Supply Of Terrigenous Material Research Articles

Lithologic and facies characteristics of the Lower Cambrian Usolka Formation and its age analogs in the Cis-Yenisei sedimentary basin, West Siberia

Based on the correlation between Lower Cambrian sections of deep wells on the left bank of the Yenisei River and outcrops in the westernmost Yenisei Ridge, the sedimentologic characteristics of the Usolka Formation and coeval deposits are compared. Three paleogeographic regions (subbasins) are distinguished in the Cis-Yenisei basin in Usolka time. The leading role in the sediment genesis was played by the region of barrier reefs stretching northwestward and northward as a ~70 km wide band to their joint with the reefs of the Igarka-Noril’sk facies region in the north. The salt basin east of the barrier reef ridge was a bay of the East Siberian salt basin, separated from the latter by the Yenisei paleoislands (at the place of the Yenisei Ridge). Sedimentation in that basin was controlled by evaporite processes, the supply of terrigenous material from the islands and carbonate debris from the opposite side (barrier reef), and the predominance of storm processes. The subbasin west of the barrier reefs evolved under different scenario. Since the Early Cambrian, a trough has been forming here, which was initially characterized by a regime of starvation and the first appearance of carbonaceous rocks (Lower Churbiga Subformation), regarded as Domanic oil source rocks, in the general Cambrian section. On the estimation of the prospects for the distribution of reservoirs whose origin depends on the facies regularities, the leading role is played by the barrier reef region. Importantly, the Lower Cambrian section of the Cis-Yenisei basin contains two large adjacent paleogeomorphologic structures and the corresponding facies zones of a starved prereef depression with the Domanic oil source rocks of the Lower Churbiga Subformation at the early stage of evolution and a potentially productive barrier reef system with a steep slope toward the basin. The favorable combination of these factors suggests that the Cis-Yenisei basin has a high petroleum potential.

Variability in transport of terrigenous material on the shelves and the deep Arctic Ocean during the Holocene

Arctic coastal zones serve as a sensitive filter for terrigenous matter input onto the shelves via river discharge and coastal erosion. This material is further distributed across the Arctic by ocean currents and sea ice. The coastal regions are particularly vulnerable to changes related to recent climate change. We compiled a pan-Arctic review that looks into the changing Holocene sources, transport processes and sinks of terrigenous sediment in the Arctic Ocean. Existing palaeoceanographic studies demonstrate how climate warming and the disappearance of ice sheets during the early Holocene initiated eustatic sea-level rise that greatly modified the physiography of the Arctic Ocean. Sedimentation rates over the shelves and slopes were much greater during periods of rapid sea-level rise in the early and middle Holocene, as a result of the relative distance to the terrestrial sediment sources. However, estimates of suspended sediment delivery through major Arctic rivers do not indicate enhanced delivery during this time, which suggests enhanced rates of coastal erosion. The increased supply of terrigenous material to the outer shelves and deep Arctic Ocean in the early and middle Holocene might serve as analogous to forecast changes in the future Arctic.Keywords: Arctic; riverine input; coastal erosion; land–ocean interaction; Holocene.(Published: 9 December 2015)To access the supplementary material for this article, please see supplementary files in the column to the right (under Article Tools).Citation: Polar Research 2015, 34, 24964, http://dx.doi.org/10.3402/polar.v34.24964

Fossils from the Silesian-Subsilesian series of the Polish Western Carpathians: the implications for changes in sea-level and the marine environment during the Albian-Turonian

Fossils and exotics from the Albian-Cenomanian deposits of the Western Polish Carpathians are discussed in relation with changes in depositional environments. Environmental conditions were controlled by geotectonic activity, sea-level changes and also anoxic and biotic events. During the Albian-the Early Cenomanian, and in the Turonian the fall in sea level led to increased supply of coarse-grained material rich in siliceous and sometimes calcareous bioclasts and exotics. This cyclic process has contributed to changes in the marine biota. In the Albian monogenic foraminiferal assemblages with the surficial epifauna corresponding to the organic influx and oxygen deficiency (OAE 1b) were evolved into more variable associations including deep infauna, which indicated more aerobic conditions. Under these conditions also preserved planktonic and calcareous benthic fossils, which indicated the supply of terrigenous material from shallow-water environments and land. During the Albian-Turonian transition intensive subsidence and volcanic activity associated with eustatic sea-level rise led to intensive production of phytoplankton. The sea-surface productivity and enhanced upwelling resulted in expanded short-term oxygen minima at the end of the Albian (OAE 1d) and the Cenomanian (OAE 2). In the latter interval benthic forms almost extinct while siliceous and calcareous plankton survived. In the Turonian changes in sea-level and sedimentary regime led to re-colonization of the basin bottom.

Protoliths of Paleoproterozoic calciphyres from the Irkut block (Sharyzhalgai uplift of the Siberian craton): composition and origin

The paper presents data on high-grade silicate–carbonate rocks (calciphyres) from the Irkut block (Sharyzhalgai uplift, southwestern Siberian craton). Their origin and age were determined from the rock characteristics, U–Pb dating, REE content, and Hf isotope composition of zircon. The calciphyres occur both as independent section fragments and as interbeds within Paleoproterozoic garnet-bearing and high-alumina (cordierite- and sillimanite-bearing) gneisses. They were produced by metamorphism of terrigenous-carbonate sediments. The terrigenous sediments range in maturity from arenites and wackes to argillaceous rocks; this is consistent with the reconstruction of the sedimentary protoliths of paragneisses, which are predominant in the metasedimentary rocks. The petrogeochemical features of the calciphyres, their LREE enrichment relative to “pure” carbonate rocks, and a distinct Eu anomaly were inherited from the terrigenous component of calc-silicate sediments. The Nd model age (2.4–2.7 Ga) of the calciphyres and the value THf(DM-2st) = 2.5–3.0 Ga for zircon from these rocks indicate that carbonate accumulation was accompanied by the supply of terrigenous material, which formed during the erosion of Archean and Paleoproterozoic crust. Zircon from the calciphyres is similar to metamorphic zircon in REE patterns and Th/U ratios. It might have been of detrital origin and then recrystallized during high-temperature metamorphism. Terrigenous-silicate rocks were metamorphosed at ca. 1.87 Ga. This is close to the previous age estimates for the terrigenous rocks metamorphism (1.85–1.86 Ga) and the age of baddeleyite from apocarbonate metasomatic rocks (1.86 Ga).

Quaternary seismic facies of the atlantic continental rise

High-resolution seismic profiles collected by Parasound and SES-2000 deep profilers during Cruise 26 of the R/V Akademik Sergei Vavilov (2009) along the continental slope base of South America, NW Africa, and West Europe are correlated with the deep-sea drilling boreholes. Lithofacies interpretation of the Quaternary deep-water seismic facies of hemipelagites, bottom current deposits (contourites), and gravitites (turbidites, mud flow deposits) is presented. The data obtained reveal the domination of contourites in the accumulation of continental rise apron under conditions of relatively scarce terrigenous material supply. It is shown that acoustically stratified seismic facies under these conditions commonly reflect interbedding of the terrigenous clay and biogenic calcareous ooze related to the Pleistocene glacial/interglacial cycles.

Estudo petrográfico e geoquímico dos ironstones da base da Formação Pimenteiras, Borda Oeste da Bacia do Parnaíba, Tocantins

Ironstones that occur at the base of the Devonian Pimenteiras Formation (northwestern border of the Parnaíba basin) were investigated along the Xambioá-Vanderlândia and Colinas do Tocantins-Couto Magalhães sections. The ironstones consist of discontinuous decimeter-thick layers intercalated in sandstones and shales that underlie rocks of the Neoproterozoic Araguaia belt. The Xambioá-Vanderlândia ironstones are texturally and chemically quite distinct from those of the Colinas do Tocantins-Couto Magalhães area. Besides the presence of oolites, the former shows smaller amounts of terrigenous material (especially quartz) and higher iron oxide-hydroxides proportions. They also are more enriched in V, Sr, Zr and ΣREE, and poorer in Al2O3 and Rb. The North American Shale Composite (NASC) normalized REE distribution pattern is also different, especially concerning the IREE N values, which, being higher in the oolithic ironstones, display convex curves and, being lower in the non-oolithic ironstones, display concave ones. In the field, spatial relationships could not be defined between both ironstone types. It is then suggested that they represent different lithological facies of the same iron formation. Probably, the deposition of the non-oolithic facies occurred in deeper and quieter waters away from the continental border, where larger amounts of detrital sediments were discharged, whereas the deposition of the oolithic facies took place in shallower and more agitated waters, with less supply of terrigenous material. Iron was largely derived from the erosion of continental areas where reduced environments favored its mobilization and transport by rivers as suspended particles, colloids, and organic complexes.

Microfacies of Mesozoic Carbonate

Carbonate rocks of Mesozoic age are widespread in Slovenia where they consitute about 40 % of its territory, and attaining total thickness of more than 5000 metres . With respect to microfacies almost all structure types can be recognized, the limestones and dolomites being formed in various sedimentary environments, such as in open and in restricted parts of carbonate shelf, in lagoons and on coastal plains, in different types of reefs, on slopes and in the basin. Carbonate sedimentation was often accompanied also by the supply of terrigenous material and products of volcanic activity. Among diagenetic processes in investigated carbonate rocks the most extensive are dolomitization and silicification. In the present text 250 microscopic photographs of characteristic limestones and dolomites from Slovenian territory are assembled. In the introductory part, to which for orientation schematic stratigraphic columns are added, the geologic development od these carbonate rocks is briefly outlined. For the sake of completeness in presenting the »carbonate era« in the overview, Upper Permian limestones and dolomites are also described next to Mesozoic beds.

Sedimentary Evolution in the Northern Slope of the South China Sea Since the Oligocene and Its Response to Tectonics

AbstractThe sedimentary evolution of the South China Sea (SCS) since the Oligocene and its response to tectonics was reconstructed based on a multi‐proxies approach including monomineralic quartz oxygen isotope ratios (δ18O), terrigenous grain‐size and accumulation rate, and scanning electron microscopy (SEM) observation of isolated quartz in sediments from Ocean Drilling Program (ODP) Site 1148 in the northern SCS. The sedimentary evolution of SCS could be divided into five stages: initial expansion (34~28.5 Ma), intense tectonic activity (28.5~23 Ma), reduced tectonic activity (23~16.5 Ma), thermal subsidence (16.5~3.5 Ma), and Taiwan uplift (3.5 Ma to present). Significant variations of the composition of terrigenous minerals and oxygen isotope values of quartz between 28.5 Ma and 23 Ma suggest a change in sediments provenance, which may be related to the strongest tectonic activity of the SCS in the Oligocene. Terrigenous materials at the study site were mainly originated from the southern source (presumptively from Palawan) during the early spreading period of the SCS. With the extensive spreading of the SCS, especially when the spreading axis of the SCS jumped southwards during 25~23 Ma, the Palawan continental block moved away from the study site. Moreover, the northern sources (South China) were not significant because of low topography at that time. Therefore, the terrigenous mass accumulation rate (MAR) was very low. Because of the rapid uplift of the Qinghai‐Tibet Plateau, Pearl River developed gradually and thus South China became the main source of ODP Site 1148. With the formation of the Taiwan island since 3.5 Ma, Taiwan contributed significant terrigenous materials to the northern SCS. The hiatus in sediments at ODP Site 1148 in the late Oligocene possibly resulted from the influence of low terrigenous materials supply, rising sea level and relatively stronger currents during provenance change.

Geochemical occurrences of rare earth elements in oil shale from Huadian

Distribution characteristics and occurrence modes of rare earth elements (REE) in oil shale from Huadian, Jilin province were determined by sequential chemical extraction process. Content of REE were determined by inductively coupled plasma-mass spectrometry (ICP-MS). The results show that the enrichment of light rare earth elements (LREE) in Huadian oil shale is richer than that of heavy rare earth elements (HREE), relative to those in coals from China. The REE in oil shale are positively correlated with terrigenous clastic rock, and the supply of terrigenous materials is relatively stable. The fractionation between LREE and HREE is clear and shows a moderate LREE-enriched pattern. The occurrence of rare earth elements are mainly in minerals fractions. The enrichment of sulfide fractions inclines to LREE; besides, carbonate fractions, ferromanganese oxyhydroxides bound fraction and aluminosilicate bound fraction are more inclined to enrich HREE. Moreover, here is lack of the contents of rare earth elements in exchangeable and organic matter fractions. Additionally, the fractionation effects of rare REEs in different substances have some differences under various sedimentary environments.

Variations of the oxygen minimum zone of the Okhotsk Sea during the last 50 ka as indicated by benthic foraminiferal and biogeochemical data

Benthic foraminiferal and sediment biogeochemical data (total organic carbon, calcium carbonate and biogenic opal contents) in two cores (1265 and 1312 m water depths) from the southeastern Sakhalin slope and one core (839 m water depth) from the southwestern Kamchatka slope were investigated to reconstruct variations of the oxygen minimum zone during the last 50 ka in the Okhotsk Sea. The oxygen minimum zone was less pronounced during cooling in the MIS 2 that is suggested to be caused by a maximal expansion of sea ice cover, decrease of marine productivity and increase of production of the oxygenated Okhotsk Sea Intermediate Water (OSIW). A two-step-like strengthening of oxygen minimum zone during the warmings in the Termination 1a and 1b was linked to (1) enhanced oxygen consumption due to degradation of large amount of organic matter in the water column and bottom sediments, originated from increased marine productivity and supply of terrigenous material from the submerged northern shelves; (2) sea ice cover retreat and reduction of OSIW production; (3) freely inflow of the oxygen-depleted intermediate water mass from the North Pacific.

Origin of ferruginous quartzites of the Kursk magnetic anomaly

Based on electron microscopic studies of minerals from iron-ore formations, a conclusion on different geneses of the composing rocks is made. Quartz of ferruginous quartzites originated through metasomatic transformation of primary biogenic limestones, while iron minerals were formed due to cyclic iron supply from deep-seated sources. Schists’ interlayers correspond to breaks in carbonate precipitation in periods of supply of terrigenous material from land or pyroclastics from volcanoes.

Carbonate and organic carbon content changes over last 20 ka in the Southeastern Arabian Sea: Paleoceanographic implications

Two Gravity cores (AAS 38-4 and AAS 38-5) recovered from the eastern Arabian Sea were analyzed for calcium carbonate (CaCO 3), organic carbon, aluminium (Al) and titanium (Ti) in order to understand the calcium carbonate and terrigenous fluctuations during the Holocene and Last Glacial Period. High CaCO 3 and low Al and Ti during the Holocene, and low CaCO 3 and high Al and Ti during the Last Glacial Period suggest that CaCO 3 content in these two cores appears to be controlled by the dilution of terrigenous material. The supply of terrigenous material to the core sites was higher during the Last Glacial Period than in the Holocene. Organic carbon values were lower (<2%) during the Holocene and higher (>2%) during the Last Glacial Period in core AAS 38-4; but the opposite was found in core AAS 38-5. This inconsistent pattern of organic carbon changes in the two cores studied indicates that the distribution of organic carbon in the eastern Arabian Sea is controlled not only by the supply of organic matter from the water column but also by sediment texture and dilution of sediment components.

Provenance and sea‐ice transportation of Mid‐Pliocene and Quaternary sediments, Yermak Plateau, Arctic Ocean (ODP Site 911)

In this study, the clay and heavy mineral analysis of ODP Site 911 sediments is used to investigate the sources and transport mechanisms (sea ice and oceanic currents) of sediments in the Arctic Ocean during the Mid to Late Pliocene (3.10–2.78 Myr) and upper Quaternary (800 kyr to the present). The time period between 3.10 and 3.00 Myr is characterized by a decreasing smectite and increasing illite content, which is interpreted as reflecting cooling conditions. At the beginning of the Mid‐Pliocene Global Warmth period at ∼3.00 Myr, the smectite content shows an abrupt increase. This change can also be seen as a drop in the amount of kaolinite and TOC. After 3.00 Myr the kaolinite and TOC values start to increase, probably indicating high rates of reworked glacially eroded matter. During the Pleistocene, smectite shows a lower and illite a higher fluctuation level compared with the Pliocene. This might be due to reigning glacial conditions during the Pleistocene, when the freshwater input was much lower than during the Pliocene. During the Pliocene, the fluctuating heavy minerals might reflect changes in freshwater input from the great Siberian rivers, which would have led to changes in the supply of terrigenous material delivered to the shelf by the rivers. The heavy mineral fluctuation also reflects changes in the amount of sea‐ice formation, which correlates with climate variations and the freshwater input from the continent. Based on the composition of the clay and heavy mineral groups in this study, the most likely transportation path is the Siberian branch of the Transpolar Drift.

Late Quaternary changes in depositional processes along the western margin of the Indus Fan

Detailed sedimentological, geochemical and isotopic analyses were carried out on sediment samples from ODP Site 720A on the Indus Fan, Arabian Sea. High values of calcium carbonate associated with low values of Al and Ti from 0 to 375 ka, and low values of calcium carbonate along with high values of Al and Ti from 375 to 525 ka represent two distinct sedimentary sequences. The sediments deposited from 525 to 375 ka correspond to a turbidite sequence, characterized by a high terrigenous input of coarse-grained sediments composed mostly of sand and silt. The sediments deposited from 375 ka to the present day comprise a pelagic sequence, consisting of pelagic material and clay. The major turbidity flow between 375 and 525 ka resulted in the greatest development of the Indus Fan during the late Quaternary. Most of the active channels were buried by 375 ka, followed by deposition of mainly pelagic sequences since then. Enrichment of an Indus-derived Himalayan clay mineral assemblage (illite and chlorite) in both the turbiditic and pelagic sequences reveals that the source and supply of clay minerals to the Indus Fan were the same during pre- and post-turbidite deposition. At ODP Site 720A, Al, Ti and terrigenous material do not show any systematic changes with respect to glacial and interglacial periods, suggesting that sea-level changes are not directly responsible for the terrigenous material supply to this site. Rather, a major switch in distributary channels away from the western margin of the Indus Fan is suggested.

Climate cyclicity in late Holocene anoxic marine sediments from the Seymour–Belize Inlet Complex, British Columbia

An 8.72 m late Holocene sediment core (VEC02A07) obtained from Alison Sound in the Belize–Seymour Inlet Complex of central British Columbia, Canada was deposited between ∼ 3500–1000 yr BP under primarily anoxic marine conditions. This core contains a detailed cyclic record of land–sea interactions as evidenced by significant fluctuations in marine primary productivity and changes in the supply of terrigenous material that can be related to long term variation in the relative influence of the Aleutian Low (AL) and North Pacific High (NPH). Sedimentologically, the core is characterized by alternating intervals of fine-grained massive intervals (70%), laminated intervals (23%), turbidites (5%) and graded silt–clay layers (2%). The laminated intervals are comprised of couplets that vary between light-coloured, diatom-rich layers, deposited primarily during the summer months, and dark-coloured, mineral-rich layers deposited during winter. Laminated couplets are most common in portions of the core deposited between ∼ 3150 and 2700 yr BP, which corresponds to an episode of regional neoglaciation. Time-series analysis was carried out on high-resolution particle size measurements obtained from core sub-samples and on sediment grey-scale colour variability derived from X-ray scans of the core. Non-linear time-series analyses revealed that the succession of massive and laminated sedimentation displayed characteristics of self-organization following a power law relationship for core length segments of < 13 cm (< ∼ 50 years of deposition). Wavelet and spectral time-series analysis indicated that core length segments of > 13 cm (> ∼ 50 years of deposition) contained evidence of sedimentary depositional cycles of ∼ 70–96, 135–155 and 250–330 years that reflect changes in AL and NPH mediated regional precipitation patterns that can in turn be related to larger-scale climate drivers such as the Pacific Decadal Oscillation (PDO) or solar irradiance cyclicity.

Biological productivity, terrigenous influence and noncrustal elements supply to the Central Indian Ocean Basin: Paleoceanography during the past ∼ 1 Ma

A 2m-long sediment core from the siliceous ooze domain in the Central Indian Ocean Basin (CIOB; 13‡03′S: 74‡44′E; water depth 5099m) is studied for calcium carbonate, total organic carbon, total nitrogen, biogenic opal, major and few trace elements (Al, Ti, Fe, K, Mg, Zr, Sc,V, Mn, Cu, Ni, Zn, Co, and Ba) to understand the productivity and intensity of terrigenous supply. The age model of the sediment core is based on U-Th dating, occurrence of Youngest Toba Tuff of ∼ 74 ka and Australasian microtektites of ∼ 770 ka.Low carbonate content (< 1%) of sediment core indicates deposition below the carbonate compensation depth. Organic carbon content is also very low, almost uniform (mean 0.2 wt%) and is of marine origin. This suggests a well-oxygenated bottom water environment during the past ∼ 1100ka. Our data suggest that during ∼ 1100 ka and ∼ 400 ka siliceous productivity was lower, complimented by higher supply of terrigenous material mostly derived from the metasedimentary rocks of High Himalayan crystalline. However, during the last ∼ 400 ka, siliceous productivity increased with substantial reduction in the terrigenous sediment supply. The results suggest that intensity of Himalayan weathering, erosion associated with monsoons was comparatively higher prior to 400 ka. Manganese, Ba, Cu, Ni, Zn, and Co have around 90% of their supply from noncrustal (excess) source and their burial to seafloor remained unaffected throughout the past ∼ 1100 ka.

Evolution of geochemistry and depositional settings of Early Palaeozoic siliciclastics of the Barrandian (Teplá-Barrandian Unit, Bohemian Massif, Czech Republic)

Cambrian and Ordovician-Middle Devonian sequences of two successive Early Palaeozoic basins of the Barrandian unconformably overlie Cadomian basement in the Bohemian Massif NW interior (Tepla-Barrandian unit) which is the easternmost peri-Gondwanan remnant within the Variscides. Correlation of stratigraphy and geochemistry of the Early Palaeozoic siliciclastic rocks elucidated sediment provenances. Sandstones of the Middle Cambrian Přibram-Jince Basin were derived from a Cadomian Neoproterozoic island arc. The source area of the Ordovician shallow-marine siliciclastics of the successor Prague Basin is a dissected Cadomian orogen. Late Cambrian acid volcanics of the Barrandian and Cambrian (meta)granitoids emplaced in the W part of the Tepla-Barrandian Cadomian basement are also discernible in these sediments. Old sedimentary component increased during the Ordovician. Early Llandovery siliciclastic rocks show characteristics of an abruptly weakened supply of terrigenous material and an elevated proportion of synsedimentary basic volcanics as a result of Silurian transgression. Emsian siliciclastics (intercalated in the Late Silurian to Early Devonian limestone suite) presumably comprise an addition of coeval basic/ultrabasic volcaniclastics. Middle Devonian flysch-like siliciclastics indicate reappearance of Cadomian source near the Barrandian during early Variscan convergences of Armorican microplates that preceeded accretion of the Tepla-Barrandian unit within the Bohemian Massif terrane mosaic.

Sediment-magnetic signature of land-use and drought as recorded in lake sediment from south-central Minnesota, USA

Sediment magnetic properties of a short core from Sharkey Lake, MN, record the effects of Euroamerican settlement and climate change over the last 150 yr. The onset of European-style farming led to increased erosion, reflected in high values of concentration-dependent parameters such as magnetic susceptibility (ĸ), Isothermal Remanent Magnetization (IRM), and Anhysteretic Remanent Magnetization (ARM). These high values are only partially due to increased supply of terrigenous material to the lake, and recent sediment contains an additional component of authigenic fine (single-domain) magnetite, most likely magnetosomes from magnetotactic bacteria. High organic productivity in the lake during the 1920s to 1940s drought increased this authigenic component resulting in highly magnetic fine-grained sediment. A comparison with older Holocene sediment from the same lake shows that, over time, most of the fine magnetic signal is lost after deposition, leading to decreases in magnetization and a bimodal grain size distribution of ultrafine, superparamagnetic grains and coarser multidomain particles, evident from measurements of ARM/IRM ratios, hysteresis measurements, and low-temperature analyses. The effects of dissolution and the superposition of climate and land-use signals complicate the use of recent sediments as modern analogs for sediment magnetic analyses.

On the significance of sea-level variations and shelf paleo-morphology in governing sedimentation in the southern South China Sea during the last deglaciation

Deglacial sedimentation on the outer Sunda Shelf, the shelf margin and slope shows a close correlation with the stages of flooding of the emerged shelf. It is mainly controlled by the relationship between shelf paleo-physiography and changes in sea level and sediment supply. Based on the sedimentological and geochemical variability at five sites along a transect across the outer shelf and the continental slope covering the last 20 000 years, four intervals of significant depositional changes are identified. The first reorganization in the sedimentation regime, which was established during sea-level lowstand, is associated with the drowning of the lower course of the North Sunda River between 16.5 and 14.5 ka. During and following the rapid rise in sea level at 14.5–14 ka, sedimentation on the slope is characterized by an accelerated decrease in the supply of terrigenous material, associated with the flooding of the middle part of the paleo-valley. This abrupt change in sedimentation is followed by a period of gradual decrease of terrigenous supply to the slope, when the surrounding plains of the river valley were flooded (14–8.5 ka). The final change occurred between ca. 8.5 and 6 ka, when the coastline reached its modern position, and modern sedimentary patterns are established. This change probably marks the end of reworking by transgression. Given the synchroneity of sedimentological changes along the transect across the Sunda Shelf and into the deep sea with the environmental shifts on the central shelf, sedimentation on the margin and slope appears to be mainly controlled by the interrelationship of sea level, shelf paleo-physiography and sediment supply. Moreover, the records display lateral changes through time associated with stages of the deglacial transgression, which mask any potential sedimentological variability due to changes in precipitation, vegetation or atmospheric circulation. This fact cautions the interpretation of near-shore sedimentary records as unequivocal recorders of local climate change (e.g. SE Asian monsoon), and highlights the need to include variations in shelf physiography and sea level in future paleoceanographic studies.

Rock fragments from mud volcanic deposits of the Gulf of Cadiz: an insight into the Eocene–Pliocene sedimentary succession of the basin

Two hundred clasts from the mud breccia extruded by the Yuma mud volcano in the Gulf of Cadiz are used to establish an offshore stratigraphy. The clasts are a very complex mixture of material from the sedimentary successions through which the mud volcano erupted and provide important information about the composition and genesis of deep-seated strata. We deal with fragments of rocks that were deposited millions of years ago, subsequently buried and later erupted on to the seafloor. Rock fragments from the mud breccia, studied in thin section under a polarizing microscope, provide genetic indications suggestive of deep-sea conditions during the accumulation of strata. A reconstruction of the sedimentary succession through which the Yuma mud volcano erupted and the depositional evolution of the Gulf of Cadiz was made on the basis of lithology and age determinations of the rock. Age and depositional environment documented by the clasts indicate that a marine basin existed in the Gulf of Cadiz area at least from the Eocene, and that in the Early and Middle Eocene a deep-sea fan depositional environment prevailed in the region, resulting in the accumulation of thick turbidites. The Late Eocene and Oligocene are not represented among rock fragments from the mud breccia, suggesting regional uplift and non-deposition in the area. Sedimentation was re-established in the Miocene with the accumulation of a clayey Aquitanian–Burdigalian succession. Pelagic carbonate sedimentation became predominant in the Langhian time. The Serravallian–Early Tortonian is characterized by a high supply of terrigenous material, resulting in the deposition of turbiditic clays and sands. Shallow water sedimentation with accumulation of carbonate rocks prevailed in the basin during the Middle Tortonian.