Showing papers in "Journal of Sedimentary Research in 1972"
TL;DR: In this article, the transition from landsliding to turbidity currents was examined in the oceans as part of the sequence from landslides through debris flow to a turbidity current flow, and the mechanics of subaqueous debris flow were examined.
Abstract: Turbidity currents may be generated in the oceans as part of the sequence from landsliding through debris flow to turbidity current flow. Three aspects of this sequence examined here are 1) the transition from landsliding to debris flow, 2) the mechanics of subaqueous debris flow, and 3) the transition from subaqueous debris flow to turbidity-current flow. The transition from landsliding to debris flow, as observed in the subaerial environment, occurs readily if water is incorporated into the landslide debris as it is jostled and remoulded during downslope movement. Remoulding and incorporation of water reduce the strength and increase the fluid behavior of the debris, thereby causing it to flow rather than slide. Incorporation of only a few percent water typically decreases the strength of landslide debris by a factor of two or more; therefore, landslide debris commonly becomes very fluid with incorporation of a small amount of water. The ready availability of water in the marine environment suggests that conditions are favorable for the development of subaqueous debris flows from subaqueous landslides. Debris flow has been modeled as flow of a plastico-viscous substance, which has a yield strength and deforms viscously at stresses greater than the yield strength. The conditions required for movement of a subaqueous debris flow are described in terms of a critical thickness of debris, which varies directly with strength and inversely with submerged trait weight and slope angle. Within a debris flow, viscous shear occurs where shear stress exceeds the shear strength of the debris, but where shear stress is less than shear strength the material is rafted along as a nondeforming plug. Distinct zones of viscous shear and nondeformation exist in a subaqueous debris flow. Transition from subaqueous debris flow to turbidity-current flow involves extensive dilution of debris-flow material, reducing the density from about 2.0 gm/cm3 to about 1.1 gm/cm3. In experiments, subaqueous debris-flow material was mixed with the surrounding water by erosion of material from the front of the flow and ejection of the material into the overlying water to form a dilute turbulent cloud (turbidity current). The amount of mixing, and hence the size of the turbidity current, varied inversely with the strength of the debris. Conditions that cause mixing at the front of a subaqueous debris flow are illustrated by analyzing flow around a half-body, with boundary-layer separation. Turbidity, currents also may be generated from subaqueous debris flows by mixing water directly into the body of the flow, behind the front, although this type of mixing was not observed in experiments. Mixing into the body of the flow can result from flow instability, either by breaking interface waves or by momentum transfer associated with turbulence, but available information suggests that mixing due to instability is inhibited by the presence of clay and coarse granular solids in debris. Mixing by erosion from the front of a debris flow is favored as being a more typical process of generating turbidity currents because this mixing is a natural consequence of debris flowing through water; it requires no special conditions to operate.
491 citations
TL;DR: In this paper, a correlation of a white rhyolitic volcanic ash bed with the Bishop Tuff of eastern California was confirmed by neutron activation analysis, and a coefficient was introduced as a simple measure of multivariate similarity.
Abstract: Neutron activation analyses confirmed a previous correlation of a white rhyolitic volcanic ash bed with the Bishop Tuff of eastern California. Distinctions were made between the glass fractions of Bishop and Pearlette-like ashes, both of which occur in middle Pleistocene deposits of California, Utah, Colorado, and Nebraska. A third type of ash (ash of Green Mountain Reservoir), petrographically similar to the Bishop Tuff, appeared to be chemically distinct. A coefficient was introduced as a simple measure of multivariate similarity. Discriminant function analysis indicated that Mn and Sm were most useful in distinguishing chemically between Bishop, Green Mountain Reservoir, and Pearlette-like ashes. Both statistical methods confirmed conclusions drawn from visual observation of the da a.
226 citations
TL;DR: A detailed study of Holocene profiles, developed in late Pleistocene reef limestones on northern Barbados, reveals that diagenesis of limestone in such profiles creates a diagnostic, repeatable set of textures and fabrics as discussed by the authors.
Abstract: Surficial, calcareous crust profiles, hard, irregular, subhorizontal, calcareous laminae, surrounded by crumbly, chalky carbonate, form at the surface of many limestone successions in semi-arid areas. Detailed study of Holocene profiles, developed in late Pleistocene reef limestones on northern Barbados, reveals that diagenesis of limestone in such profiles creates a diagnostic, repeatable set of textures and fabrics. The original limestone is altered by brecciation, recrystallization (to microspar), micritization and boring. The CaCO3 thus put into solution and augmented by CaCO3 from fallout and salt spray is reprecipitated as calcite (less than 4 mole percent MgCO3), in the form of crystals often, quite different from those in the vadose zone below. Calcite crystals are precipitated as flower spar, micrite, random needle fibres, and tangential needle fibres. Several of these crystal morphologies are similar to those precipitated from highly supersaturated solutions or solutions that contain appreciable amounts of other dissolved ions. These 4 basic crystal types are not only precipitated as void-filling cement, but, more important, combine to form characteristic structures such as oolith-like coated particles, pelletoids, and the laminar crusts themselves. The diagenetic textures and fabrics described above are also the basic units of many Florida and Middle East calcareous crust (caliche) profiles, suggesting that the above features may be characteristic of calcareous crust profiles in general. Fossil calcareous crusts and associated features, buried in the Pleistocene limestone succession on northern Barbados without alteration, indicate that these features may well be preserved as indicators of subaerial exposure in the fossil record.
224 citations
TL;DR: In this article, a planar cross-stratification of transverse bars in the sand-bed Platte River in Nebraska has been studied, and the results show that only 30.5% of the bar foreset directions correspond to within 5° of the currents that formed them.
Abstract: Tabular sets of planar cross-stratification are characteristic structures produced by transverse bars in the sand-bed Platte River in Nebraska. Certain sedimentologic characteristics of the Platte bars provide potentially useful information for interpreting the origin of planar cross-strata in ancient deposits. Alternating coarse and fine-graded foreset laminations result from continuous avalanching at bar margins of sediment previously sorted by small scale bed forms on the bar surface. Surface dune transport yields thicker and more distinct coarse-fine foreset laminae than ripples. Foreset angles of inclination tend to decrease with increasing flow regime. Several structures are produced at active bar margins swept by side currents, including ripples and dunes perpendicular to the bar slip face, foreset spurs, and straight-crested ripples on the slip face. Each of these structures produce small scale cross-stratification oriented at high angles to the associated planar cross-bed. Large differences between current and foreset dip azimuths frequently occur because of the irregular and lobate shapes of transverse bars. Only 30.5% of the bar foreset directions correspond to within 5° of the currents that formed them. Foreset dip azimuths in a straight 2.1-km reach of the lower Platte are widely dispersed, although their vector mean accurately identifies the direction of the main channel complex. Planar cross-bed orientations computed for the entire Platte plus the Nebraska portion of the South Platte yielded a variance of 6,129 arid a vector magnitude of 35.6%, indicating dispersions greater than commonly assumed for braided streams. Possibilities for distinguishing planar cross-stratification formed by braided stream transverse bars from similar stratification types produced in other environments are discussed.
162 citations
TL;DR: In this article, three major sediment units are recognized in the surficial sediments of Lake Ontario on the basis of extensive sampling and echo sounding: (1) glacial till and bedrock; (2) glaciolacustrine clay; (3) postglacial mud.
Abstract: Three major sediment units are recognized in the surficial sediments of Lake Ontario on the basis of extensive sampling and echo sounding: (1) glacial till and bedrock; (2) glaciolacustrine clay; (3) postglacial mud. Sand and silt are minor units in the Ontario surficial sediments. The sediment distribution pattern is essentially simple with a natural superposition of sediment units reflecting the glacial and postglacial history of the lake. The inshore region of Lake Ontario is composed of glacial till and bedrock. The till is overstepped in deeper water by glaciolacustrine clays which are themselves overstepped by postglacial muds. Two northsouth sills, composed of glaciolacustrine clay, subdivide the main basin of Lake Ontario into three distinct basins of postglacial mud accumulat on. The surficial sediments contain variable amounts of quartz, feldspar, clay minerals, organic carbon and calcite. Quartz and feldspar contents are greatest in the coarser inshore sediments while clay minerals and organic carbon are greatest in the finer offshore sediments. Carbonate is generally low throughout the lake. Illite is the dominant clay mineral with lesser amounts of chlorite and kaolinite. Mean rates of sedimentation ranging from 114 to 309 g/m2/yr are estimated for the basins of modern mud accumulation. The primary source of detrital material is believed to be the extensive glacial deposits of southern Ontario and northern New York State. An estimated 55 percent of this material is derived from the drainage basin with the remaining 45 percent being the result of shoreline and lake bottom erosional processes. The textural characteristics, defined by moment measures, of the modern sediments can be interpreted as resulting from the varying degrees of mixing between a sand and a clay size end member population; the former occurring in the nearshore zone and the latter in the offshore basin deposits. Both end member populations are leptokurtic and skewed due to the introduction of silt size material in the form of CaCO3 probably as the product of lakewide precipitation. Mean gr in size and standard deviation, predictably show trends from nearshore to offshore, with decreasing grain size, related to increasing water depth and hence to decreasing energy from a wave- and current-active nearshore region to an offshore region of quiet water with sedimentation from suspension. In addition, skewness and kurtosis show trends relative to mean grain size and standard deviation which can be explained in terms of increasing distance from shore. Variations in the compositional phases of the sediment in terms of quartz, clay and organic carbon, and also variations in the redox potential can in turn be related directly to textural characteristics of the sediment and consequently to the depositional environment.
142 citations
TL;DR: In this paper, the authors defined four types of calcite phases with different amounts of ferrous iron, i.e., non-ferroan calcite (00% FeO; red stain), red stain, red-purple stai and red-blue stain.
Abstract: Calcite phases with different amounts of ferrous iron (determined by microprobe analysis) are distinguishable by study of stained thin sections and stained acetate peels We have defined four such phases, they are (a) non-ferroan calcite (00% FeO; red stain), (h) ferroan calcite I (05% to 15% FeO; red-purple stai,), (e) ferroan calcite II (15% to 25% FeO; purple stain), and (d) ferroan calcite III (25% to 35% FeO; purple-blue stain) Several factors, including acidity and temperature of staining solution, affect the color (hue) of the stain, indicating that a standard procedure must be followed if colorimetric techniques are to be used in the determination of ferrous iron content in calcite
142 citations
TL;DR: In this article, it was shown that the inner nearshore areas of Lake Michigan are basically the same as northern Massachusetts except for scale of the morphologic features and tidal range; in Lake Michigan spring tides reach 0.25 feet whereas in Massachusetts they reach 13 feet.
Abstract: Beach and inner nearshore areas of Lake Michigan are basically the same as northern Massachusetts except for scale of the morphologic features and tidal range; in Lake Michigan spring tides reach 0.25 feet whereas in Massachusetts they reach 13 feet. Ridge and runnel topography is developed in the inner nearshore zone at both locations is the result of storm activity. These ridges migrate shoreward during low energy conditions and eventually weld onto the beach. Overall morphology, surface features and internal structures are quite similar in both areas. The only appreciable differences between the two areas are the scale and rate of migration. Apparently tides have no appreciable affect on the sediment sequence that accumulates as ridges weld to the beach although tides are significa t in determining the rate at which the shoreward migration of the ridges takes place.
137 citations
TL;DR: Laterally extensive dolomite beds seven to 12 meters below present sea level in Baffin Bay, Texas yield C14 ages of from 2,300 to 4,300 years B. P. and therefore must have formed subtidally as discussed by the authors.
Abstract: Laterally extensive dolomite beds seven to 12 meters below present sea level in Baffin Bay, Texas yield C14 ages of from 2,300 to 4,300 years B. P. and therefore must have formed subtidally. The one to five micron dolomicrites show no replacement textures and may have formed by direct precipitation. The dolomite is enriched approximately 3 permil in O18 over co-existing aragonite and Mg-calcite and contains approximately 800 ppm Sr. The Sr content of these dolomites is considerably higher than most ancient dolomites.
120 citations
TL;DR: The Caithness Flagstones are part of a thick Middle Devonian sequence, generally considered part of the continental Old Red Sandstone facies, which crops out in northeast Scotland, including the islands of Orkney and Shetland as mentioned in this paper.
Abstract: The Caithness Flagstones are part of a thick Middle Devonian sequence, generally considered part of the continental Old Red Sandstone facies, which crops out in northeast Scotland, including the islands of Orkney and Shetland. The succession consists of lacustrine and fluvial beds deposited in a large internal basin with no evidence of marine connections. Between 5 and 6 km thickness of light gray, red-brown and gray-green cross-bedded sandstone, greenish-gray laminated siltstone and gray-black laminite and limestone are exposed along the east and north coasts of Caithness. Many of the gray-black laminites and a few of the greenish-gray laminated siltstones exhibit numerous small-scale (50 mm plan length) linear cracks. The cracks are in fine siltstone and have been infilled by coarse siltstone. They are attributed to subaqueous shrinkage by a syneresis mechanism. About one-half of the crack-bearing beds show a persistent crack orientation in plan, the direction of which corresponds with the long axes of ripple marks. The preservation of the cracks is a reflection of the placidity of the lacustrine environment.
99 citations
TL;DR: In this article, a scanning electron microscope was used to examine quartzose sandstones and reveal details and complexities not discernible with a petrographic microscope, such as overlap and/or mergence of individual subunit overgrowths with the same crystallographic orientation unitl so tightly packed that an atom cannot distinguish between subunits and growth continues as a single crystal.
Abstract: Examination of quartzose sandstones with the scanning electron microscope reveals details and complexities not discernible with a petrographic microscope. Incipient quartz overgrowths occur either as growths with poorly defined crystal facies that are loosely interconnected over the surface of the detrital nucleus or as isolated growths with well defined crystal faces. If sufficient void space is present these incipient overgrowths may enlarge to partly envelop the nucleus and form well defined crystal faces. This appears to take place in the following ways: (1) overlap and/or mergence of individual subunit overgrowths with the same crystallographic orientation unitl so tightly packed that an atom cannot distinguish between subunits and growth continues as a single crystal; (2) envelo ment of earlier multiple overgrowths by an outer shell so that the underlying complex nature of the overgrowth is masked. The crystal lattices of the overgrowth and nucleus are connected at isolated points. Much of the area between overgrowth and nucleus is void space, which forms the "dust" line visible in thin section. Secondary quartz probably eventually infills many of these voids, which destroys the "dust" line unless impurities are present also. Presolved surfaces between quartz grains vary from relatively smooth to rough with ridges, knobs, furrows, and pits. A pressure solution surface may have a series of ridges and furrows, commonly in a radial pattern, along the margin.
93 citations
TL;DR: In this paper, a cyclic pattern to processes and responses in this non-tidal environment is described, which is the result of complex interaction between changes in shoreline configuration, discontinuous nearshore sand bars, and environmental variables such as barometric pressure, wind velocity, breaker height, and longshore current velocity.
Abstract: Detailed daily topographic maps of beach and inner nearshore areas indicate a cyclic pattern to processes and responses in this non-tidal environment. This pattern is the result of complex interaction between changes in shoreline configuration, discontinuous nearshore sand bars, and environmental variables such as barometric pressure, wind velocity, breaker height, and longshore currents. Of the 18 variables measured, barometric pressure appears to provide the best index for changes in coastal processes. The results of these variations are morphologic changes in the beach and inner nearshore area. As a low pressure system approaches the coast there is an increase in wind velocity, breaker height and longshore current velocity as barometric pressure drops. When the low pressure system passes barometric pressure rises and there is a reversal of wind direction with an accompanying reversal of longshore current direction. This cycle in conditions is accompanied by a pattern of responses in the position and morphology of the shoreline and sand bars. During high pressure and low energy conditions shallow discontinuous sand bars have somewhat regularly spaced rip channels. The shoreline is slightly sinuous with protuberances behind the sand bars. Longshore currents are slow and small waves break on the bars causing their shoreward migration. Shoreline sinuousity increases as protuberances grow and embayments are slightly eroded. An approaching low pressure system causes increase in wind, waves and longshore current velocity. As the pressure system passes there is reversal of longshore current direction at the time of maximum wind velocity and wave height. During this time rapid longshore currents are defl cted by the sinuous shoreline such that strong rip currents are formed. These rip currents pass over sand bar crests and excavate channels. At the same time new bars are forming as sediment accumulates in relatively quiet areas between rip channels. As a result there is apparent migration of the bar form. The return to low energy conditions yields a pattern much like that during the previous time of low energy. In response to these coastal processes, the bar form oscillates back and forth alongshore rather than migrating down the beach. although the sediment does move alongshore.
TL;DR: In this paper, the authors measured the long axis orientations of elongate pebbles in dry channels on river braid bars and found that the highest degree of preferred orientation was obtained from populations of large pebble isolated on sand beds.
Abstract: Measurements of long axis orientations of elongate pebbles in dry channels on river braid bars show that the highest degree of preferred orientation is obtained from populations of large pebbles isolated on sand beds. Smaller size or increased concentration of the pebbles reduces the degree of preferred orientation. With flat pebbles, a stronger upstream imbrication mode is developed when the pebbles are in contact.
TL;DR: In this paper, the authors quantitatively determined the resuspension of fine grained estuarine sediments by small amplitude waves in the Greay Bay estuary of New Hampshire.
Abstract: Resuspension of fine grained estuarine sediments by small amplitude waves was quantitatively determined in the Greay Bay estuary of New Hampshire. By examining the relationship between wave height and sediment concentration an empirical, linear equation was calculated that appears valid for shallow waters on the flooding tide. Residence time of resuspended sediment appears low, with probably most resuspended sediment removed from tile water within a 24 hour period.
TL;DR: In this paper, the interior of hollow particles (chambers) in West Indian and Mediterranean nearshore calcareous sediments was investigated, and four kinds of fabric were found: ordered arrangement in monomineralic fringes of aragonite, resp. Mg-calcite; random arrangement in Mg calcite micrite.
Abstract: Non-skeletal aragonite and Mg-calcite is formed in the interior of hollow particles (chambers) in West Indian and Mediterranean nearshore calcareous sediments. The calcite has 15 to 17 mole percent MgCO3 in solid solution. The intragranular fillings are best developed in sediments from turbulent environments; the carbonate is an addition to the particles, not re-organized initial grain substance. The growth processes are not related to the activity of organisms; they are supposed to represent slow precipitation under supersaturated conditions. The time needed for precipitation is estimated to 100-1,000 years; the radiocarbon age of a Mediterranean chamber assemblage was 890 ± 115 years. Four kinds of fabric are found: ordered arrangement in monomineralic fringes of aragonite, resp. Mg-calcite; random arrangement in Mg-calcite micrite, and in aragonite clusters. Changes in mineralogy during growth are from Mg-calcite to aragonite; changes in fabric are from ordered to random arrangement. Mineralogy and fabric vary on a microscopic scale, and the two mineral polymorphs are evidently formed from natural seawater under the same general conditions. One important controlling factor is the growth substrate; biogenic aragonite induces nucleation and growth of aragonite, while biogenic calcite favors precipitation of Mg-calcite. The organic calcification matrices in the biogenic carbonates are probably active in the process. The intragranular precipitate is related in fabric and ultrastructure to various other shallow-marine carbonates, such as: beachrock cement; shallow submarine cement; and internal cement in reef-algal frameworks. Also the secondary carbonate in micrite envelopes appears to have the same properties.
TL;DR: In this article, the interaction of waves and tidal currents appears to be most important to the sediment budget of sand shoals, and the resultant "sediment gyres" are "dynamic sedim nt traps" which cause accumulations of sand in swash platforms.
Abstract: Sand shoals which extend seaward of Georgia estuary entrances are affected by a variety of sedimentary processes. Among these the interaction of waves and tidal currents appears to be most important to the sediment budget. As waves approach the shoreline they are refracted and wrap around the shoal margins. Wave crests interfer over the shoal surfaces and result in surges of water toward the shoreline. Waves also commonly "break" at points of interference and create wave bores which travel shoreward and interact with tidal currents. During the ebbing tide, this interaction is of particular importance to the sediment budget of the shoals. Sediment being transported seaward by tidal flow is diverted landward in gyral-paths by wave bores. The resultant "sediment gyres" are "dynamic sedim nt traps" which cause accumulations of sand in swash platforms. Swash platforms associated with shoals can be recognized by the sand-body geometry and characteristic internal structures.
TL;DR: In this paper, a 7 m core from the center of the basin of the Santa Clara River was used to investigate the origin of the gray layers of the sediment in the Santa Barbara Basin.
Abstract: Holocene sediments in Santa Barbara Basin, California Continental Borderland, consist primarily of laminated olive gray lutite intercalated with abundant layers of gray lutite. On the basis of detailed sedimentologic and mineralogic analyses of representative river sediments and a 7 m core from the center of the basin, the gray layers, previously interpreted as turbidites, have been found to be suspended-load deposits derived mainly from the Santa Clara River during large floods. Average periodicity of the gray layers is estimated at 120 years. The Santa Clara River is also the major source of laminated lutite. Predominance of Santa Clara River sediments is suggested by drainage area calculations, and supported by a comparison of <62µ mineral suites and chlorite content of basin sediments and sediments of peripheral rivers. An origin as flood deposits is postulated for the gray layers on the basis of their smaller mean diameter, better sorting, smaller sand fractions, lower carbonate content, and greater mineralogic similarity to the Santa Clara River than the laminated lutite. Mineralogic variations within the core occur mainly in the silt size-range, and are caused by source variations. The modern Santa Clara River suite becomes less dominant in the lower half of the core, probably as a result of more abundant shelf sediment that was available during lowered sea level.
TL;DR: The Castlegate Sandstone as discussed by the authors is one of several regressive sandstone tongues of the Late Cretaceous Mesaverde Group of east-central Utah and is the rock record of a fluvial-delta complex.
Abstract: The Castlegate Sandstone is one of several regressive sandstone tongues of the Late Cretaceous Mesaverde Group of east-central Utah. The Castlegate is the rock record of a fluvial-delta complex. The sedimentary facies change seaward (east) from piedmont red-bed conglomerates in central Utah to fluvial sandstones, then delta-plain sandstones, mudstones, and coals, and farther east to shoreline sandstones and finally delta-front interbedded sandstones and mudstones. The Castlegate wedges out as a rock unit into mudstones of the Mancos Shale near the Utah-Colorado state line. The depositional facies differ significantly in paleocurrent directions, measured on imbricated pebbles in conglomerates and trough cross-beds in sandstones. Paleocurrent directions in piedmont conglomerates are polymodal but with a dominant eastward directions. The average paleocurrent direction for fluvial sandstones is eastward but there is considerable variation among outcrops. Distributary channel sandstone of the delta-plain facies have polymodal paleocurrent directions due to tidal fluctuations. The shoreline sandstones have bimodal cross-bed directions both landward (west) and seaward. Delta-front bottom currents flowed landward. Grain-size decreases eastward from the piedmont through delta-front facies. Most Castlegate sandstones and siltstones from all facies are texturally similar to Holocene fluvial sands. Sedimentary rocks uplifted in western Utah and eastern Nevada during the Laramide orogeny were the source for Castlegate detritus. The grains consist largely of quartz plus fragments of chert, orthoquartzite sandstone, carbonate rock, and mudstone. Clay minerals are kaolinite, illite, and montmorillonite. The cements are silica, carbonates, and iron-oxides. Feldspars, micas, and metamorphic fragments constitute only a few percent. Non-opaque heavy minerals are 99% zircon, tourmaline, and rutile, largely reworked from older sandstones.
TL;DR: The faunal and textural characteristics of these phosphorites are strikingly similar to those of certain unphosphatized Miocene limestones dredged from the same area.
Abstract: Phosphorites (phosphatized limestones) are areally widespread on the South African continental margin. These rocks have packstone or wackestone textures and are typically composed of microfossils (chiefly planktonic foraminifers), with lesser amounts of macrofossil fragments and terrigenous grains set in a collophane/micrite matrix. The average P2O5 content of these rocks is about fifteen percent. Some varieties are exceedingly ferruginous, owing to the intimately mixed goethite in their matrices. The faunal and textural characteristics of these phosphorites are strikingly similar to those of certain unphosphatized Miocene limestones dredged from the same area. Mineralogical and geochemical evidence indicates that the lime mud matrix of some of these limestones was replaced by francolite. Phosphatization was accomplished under submarine conditions by permeating, phosphate-rich solutions.
TL;DR: In this article, surface breakage features described as diagnostic for glacial environments were observed using scanning electron microscopy (SEM) and differential interference-contrast (DIC) microscopy.
Abstract: Observation of surface breakage features described as diagnostic for glacial environments, scanning electron microscopy, differential interference-contrast microscopy
TL;DR: In this paper, the Wentworth and Halton ice sheets from the Credit River Valley of Southern Ontario were replaced by a coarsening-upward sequence of cross-laminated silts and ripple-drafted sands.
Abstract: Braided outwash streams deposited sands and gravels during the withdrawal of the Wentworth and Halton (both late Wisconsin) ice sheets from the Credit River Valley of Southern Ontario. The gravels are crossbedded on a scale of several feet, and fine upward into sandy cross-laminated and tabular cross-bedded facies. The Wentworth outwash sediments rest on Ordovician bedrock, and are separated from the Halton outwash sediments (above) by varved clays with dropstones and the Halton Till. Within the sandy facies are several newly recognized coarsening-upward sequences. These begin with very fine clay, coarsening upward into faintly cross-laminated silts and ripple-drafted sands. Above the sands there is normally an erosive surface, then tabular cross-bedded coarse and pebbly sands. Above a second erosive surface lies large scale cross-bedded sandy gravels. The sequence is interpreted as a channel fill. The clay represents overbank flooding into an old disused channel within the braided system. As the flood stage rises, more and more suspended sediment is washed overbank, and flow within the channel gives rise to the cross-laminated silts and sands. The tabular cross-bedded coarse and pebbly sands indicate bed load material being washed into the new channel, and the uppermost erosion surface, followed by cross-bedded sandy gravels, suggests levee-breaching, and final incorporation of the old channel into the active part of the braided system.
TL;DR: In the Tully Limestone, carbonate spar-filled, smooth-bottomed, unsheltered cavities known as stromatactis have been found.
Abstract: Massive pure calcilutite mounds in the Tully Limestone contain the distinctive carbonate spar-filled, smooth-bottomed, unsheltered cavities known as stromatactis, for which this report offers a possible inorganic origin. Contrasting with continual uniform compaction observed in more argillaceous sediments, compaction in the Tully mounds apparently was nonuniform, local, and occurred only during initial unmixing of water from an originally partly water-supported accumulation of pure lime mud. Sediment collapse in local areas of loosely packed lime mud formed cavities bounded along the top by irregular surfaces that separated more tightly packed coherent mud above, from loosely packed incoherent mud below. The collapsed mud flowed until supported, either in place or through a network of connected voids, and left water-filled smooth-bottomed cavities that are called stromatactis when filled with spar. Shapes of loosely packed zones, positions of larger grains and so forth, contributed to differences apparent in stromatactis. Some differences in size, associated structures, and spar mineralogy are related to stage of dewatering of the mound in which the cavity was preserved. Many small cavities were filled early by various forms of calcite spar. Large connected cavities containing pebbles of more coherent mud and fossil fragments served as channels for later water movement; these and even later desiccation cracks joining them were filled subsequently by ferroan dolomite spar. This hypothesis of stromatactis formation may explain the occurrence of similar features in other pure calcilutite mounds, and obviates the need for postulating either total obliteration of rigid skeletons or decay of soft organisms as a cause where no definite evidence exists.
TL;DR: In this paper, a sand-bottomed flume at velocities of 25 cm/sec and 60 cm /sec was used to investigate the properties of mud clasts in sedimentary deposits.
Abstract: 3 cm square by 0.5 cm thick mud clasts of three different sediment samples and varying water contents were eroded in a sand-bottomed flume at velocities of 25 cm/sec and 60 cm/sec. It was found that clay-rich and initially plastic clasts resist erosion the best, but that all clasts abrade and round quickly if velocities are high enough to transport them. The results suggest that (1) desiccation cracks are insignificant sources of natural mud clasts, and (2) most mud intraclasts in sedimentary deposits probably underwent little transportation from their site of origin.
TL;DR: Two tidal fiats associated with barrier island beaches have been examined in a cooperative study between a geologist and a biologist as mentioned in this paper, and the results of this work point out the interaction of physical and biological factors in controlling the sedimentary record of two similar subfacies.
Abstract: Two tidal fiats associated with barrier island beaches have been examined in a cooperative study between a geologist and a biologist. The results of this work point out the interaction of physical and biological factors in controlling the sedimentary record of two similar subfacies. In the two flats described, sand size is similar and both fiats occur as parts of barrier island beaches. The resulting depositional record is different, however, because of slight differences in the geographic settings and the responses of physical and biological processes to these differences. Similarities do exist in terms of the high degree of biogenic reworking which characterizes both tidal fiats. Fifty species of macrobenthic organisms were found to inhabit each of the two tidal fiats examined. Twenty-seven of these occupied both fiats. At Nannygoat flat where mud is an important sediment constituent (5 to 16 percent), polychaetes made up 38 per cent of the fauna and crustaceans 36 percent. At Cabretta flat where mud comprises a much smaller fraction (0.5-1.5 percent), polychaetes accounted for 28 percent of the species and crustaceans represented 40 percent of the species. If these two flats were preserved in a depositional sequence, they would both be lens or wedge-shaped sand bodies composed of bioturbated sand and both would be incorporated into a normal beach sequence. They would differ, however, in the percentage of mud fraction and in the type of specific trace fossils found.
TL;DR: In this paper, the authors attributed fine-grained greywackes, silts and shales to the Southern facies of the Lower Ecca of the Karroo System.
Abstract: At Coffee Bay fine-grained greywackes, silts and shales are attributed to the Southern facies of the Lower Ecca of the Karroo System. Within this sequence a structureless shale is riddled with intrusive sandstones; sheets, often branching, dominate the complex, but flat cross-cutting sheets and offshoots, and steeper folded dykes, are also developed. Irregularities in the structures reflect anisotropies in the host material, or post-injection folding and (rarely) boudinage. Certain joints were in existence at the time of injection, but nevertheless appreciable compaction took place thereafter. Lack of any age difference where intrusives with different attitudes are in contact indicates the rapid coeval injection of all the sandstones; this took place through a thickness of 40 m, to which a compaction factor must be added. The origin of these intrusions is speculative, although clearly they are derived from turbidite greywackes. Their random orientation may reflect an isotropic state in both the stress field and the host rock. Or, more speculatively the sheets may result from compression in an adjacent source area, with, in contrast, the more discordant features reflecting differing conditions in the area of study.
TL;DR: Authigenic silica occurs in carbonate rocks of Upper Carboniferous and Permian age from Bear Island (Svalbard). Fibrous, length-slow spherulitic silica in the form of quartzine and/or lutecite, megaquartz and microcrystalline quartz have been differentiated.
Abstract: Authigenic silica occurs in carbonate rocks of Upper Carboniferous and Permian age from Bear Island (Svalbard). Fibrous, length-slow spherulitic silica in the form of quartzine and/or lutecite, megaquartz and microcrystalline quartz have been differentiated. In the Carboniferous rocks (Fusulina Limestone Formation) all of these varieties of quartz reveal relict fibrous structure and inclusions of sulphates, while in the Permian (Spirifer Limestone Formation) no traces of sulphates were discernible. Association of length-slow fibrous silica (quartzine and/or lutecite) with sulphates is a commonly observed feature in the geological record and this particular variety was considered by Pittman and Folk (1970; 1971) as diagnostic of ancient evaporite environments.
TL;DR: Coastal dunes of Brazil differ considerably from desert dunes in their internal structure, primarily because of differences in the degree of cohesion within the sand as discussed by the authors, and the roots of plants growing on the dunes have further contorted and ruptured cross-lamination in the sand, forming additional distinctive structures.
Abstract: Coastal dunes of Brazil differ considerably from desert dunes in their internal structure, primarily because of differences in the degree of cohesion within the sand. The coastal dunes have formed under conditions of high humidity and heavy rainfall, and the avalanching of sand on the lee sides of these dunes has produced many distinctive deformational structures characteristic of wet, cohesive sand. The roots of plants growing on the dunes have further contorted and ruptured cross-lamination in the dunes, forming additional distinctive structures.
TL;DR: In this paper, the authors describe a snow slump and compare fold-axis orientations and axial-plane dips with slope-dip direction, showing that the axial planes of folds on the slope are normal to the slope surface, whereas at the base of the slope they are inclined down-slope.
Abstract: This paper describes a snow slump and compares fold-axis orientations and axial-plane dips with slope-dip direction. Many "preferred" orientations of fold axes exist within the slump: on the slope the strikes range from nearly parallel to 45 degrees to the direction of slope-dip; at the base of the slope the strikes are perpendicular to the displacement of the snow bed. Folds on the slope are generally rooted with their axial planes normal to the slope surface, whereas at the base of the slope they are not, and their axial planes may be inclined down-slope. A few folds have axial planes inclined up-slope.
TL;DR: Geochemical studies of sediments and pore fluids of recent deep sea sediments in the vicinity of the equatorial East Pacific Rise were carried out to delineate diagenetic and hydrothermal activity.
Abstract: Geochemical studies of sediments and pore fluids of recent deep sea sediments in the vicinity of the equatorial East Pacific Rise were carried out to delineate diagenetic and hydrothermal activity. Pore fluids were extracted onboard ship at in situ temperatures to yield the pore water data free of thermal artifacts. Dissolved Cl SO4, Mg, Ca, and K display remarkably few variations from bottom water concentrations even through various sediment types from CaCO8 ooze to siliceous ooze, red clay, and "hydrothermal" heavy metal muds. However, a few examples of enrichment of K were noted. Dissolved Mn and SiO2, in contrast, displayed marked enrichments, with solubilities likely controlled by rhodochrosite and sepiolite, respectively. No evidence for removals of dissolved components was found.
TL;DR: In this paper, the formation of sand-sized material begins with the dismemberment and dissolution of the saprolite and parent rock and forms grains with solution embayments until grains show very irregular and skeleton-like outlines.
Abstract: Studies of vertical profiles of quartz-rich Ultisols of the Carolina piedmont and coastal plain reveal patterns of grain dissolution which may be used as an indicator of weathering intensity. The formation of sand-sized material begins with the dismemberment and dissolution of the saprolite and parent rock and forms grains with solution embayments. Further dismemberment occurs until grains show very irregular and skeleton-like outlines. Skeletal grains characterize the root zone which is probably the zone of greatest solution activity. The repetitive nature of the observed patterns of dissolution and grain production enables one to formulate a model based on the degree and the amount of embayed quartz in the soil. The model proposes that after the initial release of the fragment, it i further modified by the soil water and as time proceeds and dismembering of the fragments occurs, dissolution at the grain contacts continues. Eventually, as the zone of greatest activity develops, it is possible that a soil profile consisting dominantly of embayed monocrystalline quartz would develop.
TL;DR: In this article, the basic methods of sizing fine suspended sediments described in this paper are microscopic analysis, optical-sedimentation analysis, direct optical analysis, and electronic (Coulter Counter) analysis.
Abstract: Particle size analysis is one of the potentially most powerful tools available for the interpretation of any population of sedimentary particles. The size distribution characterizes the particles as a product, providing information on the actual particle sizes, and also is a prerequisite to understanding their roles in a set of sedimentary processes. Fine-grained suspended sediments are the least amenable to size analysis because of the difficulty of preserving the natural state of aggregation throughout sampling and analysis. Fine suspended sediments are composed of inorganic mineral matter and living and dead organic matter which occur as individual particles, and as agglomerates and aggregates. The projected areas, volumes, and diameters of the particles are highly variable as are their electrical and optical properties. The various methods of size analysis measure very different properties of the particle population. The basic methods of sizing fine suspended sediments described in this paper are microscopic analysis, optical-sedimentation analysis, direct optical analysis, and electronic (Coulter Counter) analysis. The microscopic method is the only one which permits direct visual observation of the particles, but yields a number frequency distribution rather than a weight or volume-size distribution. Optical-sedimentation methods permit analysis of the hydraulic behavior of the sediment in its natural medium, but at present are limited by concentration and size range. The Coulter Counter method is in some respects the most versatile method, but it yields a volume distribution which can not be directly related to settling velocity.