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953 records · Page 53Linked to original sources
USGS1987

Integration of channel and floodplain suites. I. Developmental sequence and lateral relations of alluvial paleosols.

The lower Eocene Willwood Formation of the Bighorn Basin, northwest Wyoming, consists of about 770 m of alluvial rocks that exhibit extensive mechanical and geochemical modifications resulting from Eocene pedogenesis. Willwood paleosols vary considerably in their relative degrees of maturity; maturity is defined as stage of development as a function of the amount of time required to form. Five arbitrary stages are proposed to distinguish these soils of different maturities in the Willwood Formation. Stage 1 soils, the least mature, are entisols; stage 2 and stage 3 soils are intermediate in maturity and are probably alfisols; and stage 4 and stage 5 soils, the most mature, are spodosols. These stages are not only time-progressive elements of an in situ maturation sequence for Willwood soil formation, but, in the lateral dimension, they are also usually distributed sequentially. Study of Willwood paleosols indicates that an inverse relationship exists between soil maturity and short-term sediment accumulation rate. The least mature Willwood paleosols formed in areas of relatively high net rates of sediment accumulation on 1) channel, levee, and crevasse-splay sediments of the proximal alluvial ridge, and 2) deposits filling large and small paleovalleys formed by major episodes of gullying (lowered baselevels). In contrast, the fine-grained sediments of the distal floodplain, where net sediment accumulation rates were relatively low, experienced development of much more mature soils. Soils of intermediate maturities occur in the order of their stage on intervening proximal floodplain and distal alluvial ridge sediments. Adjacent bodies of sedimentary rock that differ in their ancient soil properties because of distance from areas of relatively high sediment accumulation are denoted by the new term pedofacies . The remarkable sequence of paleosols in the Willwood Formation clearly illustrates several important principles of soil-sediment interrelationships in aggrading alluvial systems that have broad application to other deposits. This is especially true in view of the widespread distribution of paleosols in nearly all ancient fluvial rocks. Further study of Willwood paleosols will not only enable precise lateral correlation of coeval alluvial sediments, and thereby fluvial sedimentary events, from the distal to the proximal realms of the floodplain but will also contribute to increasingly informative evaluations of the nature, tempo, and mode of alluvial succession.

Journal of Sedimentary Petrology↗
USGS1989

Whitings, a sedimentologic dilemma

Whitings, drifting clouds of water, milky because of suspended carbonate, have been claimed to originate from either the action of bottom-feeding fish or direct precipitation of calcium carbonate. Five cruises during different seasons were made to the Great Bahama Bank to collect data pertinent to the controversy. Measurements of particulate concentrations average 10 mg/liter with a maximum of 20 mg/liter of carbonate sediment suspended in whiting water, compared with an average of 1.5 mg/liter for clear water outside the whitings. The particles are dominantly acicular aragonite, but Mg calcite composes as much as 20 percent of some whitings. Sedimentation rates, measured with fixed and drifting sediment traps, were as great as 34 g/m 2 /hr. Sediment suspended in whitings aggregated into silt- and sand-size fioccules and settled to the bottom of settling tanks within six hours, even on a rocking ship. Sediment in artificial whitings, created by stirring sediment from the bottom with a shrimp trawl, settled to the bottom in about the same time. Natural whitings, on the other hand, were never observed to dissipate. Because sedimentation from whitings occurs at rates sufficient to cause dissipation of the whitings within six hours, we conclude that the natural whitings are continually replenished by direct precipitation. The search for fish in whitings utilized sidescan sonar and fathometer imaging, shrimp trawls, rotenone, remote video, and direct scuba observation. These methods and 25 years of casual observations leading to this study indicate that fish are not involved in the formation of most Bahamian whitings. Several whitings were found over rocky or sandy bottoms where there was no mud available for fish to suspend. The distance of these whitings from areas of muddy bottom precluded their having been made elsewhere by fish. Stable carbon- and oxygen-isotopic analyses and Delta 14 C activity are interpreted to indicate that the suspended sediment in whitings contains some precipitated calcium carbonate and is not merely bottom sediment stirred into suspension. Estimates indicate that the amount of new carbonate produced in whitings on the Great Bahama Bank is substantially higher than that arising from algal production. Consequently, the amount of sediment transported to deep water may be much greater than previously thought.

Journal of Sedimentary Petrology↗
USGS1989

Subaqueous grain flows at the head of Carmel Submarine Canyon, California

The head of Carmel Submarine Canyon lies in 15 m of water about 200 m off a coarse-sand beach in the southeast corner of Carmel Bay, California. Very coarse sand is the predominate material on the beach, adjacent shelf, and upper canyon-head slopes, while silt and clay cover the surface below a water depth of about 35 m. Along a shore-normal transect, median grain size decreases between the beach and canyon rim but increases down the upper canyon-head slope. On angle-of-repose slopes in the upper canyon head, downslope-coarsening deposits, which are everywhere there is active sand movement, are similar to a type of sediment gravity flow deposit formed by grain flows (sand avalanches). Using three sand fractions that were dyed different fluorescent colors, scuba divers generated sand avalanches that produced deposits similar to the natural deposits. The dyed-sand deposits, which extended as far as 25 m below the initiation point, were inversely graded and increased in grain size downslope. Inverse grading was well developed within two m of the initiation point, though the thicknesses of the three layers varied in a nonsystematic manner both across and down slope. The minor amount of native material found within the dyed-sand layers showed that entrainment of the underlying sand was minimal.

Journal of Sedimentary Petrology↗
USGS1989

Observed parameters for turbidity-current flow in channels, Reserve Fan, Lake Superior

Fine-grained tailings discharged from a taconite-ore processing operation near the shore of Lake Superior produced turbidity currents that transported the sediment from a small delta into deep water at Silver Bay, Minnesota. Deposition over nearly 20 years produced a sublacustrine fan with two prominent channels. During 1972 and 1973, a current meter anchored 5 m above the lake floor adjacent to one of the channels recorded episodic turbidity-current flow events lasting as long as two weeks. To understand flow parameters for turbidity currents better, a short-term experiment within a channel on Reserve Fan in 1975 measured those variables not previously directly observed for channelized turbidity currents: flow thickness, flow density, and concurrent velocity. The observed flow thickness, approximately 16 m, is nearly four times the channel depth. Calculations using the average flow speeds (8 to 12 cm/sec) and the dilute concentration of the flow as measured during the experiment yield a value for the drag coefficient that is in remarkable agreement with estimated values commonly used for deriving speeds of turbidity currents using dimensions of submarine channels and properties of the sediments.

Journal of Sedimentary Petrology↗
USGS1989

Significance of loessite in the Maroon Formation (Middle Pennsylvanian to Lower Permian), Eagle Basin, northwest Colorado

Quaternary loess deposits are widespread on the earth's surface, yet pre-Quaternary loess deposits have rarely been reported. The Maroon Formation (Middle Pennsylvanian to Lower Permian) of the Eagle Basin, northwest Colorado, includes a siltstone-dominated facies interpreted as loessite (lithified loess) along its downwind basin margin. The section of inferred loessite in the Maroon Formation is locally at least 490 m thick and consists in large part of structureless and nearly structureless beds of homogeneous sandy siltstone. Bed contacts are generally planar to undulatory and are either horizontal or are characterized by gentle relief. Loessite beds are separated by common claystone drapes and weakly developed paleosols, and by rare pond deposits, channel deposits, and eolian-ripple-laminated deposits. The loess interpretation is based on 1) the homogeneity and dominance of the sandy silt grain-size; 2) the relative lack of primary sedimentary structures; 3) the gentle character of most bedding contacts and the common mantling of irregular depositional topography; 4) the inferred paleogeographic setting; and 5) the absence of suitable alternative interpretations. The loessite grades laterally into mixed fluvial-eolian deposits of the Maroon Formation in the main part of Eagle Basin, which served as the loessite sediment source. Deposition of the Maroon Formation was probably strongly affected by cyclic climatic changes synchronous with fluctuations in late Paleozoic continental ice sheets. The paleogeography and paleoclimatology of the Maroon Formation depositional system are not unique, suggesting that there are probably many other ancient loessites that have gone unrecognized.

Journal of Sedimentary Petrology↗
USGS1990

Eocene diatom chert from Adak Island, Alaska

Bedded quartz cherts that contain recognizable diatoms are rare in the geologic record and are described here for the first time. The Eocene Andrew Lake Formation on Adak Island, Alaska consists of about 800 m of sedimentary and volcanogenic rocks. Quartz cherts containing diatoms occur in the upper part of the Andrew Lake Formation and crop out on the northern part of the island. The quartz chert formed at about 70 degrees C as determined by its oxygen isotopic composition. The diatoms were preserved in the chert because early and rapid alteration of ubiquitous volcanic glass in the section released silica and saturated the pore waters with respect to opal-A. Then, temperature rapidly increased with burial and the pore waters became undersaturated with respect to opal-A (biogenic silica), which occurred at a temperature greater than that needed to convert opal-CT to quartz. At this stage, delicate species of diatoms dissolved and quartz precipitated around the remaining more robust diatoms, forming diatom theft. Subsequently, grain-growth occurred and quartz replaced the frustules on a very fine scale.

Alaska↗
USGS1956

Heavy-mineral suites in unconsolidated Paleocene and younger sands, western Tennessee

Heavy-mineral suites from unconsolidated sands of Wilcox and Claiborne age (Eocene) in the subsurface of western Tennessee were tabulated and compared with heavy-mineral suites obtained from outcropping sands known to be of Midway (Paleocene) and Wilcox age and younger. In the subsurface at Memphis, both pink and colorless garnet are relatively abundant in the Claiborne but rare in the Wilcox. Garnet, however, is very rare in both the Claiborne and the Wilcox in the subsurface 35 miles northeast of Memphis. The mineral is very rare also in the terrace sands of western Tennessee and in samples of the Pliocene(?) and Pleistocene deposits of the Tennessee River in eastern and western Tennessee. It is possible, therefore, that the relative abundance of the mineral garnet is related to the quantity of sediment received from differing source areas in Wilcox and Claiborne times, but that, owing to the shifting of the axis of the embayment, no one source area furnished all the sediment for any formation. Heavy-mineral suites from Pliocene(?) and Pleistocene terrace deposits of the Tennessee River in both eastern and western Tennessee, and heavy-mineral suites from Pliocene(?) deposits of the Mississippi River are much alike, and the only isotropic mineral noted in these sediments was a very rare green mineral. Heavy-mineral suites from Recent deposits of the Mississippi River at Memphis and reported heavy-mineral suites from Cambrian sandstones of Wisconsin and Minnesota differ greatly from heavy-mineral suites of Pliocene(?) terrace deposits of the Tennessee and Mississippi Rivers and include much pink and colorless garnet. The possibility, therefore, is suggested that the Pliocene(?) terrace deposits of the Mississippi River in western Tennessee were derived largely from the basin of the Tennessee River.

Tennessee↗
USGS1964

Bottom sediments of Saginaw Bay, Michigan

Saginaw Bay is a southwest extension of Lake Huron on the east shore of the Southern Peninsula of Michigan. It is a shallow-water derivative of the Pleistocene Lake Saginaw. Sixty-one bottom samples were collected on a semigrid pattern and analyzed physically. Findings were treated statistically. Sediments range in size from large pebbles to clay. Medium- to fine-grained clear quartz sand is common to all parts of the bay. Currents and wave action are primarily responsible for both median diameter and sorting distribution patterns. Only a very general correlation can be established between depth and median diameter. Heavy minerals occur in abundance locally and show an affinity to shallow-water areas subject to prevailing currents. Shape also locally determines heavy mineral concentrations. Only general conclusions can be established from roundness and sphericity and acid-soluble content. Increased organic content is correlative with quiet water environments. The shallow-water, heterogeneous nature of Saginaw Bay is not conducive to the recognition of sedimentary criteria suitable for correlations in other than a local environment.

Journal of Sedimentary Petrology↗
USGS1966

Color variations within glacial till, east-central North Dakota--A preliminary investigation

Color variations (orange zones within buff-colored till) in drift in east-central North Dakota are believed to represent two tills of separate origin. Mean size, standard deviation, and number and type of pebbles show greater difference between the two tills than do skewness, kurtosis, and partial chemical analyses. Probably blocks of older till were moved by the last glacier crossing the area and were redeposited in a matrix of younger till.

Journal of Sedimentary Petrology↗
USGS1991

Mineralogy of the silt fraction in surficial sediments from the outer continental shelf off southeastern New England

The silt-sized heavy mineral assemblage, which is predominantly detrital, has been concentrated in this fraction by hydraulic factors and ranges between 11.8 wt. % of the silt fraction in the sandy sediments near Georges Bank to 3.4% in the clayey silt deposit south of Martha's Vineyard. By contrast, the sand fraction averages only 1.5% heavy minerals. Lateral variability within the silt-sized heavy mineral assemblage is considerable. Zircon and ilmenite abundances progressively decrease from east to west on the continental shelf off southeastern New England. Conversely, abundances within the amphibole and the epidote groups increase from east to west.

Journal of Sedimentary Petrology↗
USGS1991

Modern sedimentary environments in Boston Harbor, Massachusetts

Analyses of sidescan-sonar records supplemented by available bathymetric, sedimentary, subbottom, and bottom-current data reveal the distributions of the following three categories of sedimentary environments within the glaciated, topographically complex Boston Harbor estuary in Massachusetts. 1) Environments of erosion appear on the sonographs either as patterns with isolated strong reflections or as uniform patterns of strong reflectivity. These patterns define outcrops of bedrock or till and coarse lag deposits that are being scoured and winnowed by tidal- and wave-induced currents. Erosional areas are located primarily along mainland and insular shores, within large channels that have strong tidal currents, atop submerged ridges and knolls, and across much of the harbor entrance. 2) Environments of deposition are depicted on the sidescan-sonar records as smooth, featureless surfaces that have low to moderate reflectivity. Depositional environments are found predominantly over shallow subtidal flats and in broad bathymetric lows where tidal currents are weak. Sediments within depositional areas are organic-rich sandy and clayey silts that are accumulating at rates ranging from 0.01 to 0.11 g/cm 2 /yr or 4000 to 46,100 metric tons/yr. The cumulative mass of modern mud in harbor depocenters is 24.3 million metric tons. 3) Environments of sediment reworking constitute areas affected by a combination of erosional and depositional processes. They are characterized on the sonographs by mosaics of light and dark patches produced by relatively subtle and gradational changes in reflectivity. Reworked sediments have diverse grain sizes that overlap and are transitional between those of the other two sedimentary environments, and they are indicative of highly variable bottom currents.

Massachusetts↗
USGS1991

Porosity trends of the Lower Cretaceous J Sandstone, Denver Basin, Colorado

This study examines relationships between porosity and time-temperature history, and the influence of rock properties upon porosity, for the Lower Cretaceous J Sandstone in the Colorado portion of the Denver basin. The J Sandstone is classified as a quartzarenite to litharenite and was deposited in nearshore-marine, deltaic, and fluvial-estuarine (valley-fill) settings. Principal elements of its paragenetic sequence include quartz cementation and pressure solution, carbonate cementation and dissolution, dissolution of feldspar and rock fragments, and formation of authigenic clays. Porosity versus vitrinite reflectance (R 0 ) regression lines of the form Phi = A(R 0 )Beta (where B is a negative number) depicting the 10th, 25th, 50th, 75th, and 90th porosity percentiles of the J Sandstone were derived from 963 core-plug measurements representing 31 wells. The data span a thermal maturity range of R 0 = 0.41%-1.14%. Porosity distributions at different locations within the basin can be estimated as a function of thermal maturity on the basis of these regression lines. Porosity trends of the J Sandstone, if considered as a function of R 0 , are similar to those of broad, composite data sets representing sandstones in general. The petrographic factors that most affect J Sandstone porosity variability at a given level of thermal maturity are carbonate cementation and clay content. Carbonate cement, where present, reduces porosity. If previously more widespread, carbonate cement could also introduce porosity heterogeneity by temporarily preserving the pore network relative to uncemented intervals. Abundant detrital and authigenic clay reduces porosity by occupying pores. Low clay content indirectly reduces porosity because the inhibiting effects of clay upon quartz cementation and pressure solution are largely absent.

Journal of Sedimentary Petrology↗
USGS1992

Role of microbial processes in linking sandstone diagenesis with organic-rich clays

Numerous chemical reactions within clay sequences have been proposed to produce dissolved material for diagenesis of deeply-buried sands. However, reactions responsible for solubilizing inorganic and organic constituents in clays at intermediate depths, and their importance to sandstone diagenesis, have not been evaluated. Results from this study show that the processes of microbial organic-acid production (via fermentation) in clays and microbial organic-acid consumption (via sulfate reduction) in sands effectively link organic-rich clays to sandstone diagenesis in the Black Creek Formation of South Carolina. Diagenetic processes have resulted in the formation of 10 volume percent calcite cement, 0.1 volume percent authigenic pyrite, and 1.5 volume percent secondary porosity in Black Creek sands. However, the distribution of these diagenetic processes is not uniform, resulting in net destruction of porosity in some parts of the sand and net porosity enhancement in other parts. Mass balance-derived rates of microbial organic-acid production (10 (super -5) mmole carbon 1 (super -1) yr (super -1) ) and microbial CO 2 production (4 x 10 (super -5) mmole l (super -1) yr (super -1) ) show that microbial processes can account for all organic carbon in the calcite cements (at least 11% of carbonate carbon based on isotope-balance calculations), all observed authigenic pyrite, and all observed secondary porosity. These findings show that microbial processes can serve to link organic-rich clays with sandstone diagenesis at intermediate depths.

Journal of Sedimentary Petrology↗
USGS1992

Lithofacies analysis of colluvial sediments - an aid in interpreting the recent history of Quaternary normal faults in the Basin and Range Province, western United States

Inferring the frequency and magnitude of past earthquakes from the stratigraphy in exposures of normal-faulted sediments is difficult because colluvial lithofacies assemblages adjacent to faults are complex. Similarities in facies assemblages adjacent to young fault scarps in arid to semiarid areas, such as the Basin and Range province, allow lithofacies to be grouped into two genetic architectural elements: debris and wash elements. Upper and lower facies associations can commonly be recognized within each element. A lithofacies code scheme, similar to those used in the analysis of fluvial and glacial lithofacies sequences, provides a concise way of illustrating lithofacies relations in fault exposures. The source lithology of colluvial lithofacies is shown in the code, and soil-horizon symbols can be included. The architecture of lithofacies assemblages near fault scarps in semiarid areas is explained by a model of colluvial sedimentation in response to a single surface faulting event. Analysis of lithofacies assemblages exposed in three trenches across normal faults in the eastern Basin and Range shows how the model can be used to interpret fault histories. Similar facies analysis methods may be useful in interpreting colluvial sequences formed by non-tectonic processes.

Journal of Sedimentary Petrology↗
USGS2011

Measured reflectance suppressed by thin-film interference of crude oil smeared on glass - as on vitrinite in coal or petroliferous rocks

The tool of measuring "vitrinite reflectance" under a microscope has great value in petroleum exploration and coal utilization, and the reflectance is a simple number, such as 1.4% Ro, with some slight variations depending on technique. Sample collection, preparation and measurement are simple and many sedimentary rocks yield vitrinite. However, the reported number can lead one astray if its origin and quality are not fully understood. I analyze here just one factor, "smear" of crude oil on the polished surface (from the sample), which may reduce reflectance because of thin-film interference. Some other causes of error are listed in an addendum to this note.

Society for Organic Petrology Newsletter↗
USGS1998

Anorogenic nature of magmatism in the Northern Baikal volcanic belt: Evidence from geochemical, geochronological (U-Pb), and isotopic (Pb, Nd) data

The Northern Baikal volcanic belt has an age of 1.82-1.87 Ga and extends along the boundary between the Siberian Platform and the Baikal foldbelt. The volcanic belt is composed of volcanics of the Akitkan Group and granitic rocks of the Irel and Primorsk complexes. The geochemistry of the rocks points to the intraplate anorogenic nature of the belt. U-Pb zircon dating of the Chuya granitoids revealed that they are older (2020-2060 Ma) than the Northern Baikal volcanic belt and, thus, cannot be regarded as its component. Data on the Pb isotopic system of feldspars from the granitoids confirm the contemporaneity of all volcanic rocks of the belt except the volcanics of the upper portion of the Akitkan Group (Chaya Formation). Our data suggest its possibly younger (???1.3 Ga) age. The isotopic Nd and Pb compositions of the acid volcanic rocks provide evidence of the heterogeneity of their crustal protoliths. The volcanics of the Malaya Kosa Formation have ??Nd(T) = -6.1, ??2 = 9.36, and were most probably produced with the participation of the U-depleted lower continental crust of Archean age. Other rocks of the complex show ??Nd(T) from -0.1 to -2.4, ??2 = 9.78, and could have been formed by the recycling of the juvenile crust. The depletion of the Malaya Kosa volcanics in most LILEs and HFSEs compared with other acid igneous rocks of the belt possibly reflects compositional differences between the Late Archean and Early Proterozoic crustal sources. The basaltic rocks of the Malaya Kosa Formation (??Nd varies from -4.6 to -5.4) were produced by either the melting of the enriched lithospheric mantle or the contamination of derivatives of the depleted mantle by Early Archean lower crustal rocks, which are not exposed within the area. Copyright ?? 1998 by MAEe Cyrillic signK Hay??a/Interperiodica Publishing.

Petrology↗