Turbidite Deposits Research Articles

Geology and Oil and Gas Bearing Potential of the East Canadian Continental Margin

Within the East Canadian continental margin, three oil and gas bearing regions have been identified from north to south: the Labrador Sea shelf, the margin of the Grand Banks of Newfoundland, and the Nova Scotia continental margin. In each of these regions, a number of sedimentary basins are distinguished and completely submerged. The following large sedimentary basins are distinguished on the Labrador Sea shelf: the Saglek, Hopdale, and Havke; on the margin of the Grand Banks of Newfoundland, the following basins are known: the Jeanne d’Arc, Flemish Pass, and Orphan. The Scotian Shelf distinguishes the Nova Scotia and Sable basins. It is noteworthy that at high latitudes, such as the Labrador Sea region, the age of productive sediments begins with more ancient rocks (since the Paleozoic) than in the basins to the low latitude (since the Mesozoic), due to which the stratigraphic range of oil and gas bearing in the high latitude basins is much wider. The oil and gas bearing potential in the entire region is mainly related to the continental slopes and turbidite deposits occurring within them. Late Jurassic and Early Cretaceous reservoirs will be the target sediments during deep drilling. Widespread Late Cretaceous and Early Tertiary formations with oil and gas potential are quite realistic, since they do not lie at deep horizons. The oil and gas bearing potential on the margins of basins is associated with Late Cretaceous and Tertiary sediments, alluvial fan deposits, and salt diapirs.

Discovery and prediction of high natural gamma sandstones in Chang 73 Submember of Triassic Yanchang Formation in Ordos Basin, China

The large scale development of high natural gamma sandstones has been discovered in the Chang 73 Submember of the Triassic Yanchang Formation in the Ordos Basin, China. High natural gamma sandstones consist of terrigenous detrital rocks with particle sizes ranging from silt to sand. They represent turbidite deposits characterized by high gamma ray values that are more than 180 American Petroleum Institute (API) units on a natural gamma ray log profile. For a long time, very high natural gamma sandstones had been identified as high-quality source rocks, such as oil shales, from conventional well log profiles, such as natural gamma ray well logs. Therefore, predicting the distribution of high natural gamma sandstones was studied. The sedimentary, lithological, and well log characteristics, as well as the genesis of the high radioactivity of high natural gamma sandstones were analyzed in the Chang 73 Submember. Thorium (Th), uranium (U) and other radioactive elements were found, carried by deep hydrothermal activity, and probably resulted in the formation of a relatively high radioactive zone in the cross-section, where high natural gamma sandstones usually develop in large quantities. This caused many turbidite sand bodies, which should have a continuous distribution in the cross-section, to appear to have a discontinuous distribution, when using conventional well log profiles, such as natural gamma ray well logs. From the above mentioned apparent discontinuous distribution of turbidite sand bodies in the cross-section, a continuous distribution can be predicted. It is obvious that the prediction of areas of continuous turbidite sand bodies in the cross-section usually corresponds with areas where high natural gamma sandstones are developed in large quantities. Exploration and development practice demonstrated that the developed method is fast and effective in predicting high natural gamma sandstones in the Chang 73 Submember.

Characteristics of Authigenic Minerals around the Sulfate-Methane Transition Zone in the Methane-Rich Sediments of the Northern South China Sea: Inorganic Geochemical Evidence.

Sediments at marine cold seep areas provide potential archives of past fluid flow, which allow insights into the evolution of past methane seepage activities. However, signals for anaerobic oxidation of methane (AOM) might be obscured in bulk sediments in cold-seep settings due to several factors, especially flood and turbidite deposition. Comprehensive inorganic data were gathered in this study to explore the availability of related records at cold seeps and to provide insights into the evolution of past methane seepage activities. Sediments collected from the site 973-4 in the Taixinan Basin on the northern slope of the South China Sea were characterized in terms of total carbon and sulfur, δ13C values of total organic carbon (δ13CTIC), δ34S values of chromium reducible sulfur (δ34SCRS), and foraminiferal oxygen and carbon isotopes. The results confirmed a strong correlation between formation of authigenic minerals and AOM. Moreover, the 34S enrichments and abundant chromium reducible sulfur (CRS) contents in the authigenic sulfides in the sulfate–methane transition zone (SMTZ) within 619–900 cm below seafloor (cmbsf) reflected past high methane fluxes supported by constant methane seepages. Lithological distribution and AMS (Accelerator Mass Spectra) 14C dating of planktonic foraminifera show that the turbidite (~35.14 ka) was related to a foraminifera-rich interval (Unit II: 440-619 cmbsf) and increased carbonate productivity during the last glacial maximum (LGM). Enrichment of Mo and U was observed accompanied by low contents of nutrient metals (Al, Ti, V, Ni, Fe, Mn, and Cu) in Unit II. The foraminifera-rich interval (Unit II) of cold seep sediments was probably linked to the phenomenon of inconsecutive sedimentary sequence due to the turbidites, which resulted in the lack of Fe, Mn, and Ba enrichment. There is no U enrichment but only Mo enrichment within Unit III, which might be related to H2S produced by AOM during the methane seepages. Based on the above results, it can be speculated that this area has experienced multiple-episodes of methane seep events. Further exploration of AOM should focus on the risks of rapid deposition, especially the impact of turbidity current on sediments.

Key evidence for distal turbiditic- and bottom-current interactions from tubular turbidite infills

Infilling of trace fossils can serve as a proxy for sediment otherwise missing from basin deposits. The Petra Tou Romiou section (southern Cyprus) includes calcilutite/calcarenite material that represents deep-marine deposits of Eocene age. Lateral and vertical variation indicates pelagic, gravitational, and bottom-current processes simultaneously influencing sedimentation. Detailed ichnological analysis resolved interactions between these deep-marine sedimentary processes in this distal marine setting. Calcarenite turbiditic beds occur as well-preserved and continuous tabular beds that disappear laterally. In some cases, trace fossils infilled with calcarenitic material are termed tubular turbidites. These structures correspond to actively filled Planolites formed in softground conditions and infilled by calcarenitic sediment interpreted as the record of missing turbiditic deposits when calcarenite turbiditic beds disappeared due to erosion. The variable preservation of calcarenite turbidite beds along with the presences of tubular turbidites indicate rapid erosion following turbidite deposition and post-depositional reworking of turbidites by bottom-currents. A refined interpretation of tubular turbidites can help constrain sedimentary processes that form deep-marine deposits and as such, has considerable paleoceanographic and economic implications.

Response of unconfined turbidity current to deep‐water fold and thrust belt topography: Orthogonal incidence on solitary and segmented folds

AbstractSea‐floor topography of deep‐water folds is widely considered to have a major impact on turbidity currents and their depositional systems, but understanding the flow response to such features was limited mainly to conceptual notions inspired by small‐scale laboratory experiments. High‐resolution three‐dimensional numerical experiments can compensate for the lack of natural‐scale flow observations. The present study combines numerical modelling of thrusts with fault‐propagation folds by Trishear3D software with computational fluid dynamics simulations of a natural‐scale unconfined turbidity current by MassFlow‐3D™ software. The study reveals the hydraulic and depositional responses of a turbidity current (ca 50 m thick) to typical topographic features that it might encounter in an orthogonal incidence on a sea‐floor deep‐water fold and thrust belt. The supercritical current (ca 10 m sec−1) decelerated and thickened due to the hydraulic jump on the fold backlimb counter‐slope, where a reverse overflow formed through current self‐reflection and a reverse underflow was issued by backward squeezing of a dense near‐bed sediment load. The reverse flows were re‐feeding sediment to the parental current, reducing its waning rate and extending its runout. The low‐efficiency current, carrying sand and silt, outran a downslope distance of >17 km with only modest deposition (<0·2 m) beyond the fold. Most of the flow volume diverted sideways along the backlimb to surround the fold and spread further downslope, with some overspill across the fold and another hydraulic jump at the forelimb toe. In the case of a segmented fold, a large part of the flow went downslope through the segment boundary. Preferential deposition (0·2 to 1·8 m) occurred on the fold backlimb and directly upslope, and on the forelimb slope in the case of a smaller fold. The spatial patterns of sand entrapment revealed by the study may serve as guidelines for assessing the influence of substrate folds on turbiditic sedimentation in a basin.

Sedimentation Process of Rambatan Formation in Larangan Brebes, North Serayu Range, Central Java

DOI:10.17014/ijog.6.2.141-151Rambatan Formation in the western part of North Serayu Basin, Brebes, Central Java, comprises generally flysch facies of turbidite sediments deposited in a deep marine environment. This formation is equivalent to Merawu Formation found in the eastern part of the basin and deposited in the environment of tidal flat to subtidal. The turbidite sediments were highly controlled by a rapid downward movement taking place continuously during Early to Late Miocene. The variation of the depositional environment has been the object of this research which aims to understand the sedimentation process of Rambatan Formation in this type locality with a modern turbidite approach. Rambatan Formation was deposited in N13-N19, as a deep marine sediment channel, turbidite, and deep marine tidal zone. The sedimentation was affected by gravity flow and contourite. The sediments on N13-N14 were marked by turbidite sediments until Middle N17. The sediment supply increased on Middle N17, as a sediment filler on a channel marked by contourite mud layer (muddy slump) and debris flow, with sources from the north. The increase of sediment supply was followed by an environmental transformation from a deep marine channel into deep marine tidal area. In N19, the sediments were redeposited as turbidite sediment, starting with debris flow in Middle N18.

A late Pleistocene sedimentation in the Indus Fan, Arabian Sea, IODP Site U1457

AbstractThe intensity of turbidite sedimentation over long timescales is driven by sea-level change, tectonically driven rock uplift and climatically modulated sediment delivery rates. This study focuses on understanding the effect of sea-level fluctuations and climatic variability on grain-size variations. The grain size and environmental magnetic parameters of Arabian Sea sediments have been documented using 203 samples, spanning the last 200 ka, obtained from International Ocean Discovery Program (IODP) Site U1457. Grain-size end-member modelling suggests that between ~200 and 130 ka there was an increase in the coarse silt fraction caused by sediment transport following reworking of the Indus Fan and development of deep-sea canyons. The sediment size and enhanced magnetic susceptibility indicate a dominant flux of terrestrial sediments. Sedimentation in the distal Indus Fan atc. 200–130 ka was driven by a drop in sea level that lowered the base level in the Indus and Narmada river systems. The low sea-stand caused incision in the Indus delta, canyons and fan area, which resulted in the transportation of coarser sediment at the drilling site. Magnetic susceptibility and other associated magnetic parameters suggest a large fraction of the sediment was supplied by the Narmada River during ~200–130 ka. Since ~130 ka, clay-dominated sedimentation is attributed to the rise in sea level due to warm and wet climate.

OH defects in quartz as a provenance tool: Application to fluvial and deep marine sediments from SW Japan

Hydrogen-related point defects (OH defects) in the crystal lattice of detrital, monocrystalline quartz have been proposed as an indicator to distinguish different sediment sources, making it a potential tool for provenance analysis. This study tests this novel technique on samples from SW Japan by comparing the results of OH defect analyses with those of “classical” provenance studies. OH defects of 188 detrital, monocrystalline quartz grains from five rivers (Fuji, Tenryu, Nagara, Yoshino, and Shimanto) and four offshore wells drilled in the Nankai Trough area (ODP site 1177; IODP sites C0002, C0007, C0012) are characterized using Fourier-transform infrared (FTIR) spectroscopy. Considerable differences in OH defect concentrations are identified between individual river samples. A general increase of values from east to west is observed. Possible links to the respective source geology are established. Very low OH defect contents (<1 wt. ppm water) of sediment from the Fuji and Tenryu rivers may be a result of high deformation and exhumation in the Izu-Honshu collision zone. Moderate to high OH defect contents of Nagara and Yoshino river samples (up to 50 wt. ppm water) are similar to the values of the global average in continental crust, possibly due to a mixing of various source lithologies. High and very diverse OH defect contents of Shimanto River sediments (up to 211 wt. ppm water) are likely an effect of extensive sediment reworking and mixing in the Nankai accretionary wedge. The OH defect signal is shown to be traceable through the offshore sedimentary record. In the western Shikoku Basin (ODP site 1177), turbidite deposits at 15 Ma and 7 Ma show a very similar signal as recent Shimanto river sediment, whereas eastern Shikoku Basin sediments (IODP Site C0012), at 15 Ma and 6 Ma strongly resemble present day Nagara and Yoshino river sediments. Sediments deposited in the Nankai trench wedge at 1 Ma (IODP Site C0007) indicate a shift towards lower OH defect concentrations. This may be due to increased, trench parallel sediment flux from the low-OH defect Fuji and Tenryu river sources, as proposed by previous studies. This study presents the first OH defect dataset in detrital quartz from rivers and offshore drill sites in a subduction zone environment, introducing OH defects as a new useful tool for sediment provenance analysis in active convergent margin settings.

Conceptual model of the \u015eav\u015fat (Artvin/NE Turkey) Geothermal Field developed with hydrogeochemical, isotopic, and geophysical studies

The Şavşat (Artvin, Turkey) Geothermal Field (ŞGF) is located on the northeastern border of Turkey. This field is characterized by thermal and mineralized springs and travertine. The temperature of the thermal water is 36 °C, whereas that of the mineralized spring in the area is approximately 11 °C. The Na–HCO3–Cl-type thermal water has a pH value of 6.83 and an EC value of 5731 µS/cm. The aim of this study is to characterize the geothermal system by using geological, geophysical, and hydrogeochemical data and to determine its hydrochemical properties. A conceptual hydrogeological model is developed for the hydrogeological flow system in the ŞGF. According to the hydrogeological conceptual model created by geological, geophysical, and hydrogeochemical studies, the reservoir comprises volcanogenic sandstone and volcanic rocks. The cap rock for the geothermal system is composed of turbiditic deposits consisting of mudstone–siltstone–sandstone alternations. An increase in the geothermal gradient is mainly due to Pleistocene volcanic activity in the field. The isotopic values of thermal water (δ18O, δ2H, δ3H) indicate a deeply circulating meteoric origin. The estimated reservoir temperature calculated by silica geothermometers is 100–150 °C, and the mixing rate of cold groundwater with geothermal waters is approximately 70%. It may be possible to obtain warmer fluids from a 300-m-deep borehole cutting through a fracture zone identified by geophysical studies. Heating by conduction via the geothermal gradient resulting from young volcanic activity drives geothermal waters upwards along faults and fractures that act as hydrothermal pathways. The positive δ13CVPDB value (+ 4.31‰) indicates a metamorphic origin for the thermal water. The 34SCDT value (~ 10‰) shows that the sulfur in the geothermal water is derived from volcanic sulfur (SO2).

Micro‐fabrics and Genesis of Pyrite from Zhaoyuan Golden Deposits in Shandong Province, North China

AbstractNorth China Craton experienced significant lithospheric destruction or delamination during the Late Mesozoic, accompanied with the emergence of numerous basins and intensive volcanic activities. Extensional basins also formed in eastern Shandong Province. Even though they have been researched for decades, the relation between basin development and deep tectonic processes still remains obscure. Recently, a set of Early Cretaceous strata, characterized by translating from turbidite deposits to terrestrial strata unit and ending up with a unique volcanicalstic formation within a pretty short time span, has been found on Lingshan Island. Previous Studies have reached an agreement that Lingshan Island strata was formed in a distinct sedimentary background compared with the coeval sedimentary units in Jiaolai Basin. Essential information about basin development and its tectonic setting in the region during Early Cretaceous are preserved in the Lingshan Island strata. In this article, we show the characteristic of heavy mineral assemblage from the bottom to the top, and the characteristic of detrital minerals’ chemical component in the two representative samples. Based on these new works, we indicate that the Lingshan Island basin was developed in transpressional tectonic setting with complex provenance materials mainly from Qianliyan‐Uplift during the period ca.123∼120Ma. Then, the basin evolved within a extensional region and filled with locally derived clastics during 120 to 105Ma. Additionally, the basin was evolved during the procedure of progressive lithospheric thinning and asthenosphere upwelling, which could be proven by stratigraphic characteristics and chemical component of detrital spinels.

Lithofacies characterization of gas hydrate prospects discovered during the National Gas Hydrate Program expedition 02, offshore Krishna-Godavari Basin, India

Abstract Lithofacies of host sediments associated with gas hydrate reservoirs may have a significant influence on the formation of hydrates. The type of sediments and the depositional processes responsible for the gas hydrate-bearing sediments along the eastern margin of the India have been studied by integrating core data and logging-while-drilling downhole logs. Borehole data correlated with seismic data were used for the interpretation of geological process responsible for gas hydrate formation. The acquired seismic profiles were correlated with the downhole logs by identifying the shape of the well logs curves that indicate finning up and blocky patterns. Turbidite sands and debris flows were also identified from the log and core sediment studies. This study identified two prominent types of depositional systems: (1) turbidity currents and (2) debris flows were mainly responsible for the deposition of gas hydrate-bearing reservoirs in the study area. Based on these studies two well-developed gas hydrate systems have been identified in the Krishna-Godavari Basin and hydrates were determined to be distributed mostly in sand dominated facies. Fine-grained sand in the identified turbidite deposits were shown to be a good hydrate reservoir. The hydrate-bearing sediments in the central part of the Krishna-Godavari Basin (Area C in D6 block) consist of mostly debris flows, which is consistent with scattered gravel- and sand/silt-sized grains in channel-levee systems.

Using foraminiferal test-size distribution and other methods to recognise Quaternary bathyal turbidites and taphonomically-modified faunas

Abstract The aim of this study was to develop a simple methodology using foraminifera to distinguish between sediment that has been displaced downslope (as in a turbidity current) and in-situ hemipelagic sediment. These same methods will also be useful to identify seafloor foraminiferal faunas that have suffered considerable taphonomic modification (e.g., through dissolution, winnowing, mixing), which render them unsuitable as modern analogues for paleoenvironmental reconstructions. To help develop this methodology we used Late Quaternary samples from cores containing identified turbiditic sand-mud couplets that had been deposited at lower bathyal to upper abyssal depths (1400–3000 m) off the earthquake-prone east coast of New Zealand. Comparison of the proportions of the total planktic and benthic foraminiferal tests in each of three size categories (63–125 μm, 125–250 μm, >250 μm) with those in unmodified, in-situ modern bathyal faunas from off New Zealand showed an increased proportion of larger tests in the lower sandy turbidite layers and a slight increase of smaller tests in the upper muddy layers presumably as a result of winnowing processes during deposition. A regression formula was used to estimate depositional depths based on the relative abundance of planktics in the Quaternary foraminiferal faunas (>63 μm). In all but one of our core samples, these depth estimates were considerably shallower than the cores' present depth and suggested that most sediment (both sand and mud) had been transported downslope. Modern Analogue Technique (MAT) was used to estimate depths of deposition of the core samples based on a modern benthic foraminiferal dataset (>63 μm) from around New Zealand. There was no great difference between estimates based on species % and on genus %. Some MAT depth estimates were inconsistent with those from the other foraminiferal and sedimentological proxy methods that suggested turbiditic displacement. Because of the inconsistent results and the much greater work required to acquire the species census data we exclude the MAT method from our suggested methodology. Genera were lumped into groups with similar bathymetric range and the relative abundances of these groups in each core sample were used to infer sediment provenance and mixing during downslope transport. We recommend a methodology using three elements: Test size distribution, planktic percentage, and relative abundance of bathymetric groups of benthic genera. The first two require the least amount of work and can reliably identify the majority of displaced and taphonomically-modified faunas. The third requires some taxonomic skills to identify key genera but gives more information on the provenance depth and amount of mixing in displaced turbiditic sediment. Although developed using New Zealand modern and Late Quaternary foraminiferal data, we contend that these methods should be applicable for use throughout most of the Neogene in other temperate and subtropical parts of the world's oceans. Before use elsewhere, studies in the local region may be needed to test, recalibrate and tweak the modern analogue data on local test-size distribution and planktic percentage. Our study also suggests that these methods can be useful to identify seafloor foraminiferal faunas that have suffered considerable taphonomic modification (e.g., through dissolution, winnowing, mixing), which render them unsuitable as modern analogues for paleoenvironmental reconstructions.

Perkembangan Fasies Sedimen Formasi Mamberamo Berumur Miosen Akhir-Pliosen di Cekungan Papua Utara

North Papua Basin is a fore arc basin located in northern coastal of Papua Island. This basin filled by Middle-Upper Miocene turbidite sediment and overlied by Upper Miocene – Quarternary clastic sediment. Upper Miocene – Quaternary clastic sediments (Mamberamo Formation) composed by interbedding conglomerate, sandstone and shale as molasses deposit. A detailed stratigraphic study was performed to identify facies and its association of the Mamberamo Formation to that give a new perspective on the characteristics and development of facies succession of Lower Mamberamo Formation. Result shows that the Lower Mamberamo Formation consists of three facies: A) cross bedding sandstone (subtidal), B) heterolothic silty shale (intra-tidal), C) carbonaceous shale (supra-tidal) deposited on Late Miocen to Plio-Pleistocene during centra range orogeny (syn-orogeny) as molasses deposits.Keywords: Fore arc basin, North Papua Basin, Mamberamo Formation, molasse deposits.

Perkembangan Fasies Sedimen Formasi Mamberamo Berumur Miosen Akhir-Pliosen di Cekungan Papua Utara

North Papua Basin is a fore arc basin located in northern coastal of Papua Island. This basin filled by Middle-Upper Miocene turbidite sediment and overlied by Upper Miocene – Quarternary clastic sediment. Upper Miocene – Quaternary clastic sediments (Mamberamo Formation) composed by interbedding conglomerate, sandstone and shale as molasses deposit. A detailed stratigraphic study was performed to identify facies and its association of the Mamberamo Formation to that give a new perspective on the characteristics and development of facies succession of Lower Mamberamo Formation. Result shows that the Lower Mamberamo Formation consists of three facies: A) cross bedding sandstone (subtidal), B) heterolothic silty shale (intra-tidal), C) carbonaceous shale (supra-tidal) deposited on Late Miocen to Plio-Pleistocene during centra range orogeny (syn-orogeny) as molasses deposits.Keywords: Fore arc basin, North Papua Basin, Mamberamo Formation, molasse deposits.

Perkembangan Fasies Sedimen Formasi Mamberamo Berumur Miosen Akhir-Pliosen di Cekungan Papua Utara

North Papua Basin is a fore arc basin located in northern coastal of Papua Island. This basin filled by Middle-Upper Miocene turbidite sediment and overlied by Upper Miocene – Quarternary clastic sediment. Upper Miocene – Quaternary clastic sediments (Mamberamo Formation) composed by interbedding conglomerate, sandstone and shale as molasses deposit. A detailed stratigraphic study was performed to identify facies and its association of the Mamberamo Formation to that give a new perspective on the characteristics and development of facies succession of Lower Mamberamo Formation. Result shows that the Lower Mamberamo Formation consists of three facies: A) cross bedding sandstone (subtidal), B) heterolothic silty shale (intra-tidal), C) carbonaceous shale (supra-tidal) deposited on Late Miocen to Plio-Pleistocene during centra range orogeny (syn-orogeny) as molasses deposits.Keywords: Fore arc basin, North Papua Basin, Mamberamo Formation, molasse deposits.

Perkembangan Fasies Sedimen Formasi Mamberamo Berumur Miosen Akhir-Pliosen di Cekungan Papua Utara

North Papua Basin is a fore arc basin located in northern coastal of Papua Island. This basin filled by Middle-Upper Miocene turbidite sediment and overlied by Upper Miocene – Quarternary clastic sediment. Upper Miocene – Quaternary clastic sediments (Mamberamo Formation) composed by interbedding conglomerate, sandstone and shale as molasses deposit. A detailed stratigraphic study was performed to identify facies and its association of the Mamberamo Formation to that give a new perspective on the characteristics and development of facies succession of Lower Mamberamo Formation. Result shows that the Lower Mamberamo Formation consists of three facies: A) cross bedding sandstone (subtidal), B) heterolothic silty shale (intra-tidal), C) carbonaceous shale (supra-tidal) deposited on Late Miocen to Plio-Pleistocene during centra range orogeny (syn-orogeny) as molasses deposits.Keywords: Fore arc basin, North Papua Basin, Mamberamo Formation, molasse deposits.

The Early Cretaceous sedimentary‐tectonic attributes of Lingshan Island Basin, East Shandong Province, China: Constraints from the chemical compositions of detrital heavy minerals

North China Craton experienced significant lithospheric destruction or delamination during the Late Mesozoic, accompanied with the emergence of numerous basins and intensive volcanism. Extensional basins also formed in East Shandong Province. Even though they have been studied for decades, the relationship between basin development and tectonic processes still remains obscure. Recently, a set of Early Cretaceous strata has been found in Lingshan Island. It is characterized by translating from turbidite deposits to terrestrial strata units and ending up with a unique volcaniclastic layer within a relatively short time span. Previous studies have reached an agreement that Lingshan Island strata are formed in a distinct sedimentary background compared with the coeval sedimentary units in Jiaolai Basin. Essential information about basin development and its tectonic setting in this region during Early Cretaceous are preserved in Lingshan Island strata. In this study, it shows the characteristics of heavy mineral assemblage and the characteristics of detrital minerals' chemical component in the two representative samples. Based on these studies, it indicates that Lingshan Island Basin was developed in a transpressional tectonic setting with complex source materials, mainly from Qianliyan Uplift during the period ca. 123–120 Ma. Then, the basin evolved within an extensional setting and was filled with locally derived clastics during 120 to 105 Ma. In addition, the basin evolved during the process of progressive lithospheric thinning and asthenosphere upwelling.

Turbidite deposition and diagenesis in the southwestern Black Sea: Implications for biogeochemical cycling in an anoxic basin

The biogeochemical cycles of iron, phosphorus and sulfur are intimately linked and the fate of these elements is highly redox-dependent. Under anoxic conditions, iron is reduced to Fe(II), for an important part driven by reaction with sulfide. Reduction and sulfidation diminish the affinity of iron for phosphorus, thereby affecting sedimentary phosphorus retention. The coupled cycling of iron-phosphorus-sulfur as a function of redox conditions thereby helps control nutrient availability and primary productivity in marine systems. The Black Sea is the world's largest permanently stratified basin with a strong gradient from oxic surface waters to anoxic and strongly sulfidic deep waters, and is therefore well-suited to investigate redox-dependent changes in coupled iron-phosphorus-sulfur cycling. The presence of sulfide in the deep Black Sea alters the chemical speciation of iron (Fe) and phosphorus (P) in particulate matter in the water column and sediment. These alterations and their impact are poorly constrained for turbidites, which are deposits formed by mass transport from the continental slope into the deep basin of the Black Sea through turbidity currents. Here, we compare the geochemistry of sediments on the southwestern (SW) Black Sea slope overlain by oxygenated waters (234 m below sea surface, mbss) with that of a sediment record with turbidite intervals from the sulfidic SW deep basin (2169 mbss). The aims were to investigate the potential of SW slope sediment as source material for turbidites, and to assess the geochemical impact of reaction with sulfide. The bulk chemistry (Al, CaCO3, Fe) of the SW deep Black Sea turbidite intervals was similar to that of SW Black Sea slope sediments (234 m water depth), suggesting that the latter are source material for deep SW Black Sea turbidites. The source sediment is characterized by strong enrichments in highly reactive Fe(III) and Mn phases, high rates of sulfate reduction and the presence of methane. Similar total Fe contents in the slope and deep turbidite sediments suggest that Fe is efficiently retained in the sediment. In contrast, Mn is depleted during down-slope transport and P contents in the turbidite intervals are about 50% lower than in the slope sediment, indicating significant P release during and after turbidite deposition. Calculations using the obtained data and conservative estimates of the areal extent of turbidite deposition in the SW Black Sea indicate that turbidity currents have the potential to impact coupled Fe-P-S biogeochemical cycling by boosting Fe input, dissolved P accumulation, sulfide oxidation and FeS2 burial in the deep Black Sea.

Pre-1.94 to post-1.88 Ga sediment depositional environment and c. 1.94 Ga felsic magmatism in the Knaften area, northern Sweden

ABSTRACTThe Knaften area is situated in the northern part of the Bothnian Basin in the central Svecofennian province of Sweden. Sedimentary rocks are here conformably intercalated with mafic to intermediate volcanic rocks. The depositional environment in the south-eastern part of the Knaften area was syn-orogenic deep water where tectonic activity caused volcanism and faulting. Mass flow processes transported material down slope and formed turbidites and debris flow deposits. Later, two phases of deformation affected the supracrustal rocks. Detrital zircons in a turbiditic sedimentary rock gave ages between 2.07 and 1.88 Ga, and between 2.93 and 2.62 Ga, indicating a substantial Archean component. The 1.88 Ga maximum depositional age is coeval with those of other supracrustal successions in the region, e.g., the mainly sedimentary Härnö and Vargfors groups, as well as the mainly volcanic Skellefte and Arvidsjaur groups. Zircons in the Knaften granite and the Knaften porphyry dyke have U-Pb ages of 1939 ± 3 Ma and 1939 ± 4 Ma, respectively. They confirm previously poorly constrained 1.95–1.94 Ga ages for these rocks. The intrusions cross-cut the mafic to intermediate volcanic rocks that, by consequence, must be older than 1.94 Ga. The new zircon data thus point to an age difference of about 50 to 60 million years between the felsic magmatism and the deposition of the dated turbiditic sediments. The oldest volcanic rocks (pre-1.94 Ga) in the Knaften area are evidence of at least one additional depositional stage in the Svecofennian tectonic evolution.

Influence of an Upper Bathyal Whale-fall on Benthic Foraminifera of Monterey Canyon, California (USA)

Aremotely operated vehicle was used to sample a graywhale carcass five days after it was deployed at a depth of 382 m in Monterey Canyon, California. Visual observations of the whale-fall (Whale-382p) documented that it was in the first stage of decomposition (the “necrophage†stage), with abundant hagfish and amphipods surrounding the carcass. A 21-cm, lithologically consistent fine-grained push core was taken under the carcass and analyzed for benthic foraminifera. No endemic foraminiferal species were found at this site. Pseudoparrella pacifica dominated both the living and dead assemblages. A general trend of decreasing foraminiferal abundance and species richness among the living and dead faunas was evident downcore, although several intervals below 5 cm contained a higher-than-expected abundance, species richness, and estuarine or shelfal benthic foraminifera, suggesting deposition of distal turbiditic deposits at the core site which is a common occurrence in Monterey Canyon.Because the percentage abundance of living and dead specimens of P. pacifica were similar in the upper 5 cm of the core (89% and 82%, respectively), the whale-fall does not appear to have influenced the benthic foraminiferal assemblage after five days on the seafloor.