Deep Basin Sediments Research Articles

Disentangling the History of Deep Ocean Disposal for DDT and Other Industrial Waste Off Southern California.

Ocean disposal of industrial waste from technical DDT [mainly 1,1'-(2,2,2-trichloroethane-1,1-diyl)bis(4-chlorobenzene), or 4,4'-DDT] manufacture occurred historically in the Southern California Bight. However, the paucity of historical records highlights uncertainties as to the mode, location, and timing of disposal or ongoing ecological effects of these wastes. This study combines sampling, chemical analysis, and numerical modeling of deep San Pedro Basin sediments revealing substantial DDT contamination that extends at least 25 km from the mainland. These findings narrate bulk DDT waste disposal to the offshore that peaked in the 1950s, prior to the onset of formal regulations; was agnostic to later-designated disposal sites; and has experienced sluggish transformation. Our findings further indicate an attenuating secondary source for the DDT daughter product, 1-chloro-4-[2,2-dichloro-1-(4-chlorophenyl)ethenyl]benzene (4,4'-DDE), which still deposits into deep San Pedro Basin sediments. While demonstrating the severity of DDT contamination to the region, these findings further define the burial potential of DDT wastes and inform the past, present, and future contamination potential that is needed to understand and predict ecological consequences. This work also points firmly to bulk, not containerized, disposal of DDT waste and to potential alternative contents of collocated waste.

Age, genesis, and geological significance of Permian–Triassic boundary volcanic tuffs in the northeastern margin of South China

The Permian–Triassic boundary (PTB) volcanic tuffs are widely distributed in the East Palaeo‐Tethys region, but their age and origin have been controversial. The Permian–Triassic deep‐water sediments in the northeastern margin of South China are favourable research objects, and we report new results from the PTB deep basin sediments in the Susong area, Anhui Province, in this paper. Two volcanic tuffs are found in the Zuoshan PTB in the Zuoshan section, and Laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) U–Pb zircon dating indicates that the upper and lower tuffs are 251.3 ± 1.7 Ma and 252.3 ± 2.1 Ma, respectively. The PTB age is 251.6 Ma according to a numerical interpolation method of the average deposition rate of the PTB. Fusulinids and non‐fusulinid foraminifers in the limestone overlying the lower tuff define the rock as end‐Permian. Zircon trace elements show that both tuffs are sourced from felsic volcanism in continental arc background, and their source magmas were derived from the continental crust. Zircons of PTB age from the upper tuff on the bottom of the Triassic have negative εHf(t) value from −8.02 to −3.75, and the Palaeo‐Mesoproterozoic two‐stage model ages of 1502–1780 Ma, showing that their source rocks were only derived from the remelting of the Palaeo‐Mesoproterozoic continental crust. The zircons from the lower tuff on the top of the Permian show two types, including negative εHf(t) values from −6.48 to −1.25 and Palaeo‐Mesoproterozoic two‐stage model ages of 1350–1679 Ma, and positive εHf(t) values from +3.98 to +10.15, and Neoproterozoic two‐stage model ages of 629–1023 Ma, indicating that their sources were derived from the reworking of the Palaeo‐Mesoproterozoic continental crust and early Neoproterozoic depleted mantle joined in juvenile crust growth in the northern margin of the South China Block at the beginning of the collision between the South China and North China blocks. The initial collision started no later than 252.3 Ma and developed significantly from east to west.

Postglacial evolution of Lake Constance: sedimentological and geochemical evidence from a deep-basin sediment core

The modern, over 250-m-deep basin of Lake Constance represents the underfilled northern part of an over 400-m-deep, glacially overdeepened trough, which reaches well into the Alps at its southern end. The overdeepening was formed by repeated glacial advance-retreat cycles of the Rhine Glacier throughout the Middle to Late Pleistocene. A seismic survey of Lake Constance revealed a Quaternary sediment fill of more than 150 m thickness representing at least the last glacial cycle. The stratified sedimentary fill consists at the base of ice-contact deposits on top of the molasse bedrock, overlain by glaciolacustrine to lacustrine sediments. During the successful field test of a newly developed, mid-size coring system ("HIPERCORIG"), the longest core (HIBO19) ever taken in Lake Constance was retrieved with an overall length of 24 m. The sediments recovered consist of a nearly continuous succession of lacustrine silts and sands including more than 12 m of Late Glacial sediment at the base. 14 lithotypes were identified through petrophysical and geochemical analyses. In combination with a 14C- and OSL-based age-depth model, the core was divided into three main chronostratigraphic units. The basal age of ~ 13.7 ka BP dates the base of the succession back to the Bølling-Allerød interstadial, with overlying strata representing a complete and thick Younger-Dryas to Holocene succession. The sediments offer a high-resolution insight into the evolution of paleo-Lake Constance from a cold, postglacial to a more productive and warmer Holocene lake. The Late Glacial succession is dominated by massive, m-thick sand beds reflecting episodic sedimentation pulses. They are most likely linked to a subaquatic channel system originating in the river Seefelder Aach, which is, despite the Holocene drape, still apparent in today’s lake bathymetry. The overlying Holocene succession reveals a prominent, several cm-thick, double-turbiditic event layer representing the most distal impact of the Flimser Bergsturz, the largest known rockslide of the Alps that occurred over 100 km upstream the river Rhine at ~ 9.5 ka BP. Furthermore, lithologic variations in the Holocene succession document the varying sediment loads of the river Rhine and the endogenic production representing a multitude of environmental changes.

Hybrid broadband ground motion simulations in the Indo-Gangetic basin for great Himalayan earthquake scenarios

This study presents broadband ground motions for the Indo-Gangetic basin, a large sedimentary basin in India, for potential future great (Mw 8.5) Himalayan earthquakes. We use a recently developed 3D earth structure model of the basin as an input to simulate low-frequency ground motion (0–0.5 Hz). These ground motions are further combined with high-frequency scattering waveforms by using a hybrid approach, thus yielding broadband ground motions (0–10 Hz). We calibrate the 3D model and scattering parameters by comparing the simulated ground motions against available recorded data for two past earthquakes in Himalaya. Our approach accounts for the physics of interaction between the scattered seismic waves with deep basin sediments. Our results indicate that the ground motion intensities exhibit frequency-dependent amplification at various basin depths. We also observe that in the event of a great earthquake, the ground motion intensities are larger at deep basin sites near the source and exhibit an attenuating trend over distance similar to the ground motion models. The extreme ground motion simulations performed in our study reveal that the national building codes may not provide safe recommendations at deep basin sites, especially in the near field region. The period-dependent vertical-to-horizontal spectral ratio deviates from the code-recommended constant 2/3 at least up to 6 s at these sites.

Sedimentary responses to rifting of the Upper Yangtze Block (Sichuan basin area) in the Middle-Late Permian

中-晚二叠世，上扬子（四川盆地区）碳酸盐岩台地内发育三条北西-南东走向的裂谷，它们是重要的油气储集区带，如普光和元坝气田就产于开江-梁平裂谷两侧。但是对这些裂谷的开始时代和构造成因等关键地质问题，还缺乏详细的沉积学研究，且存在较大争议。本文通过大比例露头剖面和钻井岩芯测量以及详细的沉积相分析对比，对开江-梁平裂谷的构造沉积过程进行了深入细致的研究。调查发现，在开江-梁平裂谷北缘，中二叠统栖霞组上段至茅口组2段发育大规模斜坡相碳酸盐岩滑塌堆积，揭上扬子地块四川盆地区于中二叠世栖霞晚期开始发生伸展裂解。茅口组3段至上二叠统长兴组为超覆于滑塌堆积之上的硅质岩和碳-硅质泥岩等深水盆地相沉积，表明开江-梁平裂谷从中二叠世茅口晚期开始由伸展裂解转变为区域沉降，即开江-梁平裂谷经历了伸展裂解和区域沉降两个构造沉积阶段。伸展裂解阶段，开江-梁平裂谷是一个发育于碳酸盐岩台地内的不对称海相半地堑盆地，北侧为发育大规模碳酸盐岩滑塌堆积的下盘断斜坡带，南侧为发育缓斜坡生物碎屑滩和礁灰岩的上盘缓斜坡带；区域沉降阶段，开江-梁平裂谷表现为东翘西降的不均匀沉降，发育自东向西不断进积的潮坪-潟湖相和高能浅滩相沉积等。本文研究成结果对分析和圈定四川盆地区中-晚二叠世油气储集相带的时空分布具有重要科学意义，也为研究碳酸盐岩滑塌堆积提供了一个新范例。;Three rift valleys in NW-SE strike have been outlined by the gas and oil explorations in the Upper Yangtze Block in the past 20 years. More importantly, these two rift valleys are the locations of proved gas fields in the present Sichuan Basin, such as the Puguang and Yuanba gas fields developed on both sides of the Kaijiang-Liangping (KL) rift valley. However, the initiating ages of these rift valleys and their tectono-sedimentary evolutionary processes are still unclear, mainly because of lacking the sedimentary constraints. Based on careful observations of field outcrops along three sections and a drill core, we analyzed the sequences of the KL rift valley in the Permian and reconstructed its tectonic and filling processes. The results presented in this paper show that carbonate olistostromes were highly developed in the upper section of the Qixia Formation to the second member of the Maokou Formation of the Middle Permian in the northern flank of the KL rift valley, floored by platform carbonates and overlapped by deep-water deposits, which indicates that the slope facies related to the rifting occurred in the Upper Yangtze carbonate platform in the Middle Permian. The lowest carbonate olistostromes suggest the rifting initiated at the Middle Qixia Stage (approximately the Early Wordian) and gradually developed from west to east. Overlapped deep basin deposits in the third member of the Maokou Formation to the Changhsing Formation of the Upper Permian demonstrate the change from the rifting to post-rift subsidence at the beginning of the Late Maokou Stage (approximately the Late Capitanian). In a word, the KL rift valley underwent the tectono-sedimentary processes of the rifting and then post-rift subsidence. During the rifting, the KL rift valley was a marine half-graben developed on the Upper Yangtze carbonate platform, and its northern flank was a fault-controlled slope and characterized by massive carbonate olistostromes. The drill core (Yuanba 8) shows that deeply buried southern flank of the half-graben was a gentle slope and deposited bioclastic and reef limestones. During the post-rift subsidence, the KL rift valley was characterized by cherts and cherty mudstones of the deep basin facies enriched the fossils such as Ammonites. The post-rift subsidence was highly uneven and therefore resulted in the lagoon-tidal flat facies and high-energy shoal facies progressively overlapping the deep basin sediments from east to west along the KL rift valley.

Thriving or surviving? Evaluating active microbial guilds in Baltic Sea sediment.

Microbial life in the deep subsurface biosphere is taxonomically and metabolically diverse, but it is vigorously debated whether the resident organisms are thriving (metabolizing, maintaining cellular integrity and expressing division genes) or just surviving. As part of Integrated Ocean Drilling Program Expedition 347: Baltic Sea Paleoenvironment, we extracted and sequenced RNA from organic carbon-rich, nutrient-replete and permanently anoxic sediment. In stark contrast to the oligotrophic subsurface biosphere, Baltic Sea Basin samples provided a unique opportunity to understand the balance between metabolism and other cellular processes. Targeted sequencing of 16S rRNA transcripts showed Atribacteria (an uncultured phylum) and Chloroflexi to be among the dominant and the active members of the community. Metatranscriptomic analysis identified methane cycling, sulfur cycling and halogenated compound utilization as active in situ respiratory metabolisms. Genes for cellular maintenance, cellular division, motility and antimicrobial production were also transcribed. This indicates that microbial life in deep subsurface Baltic Sea Basin sediments was not only alive, but thriving.

The influence of dissolved oxygen on dinoflagellate cyst distribution across Sluice Pond, a meromictic lake in NE Massachusetts, USA

ABSTRACTAssemblages of dinoflagellate cysts in lakebed sediments across the deep, meromictic basin of Sluice Pond (Lynn, Massachusetts) were compared with measurements of water quality and sediment geochemistry and with testate amoeba and tintinnid assemblages. Lakebed sediments below oxygenated waters (DO >2 mg/L) contain diverse testate amoebae, but sparse Peridinium willei-dominated dinoflagellate cyst assemblages. Sediments collected under hypoxic conditions (DO < 2 mg/L) showed higher preservation of organic carbon and nitrogen, and these deep basin sediments are characterised by diverse dinoflagellate cyst assemblages, but sieved microfossil assemblages are typically dominated by the planktonic Codonella cratera and the pseudo-planktonic Cucurbitella tricuspis. Strong inverse relationships of cysts of Peridinium willei (R2 = 0.81) and Difflugia oblonga tests (R2 = 0.7) with water depth are attributed to variations in bottom water oxygen concentrations. Both ecological and taphonomic factors must be considered when reconstructing palaeoenvironments from microfossil assemblages.

Seasonal distribution of archaeal lipids in surface water and its constraint on their sources and the TEX86 temperature proxy in sediments of the South China Sea

AbstractThe applicability of the temperature proxy based on a tetraether index of 86 carbon atoms (TEX86) from isoprenoidal glycerol dialkyl glycerol tetraethers (isoGDGTs) has increasingly been examined in the South China Sea (SCS). Views on the proxy differ on whether it is biased to a particular season or to depth in this sea. Here we studied isoGDGTs in a large number of suspended particulate matters (SPM) in surface water during summer and winter as well as several surface sediments of the northern SCS. The integration of these novel data with already published data demonstrated that isoGDGTs were similar in distribution between surface water SPM and shallow shelf sediments. They can be characterized by low ratio (&lt;4) of [GDGT‐2]/[GDGT‐3] and low‐percentage abundance (&lt;4%) of the crenarchaeol regioisomer; however, those in deep basin sediments showed higher values for both parameters, suggesting a substantial contribution of “deep‐water” Thaumarchaeota. The relationship between TEX86 in SPM and in situ measured sea surface temperature differed from a global calibration and showed distinct trends between summer and winter, reflecting archaeal seasonality in surface waters. By assuming the TEX86 temperature signal in shallow sediments as the weighted mean of summer and winter signals, we revealed spatial changes in the relative contribution of summer and winter archaeal isoGDGTs to sediments, with a likely higher winter contribution further offshore. This occurrence may complicate the interpretation of the shallow sedimentary TEX86 record, and further investigation is required to fully understand seasonal archaeal lipid production and sedimentation.

Major Bottom Water Ventilation Events Do Not Significantly Reduce Basin-Wide Benthic N and P Release in the Eastern Gotland Basin (Baltic Sea)

Redox-sensitive mobilization of nutrients from sediments strongly affects the eutrophic state of the central Baltic Sea; a region associated with the spread of hypoxia and almost permanently anoxic and sulfidic conditions in the deeper basins. Ventilation of these basins depends on renewal by inflow of water enriched in oxygen (O2) from the North Sea, occurring roughly once per decade. Benthic fluxes and water column distributions of dissolved inorganic nitrogen species, phosphate (PO43-), dissolved inorganic carbon (DIC), sulfide (HS-) and total oxygen uptake (TOU) were measured along a depth gradient in the Eastern Gotland Basin (EGB). Campaigns were conducted during euxinic conditions of the deep basin in Aug./Sept. 2013 and after two inflow events in July/Aug. 2015 and March 2016 when O2 concentrations in deep waters reached 60 µM. The intrusion of O2-rich North Sea water into the EGB led to an approximate 33 % and 10 % reduction of the seabed PO43- and ammonium (NH4+) release from deep basin sediments. Post-inflow, the deep basin sediment was rapidly colonized by HS- oxidizing bacteria tentatively assigned to the family Beggiatoaceae, and HS- release was completely suppressed. The presence of a hypoxic transition zone (HTZ) between 80 and 120 m water depth was confirmed not only for euxinic deep-water conditions during 2013 but also for post-inflow conditions. Because deep-water renewal did not ventilate the HTZ, where PO43- and NH4+ fluxes were highest, high seabed nutrient release there was relatively unchanged. Extrapolation of the in situ nutrient fluxes indicated that, overall, the reduction in PO43- and NH4+ release in response to deep-water renewal can be considered as minor, reducing the internal nutrient load by 2 and 12 % only, respectively. Infrequent inflow events thus have a limited capacity to sustainably reduce internal nutrient loading in the EGB and mitigate eutrophication.

Phosphorus burial in sediments of the sulfidic deep Black Sea: Key roles for adsorption by calcium carbonate and apatite authigenesis

Sedimentary burial of the essential nutrient phosphorus (P) under anoxic and sulfidic conditions is incompletely understood. Here, we use chemical and micro-scale spectroscopic methods to characterize sedimentary P burial along a water column redox transect (six stations, 78–2107m water depth) in the Black Sea from the shelf with its oxygenated waters to the anoxic and sulfidic deep basin. Organic P is an important P pool under all redox regimes, accounting for up to 60% of P burial. We find a general down-core increase in the relative importance of organic P, especially on the shelf where P bound to iron (Fe) and manganese (Mn) (oxyhydr)oxides is abundant in the uppermost sediment but rapidly declines in concentration with sediment depth. Our chemical and spectroscopic data indicate that the carbonate-rich sediments (Unit I, ∼3000years, ∼0–30cm depth) of the sulfidic deep Black Sea contain three major P pools: calcium phosphate (apatite), organic P and P that is strongly associated with CaCO3 and possibly clay surfaces. Apatite concentrations increase from 5% to 25% of total P in the uppermost centimeters of the deep basin sediments, highlighting the importance of apatite formation for long-term P burial. Iron(II)-associated P (ludlamite) was detected with X-ray absorption spectroscopy but was shown to be a minor P pool (∼5%), indicating that lateral Fe–P transport from the shelf (“shuttling”) likely occurs but does not impact the P burial budget of the deep Black Sea. The CaCO3–P pool was relatively constant throughout the Unit I sediment interval and accounted for up to 55% of total P. Our results highlight that carbonate-bound P can be an important sink for P in CaCO3-rich sediments of anoxic, sulfidic basins and should also be considered as a potential P sink (and P source in case of CaCO3 dissolution) when reconstructing past ocean P dynamics from geological records.

Sr isotopic compositions of the interstitial water and carbonate from two basins in the Gulf of Mexico: Implications for fluid flow and origin

Strontium isotopic compositions of the interstitial water and carbonate from marine sediments sampled during IODP 308, in two basins (the normally-pressured Brazos-Trinity Basin IV and the over-pressured Ursa Basin) on the northern slope of the Gulf of Mexico, are present in this study. In the Brazos-Trinity Basin IV, the 87Sr/86Sr ratios of the interstitial water range from 0.70917 to 0.70954, with carbonates sharing similar or slightly lower values from 0.70851 to 0.70952. The interstitial water above 31m shows similar 87Sr/86Sr ratio close to that of seawater, whereas the interstitial water below 31m shows more radiogenic 87Sr/86Sr ratios, possibly indicating a water/rock interaction between the fluid and silicate component in the deep basin sediments. The Sr-isotope ratios of the carbonates are less radiogenic than the seawater, which may reflect a terrestrial carbonate input (such as limestone) transported through the Brazos and Trinity rivers. In the Ursa Basin, the 87Sr/86Sr ratios of the interstitial water range from 0.70887 to 0.70999, those of the carbonate vary from 0.70808 to 0.70930. Both the interstitial water and carbonate show a similar trend of 87Sr/86Sr ratios throughout the depth. The 87Sr/86Sr ratios of the interstitial water decrease from the sea floor surface to the minimum at the Seismic Reflector S10. A lateral fluid incursion with less radiogenic 87Sr/86Sr ratios along the Seismic Reflector S10 can be inferred in the Ursa Basin. It is suggested that the lateral fluid incursion shows a seawater origin, modified by diagenetic reactions including the dissolution of halite. Between the Seismic Reflector S10 and S40, 87Sr/86Sr ratios of the interstitial water increase linearly to the maximum. Along the Seismic Reflector S40, a lateral fluid incursion with more radiogenic 87Sr/86Sr ratios is again recognized. The fluid may have also originated from seawater, but modified by the diagenesis of terrigenous sediments, likewise characterized by highly radiogenic 87Sr/86Sr compositions. A two-dimension fluid-flow model in the Ursa Basin is established.

Hypoxia‐driven variations in iron and manganese shuttling in the Baltic Sea over the past 8 kyr

AbstractThe Baltic Sea has experienced three major intervals of bottom water hypoxia following the intrusion of seawater circa 8 kyr ago. These intervals occurred during the Holocene Thermal Maximum (HTM), Medieval Climate Anomaly (MCA), and during recent decades. Here we show that sequestration of both Fe and Mn in Baltic Sea sediments generally increases with water depth, and we attribute this to shelf‐to‐basin transfer (“shuttling”) of Fe and Mn. Burial of Mn in slope and basin sediments was enhanced following the lake‐brackish/marine transition at the beginning of the hypoxic interval during the HTM. During hypoxic intervals, shelf‐to‐basin transfer of Fe was generally enhanced but that of Mn was reduced. However, intensification of hypoxia within hypoxic intervals led to decreased burial of both Mn and Fe in deep basin sediments. This implies a nonlinearity in shelf Fe release upon expanding hypoxia with initial enhanced Fe release relative to oxic conditions followed by increased retention in shelf sediments, likely in the form of iron sulfide minerals. For Mn, extended hypoxia leads to more limited sequestration as Mn carbonate in deep basin sediments, presumably because of more rapid reduction of Mn oxides formed after inflows and subsequent escape of dissolved Mn to the overlying water. Our Fe records suggest that modern Baltic Sea hypoxia is more widespread than in the past. Furthermore, hypoxia‐driven variations in shelf‐to‐basin transfer of Fe may have impacted the dynamics of P and sulfide in the Baltic Sea thus providing potential feedbacks on the further development of hypoxia.

Fluxes of clay minerals in the South China Sea

In order to assess dominant settling processes that change the composition of the detrital clay fraction during transport from neighboring estuaries to a deep sea basin, we studied relative clay mineral abundances and absolute clay mineral fluxes of clay-sized sinking particulate matter collected by eight sediment trap systems deployed from shallow to deep water depth in the South China Sea. This is the first basin-wide study on recent sedimentation processes in the western Pacific marginal seas.Annual averages of relative clay mineral abundances at the shallow traps are temporally more variable and regionally more diverse, resembling those of surrounding drainage basins. In contrast, higher fluxes of material reach the deeper traps. Their characteristics trend temporally and spatially towards uniformity and are enriched with smectite in the entire deep basin.Sinking particulate matter that reaches the shallow traps spends less time in pelagic transport and is affected by monsoonal current reversals. The enrichment in smectite in the deeper traps is a result of longer duration in transport at low velocities, which may increase the effect of differential settling during transport. The trend is caused by lateral advection driven by the cyclonic deep circulation, and this is considered as the main transport process in the northern and central deep basin. The high fluxes in the south-western deep basin could be the result of laterally advected re-suspended sediments from the neighboring shelves.The effects on the composition of the detrital clay fraction caused by oceanographic control, which indirectly include those by differential settling, mask the climatic signal from surrounding drainage basins in the deep basin sediments. This strongly affects the interpretation of the clay mineralogical record in sediments deposited under recent conditions in the South China Sea deep basin.

Sedimentary sources and processes in the eastern Arabian Sea: Insights from environmental magnetism, geochemistry and clay mineralogy

The spatial distribution patterns of surficial sediment samples from different sedimentary domains (shallow to deep-sea regions) of the eastern Arabian Sea were studied using sediment proxies viz. environmental magnetism, geochemistry, particle size and clay mineralogy. Higher concentrations of magnetic minerals (high χlf) were recorded in the deep-water sediments when compared with the shallow water sediments. The magnetic mineralogy of one of the shallow water samples is influenced by the presence of bacterial magnetite as evidenced from the χARM/χlfvs. χARM/χfd biplot. However, the other samples are catchment-derived. The high correlation documented for χlf, anhysteretic remanent magnetisation (χARM) and isothermal remanent magnetisation (IRM) with Al indicates that the deep-sea surficial sediments are influenced by terrigenous fluxes which have been probably derived from the southern Indian rivers, the Sindhu (the Indus) and the Narmada-Tapti rivers. A lower Mn concentration is recorded in the upper slope sediments from the oxygen minimum zone (OMZ) but a higher Mn/Al ratio is documented in the lower slope and deep-sea sediments. Clay minerals such as illite (24–48.5%), chlorite (14.1–34.9%), smectite (10.6–28.7%) and kaolinite (11.9–27.5%) dominate the sediments of shallow and deep-sea regions and may have been derived from different sources and transported by fluvial and aeolian agents. Organic carbon (OC) data indicate a low concentration in the shallow/shelf region (well oxygenated water conditions) and deeper basins (increased bottom-water oxygen concentration and low sedimentation rate). High OC concentrations were documented in the OMZ (very low bottom-water oxygen concentration with high sedimentation rate). The calcium carbonate concentration of the surface sediments from the continental shelf and slope regions (<1800 m) up to the Chagos-Laccadive Ridge show higher concentrations (average = 58%) when compared to deep basin sediments (average = 44%). Our study demonstrates that particle size as well as magnetic grain size, magnetic minerals and elemental variations are good indicators to distinguish terrigenous from biogenic sediments and to identify sediment provenance.

Persistent organic pollutants in ocean sediments from the North Pacific to the Arctic Ocean

AbstractConcentrations of polychlorinated biphenyls (PCBs), organochlorine pesticides (OC pesticides), and polybrominated diphenyl ethers (PBDEs) are reported in surficial sediments sampled along cruise transects from the Bering Sea to the central Arctic Ocean. OCs and PCBs all had significantly higher concentrations in the relatively shallow water (&lt;500 m depth) of the Bering‐Chukchi shelf areas (e.g., ΣPCB 286 ± 265 pg g−1 dw) compared to the deeper water regions (&gt;500 m) of the Bering Sea and Arctic Ocean (e.g., Canada Basin ΣPCB 149 ± 102 pg g−1 dw). Concentrations were similar to, or slightly lower than, studies from the 1990s, indicating a lack of a declining trend. PBDEs (excluding BDE‐209) displayed very low concentrations (e.g., range of median values, 3.5–6.6 pg/g dw). In the shelf areas, the sediments comprised similar proportions of silt and clay, whereas the deep basin sediments were dominated by clay, with a lower total organic carbon (TOC) content. While significant positive correlations were observed between persistent organic pollutant (POP) concentrations and TOC (Pearson correlation, r = 0.66–0.75, p &lt;0.05), the lack of strong correlations, combined with differing chemical profiles between the sediments and technical formulations (and/or marine surface waters), indicate substantial chemical processing during transfer to the benthic environment. Marked differences in sedimentation rates between the shallow and deeper water regions are apparent (the ∼5 cm‐depth grab samples collected here representing ∼100 years of accumulation for the shelf sediments and ∼1000 years for the deeper ocean regions), which may bias any comparisons. Nonetheless, the sediments of the shallower coastal arctic seas appear to serve as significant repositories for POPs deposited from surface waters.

The rare earth element geochemistry of surface sediments in four transects in the South China Sea and its geological significance

Seventy-five samples of surface sediment were collected from four transects in the South China Sea (SCS) for analyses of rare earth element (REE) geochemistry. Total REE abundance (∑REE) in the SCS varies from 45 to 195 ppm (average 128 ppm), lower than that of the upper continental crust. The spatial distribution of REE is strongly dependent upon the geographical location and depositional environment. Low ΣREE concentrations are observed on the continental slope (e.g., Xisha and Nansha islands), while high ΣREE concentrations are present in the deep basin. Sediments on the slope are also characterized by lower LREE/HREE, (La/Yb)N, Eu/Eu*, and Ce/Ce* ratios relative to deep-basin sediments. There is a positive correlation between Al2O3 and ΣREE, and a negative correlation between CaO and ΣREE. Conversely, the relatively insignificant Fe–Mn oxide accumulation in the SCS suggests that manganese nodules do not make a significant contribution to the bulk REE composition of sediments. Therefore, the sediment REE geochemistry is mainly controlled by terrigenous and biogenic sources. Biogenic carbonate has a diluting effect on ΣREE concentrations, but a significant influence on LREE/HREE, Ce/Ce*, and (La/Yb)N values is found only in sediments with especially high biogenic carbonate levels. The REE geochemistry of SCS surface sediments indicates that their source is mainly post-Archean felsic rocks. In the eastern sub-basin, the relatively low LREE/HREE ratios and high Eu/Eu* values of the sediments indicate that significant terrigenous materials are derived from young volcanic rocks (e.g., rocks in the Luzon arc).

Formation, distribution, potential and prediction of global conventional and unconventional hydrocarbon resources

Abstract Since the Neoproterozoic, two important cycles of separation and junction of the Rodinia and Pangea supercontinents controlled the formation of the Tethys, Laurasia, Gondwana and Pacifica domains, as well as the sedimentary basin types including craton, passive margin, rift, foreland, fore-arc, and back-arc basins. Sixty-eight percent of the discovered reserves are from the Tethys domain, while 49% of the undiscovered possible reserves are in passive margin basins. Six major sets of source rocks, two types of reservoirs (carbonates and clastics), and two regional seals (shale and evaporite) formed in global evolution of basins. Ten patterns are summarized from the above factors controlling the distribution of global hydrocarbon resources. (1) Conventional-unconventional hydrocarbon is accumulated “orderly”. (2) Distribution of Tethys controls the accumulation of the global hydrocarbons. (3) Foreland thrusting zones control the distribution of structural oil/gas fields; (4) Intra-craton uplifts control the distribution of giant oil/gas fields; (5) Platform margins control the banded distribution of giant organic reef and bank type oil/gas fields. (6) Passive margins control the distribution of giant marine oil/gas fields. (7) Foreland deep slopes control the occurrence of large scale heavy oil and bitumen. (8) Basin deposition slopes control the accumulation of tight oil & gas and coalbed methane. (9) Organic rich deep basin sediments control the retention of shale oil and gas. (10) Low temperature and high pressure seafloor sediments control the distribution of hydrate. The conventional/unconventional resources ratio is 2:8. The conventional resources are mainly distributed in the Middle East, Russia, North America, and Latin America. The unconventional resources are mainly distributed in North America, Asia Pacific, Latin America, and Russia. According to the ten trends of global petroleum industry, hydrocarbon exploration is mainly focused on marine deep water, onshore deep layer, and unconventional oil & gas. The peak of oil production will probably come around 2040, and the life span of petroleum industry will last another 150 years. Renewable energy will replace fossil energy, not for the exhaustion of fossil energy, but because it is cheaper and cleaner.

Discrimination of sediment provenance using rare earth elements in the Ulleung Basin, East/Japan Sea

Abstract In order to discriminate the origins of Ulleung Basin (East/Japan Sea) sediments using rare earth elements (REEs), sediments from 15 box cores and one piston core collected in the shelf, slope, and basin were analyzed for major elements (Al, Fe, Ca, and Mn) and REEs. The major sedimentary components in this basin were presumed to be detrital materials from land, even in the basin sediments, based on Al and organic contents (carbon and opal). Post-depositional recycling processes involving Fe and Mn were identified in the basin sediments. Thus, the Ce anomaly and the fractionation factors of light REEs (LREEs) and middle REEs (MREEs) relative to heavy REEs (HREEs) could not be used as provenance indicators in the deep basin sediments (> 2000 m of water depth) based on a feasibility check using their covariation with Fe and Mn. For the shelf, slope, and basin B (sites near islands; water depths of 1200–1800 m) regions, the Eu anomaly, LREEN/HREEN, and MREEN/HREEN could be successfully used to discriminate possible provenances, including Nakdong River sediments (NRS), Chinese River sediments (CRS), Ulleungdo volcanic rocks (UVR), and Dokdo volcanic rocks (DVR). From the provenance indicators, slope as well as the shelf sediments (called the Korea Strait shelf mud; KSSM) in the Ulleung Basin can be regarded as mixtures of NRS and CRS with decreasing portions of NRS in the KSSM with distance from the Nakdong River. Basin B sediments were mixtures of UVR or DVR and CRS. These findings can be explained if sediments discharged from the Nakdong River were transported and deposited (KSSM) northward within the strong coastal front in normal periods and if sediment flumes from summer floods flowed out across the coastal front, were carried with the Tsushima Warm Current, and then deposited in the slope area. This study indicated that CRS were very important detrital sediments and that REE compositions can be successfully used as a provenance indicator in even hemipelagic sediments close to land.

Evidence for hyperextension along the pre-Caledonian margin of Baltica

We propose that a mantle-peridotite-bearing mélange unit, which has been mapped for more than 400 km in southern Norway, represents vestiges of deep basin(s) formed by hyperextension of the Baltic margin during the inception of the Caledonian Wilson cycle. In the mélange, which occurs below the crystalline nappes of the Middle Allochthon in southern Norway, solitary mantle peridotites, detrital serpentinites, metabasalts, gabbros and deep basin sediments are interlayered and imbricated with allochthonous, coarse-grained siliclastic sediments and slivers of Proterozoic basement rocks. The siliciclastic sediments have detritus derived from Proterozoic rocks, similar to those of the large crystalline nappes and the autochthonous basement of Baltica. The mélange unit shares many similarities with the hyperextended Tethyan margin complexes that have been described from the Alps, the Pyrenees and several segments of the present-day passive ocean margins, and we interpret it to represent an ancient late Proterozoic to Palaeozoic analogue to present-day hyperextended passive margins. Regional maps show that the mélange continues into the central Scandinavian Caledonides and that this basin assemblage may have had a much wider geographical distribution. The new model suggests that a major reinterpretation of the Lower and Middle Allochthons of the Scandinavian Caledonides is required.

Recent sedimentation in the Black Sea: New insights from radionuclide distributions and sulfur isotopes

The Black Sea is the world's largest anoxic–sulfidic marine basin and has unique sedimentation conditions. Recent studies suggested that mass accumulation rates (MAR) in this environment have increased in the past century when compared to the last 2000 years (Unit 1 period). In this paper we test this hypothesis with new MAR data and further explore the relationship between the depositional pattern and pyrite–sulfur isotopic signature. Based on 15 cores sampled in 2001 and 2003, our dataset comprises radioactive isotopes (210Pb, 226Ra, 137Cs) and sulfur stable isotopes (δ34SVCDT) along with organic, inorganic carbon and pyrite–sulfur. We calculated MARs using 210Pb profiles and/or Chernobyl-derived 137Cs horizon buried in the sediment column. Our turbidite-free deep basin sediment MARs (61 to 76gm−2yr−1) agreed with the previous results (50–100gm−2yr−1) and confirm the view that MARs of the deep Black Sea basin have been increasing. A unique feature of our dataset was the presence of Chernobyl-derived radionuclides below up to 20cm thick turbidite layers (deposited between 1986 and 2003), which enabled us to compute MARs for these coring locations. MARs were 1120±103 and 5230±125gm−2yr−1 for the last two decades in two turbidite-impacted western central basin cores, 20–100 times the long-term rates of the deep basin. This fast depositional pattern was reflected in the geochemical and isotopic data as well. Turbidites had isotopically heavier pyrite–sulfur compared to the Unit 1-type water column formed pyrite. This is probably because the turbidites originated from slope and transported slope pyrite isotopic signature to the deep basin. Diagenetic effects within the turbidite can make pyrite–sulfur even heavier. These tightly linked results demonstrate the importance of turbidites in recent sedimentation of the Black Sea.