Showing papers in "Journal of Sedimentary Research in 1978"
TL;DR: Most calcite in speleothems is composed of columnar crystals (palisade calcite) and exhibits fabrics similar to those in some porefilling calcites interpreted to be replacive after acicular carbonate cements as discussed by the authors.
Abstract: Most calcite in speleothems is composed of columnar crystals (palisade calcite) and exhibits fabrics similar to those in some porefilling calcites interpreted to be replacive after acicular carbonate cements. The columnar crystals do not interfere with each other's growth (suggesting that they are secondary features) and this, together with the occurrence of layers of acicular calcite in some speleothems, leads to a conclusion that columnar crystals have replaced acicular carbonate. The evidence, however, is misleading. The same crystal fabrics can be explained by normal, but somewhat complex, growth processes. Inclusions (and patterns made by them) constitute the most important clues to the origin of the columnar crystals. Most inclusions are fluid-filled cavities and six types of growth layering are distinguished on the basis of variations in inclusion abundance, size and pattern. Growth layers defined by parallel, linear inclusions are interpreted to have formed during the incomplete lateral coalescence of numerous syntaxial overgrowth crystallites which grow upon the speleothem surface. The linear inclusions represent remnants of the former inter-crystallite spaces. Complete crystallite coalescence generates inclusion-free calcite, whereas inhibition of the lateral coalescence of the overgrowth crystallites generates layers of acicular calcite. During episodes of cave-flooding, however, he crystallites merge and overgrow each other and precipitation eventually occurs upon large, planar crystal faces. It is believed that the distinctive fabrics of palisade calcite are formed because precipitation usually occurs from thin water films that flow over the growing speleothem surfaces. Large crystal terminations do not form on the speleothem surface because they form projections that disturb the water flow away from the projections which, as a consequence, are gradually eliminated. Small crystal terminations (crystallites), on the other hand, do not disturb the water-flow and thus come to dominate the growth surfaces. Petrographic distinction columnar calcite crystals in speleothems (and other vadose calcites with similar fabrics) and mosaics of columnar crystals that have replaced earlier, acicular-carbonate cements is commonly difficult. Such distinctions are attempts to distinguish between calcite crystals that have grown penecontemporaneously from numerous syntaxial overgrowths (calcites in speleothems) and other calcites in which replacement occurs at a much later date, possibly accompanied by replacement of a metastable phase (replacement of acicular cements).
188 citations
TL;DR: In the Galeta reef off Galeta Point, Panama as mentioned in this paper, the concentration and distribution of submarine cements vary considerably throughout a section of a modern coral reef, as disclosed by cores from thirteen drill holes up to 14 m deep.
Abstract: Petrographic characteristics and distribution of submarine cements vary considerably throughout a section of a modern reef off Galeta Point, Panama, as disclosed by cores from thirteen drill holes up to 14 m deep. Core holes were closely spaced along two transect lines which, when combined, extend from inshore mangroves to the outer reef slope of this Caribbean fringing reef. The submarine cement is predominantly dense, submicrocrystalline-microcrystalline to porous, submicrosucrosic magnesium calcite (15 to 19 mole percent MgCO3), with minor amounts of acicular aragonite. Magnesium calcite coats, infills and forms a matrix around various reef components, whereas aragonite is generally restricted to rim cement in skeletal cavities of corals. Variations in concentration and type of submarine lithification are not related to depth in Galeta reef. Rather, submarine cementation appears to be a relatively near-surface phenomenon most prevalent in sedimentological units (facies) of the reef which were formed under conditions of high agitation and/or slow accumulation. Therefore, well-developed cement crusts and infilled rims of the Acropora palmata facies, formed under high agitation but also at a rapid rate of accumulation, grade into dense matrix cement in the agglomerate limestone of the slower accreting fore-reef pavement facies and in the extensively bored and filled corals of the coral-head facies in the fore reef. Cements are absent or generally poorly developed in the deeper fore-reef talus or in protected reef-f at rubble and back-reef sediments.
157 citations
TL;DR: Macaronichnus segregatis as mentioned in this paper is a trace fossil that occurs in Jurassic and younger sand or sandstone, and it was found only in deposits thought, on the basis of other evidence, to be shallow marine origin.
Abstract: The name Macaronichnus segregatis is here proposed for a distinctive trace fossil that occurs in Jurassic and younger sand or sandstone. The trace fossil consists of a cylindrical smooth-sided, sinuous intrastratal trail, 0.3-0.5 cm in diameter, filled with sand slightly fighter in color than the host sand. Mica flakes or heavy minerals generally are concentrated around the margin. The trails interpenetrate but do not branch, tend to be more or less horizontal, and generally occur in dense concentration. The trace fossil has been found only in deposits thought, on the basis of other evidence, to be of shallow marine origin. A similar intrastratal trail occurs in modern intertidal and shallow subtidal sand in Willapa Bay, Washington, where it is produced by the marine polychaete, Ophelia limacina. This polychaete is a deposit feeder that largely sustains itself on bacteria and organic matter on the surface of sand grains. The trail is a feeding trace, apparently formed by the selective ingestion of grains with rough surface texture, which have a relatively larger surface area and potentially higher bacteria count than do smooth grains such as mica flakes, clay mineral aggregates, or certain heavy minerals. When engaged solely in locomotion, O. limacina produces a trace that disrupts layering but shows no mineralogic segregation. The genus, Ophelia, occurs in intertidal and shallow subtidal sands over a broad geographic range. The ancient examples of Macaronichnus segregatis, although not necessarily produced by Ophelia, were probably formed by a deposit feeding polychaete of similar size and shape. The depositional setting of the known occurrences of this trace fossil, and the production of the trace by a modern shallow marine polychaete, suggest that it may be an excellent indicator of ancient intertidal and shallow subtidal deposits.
146 citations
TL;DR: The origin of calcite, Mg-calcite, and aragonite cements formed near the water table and in the intertidal zone of tropical and subtropical beach sediments has been the subject of extended debate as discussed by the authors.
Abstract: The origin of calcite, Mg-calcite, and aragonite cements formed near the water table and in the intertidal zone of tropical and subtropical beach sediments has been the subject of extended debate. Following Field (1919), it is proposed here that much of this cement is precipitated as a consequence of loss of CO2 from carbonate-saturated beach groundwaters. Mass-transport calculations support the further proposal that vertical fluid dispersion in the phreatic zone resulting from tidal oscillation of the water table is sufficient to induce degassing of CO2 from a seaward-flowing groundwater. Loss of CO2 is further enhanced by tidal pumping of the gas phase in the vadose zone across the sediment-atmosphere interface. As sediment porosity is lowered by pre ipitation of cement, the ability of the groundwater system to degas and form new cements is reduced. As long as the system remains thermodynamically open with respect to CO2 and close to saturation with respect to calcite or aragonite, however, it remains an unlikely site for the precipitation of dolomite. The hypothesis that degassing alone is sufficient to cause supersaturation and cementation is supported by an experimental study of degassing of mixed beach and marine waters from St. Croix, U.S. Virgin Islands, in which 30 µm-thick, low-Mg calcite crusts were formed which closely resemble natural water-table cements. The waters were spiked with Hg2Cl2 to retard biological involvement. The maximum observed rate of precipitation of calcite in solutions in direct contact with the atmosphere was 10-9 moles cm-2 sec-1, which is a rate sufficient to indurate a beach sediment within a period of 12 hours. Thermodynamic calculations indicate that precipitation could not have been induced by mixing of marine and meteoric waters, as h s been proposed by others, but that loss of CO2, a process independent of mixing, was necessary to cause supersaturation.
140 citations
TL;DR: In this article, a general model of trace element behavior is proposed for diagenetic processes in limestones, where the trace element/calcium ratio in a calcite being precipitated is always greater than the ratio in the solution.
Abstract: The partitioning behaviors of zinc and manganese can serve as important tracers of diageneticprocesses in limestones. A review of the literature indicates kcalciteZn2+, the trace element partition coefficient of zinc into calcite, equals 5.5 and kcalciteMn2+e 15, at the probable temperatures and solution compositions under which most limestone lithification is achieved. Since k is greater than unity for both these elements, the trace element/calcium ratio in a calcite being precipitated is always greater than the ratio in the solution. Thus in aragonite/calcite transformation by dissolution-reprecipitation in a closed system, the initial calcite is greatly enriched in e ther zinc or manganese relative to the parent aragonite. As closed system, homogeneous dissolution-reprecipitation progresses, the enrichment of the calcite falls exponentially until the ratio in the calcite being precipitated equals the ratio in the aragonite being dissolved. In an open system, dissolution-reprecipitation usually results in a calcite that is enriched in zinc or manganese. The more pure water that enters and leaves the diagenetic site, the greater excess loss of calcium occurs, since calcium preferentially remains in the liquid phase during calcite precipitation. In order to integrate the information provided by the distributions of manganese and zinc in calcites with that of strontium and magnesium, a general model of trace element behavior is proposed. Using the parameters of distribution coefficient, water flow relative to reaction rate (open or closed), and chemistry of the water before it enters the diagenetic site, it is possible to determine the enrichment or depletion of a calcite relative to its parent aragonite. Four distinct situations are noted. Autodepletion refers to the preferential loss of trace element from the diagenetic site due to a high water flow rate relative to reaction rate, where the trace element has a partition coefficient less than unity. A calcite depleted in trace element relative to the parent arag nite (or calcite) results. Autoenrichment is the preferential removal of calcium from the diagenetic site, with consequent enrichment of the calcite in trace element. This may occur for trace elements with k greater than unity. Alloenrichment is the result of calcite precipitation from a liquid that was enriched in trace element (a trace element/calcium ratio greater than that of the parent aragonite or calcite) before it entered the diagenetic site. It may occur for any value of k, but the trace element/calcium ratio of the liquid required for such enrichment increases with decreasing k. Allodepletion results when a liquid rich in calcium and poor in trace element flushes through the diagenetic site. For values of k close to one, each cycle of liquid may introduce s much calcium that after the liquid dissolves aragonite, its trace element/calcium ratio is still less than that of the aragonite. A depleted calcite is precipitated. Examination of the Zn2+, Mn2+, Mg2+, and Sr2+ content of Pleistocene corals from Barbados, West Indies, reveals an increase in Mn2+ and Mg2+ as a result of aragonite/calcite transformation. Sr2+ was lost in this process and Zn2+ remained approximately the same. Note that unlike kcalciteZn2+ and kcalciteMn2+, kcalciteSr2+ and kcalciteMg2+ are both < 1. Such changes denote an open diagenetic water system. Strong intercorrelations among these elements were found in corals altered under late vadose conditions. These suggest that liquid flow rate controlled the trace ele ent chemistry of these corals. Corals altered under phreatic conditions did not exhibit such systematic behavior; their chemistry was likely influenced by neighboring diagenetic events. The general trace element model gives a quantitative indication of the "openness" of these diagenetic systems. On average each liter of diagenetic liquid dissolved and reprecipitated between 10 and 20 millimoles of calcium carbonate. The trace element model can be applied to calcite/calcite recrystallization and cement precipitation later in the evolution of a limestone. Where there is no significant external source of these trace cations, later calcites should be depleted in strontium and magnesium, and enriched in zinc and manganese.
121 citations
TL;DR: In this article, a sequence of authigenic minerals in a Pennsylvanian deltaic sandstone from the Strawn Series, north-central Texas, is described: growth of chlorite rims around quartz grains, cementation by an average of 11% syntaxial quartz overgrowths, dissolution of calcite cement, feldspar grains and rock fragments, and finally e cementation by Fe-calcite, ankerite, and kaolinite.
Abstract: The sequence of authigenic minerals in a Pennsylvanian deltaic sandstone from the Strawn Series, north-central Texas, is: a) growth of chlorite rims around quartz grains, b) cementation by an average of 11% syntaxial quartz overgrowths, c) cementation by calcite, d) dissolution of calcite cement, feldspar grains and rock fragments, and finally e) cementation by Fe-calcite, ankerite and kaolinite. Isotopic analyses of the authigenic phases and formation water lead to the following conclusions. Chlorite formed during shallow burial soon after deposition when amorphous aluminosilicates and iron oxides-hydroxides reacted with pore waters to form the iron-rich, lb polytype. Quartz overgrowths have a O18 of approximately +24 IMG SRC="../../../misc/other/pmil.JPG" ALT="^pmil"> and formed under conditions of near maximum burial (2.1 km) as compaction of adjacent shales and simultaneous degradation of smectite released silica-bearing solutions which escaped through the porous sandstone aquifers. Calcite cement formed when the rate of burial slowed sharply in the middle Mesozoic and simultaneously ended the smectite reaction and the fluid migration required for quartz cementation. The CaCO3 was probably derived from slow stylolitization of underlying carbonates. Dissolution may have been caused by the late maturation and migration of hydrocarbons at the relatively cool burial temperatures of these rocks. Today the off field is being cemented at a depth of approximately 1.4 km by Fe-calcite and ankerit , and the H+ thus released is forming kaolinite at the expense of detrital feldspar. The formation fluid today appears to be in near ionic equilibrium with kaolinite, albite, K-spar, calcite, and ankerite, and in near isotopic equilibrium with kaolinite, calcite, and ankerite.
116 citations
TL;DR: Bioturbation traces are very common in one coastal and 11 inland dune fields as discussed by the authors, and arthropod tracks and trails have been documented in Permian and younger eolianites.
Abstract: Bioturbation traces are very common in the one coastal and 11 inland dune fields we have studied. These fields occur in a variety of geographic settings in both cold and warm climates. The burrowing behavior of selected invertebrates, particularly arthropods such as sand wasps, sand-treader camel crickets, wolf spiders, crane fly larvae, beetles, ants, and termites, is illustrated in the variety of burrows in dune fields. The burrows of arthropods are significant because their traces in Permian eolianites seem to be similar to their traces in modern dune fields, and arthropods represent approximately 75 percent of the entire animal kingdom. Bioturbation traces are recognizable and preserved in eolian sand that is cohesive, organism reinforced, or rapidly buried. Although some geologis s are reluctant to associate bioturbation traces with eolianites, groups of invertebrates capable of burrowing in dunes are known to have occurred for at least 300 million years; and tracks and trails have been documented in Permian and younger eolianites.
103 citations
TL;DR: In this article, the authors used the transport formulae of Bagnold (1941, 1956, 1963), Einstein (1950), and Yalin (1963) to calculate cohesionless bottom-sediment movement within the New York Bight.
Abstract: Calculations of cohesionless bottom-sediment movement within the New York Bight have been made by applying the transport formulae of Bagnold (1941, 1956, 1963), Einstein (1950), and Yalin (1963) to near-bottom current meter and surficial sand size observations. Current data were drawn from the records of eighteen long-term Savonius rotor current meter deployments at various locations within the Bight during Fall of 1973 and Spring of 1974. The assumptions underlying the calculations are that wave activity was minimal at recording sites, that a drag coefficient of 3 10-3 reflecting small scale roughness and large boundary layer Reynolds number is suitable to convert measured currents to friction velocities, and that laboratory threshold velocities apply in the marine environment. The calculations suggest that oceanic bottom sediment movement reaches maximum intensity during the fall and winter due to the added energy input from strong meterological events. Calculated transport quantities on the inner shelf tend to decrease as depth and distance from shore increase. However, during the Fall of 1973, the deep waters near the head of the Hudson Shelf Valley exhibited current flows directed to the north in excess of 40 cm/sec. These up-channel flow events appear to be in response to strong, sustained westerly winds. The maximum sediment transport rate caused by these current velocities is two orders of magnitude greater than that occurring at much shallower depths along the New Jersey coast during the same measurement period. The Spring 1974 current velocity field yields transport rates of lesser magnitudes relative to the previous fall, with a net down-channel sediment flux at the head of the Hudson Shelf Valley. The New York Harbor entrance appears to be the site of near-continual sediment transport generated by swift tidal currents.
102 citations
TL;DR: In this article, the mechanics of ion incorporation into a crystal are examined in order to evaluate mechanisms of calcite growth inhibition and morphology control, and the surface charge model for morphology control successfully predicts the approximate Ca+2/CO3-2 ratio of water yielding equant calcite crystals and the morphology of aragonite crystals precipitated from sea water.
Abstract: The mechanics of ion incorporation into a crystal are examined in order to evaluate mechanisms of calcite growth inhibition and morphology control. Crystallographic considerations indicate that while the Folk (1974) mechanisms of Mg+2 interaction with calcite may be responsible for inhibiting crystal growth, it is inadequate to explain morphologic variation. Experimental evidence on the kinetics of calcite crystal growth indicate that dewatering of surface adsorbed Ca+2 ions may be the rate-determining step in calcite growth, thus supporting, by analogy, the heat of hydration mechanism for Mg+2 poisoning of calcite growth. Surface charge and colloid chemical considerations indicate that differential charge development on crystal faces is responsible fo morphologic variation in calcite. The surface charge model for morphology control successfully predicts the approximate Ca+2/CO3-2 ratio of water yielding equant calcite crystals and the morphology of aragonite crystals precipitated from sea water.
79 citations
TL;DR: In this paper, a 6 m core and on a series of 1-3 m cores taken over 100 km of the Hudson Estuary were used for geochemical and sedimentological studies, showing that the top 10 cm of the inner harbor sediment is highly liquefied and the top meter shows extensive turbation.
Abstract: Geochemical and sedimentological studies have been conducted on one 6 m core and on a series of 1-3 m cores taken over 100 km of the Hudson Estuary. Each gram (dry-weight basis) of estuarine silt contains: organic matter 30-100 mg; carbonate generally < 30 mg; quartz 250-400 mg; potassium 18-24 mg; zinc 50-550 µg; copper 15-400 µg; and lead 20-800 µg. In most localities, the higher trace metal levels, as well as anthropogenic detritus (e.g., metalliferous slags, fly ash and coal), and reactor- and bomb-produced radionuclides (e.g., 137Cs, 134Cs 60 Co) are confined to the upper 10 cm of the sediment; but in the inner harbor area of New York they have been observed to s diment depths of 250 cm. In some areas of the inner harbor the vertical distribution of anthropogenic radionuclides indicates sedimentation rates of 5-20 cm/yr. The top 10 cm of the inner harbor sediment is highly liquefied and the top meter shows extensive turbation, although distinct sand layers and laminated zones are present. The turbation may have resulted from the release or entrapment of biochemically formed gases, as well as from mechanical mixing of sediment by organisms. 14C analyses of organic matter in inner harbor surface sediments indicate that the major source of carbon is recent sewage, nearly all of which is discharged in this area of the estuary. The fine-grained sediments of the natural channel and subtidal bank, upstream of the inner harbor, are characterized by alternating layers of fine sandy silts and clay-rich silts on a mm to cm scale. Downstream from the Tappan Zee, sand-shell layers, 1-20 cm thick, occur at the channel surface and are interlayered with zones of laminated, fine-grained sediment at depth. Radiocarbon dating of shells and shell layers indicates a minimum net sedimentation rate of 1-3 mm/yr in this area of the estuary during the past 3000 years. In cores taken on the subtidal bank, coarse sand-shell layers are absent, but turbate zones, 1-10 cm thick, occur at the surface and are interlayered with the laminated zones at depth. One possible interpretation of the sedimentary structures is: (1) the laminated fine-grained sediments are deposited when the Hudson transports relatively high concentrations of sediment, such as during and after severe storms or other short term events of large scale resuspension; (2) the sand-shell layers result from increased sand transport during high-energy (storm) conditions or from tidal scour under normal flow conditions; and (3) the turbate zones represent periods of slower or no deposition during normal flow conditions. Consequently, it appears that everyday tidal and estuarine processes are causing the rapid accumulation of recent "polluted" sediment in specific areas, such as the inner harbor, whereas storm deposits characterize the sedimentary record in the channel and subtidal bank environments of the river estuary, upstream of New York City. This large variation in both patterns and rates of sediment deposition in the Hudson Estuary has not been previously identified on the basis of grain-size and mineralogical analyses.
69 citations
TL;DR: It is concluded that all populations studied belong to the same microbial species, irrespective of differences in environmental conditions within the range of its distribution and bears relevance to the interpretation of ancient stromatolitic structures.
Abstract: Populations of a modern, stromatolite-building microorganism have been studied in the subtropical Atlantic and the Caribbean area. In four geographically distinct populations, growing under different ecological conditions (exposed to protected, subtidal to intertidal) the same nocti-diurnal rhythm in filament orientation and growth dynamics was maintained. This resulted in the formation of characteristic finely laminated stromatolitic domes. High degree of similarity and overlap in morphometric properties leads to the conclusion that all populations studied belong to the same microbial species. An historic confusion concerning the taxonomic identity of this microorganism has now been resolved and its valid name established: Phormidium hendersonii Howe 1918 (Oscillatoriaceae, Cyanophyta). Stromatolite morphology in this case is determined by the biological (genetic) properties of the organism irrespective of differences in environmental conditions within the range of its distribution. This conclusion bears relevance to the interpretation of ancient stromatolitic structures.
TL;DR: In this paper, a complex depositional history, dominated by barrier retreat and inlet formation and migration, is found within the Holocene section of southern Core Banks, a transgressive, microtidal barrier island.
Abstract: A complex depositional history, dominated by barrier retreat and inlet formation and migration, is found within the Holocene section of southern Core Banks, a transgressive, microtidal barrier island. The common occurrence of barrier sands overlying backbarrier silty-sands and salt marsh peats indicate that oceanic overwash and consequent landward migration have been active processes in this island's evolution. However, in five isolated sections, the Holocene section is completely reworked by the action of a migrating inlet environment. Drill hole transects located seaward of arcuate, relict flood-tidal deltas associated with historically recorded inlets show five inlet-fill bodies within the Holocene stratigraphy. Each inlet-fill body has a distinct stratigraphic sequence typically represented by three depositional facies: (1) inlet floor, a coarse shell and pebble gravel lag; (2) channel, medium- to coarse-grained sand and abraded shell material; and (3) inlet margin (spit platform), a clean, very fine- to medium-grained sand capping the sequence. The inlet sequences vary in thickness from 2.8 to 16.8 m and in maximum width from 0.72 to 2.1 km, making them readily comparable to the dimensions of modern active inlets along the Outer Banks and in other microtidal environment. This study documents the high preservation potential of inlet-fill bodies and the importance of the migrating inlet environment within barrier island stratigraphy. This depositional environment represents 14-16% of the Holocene sediments beneath Core Banks and may well represent a significant percentage of the material preserved within barrier systems in the rock record.
TL;DR: Tidal-flat facies of the Middle Ordovician (Chazyan) New Market Limestone (0-67 m), southwestern Virginia as mentioned in this paper are fenestral fabrics.
Abstract: Tidal-flat facies of the Middle Ordovician (Chazyan) New Market Limestone (0-67 m), southwestern Virginia. are fenestral. pellet-intraclast packstone/wackestone and lime mudstone. The unit unconformably overlies Lower Ordovician dolomites (Knox Group), interfingers with laterally equivalent skeletal limestone and is overlain by skeletal wackestone (Lincolnshire Limestone). Fenestral fabrics consist of: (1) tubular fenestrae (0.1-2 mm dia.), subvertical, cylindrical and straight to curved; (2) laminoid fenestrae (0.1-1 mm high), parallel to curved and less than 15 mm long; (3) irregular fenestrae (0.5-5 mm dia.), equidimensional to irregular. Counts of the fenestrae in two measured sections indicates that all three fenestral types occur together forming complex fabrics; the fabrics are not cyclically repeated but are influenced by depositional fabric. Tubular fenestrae probably formed by burrowing organisms in soft, wet intertidal and/or shallow subtidal sediments. Irregular and laminoid fenestrae formed by desiccation/lithification in more frequently exposed sediments resulting in hard, indurated surfaces in tidal flats, which inhibited further burrowin . New Market fenestral fabrics suggest that tidal flat sedimentation kept pace with subsidence or sea level rise so that the depositional surface remained in tidal/supratidal zones for long periods, causing complex overprinting of fabrics. General absence of cryptalgalaminates reflects intense browsing/burrowing probably related to non-hypersaline tidal waters. Associated diagenetic features (abundant vadose silt; commonly pendant equant calcite cements, equant calcite cements which predate vadose silt; molds of shells; and solution-enlarged molds of shells) indicate early lithification and widespread vadose-meteoric diagenesis. Rare beds containing columnar (fibrous) calcite cements suggest precipitation of cements from more saline waters. Intra-and interformational erosional surfaces that truncate grains and diagenetic fabrics are further evidence of early lithification. Fenestral and associated vadose diagenetic fabrics, and the lack of dolomites, evaporites, intraclast breccias and cryptalgal sediments indicate that New Market sediments formed under the influence of non-hypersaline (normal marine to meteoric) tidal and ground waters and "wet" climatic conditions. Such fabrics may characterize other carbonate tidal deposits formed under similar conditions.
TL;DR: The Snuggedy swamp contains peat deposits up to 100 inches (250 cm) thick underlain by about 10 inches (25 cm) of rooted and unbedded clay as mentioned in this paper.
Abstract: The Snuggedy swamp contains peat deposits up to 100 inches (250 cm.) thick underlain by about 10 inches (25 cm.) of rooted and unbedded clay. This clay has a kaolinite/montmorillonite ratio of more than 2/1 and a pH less than 5. On the other hand, the clay below this zone, or where the peat is absent, is bedded, contains no roots, has a kaolinite/montmorillonite ratio below 1, and a pH greater than 5. There is strong evidence to suggest that the clay zone immediately beneath the peat was not kaolinite-rich when deposited, but was enriched due to leaching by humic-acid solutions which filtered down from the peat. This phenomenon may be similar to the formation of underclays below certain Paleozoic coals.
TL;DR: In this article, the authors reviewed literature on morphology of desert quartz grains and found that the Simpson desert consists of longitudinal dunes and the sand grains do not move back and forth as is the case with complex dunes.
Abstract: Literature on morphology of desert quartz grains is reviewed. Most works claim that desert sands are typically well-rounded and frosted by abrasion. By contrast, Simpson desert grains are subangular to angular, and no noticeable rounding is being accomplished in the present desert dune environment. This is probably because the Simpson desert consists of longitudinal dunes and the sand grains do not move back and forth as is the case with complex dunes. There is a small proportion of inherited rounded grains. No abrasional surface features are being produced in the present environment. Silica is being precipitated as scabby, "turtle-skin" crusts on top of the grains, imparting a very characteristic greasy luster to the dune sands. The source of the silica is most likely solution of opal phytoliths, and reprecipitation of the silica as the containing water evaporates deeper within the dunes.
TL;DR: Six species of parrotfish (Scaridae) in reef environments on the west coast of Barbados show a variety of feeding behaviours, and Spari oma viride is the only species that causes significant bioerosion and new sediment production.
Abstract: Six species of parrotfish (Scaridae) in reef environments on the west coast of Barbados show a variety of feeding behaviours. They were observed to spend 80% of their time feeding on surfaces covered with filamentous algae and 20% on sand. Only Sparisoma viride consistently leaves well-defined scars on live coral. The biomass of all parrotfish species in the three environments studied ranges from 20 to 58 kg/ha (2 to 5.8 g·m-2). The gut turnover rate of these parrotfish is estimated at 8 times per day. The composition of the sediments in the reef environments was compared to that in the guts of the various parrotfish species to determine the amount of sediment produced from the rocky substrate and the amount of sediment recycled by parrotfish feeding. Spari oma viride is the only species that causes significant bioerosion and new sediment production; the other parrotfish recycle old sediment. The rate of bioerosion on the fringing reef is 61 g·m-2·a-1, on the bank reef it is 40 g·m-2·a-1, and the Moorings study area 168 g·m-2·a-1.
TL;DR: Radiolarites of the Ligurian sequence are rhythmic alternations of generally red chert and shale beds from 1 to 10 cm thick that overlie ophiolite rocks of presumed oceanic crust and underlie pelagic and redeposited limestone.
Abstract: Radiolarites of the Ligurian sequence are rhythmic alternations of generally red chert and shale beds from 1 to 10 cm thick that overlie ophiolite rocks of presumed oceanic crust and underlie pelagic and redeposited limestone. The rhythmic bedding is the product of deposition of radiolarian sand beds and some overlying mud by turbidity currents and possibly other marine bottom currents that alternated with episodes of slow deposition of hemipelagic red clay. Evidence of current deposition of radiolarian sand beds includes: tightly packed Radiolaria; presence of hydraulically-equivalent clasts of red clay and ophiolite debris; beds with grading, laminations, current-ripple cross-beds, and flute and groove casts. Chert beds formed principally by dissolution of the more delicate Radiolaria and reprecipitation of silica cement as either microcrystalline quartz or opal C-T around more resistant Radiolaria during burial diagenesis. Radiolarite has abrupt lateral differences in thickness (from absent to 200 m), which reflects deposition on a highly uneven sea floor. An interpretation of the depth of water during radiolarite deposition depends in part on how one interprets the origin of ophicalcite that locally underlies radiolarite. Ophicalcite consists of clasts of serpentinite and locally gabbro and peridotite in a pink calcite microspar matrix, the whole cut by white vein-filling calcite of younger tectonic origin. Ophicalcite can be interpreted as a breccia formed by total recrystallization, in part, of pelagic carbonate ooze deposited along ocean spreading ridges or as paleocaliche that developed upon ophiolite exposed above sea level. Evidence to support a pedogenic origin of ophicalcite includes textures and structures identical with caliche, silicified serpentinite masses (jasper) whose texture and mineral composition mimic modern soils on serpentinite, presence of a flat ?wave-cut surface beneath radiolarite, upward increase within ophicalcite of both calcite and oxidized serpentinite debris, and absence or thinness of radiolarite on paleotopographic highs. Many unanswered problems exist to both the above hypotheses. The deep-water hypothesis (favored by EFM) is that deposition took place on oceanic crust in water deeper than wave base (>200 m) and probably deeper than 2500 m; the latter depth implies the existence of a CCD during Late Jurassic time to account for the absence of carbonate in radiolarite. The shallow-water hypothesis (favored by RLF) is that deposition took place on previously exposed subsiding oceanic crust in water depths from a few meters to a few hundred meters; the absence of carbonate in radiolarite is attributed to local scarcity of carbonate-producing plankton compared to the overwhelming supply of clay from weathered ophiolite. Both hypotheses involve the interpretation that radiolarian-rich sediment, initially deposited on topographic highs, was transported into adjacent troughs by turbidity and other marine currents; the deeper troughs were floored by pillow lavas.
TL;DR: Pisoliths from two Michigan lakes studied in this paper are subspherical and consist of annual couplets of porous and dense concentric laminae surrounding a nucleus, and boundary boundaries between successive couplets are always sharp.
Abstract: Lacustrine algal pisoliths are growing today in many calcareous lakes throughout the midwestern United States. Pisoliths from two Michigan lakes studied are subspherical, and consist of annual couplets of porous and dense concentric laminae surrounding a nucleus. Porous laminae display radial fabric resulting from the growth of algal filaments perpendicular to the nodule surface; these grade outward into dense laminae that contain sparse unoriented filaments. Boundaries between successive couplets are always sharp. Basal flattening, thinning of the porous layer below the center of the pisoliths, and growth in low energy mud-floor environments indicates that these structures form in situ, and are only rarely overturned on the marl platform surfaces.
TL;DR: In the sandy, braided South Saskatchewan River, ripples, sand waves, and dunes are recognized as lower flow regime bedforms on the basis of a morphological classification.
Abstract: In the sandy, braided South Saskatchewan River, ripples, sand waves, and dunes are recognized as lower flow regime bedforms on the basis of a morphological classification. Sand waves are straight-crested to rhomboidal and are very regular in the direction transverse to flow, lacking scour troughs or spurs. The amplitudes of sand waves may gradually increase or decrease along their crestlines, but abrupt changes are rare. Dunes are sinuous to strongly three-dimensional bedforms, showing marked irregularities in crestline height and well developed spurs and scour troughs. Sand waves occur with ripples superimposed on their stoss sides at flow velocities less than 0.5-0.7 m/sec depending on depth. Dunes occur in most cases with no superimposed ripples at velocities greater than sand waves for each depth. Slipface-bounded bars up to 3 m in height form where the flow is non-uniform and expands laterally or vertically. This happens where channels widen or bend or where the flow passes over an abrupt downward step such as the junction of channels of different depths. Bars may have ripples, sand waves, or dunes superimposed on their upper surfaces and are less sensitive to changing flow conditions than are these others. Sand flats are large-scale sandy braid bars which are complexes of all the smaller forms. They are comparable in scale to the point bars of meandering streams.
TL;DR: In this article, an abrasion durability scale derived from experiments with monolithologic pebble populations was subdivided into four groups: weakly durable marble and schist; moderately durable basalt, granodiorite, gneiss and gabbro; durable obsidian, metasandstone and metabreccia; and ultradurable silicic rhyolite, quartzite, and chert.
Abstract: A variety of rock types subjected to abrasion durability tests in a tumbling mill yielded variable attrition rates. An abrasion durability scale derived from experiments with monolithologic pebble populations was subdivided into four groups: weakly durable marble and schist; moderately durable basalt, granodiorite, gneiss and gabbro; durable obsidian, metasandstone and metabreccia; and ultradurable silicic rhyolite, quartzite, and chert. In experiments with polylithologic pebble populations the relative durabilities remained the same but attrition rates of less durable rock types increased whereas rates of more durable types decreased. The longer the tumbling time (or travel distance), the greater the concentration of high durability clasts. Further, the presence of relatively low durability clasts increased the distance of transport necessary to achieve a given attritional loss for high durability clasts. Upper Cretaceous and Eocene conglomerates of the San Diego area are understood more clearly using these experiment-derived principles. Conglomerates of both ages were derived from the east but the Cretaceous clast populations are comprised of Peninsular Ranges detritus whereas Eocene clast populations are nearly 3/4 silicic rhyolite of exotic origin. Cretaceous conglomerates contain rock types that reflect outcrops in the nearby Peninsular Ranges; clasts vary from weakly durable to durable. The mixed durability clast suite, together with representation of all major Peninsular Ranges bedrock exposures, indicates short-distance fluvial transport. Eocene conglomerates are dominated by ultradurable rhyolite clasts that do not occur in bedrock outcrops in the Peninsular Ranges. Evidently the rhyolite clasts were introduced to a major, west-flowing fluvial system possibly originating in the modern-day area of north-central Sonora. The attrition rates of the ultradurable rhyolite clasts were decreased at the expense of the less durable, but more locally derived, Peninsular Ranges clast suite to produce conglomerates in the San Diego area that are overwhelmingly dominated by exotic rhyolite clasts, although the rhyolite source rocks probably constituted only a small fraction of the total source terrane.
TL;DR: The effect of burial on benthic invertebrates was investigated using SCUBA techniques in Buzzards Bay, Massachusetts as discussed by the authors, where various thicknesses of sediment, free of macrofauna, were used to cover the bottom and its natural fauna within the constraints of small boxes and tubes.
Abstract: The effect of burial on natural assemblages of benthic invertebrates was investigated using SCUBA techniques in Buzzards Bay, Massachusetts. Various thicknesses of sediment, free of macrofauna, were used to cover the bottom and its natural fauna within the constraints of small boxes and tubes. The taxa and number of organisms escaping this burial were determined by partitioning the containers into vertical sections. Most animals common to a soft-bottom community could escape a burial of 5 to 10 cm. but at depths of about 30 cm none even attempted to crawl up through the column of burying sediment. We suggest that "overburden stress," a measure which relates bulk density and burial depth, reaches a critically high value above which the animals cannot initiate an escape response.
TL;DR: The transition from alluvial to lacustrine rocks in the Laney Member of the Green River Formation includes Gilbert-type deltas whose depositional features provide information about the history and nature of Lake Gosiute, and document proximal to distal sedimentation on the delta fronts.
Abstract: The transition from alluvial to lacustrine rocks in the Laney Member of the Green River Formation includes Gilbert-type deltas whose depositional features provide information about the history and nature of Lake Gosiute, and document proximal to distal sedimentation on the delta fronts. Gilbert-type deltaic rocks in the Laney are composed of cycles each consisting of constructional and destructional phases. The constructional phases are represented by an upward-coarsening sequence produced by lakeward progradation of delta topset and foreset beds over prodeltaic sediments. During the destructional phase erosion and reworking of delta-plain and -slope beds resulted in formation of an erosional surface, and locally, a sandstone shoreline veneer. These features of Laney deltaic deposits re similar to constructional and destructional phases of late Quaternary and modern Gilbert-type delta deposits of the Truckee River at Pyramid Lake, Nevada. They are attributed to fluctuation in lake level or shifting of the stream mouth entering the lake. The most characteristic feature of the delta deposits is foreset bedding with depositional dips of up to 20 degrees. The maximum thicknesses of foreset deposits range from 10 to 25 meters. The geometry of the foreset deposits suggests that the lake was shallow with maximum depths of 25 meters where deltas were constructed. Foreset beds grade upward into flat-lying sandstone and mudrock topset beds, and grade downward into flat-lying mudrock bottomset beds. The delta fronts consist of repetitive sequences of sandstone and mudrock with sporadic, thick, massive sandstone beds. In the Bridger and Washakie Basins local foundering of deltaic sandstone and mudrock into lacustrine oil shale resulted in large load casts, slump folds, and sandstone pillows that partly or wholly obliterated orig nal bedding features of topset, foreset, and bottomset beds. Proximal to distal delta-front sedimentation patterns include: thinning of stratigraphic intervals of 50 to 70 percent; increase in the ratio of mudrock to sandstone; and decrease in the total number of beds in a stratigraphic interval. Bedding sequences in delta-front rocks are 1) ripple-bedded fine-grained sandstone overlain by parallel-laminated mudrock; 2) ripple-bedded fine-grained sandstone, parallel-laminated fine-grained sandstone, and parallel-laminated mudrock; and 3) parallel-laminated fine-grained sandstone overlain by parallel-laminated mudrock. These sequences were produced by interflow and mixing of sediment-laden stream water in lake water of equal density, and by wave action on the delta front.
TL;DR: In this paper, a model based on measured concentrations of suspended sediments in the surf zone indicates that the suspended load comprises some 25 percent or less of the total drift, the bed-load forming the remaining 75 percent.
Abstract: Uncertainty and debate have existed as to whether suspension or bed-load transport is most important in the longshore movement of sands on beaches. The evidence pertaining to this fundamental question is examined. A model based on measured concentrations of suspended sediments in the surf zone indicates that the suspended load comprises some 25 percent or less of the total drift, the bed-load forming the remaining 75 percent. Such estimates are obtained even when all approximations and assumptions made in developing the model are made in favor of the estimate of the suspension load. An examination of the relative rates of longshore movements of sand tracer grains as compared to the longshore currents indicates that the sand grains lag far behind the water flow. This indicates not only that suspension transport must be small, but also that our 25 percent upper estimate of suspension transport in the model must be revised downward, possibly to less than 10 percent. Other evidence is also presented that indicates the suspension load is much less significant than the bed-load transport on beaches.
TL;DR: Sand-sized spheroids in the 3.4 billion-year old Onverwacht Group, South Africa, previously interpreted as silicified marine carbonate ooids, were constructed of loose volcanic dust and ash and closely resemble accretionary lapilli found in younger volcanic sequences.
Abstract: Sand-sized spheroids in the 3.4 billion-year old Onverwacht Group, South Africa, previously interpreted as silicified marine carbonate ooids, were constructed of loose volcanic dust and ash and closely resemble accretionary lapilli found in younger volcanic sequences. They commonly show concentric internal structuring, including a nucleus, a relatively coarse-grained detritus layer made up of recrystallized vitric and crystal grains, and an outer rind of recrystallized fine-grained ash. The outer rind was rigid when the grains were deposited whereas the detritus layer was soft and plastic. Graded lap Jill beds lacking current structures represent air-fall lapilli and ash which accumulated rapidly under shallow water to subaerial conditions. The tops of many units were reworked by curr nts to form flat- and cross-laminated layers. Accretionary lapilli are known from many younger volcanic sequences, but seldom represent more than trace accumulations and are rare as water-deposited grains. Their apparent abundance in Archean terranes in both South Africa and Australia may suggest that the geologic and hydrologic setting of certain Archean volcanic complexes favored the formation and preservation of accretionary lapilli. It may reflect, however, an abnormally wet early atmosphere or the relatively higher rate of outgassing of volatiles through early Precambrian volcanoes.
Abstract: The Middle Triassic Edderfugledal Member of East Greenland is interpreted as lacustrine because of: (A) nonmarine fossils such as conchostracans and small bivalves, (B) non-marine trace fossils such as Isopodichnus, Cruziana, Pelecypodichnus and Fuersichnus, (C) stromatolites with algal moulds, (D) sedimentary structures, which indicate shallow water, weak to moderately strong wave action and frequent subaerial exposure, (E) absence of tidal current generated structures and (F) great lateral continuity of single beds, which indicate a low topographic gradient in the basin. Six major facies are distinguished within this ancient lake content: (1) green mudstone (open lacustrine), (2) yellow dolostone (carbonate mudflat), (3) flat pebble conglomerate (beach la or stromatolite breccia), (4) stromatolitic limestone (nearshore lacustrine), (5) greyish wave rippled sandstone (shoreline sandflat) and (6) reddish sandstone and mudstone (alluvial mudflat). The stromatolitic columns, commonly between 5 and 15 cm high, are subcylindrical to hemispheroidal, discrete and laterally linked. They consist of mm-thin couplets of organic-rich micrite laminae with both coccoid and filamentous algal moulds and dolomicrite laminae. The member displays well developed cyclic sedimentation both in the basal open lacustrine unit (the Sporfjeld Beds) and in the overlying shallow lacustrine unit (the Pingel Dal Beds). In the Sporfjeld Beds open lacustrine facies dominate and marginal lacustrine facies are restricted to carbonate mudflats. In the Pingel Dal Beds open l custrine facies become relatively rare and shoreline sandflats and alluvial mudflats are added to the marginal lake environment. This change in sedimentation is explained mainly in terms of intermittent tectonic uplift. These tectonic events were probably accompanied by a gradual change towards more humid conditions during the Middle Triassic.
TL;DR: A sequence of limestone and chert in the central portion of the Durham Sub-basin of the Deep River Basin of North Carolina is unusual for these continental beds as mentioned in this paper, and it is probably an inorganic precipitate and comparable to the silica gel being deposited in certain lakes in South Australia.
Abstract: A sequence of limestone and chert in the central portion of the Durham Sub-basin of the Deep River Basin of North Carolina is unusual for these continental beds At the best outcrop an 88 m section of typical red-brown mudstone and sandstone contains continuous but wavy-bedded layers of impure limestone from 1 to 20 cm thick They are dark laminated micrite which is non-porous, pelletoidal, chemical, and lacustrine in origin Void-filling medium crystalline calcite spar has eliminated most of the original pore spaces There may be a caliche fabric overlay on this limestone, which was originally a calcareous tufa A few beds of chert up to 60 cm thick are associated with the limestone The chert is of two types One is a dense dark gray chert which is medium crystalline chalcedony with a very finely crystalline quartz It is probably an inorganic precipitate and is comparable to the silica gel being deposited in certain lakes in South Australia The second is a light brown porous chert which has replaced some of the previously mentioned limestone Calcite nodules of typical caliche fabric were formed around the periphery of this Triassic lake which had Mg/Ca ratios of less than 7 and a fluctuating pH of 65-105 The lake was a playa which formed in a warm to hot climate with a mean annual temperature of about 20° C and a seasonally distributed rainfall of 100 to 500 mm These playa and caliche deposits lie in the center of the Durham Sub-basin within a Late Triassic sequence which contains both fluvial and lacustrine strata The latter also contain both gray and red lacustrine shales which contain fish scales, ostracods, and conchostracans The Newark strata were probably deposited during a time of cyclic climate that ranged from dry to moist and back again The coals of the Sanford Sub-basin and some of the lacustrine shales of the Durham Sub-basin were deposited during the wet parts of the cycles The lacustrine limestones and chert were deposited, and the caliches formed, during the dry parts of the cycles
TL;DR: In the North Atlantic shelf, the length-to-width ratios observed by side-scan sonar are in excess of 10:1 as mentioned in this paper, indicating that the shelf floor is responding to the modern hydraulic regime.
Abstract: Elongate bedforms of less than one meter relief are abundant on the North Atlantic shelf floor. Spacing between features, and width of solitary forms, ranges from 15 to 50 m. Length-to-width ratios observed by side-scan sonar are in excess of 10:1. The most common form consists of a band of coarse sand or shelly gravel that is depressed slightly below the level of the finer sand on either side. In some cases these bedforms appear to be erosional windows exposing the basal coarse sand or gravel of the Holocene Transgression; elsewhere they are merely localized lag concentrates. Bedforms on the shore face and adjacent inner shelf tend to be nearly shore-normal with slightly acute angles opening to the northeast. Further seaward most bedforms are parallel to the coast, and to the generalized trend of the isobaths. These relationships lead to the inference that the nearshore features are the troughs of low amplitude, flow-transverse sand waves, and that they are probably responses to the intense, downwelling, along-coast flows that occur during northeaster storms. The offshore bedforms may also be responses to storm flow, but their orientation suggests that they are flow-parallel current lineations, perhaps responses to longitudinal vortices in the flow. The bedforms indicate that the shelf floor is responding to the modern hydraulic regime. Time-averaged bed l ad transport is directed downshelf, to the south and west. On the inner shelf there is also an offshore transport component.
TL;DR: The Green River Formation (Eocene) in Sanpete Valley, central Utah, contains many thin beds of shiny brown oolites in a very sparse to abundant matrix of calcite and minor quartz as mentioned in this paper.
Abstract: The Green River Formation (Eocene) in Sanpete Valley, central Utah, contains many thin beds of shiny brown oolites in a very sparse to abundant matrix of calcite and minor quartz. Analytical techniques revealed that the oolites are composed primarily of the smectite stevensite. The brown color of the oolites is a result of organic matter. The stevensite oolites probably were precipitated in place in Lake Uinta.
TL;DR: In this article, it was shown that ooids with nuclei composed of calcite in the form of crinoidal, foraminifera, and molluscan debris remained intact and were unaffected during this early burial event.
Abstract: Early diagenetic dissolution removed aragonitic molluscan debris which served as nuclei for ooids in the Jurassic Twin Creek Formation in northwestern Wyoming. The resulting hollow elliptical shells were subsequently crushed during burial and compaction to produce the crushed ooids typical of this Jurassic unit. Alternatively, ooids with nuclei composed of calcite in the form of crinoidal, foraminifera, and molluscan debris remained intact and were unaffected during this early burial event. Precompactional dissolution of aragonitic ooid nuclei is indicated by flattened ooids and confirmed by the orientation of fractures developed in the cortical coatings. Hollow colds were flattened by tensional microfracturing of the cortical exterior in planes oriented parallel and perpendicular to bedding. Boring by microendoliths preceding and accompanying ooid formation provided additional permeability for carbonate diffusion from ooid interiors during their dissolution. Cortices of Twin Creek ooids are now composed of radial calcite. Textural evidence suggests that both the fabric and mineralogy of the radial calcite are primary. This evidence supports the postulate of Sorby (1879) and Sandberg (1975) that radial fabric in many ancient calcite oolites is primary and not related to postdepositional diagenetic modification.
TL;DR: In this paper, sediment is delivered to basins or rises by a number of discrete processes or sets of processes working from several sources including terrigenous, biogenous, and hydrogenous which may deliver sediments continuously or discontinuously.
Abstract: Sediments are delivered to basins or rises by a number of discrete processes or sets of processes working from several sources including terrigenous, biogenous, and hydrogenous which may deliver sediments continuously or discontinuously. The processes can be grouped in terms of the zone from which they move sediments directly to the deposition site. These include river and shore systems, shelf systems, canyon systems, slope systems, and the processes operating in the overlying water column. River and Canyon-centered processes work from point sources; shore, shelf and slope-centered processes deliver from linear sources; and the water mass-centered processes operate from area sources. These are the primary determinants of the patterns of sediments deposited from these sets. Of these sets of processes and their resulting products, the river-shore system and the canyon system are easily the best known. A new surge of interest has begun for the slope system, but the water mass process system and the resulting hemipelagic and pelagic sediments and sedimentary rocks have been only narrowly studied although they produce the most complete records of environmental (climatic) changes and provide the best correlation data. Another area of research yet to be broadly developed lies in the study of interactions between processes and process sets and in the factors that modulate process systems. How each of the major process groups work together and what synergistic effects come from those linkages offer productive areas of study. All of these should be examined to aid us in our primary goal of describing the Earth9s history.