard deviation values for the inner shelf sands class them as moderately well sorted for the most part; skewness, in general, is slightly positive. Standard deviation values for the middle shelf sands class them as moderately sorted; both negative and positive skewness values characterize middle shelf sands. The outer shelf sediments are positively skewed and poorly to extremely poorly sorted because of the increasing percentage of fines. The grain size distributions were plotted on log-phi scale and distinct populations were separated using Hald's technique (1952). In the distributions of the inner and middle shelf sands, three populations (A, B, and C) were recognized which appear to correspond to the three populations described by Moss (1962, 1963) which he supposed resulted from saltation (A), interstitial entrapment and/or suspension (B), and sliding and rolling (C). The interrelationships among skewness, mean grain size, and standard deviation are in light of the dissection of the frequency curves and the influence of flues (< 62 microns). Using the population concept as well as statistical moment measures of the size distribution, the relict nature of the shelf sediments are interpreted as representing various relict environments. The absence of the B population indicates deposition in the surf zone where intense winnowing occurs. The presence of the C population also suggests deposition in the surf zone. Deposition from currents is indicated by the presence of the B population. Very few of the shelf sands have the size characteristics of beach swash zone deposits. Most are, however, relict of shallow nearshore environments. Most of the inner shelf sands appear to have been modified by currents, whereas man of the middle shelf sands are relict of deposition in the surf zone. The outer shelf sands are bimodal and by graphical dissection of the size distribution, a distinct fine sand mode can be traced as a separate sedimentation unit. When the sea was at about 35 fathoms, the fine sand was swept by currents (B population is present) from shoal areas to the northeast of the study area into an embayment area. This relict fine sand deposit spread to the southwest and mixed with the coarser basal sands of the transgression. Short cores on the inner shelf indicate that fine winnowed sand on the inner shelf probably represents the reworking of a backbarrier facies by the transgressive sea. The inner shelf sands are mineralogically more mature (orthoquartzose) but more angular (mean roundness (rho) for medium quartz grains) than the middle and outer shelf sands (subarkosic).

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TL;DR: In the lower Mesopotamian plain of Iran, the minimum sediment accumulation is 0.1 cm/year, but if restricted to the marsh areas is 1.0 cm/ year.
Abstract: Clay mineral fractions of the Euphrates and Tigris Rivers show marked differences related to the nature of the provenance area. The Euphrates is richer in both chlorite and expandable lattice clays. All the suspension load of the two rivers is deposited prior to entering the Persian Gulf. Minimum sediment accumulation in the lower Mesopotamian Plain is 0.1 cm/year, but if restricted to the marsh areas is 1.0 cm/year. Downwarp to form the present plain began in upper Miocene and is presently continuing. Marginal upwarping has occurred since human habitation of the region.

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TL;DR: In this paper, the authors interpreted variations in clast lithologies in terms of dispersal on eleven alluvial fans as inter-fan in origin (gross differences between adjacent fans), and measured maximum clast size revealed intra-fan changes, namely decrease with distance of transport.
Abstract: Lower-Middle Devonian continental conglomerates, with minor sandstones, form a belt 150 miles long and up to 10 miles wide in eastern Prince of Wales Island, bordering an uplifted area of Lower Paleozoic and Precambrian rocks (Boothia Uplift). The succession forms part of the Peel Sound Formation; it reaches 1000 feet in thickness and towards the west the coarse clastics intertongue into sandstones, which in turn grade into shales and carbonates. Conglomerate clast types and directional sedimentary structures indicate derivation from the Boothia Uplift. The conglomerates are poorly sorted and mean grain size lies in the pebble range, comparing closely with modern alluvial fan deposits. Areal variations in clast lithologies are interpreted in terms of dispersal on eleven alluvial fans. Areal variations in grain size and clast roundness are interpreted as inter-fan in origin (gross differences between adjacent fans). Measurements of maximum clast size revealed intra-fan changes, namely decrease with distance of transport. Clast changes in vertical section are attributed to varying rates of uplift and erosion in the source area. Comparison of grain size and textural characteristics of the conglomerates with those of modern deposits suggests a debris flood mode of origin.

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TL;DR: A bed of kaolinite mudstone, a tonstein, about 2 inches thick was deposited over at least 3,000 sq. miles in the Coal Measures of the Midlands and of the North of England.
Abstract: A bed of kaolinite mudstone, a tonstein, about 2 inches thick was deposited over at least 3,000 sq. miles in the Coal Measures of the Midlands and of the North of England. Based on the field relationships, the petrography, the mineralogy and the geochemistry it is claimed that this band was formed by the in situ alteration of volcanic ash. This tonstein is, therefore, thought to be a bentonite. A review is also given of the literature on tonsteins and postulated origins.