Coarse Fraction Analysis Research Articles

PROCESSOS SEDIMENTARES SAZONAIS E ANÁLISE DA FRAÇÃO ARENOSA NO SISTEMA AMBIENTAL DO SUESTE, FERNANDO DE NORONHA, ESTADO DE PERNAMBUCO

O arquipélago de Fernando de Noronha é o topo de uma montanha vulcânica extinta, possui 21 ilhas e está localizado a 540 km de Recife-PE, no Atlântico Sul Equatorial (4°S/32°W). Devido à construção de uma barragem e uma estrada, a principal entrada de água doce para o sistema ambiental da baía do Sueste foi reduzida nos últimos anos, prejudicando o comportamento hidrológico e morfodinâmica da praia. O objetivo da pesquisa é a avaliação da análise da fração arenosa como uma ferramenta para o refinamento de dados sedimentológicos dos sedimentos superficiais do sistema ambiental do Sueste (praia, manguezal, laguna, dunas e baía), localizado no sudeste da ilha principal. Foram coletadas 146 amostras de sedimentos superficiais em sete trabalhos de campo sazonais entre os anos de 2010/2011. Os métodos de pesquisa incluem a análise da fração arenosa, granulométrica, do carbonato de cálcio e da matéria orgânica elementar e isotópica. As amostras coletadas foram, predominantemente, de areia fina, bem a moderadamente selecionadas e bioclásticas, apresentando alto teor carbonático (>90% em 83,5% das amostras). A análise da fração arenosa indicou uma homogeneidade espacial e temporal dos grãos, apresentando predominantemente índices BM de 0,80-0,85 indicando forte influência marinha nos processos sedimentares atuais, sendo composto principalmente de fragmentos de conchas de moluscos e corais. Os valores gerais dos dados obtidos foram também indicados na origem oceânica da matéria orgânica sedimentar (C/N<12 e δ13C>19‰PDB) e nas características erosivas dos perfis praiais.

Atmospheric particulate analysis by synchrotron radiation total reflection (SR‐TXRF)

AbstractX‐ray fluorescence with synchrotron radiation total reflection was used to analyze the atmospheric particulate collected in Campinas, SP, Brazil, in fine and coarse fractions, using a stacked filter unit. After treatment with acid solution and pipetting on to Perspex disks, the samples were measured at the x‐ray fluorescence beamline at the National Synchrotron Light Laboratory (LNLS), Campinas, using a polychromatic beam for sample excitation. The detection limits obtained ranged from 0.3 to 8.9 ng m−3 for the majority of the elements. The data obtained were treated using analysis receptor models of the principal components, then absolute principal component analysis was applied to obtain the contribution of each source to the total of both particulate fractions. Four sources were identified for the fine fraction for autumn/winter and summer periods: (1) soil dust (22 and 29%); (2) industry (26 and 23%); (3) sulfate (23 and 20%); (4) motor vehicle (22 and 20%); and 7% and 8% non‐explained, in the autumn/winter and summer periods, respectively. In coarse fraction analysis, two sources were identified for the autumn/winter and summer periods and with similar rates for source contribution. The obtained sources were: (1) soil dust (77 and 78%); (2) industry (18 and 16%); and non‐explained rates of 5 and 6%, in the autumn/winter and summer periods, respectively. Copyright © 2002 John Wiley & Sons, Ltd.

Characterization of Energy Gradient in Enclosed Bays of Ubatuba Region, South-eastern Brazil

This paper deals with the characterization of the energy gradient of the sedimentary dynamics of enclosed bays of south-eastern Brazil through the utilization of coarse fraction analysisIn the Ubatuba coastal region, south-eastern Brazil, the use of traditional sedimentological techniques, such as grain size and compositional analysis of surface sediments revealed little information on the spatial variability of the bottom dynamics.Many advances in the comprehension of the sedimentary processes were obtained with the utilization of coarse fraction analysis, which allowed the identification of the sectors of marine and continental influence. The utilization of a multivariate technique, the correspondence analysis, on coarse fraction analysis data reveals, through a plot of the two first factors produced by the multivariate technique, the existence of an energy gradient acting over the area, inside and between the bays, leading to the deposition of different constituents.

Late Eocene-Oligocene paleoceanography in the southern Indian Ocean (ODP Site 744)

The late Eocene through Oligocene changes in the paleoceanography of the southernmost Indian Ocean have been reconstructed by means of a coarse fraction analysis of closely spaced samples (20 cm = about 20 kyr) from ODP Site 744, Kerguelen Plateau. Surface water productivity, reconstructed from accumulation rates of opal skeletons and benthic foraminifers is low in the early late Eocene, increases at about 36 Ma and shows a sharp increase to maximum values in the earliest Oligocene. In the early late Oligocene it decreases gradually to a minimum and increases again to a maximum in the latest Oligocene. Beside this general trend productivity varies in short-term cycles of a duration of about 400 kyr (340 kyr in the latest Oligocene) with maxima in productivity in warmer Oligocene periods. These productivity variations are reflected by strong variations in carbonate dissolution. Changes in bottom water mass chemistry have been deduced from the degree of carbonate dissolution and it's relation to productivity proxies. Following Kennett and Stott (1990), it is suggested that a proto-antarctic bottom water (proto-AABW) and an overlying warm, saline deep water (WSDW) from low latitudes shifted vertically and latitudinally with time and exerted their influence on the sediments of Site 744. Proto-AABW is detected by means of strong carbonate dissolution when productivity is low. WSDW is detected by means of an excellent carbonate preservation despite high productivity. Terrigenous material occurs as very coarse ice-rafted detritus (IRD) in the late Eocene (167–168.5 mbsf) and after a main shift in oxygen isotopes in the early Oligocene. Very low amounts of 40–125 μm sized mica and very few quartz grains occur only in high productivity periods and at the transition from low to high productivity periods. These occurrences are attributed to wind/current supply during warmer Oligocene intervals.

Middle Eocene to early Oligocene paleoceanography of the Antarctic Ocean (Maud Rise, ODP Leg 113, Site 689): change from a low to a high productivity ocean

The sediment record from the middle Eocene (about 45 Ma) to the early Oligocene (about 33 Ma) on Maud Rise Site 689, Weddell Sea (paleodepth 1400–1650 m), has been studied by means of a coarse fraction analysis in order to reconstruct variations in surface water productivity and bottom water masses. Productivity has been estimated using carbonate dissolution and accumulation rates of radiolaria, diatoms, benthonic and planktonic foraminifers, sponge debris, ostracods and echinoids. Accumulation rates of Bolboforma spp. vary parallel to these proxies. Productivity increased with time. Three episodes were found in which productivity increased sharply, and productivity varied cyclically with a period of 430 ky. The middle Eocene, ca. 45.44-37.26 Ma, was a period of generally low productivity. No opal was deposited and carbonate preservation was excellent. During periods of a slight increase in productivity accumulation rates of benthonic and planktonic foraminifers, ostracods and echinoids increased in spite of an increase in carbonate dissolution. In the period ca. 41.62–43.07 Ma productivity rose in three distinct pulses. Clinoptilolite, formed from biogenous opal, is a common mineral in these sediments. These three productivity maxima coincide with a mica-rich unit. Mica probably originated from erosion on Antarctica, and was transported by an intermediate water depth current. In the late Eocene, ca. 36.9–34.95 Ma, productivity increased considerably and opal skeletons were deposited. Carbonate dissolution increased but planktonic foraminifer accumulation rates were not markedly decreased in periods of higher productivity, because productivity increase exceeded or equalled rises in dissolution rates. Increasing opal accumulation rates coincided with increases in the rates for benthonic foraminifers, sponge debris, ostracods and echinoids. In the late Eocene-early Oligocene period, 34.95-33.05 Ma, a further increase in productivity led to a strong dissolution of planktonic foraminifers in high productivity periods. The productivity increase is probably due to the increasing pole-equator temperature gradient which led to stronger atmospheric and oceanic turnover and mixing in the oceans. In the uppermost late Eocene two unusual layers suggest changes in bottom water masses affecting the seafloor at Site 689. A sediment interval with especially well-preserved carbonate microfossils underlies an interval that has poor carbonate preservation despite evidence of low productivity. These intervals suggest a change in bottom water conditions from Warm Saline Deep Water (WSDW), which favors carbonate preservation, to Antarctic Bottom water (AABW), which promotes carbonate dissolution. Cooling of surface waters over a period of 300 ky led to a thickening of the deep AABW layer, and an upward shift of the overlying WSDW, until the AABW finally reached the top of the Maud Rise in the area of Site 689. This period of AABW influence on top of the Maud Rise lasted 200 ky.

Paleoceanographic and paleoclimatic evolution in the Weddell Sea (Antarctica) during the middle Eocene-late Oligocene, from a coarse sediment fraction and clay mineral data (ODP Site 689)

Paleoceanographic and paleoclimatic variations from the middle Eocene to the late Oligocene in the Antarctic area, Atlantic sector, have been deduced from a coarse fraction and clay mineral analysis of ODP Site 689 (Leg 113) sediments. In the middle Eocene, smectite-rich sediments were a consequence of warm climate with alternating wet and dry seasons on the Antarctic margins. Productivity in the Maud Rise area of the Southern Ocean was low: no opal was deposited, preservation of carbonate is very good. Carbonate preservation shows cyclic changes. Clinoptilolite is a common mineral. At the middle/late Eocene boundary (40.8 Ma), productivity suddenly increased enough to allow preservation of opal skeletons. Clinoptilolite disappeared where opal appeared. Illite appearance points to cooling of Antarctic climates. The presence of detrital kaolinite indicates a change in oceanic circulation. In the late Eocene, cyclic changes in productivity (cycle length 0.42 Ma) were associated with clay mineral compositional variations: sediments from colder, highly productive periods generally contain more illite and less smectite than warmer ones. The early Oligocene was a period of very high productivity. Highest opal accumulation rates correspond to strongest carbonate dissolution. Cyclic changes in productivity—with a mean cycle duration of 0.4–0.5 Myr—were associated with cyclic changes in clay mineral composition. Highest productivity intervals are generally those with highest smectite content, because of strong erosion of sediments of the Antarctic margins. Sediments from less productive warmer periods most of the time contain more illite. In the late Oligocene, the intensity of physical weathering on Antarctica was stronger, as documented by increasing fluxes of illite, muscovite, amphiboles and talc. Ice expanded on the East-Antarctic continent. Lower productivity than in the early Oligocene is indicated by lower accumulation rates of opal and weaker carbonate dissolution. Cyclic variations in productivity correlate to cyclic variations in illite and smectite contents as in the early Oligocene.

Eocene/Oligocene paleoceanography in the Antarctic Ocean, Atlantic sector (Maud Rise, ODP leg 113, Site 689B and 690B)

Middle Eocene to Late Oligocene sediments from near the crest (Site 689B, water depth 2080 m) and flank (water depth 2914 m) of the Maud Rise (62°S) have been investigated by coarse fraction analysis and have revealed the following: 1. (1) The middle Eocene (50-40 Ma) was a period of pure carbonate sedimentation, with good preservation of carbonate microfossils. No opal > 40 μm is present. 2. (2) In the late Eocene (40-36.5 Ma) opal fossils (mainly radiolaria, and some diatoms > 40 μm) appeared for the first time. Three maxima in opal sedimentation (Eocene/Oligocene boundary, middle early Oligocene and early/late Oligocene boundary) are separated by increases in carbonate sedimentation. The dissolution of carbonate fossils is strong in the opal-rich layers. Opal sedimentation is attributed to cooling and probably more vigorous atmospheric circulation and increased upwelling. 3. (3) Carbonate dissolution increased with water depth in the Oligocene, whereas in the middle Eocene excellent carbonate preservation in the deeper Site 690B and stronger dissolution in the shallower Site 689B is attributed to different bottom-water characteristics. The middle Eocene bottom water probably was formed by strong evaporation at low latitudes, whereas by the earliest Oligocene formation of Antarctic Bottom Water (AABW) had set in. 4. (4) Current influence, not on top but on the flank of the Maud Rise, could be recorded by means of larger grain sizes of benthonic and planktonic microfossils. 5. (5) Ice-rafted debris was not found. Quartz and other minerals are very rare and not larger than 125 μm and may have been supplied by ice as well as by wind or by deep currents. Mica contents were up to 10 times higher in the middle Eocene on the flank compared to on the crest of the Maud Rise, indicating deep current supply.

Gulf of Mexico Outer Shelf/Slope Research Consortium Corehole in Main Pass 303, Louisiana Continental Shelf: Integrated Biostratigraphic, Lithostratigraphic, Isotopic Investigation of Highstand and Transgressive System Tracts

Investigation of a 300 ft continuously cored section through an outer shelf delta, including coarse fraction analysis, X-radiography, and a gamma ray log reveal an upward succession consisting of shale greater than carbonate-rich shale, which is greater than silty shale with fine sandy laminae, which is greater than bedded, cross laminated fine to medium sand, which is greater than shale with terrigenous organic matter, which is greater than massive, medium to coarse sand, which is greater than carbonate-rich shale. Paleo sea-level estimates based on benthic foraminifera indicate an upward inner shelf which is greater than outer neritic, which is greater than marginal marine, which is greater than outer neritic transition. Planktonic biostratigraphy and isotope data are consistent with a last interglacial age for the lower, and a Holocene age for the upper, high sea-level stands. Multiple data sets define a maximum flooding surface (MFS) near the base of the high interglacial sea-level interval, and another MFS within the upper carbonate-rich shale. The interval extending upward from the interglacial MFS encompasses condensed, limestone/nodular section that may represent a significant portion of interglacial time. The fine to medium sand overlying the interglacial contains a record of declining sea levels, declining planktonic foraminiferalmore » abundance, and increasing terrigenous sand content documenting a progradational high-stand system tract bounded above by a ravinement surface or type 1 (para) sequence boundary which is evident in X-radiographs.« less

Sea level changes, carbonate dissolution and history of the Benguela Current in the Oligocene-Miocene off Southwest Africa (DSDP Site 362, Leg 40)

A coarse fraction analysis has been performed on sediments from DSDP Site 362 (Leg 40), in a water depth of 1325 m at the Eastern Walvis Ridge. The influence of carbonate dissolution has been revealed by benthos/plankton foraminifera ratio variations and by fragmentation of planktonic foraminifera. Carbonate dissolution shows strong variations: An Early Oligocene preservation spike, followed by a Middle Oligocene dissolution pulse, an Early Miocene preservation maximum, a dissolution increase in the Middle Miocene (14–15 m.y. ago) and a strong increase in dissolution at 10 m.y. ago, with several small-scale cyclic changes, with a maximum in dissolution between 10 and 9.5 m.y. ago and between 6 and 5.2 m.y. ago. These dissolution variations can be related to sea level fluctuations and ice extent in Antarctica. The history of the Benguela Current can be recreated by means of the opal content of the sediments. The W-turning Benguela Current transports opal from the near-coastal upwelling area to the continental slope. The Benguela Current first reached the Walvis Ridge 10 m.y. ago. During glacial periods in the interval 6–10 m.y. ago, the Benguela Current turned to the west over the Walvis Ridge and produced high opal contents. During interglacial periods in the interval 6–10 m.y. ago, the Benguela Current turned to the west within the Cape Basin. Opal contents in interglacial sequences of Site 362 in the interval 6–10 m.y. ago are lower than the glacial opal contents. Beginning at 5.2 m.y. ago, the reverse relationship has been found: The highest opal contents occur in interglacial sediments, and the smallest contents occur in glacial sequences. This observation reflects the northward shift of the Benguela Current.

Palaeoclimatic and palaeoceanographic development in the Pliocene North Atlantic: Discoaster accumulation and coarse fraction data

Summary Accumulation variations of the calcareous nannofossil genus Discoaster have been determined from a high latitude North Atlantic sediment sequence (DSDP Hole 552A) of late Pliocene age. Spectral analysis for the preglacial Pliocene reveals a dominant quasiperiodicity associated with obliquity-induced temperature variations in surface water. Spectral peaks corresponding to the 100 Kyr eccentricity and the 21 Kyr precession periodicities are also detected. Coarse fraction analysis of core V26-145 (Blake Plateau) illustrates the Pliocene development of an increasingly intense subtropical circulation in the North Atlantic. A trend towards increased current velocity occurs through the early Pliocene and probably reflects the progressive emergence of the Panamanian Isthmus, and concomitant intensification of surface water circulation of the North Atlantic subtropical gyre system. In the Rockall Plateau area (Hole 552A), however, no evidence is seen for a related surface water warming. Discoaster accumulation data indicate that the preglacial Pliocene development of surface water temperature in the high latitude North Atlantic reflects a progressive climatic deterioration.

Late Quaternary sedimentation on the Eastern Walvis Ridge, SE Atlantic (HPC 532 and four piston cores)

Five sediment cores from the Eastern Walvis Ridge have been investigated by means of a quantitative coarse fraction analysis (>40 μm. Numerous biogenous, terrigenous and authigenic particles have been distinguished. The variations in composition suggest the following conclusions: • — Core Walda KS 12 from the northern flank of the Walvis Ridge consists entirely of a slump, which contains mainly glacconite sands and biogenous opal, foraminiferal skeletons and terrigenous matter. • — The sediments in the other four cores comprise the Late Quaternary oxygen isotope stages 1—6. • — There are several levels, at the transition from warm to cold intervals, where benthos/plankton foraminiferal ratios increase from <10 up to 50–90%. Here imperforate benthonic foraminifera decrease strongly. Dissolution of planktonic foraminifera can only partly explain this finding. Lateral supply of benthos or the influence of reduced oxygen content in the bottom water might have played an additional role. • — Calcium-carbonate dissolution as revealed by the fragmentation of planktonic foraminifera shows intermediate values in coldest and warmest periods. Dissolution maxima occur at warm/cold stage boundaries. Dissolution minima have been found at the transition from cold to warm periods. • — Upwellinginfluence is reflected in varying amounts of biogenous opal. In interglacial periods the influence of upwelling is strong in all cores, with an increase in intensity to the east (core V19-259). It is explained by eddies of upwelled water which drifted westward under the influence of the westward-turning Benguela Current. In glacial periods the influence of upwelling at the core sites was very reduced. The Benguela Current problably was close to the continent and turned westward only at 17°S. Thus it did not affect the core sites. • — Climate in the near-coastal area has been arid in the latitude of 20°S throughout the investigated time slice. • — Accumulation rates reflect the position of the cores: HPC 532 and Circe Gb 211 are in the area of the sediment-filled trough which forms the Walvis Ridge Terrace. Here accumulation rates are 2 to 3 times higher in stages 2, 4 and 5 than in V19-259 and Walda KS 09, which are from the steeper flank of the Terrace outside the trough. Mean values of calcium-carbonate dissolution are similar in all cores. Lower CaCO 3 content in V19-259 and lower sand fraction percentages are explained by lateral supply of fine-grained terrigenous matter in the area of core V19-259, which probably received insoluble material from the Kuene shelf area by the N—S-flowing countercurrent.

Basin model for hemipelagic sedimentation in a tectonically active continental margin: Santa Barbara Basin, California Continental Borderland

Summary A variety of Holocene sedimentary processes and depositional environments in Santa Barbara Basin may serve as a model for terrigenously-dominated hemipelagic basins devoid of submarine canyons: (1) suspensate transport; (2) turbidity current transport; (3) mass movement on the lower slope; (4) the imprint of current patterns on both fine-grained suspended load and bedload transport; and (5) preservation of resulting stratigraphy on the deep basin floor by anoxic water conditions which result in annual varves plus turbidites and flood suspensate layers. Silt patterns define a river-derived suspensate pathway driven by surface currents, which coincides with the distribution of 1969 flood layer sediments. A ‘hemipelagic core’ is present on the western portion of the basin floor, where terrigenous and biogenous input are most balanced. Mass-movement covers 13% of the basin-slopes and is typified by mud-flows interpreted from seismic profiles and characteristic sedimentary structures in cores. A generalized vertical sequence of sedimentary structures derived from radiograph analysis may serve as a model for mud-flow deposits. Turbidites and flood suspensate layers have been traced from the middle slope to the basin floor on a canyonless slope and their distribution is controlled by surface current delivery of suspensates. Vertical sequences of turbidite sedimentary structures in grey-layer turbidites provide support for Piper’s (1978) model for fine-grained turbidites. Varve counting in the central basin yields a sedimentation rate of 173 cm/1000 years and frequencies of 59 years for all grey-layers (flood + turbidite), and 120 years for grey-layer turbidites, which probably reflect roughly 50 and 100 year frequency floods. Fine-grained sedimentary processes in hemipelagic settings with high sedimentation rates and low slope gradients may be typified by: (1) mud-flows on the lower slope; (2) unchannelized turbidity currents and flood layer deposition controlled by surface currents and proximity to source; (3) laminated sediments in the deep basin if oxygen levels are sufficiently low, or preservation of only flood suspensate layers and turbidites if bottom waters are not anoxic; (4) sediment pathways definable from texture and coarse fraction analysis.

The use of coarse fraction analysis in paleoenvironmental interpretation: Upper Oxfordian and lower Kimmeridgian (Jurassic) sediments in Dorset, England

Upper Oxfordian and Lower Kimmeridgian shelf sediments contain several environments which can be compared to those in the Gulf of Mexico. The use of coarse fraction analysis, developed by Shepard and Moore (1954), enabled environments to be more precisely discriminated, and the method seems useful even where the sediments are not exactly analogous to those of the Gulf of Mexico. Coarse fraction analysis can be applied to borehole samples where macrofaunal remains and sedimentary structures are rare or difficult to distinguish; and it may also be reasonably successful where microfaunal remains are scarce.

No current reversal at 10,000 B.P. in the Strait of Gibraltar

Two cores taken west of Gibraltar within the region of recent current influence of Mediterranean bottom outflow, have been studied. A coarse-fraction analysis has been made in order to see if current influence occurs in the lutitic sediments and whether there has been a change in current systems. In most parts of the cores, the curves of median diameters of planktonic and benthonic foraminifers are parallel. The sediments are sorted due to the Mediterranean bottom outflow, which reduces sedimentation of small sand-sized particles. In some core sections there is no sorting. Sorted and non-sorted layers are contemporaneous in the two cores. Current reversal in Holocene and Late Pleistocene, from 10,000 to 17,000–21,000 years B.P., is most unlikely. The two non-sorted layers in the lower core sections (17,000–21,000 to 34,000–46,000 years B.P.) may have been produced by current reversals or by a northerly shift of the Mediterranean bottom outflow in the Bay of Cadiz.