Sediment Geochemistry

128 samples from Ocean Drilling Program (ODP) Site 1143 in the southern South China Sea were analyzed for grain size, clay minerals, biogenic opal content and quartz in order to reconstruct changes in East Asian monsoon climate since 8.5 Ma. An abrupt change of terrigenous mass accumulation rate (MAR), clay mineral assemblage, median grain size and biogenic opal MAR about 5.2 Ma suggests that between 8.5-5.2 Ma the source of terrigenous sediment was mainly in the region of surface uplift and basaltic volcanism in southern Vietnam. A simple model of East Asian summer monsoon evolution was based on the clay/feldspar ratio, kaolinite/chlorite ratio and biogenic opal MAR. The summer monsoon has two periods of maximum strength at 8.5-7.6 Ma and 7.1-6.2 Ma. Subsequently, there was a relatively stable period at 6.2-3.5 Ma, continued intensification about 3.5-2.5 Ma, and gradually weakening after 2.5 Ma. Since 1 Ma the monsoon has intensified, with remarkable high-frequency and amplitude variability. Simultaneous increase in sedimentation rates at ODP Sites 1143, 1146 and 1148, as well as in MAR of terrigenous materials, quartz, feldspar and clay minerals at ODP Site 1143 at 3.5-2.5 Ma, may be the erosional response to both global climatic deterioration and the strengthening of the East Asian summer monsoon after about 3-4 Ma.

We here reconstruct the past change of the East Asian monsoon since 20 Ma using samples from Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea based on a multi-proxy approach including a monomineralic quartz isolation procedure, identification of clay minerals by X-ray Diffraction (XRD) and grain-size analysis of isolated terrigenous materials. Terrigenous supply to ODP Site 1146 was dominated by changes in the strength of multiple sources and transport processes. Grain-size data modeled by an end-member modeling algorithm indicate that eolian dust from the arid Asian inland and fluvial input have contributed on average 20% and 80% of total terrigenous material to ODP Site 1146, respectively. Specifically, about 40-53% of the total (quartz + feldspar) and only 6-11% of the total clay is related to eolian supply at the study site. Detailed analysis of the sedimentary environment, and clay minerals combined with previous studies shows that smectite originates mainly from Luzon, kaolinite from the Pearl River and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The proportion and mass accumulation rate (MAR) of the coarsest end-member EM1 (interpreted as eolian dust), ratios of (illite + chlorite)/smectite, (quartz + feldspar)% and mean grain-size of terrigenous materials at ODP Site 1146 were adopted as proxies for East Asian monsoon evolution. The consistent variation of these independent proxies since 20 Ma shows three profound shifts in the intensity of East Asian winter monsoon relative to summer monsoon, as well as aridity of the Asian continent, occurred at ∼15 Ma, ∼8 Ma and the youngest at about 3 Ma. In comparison, the summer monsoon intensified contemporaneously with the winter monsoon at 3 Ma. The phased uplift of the Himalaya-Tibetan plateau may have played a significant role in strengthening the Asian monsoon at ∼15 Ma, 8 Ma and 3 Ma.

Two discriminant-function-based © multidimensional major-element diagrams for the tectonic discrimination of siliciclastic sediments were recently published from a coherent statistical methodology of log e -ratio transformation and linear discriminant analysis. These diagrams were constructed based on worldwide examples of Neogene-Quaternary siliciclastic 10 sediments from known tectonic settings. In this work, these two tectonic discrimination diagrams were first successfully tested from Holocene (<0.0117-0 Ma) beach and © deep-sea sediments from the Gulf of Mexico. These diagrams were used to decipher tectonic setting of 11 case studies of the Precambrian clastic sedimentary rocks (~512-2800 Ma) from Argentina, U © S © A © , . The test and application results obtained from these discrimination diagrams were generally consistent with the geology of the Precambrian source areas. Therefore, the two 15 © multidimensional diagrams can be considered as a useful tool for successfully discriminating the tectonic setting of older sedimentary basins, which may consist of one or more tectonic assemblages. Comparison of results of this study with the previously published tectonic discrimination diagrams is illustrated and the probable reasons for some inconsistent inferences were also discussed.

We here reconstruct the past change of the East Asian monsoon since 20 Ma using samples from Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea based on a multi-proxy approach including a monomineralic quartz isolation procedure, identification of clay minerals by X-ray Diffraction (XRD) and grain-size analysis of isolated terrigenous materials. Terrigenous supply to ODP Site 1146 was dominated by changes in the strength of multiple sources and transport processes. Grain-size data modeled by an end-member modeling algorithm indicate that eolian dust from the arid Asian inland and fluvial input have contributed on average 20% and 80% of total terrigenous material to ODP Site 1146, respectively. Specifically, about 40-53% of the total (quartz + feldspar) and only 6-11% of the total clay is related to eolian supply at the study site. Detailed analysis of the sedimentary environment, and clay minerals combined with previous studies shows that smectite originates mainly from Luzon, kaolinite from the Pearl River and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The proportion and mass accumulation rate (MAR) of the coarsest end-member EM1 (interpreted as eolian dust), ratios of (illite + chlorite)/smectite, (quartz + feldspar)% and mean grain-size of terrigenous materials at ODP Site 1146 were adopted as proxies for East Asian monsoon evolution. The consistent variation of these independent proxies since 20 Ma shows three profound shifts in the intensity of East Asian winter monsoon relative to summer monsoon, as well as aridity of the Asian continent, occurred at ∼15 Ma, ∼8 Ma and the youngest at about 3 Ma. In comparison, the summer monsoon intensified contemporaneously with the winter monsoon at 3 Ma. The phased uplift of the Himalaya-Tibetan plateau may have played a significant role in strengthening the Asian monsoon at ∼15 Ma, 8 Ma and 3 Ma.

A sedimentological, petrographic, and geochemical study of beach, dune, and river sands was carried out along the northwestern Gulf of Mexico. The main goal of this work is to show how beach and dune sands are controlled texturally, compositionally, and chemically by the nearby rivers for each beach location using a particle size analyser, a polarized microscope, a X-ray fluorescence and ICP mass spectrometer to obtain the following: grain-size values from one river (Carrizal River) are similar in range to their counterpart beach sands but not similar to the dune sands (Barra del Tordo). Rivers (Panuco and Carrizal) are compositionally controlling the quartz and feldspar contents of their counterpart beach and dune sands (i.e., Playa Miramar and Barra del Tordo). Rivers (Soto La Marina River) are directly influencing the composition of the beach sands (La Pesca) based upon the total quartz content, beach and dune sands. The concentration of magnetite grain fractions (Barra del Tordo beach and dune sands) is not under the influence of the nearby river (Carrizal River). In this case the compositional influence of beach and dune sands is related to sediment discharges by other fluvial systems, redistribution of the beach and dune sands along the coast and deflation/winnowing of light minerals. The Eu positive anomaly in the beach and dune sands from the three sites (i.e. Playa Miramar, Barra del Tordo, La Pesca) is linked to an increase in the P(plagioclase)/K(potash feldspar) ratio. The (La/Lu) cn highest ratio for river sands (Carrizal River) suggests quartz enrichment compared to their beach and dune sands counterparts. The (Gd/Yb) cn ratio for one river (i.e., Carrizal River) indicates that it is low in heavy rare earth elements. HREE compared to their beach and dune sands counterparts indicates less concentration of heavy minerals as potential carriers of HREE seawards. multifactorial roles that control the composition of coastal sands. The main goal of this paper is to show evidence of whether the river inputs near the beach and dune sites studied influence the sands composition or the beach and dune sands may be controlled by other coastal processes such as redistribution of sediments (recycling) and/or deflation/winnowing processes. In this paper, we show how the petrologic ternary diagrams and geochemical data sets, based upon major, trace and rare earth elements, can be useful to provide the compositional differences between beach and dune, and nearby river sands. Our hypothesis is that nearby rivers to the beaches studied may not be the only contributors to the sedimentological

We here reconstruct the past change of the East Asian monsoon since 20 Ma using samples from Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea based on a multi-proxy approach including a monomineralic quartz isolation procedure, identification of clay minerals by X-ray Diffraction (XRD) and grain-size analysis of isolated terrigenous materials. Terrigenous supply to ODP Site 1146 was dominated by changes in the strength of multiple sources and transport processes. Grain-size data modeled by an end-member ...

Although ocean acidification is expected to reduce carbonate saturation and yield negative impacts on open-ocean calcifying organisms in the near future, acidification in coastal ecosystems may already be affecting these organisms. Few studies have addressed the effects of sedimentary saturation state on benthic invertebrates. Here, we investigate whether sedimentary aragonite saturation (Ωaragonite) and proton concentration ([H+]) affect burrowing and dispersal rates of juvenile soft-shell clams (Mya arenaria) in a laboratory flume experiment. Two size classes of juvenile clams (0.5–1.5 mm and 1.51–2.5 mm) were subjected to a range of sediment Ωaragonite and [H+] conditions within the range of typical estuarine sediments (Ωaragonite 0.21–1.87; pH 6.8–7.8; [H+] 1.58 × 10− 8–1.51 × 10- 7) by the addition of varying amounts of CO2, while overlying water pH was kept constant ~ 7.8 (Ωaragonite ~ 1.97). There was a significant positive relationship between the percent of juvenile clams burrowed in still water and Ωaragonite and a significant negative relationship between burrowing and [H+]. Clams were subsequently exposed to one of two different flow conditions (flume; 11 cm s− 1 and 23 cm s− 1) and there was a significant negative relationship between Ωaragonite and dispersal, regardless of clam size class and flow speed. No apparent relationship was evident between dispersal and [H+]. The results of this study suggest that sediment acidification may play an important role in soft-shell clam recruitment and dispersal. When assessing the impacts of open-ocean and coastal acidification on infaunal organisms, future studies should address the effects of sediment acidification to adequately understand how calcifying organisms may be affected by shifting pH conditions.

The Okinawa Trough is a natural laboratory for the study of later Quaternary land-ocean interaction and paleoenvironmental changes. In this study we reconstruct the evolution of clay mineral assemblages in Core DGKS9604 retrieved from the central Okinawa Trough. Illite dominates the clay mineral compositions, with average contents above 60%. Clay mineral evolution since 28 ka is closely related to changes in sediment provenance and paleoenvironment. Sea level rise and the strength of the Kuroshio Current control the dispersal and deposition of clays on the East China Sea shelf and in the Okinawa Trough, and thus, determine the clay mineral compositions in the core sediments. During the late last glacial period (28.0-14.0 ka), the paleo-Changjiang River mouth was situated at the shelf edge close to the central Okinawa Trough and thus, together with the outer shelf, supplied large volumes of terrigenous sediments directly into the trough. From 14.0 to 8.4 ka influence from the Changjiang decreased while the mid-outer shelf of the East China Sea became the dominant sediment source to the central Okinawa Trough as sea level rose and the Changjiang river mouth migrated west. Strong sediment reworking and erosion at the shelf edge at 15-13 ka significantly increased the lateral transport of fine-grained shelf sediments to the central Okinawa Trough. Since ca. 8.4 ka clays from Taiwan have dominated the sediment flux to the site, coinciding with the re-entry of the Kuroshio Current into the trough. The increasing influence of the Changjiang-sourced sediments since 1.5 ka was probably related to the weakening of the Kuroshio Current and/or a higher river flux.

Of the two nanocrystal (magnetosome) compositions biosynthesized by magnetotactic bacteria (MTB), the magnetic properties of magnetite magnetosomes have been extensively studied using widely available cultures, while those of greigite magnetosomes remain poorly known. Here we have collected uncultivated magnetite- and greigite-producing MTB to determine their magnetic coercivity distribution and ferromagnetic resonance (FMR) spectra and to assess the MTB-associated iron flux. We find that compared with magnetite-producing MTB cultures, FMR spectra of uncultivated MTB are characterized by a wider empirical parameter range, thus complicating the use of FMR for fossilized magnetosome (magnetofossil) detection. Furthermore, in stark contrast to putative Neogene greigite magnetofossil records, the coercivity distributions for greigite-producing MTB are fundamentally left-skewed with a lower median. Lastly, a comparison between the MTB-associated iron flux in the investigated estuary and the pyritic-Fe flux in the Black Sea suggests MTB play an important, but heretofore overlooked role in euxinic marine system iron cycle.

1] We present a multiproxy geochemical analysis of two cores recovered from the Indus Shelf spanning the Early Holocene to Recent (<14 ka). Indus-23 is located close to the modern Indus River, while Indus-10 is positioned $100 km further west. The Holocene transgression at Indus-10 was over a surface that was strongly weathered during the last glacial sea level lowstand. Lower Holocene sediments at Indus-10 have higher ɛ Nd values compared to those at the river mouth indicating some sediment supply from the Makran coast, either during the deposition or via reworking of older sediments outcropping on the shelf. Sediment transport from Makran occurred during transgressive intervals when sea level crossed the mid shelf. The sediment flux from non-Indus sources to Indus-10 peaked between 11 ka and 8 ka. A hiatus at Indus-23 from 8 ka until 1.3 ka indicates non-deposition or erosion of existing Indus Shelf sequences. Higher ɛ Nd values seen on the shelf compared to the delta imply reworking of older delta sediments in building Holocene clinoforms. Chemical Index of Alteration (CIA), Mg/Al and Sr isotopes are all affected by erosion of detrital carbonate, which reduced through the Holocene. K/Al data suggest that silicate weathering peaked ca. 4-6 ka and was higher at Indus-10 compared to Indus-23. Fine-grained sediments that make up the shelf have geochemical signatures that are different from the coarser grained bulk sediments measured in the delta plain. The Indus Shelf data highlight the complexity of reconstructing records of continental erosion and provenance in marine settings.

The Okinawa Trough is a natural laboratory for the study of later Quaternary land-ocean interaction and paleoenvironmental changes. In this study we reconstruct the evolution of clay mineral assemblages in Core DGKS9604 retrieved from the central Okinawa Trough. Illite dominates the clay mineral compositions, with average contents above 60%. Clay mineral evolution since 28 ka is closely related to changes in sediment provenance and paleoenvironment. Sea level rise and the strength of the Kuroshio Current control the dispersal and deposition of clays on the East China Sea shelf and in the Okinawa Trough, and thus, determine the clay mineral compositions in the core sediments. During the late last glacial period (28.0-14.0 ka), the paleo-Changjiang River mouth was situated at the shelf edge close to the central Okinawa Trough and thus, together with the outer shelf, supplied large volumes of terrigenous sediments directly into the trough. From 14.0 to 8.4 ka influence from the Changjiang decreased while the mid-outer shelf of the East China Sea became the dominant sediment source to the central Okinawa Trough as sea level rose and the Changjiang river mouth migrated west. Strong sediment reworking and erosion at the shelf edge at 15-13 ka significantly increased the lateral transport of fine-grained shelf sediments to the central Okinawa Trough.