Hemipelagic Sediments Research Articles

Actively forming Kuroko-type volcanic-hosted massive sulfide (VHMS) mineralization at Iheya North, Okinawa Trough, Japan

Modern seafloor hydrothermal systems provide important insights into the formation and discovery of ancient volcanic-hosted massive sulfide (VHMS) deposits. In 2010, Integrated Ocean Drilling Program (IODP) Expedition 331 drilled five sites in the Iheya North hydrothermal field in the middle Okinawa Trough back-arc basin, Japan. Hydrothermal alteration and sulfide mineralization is hosted in a geologically complex, mixed sequence of coarse pumiceous volcaniclastic and fine hemipelagic sediments, overlying a dacitic to rhyolitic volcanic substrate. At site C0016, located adjacent to the foot of the actively venting North Big Chimney massive sulfide mound, massive sphalerite-(pyrite-chalcopyrite±galena)-rich sulfides were intersected (to 30.2% Zn, 12.3% Pb, 2.68% Cu, 33.1ppm Ag and 0.07ppm Au) that strongly resemble the black ore of the Miocene-age Kuroko deposits of Japan. Sulfide mineralization shows clear evidence of formation through a combination of surface detrital and subsurface chemical processes, with at least some sphalerite precipitating into void space in the rock. Volcanic rocks beneath massive sulfides exhibit quartz-muscovite/illite and quartz-Mg-chlorite alteration reminiscent of VHMS proximal footwall alteration associated with Kuroko-type deposits, characterized by increasing MgO, Fe/Zn and Cu/Zn with depth. Recovered felsic footwall rocks are of FII to FIII affinity with well-developed negative Eu anomalies, consistent with VHMS-hosting felsic rocks in Phanerozoic ensialic arc/back-arc settings worldwide.Site C0013, ∼100m east of North Big Chimney, represents a likely location of recent high temperature discharge, preserved as surficial coarse-grained sulfidic sediments (43.2% Zn, 4.4% Pb, 5.4% Cu, 42ppm Ag and 0.02ppm Au) containing high concentrations of As, Cd, Mo, Sb, and W. Near surface hydrothermal alteration is dominated by kaolinite and muscovite with locally abundant native sulfur, indicative of acidic hydrothermal fluids. Alteration grades to Mg-chlorite dominated assemblages at depths of >5mbsf (metres below sea floor). Late coarse-grained anhydrite veining overprints earlier alteration and is interpreted to have precipitated from down welling seawater as hydrothermal activity waned. At site C0014, ∼350m farther east, hydrothermal assemblages are characterized by illite/montmorillonite, with Mg-chlorite present at depths below ∼30mbsf. Recovered lithologies from distal, recharge site C0017 are unaltered, with low MgO, Fe2O3 and base metal concentrations.Mineralization and alteration assemblages are consistent with the Iheya North system representing a modern analogue for Kuroko-type VHMS mineralization. Fluid flow is focussed laterally along pumiceous volcaniclastic strata (compartmentalized between impermeable hemipelagic sediments), and vertically along faults. The abundance of Fe-poor sphalerite and Mg-rich chlorite (clinochlore/penninite) is consistent with the lower Fe budget, temperature and higher oxidation state of felsic volcanic-hosted hydrothermal systems worldwide compared to Mid Ocean Ridge black smoker systems.

Planktic14C Plateaus: A Result of Short-Term Sedimentation Pulses?

AbstractThe tuning of plateaus in glacial and deglacial planktic radiocarbon records to pertinent structures in the atmospheric14C record of Lake Suigetsu results in both a record of surface water reservoir ages and a centennial-scale absolute age model. However, the atmospheric origin of planktic14C plateaus may be questioned. Alternatively, plateaus may result from short pulses of increased hemipelagic sediment deposition, which challenges the technique of14C plateau tuning. To test the two rationales for the interval 23–12 cal ka, we calculated hypothetical sedimentation rates for all14C plateaus identified in five Atlantic sediment cores assuming sediment pulses that either span 10, 100, 200, or 300 yr each. These rates were compared to rates derived by14C plateau tuning that assumes an atmospheric origin of the plateaus. In each plateau suite, our hypothetical sedimentation rates result in at least one or two cases in extreme values that exceed the rates reported for short-lasting pulses of sediment deposition in contourites by a factor of 50 and therefore appear unrealistic. Moreover, they result in entire suites of plateau structures that incidentally appear closely aligned to the pattern of atmospheric14C plateau suites rather than to any pulses of climate-controlled sediment discharge.

Sedimentology of the Baluti Formation in the Galley Derash, Amadiya, North Iraq: insight on carbonate turbidite facies and their depositional environmental

The Baluti Formation is exposed succession of the Rhaetian age (Upper Triassic). These strata are interpreted herein for the first time to redeposit in a deep marine setting (distally steepened carbonate ramp/medial to distal slope) on the northwestern margin of the Neo-Tethys. The Galley Derash section is apparently continuous with no evidence for either subaerial exposure or submarine erosion. The absence of erosional scours in the study area confirms emplacement of these strata below both fair-weather and storm wave base. Event beds, particularly those resulting from sediment gravity flows, dominate the Rhaetian interval. The Upper Rhaetian strata are primarily assigned to the Galley Derash Valley. It records an upward transition from moderate-scale, olistolith-bearing debris flow deposits (debrite) to medium-/thin-bedded turbidites remobilized as sediment slumps/slides. The succession is dominated by medium- to thin-bedded calcareous turbidites and hemipelagic suspension deposits. Very low fossil assemblages, particularly stromatolite fragments, and planktonic bivalves occur within some intervals in the section. Rapid and relatively continuous sedimentation is attested to by the thickness of the section, the abundance of calcareous turbidites, and the thin nature of the intercalated hemipelagic beds. Low content of badly preserved fossils and evidence of continuous and rapid sedimentation refer to alteration by tectonic disturbances or diagenesis. This makes the Baluti Beds as a supplementary section for the Rhaetian successions in Iraq.

The 2013 eruption of Chaparrastique volcano (El Salvador): Effects of magma storage, mixing, and decompression

On December 29, 2013, an isolated vulcanian-type eruption occurred at Chaparrastique volcano (El Salvador) after 12years of inactivity. The eruption was classified as VEI 2 and produced an ash plume with a maximum height of ~9km. Textural and compositional data from phenocrysts from the erupted products have been integrated with geochemical and isotopic information from bulk rocks to elucidate the magmatic processes responsible for the reawakening of volcanic activity.Phenocrysts consist of Fo-rich poikilitic olivines hosting high-Mg titanomagnetites, and Fo-poor olivines coexisting with low-Mg titanomagnetites. Mineral-melt equilibria suggest an origin for the distinct phenocryst populations by mixing between a high-T (~1130–1150°C), basaltic magma with fO2 (NNO buffer) typical of the lower crust in arc systems and a low-T (~1060–1080°C), basaltic andesitic magma with fO2 (NNO+1 buffer) commonly encountered in shallower, more oxidized crustal reservoirs. Thermobarometry based on Fe-Mg exchange between orthopyroxene and clinopyroxene constrains the crystallization before eruption at relative low-P (~150–250MPa) and low-T (~1000–1050°C). Mixing between two chemically distinct magmas is also evidenced by the occurrence of reverse zoned plagioclase phenocrysts with resorbed sodic cores and re-growth of sieve-textured calcic mantles. Conversely, plagioclase rims exhibit disequilibrium compositions addressed to decompression kinetics (~10−3MPa/s) driven by rapid magma ascent to the surface (~0.03m/s).Major and trace element modelling excludes fractional crystallization as the primary mechanism controlling the bulk rock variability, whereas geochemical data align along a mixing trend between two end-members representative of the primitive basalt and the differentiated basaltic andesite. Trace element and isotope data indicate that the primary source of magmatism is an enriched MORB-like mantle with the contribution of fluxes of metasomatic fluids and/or melts produced by the subducted slab. The role played by slab-fluid inputs of carbonate origin and slab-melts from the hemipelagic sediments seems to be minimal. Assimilation/contamination processes of magmas by crustal rocks are also negligible. In contrast, the geochemical signature of magmas is greatly influenced by slab-derived aqueous fluids produced prevalently by progressive dehydration of marine sediments and altered basaltic crust.

Sedimentary impacts of recent moderate earthquakes from the shelves to the basin floor in the western Gulf of Corinth

In seismically active areas, long term records of large earthquakes are indispensable to constrain reccurence patterns of large earthquakes. In the western Corinth Rift, one of the most active areas in Europe in terms of seismicity, data about ancient earthquakes are still insufficient, despite historical records covering the last two millenia and several studies in onshore paleoseimology. In this paper, we test the use of offshore sediments from the Gulf of Corinth to identify sediment failures and tsunamis that have been triggered by historical earthquakes. Two shelves (40–100m deep), one sub-basin (180m) and the basin floor (330m) have been sampled by short gravity cores. The cores were analyzed in order to identify and characterize event deposits. The age control has been provided by 137Cs and 210Pb activity measurements showing that the cores represent 2 to 4 centuries of sedimentation. In each site, sandy event deposits are interbeded in the muddy, hemipelagic sedimentation. The age of event deposits has been compared to the record of historical earthquakes using new and published macroseismic data. This comparison shows temporal coincidence of some event deposits and documented earthquakes with a macroseismic intensity≥VII in the area, e.g. in 1861CE, 1888CE and 1909CE. In nearshore, shallow-water settings, the record of event deposits does not exactly fit with the historical record of large earthquakes because too few event deposits are present. This may be due to the absence of sediment failures or to a lower preservation of the deposits in such settings. In the deepest site, in the basin floor, the correspondence is better: a sandy turbidite probably corresponds to each large earthquake since 1850CE, except one aseismic sediment density flow that occurred at the end of the 20th century. Surprisingly, the Ms=6.2, June 15, 1995 Aigion earthquake is only possibly recorded in one nearshore site on the Aigion Shelf, in the form of a tsunami back-wash flow deposit. This study showed that moderate earthquakes (M 5.8–6.5) can significantly impact marine sediments. Regarding the evaluation of seismic hazard in the area, the basin floor is proposed as a promising site for long term paleoseismology in the Gulf of Corinth, while shallower settings need to be considered more carefully.

Turbidite chronostratigraphy off Algiers, central Algerian margin: A key for reconstructing Holocene paleo-earthquake cycles

Northern Algeria is threatened by moderate to large magnitude earthquakes resulting from the slow convergence between the African and European plates. Main active faults are located offshore along the Algerian coast, as exemplified by the 2003 Mw 6.8 Boumerdès earthquake. This event triggered numerous and widespread turbidity currents over ∼150km along strike in the Algerian basin (reaching 2800m of water depth) and demonstrates the multi-source and multi-path characteristics of earthquake-triggered turbidity flows along this margin segment.We rely on the sedimentological analysis of five cores located at the toe of the Algiers margin, close to the 2003 cable break sites, to explore the potential for Holocene turbidite paleoseismology. Radiocarbon measurements provide age models for hemipelagic sediments. Based on sedimentary facies identification, analysis of depositional sequences (stacking pattern) and a stratigraphic framework established by age models, a first correlation of turbidites between the 5 cores is attempted. The number of turbidites is constant at the base of the continental slope and decreases seawards (over 80km away from the coast). From turbidite correlations, 36 synchronous events are identified along the Algiers margin segment over the last 9kyr, and are tentatively interpreted as seismically triggered, providing a 250yr mean recurrence interval.The main historical earthquakes in the Algiers area (2003, 1716 and 1365CE) reasonably correlate with three out of the four last turbidites, strengthening the hypothesis that turbidites are suitable markers for Holocene paleoseismology. Recurrence intervals of turbidites range between 50 and 900yr, defining quiescence periods exceeding 450yr. Three quiescence periods lasting about 800, 1400 and 500yr (7–6.2ka BP, 5.4–4ka BP, and 1.5–1ka BP, respectively) support irregular earthquake cycling. Earthquake-triggered turbidites are more frequent in the study area than in the western adjacent margin segment (offshore El Asnam). This higher frequency could arise from the close location of the seismogenic faults beneath the continental slope, whereas they are located several tenths of kilometers onland in the El Asnam area, implying less instabilities of the submarine slope.

Modern sedimentation processes in Laguna de Medina, southern Spain, derived from lake surface sediment and catchment soil samples

<p>Modern processes influencing sediment composition in the endorheic lake Laguna de Medina, southern Spain, are disentangled by analysis of 46 lake surface sediment and 32 catchment soil samples. Based on statistical analysis of the mineralogical, geochemical, elemental, and granulometric compositions of all samples, the lake surface sediments can be divided into six provinces of individual composition and depositional processes. High quartz contents and coarse grain sizes, reflecting input from ancient terraces of the Guadalete River that are exposed in the adjacent hinterland, characterize the lake sedimentation close to the northern shore. At the south-eastern shore, sedimentation is characterized by terrestrial input of the Triassic Keuper facies <em>via</em> the most important inlet, the Arroyo Fuente Bermeja, as reflected by high relative intensities of Ti, K, Al, Fe, Mg, Rb. Sediments close to the northern shore are characterized by high calcite contents, reflecting predominant sediment supply from the adjacent Cretaceous 'capas rojas', a series of Subbetic deep-water marlstones and limestones. Close to the western shore, relatively high gypsum contents presumably are due to precipitation from upwelling ground water. Anthropogenic influence is only indicated in the north-western and central eastern parts of the lake, where the surface sediments are significantly enriched in TOC and TN, reflecting enhanced primary production due to terrestrial organic matter supply from anthropogenic areas in the respective catchment. The central part of the lake is characterized by distal hemipelagic sedimentation, with high concentrations of clay and silt and a chemical and mineralogical composition that reflects a mixture of the sediment sources characterizing individual parts of the lake shores. The results of this study shed new light on the depositional processes and their potential spatial heterogeneity in small endorheic lakes. Furthermore, they will provide important information concerning the interpretation of the climate-controlled sedimentary processes through time, which are reflected in a 25.7 m long sediment record (Co1313) that was recovered in the lake centre in 2014 and 2015.</p>

Origin and fate of sedimentary organic matter in the northern Bay of Bengal during the last 18 ka

The Northern Bay of Bengal (NBoB) is a globally important region for deep-sea organic matter (OM) deposition due to massive fluvial discharge from the Ganges-Brahmaputra-Meghna (G-B-M) rivers and moderate to high surface productivity. Previous studies have focused on carbon burial in turbiditic sediments of the Bengal Fan. However, little is known about the storage of carbon in pelagic and hemipelagic sediments of the Bay of Bengal over millennial time scales. This study presents a comprehensive history of OM origin and fate as well as a quantification of carbon sediment storage in the Eastern Bengal Slope (EBS) during the last 18ka. Bulk organic proxies (TOC, TIC, TN, δ13CTOC, δ15NTN) and content and composition of total hydrolysable amino acids (THAA) in a sediment core (SO188-342KL) from the EBS were analyzed. Three periods of high OM accumulation were identified: the Late Glacial (LG), the Bölling/Alleröd (B/A), and the Early Holocene Climatic Optimum (EHCO). Lower eustatic sea level before 15ka BP allowed a closer connection between the EBS and the fluvial debouch, favoring high terrestrial OM input to the core site. This connection was progressively lost between 15 and 7ka BP as sea level rose to its present height and terrestrial OM input decreased considerably. Export and preservation of marine OM was stimulated during periods of summer monsoon intensification (B/A and EHCO) as a consequence of higher surface productivity enhanced by cyclonic-eddy nutrient pumping and fluvial nutrient delivery into the photic zone. Changes in the THAA composition indicate that the marine plankton community structure shifted from calcareous-dominated before 13ka BP to siliceous-dominated afterwards. They also indicate that the relative proportion of marine versus terrestrial OM deposited at site 342KL was primarily driven by relative sea level and enlarged during the Holocene. The ballasting effect of lithogenic particles during periods of high coastal proximity and/or enhanced fluvial discharge promoted the export and preservation of OM. The high organic carbon accumulation rates in the EBS during the LG (18–17ka BP) were 5-fold higher than at present and comparable to those of glacial upwelling areas. Despite the differences in sediment and OM transport and storage among the Western and Eastern sectors of the NBoB, this region remains important for global carbon sequestration during sea level low-stands. In addition, the summer monsoon was a key promotor of terrestrial and marine OM export to the deep-ocean, highlighting its relevance as regulator of the global carbon budget.

Complete archive of late Turonian to early Campanian sedimentary deposition in newly drilled cores from the Tarfaya Basin, SW Morocco

An expanded succession of organic-rich marlstones and limestones deposited in the Tarfaya Basin provides an outstanding opportunity to closely retrace climate evolution and sea-level changes during the Cretaceous greenhouse period. We present high-resolution X-ray fluorescence (XRF) scanning and bulk carbon- and oxygen-isotope records from two newly drilled sediment cores in the Tarfaya Atlantic coastal basin, which recovered a continuous Upper Turonian to Campanian succession of ∼290 m thickness. The XRF core scanning records reveal three long-term oscillations in the abundance of terrigenous elements (increase of Al, Ti, K, Si, and Fe normalized against Ca), which correspond to progressive transgressive phases followed by rapid regressions during the Coniacian and early Santonian. Sea-level highstands during this interval corresponding to the Coniacian−Santonian oceanic anoxic event 3 (OAE 3) are characterized by overall oxygen-depleted to anoxic conditions at the seafloor (indicated by the high organic carbon content, the presence of laminations, and low log[Mn/S], high log[V/Ca], and high log[Br/Ca]). The upper Santonian interval marks the transition from anoxic to oxic bottom-water conditions, prevalent through the early Campanian. The composite bulk carbonate δ 13 C curve exhibits strong similarities to the global stacked δ 13 C reference curve, characterized by negative excursions in the early Coniacian (Navigation and East Cliff events) and late Santonian (bracketed by the Haven Brow and Buckle events) and by positive excursions in the latest Turonian (Hitchwood event), middle Coniacian (Wight Fall event), and at the Santonian-Campanian boundary. During the early Campanian, enhanced accumulation of fine-grained carbonate and clay-rich hemipelagic sediments, increasing bulk carbonate δ 18 O, and low log(Br/Ca) and log(V/Ca) values indicate climate cooling, associated with a substantial improvement in bottom-water ventilation. Two long-term δ 13 C cycles of ∼2 m.y. duration, probably related to variations in Earth’s orbital eccentricity, are associated with the long-term cooling trend initiating the Campanian−Maastrichtian climate transition toward a cool greenhouse state.

The importance of site selection, sediment supply, and hydrodynamics: A case study of submarine paleoseismology on the northern Cascadia margin, Washington USA

The Washington continental margin presents both a classic test of submarine paleoseismology, and an opportunity to explore advancement of the field through analysis of sediment dispersal in a heterogeneous system. New and archive core, bathymetric, backscatter and seismic reflection data from the Washington Cascadia margin show that during high-stand conditions, the northernmost canyons, Barkley, Nitinat, Juan de Fuca (JDF), and to some extent Quillayute are relict systems, with little Holocene recharge. The remaining canyons, Quinault, Grays, Guide, and Willapa, are recharged to a varying degrees by northward transport of Columbia River derived sediment. All systems are nonetheless active conduits for turbidity currents during the Holocene, which are weaker and more restricted than their Pleistocene counterparts. Sedimentologic and CT analysis, supported by radiocarbon ages, micropaleontology, and the Mazama ash datum show that the Holocene sedimentary sequence consists of a series of sand to mud turbidites in the active portions of all systems, interbedded with hemipelagic sediment. However, the Pleistocene Astoria and Nitinat fans are largely inactive in the Holocene, with turbidity current activity limited to the proximal parts of the main channels. Within active systems, the turbidite record is modulated by local landsliding and growth of active folds and faults.In the relict systems, the turbidite record begins in the middle canyon reaches, as opposed to the actively recharged systems which have a turbidite record in the more proximal canyon reaches. Deposits in the relict systems increase in thickness and modal grain size downstream, suggesting multiple sources and or entrainment of material along the canyon walls.Hydrodynamic models using Monte Carlo model searches for best fitting flow parameters show the most likely pathways by which Holocene and Pleistocene currents flowed through the complex accretionary wedge to the abyssal plain. Model results, supported by heavy mineral distributions, show that the northern canyon systems (Barkley, Nitinat, JDF, Quillayute) are independent of the southern systems, (Quinault, Guide, Grays, Willapa) during the Holocene, supporting the classic “confluence test”. Balancing of sediment volumes required suggests sediment supplied to the slope canyons and abyssal channels in turbidity current events is 2–5 times greater than that supplied by recharge to the canyon heads by external sources. This implies a process that is independent of recharge that scavenges the plentiful relict and hemipelagic sediment supply on the continental slope.Lithostratigraphic correlation and age models suggest similar sequences were deposited in most systems independently, and likely synchronously. The correlated turbidite sequence suggests deposition of ~23 Holocene and 16 post Mazama turbidites in most parts of the canyon systems, with only modest variation, mostly attributable to evidence of bypassing and erosion. The best candidate for triggering of these sequences remains great earthquakes, and the sequence correlates well to onshore and other offshore paleoseismologic evidence.The new data, including new cores in northern Oregon, suggest revisions to segmented rupture boundaries. Several partial ruptures (Segment B) likely extended further north to Juan de Fuca Canyon; one event was resolved into two, and one Washington only event was added. Most “Segment C” ruptures were found to extend further northward to the latitude of Astoria Canyon. Mean recurrence times are therefore revised to ~434years for the Washington Coast, and ~340years for the central and northern Oregon coast. Conditional probabilities in the next 50years also are revised to 10–17% for the Washington coast, and 16–22% for the central and northern Oregon coast.In Cascadia, Sumatra and other locales globally, core siting, spatial sample density, high-resolution analysis of core and regional geophysics and understanding of flow dynamics are critical to capturing a paleoseismic record. Sedimentary records vary across turbidity current systems of varying sediment supply, physiography and sediment sources. Variations in the record will reflect these factors, yet may still present a consistent paleoseismic history. This analysis highlights the importance of a thorough understanding of flow paths, hydrodynamics and the interplay of sedimentation and local tectonics when testing for evidence of earthquakes in the sedimentary record of active margins.

Seismic stratigraphy and tectono-sedimentary framework of the Pliocene to recent Taixinan foreland basin in the northeastern continental margin, South China Sea

The Pliocene to recent Taixinan basin is a unique foreland basin built on the northeastern part of the northern passive margin of the South China Sea (SCS). We have used multichannel seismic profiles tied to well controls from ODP Leg 184 to investigate the tectonic and sedimentary characteristics of the foreland basin. We defined three seismic sequences, dated respectively to the Pliocene (5.33–2.5 Ma), early Quaternary (2.5–1.0 Ma), and late Quaternary (1.0 Ma–present). They represent three stages of evolution of the foreland basin. We have recognized seven types of seismic facies, which are parallel-to-subparallel, progradational, fill-type, divergent mounded, wavy, lenticular, and chaotic facies, and are interpreted as hemipelagic deposits, deltas, submarine canyon fills, levees, sediment waves, submarine fans, and mass transport deposits, respectively. Seismic facies analysis indicates that sedimentation within the foreland basin has been dominated by turbidity currents and the other gravity transport processes. Tectonically, the foreland basin consists of three structural zones: an eastern wedge-top, a central foredeep, and a western forebulge zones. Different from a typical foreland basin, however, the basin extends in the northeast–southwest direction, which is oblique to the north–south-striking Taiwan orogenic zone, but parallel to the northern SCS passive margin, where the basin is hosted, suggesting that the foreland basin is significantly influenced by the development of the passive margin. In addition, the basin displays a distinctive inverted-triangle-shaped downstream-converging sediment dispersal system instead of ideal transverse or longitudinal drainage systems common in a typical foreland basin. We have suggested that the Pliocene to recent Taixinan basin is an atypical foreland basin, which was formed as a flexural response of tectonic loading by the Taiwan orogenic wedge, but strongly affected by its passive continental margin background.

An early Permian coastal flora dominated by Germaropteris martinsii from basinal sediments in the Midland Basin, West Texas

Fossils found in cores from wells in the Midland Basin of West Texas include several kinds of terrestrial plants and a variety of marine animal remains. Depositional settings ranged from basin slope to deep-water basin floor, hence the presence of land plants was unexpected. The fossil plant assemblage is depauperate, dominated by Germaropteris martinsii, a Permian-age peltasperm. Other specimens include the peltasperm Supaia, Sphenopteris germanica, axes of uncertain affinity, and incertae sedis remains presumed to be terrestrial plants. Fossil plants are found predominantly in fine-grained, siliceous mudrocks between coarser-grained calcareous floatstones and wackestones/packstones interpreted as debrites and turbidites, suggesting that the plants were carried from land by surface currents before sinking to the basin floor and being buried by slowly accumulating hemipelagic sediment. Specimens were examined from drillcores in 14 wells spanning an interval from the lower Wolfcamp through the lower Leonard. This record of G. martinsii in lower Permian Wolfcamp rocks is among the earliest occurrences of these plants, which have been found most abundantly in upper Permian strata of Western Europe.

Zoophycos in deep‐sea sediments indicates high and seasonal primary productivity: Ichnology as a proxy in palaeoceanography during glacial–interglacial variations

AbstractTrace fossils provide valuable palaeoenvironmental information in hemipelagic settings. This is particularly true in the case of Zoophycos, an easily recognizable trace fossil in core. At IODP site U1385, Zoophycos was found throughout an interval representing 1.5 Ma, covering 45 glacial–interglacial cycles mediated by obliquity (41 ka) and short‐term eccentricity (100 ka). Zoophycos is most common in sediments deposited during glacial times and when the sedimentation rate was intermediate and primary production was high and seasonal. Occurrences of Zoophycos elsewhere support a similar relationship with seasonal organic‐matter deposition. This is particularly significant considering that seasonality of organic‐matter deposition is difficult to decipher from the sediment record. Zoophycos appears to represent a useful proxy to characterize high and seasonal organic‐matter deposition and primary productivity in Neogene hemipelagic deposits.

Climatic control of sediment transport from the Himalayas to the proximal NE Bengal Fan during the last glacial-interglacial cycle

Clay mineralogy, siliciclastic grain-size, major elements, 87Sr/86Sr, and eNd analyses of deep-sea sediments cored in the north-eastern Bay of Bengal are used to reconstruct evolution of detrital sources and sediment transport to the proximal part of the Bengal deep-sea fan during the last climatic cycle. eNd values (−13.3 to −9.7) and 87Sr/86Sr ratios (0.721–0.733) indicate a mixture of sediments originating from the Ganges-Brahmaputra rivers and the Indo-Burman ranges. Interglacial Marine Isotopic Stages (MIS) 5 and 1 are associated with a higher contribution of sediments from the Ganges-Brahmaputra river system than is the case for glacial MIS 6, 4, 3, and 2. Siliciclasitic grain-size combined with Si/Al and Si/Fe ratios indicate coarser glacial sediments with numerous turbidite layers. Glacial turbidite layers display similar clay mineralogical compositions to hemipelagic sediments. Only few of turbidite layers (MIS 6, 4, and 2) are slightly unradiogenic (eNd −13.3), suggesting a higher contribution of Ganges-Brahmaputra river sediments. Independently of changes in the sedimentary sources, the smectite/(illite + chlorite) ratio of cores located on the NE Bengal Fan indicates higher inputs of primary minerals (illite and chlorite) from the highlands of the river basins (relief) during glacial MIS 6, 4, 3, and 2 and an increased contribution of pedogenic minerals (smectite and kaolinite) during interglacial MIS 5 and 1. Maximum smectite/(illite + chlorite) ratios during the warm sub-stages of MIS 5 suggest an intensification of summer monsoon rainfall associated with higher rates of physical erosion of the Indo-Gangetic flood-plain and/or dominant summer hydrological conditions transporting a higher proportion of sediments deriving from the Ganges-Brahmaputra rivers to the NE Bengal Fan. In addition, a higher production of smectite in soils of the Indo-Gangetic flood-plain during periods of intensification of monsoon rainfall cannot be excluded.

Chronostratigraphy of uplifted Quaternary hemipelagic deposits from the Dodecanese island of Rhodes (Greece)

An integrated magneto-biostratigraphic study, based on calcareous nannofossils and foraminifers, together with the radiometric dating of a volcaniclastic layer found in several outcrops, was carried out on the hemipelagic deposits of the Lindos Bay Formation (LBF) at six localities on the island of Rhodes (Greece). Our highly refined chronostratigraphic framework indicates that the lower and upper lithostratigraphic boundaries of the LBF are diachronous. Associated with the 40Ar/39Ar age determination of 1.85 ± 0.08 Ma for the volcaniclastic layer, our data show that among the investigated outcrops, the Lindos Bay type locality section provides the longest record (1.1 Ma) of the LBF. Hemipelagic deposition occurred continuously from the late Gelasian (∼1.9 Ma) to the late Calabrian (∼0.8 Ma), i.e., from Chrons C2n (Olduvai) to C1r.1r (Matuyama) and from nannofossil Zones CNPL7 to CNPL10. This long record, together with the hemipelagic nature of the deposits, make the Lindos Bay type locality section a unique element in the eastern Mediterranean region, allowing future comparisons with other early Quaternary deep-sea sections available in the central and western Mediterranean regions.

Chronostratigraphy of uplifted Quaternary hemipelagic deposits from the Dodecanese island of Rhodes (Greece)

AbstractAn integrated magneto-biostratigraphic study, based on calcareous nannofossils and foraminifers, together with the radiometric dating of a volcaniclastic layer found in several outcrops, was carried out on the hemipelagic deposits of the Lindos Bay Formation (LBF) at six localities on the island of Rhodes (Greece). Our highly refined chronostratigraphic framework indicates that the lower and upper lithos-tratigraphic boundaries of the LBF are diachronous. Associated with the40Ar/39Ar age determination of 1.85 ± 0.08 Ma for the volcaniclastic layer, our data show that among the investigated outcrops, the Lindos Bay type locality section provides the longest record (1.1 Ma) of the LBF. Hemipelagic deposition occurred continuously from the late Gelasian (~1.9 Ma) to the late Calabrian (~0.8 Ma), i.e., from Chrons C2n (Olduvai) to C1r.1r (Matuyama) and from nannofossil Zones CNPL7 to CNPL10. This long record, together with the hemipelagic nature of the deposits, make the Lindos Bay type locality section a unique element in the eastern Mediterranean region, allowing future comparisons with other early Quaternary deep-sea sections available in the central and western Mediterranean regions.

Geochemical records from loess deposits in Japan over the last 210 kyr: Lithogenic source changes and paleoclimatic indications

AbstractThe generation, transport, and accumulation of tropospheric dust have changed with the paleoclimatic changes of the Quaternary period. Such dust has accumulated in Japan ∼3000 km leeward of the source deserts in China. We analyzed the fractions of windblown fine quartz and bulk major and trace elements, and Sr‐Nd‐Pb isotopic compositions of loess in SW Japan deposited over the past 210 kyr. The results indicated extensive accumulation of tropospheric dust mixed with tephra fragments derived from the nearby Daisen volcano. The accumulation rate of fine quartz and selected elemental/isotopic compositions can be used as climatic proxies that reflect greater accumulation of dust in times of colder climate. Chemical indices for weathering show enhanced effects of weathering during times of warmer climate. The trace element compositions of the loess deposits are surprisingly similar to those of the Chinese loess, hemipelagic sediments in the Sea of Japan and the western Pacific Ocean, and the distal Chinese dust found in Canada. This similarity indicates that the loess dust shares major fractions of these fine‐grained sediments and that geochemical fractionation during the transport was limited. The Sr‐Nd‐Pb isotope compositions of the SW Japan loess indicate an origin predominantly in the Gobi Desert. The high‐latitude Pacific sediments and high‐latitude dust in Canada also show the same signature. However, isotopic compositions of samples from the southern Chinese loess plateau and mid to low‐latitude Pacific sediments are largely derived from the Taklimakan desert, which indicates different delivery pathways of the tropospheric dusts.

Sedimentology of a Middle Jurassic Base-of-Slope environment, Cutri Formation, Mallorca

The Cutri Formation’s, type location, exposed in the NW of Mallorca, Spain has previously been described by Álvaro et al., (1989) and further interpreted by Abbots (1989) unpublished PhD thesis as a base-of-slope carbonate apron. Incorporating new field and laboratory analysis this paper enhances this interpretation. From this analysis, it can be shown without reasonable doubt that the Cutri Formation was deposited in a carbonate base-of-slope environment on the palaeowindward side of a Mid-Jurassic Tethyan platform. Key evidence such as laterally extensive exposures, abundant deposits of calciturbidtes and debris flows amongst hemipelagic deposits strongly support this interpretation.

Organic matter in upper Albian marine sediments in the High-Tatric units, central western Carpathians related to Oceanic Anoxic Event 1d—Geochemistry, microfacies and palynology

A multidisciplinary study of upper Albian hemipelagic sediments related to the Oceanic Anoxic Event 1d (OAE1d) from the High-Tatric units (central western Carpathians, Polish part of the Tatra Mountains) was undertaken to characterize organic matter (OM) and to investigate its origin. Microfacies and palynological records combined with mineralogical and geochemical data from these sediments show the occurrence of both marine and land-derived OM in the limestone and marl successions whose deposition corresponds to the Parathalmanninella apenninica Zone in the late Albian. Both types of OM were strongly degraded under the oxic conditions that prevailed during the entire time of their deposition. The sedimentation of marls with low contents of total organic carbon (<0.24%), dominated by land-derived OM, occurred during the final phase of OAE1d. It was probably related to a sudden change in the circulation pattern at the margins of the Tatric–Zliechov sedimentary basin connected with a sea-level rise. The coastal upwelling along the Tatric Ridge that prevailed during the early late Albian gradually weakened or disappeared and was replaced by a downwelling current flowing from the shallow parts of the basin that transported land-derived OM from nearshore coastal plains.

Evidence of early bottom water current flow after the Messinian Salinity Crisis in the Gulf of Cadiz

Integrated Ocean Drilling Program (IODP) Expedition 339 cored multiple sites in the Gulf of Cadiz in order to study contourite deposition resulting from Mediterranean Outflow water (MOW). One Hole, U1387C, was cored to a depth of 865.85m below seafloor (mbsf) with the goal of recovering the latest Miocene to Pliocene transition in order to evaluate the history of MOW immediately after the end of the Messinian Salinity Crisis. To understand this history, an accurate age model for the succession is needed, but is challenging to construct, because the Miocene–Pliocene boundary is not marked by a clear biostratigraphic event in the Atlantic and coring gaps occur within the recovered stratigraphic record. These limitations are overcome by combining a variety of chronostratigraphic datasets to construct an age-model that fits the currently available age indicators and demonstrates that coring in Hole U1387C did indeed recover the Miocene–Pliocene boundary at about 826mbsf. This boundary is associated with a distinct and abrupt change in depositional environment. During the latest Messinian, hemipelagic sediments exhibiting precession-induced climate variability were deposited. These are overlain by Pliocene sediments deposited at a much higher sedimentation rate, with much higher and more variable XRF core scanning Zr/Al ratios than the underlying sediment, and that show evidence of winnowing, particle sorting and increasing grain size, which we interpret to be related to the increasing flow of MOW. Pliocene sedimentary cyclicity is clearly visible in both the benthic δ18O record and the Zr/Al data and is probably also precessionally controlled. Two contouritic bigradational sandy-beds are revealed above the third sedimentary cycle of the Pliocene. On the basis of these results, we conclude that sedimentation associated with weak Mediterranean–Atlantic exchange, began in the Gulf of Cadiz virtually at or shortly after the Miocene–Pliocene boundary.