Terrigenous Fraction Research Articles

The Baroch Nala section (NE Pakistan): A new PETM standard for the eastern Tethys

We present an integrated, high-resolution, biostratigraphical, mineralogical, and geochemical characterization of the well-exposed Upper Paleocene - Lower Eocene stratigraphic succession of the Surghar Range (Baroch Nala section, NE Pakistan). The faunal assemblages from the Baroch Nala section, dominated by hyaline benthic foraminifera and green calcareous algae, along with the significant terrigenous fraction and the presence of terrestrially derived organic matter, testify to the deposition in a low-energy shallow-marine environment. Such environmental conditions, coupled with weak diagenetic effects, allow us to integrate a continuous record of carbon stable isotopes with a detailed account of the biotic response by carbonate-producing assemblages, paleoclimatic information based on clay-minerals, and information on volcanic activity based on mercury concentrations. The environmental evolution from the Late Paleocene up to the Paleocene Eocene Thermal Maximum (PETM) is clearly documented, including the weaker warm excursion that precedes the PETM (i.e. the Pre-Onset Excursion “POE”), and the evolution of large benthic foraminiferal assemblages. The overall record perfectly shows how the turnover in benthic carbonate producers started with the onset of the PETM and was completed by the time the excursion ended, highlighting how (geologically) brief environmental oscillations can have long lasting effects on the biosphere.

From swamp to sea: Quantifying terrestrial dissolved organic carbon in a tropical shelf sea using hydrogen isotope ratios

Dissolved organic carbon (DOC) is a key component of coastal biogeochemical cycles, but its composition and reactivity depend on the relative contribution of autochthonous aquatic versus allochthonous terrigenous DOC (tDOC). In complex coastal waters, tDOC is commonly quantified using the bulk DOC stable carbon isotope ratio (δ13CDOC). However, several limitations can hamper the use of δ13CDOC in marine ecosystems, such as (1) the narrow and often overlapping separation of the autochthonous and allochthonous endmembers, and (2) mineralization of tDOC to dissolved inorganic carbon creates a reservoir effect such that autochthonous DOC can acquire a terrigenous-like δ13CDOC. The stable isotope ratio of non-exchangeable hydrogen in the DOC (δ2Hn) has emerged as a new tool that can potentially overcome these limitations: (1) δ2Hn has a large separation between aquatic and terrigenous endmembers (>50‰) and (2) it is not subject to reservoir effects caused by tDOC mineralization. Here, we evaluate the potential of δ2Hn obtained from solid phase-extracted dissolved organic matter (SPE-DOM), by comparing it to δ13CDOC and chromophoric DOM (CDOM) optical properties. We collected samples at a site in Southeast Asia’s Sunda Shelf that experiences substantial seasonal variation in tDOC input, driven primarily by the monsoon-induced physical advection of peatland-derived tDOC. Over a 1-year monthly time series, the terrigenous fraction of DOC (fterr) determined using δ2Hn of SPE-DOM and δ13CDOC of bulk DOC was well correlated (r2 = 0.42), and there was no significant difference in fterr between the two isotope systems. In fact, δ2Hn displayed slightly stronger correlations with salinity and CDOM optical properties compared to δ13CDOC. Our results indicate that δ2Hn of SPE-DOM is effective for quantifying tDOC across coastal gradients, potentially offering greater sensitivity than δ13CDOC, and is a viable alternative in settings where δ13CDOC is inadequate.

Controls on the terrigenous fractions in Early Kimmeridgian shallow-water carbonate deposits in Southern Iberia

AbstractTwo Kimmeridgian shallow-marine carbonate successions (mid-shelf), sharing a similar paleoclimatic framework (climatic zone), were previously explored using carbonate chemostratigraphy. Before, the goal was to detect signals related to paleoplatform bottom physiography, degree of connection with oceanic waters and overall circulation patterns. In this contribution, complementary bulk mineralogical composition and clay mineral fractions are investigated to contrast and complement previous information, aiming for a more complete overview of continent-ocean dynamics along shallow-carbonate platforms of southern Iberia. The goal is now to explore complex patterns of continental influence along proximal settings and their relative spatial distribution across differentiated settings without relevant difference in paleolatitude. The choice of both stratigraphic sections is based on this distinctness: Rocha Poço (Algarve Basin, Portugal) represents a more restricted and relatively proximal setting, in contrast to Puerto Lorente (South Iberian Paleomargin, S Spain) placed at a relatively more open and probably distal shallow-water context. Accordingly, quartz content was higher at Rocha Poço, especially at the lower siliciclastic interval of this section. Quartz contribution fades out at Puerto Lorente, where it was mainly controlled by short-lived terrigenous pulses. Clay mineral assemblages also differed, being more varied (smectite, illite and traces of kaolinite) and abundant at Rocha Poço, and generally leaner at Puerto Lorente. At the latter site, terrigenous pulses do not contribute to clay mineral abundance, only showing abundant illite at the topmost horizons. New information retrieved from mineralogical data provided evidence on depositional contrasts resulting from local differences in platform configuration, allowing a better understanding of mechanisms controlling the terrigenous fraction in the shallow-water carbonates analyzed.

Pyroclastic component influence on the weathering indices assessment in marine sediments – Lessons from Upper Ordovician of the Baltic Basin

The chemical weathering indices of the sediments can serve as tools for estimating the intensity of weathering in the sediment source rock area and its changes in response to the dynamic interplay of climate, tectonics, and bioevolution. The siliciclastic terrigenous component, comprising sediment particles formed during weathering, carries information regarding weathering. Nevertheless, the presence of volcanic material with silicate composition in the sedimentary record can introduce bias to the weathering estimate by incorporating pyroclastic material that has not undergone weathering but is susceptible to diagenetic alteration. Therefore, a comprehensive understanding of the nature and significance of the volcanic component in sediments is imperative for accurately interpreting weathering derived from sedimentary successions. Our study focuses on investigating the presence of the volcanic component and its influence on weathering indices calculation in the Upper Ordovician sedimentary succession of the Baltic Basin. The results from geochemical massbalance mixing modelling reveal that volcanic material is not confined solely to discrete altered volcanic ash beds (bentonites), and a substantial amount of volcanic material is dispersed or re-deposited into the host rock. Within the interval containing discrete bentonite beds, the volcanic component in the carbonate host rock sections ranges from 50% to 90%, and significantly impacts the terrigenous fraction weathering index calculations. This underscores the necessity of considering the nature and significance of the volcanic component when interpreting geochemical-mineralogical signals.

Chemical Elements Concentration, Variations in Mineral Composition, and Current Rate of Sedimentation in Sapropel Deposits of Small Lakes in the Taiga Zone of Southern Siberia

Abstract —We studied the bottom sediments of lake systems located in the taiga landscape of Siberia. In the south of Western Siberia, there are 11 lakes in the subzone of the south taiga and 9 lakes in the subtaiga subzone. On the territory of the south of Eastern Siberia in the taiga zone there are 10 lakes on the southern coast of Lake Baikal, 5 lakes on its east coast and 6 lakes are located on the territory of the national park “Alkhanai” in Transbaikalia. Studies of the chemical composition of water, soil, and sediment samples were conducted at the Analytical Center for Multi-Elemental and Isotope Research SB RAS, Novosibirsk. The use of a complex of modern analytical methods in the study of the same lake samples made it possible to obtain more reliable information (1861 samples of bottom sediment were studied). Quartz and feldspars of pelitic dimension dominate in the mineral composition of the terrigenous fraction, organic matter and authigenic minerals (opal, pyrite, illite and sometimes calcite) are added to them during the bottom sediments formation. The absolute contents of the studied elements in the bottom sediments of all lakes are lower than their concentrations in the upper continental crust and sedimentary rocks of the Russian Plate, with the exception of Si, Hg, Cd. In the lakes of the subtaiga of the south of Western Siberia, an exception was established for Ca in the bottom sediments of which carbonates predominate. Contents variations of a number of elements in the bottom sediments of taiga lakes in different regions do not significantly differ. The dispersion of their concentrations between lakes with a total catchment area and lakes from different regions are comparable (Ca, Sr, Al, Mn, Fe, Cd, Hg, etc.). The current sedimentation rate in natural occurrence in the lakes of the taiga zone (southern Siberia) vary from 1.1 to 2.9 mm/year. Moreover, it is comparable to the current sedimentation rate in the lakes of the forest-steppe and steppe zones of south of Western Siberia.

The spatio-temporal distribution of elements in the bottom sediments of Lake Onego and small lakes located on the catchment area of Onego Ice Lake

The work presents the results of a comprehensive mineralogical and geochemical study of Late Pleistocene-Holocene bottom sediments of Lake Onego and small lakes located in the territory belonging to Onego Ice Lake. Methods of ICP-MS, atomic absorption spectrometry, X-ray fluorescence analysis, X-ray phase method (XRD), scanning electron microscopy (SEM), and gamma-spectrometric method were used. The geochemical composition of the terrigenous fraction reflects the mineral composition and is permanent for the all bottom sediments cores of Lake Onego and small lakes during time interval about 12,000 years. For the first time, detailed mineralogical studies of sediments have shown that the composition of mineral associations of the terrigenous fraction is similar in the bottom sediment cores of Lake Onego and small lakes. The association of authigenic minerals in bottom sediments is distinguished by the presence of pyrite framboids in small lakes, and crystalline aggregates of Fe-phosphate, ferruginous illites and chlorites in Lake Onego. Sedimentation rates established by the study of correlations the indicator technogenic radioisotope 137Cs and atmospheric 210Pb. In the bottom sediments of small lakes, sedimentation rates vary from lake to lake, as well as in various areas of Lake Onego in the range from 0.05 cm/year to 0.30 cm/year.

Late Burdigalian to early Messinian environmental and climatic evolution of the central paleo Adriatic domain from the shallow water sedimentary record (Bolognano Fm, Eastern Majella, Central Apennines)

During the Miocene, Earth's climate evolved from a prolonged phase of global warmth into a colder mode. In the same time interval, the Mediterranean area was affected by important geodynamic and oceanographic changes evolving from a wide open basin to small enclosed basins. This work aims identifying the controlling factors of the paleoadriatic basin evolution, in one of the enclosed basins of the Mediterranean analyzing the ramp succession in the eastern Majella (Central Apennines).The stratigraphic architecture of the investigated succession shows an initial regressive phase, testified by the deposition of middle to outer ramp deposits followed by a long lasting transgressive phase between late Burdigalian to Tortonian during which hemipelagic to outer ramp sediments were deposited. At the end of the Tortonian a drop in sea level caused an erosional unconformity, reworking and deposition of inner ramp sediments. The succession evolves upward to alternating bioclastic and fine laminated organic rich deposits showing a deepening upward trend interrupted by a major sea level drop linked to the Messinian Salinity Crisis. The lower Messinian portion of the succession shows high TOC values, Al and redox-sensitive trace elements correlated with laminated sediments interpreted as deposited under anoxic conditions. The lithological alternation (bioclastic and laminated deposits) of the early Messinian interval, was likely produced in an astronomically-controlled humid and arid climate fluctuation. The increase of the terrigenous fraction coincides with an increase of Al concentrations that is associated with terrestrial organic matter. The increasing terrigenous input in the sediments is related to approaching Adriatic foredeeps during the early Messinian, promoting the progressive decay of environmental conditions in the basin.

ОСОБЕННОСТИ РАСПРЕДЕЛЕНИЯ УРАНА В КОМПОНЕНТАХ ОЗЕРНЫХ СИСТЕМ, РАСПОЛОЖЕННЫХ В СТЕПНОМ ЛАНДШАФТЕ ЮГА СИБИРИ (КУЛУНДИНСКАЯ И ТАЖЕРАНСКАЯ СТЕПЬ)

Small lakes located compactlyon small territories in the steppe landscape of different regions of Siberia have been studied. High uranium contents in waters of lakes of sodium bicarbonate composition with high alkalinity, as well as increased concentrations of uranium in the bottom sediments of some lakes were revealed. It has been determined that carbonates are deposited in these lakes against the background of the predominant terrigenous fraction (quartz, feldspars) as a result of chemogenic and biogenic processes with the participation of carbon dioxide gas, which is formed due to the bacterial destruction of organic matter. Сalcite-dolomite carbonates are shown to be predominated in the bottom sediments, and reducing conditions are created due to the destruction of organic matter. During the carbonate crystallization the U sorption occurs by newly formed minerals.

New REE-Constrained Terrigenous Depositional Changes in the Central Okinawa Trough and their Responses to Climate since 92 Millennia

Abstract The continental margin is one of the major depocenters for terrigenous sediments in the world ocean. Complex interactions between land and sea control the sedimentary processes along the continental margin. The Okinawa Trough (OT) receives huge amounts of terrigenous materials transported by rivers from the adjacent landmass, while the Kuroshio Current (KC) and the North Pacific Intermediate Water jointly play major roles in oceanic climate and regional deposition patterns of terrigenous sediments. Various studies have investigated the changes in terrigenous sediment provenance in the central OT only since the last glacial. Still, few studies focus on more long-term variations in terrigenous deposition over the last few glacial-interglacial cycles. Here, we report a new high-resolution sediment geochemistry record of a well-dated core MD01-2404 taken from the central OT covering a timespan of 92 kyr. Our results show dynamic glacial-interglacial changes in sediment compositions and terrigenous deposition patterns. Bulk sediments in MD01-2404 comprise relatively high biogenic components during interglacials, while higher terrigenous fractions during the last deglacial and glacial periods. We suggest that the provenance of terrigenous sediments is mainly derived from Taiwanese rivers, Yangtze River, and Yellow River with hydrothermal inputs. During the time interval of 37 to 46 kyr, a new finding of “Negative Ce Anomaly Event” in the central OT firstly reported here is attributed to a combination of suboxic conditions in deep and pore waters and the addition of depleted Ce-bearing sediments. Temporal changes of deposition patterns in the central OT are attributed to complex interactions among dynamic glacial-interglacial changes in eustatic sea level, the East Asian summer monsoon, and the KC.

Chemical isolation and isotopic analysis of terrigenous sediments with emphasis on effective removal of contaminating marine phases including barite

The radiogenic isotope composition (e.g. 87Sr/86Sr and εNd) of the terrigenous fraction is commonly used to determine the provenance and transport history of sediments. In ocean sediments, the terrigenous fraction must be isolated prior to analysis to avoid contamination by marine phases. While the removal of calcium carbonate, organic matter, biogenic opal, authigenic coatings and adsorbed cations is widely advised, steps to remove all these phases are not consistently employed, and there is no standard procedure for the effective removal of marine barite. Marine barite is found throughout the world's oceans, particularly in regions of high export production, is highly enriched in strontium (Sr) and therefore has the potential to bias measurements of terrigenous 87Sr/86Sr towards seawater. Here we present results from sequential leaching experiments on marine sediments from the Atlantic and the Pacific Oceans to quantitatively determine the contaminating effect on 87Sr/86Sr and εNd exerted by the presence of barite and develop a protocol to successfully isolate the terrigenous fraction. Our results show that marine barite can skew measurements of terrigenous 87Sr/86Sr by >0.01 towards the 87Sr/86Sr value of seawater, and we highlight the importance of assessing the location-specific impact of barite contamination on terrigenous 87Sr/86Sr. Our results show that marine barite can severely contaminate terrigenous 87Sr/86Sr, even where marine barite accumulation rates are modest (< ~5 mg/m3/yr and <~20 g C/m2/yr, respectively). Barite contains Nd in very low concentrations so barite contamination of terrigenous εNd is not a major concern but an important aspect of our protocol is that it has minimal effect on terrigenous εNd, allowing 87Sr/86Sr and εNd to be analysed on identically cleaned aliquots. Our systematic graduated approach will help standardise 87Sr/86Sr data, allow for robust comparisons between sites, and will contribute to an improved understanding of the provenance, transport and weathering histories of windblown continental dust and riverine sediments.

Skeletal assemblages and terrigenous input in the Eocene carbonate systems of the Nummulitic Limestone (NW Europe)

Terrigenous input is often considered detrimental for carbonate producing organisms, however, the common occurrence of mixed siliciclastic–bioclastic deposits indicates that the relationship between carbonate factories and terrigenous fluxes is a complex issue. To investigate this subject, we analyzed the skeletal assemblages of the Paleogene Alpine foreland basin in a wide area encompassing NW Italy and SE France. Four different sections, Mortola, Loreto, Braux and Lauzanier, deposited between the Bartonian and the Priabonian, were studied in detail and, based on microfacies analysis, six main biofacies were recognized: i) nummulitid biofacies and ii) acervulinid and coralline algal biofacies related to shallow water; iii) nummulitid and orthophragminid biofacies and iv) coralline-algal branches and large benthic foraminifera biofacies related to intermediate depth; v) orthophragminid biofacies and vi) orthophragminid and coralline algal biofacies related to deeper settings. Thin sections and X-ray diffraction analyses show that these biofacies can be related to two major carbonate factories. The former was dominated by free-living benthic foraminifera and was characterized by a relevant terrigenous fraction, indicating free-living benthic foraminifera as the most terrigenous-tolerant group of carbonate producers of the Nummulitic Limestone system. The latter was dominated by encrusting acervulinids and coralline algae and thrived far-off major terrigenous sources. Conversely, recent and Neogene coralline algae are known to be able to tolerate high sedimentation rates. The distribution of coralline-algal-rich skeletal assemblages in the Nummulitic Limestone thus hints that Eocene coralline algae might have been fundamentally different (probably less adaptable) than their more modern counterparts.

Fate of terrigenous organic carbon in muddy clinothems on continental shelves revealed by stratal geometries: Insight from the Adriatic sedimentary archive

Continental shelves host 90% of modern Organic Carbon (OC) burial and play a key role in the sequestration of terrigenous OC over geological timescales. The efficiency of OC burial in these systems, however, varies greatly depending on the duration of exposure to oxic-suboxic conditions during sediment transport. In this study, we use observations across a wide range of stratigraphic and sedimentological scales coupled with geochemistry data from muddy shelf deposits along the western Adriatic to investigate the relation between sediment transport and burial of terrigenous (land-derived) fraction of OC (OCTerr). Our analysis focused on the Little Ice Age (LIA, 1500–1850 CE) interval, which was characterized by wet, cold, and stormy weather conditions, before the time of widespread regulation and damming of rivers. On the Adriatic shelf, LIA deposits are organized as clinothem: strata that dip gently seawards. The LIA clinothem becomes progressively steeper and deeper from north to south. Basin-scale seismic-stratigraphic analysis and biogeochemical data show evidence of elongated stratal units associated with low OCTerr content in the northern sector of the LIA clinothem, whereas farther south, where clinoforms are steeper, the LIA clinothem exhibits wavy stratal units with limited cross-shelf continuity and high OCTerr concentrations. Based on these data we infer two contrasting scenarios for OCTerr deposition during the LIA: 1) protracted sediment redistribution under the influence of coastal currents with efficient OCTerr degradation prior to final burial in the northern sector; and (2) rapid deposition of OCTerr-rich event beds as a result of flood-driven hyperpycnal flows with limited dispersion across the shelf in the southern sector. The latter scenario of deposition resulted in scattered hot spots of OCTerr burial along the apparently homogeneous western Adriatic shelf deposit. Our work documents significant lateral variability of a fine-grained system in which hot spots of OCTerr can be preserved in scattered prodelta bedsets (<1 km in across-shelf lateral continuity) over a 600 km long shelf. Shelfal clinothems worldwide should not be considered as homogeneous pools of OCTerr because of the influence of river, storm, and oceanic currents.

Detecting initial aragonite and calcite variations in limestone–marl alternations

AbstractLimestone–marl alternations are commonly used for high‐resolution cyclostratigraphic studies and palaeoenvironmental reconstructions, but diagenetic studies indicate that not all limestone–marl alternations reflect genuine differences in the initial sediment composition driven by environmental changes. Differences in the ratios of diagenetically inert trace elements between limestones and marls indicate changes affecting the terrigenous fraction of the precursor sediment. Contrarily, limestone–marl alternations without these differences can be the product of: (i) variations in CaCO3 input (aragonite, calcite); (ii) distortion of the latter by diagenetic CaCO3 redistribution; or (iii) diagenetic CaCO3 redistribution in a homogeneous precursor sediment. The aim of this study is to provide a method to differentiate these cases and to identify variations in the proportion of calcite and aragonite in the precursor sediment composition. The model of differential diagenesis assumes that the concentration of diagenetically inert elements is inversely proportional to the amount of redistributed CaCO3. Consequently, the difference between ratios of diagenetically inert elements from two adjacent beds is a measure for CaCO3 redistribution. This is quantifiable by the vector length between ratios from two adjacent beds. The approach is illustrated here by evaluation of a case study from the Silurian of Gotland, Sweden. Trace elements were compared according to their solubility during diagenesis. All elements bound to clay minerals or calcite show similar patterns of vector length, while vector length of elements which fit into the aragonite lattice, and are diagenetically mobile, differ. The vector length approach provides a tool to test the diagenetic origin of limestone–marl alternations, to identify initial variations in CaCO3 input and to test a limestone–marl alternation’s suitability for cyclostratigraphic analyses.

The imprint of windblown dust from the North American Southwest on the California Channel Islands and Pacific Ocean sediments

Climate projections for the North American Southwest (NASW) predict an increasing frequency and duration of droughts over the 21st century in response to human-induced warming, with potentially severe economic and social consequences. The geological record provides a way to contextualise this prediction because of the past occurrence of abrupt hemispheric warming events and sustained intervals of atmospheric carbon dioxide loading equivalent to those projected for AD 2100 (between ∼500 and 900 ppmv). Yet, terrestrial climate archives are typically too short and incomplete to provide a full record of these events. In principle, drill cores from deep sea sediments in the eastern Pacific Ocean can be used to overcome this problem because they contain long records of continental dust and distal riverine-supplied sediments from North America. Yet our limited understanding of the provenance and transport pathways of these sediments impedes use of these marine archives for this purpose. Here we present radiogenic isotope data (Sr, Nd and Pb) from known NASW dust-producing hot spots – playa lakes in the Mojave Desert, Quaternary silts mantling the California Channel Islands and the terrigenous fraction from marine sediments of the eastern Pacific Ocean, supported by new maps of bedrock isotopic composition in the NASW. We use these and published data sets to infer the origin of playa lake silts in the Mojave Desert and the source of windblown sediments to the California Channel Islands and nearby ocean basins. Our Results rule out a significant contribution from the distal tails of either the Pacific Asian dust plume or the North African dust plume to the Quaternary Channel Island silt mantles, corroborating the suggestion that they are aeolian in origin and sourced from the NASW on the Santa Ana winds. We identify the Outer California Borderland basins as an attractive proposition for studying past dust flux and palaeoaridity in the North American Southwest.

Assessing Sedimentary Detrital Pb Isotopes as a Dust Tracer in the Pacific Ocean

AbstractMineral dust particles from different source regions typically have distinct Pb isotope ratios. Theoretically, Pb isotopic composition of terrigenous minerals isolated from open‐ocean sediments should allow for dust provenance reconstructions. However, Pb isotopes of terrigenous fractions of sediments have frequently been inconsistent with expected source region signatures. This study investigates the reason(s) for offsets between the Pb isotope values of the dust component in sediment cores and those expected from source regions with focus on changes in sediment composition, sediment age, and sediment processing for analysis. Pb isotope ratios from Pacific Ocean core‐top sediments show a general delineation of the Intertropical Convergence Zone (ITCZ). Isotope mixing models support these general trends, though similarity in Pb isotope ratios of disparate source regions makes constraining specific sources challenging. Pb isotope ratios in downcore samples varied on glacial/interglacial time scales, being less radiogenic during the last glacial maximum, suggesting either a weakened ITCZ or the addition of a new, less radiogenic, source to the system. Finally, Pb isotope ratios in some source region samples yielded different Pb isotope signatures in bulk source sample than in the insoluble terrigenous fraction of the source sample, indicating that differential mineral preservation within the terrigenous component in sediments may cause offsets from source signatures. Overall, while Pb isotopes show distinct basin‐scale variations, high‐resolution spatial reconstructions require tight age controls and consistency in analytical treatment if used to define ocean sediment source regions.

Geochemistry of metacherts associated with continental margin volcanic seamount hydrothermal activity: metamorphic sole rocks of the UAE

The metacherts of the Asima Window, in northeastern U.A.E. at the southeastern corner of the Arabian Peninsula, are the dominant metamorphic sole lithologies of the Semail ophiolite that was obducted onto the Arabian continental margin at the end of the Cretaceous. There have been no previous geochemical studies of these metacherts. The Asima metachert samples of this study form four groups based on geochemistry, petrography and field association: (1) black hematitic, (2) green epidote-chlorite rich, (3) pink piedmontite-bearing and (4) grey micaceous metacherts. A continental margin setting for the parent cherts is indicated geochemically by Al2O3 to Fe2O3 and SiO2 ratios, low ΣREE, low La, moderate positive Ce/Ce* and Lan/Cen ~ 1. A significant terrigenous fraction was composed of illite, chlorite and Fe hydroxides. A hydrothermal component can be recognized in all of the metachert groups but is particularly evident in the black and green metacherts by low Al/(Al + Fe + Mn), high (Fe + Mn)/Ti, high Ba and Ba/Sr ratios, positive Eu/Eu* and left-leaning REE profiles. Most silica was biogenic. A hydrogenous component included REE’s, Cu, Ni, Zn, V, Ba and Co that were adsorbed onto clays, Fe hydroxide and Mn oxide particles. The Asima cherts were deposited in a marine basin adjacent to but separated from the continental margin by seamounts of the Al Hala Volcanics. These volcanics provided Fe,Mn-rich hydrothermal fluids that mixed with the oxygenated seawaters, leading to rapid hematite deposition (black metacherts) and slow Mn oxidation to form Mn oxide particles that accumulated in the pink metacherts. Grey metacherts were deposited farther from the vents. Green metacherts have similarities to the hydrothermal black metacherts.

Provenance of Cenozoic Indus Fan Sediments (IODP Sites U1456 and U1457)

ABSTRACTProvenance analysis of IODP Expedition 355 cores in the Laxmi Basin sheds new light on the erosional evolution of the Himalayan belt and its western syntaxis during the Neogene and on large-scale mass-wasting and magmatic events that affected the western continental margin of India in the mid-Miocene and early Paleocene. In the cored Laxmi Basin succession, heavy minerals are far less affected by selective diagenetic dissolution than in foreland-basin sandstones exposed along the Himalayan front. Occurrence of euhedral aegirine and apatite in lower Paleocene mudrocks can be tied to alkaline volcanism affecting the adjacent western Indian margin during the late stage of Deccan activity. In the mid-Miocene Nataraja Slide (the second-largest mass-transport deposit reported from passive margins worldwide), dominant carbonate detritus and depleted heavy-mineral suites (including apatite, garnet, and locally augite or rare aegirine) reveal gravitational failure and sliding of the entire succession of carbonate and siliciclastic Paleogene to lower Neogene strata originally accumulated offshore of the Saurashtra margin of western India. Contrary to previous inferences, reworking of Indus-derived detritus by the slide was negligible. The overlying upper Miocene to lower Pleistocene turbidite package has the same feldspatho-litho-quartzose to litho-feldspatho-quartzose signature of modern Indus fluvio-deltaic sand, indicating that amphibolite-facies metamorphic rocks have been widely exposed in the Himalaya–Karakorum orogen since at least the mid-Miocene. Pleistocene nannofossil oozes with planktonic foraminifera at the top of the fan contain a very subordinate litho-feldspatho-quartzose terrigenous fraction including augitic clinopyroxene, suggesting mixing of dominant biogenic debris with minor detritus contributed both by the Indus River and by a river draining western peninsular India, possibly the paleo-Narmada or the paleo-Tapti.

Indo‐Pacific Hydroclimate in Response to Changes of the Intertropical Convergence Zone: Discrepancy on Precession and Obliquity Bands Over the Last 410 kyr

AbstractThe Intertropical Convergence Zone (ITCZ), which is the heaviest rain belt on Earth, significantly influences global hydroclimate change and livelihood of nearly 40% of the global population. However, long‐term precipitation records are sparse from the Indo‐Pacific region, especially from the southern margin of the Indo‐Pacific ITCZ, restricting our understanding of the overall natural variability of the ITCZ in the past. In this study, we present a new summer monsoonal precipitation record that spans the last 410 kyr from the southern margin of the Indo‐Pacific ITCZ, based on the logarithmic ratio between terrigenous fraction K and pelagic fraction Ca (ln(K/Ca)). Contents of both elements were derived from X‐ray fluorescence scanning on sediment cores from Site U1483 (13°05.24′S, 121°48.25′E, water depth 1,733 m) that was drilled offshore northwestern Australia during International Ocean Discovery Program Expedition 363. Comparison of the new precipitation record with published precipitation records from the northern margin and meteorological center of the Indo‐Pacific ITCZ shows that precipitation changed nearly in‐phase between the hemispheres on the precession band, possibly linked to expansion and contraction in the latitudinal extent of the Indo‐Pacific ITCZ. In contrast, interhemispheric precipitation was nearly in anti‐phase on the obliquity band, likely due to latitudinal migration of the Indo‐Pacific ITCZ. Our findings imply that tropical hydroclimate cycles were regulated by the orbital forcing but with significantly different response to changes of the ITCZ on precession and obliquity bands.

Radiogenic isotopic and clay mineralogical signatures of terrigenous particles as water-mass tracers: New insights into South Atlantic deep circulation during the last termination

The past evolution of the Southern Ocean, one of the major components of the climatic system, is still a matter of debate. This study provides new insights into the deep Southern Ocean circulation based on the radiogenic isotopes and clay mineralogical signature of the terrigenous fractions transported by the main deep water masses to sediments recovered in core MD07-3076Q from the central South Atlantic. This approach successfully permits: (1) provenance identification of the various grain-size fractions (clay, cohesive silt and sortable silt); (2) assignment of each grain-size fraction to a specific water-mass; (3) reconstruction of past changes in the main deep water-mass pathways. These data document the evolution of deep-water masses in the South Atlantic Ocean during the last deglaciation. The Antarctic Bottom Water (AABW) speed and northward extension were maximum at the end of the Last Glacial Maximum (LGM), associated with strong bottom water production in the Weddell Sea, together with a vigorous Lower Circumpolar Deep Water (LCDW). In contrast the North Atlantic Deep Water (NADW) circulation was weaker than today. The onset of the deglaciation (from 17.5 ka to 15 ka, ∼Heinrich Stadial 1, HS 1) was marked by weakening and southerly retreat of the AABW and by an increase of mixing between AABW and LCDW. The speed of the AABW remained at its lowest during the Bølling Allerød (B/A) and the Younger Dryas (YD), and the LCDW slowed and retreated to the south, while the NADW progressively migrated southward, deepened, and strengthened between the beginning of the Bølling Allerød and the Holocene (from ∼15 to 10 ka).

An over 200-Year Environmental Change Record from the Highly Impacted Small, Hardwater Lake Pniówno (Chełm Hills)

&lt;p&gt;Artykuł przedstawia wyniki analiz paleoekologicznych i chemicznych osadów dennych małego, twardowodnego jeziora Pniówno. W profilu o niezaburzonej strukturze zanalizowano zmiany składu subfosylnej fauny wioślarek (Cladocera, Crustacea), oznaczono zawartość węgla organicznego, węglanów i krzemionki (z wydzieleniem frakcji terygenicznej i biogenicznej) oraz wiek osadów za pomocą datowania metodą 210Pb. Dodatkowo, w oparciu o mapy archiwalne, przeanalizowano zmiany sieci wód powierzchniowych i użytkowania zlewni w okresie od początku XIX w. po czasy współczesne. Mimo powszechnego poglądu o pogarszającym się stanie wód powierzchniowych na skutek wzrostu presji antropogenicznej w okresie objętym analizą stwierdzono okresową poprawę stanu wód, którego przyczyną były najprawdopodobniej zmiany hydrologiczne i klimatyczne, umożliwiające rozwój roślinności zanurzonej, a także pustka osadnicza spowodowana działaniami podczas I wojny światowej.&lt;/p&gt;