Percentage Of Heavy Minerals Research Articles

Detrital Tourmalines in the Cretaceous–Eocene Julian and Brkini Flysch Basins (SE Alps, Italy and Slovenia)

In the SE Alps, two Cretaceous–Eocene flysch basins, Julian and Brkini, filled with turbidite sediments, are present. This study novelly reports heavy mineral assemblage counts and detrital tourmaline characterization for 11 samples. It is possible to define three different groups, characterized by the presence of (1) a clinopyroxene–epidote–low-ZTR (zircon+tourmaline+rutile; 5%) sample association, (2) a high-ZTR (>48%)–garnet–apatite association and (3) a low-ZTR (<40%)–Cr-spinel–garnet association. Detrital tourmalines from both the Julian and Brkini flysch basins are rather similar in composition, associated with metapelites and metapsammites coexisting or not coexisting with an Al-saturating phase, ferric-iron-rich quartz–tourmaline rocks and calc–silicate rocks; however, their number is drastically different. In fact, even if the percentage of heavy minerals is very low and similar in both basins (0.17–1.34% in weight), in the Julian basin, the number of tourmaline crystals is much lower than that in Brkini (1–14 vs. 30–100), suggesting an important change in the provenance area. Interestingly, the presence of a high amount of tourmaline derived from ferric-iron-rich quartz–tourmaline rocks and calc–silicate rocks makes these two basins different from all the Cretaceous flysch basins of Bosnia and the Northern Dinaric zone, where these supplies are missing or very limited.

Source areas of the Eastern Ebro Valley loess (NE Iberian Peninsula): Heavy mineral composition as a provenance indicator

AbstractLoess deposits of the Eastern Ebro Valley (NE Iberian Peninsula) occupy an area of ~2000 km2 mostly on the east of the Ebro depression and locally in the Móra Basin. We studied 38 samples of loess and 47 samples of their possible source areas, in order to determine the location of the origin of the loess materials, based on their particle size distribution and composition of heavy minerals. Our results clearly differentiate two depositional loess basins disconnected by the reliefs of the Pre‐Coastal Range with different mineralogical signatures: the Ebro Basin and the Móra Basin. The most relevant variables to discern source areas were the percentage of heavy minerals, the concentrations of zircon, staurolite, rutile and inosilicates, and the presence of gypsum. In the Ebro Basin, the largest set of loess deposits is located around a depocenter in the Batea region and along several lateral areas, with materials that come from the central alluvial plain of the Middle Ebro River (25 to >100 km travel distance), in addition to deflated materials from Miocene interfluvial substrates. On the other hand, loess deposits of the Móra Basin come from more proximal source areas (<15 km), originating from the alluvial materials of the Lower Ebro River that contain the contributions of its tributaries, the Cinca and Segre rivers. Taking into account the homogeneity in the mineralogical composition of complex loess sequences, we deduced a general WNW–ESE wind direction, which would have remained constant over the last two cold periods (MIS‐2 and MIS‐6). Along this axis, the Pàndols–Cavalls Range, with a height difference of 200–350 m, acted as a wind barrier separating the loess of Ebro Basin from the loess of Móra Basin.

Seasonal variations of textural and heavy minerals of the Karamana river sediments and beach sediments of Trivandrum, Southern Kerala

Kerala, south western state of India is known for its abundant heavy mineral deposits along the coast. Beach placer deposits in Kerala is known for ilmenite, rutile, zircon, monazite, sillimanite and garnet. The grain size study of the sediments from Karamana river, flowing in the southern part of Kerala. Sediments from different parts of the river basin is studied, which enabled to understand the grain size variations with course of the river from the Peppara dam to Thiruvallam, very near to coast. Mineralogy of the river vary from one place to another depending different factors like host rocks in the province, climate conditions of the area, agents of transport and hydraulic condition during deposition, also can predict the actual source area associated with heavy mineral. Textural and heavy mineral studies of the placers of beach and Karamana river basins indicating the river is one of the important contributors of sediments to the western coast of the southern part of Kerala. Samples from various parts of the river indicate that the sediment is medium sand, moderately sorted, fine skewed and platykurtic. The characteristics of grain size distribution are related to the source rocks, process of weathering, and different sorting processes during transportation and deposition. The total heavy mineral percentage shows it is prominently enrichment in fine sand and very fine sands.

A study on textural characteristics, heavy mineral distribution and grain-microtextures of recent sediment in the coastal area between the Sarada and Gosthani rivers, east coast of India

The current study aimed to describe textural characteristics, heavy mineral composition, and grain microtextures of the sediment from three micro-environments (foreshore, berm, and dune). A total of forty-one (41) representative surficial sediment samples have been collected from fifteen (15) locations along the beach area between the Sarada and Gosthani rivers on the east coast of India, where the length of the stretch is more than 100 km. The study reveals that most of the coastal sediment is medium to fine sand with relatively high ratios of coarse sand at Yarada beach, and the nature of the sediment is moderately to well sorted. These characteristics indicate a high energy environment. The heavy mineral analysis of the sediment in the current study was done for coarse (+60#) and fine (+230#) size fractions. Studying the weight percentage (WT%) reveals that a high percentage of heavy minerals is associated with fine fractions. Ilmenite, sillimanite, garnet, zircon, and rutile are the major heavy minerals identified in the current investigation. The concentrations of these heavy minerals show great variations from south to north of the study area. From an economic point of view, a considerable amount of heavy minerals (average 48.41%) are present on both sides (north and south) of the Gosthani River mouth. In the Sarada Estuary, the concentration of the economic heavy minerals was found under the minimum economic range. The grain microtextures of the major heavy minerals from the different locations along the study area demonstrate the variation in grain microtextures, which is controlled by the chemical and mechanical processes. These microtextures reflect moderate to high wave energy on the beach area, in addition to high mechanical impact on the grains from the estuary point.

Mineralogy, geochemistry and economic potentialities of heavy mineral sand resources of Bangladesh

Heavy mineral sand deposits are the important mineral resources of Bangladesh. Systematic mineral exploration activities carried out in the south eastern coastal belt of Bangladesh were successful to discover seventeen heavy mineral sand (HMS) deposits in the coastal beach and off-shore islands. Mineralogy, geochemistry and mineral processing characteristics of the heavy mineral sands and their economic potentialities are presented in the present paper. On an average, HMS deposits contain 23% total heavy minerals. In heavy fraction, average weight percentage of the economic minerals is: zircon 4.20%, rutile 2.04%, ilmenite 26.03%, garnet 6.45%, kyanite 3.92%, leucoxene 2.30%, magnetite 1.87% and monazite 0.31%; and the average weight percentage of other non-economic heavy minerals is 53.88%. Heavy mineral sand deposits altogether contain 1.76 million tons of economically important heavy minerals which are: limonite (1,025,000 tonnes), garnet (223,000 tons), zircon (158,000 tonnes), leucoxene (97,000 tons), kyanite (91,000 tons), rutile (70,000 tons), magnetite (81,000 tones) and monazite (17,000 tonnes). Occurrence of large amount of economic heavy minerals in the sand bars of Brahmaputra-Jamuna River has been reported by some recent studies. On an average, total heavy mineral percentage of the Brahmaputra-Jamuna sand bars is around 8.92%. Mineral sand processing on the bulk samples has been carried out at the pilot plant comprising gravity, magnetic and electrostatic separators to characterize the separation characteristics of individual economic heavy minerals. Geochemical studies on the separated heavy minerals show that TiO2 in rutile is around 90% and ZrO2 in zircon is around 65%, which are quite satisfactory in respect of commercial grade. Ilmenite contains low level of titanium dioxide (TiO2-43%) and higher level of chromium, manganese and iron. Beneficiation and upgrading of limonite will be required to make it a market able commodity. Valuable minerals present in the heavy mineral sand deposits of Bangladesh need to be mined sustainably and utilized for the benefit of the country.

A preliminary study on the characteristics of the tailing ofthe hammermill –sluice box operation at the kraboedoin and kriki negi hill District brokopondo- Suriname

The small scale mining in Suriname is one of the most important livelihoods and biggest contributors to the economy of Suriname. However this sector needs to be evaluated continuously in order to introduce environmental friendly and more efficient methods. Another pre condition before introducing other environmental friendly and more efficient method is; knowing the compound of the ore. The Hammer mill – Sluice box method is one of the most used methods by the small scale miners. This technique uses a Hammer mill to grind the ore and a Sluice box to concentrate the gold.To study some charactistics of the tailing of the small scale gold miners at Kraboedoin and Kriki negi hills, the tailing samples were collected. The particle size distribution, the gold content and the heavy mineral percentage per fraction of these samples were determined and analyzed.The results of both sites showed that about 70% of the tailing had size between 0.250mm and 2.000mm, the average gold content in the tailing at Kraboedoin hill is 0.93ppm and at Kriki negi hillis 3.30ppm.

Investigation of natural background radiation of sediments in Rameswaram Island, Tamil Nadu, India

The aim of the study is to assess the natural background radiation in and around Rameswaram Island. In this context, samples were collected to measure the gamma radiations of 238U, 232Th, and 40K using NaI(Tl) detector-based gamma ray spectrometer. The average activity concentrations of 238U, 232Th, and 40K are noted to be well below the world average values. The calculated absorbed dose rate, radium equivalent activity, and hazard index values were below the prescribed limit. The grain size of the sediment was analyzed following Trefethen’s nomenclature, and its correlation with the natural background radioactivity was studied. The sample that contained clay show elevated activity of 40K. The percentage of heavy minerals shows concomitant variation in natural radioactivity, especially in the activity of 238U and 232Th.

Petrography of Middle Jurassic to Early Cretaceous sandstones in the Kutch Basin, western India: Implications on provenance and basin evolution

This paper investigates the provenance of Middle Jurassic to Early Cretaceous sediments in the Kutch Basin, western India, on the basis of mineralogical investigations of sandstones composition (Quartz–Feldspar–Lithic (QFL) fragment), Zircon–Tourmaline–Rutile (ZTR) index, and mineral chemistry of heavy detrital minerals of the framework. The study also examines the compositional variation of the sandstone in relation to the evolution of the Kutch Basin, which originated as a rift basin during the Late Triassic and evolved into a passive margin basin by the end Cretaceous. This study analyzes sandstone samples of Jhumara, Jhuran and Bhuj Formations of Middle Jurassic, Upper Jurassic and Lower Cretaceous, respectively, in the Kutch Mainland. Sandstones record a compositional evolution from arkosic to subarkosic as the feldspar content decreases from 68% in the Jhumara Formation to 27% in the Bhuj Formation with intermediate values in the Jhuran Formation. The QFL modal composition indicates basement uplifted and transitional continental settings at source. Heavy mineral content of these sandstones reveals the occurrence of zircon, tourmaline, rutile, garnet, apatite, monazite and opaque minerals. Sub-rounded to well-rounded zircon grains indicate a polycyclic origin. ZTR indices for samples in Jhumara, Jhuran and Bhuj Formations are 25%, 30% and 50% respectively. Chemistry of opaque minerals reveals the occurrence of detrital varieties such as ilmenite, rutile, hematite/magnetite and pyrite, in a decreasing order of abundances. Chemistry of ilmenites in the Jhumara Formation reveals its derivation from dual felsic igneous and metabasic source, while those in Jhuran and Bhuj Formations indicate a metabasic derivation. Chemistry of garnet reveals predominantly Fe-rich (almandine) variety of metabasic origin. X-ray microscopic study provides the percentage of heavy minerals ranging from 3% to 5.26%. QFL detrital modes reflect the evolution of the basin from an active rift to a passive margin basin during the Mesozoic. Integration of results from QFL modal composition of the sandstones, heavy mineral analysis and mineral chemistry, suggests sediment supply from both northern and eastern highlands during the Middle Jurassic. The uplift along the Kutch Mainland Fault in the Early Cretaceous results in curtailment of sediment input from north.

Mineralogy of Duné s Sand of Missan Dune Fields Southeastern Iraq

The aim of this study is to define the mineralogical composition of Missan dune fields South Eastern of Iraq, and try to determine the origin or the source of these dunes .
 Three main types of dunes were recognized in the studied area, these are: barchanoid ridge, barchans and nabkha dunes. The direction of these dunes is northwest to southeast.
 The dunes in Missan dune fields were divided into three fields according to the vari- eties in the composition and geographical position in the studied area, these three fields are: Al-Manziliyah, Middle Chailat, and Said Subair dune fields.
 9 samples were collected from these fields, the samples were separated into light and heavy fraction by heavy liquids. The light fraction composed from quartz, feldspar, and rock fragments, the rock fragments composed mainly of carbonate, chert, igneous, and metamorphic rock fragments .
 The heavy minerals are mostly opaques, chlorite, pyroxenes, amphiboles, epidotes, zircon, garnet, muscovite, biotite, kyanite, staurolite, and rutile .
 The percentages of heavy minerals fraction to light minerals fraction was very vari- able in which the percentage of heavy minerals in Sayid Subair field are higher than the percentage in Al-Manziliyah field.The source area of these sediments is the recent sed- iment that deposited in the flood plain and traces of the Tigris river and the outcrops of upper Miocene-Pliocene rocks in the eastern of studied area (Himreen Anticline and Zagros Mountain).

Heavy mineral distribution and geochemical studies of coastal sediments between Besant Nagar and Marakkanam, Tamil Nadu, India

The main objectives of the present study are to understand the heavy mineral distribution, trace elemental distribution and to study the variation, if any, between the grain size and trace elemental distribution within the beach. Totally 20 stations have been collected and weight percentage of heavy minerals are identified. In the present study area most of the sands are fine and medium grained, indicates beach environment and most of the grains are positively skewed. The study area contained a high percentage of orthopyroxene (hypersthene) and garnet, rounded and broken zircons inferred to have been derived from charnockites and granulite gneiss of the study area. Overall from the geochemistry studies, it is observed that the Ni and Cr are more dominant and higher concentration in Panayar (station no. 2), Mahabalipuram (station no. 6), Kalpakkam (Station no. 7) and Perunthuravu (station no. 8). The present study has clearly indicated the multiple roles of tectonically controlled coastal blocks and their geomorphological influence in redistributing the sediments with favourable NE–SW configuration and wave energy conditions must have contributed to the formation of heavy minerals in a particular zone.

Heavy mineral content and radioactivity counts of beach sands west of oreti river mouth to blue cliffs, southland, new zealand

Abstract Beach and dune deposits on the south coast of Southland were sampled and the minerals of specific gravity greater than 2.9 were extracted, magnetically separated and counted for radioactivity; the percentages of heavy minerals are estimated and the predominant minerals noted. Total quantities of beach sands west of Orepuki are estimated. The predominant heavy mineral throughout is a green amphibole. No commercially attractive quantities of ore minerals are indicated.

Unravelling the enigmas of the ‘silver sands’ in the Dutch/German/Belgian border area

AbstractBright white sands consisting almost exclusively of quartz (sometimes called ‘silver sands’) occur throughout the world; those in Europe commonly date from the late Paleogene and early Neogene. They have a clearly sedimentary origin, and they may have originated in various types of environments, but precise data are lacking because sedimentary research into these deposits (that have a high economic value) has been scarce. It is most likely that diagenetic processes are largely responsible for their exceptional appearance, but it is highly unlikely that all silver sands were subject to the same diagenetic conditions.The precise origin of most of the silver sands is still enigmatic. In the case of the silver sands in the Dutch/German/Belgian border area, it appears that long-lasting in situ leaching by humic acids (resulting in an extremely low percentage of heavy minerals), in combination with differential cementation (and later partial dissolution of the cement), must be held responsible for the wide variety of the characteristics of these sands, including locally sharp boundaries with the underlying sands, lack of precipitates at the contact plane with the underlying sands, and the joint occurrence of strongly weathered and fresh specimens of the same heavy-mineral species.

Impact of tsunami on texture and mineralogy of a major placer deposit in southwest coast of India

The great Indonesian earth quake (26 December 2004) triggered a tsunami wave across the Bay of Bengal and Indian Ocean basins and has brought a major havoc in several countries including India. The coastal segment between Thotapalli and Valiazhikal in Kerala state of southwest India, where considerably rich beach placer deposit with ilmenite percentage of more than 70% is concentrated, has been investigated to understand the impact of tsunami on coastal sediments. The grain size analysis flashes out the significant differences between the pre- and post-tsunami littoral environments. While the mineral grains collected during pre-tsunami period show well-sorted nature, the post-tsunami samples represent moderately to poorly sorted nature. Similarly, unimodal and bimodal distributions of the sediments have been recorded for pre- and post-tsunami sediments, respectively. Further, mineral assemblages corresponding to before and after this major wave activity clearly indicate the large-scale redistribution of sediments. The post-tsunami sediments register increasing trends of garnet, sillimanite and rutile. The total heavy mineral percentage of the post-tsunami sediment also shows an improved concentration, perhaps due to the large-scale transport of lighter fraction. Magnetite percentage of post-tsunami samples reflects higher concentration compared to the pre-tsunami samples, indicating the intensity of reworking process. X-ray diffraction patterns of ilmenite grains have confirmed the increased presence of pseduorutile, and pseudobrookite in post-tsunami samples, which could be due to the mixing of more altered grains. SEM examination of grains also confirms the significant alteration patterns on the ubiquitous mineral of placer body, the ilmenite. The reason for these textural, mineralogical and micromorphological changes in heavy minerals particularly in ilmenite, could be due to the churning action on the deeper sediments of onshore region or on the sediments entrapped in the near shelf region of the area, by the ∼ 6 m high tsunami waves.

Stratigraphic Framework and Heavy Minerals of the Continental Shelf of Onslow and Long Bays, North Carolina

One hundred fourteen vibracores from the Atlantic continental shelf offshore of southeastern North Carolina were opened, described, and processed over several contract years (years 6-9) of the Minerals Management Service Association of American State Geologists Continental Margins program. Reports for years 9 and 10 of the program compiled the results of the work and assembled the data for release as an interactive CD-ROM report, respectively. The continental shelf of Onslow and Long Bays consists predominantly of outcropping Cretaceous through late Tertiary geologic units. Nearshore these units are covered and incised by late Tertiary and Quaternary units. From oldest to youngest, formally recognized geologic units mapped as part of this study are the Late Cretaceous Peedee Formation a muddy, fine-to medium-grained quartz sand with trace amounts of glauconite and phosphate; the Paleocene Beaufort Forma tion a muddy, fine-to medium-grained glauconitic quartz sand with locally occurring turritelid-mold biosparrudite; the middle Eocene Castle Hayne Forma tion a sandy bryozoan biomicrudite and biosparrudite; the Oligocene River Bend Formation a sandy molluscan-mold biosparrudite; and the Miocene Pungo River Formation a medium-grained, poorly sorted slightly shelly phosphatic sand. Infor mal units include a very widespread, unnamed fine-to very fine grained, well-sorted, dolomitic muddy quartz sand that is biostratigraphically equivalent to the Oligocene River Bend Formation; several large valley-fill lithosomes composed of biomicrudite, biomicrite, and biosparrudite of Plio Pleistocene age; muddy, shelly sands and silty clays of Pliocene, Pleistocene, or mixed Plio Pleistocene age; and loose, slightly shelly, medium- to coarse-grained sands assigned a Holocene age. Heavy minerals (SG>2.96) comprise an average of 0.54 wt % (on a bulk-sam ple basis) of the sediments in 306 samples derived from the 114 vibracores. Heavy-mineral content ranges from <0.01 to 3.69 wt %. The economic heavy mineral content (EHM ilmenite zircon rutile aluminosilicates leucoxene [altered ilmenite] monazite) of the bulk samples averages 0.26 wt % in a range of <0.01-1.70 wt %. As a percentage of the heavy-mineral concentrate, the average EHM value is 45.78 % in a range of 0.27-68.60 %. The distribution of heavy minerals offshore of southeastern North Carolina is controlled by the lithostratigraphic framework. The unnamed Oligocene sand unit has the highest heavy-mineral content, averaging 0.86 wt % on a bulk-sample basis. The remaining geologic units and their heavy-mineral content (in decreasing order of abundance) are Beaufort (0.64 %), Holocene sand (0.60 %), Plio-Pleistocene muddy sand and silty clay (0.59 %), Peedee (0.42 %), River Bend (0.34 %), Plio-Pleistocene carbonate (0.12 %), and Castle Hayne (0.08 %). The heavy-mineral assemblage is fairly consistent throughout the different units. Significantly smaller percentages of heavy minerals correlate with increased amounts of CaCO3 in the sediments. The sediments analyzed in this study have significantly lower overall heavymineral content, as well as lower EHM content than sediments that are known to host commercially important heavy-mineral deposits in the southeastern United States. The potential for economic deposits of heavy minerals in the area of this study, therefore, appears to be limited.

Mineralogical and geochemical trends across the Loess Plateau, North China

The mineralogy and major element geochemistry of Malan loess, the uppermost loess layer, were studied along two transects from the Baiyu Mountains in the north to the Wei River lowlands, 350 km to the south. The mineralogy of the coarse silt, fine silt and clay fractions is generally uniform across the Loess Plateau. However, in the coarse silt fraction there is a decrease in the weight percentage of heavy minerals and in the hornblende: epidote ratio southwards. Also, in the clay fraction, mica contents increase slightly southwards and smectite increases northwards along one transect. The major element geochemistry of Malan loess shows several clear trends. Silicon, sodium and magnesium generally decrease from north to south while aluminium, iron, potassium, titanium and manganese generally increase. The observed mineralogical and chemical patterns appear to be mainly related to the changing particle size from sandy loess in the north to clayey loess in the south. Slightly higher potassium and phosphorus contents in the clayey loess suggest that this loess has a greater natural fertility. Overall, the results confirm particle size evidence that Malan loess was derived from a desert source area to the north and northwest of the Loess Plateau.

Radiostratigraphy and Heavy Mineral Content of the Weches Formation (Eocene), Nacogdoches County, Texas

ABSTRACT The Weches Formation of eastern Texas is a mudstone containing green sand-size clay aggregates. A vertical sequence of 23 samples were analyzed along an excavated cliff to determine radionuclide content. Samples average 5 ppm uranium and range from 2 ppm to about 7 ppm. Thorium averages 20 ppm and ranges from 13 ppm to almost 36 ppm. The gamma ray spectrometer employed exhibits an uncertainty of about ±10 percent (one standard deviation) at the levels measured. As there are few heavy mineral studies of mudstones, one sample of the Weches mudstone was selected for heavy mineral separation and point counting of grain mounts. A total of 2606 grains were counted giving mineral percentages of zircon (28.8), garnet (17.9), tourmaline (10.5), titanite (8.7), apatite (7.6), staurolite (6.4), green hornblende (5.2), epidote (5.1), sillimanite (2.8), monazite (2.2), kyanite (1.9), basaltic hornblende (1.5), and biotite (1.3). In addition actinolite, spinel, rutile, and collophane were observed but not counted. Previous studies found a similar heavy mineral suite in the underlying Queen City Formation, but in different proportions. Differences in heavy mineral percentages probably reflected different water flow regimes at the time of deposition. Heavy minerals in the Weches and Queen City formations are from the same general source area. Measured radionuclide ratios are similar to granitic ratios and suggest that detrital heavy minerals,particularly zircon and monazite, are the main site of uranium and thorium and their decay products in the Weches Formation.

Spatial and temporal distribution of beach heavy minerals: Mar Chiquita, Argentina

Five beach zones, from the backshore out to the breaker zone, were sampled in order to test the spatial distribution and temporal variability of beach heavy minerals retained at the 88–125 μm interval. While heavy minerals dominate to the backshore, light specimens are more abundant in the submerged zones. Opaques dominate among the heavy minerals and are negatively correlated with the translucids. To discriminate beach zones, opaques, the abundance of rock fragments/alterites, amphiboles (non-hornblendiferous) and heavy-mineral percentages are the most sensitive. Seasonal changes are shown by the lighter of the heavy grains (amphiboles, rock fragments, hornblende), and by the light/heavy relationship. Canonically correlated, heavy minerals were recognized as better estimates of zone discrimination than grain-size parameters. The importance of heavy-mineral abundance, to identify drift dispersals and environmental changes, to characterize beach zones and to search for placers based on their spatial and temporal behavior, is stressed.

Sediment Response to the Present Hydraulic Regime on the Central New Jersey Shelf

ABSTRACT Petrographic data, from vibracores and grab samples collected on the Central New Jersey Shelf, suggest a substrate still actively responding to the hydraulic regime. Radiocarbon dates of shell material from the ridge and swale topography indicates aggradation of the ridge's crest during the last 500 years and exposure of earlier Holocene material in the deeper troughs of the area. The samples from both the cores and the surficial samples were investigated for heavy mineral percentages and grain size analysis in addition to radiocarbon dating. The concentration of heavy minerals into disseminated bands, as observed in the vibracores, is compatible with sediment transport by sand ripples on the ridge's flanks. The grain size variation was subjectively analyzed by applying a Q-mode facto analysis which produced three distinct groupings of the grain size distribution. Each grouping is found to characterize a particular part of the ridge topography. Fine sand and moderate sorting occurs on the flanks, medium to fine sand and moderate sorting occurs on the crests whereas two populations are found in the troughs; coarse, poorly sorted sands and very fine, well sorted sands. This textural variation supports a hypothesis of up-flank rheologic and suspensive transport of medium and fine sand during intense storms and subsequent down-flank winnowing of fine sand during less intense meterological events. The radiocarbon dates indicate that size fractionation and heavy mineral concentrations are subsequent to isolation from a beach environment.

Composition and Weathering of Loess Mantled Wisconsin‐ and Illinoian‐age Terraces in Central Ohio

AbstractElemental and mineralogical evidence indicate that both loess and outwash deposits on relatively high Illinoian‐age terraces are more intensively weathered than comparable units of lower level Wisconsin‐age terraces. The Illinoian site, particularly in the outwash paleosol, has lower weight percentages of heavy minerals; lower hornblende contents; lower elemental Fe, K, and Ca contents; and more pronounced pedogenic transformation of micas to partially or fully expandable 14Å components. Subtle weathering trends of elemental Ca, even in the Illinoian paleosol, are attributed to its occurrence in more resistant plagioclase‐feldspars. The 50‐20µ light mineral fraction (sp. gr. &lt; 2.86) in both loess and outwash units contains appreciably higher quantities of Ti, Zr, and Fe than was originally anticipated. From 50–70% of the Ti, 20–45% of the Zr, and 85–90% of the total Fe occurs in light minerals. Essentially all of the K and 70–90% of the Ca also occurs in this isolate. Loci of Fe, Ti, and Zr in light minerals have not been established but are postulated to be either micro occlusions of primary minerals in host framework silicates or proxy for other metallic cations in these structures.

Sediments of Inner Continental Shelf off Northern Washington Coast: ABSTRACT

Much of the inner shelf off Washington is filled with well-sorted, positively to extremely positively skewed, and leptokurtic to extremely leptokurtic sediments having mean sizes between 2-3^phgr and 3-4^phgr. Gravel-rich sediments are common opposite and north of Cape Flattery, and at about depths 14-18 fm and 28 fm opposite Grays Harbor and at 14-28 fm opposite Quinault River. Only rarely are the sediments finer than sand size. These gravel and fine sediments are relatively poorly sorted compared with the other sediments. The pebbles constituting the gravel-rich sediments are smooth and rounded. Thin-section study of the pebbles from opposite Grays Harbor reveals the following rock types: (1) chert, (2) volcanics (many of these being altered and albitized basalt and some of them andesite--a few of these are hypersthene andesites), (3) sandstone, and (4) some granite and quartz diorite. Similar lithologic types are revealed in the gravel-rich sediments north of Cape Flattery. The heavy-mineral study shows that in much of the area the sediments have low percentages of heavy minerals, although opposite Grays Harbor at depths of 10-12 fm and Hoh River at 10-28 fm, heavy minerals are more abundant. The sediments off Cape Flattery, especially in the nearshore areas, have smaller percentages of orthopyroxene nd hornblende than do those farther south. Also, the proportions of hornblende, ilmenite, and magnetite generally are less in the present study area than in the sediments opposite Columbia River. These results suggest that many of the gravel sediments (of the offshore areas), representing the glacial drifts, and the heavy-mineral-rich sediments were deposited at sea levels lower than at present. The drift toward the north of the Columbia-derived sediment appears not to have diluted considerably the sediments supplied from other sources to the areas farther north of Grays Harbor. End_of_Article - Last_Page 461------------