Mineralogical compositions of sediment samples from the San Francisco Bay coastal system

The mineralogical compositions of 119 samples collected from throughout the San Francisco Bay coastal system, including bayfloor and seafloor, area beaches, cliff outcrops, and major drainages, were determined using X-ray diffraction (XRD). Comparison of the mineral concentrations and application of statistical cluster analysis of XRD spectra allowed for the determination of provenances and transport pathways. The use of XRD mineral identifications provides semi-quantitative compositions needed for comparisons of beach and offshore sands with potential cliff and river sources, but the innovative cluster analysis of XRD diffraction spectra provides a unique visualization of how groups of samples within the San Francisco Bay coastal system are related so that sand-sized sediment transport pathways can be inferred. The main vector for sediment transport as defined by the XRD analysis is from San Francisco Bay to the outer coast, where the sand then accumulates on the ebb tidal delta and also moves alongshore. This mineralogical link defines a critical pathway because large volumes of sediment have been removed from the Bay over the last century via channel dredging, aggregate mining, and borrow pit mining, with comparable volumes of erosion from the ebb tidal delta over the same period, in addition to high rates of shoreline retreat along the adjacent, open-coast beaches. Therefore, while previously only a temporal relationship was established, the transport pathway defined by mineralogical and geochemical tracers support the link between anthropogenic activities in the Bay and widespread erosion outside the Bay. The XRD results also establish the regional and local importance of sediment derived from cliff erosion, as well as both proximal and distal fluvial sources. This research is an important contribution to a broader provenance study aimed at identifying the driving forces for widespread geomorphic change in a heavily urbanized coastal-estuarine system.

Sedimentological, mineralogical, biogeochemical and micropaleontological parameters on sediment core PS69/849-2, Burton Basin, MacRobertson Shelf, East Antarctica

A multi-proxy study including sedimentological, mineralogical, biogeochemical and micropaleontological methods was conducted on sediment core PS69/849-2 retrieved from Burton Basin, MacRobertson Shelf, East Antarctica. The goal of this study was to depict the deglacial and Holocene environmental history of the MacRobertson Land-Prydz Bay region. A special focus was put on the timing of ice-sheet retreat and the variability of bottom-water formation due to sea ice formation through the Holocene. Results from site PS69/849-2 provide the first paleo-environmental record of Holocene variations in bottom-water production probably associated to the Cape Darnley polynya, which is the second largest polynya in the Antarctic. Methods included end-member modeling of laser-derived high-resolution grain size data to reconstruct the depositional regimes and bottom-water activity. The provenance of current-derived and ice-transported material was reconstructed using clay-mineral and heavy-mineral analysis. Conclusions on biogenic production were drawn by determination of biogenic opal and total organic carbon. It was found that the ice shelf front started to retreat from the site around 12.8 ka BP. This coincides with results from other records in Prydz Bay and suggests warming during the early Holocene optimum next to global sea level rise as the main trigger. Ice-rafted debris was then supplied to the site until 5.5 cal. ka BP, when Holocene global sea level rise stabilized and glacial isostatic rebound on MacRobertson Land commenced. Throughout the Holocene, three episodes of enhanced bottom-water activity probably due to elevated brine rejection in Cape Darnley polynya occured between 11.5 and 9 cal. ka BP, 5.6 and 4.5 cal. ka BP and since 1.5 cal. ka BP. These periods are related to shifts from warmer to cooler conditions at the end of Holocene warm periods, in particular the early Holocene optimum, the mid-Holocene warm period and at the beginning of the neoglacial. In contrast, between 7.7 and 6.7 cal. ka BP, brine rejection shut down, maybe owed to warm conditions and pronounced open-water intervals.

Clay mineralogical, geochemical and isotopic tracing of the evolution of the Woodleigh impact structure, Southern Carnarvon Basin, Western Australia

Chaotically structured diamictite from the inner ring syncline surrounding the central uplift of the Woodleigh impact structure contains shocked metamorphic and impact melt-rock fragments, largely derived from Ordovician and Devonian target sandstones. Coarse illite fractions (< 2 mu m) from the sandstones containing no K-feldspar yield K-Ar ages of around 400 Ma, whereas the K-Ar ages of authigenic clays of > 0.2 mu m fractions from the diamictite without smectite and K-feldspar cluster around 360 Ma, consistent with Rb-Sr data. Crystallisation of newly formed illite in the impact melt rock clasts and recrystallisation of earlier formed illite in the sandstone clasts preserved in the diamictite, are attributed to impact-induced hydrothermal processes in the Late Devonian. The illitic clays from the diamictite and from the sandstones have very similar trace element compositions, with significantly enriched incompatible lithophile elements, which increase in concentrations correlatively with those of the compatible ferromagnesian elements. The unusual trace element associations in the clays may be due to the involvement of hot gravity-driven basinal fluids that interacted with rocks of the Precambrian craton to the east of the study area, or with such material transported and reworked in the studied sedimentary succession.

Clay mineralogical and isotopic (K-Ar, delta O-18, delta D) constraints on the evolution of the North Anatolian Fault Zone, Turkey

This study presents the first attempt to constrain the evolution of the North Anatolian Fault Zone (NAFZ) by age dating and isotope tracing of clay minerals formed during near-surface faulting. Extensive illitic clay mineralisation occurred along the NAFZ related to hydrothermal alteration of the fault gouges and pseudotachylytes. Samples representing the pre-fault protoliths outside the fault zone do not contain authigenic illitic clay minerals indicating that hydrothermal processes were confined to the areas within the fault zone. K-Ar age data indicate that the hydrothermal system and the associated illite authigenesis initiated at similar to 57 Ma. This process is interpreted to reflect the onset of significant strike-slip or transtensional faulting immediately after the continental collision related to the closure of the Neotethys Ocean. Following the initiation of the fault movements in the latest Paleocene-Early Eocene, displacements along the NAFZ have continued, with probably intensified fault activities at similar to 26 Ma and later than similar to 8 Ma. Oxygen isotope compositions of the illitic clays from different locations along the NAFZ are similar, with narrow ranges in delta O-18 values indicating clay precipitation from fluids with similar oxygen isotope compositions and crystallisation temperatures. The delta O-18 and delta D values of the calculated fluid isotopic composition (delta O-18=5.9 parts per thousand to 11.2 parts per thousand, delta D=-59 parts per thousand to -73 parts per thousand) are consistent with metamorphic and magmatic origin of fluids mobilised during active tectonism. The interpretation of the fluid flow history of the NAFZ is in agreement with that reported previously for some well-known large-scale high-angle fault zones, which similarly developed along collisional-type orogenic belts and are commonly associated with significant mesothermal ore mineralisation. (c) 2005 Elsevier B.V. All rights reserved.

San Francisco Coastal System grain size and geochemical data for sand provenance study

Over 150 million cubic meter of sand-sized sediment has disappeared from the central region of the San Francisco Bay Coastal System during the last half century. This enormous loss may reflect numerous anthropogenic influences, such as watershed damming, bay-fill development, aggregate mining, and dredging. The reduction in Bay sediment also appears to be linked to a reduction in sediment supply and recent widespread erosion of adjacent beaches, wetlands, and submarine environments. A unique, multi-faceted provenance study was performed to definitively establish the primary sources, sinks, and transport pathways of beach sized-sand in the region, thereby identifying the activities and processes that directly limit supply to the outer coast. This integrative program is based on comprehensive surficial sediment sampling of the San Francisco Bay Coastal System, including the seabed, Bay floor, area beaches, adjacent rock units, and major drainages. Analyses of sample morphometrics and biological composition (e.g., Foraminifera) were then integrated with a suite of tracers including 87Sr/86Sr and 143Nd/144Nd isotopes, rare earth elements, semi-quantitative X-ray diffraction mineralogy, and heavy minerals, and with process-based numerical modeling, in situ current measurements, and bedform asymmetry to robustly determine the provenance of beach-sized sand in the region.

Mineralogical (bulk rock and clay fraction) and stable isotope composition (d13C, d18O) of Aptian deposits of the Bir Oum Ali succession, central Tunisia

Alternations between siliciclastic, carbonate and evaporitic sedimentary systems, as recorded in the Aptian mixed succession of southern Tunisia, reflect profound palaeoceanographic and palaeoclimatic changes in this area of the southern Tethyan margin. The evolution from Urgonian-type carbonates (Berrani Formation, lower Aptian) at the base of the series, to intervals dominated by gypsum or detrital deposits in the remainder of the Aptian is thought to result from the interplay between climate change and tectonic activity that affected North Africa. Based on the evolution of clay mineral assemblages, the early Aptian is interpreted as having been dominated by slightly humid conditions, since smectitic minerals are observed. Near the early to late Aptian boundary, the onset of a gypsiferous sedimentation is associated with the appearance of palygorskite and sepiolite, which supports the installation of arid conditions in this area of the southern Tethyan margin. The evaporitic sedimentation may have also been promoted by the peculiar tectonic setting of the Bir Oum Ali area during the Aptian, where local subsidence may have been tectonically enhanced linked to the opening of northern and central Atlantic. Stress associated with the west and central African rift systems may have triggered the development of NW-SE, hemi-graben structures. Uplifted areas may have constituted potential new sources for clastic material that has been subsequently deposited during the late Aptian. Chemostratigraphic (d13C) correlation of the Bir Oum Ali succession with other peri-Tethyan regions complements biostratigraphic findings, and indicates that a potential expression of the Oceanic Anoxic Event (OAE) 1a may be preserved in this area of Tunisia. Although the characteristic negative spike at the base of this event is not recognized in the present study, a subsequent, large positive excursion with d13C values is of similar amplitude and absolute values to that reported from other peri-Tethyan regions, thus supporting the identification of isotopic segments C4-C7 of the OAE1a. The absence of the negative spike may be linked to either non preservation or non deposition: the OAE1a occurred in a global transgressive context, and since the Bir Oum Ali region was located in the innermost part of the southern Tethyan margin during most of the Aptian, stratigraphic hiatuses may have been longer than in other regions of the Tethys. This emphasizes the importance of integrating several stratigraphic disciplines (bio-, chemo- and sequence stratigraphy) when performing long-distance correlation.

Mineralogical, geochemical and magnetic signatures of surface sediments from the Canadian Beaufort Shelf and Amundsen Gulf (Canadian Arctic)

Mineralogical, geochemical, magnetic, and siliciclastic grain-size signatures of 34 surface sediment samples from the Mackenzie-Beaufort Sea Slope and Amundsen Gulf were studied in order to better constrain the redox status, detrital particle provenance, and sediment dynamics in the western Canadian Arctic. Redox-sensitive elements (Mn, Fe, V, Cr, Zn) indicate that modern sedimentary deposition within the Mackenzie-Beaufort Sea Slope and Amundsen Gulf took place under oxic bottom-water conditions, with more turbulent mixing conditions and thus a well-oxygenated water column prevailing within the Amundsen Gulf. The analytical data obtained, combined with multivariate statistical (notably, principal component and fuzzy c-means clustering analyses) and spatial analyses, allowed the division of the study area into four provinces with distinct sedimentary compositions: (1) the Mackenzie Trough-Canadian Beaufort Shelf with high phyllosilicate-Fe oxide-magnetite and Al-K-Ti-Fe-Cr-V-Zn-P contents; (2) Southwestern Banks Island, characterized by high dolomite-K-feldspar and Ca-Mg-LOI contents; (3) the Central Amundsen Gulf, a transitional zone typified by intermediate phyllosilicate-magnetite-K-feldspar-dolomite and Al-K-Ti-Fe-Mn-V-Zn-Sr-Ca-Mg-LOI contents; and (4) mud volcanoes on the Canadian Beaufort Shelf distinguished by poorly sorted coarse-silt with high quartz-plagioclase-authigenic carbonate and Si-Zr contents, as well as high magnetic susceptibility. Our results also confirm that the present-day sedimentary dynamics on the Canadian Beaufort Shelf is mainly controlled by sediment supply from the Mackenzie River. Overall, these insights provide a basis for future studies using mineralogical, geochemical, and magnetic signatures of Canadian Arctic sediments in order to reconstruct past variations in sediment inputs and transport pathways related to late Quaternary climate and oceanographic changes.

The Evolution of the Los Negritos Porphyry Copper Deposit, Coquimbo, Chile: Geological, Geochronological, Mineralogical and Geochemical Evidence

The Los Negritos porphyry copper deposit is located ~ 4 km to the northeast of Carmen de Andacollo Mine in the Chilean Cretaceous metallogenic belt. The mineralization is hosted in andesite of the Quebrada Marquesa Formation and a series of at least four early to intramineral porphyry intrusive rock types: plagioclase quartz biotite porphyry (P1b and P1a dated at 109.60± 0.75 Ma and 107.22± 0.40 Ma); plagioclase biotite porphyry (P2: 106.30 ± 0.47 Ma); and quartz plagioclase biotite porphyry (P3: 106.19 ± 0.42 Ma). These units are cut by late‐ to post‐mineral plagioclase‐hornblende porphyritic rocks (P4b: 106.20 ± 0.69 Ma and P4a: 106.50 ± 0.68 Ma). The earliest intrusive units (P1) were affected by an initial stage of K‐feldspar‐biotite alteration, with chalcopyrite, molybdenite (date at 108.5 ± 0.5 Ma) and gold (up to 0.11 ppm), and the surrounding volcanic host rock was overprinted by chlorite‐epidote dominated (propylitic) alteration. Subsequent to the P2 and P3 intrusion, these rocks were affected by albite and then a second stage of potassic alteration. The Ti and Ba contents in hydrothermal biotite are notably lower (typically Ti = 0.100‐0.144 a.p.f.u. and Ba = 0.001‐0.005 a.p.f.u) than in magmatic ones (generally Ti = 0.186‐0.222 a.p.f.u. and Ba = 0.014‐0.023 a.p.f.u.), and constitute an excellent discriminant of the nature of biotite. These early stages of alteration were overprinted by copper‐molybdenum bearing chlorite‐sericite alteration at 106.60 ± 0.5 Ma (Re‐Os age in molybdenite) and by quartz‐sericite‐pyrite veins (phyllic), respectively in the southwest and northeast areas. The average temperature associated with these two alteration facies is estimated around 305 °C. Weak albite‐calcite alteration, spatially associated with sulfosalts and distributed along the margins of P3, overprinted the phyllic facies. The intrusive rock units at the Los Negritos and Carmen de Andacollo deposits are geochemically classified as diorite to granodiorite with a calc‐alkaline magmatic affinity, and formed in a volcanic arc setting from partial melting of a metasomatized mantle wedge. They are interpreted to be cogenetic, and related to a common long‐lived magma chamber that emplaced during a period of tectonic inversion known as the Subhercynian, Peruvian or Pacific event.

Source Provenance of Pre-Historic Granitic Grindstones: The Case Study of the Cogotas I Archaeological Site of Arroyo Mucientes/San Lázaro (Castronuño, Valladolid) and a Proposal on the General Methodological Flow Process

The occurrence of hand grindstones at the Cogotas I archaeological sites is considered to be a common feature. Given that a distant-provenance raw material is frequently involved, determination of its source is a basic factor in the search for a better understanding of resource management and for any Political Economy approach. To progress in these directions an overall study should be planned, using selected grindstones with a view to covering diverse sub-zones of the Cogotas I dispersal area, especially because of its considerable distance from the granite basement source. Such a study may today includes diverse analytical procedures combining successive geographic, petrographic, mineralogical and geochemical criteria. To check the plausibility of the proposed methodology, a preliminary test has been carried out on two granite grindstones, obtained at the archaeological excavation at the Castronuño (Valladolid) Cogotian site, which is fifty km away from an inferred source area that was presumably located at Peñausende (Zamora). The result obtained validates the proposed operational process, yielding a generalizable knowledge to other similar situations.

Hall Effect and transient surface photovoltage (SPV) study of Cu3BiS3 thin films

Se presentan las propiedades eléctricas del compuesto Cu3BiS3 depositado por co-evaporación. Este es un nuevo compuesto que puede tener propiedades adecuadas para ser utilizado como capa absorbente en celdas solares. Las muestras fueron caracterizadas a través de medidas de efecto Hall y fotovoltaje superficial transiente (SPV). A través de medidas de efecto Hall se encontró que la concentración de portadores de carga n es del orden de 1016 cm-3 independiente de la relación de masas de Cu/Bi. También se encontró que la movilidad de este compuesto (μ del orden de 4 cm2V -1s-1) varía de acuerdo con los mecanismos de transporte que la gobiernan en dependencia con la temperatura. A partir de las medidas de SPV se encontró alta densidad de defectos superficiales, defectos que son pasivados al superponer una capa buffer sobre el compuesto Cu3BiS3.

Mineralogical changes caused by grape production in a regosol from subtropical Brazilian climate.

Purpose Inadequate soil use and management practices promote commonly negative impacts on the soil constituents and their properties, with consequences to ecosystems. As the soil mineralogy can be permanently altered due to soil use, this approach can be used as a tool to monitor the anthropogenic pressure. The objective of the present study was to assess the mineralogical alterations of a Brazilian regosol used for grape production for 40 years in comparison with a soil under natural vegetation (forest), aiming to discuss anthropogenic pressure on soils. Material and methods Soil samples were collected at depths of 0?0.20 and 0.20?0.40 m from vineyard production and natural vegetation sites. Physical and chemical parameters were analysed by classic approaches. Mineralogical analyses were carried out on <2 mm, silt and clay fractions. Clay minerals were estimated by the relative percentage of peak surface area of the X-ray patterns. Results and discussion Grape production reduced the organic matter content by 28% and the clay content by 23% resulting in a decreasing cation exchange capacity. A similar clay fraction was observed in both soils, containing kaolinite, illite/mica and vermiculite with hydroxy-Al polymers interlayered. Neither gibbsite nor chlorite was found. However, in the soil under native vegetation, the proportion of illite (79 %) was higher than vermiculite (21 %). Whereas, in the soil used for grape production during 40 years, the formation of vermiculite was promoted. Conclusions Grape production alters the proportions of soil constituents of the regosol, reducing clay fraction and organic matter contents, as well as promoting changes in the soil clay minerals with the formation of vermiculite to the detriment of illite, which suggests weathering acceleration and susceptibility to anthropogenic pressure. Recommendations and perspectives Ecosystems in tropical and subtropical climates can be more easily and permanently altered due to anthropogenic pressure, mainly as a consequence of a great magnitude of phenomena such as temperature amplitude and rainfall that occurs in these regions. This is more worrying when soils are located on steep grades with a high anthropogenic pressure, like regosols in Southern Brazil. Thus, this study suggests that changes in soil mineralogy can be used as an important tool to assess anthropogenic pressure in ecosystems and that soil quality maintenance should be a priority in sensible landscapes to maintain the ecosystem quality.