Sediment Mixing Research Articles

Tomorrow\u2019s mundane is today\u2019s extraordinary: A case study of a plastered installation during Neolithization

For reconstructing past human ways of life we study mundane remains, but in order to detect special worldviews and behaviors we endeavor to observe the extraordinary embedded in those remains. There are many ways to define the ‘extraordinary’. Here we center on early occurrences of phenomena that later become mundane, rendering them ‘extraordinary’ through being rare compared to later frequent appearances. This study explores such extraordinary phenomena with relation to the processes of Neolithization in the Southern Levant, focusing on a round plastered installation (Feature 6) that was unearthed in the Late Natufian village of Nahal Ein Gev II (ca. 12,000 calBP). To investigate the feature’s function, we conducted a micro-geoarcheological analysis of the walls and fill to understand its use and formation processes, using Fourier-transform infrared (FTIR) spectroscopy and micromorphology. Our results show that the walls were not exposed to elevated temperatures and that the interior of the installation was filled with mixed sediments. We therefore rule out the use of the feature as a cooking installation or a kiln. The interior mixed assemblage indicates secondary infilling after the feature was no longer in use for its initial purpose, thus challenging the identification of its original function. To date, there are no parallels for such lime and clay plastered installations in the Natufian culture. Yet, this type of feature becomes increasingly common with the advance of Neolithization where such features served as storage installations, integral to the farming way of life. We conclude that Feature 6 in NEG II is ‘extraordinary’ in the context of the Late Natufian, heralding the development of clay lined storage installations. We argue that this example of ‘extraordinary’ within the long process of Neolithization in the Near East helps to illuminate the gradual process of cultural innovation in which new features appear at first as extraordinary phenomena which later will become mundane.

Significance to hydrocarbon exploration of terrestrial organic matter introduced into deep marine systems: Insights from the Lower Cretaceous in the Levant Basin

Oil shows from wells in the Levant Basin and Egypt are suggestive of potential economic discoveries within unpenetrated Mesozoic reservoirs in the Eastern Mediterranean. Analysis of some of these oils indicate a non-marine source of mixed deltaic-terrestrial or lacustrine origin for the organic matter. Data from Barremian-Aptian sediments from the MNUPH-1 core in northern Israel opens a window on potential importance of terrestrial-sourced kerogen deposited in source rocks in a marine depositional environment.Core analyses of the Barremian Nabi Sa'id Fm. demonstrate the occurrence of a gas-prone immature source rock of >77 m gross thickness averaging 4.6% TOC, peaking at 37% TOC. Rock-Eval pyrolysis, biomarker n-alkane, sterane, and tricyclic terpane indices, atomic C/N ratios, and δ13Corg ranges indicate mixed terrestrial-marine organic source rocks for the Barremian, while higher up, the Aptian Hidra Fm. contains source rocks with organic matter derived dominantly from carbohydrate-rich land plants. The interval at MNUPH-1 includes abundant evidence for off-shelf mass transport of terrestrial and proximal marine sediments into the deep marine basin. These features are used to explain the anomaly of a terrestrial source for organic matter in this setting. Mass transport and consequent mixing of distal marine, proximal marine and land-derived sediment is, in fact, the norm at the foot of continental slopes globally.The dominantly type III source rocks described here would be unlikely to expel oil but might produce thermogenic gas. Thermogenic gas identified in similar marine settings might wrongly be interpreted as having been generated from marine organic matter, misleadingly indicative of a prospective oil source. When prospecting for deep-rooted hydrocarbon accumulations in offshore marine settings, an alternative system dominated by basinward sediment transport of gas-prone ‘terrestrial’ source rocks into strategically-positioned toe-of-slope marine settings, is supported here, and could well be producing gas in the Levant Basin.

Estimation of Tsunami Characteristics from Deposits: Inverse Modeling Using a Deep‐Learning Neural Network

Tsunami deposits provide information for estimating the magnitude and flow conditions of paleotsunamis, and inverse models have potential for reconstructing hydraulic conditions of tsunamis from their deposits. The majority of the previously proposed models are based on oversimplified assumptions and possess some limitations. We present a new inverse model based on the FITTNUSS model, which incorporates nonuniform and unsteady transport of suspended sediment and turbulent mixing. The present model uses a deep neural network (DNN) for the inversion method. In this method, forward model calculations are repeated for random initial flow conditions (e.g., maximum inundation length, flow velocity, maximum flow depth, and sediment concentration) to produce artificial training data sets of depositional characteristics such as thickness and grain‐size distribution. The DNN was then trained to establish a general inverse model based on artificial data sets derived from the forward model. Tests conducted using independent artificial data sets indicated that this trained DNN can reconstruct the original flow conditions from the characteristics of the deposits. Finally, the model was applied to a data set of 2011 Tohoku‐oki tsunami deposits. The predicted results of flow conditions were verified by the observational records at Sendai plain. Jackknife resampling was applied to estimate the precision of the result. The estimated results of the flow velocity and maximum flow depth were approximately 5.4 ± 0.1 m/s and 4.1 ± 0.2 m, respectively, after the uncertainty analysis. The DNN shows promise for reconstruction of tsunami characteristics from its deposits, which would help in estimating the hydraulic conditions of paleotsunamis.

Single grain TT-OSL ages for the Earlier Stone Age site of Bestwood 1 (Northern Cape Province, South Africa)

The transition from the Earlier Stone Age (ESA) to the Middle Stone Age (MSA) in the interior of southern Africa is associated with the Fauresmith Industry. Major cultural developments found in the Fauresmith include regular use of ochre and other coloured minerals, prepared core technology including blade and point production, and the use of hafted spears. Chronological control for the Fauresmith is weak so that critical questions regarding the relationship of this industry to the evolution of modern humans remain unresolved. Here we present ages for the Bestwood 1 site, an open-air locality in the Northern Cape Province (South Africa) where an extensive Fauresmith occupation is found underlying sand deposits. Optically stimulated luminescence (OSL) was first applied to samples from the sands overlying the Bestwood 1 occupation horizon, and from the occupation horizon itself, in order to establish the chronology of the site. However, sediment mixing resulting from bioturbation processes has been observed, causing post-depositional bleaching of the majority of the grains, thus limiting the use of OSL. In addition, given the identification of the lithic assemblage to the Fauresmith, it seems likely that the sands were beyond the dating range of conventional OSL. Due to its hard-to-bleach properties, the thermally transferred-optically stimulated luminescence (TT-OSL) signal was deemed suitable for detecting the least-bleached grains. Single grain TT-OSL analyses combined with the finite mixture model (FMM) were conducted in order to isolate the oldest grains that could be contemporaneous with the time of deposition of the sediment associated with the ESA assemblage. High scattering of the equivalent doses is consistent with bioturbation processes that mixed sediment; the distribution of the equivalent dose values suggests that younger grains were incorporated into the ESA layers, thus supporting the use of the oldest component determined using the FMM to calculate the TT-OSL ages. This approach allowed us to establish the time for the Fauresmith occupation at 366 ± 32 ka, and the age of the overlying sand deposits, spanning from 350 ± 22 ka to 226 ± 13 ka.

Implications of turbulence shear by non-cohesive sediments on the break-up of kaolin flocs

The present study investigated the role of non-cohesive fraction of sediments on the flocculation of kaolin suspension. The floc characterization was achieved through micro-scale investigations using an image capturing system followed by an image processing technique. Initially, the variations in the characteristics of flocs of kaolin with salinity and turbulence were examined, followed by characterization of flocs under the addition of sand fraction at different proportions (10%, 20%, 40% and 50%). The presence of sand imparts additional shear causing the break-up of macro-flocs of size >100μm. The variation of floc volume fraction of macro-flocs with turbulence follows a power law, which was used to quantify the additional turbulence shear created by different % of sand. The breakage coefficient of macro-flocs was determined from the experimental results and a relationship for it in terms of turbulence shear is proposed. The developed relationship was further applied to predict the breakage coefficient of macro-flocs due to the addition of sand. The sensitivity analysis conducted between predicted and observed breakage coefficient of macro-flocs due to the addition of sand yielded a correlation coefficient of 0.99. The study proves that the binary breakage model, which propose the break-up of a floc into two equal sized flocs, can be applied to predict breakage coefficient only at intermediate turbulence shear in the range of 20–40 s−1; further it fails to predict the breakage coefficient of macro-flocs in mixed sediment suspensions. The study highlights the role of sand in floc break-up and suggests that the developed model can very well predict the breakage coefficient of macro-flocs in estuaries with mixed sediments as well as at all ranges of turbulence shear encountered in estuaries.

Sedimentary zonation shift of tidal flats in a meso-tidal estuary

Understanding the spatial-temporal pattern of sedimentary dynamics on tidal flats is important for examining their ecological function and evolutionary trend. In this study, the dynamic state of sediments across an open-coast tidal flat of the meso-tidal Changjiang Estuary, China, on a monthly scale from December 2014 to June 2016 was examined, based on a high-spatial-resolution sedimentological-topographic survey and a collection of related meteorological-hydrological data. The results revealed a continuously distinct zonation of sediments, which transformed seaward from sand-dominance to silt dominance over a short distance. A zoning, to divide the tidal flat into a sand zone, a mixture zone and a silt zone, was delimited based on the cluster analysis of grain size frequency distributions. The zonation was highly dynamic, with the mixture zone migrating upward during summer and experiencing an uplift of 1 m in its lower boundary over the time period examined. Within each zone, the medium size and sorting coefficient of sediments tended to be smaller in winter than those in summer. Alterations of the mean tidal level likely controlled the zonation shift and sediment variations. A higher mean tidal level indicated a landward shift of the location exhibiting shear stress maxima and the mixture zone had to migrate upward to maintain an appropriate stress for the development of mixed sediments. The impacts of waves were masked under normal conditions, but during storms strong waves dominated an embedded downward displacement of the mixture zone. Characteristics of sediments covering a large region of the tidal flat changed along with zonation shifts, resulting from altered proportions among sandy, mixed and silty sediments. The study highlights that sedimentary zonation shift, under the impacts of seasonal variations in tidal level, can be a major manifestation of tidal flat sedimentary dynamics.

Zircon as a provenance tracer: Coupling Raman spectroscopy and U[sbnd]Pb geochronology in source-to-sink studies

UPb zircon geochronology is one of the most widely used techniques in sedimentary provenance analysis. Unfortunately, the ability of this method to identify sediment sources is often degraded by sediment recycling and mixing of detritus from different source rocks sharing similar age signatures. These processes create non-unique zircon UPb age signatures and thereby obscure the provenance signal. We here address this problem by combining detrital zircon UPb geochronology with Raman spectroscopy. The position and width of the Raman signal in zircon scales with its degree of metamictization, which in turn is sensitive to temperature. Thus, combined U-Pb + Raman datasets encode information about the crystallization history of detrital zircons as well as their thermal history. Using three borehole samples from Mozambique as part of a source-to-sink study of interest for hydrocarbon exploration, we show that zircon populations with similar UPb age distributions can exhibit different Raman signatures. The joint U-Pb + Raman analysis allowed us to identify three different annealing trends, which were linked to specific thermal events. Thus we were able to differentiate a dominant Pan-African UPb age peak into several sub-populations and highlight the major effect of Karoo tectono-magmatic events. In our case study, we used Raman also as a means to systematically identify all zircon grains in heavy-mineral mounts, resulting in considerable time savings. Raman spectroscopy is a non-destructive and cost-effective method that is easily integrated in the zircon UPb dating workflow to augment the resolution power of detrital zircon UPb geochronology.

Sediment accumulation rates and vertical mixing of deep-sea sediments derived from14C and 210Pb in the southern Gulf of Mexico

Here we present new results on the sedimentation rates and vertical mixing in the deep-water region (966–3741 m) of the southern Gulf of Mexico, from a collection of 42 cores retrieved from the continental slopes and the abyssal plain. These cores were dated with the aid of accelerator mass spectrometry (AMS) 14C determinations on planktic foraminifera. We applied the Modified Mixing Box Model (MMBM) to evaluate the mean sedimentation rates (Sm), to estimate the age of surface sediments (T0) that result from mixing processes. Sm range between 5 and 9 cm kyr−1 in cores from the abyssal plain and the continental slopes, highest rates are consistently observed in specific locations on the slopes (17–24 cm kyr−1). T0 values range between 1000 and 2000 years, in cores from the abyssal plain and the continental slope sites, most probably as a result from the relatively low sedimentation rates and consequent mixing of older sediments. However, some cores from the continental slopes show consistently higher sedimentation rates, and T0 values that are close to zero age. Here we further show 210Pb profiles from 15 cores to evaluate the non-homogeneous mixing processes in surface sediments (0–10 cm). Biodiffusion coefficients (Db) derived from the solution of advection-diffusion model range between 14 and 51 cm2 kyr−1 on the abyssal plain and between 42 and 158 cm2 kyr−1 on the continental slopes.Fluxes of 210Pbex range between 60 and 111 Bq m−2 yr−1 on the abyssal plain, and higher values are consistently found on the continental slopes (158–247 Bq m−2 yr−1). We find the age of surface sediments (T0; derived from the MMBM of 14C) are linked with the transit time in the mixed layer through biodiffusion processes, derived from 210Pb profiles. One of the implications of these results is the relative low importance of benthic macrofauna in respect to the meio- and microfauna bioturbation processes to explain sediment mixing patterns in the deep-sea sediments of the Gulf of Mexico, most probably reflecting a low export of organic carbon to the sediments controlled by the oligotrophic conditions of its surface waters.

Sediment‐Induced Stratification in an Estuarine Bottom Boundary Layer

AbstractWe took field observations on the shallow shoals of South San Francisco Bay to examine how sediment‐induced stratification affects the mean flow and mixing of momentum and sediment throughout the water column. A Vectrino Profiler measured near‐bed velocity and suspended sediment concentration profiles, which we used to calculate profiles of turbulent sediment and momentum fluxes. Additional turbulence statistics were calculated using data from acoustic Doppler velocimeters placed throughout the water column. Results showed that sediment‐induced stratification, which was set up by strong near‐bed wave shear, can reduce the frictional bottom drag felt by the mean flow. Measured turbulence statistics suggest that this drag reduction is caused by stratification suppressing near‐bed turbulent fluxes and reducing turbulent kinetic energy dissipation. Turbulent sediment fluxes, however, were not shown to be limited by sediment‐induced stratification. Finally, we compared our results to a common model parameterization which characterizes stratification through a stability parameter modification to the turbulent eddy viscosity and suggest a new nondimensional parameter that may be better suited to represent stratification when modeling oscillatory boundary layer flows.

Volcanism‐induced sedimentation and model: A case study of the Upper Jurassic‐Lower Cretaceous sediments in the Liuhe‐Tonghua Basin, NE China

Understanding how the lacustrine environment adapts to volcanism and the relevant products is one of the key goals of volcaniclastic sedimentology. Mixed sediments can be deposited in lacustrine basins during the interaction between volcano and environment. This article is focus on the lithology, lithofacies, association, and sedimentary sequence of the Late Jurassic‐Early Cretaceous mixed sediments from the Liuhe‐Tonghua Basin, revealing the transportation‐accumulation processes of volcanic materials from subaerial eruption into water or subaqueous eruption mingling with terrigenous clasts. Four kinds of mixed‐sediment rocks are identified including tuffaceous sandstone, tuff‐lapilli tuff, breccia‐agglomerate/lava and tuff lava/lava, and six lithofacies associations are identified: (a) base surge and pyroclastic flow, interpreted as the middle‐distal end of a mixed‐fan delta; (b) base surge‐pyroclastic flow and turbidite flow, interpreted as the distal end of a mixed‐fan delta; (c) base surge‐pyroclastic flow‐turbidite flow and mud deposits, interpreted as a mixed subaqueous fan; (d) sand sheet of the base surge and mud deposits, interpreted as a deepwater region; (e) subaerial volcanic edifice, interpreted as a volcanic vent‐proximal slope; (f) subaqueous volcanic edifice, interpreted as a volcanic slope. These associations may exhibit different spatial occurrences and palaeogeographic distributions, representing the transition from a volcanic to a sedimentary environment in the source to sink system, and an ideal mixed sedimentation model is established based on these associations and relevant mud deposits. These associations also exhibit a typical volcanic‐sedimentary sequence including terrigenous lowstand sediments in extensional settings and mixed volcanic and terrigenous transgressive‐highstand sediments in trans‐extensional settings. This article presents a case of volcaniclastic sedimentation (mixed sedimentation) of Cretaceous volcano‐fault basin in Northeast China, which can provide a reference for the lacustrine volcaniclastic deposition in other similar genetic basins around the world.

Quantifying Marine Sedimentary Carbon: A New Spatial Analysis Approach Using Seafloor Acoustics, Imagery, and Ground-Truthing Data in Scotland

Marine sediments are important repositories of particulate organic matter, effectively burying organic carbon (OC) over geological timescales thus providing a climate regulation service. However, the spatial distribution of this marine sedimentary OC store is not well constrained. In this study we leverage a high resolution multibeam echosounder (MBES) survey taken at Loch Creran, a model fjordic site on the west coast of Scotland, to develop a new methodology for predicting the distribution of OC in surface sediments. Using an integrated approach, we combine use MBES survey, video imagery and ground-truthing data to produce a high-resolution (2 m x 2 m) map of surficial carbon and calculate a 10 cm stock. We find that the backscatter survey reliably uncovers a heterogeneous seabed and that OC correlates strongly with the MBES backscatter signal as a function of sediment composition. We estimate that there are approximately 12,346 ± 2,677 tonnes of OC held within the top 10 cm of mixed sediments across the MBES survey area (7.96 km2; 60% of the total area), upscaled to 20,577 ± 4,462 t of OC across Loch Creran (13.27 km2). Normalised by area, we find that mixed fine sediments with small fractions of sand and gravel are more effectivehold more carbon OC stores than homogenous fine sediments. This initial work proposes a novel methodological approach to using high resolution MBES surveys to improve the spatial mapping of sedimentary C carbon (C) and identification of C hotspots, enabling consideration of this resource in sedimentary carbon accounting, seabed management and climate mitigation strategies.

Seasonal effects of river flow on microbial community coalescence and diversity in a riverine network

Terrestrial microbial communities may take advantage of running waters and runoff to enter rivers and mix with aquatic microorganisms. However, the environmental factors governing the interchange of the microbial community within a watercourse and its surrounding environment and the composition of the resulting community are often underestimated. The present study investigated the effect of flow rate on the mixing of water, soil, sediment and biofilm at four sites along the Lancang River and one branch of the river in winter and summer and, in turn, the resultant changes in the microbial community within each habitat. 16S rRNA gene-based Illumina high-throughput sequencing illustrated that bacterial communities were apparently distinct among biofilm, water, soil and sediment. Biofilms had the lowest richness, Shannon diversity and evenness indices compared with other habitats, and those three indices in all habitats increased significantly from winter to summer. SourceTracker analysis showed a significant coalescence between the bacterial communities of sediment, water and biofilm samples at lower flow rates. Additionally, the proportion of Betaproteobacteria in sediment and biofilms increased with a decrease in flow rate, suggesting the flow rate had a strong impact on microbial community composition and exchange among aquatic habitats. These results were further confirmed by a Mantel test and linear regression analysis. Microbial communities in all samples exhibited a significant but very weak distance-decay relationship (r= 0.093, P= 0.024). Turbidity played a much more important role on water bacterial community structure in summer (i.e. rainy season) (BIOENV, r= 0.92). Together, these results suggest that dispersal is an important factor affecting bacterial community structure in this system.

Ecological regime shift preserved in the Anthropocene stratigraphic record.

Palaeoecological data are unique historical archives that extend back far beyond the last several decades of ecological observations. However, the fossil record of continental shelves has been perceived as too coarse (with centennial-millennial resolution) and incomplete to detect processes occurring at yearly or decadal scales relevant to ecology and conservation. Here, we show that the youngest (Anthropocene) fossil record on the northern Adriatic continental shelf provides decadal-scale resolution that accurately documents an abrupt ecological change affecting benthic communities during the twentieth century. The magnitude and the duration of the twentieth century shift in body size of the bivalve Corbula gibba is unprecedented given that regional populations of this species were dominated by small-size classes throughout the Holocene. The shift coincided with compositional changes in benthic assemblages, driven by an increase from approximately 25% to approximately 70% in median per-assemblage abundance of C. gibba. This regime shift increase occurred preferentially at sites that experienced at least one hypoxic event per decade in the twentieth century. Larger size and higher abundance of C. gibba probably reflect ecological release as it coincides with an increase in the frequency of seasonal hypoxia that triggered mass mortality of competitors and predators. Higher frequency of hypoxic events is coupled with a decline in the depth of intense sediment mixing by burrowing benthic organisms from several decimetres to less than 20 cm, significantly improving the stratigraphic resolution of the Anthropocene fossil record and making it possible to detect sub-centennial ecological changes on continental shelves.

Assessing behavioural traits of benthic foraminifera: implications for sediment mixing

The assessment of behavioural traits of marine organisms is increasingly recognized as a key issue to understanding their role in ecosystem processes such as bioturbation and nutrient cycling. The movement ability of intertidal foraminifera suggest that they may have a role, yet to be quantified, in benthic-pelagic coupling through their movement on the sediment surface, at the sediment-water interface and within the sediment. In this context, we investigated the behavioural traits of 5 benthic foraminiferal species typical of European temperate mudflats under standardized trophic light and temperature conditions. Behavioural traits related to motion ofAmmonia tepida, Haynesina germanica, Cribroelphidium williamsoni, Miliammina fuscaandQuinqueloculina seminulawere assessed through their travelled distance, velocity, tortuosity of the path, position in the sediment and activity index. By analogy with macrofauna bioturbation functional groups, we describe the studied foraminifera as biodiffusor species with 3 sub-groups defined according to their vertical position in the sediment.C. williamsonibelongs to the epifaunal-biodiffusors,A. tepidaandH. germanicabelong to the surficial-biodiffusors, andQ. seminulaandM. fuscaare considered gallery-biodiffusors. Our results further suggest that features such as velocity, activity and tortuosity may mediate sediment-mixing intensity. Therefore,Q. seminula,H. germanicaandC. williamsoni, which are the most active species, would have a larger effect on particle reworking rates than the less activeA. tepidaandM. fusca. Our results suggest that benthic foraminifera may play an underestimated role in bioturbation processes.

Unraveling sedimentary processes in fluvial sediments from two basalt dominated watersheds in northern Idaho, USA

Basaltic sediments generated from the breakdown of the Columbia River Basalts (CRB) in the Lawyer Creek and Lapwai Creek watersheds of northern Idaho demonstrate that sediment composition in these fluvial systems is impacted by a number of processes, including, chemical weathering, sediment mixing, fluvial sorting, and diagenesis. Chemical weathering is documented in the compositional transformations that occur from the parent material to fluvial detritus, specifically in the leaching of labile cations (i.e., Ca, Mg, Na, and K), an overall increase in weathering indices, and the generation of secondary weathering products (i.e., clay minerals and X-ray amorphous phases) in these sediments. While the two watersheds mainly downcut through the Columbia River Basalt, the incorporation of material derived from local, glacially-derived soil and/or second cycle detritus from interbedded sandstone units significantly modifies the chemical and mineralogical signatures that would normally be used to fingerprint a mafic provenance, highlighting a potential difficulty for provenance reconstruction in sedimentary rocks derived from mixed sources. However, the influence of this mixing is less pronounced in the clay size fraction, highlighting the potential of the <2 μm sediments to preserve the chemical weathering history of the provenance during sedimentation. In addition to weathering and mixing, fluvial sorting is also recorded in the sediment composition and results in the separation of weathering products as a function of grain size. This process is first recognized from the enrichment of secondary weathering phases as grain size decreases, thus resulting in the most chemically altered material sorted into the clay size fraction of sediment deposits downstream. Lastly, early diagenesis of fluvial sediments in the CRB watersheds results in a Ce-anomaly that also correlates with grain size, suggesting the preferential formation of oxide phases in the fine-grained fraction. Furthermore, the most positive Ce-anomaly is recorded in an ancient stream deposit, suggesting that authigenic oxide precipitation initiates during sediment accumulation and advances as the deposit is cut off from the active stream channel.

Historic and contemporary anthropogenic effects on granulometry and species composition detected from sediment cores and death assemblages, Nelson Bays, Aotearoa-New Zealand

To effectively manage anthropogenic stressors causing widespread and pervasive habitat change, resource managers and policy makers require advice on priority stressors to optimally target conservation and restoration outcomes. This is difficult in soft sediment ecosystems affected by multiple stressors operating across centuries with possible legacy interactions. Using tools from the emerging discipline of conservation paleobiology, we attempted to disentangle the effects of two stressors: i) changes to sediments (sedimentation rate, composition) and ii) fishing disturbance across pre-human to contemporary timescales by analysing death assemblages (DA) at a rare location protected from power fishing methods for ca. 30 yr in Nelson Bays, Aotearoa-New Zealand. Replicate sediment cores and surface grab samples were collected at paired stations, spread across three depth profiles (25, 30, 35 m), split inside and outside the fishing exclusion zone. Sediment core geochronologies were established using radioisotope dating and analysis of terrestrial plant palynomorphs (spores, pollen, starch) associated with Māori and European introduction to Aotearoa-New Zealand. Results unearthed a complex of brachiopods, molluscs, crustacea, bryozoan, and Māori-introduced pollen and starch remains – the latter a marine first. Following human arrival in the region (ca.1500AD) statistical models revealed separation of DAs between time periods were correlated with a 10–15% increase in sediment silt content following a ca.11-fold increase in Sediment Accumulation Rates (SAR). In contrast, separation of recent surface DAs (ca. 60yr) are now more strongly correlated with sediment mixing, detected by discordance in radioisotope profiles, consistent with exposure to homogenising effects of fishing disturbance outside the exclusion zone. We conclude that historic legacy effects, ongoing sedimentation and fishing disturbance have synergistically modified the sediment characteristics from “natural” baseline conditions. Those changes have likely contributed to the collapse and lack of recovery of Nelson Bays shellfish fisheries.

Sediment mixing of extrabasinal and intrabasinal sources in a narrow elongated half-graben? Constraints on provenance and seismic geomorphological analysis of the Upper Eocene Liaoxi Sag in the offshore northern Bohai Bay Basin (China)

The interaction of provenance systems is very complicated in narrow elongated half-graben basins, such as some small sags in the Liaodong Bay region, offshore northern Bohai Bay Basin (China). Province identification was conducted through an integrated analysis of petrographic data, heavy minerals, detrital zircon U-Pb data, and three-dimensional (3D) seismic data from the upper Eocene Liaoxi Sag, offshore Bohai Bay Basin. The (light or heavy) mineral indices together with their spatio and temporal distribution show that the Mesozoic-dominated extrabasinal source and the Neoarchaean-dominated intrabasinal source contributions to provenance mixing can be distinguished in the oilfield area. The detrital zircons sampled from the potential sediment mixing area have ages from intrabasinal and extrabasinal sources, suggesting the potential evolution of the hanging wall drainages between the syn-rift and post-rift stages. The overlapping deltaic area between the western shoal margin braided-river delta and the eastern border-fault fan deltas, providing direct visualization of provenance mixing, is well imaged, particularly during the SQ3 lowstand period, but it is not apparent from seismic geomorphological evidence throughout the entire SQ4. Further investigation also reveals that this absence may be attributed to the gradually submerged Liaoxi Low Uplift and the more frequent delta autogenic shifting due to lake-level rise. Shallower water and more efficient wave transport, however, could be another cause of sediment mixing given the presence of widely distributed lacustrine beach bars between transverse deltas from both margins during the post-rift stage. This study enhances an integrated approach to provenance analysis for distinguishing extrabasinal and intrabasinal sources as well as provenance mixing in a narrow half-graben basin on an oilfield scale, even with limited cores and cuttings for instrumental analysis in the offshore region. The study also provides further implications for reservoir properties and connectivity from different source-to-sink systems.

Sedimentary characteristics and genetic mechanisms of high-quality reservoirs in a mixed siliciclastic-carbonate system in the Qinhuangdao area, Bohai Sea, China

Mixed siliciclastic-carbonate sediments occur broadly in modern and ancient systems. Studies on mixing processes began in shallow shelf environments; however, the genetic model of marine mixed sediments is difficult to apply to continental rift basins due to the complex palaeogeographic environment. We identified three mixing types in the first and second members of the Palaeogene Shahejie Formation (E2s1–2) in the Qinhuangdao area of the Bohai Sea: (1) mixed fan delta, (2) retrogradation mixed sheet, and (3) mixed sheet without siliciclastic influx. Tectonic stability, arid climate, and saline lakes are prerequisite conditions for the development of mixed sediments, whereas the palaeogeomorphologic unit should be the critical factor. We also concluded that the primary sedimentary material contains near-source coarse terrestrial debris, and the advantageous lithologic facies producing biological components are the foundation for high-quality mixed reservoirs, which are characterized by thick layers and favorable porosities and permeabilities. The micritic coatings and early dolomitization against the background of a saline lake environment favored the preservation of primary pores, whereas the leaching by atmospheric water and organic acid erosion during thermal evolution of the source rock created many secondary pores. In addition, hydrocarbon charging protected the reservoir space from carbonate cementation.

Detrital Zircon U-Pb Ages in the East China Seas: Implications for Provenance Analysis and Sediment Budgeting

Linking marine sinks to potential terrestrial sources is one of most intriguing but challenging aspects of sediment source-to-sink studies. In this study, we analyzed 23 zircon samples (3271 filtered best ages) from surface sediments of the east China seas (ECSs) that cover a large portion of the Bohai Sea, Yellow Sea, East China Sea to part of the northeastern South China Sea. The results of U-Pb age distributions exhibit variable signatures in different seas. The Bohai Sea is characterized by 4 age populations at 203–286 Ma, 383–481 Ma, 1830–1940 Ma and 2480–2548 Ma, whereas the southern Yellow Sea and the East China Sea are featured by 5 age populations at 176–223 Ma, 383–481 Ma, 732–830 Ma, 1830–1940 Ma and 2480–2548 Ma. We propose that the presence or absence of the population of 732–830 Ma in the Yangtze Craton (YC) and the North China Craton (NCC) is a possible geochronological signature to distinguish zircon grains derived from the two source regions. Furthermore, on the basis of multidimensional scaling (MDS), U-Pb ages in the sediments of the Bohai Sea, East China Sea and the Taiwan Strait could be correspondently linked to those of the Yellow River, the Yangtze River and Taiwan rivers. The good linkages support the view that U-Pb age distributions of detrital zircons in the margin seas are mainly controlled by fluvial discharges, and ultimately, by the tectonic history of the corresponding source regions. Using a sediment forward mixing model, we obtained the relative sediment contributions and spatial variations of five most important river discharges in the region. The mixing results suggest that the major rivers in the region, i.e., the Yangtze and the Yellow Rivers, are the dominant sediment contributors to the continental margin, and their mixing coefficients could be used to infer relative sediment budgeting. In addition, spatial variations in mixing coefficient in the East China Sea indicate that sediment mixing and partitioning processes in the marine depositional environment have played a part role in propagating the provenance signals as a result of interaction of oceanic currents and tides. The combined method between provenance analysis and mixing modeling provides a feasible way to appreciate sediment budgeting in the geological past.

Geochemical characterization of FE-1 well, Onshore Western Niger Delta Basin, Nigeria

Major oxides and trace elements analysis was carried out on ditch cutting samples of FE-1 well, Onshore, Niger Delta Basin, to define their oxygen condition, paleo-climatic conditions, provenance, tectonic setting, sandstone classification and maturity of the sediments. Sedimentological analysis revealed five main lithofacies comprising of sandstone, shaly sand, mudstone, sandy clay and sandy shale. Geochemical results indicates that the average value of silica (87.1 wt. %) is far higher than the average values of the rest oxides which shows the duration and intensity of weathering and destruction of other minerals during transportation. Bivariate plot of La/Sc versus Th/Co, Zr versus TiO2, and trace elemental ratios of Th/Sc, Th/Co, Th/Cr, Cr/Th, La/Sc establishes that the source of the sediment are from felsic rock. Different chemical classification schemes characterized the sediments as quartzarenite, lithic arenites and Fe-rich sand. The plot of Log (K2O/Na2O) versus Log (SiO2/Al2O3) and K2O/Na2O versus SiO2 all plotted mainly in the passive margin zone. The low average value of uranium content, trace elemental ratios of U/Th, Ni/Co, Cu/Zn, V/Cr and binary plot of Ni/Co versus V/Cr indicated an oxic environment of deposition. However, the binary plot of Ni/Co versus V/ (V+Ni) indicates oxic to anoxic condition during deposition of the mixed marine and terrigenous source input sediment. Binary plot of SiO2 versus (Al2O3+Na2O+K2O) designates deposition mainly in humid/semi-humid climatic condition. The samples studied have a much higher SiO2/Al2O3 ratio with low Fe2O3/K2O ratio, thus, they are mineralogically mature. The Al2O3/(CaO+MgO+Na2O+K2O) ratio inferred that there are stable mobile oxides in the samples. &#x0D; Keywords: Major oxides, lithic arenites, provenance, tectonic setting.&#x0D;