Delta Sediments Research Articles

Simulating the Impact of Climate Change with Different Reservoir Operating Strategies on Sedimentation of the Mangla Reservoir, Northern Pakistan

Reservoir sedimentation reduces the gross storage capacity of dams and also negatively impacts turbine functioning, posing a danger to turbine inlets. When the sediment delta approaches the dam, further concerns arise regarding sediments passing through turbine intakes, blades abrasion due to increased silt/sand concentration, choking of outlets, and dam safety. Thus, slowing down the delta advance rate is a worthy goal from a dam manager’s viewpoint. These problems can be solved through a flexible reservoir operation strategy that prioritize sediment deposition further away from the dam face. As a case study, the Mangla Reservoir in Pakistan is selected to elaborate the operational strategy. The methodology rests upon usage of a 1D sediment transport model to quantify the impact of different reservoir operating strategies on sedimentation. Further, in order to assess the long-term effect of a changing climate, a global climate model under representative concentration pathways scenarios 4.5 and 8.5 for the 21st century is used. The reduction of uncertainty in the suspended sediments concentration is achieved by employing an artificial neural networking technique. Moreover, a sensitivity analysis focused on estimating the impact of various parameters on sediment transport modelling was conducted. The results show that a gradual increase in the reservoir minimum operating level slows down the delta movement rate and the bed level close to the dam. However, it may compromise the downstream irrigation demand during periods of high water demand. The findings may help the reservoir managers to improve the reservoir operation rules and ultimately support the objective of a sustainable reservoir use for the societal benefit.

Shale tectonic processes: Field evidence from the Parras Basin (north-eastern Mexico)

Major decollements located within buried overpressured shale commonly develop in thrust fronts, accretionary prisms and sedimentary deltas controlled by gravity tectonics. In seismic data, it is possible to observe only large scale deformation of what is commonly designed as mobile shale but the precise geometry and the dynamic evolution of these bodies remains poorly understood. It is often difficult to define if we are dealing with ductile or brittle deformation and to understand the role of the fluids in time and space during deformation. For this reason, large scale outcrops were studied in the Parras Basin (Mexico), which makes possible a direct observation of the shale tectonic processes. This work suggests changes in space and time of the deformation processes which occurred within the shale formation hosting the decollement. Distributed deformation was observed within the shale formation hosting the decollement compared to more localized deformation above. Also a change of the rheology of the shale over time occurred progressively toward brittle processes in the whole sedimentary pile. XRD and microscopic studies have shown that diagenetic processes are favored in the shear zones of penetrative deformation leading notably to reverse gradient of illitization. The isotopic analysis of cements in veins and the study of associated fluid inclusions have shown that fluid dynamics also evolved during time showing notably evidence for widespread fluid migration issued from rocks located below the decollement during the beginning of the deformation. Progressively, the tectonic system located above the decollement tends to be preserved from fluid migration coming from below the decollement and to be influenced only by local fluid migration (closed system).

Modeling paleogeographic scenarios of the last glacial cycle as a base for source-to-sink studies: An example from the northwestern shelf of the South China Sea

Sea-level (SL) data from the Last Glacial Cycle (LGC) have been superimposed on to digital elevation models of the South China Sea (SCS) and adjacent areas, to generate regional paleogeographic scenarios related to 4th- to 5th-order Milankovitch climate cycles. These scenarios—at 123, 65, 60.5, 56, 20, and 0.5 kyr BP—showed that the SCS functioned as an oceanographic interface between the Pacific and Indian oceans during the LGC. A Late Pleistocene paleo-river delta (Hainan delta) offshore west of Hainan Island (China) was an important sediment routing system on the NW shelf of the SCS. To understand the origin of the Hainan delta better, paleo-reliefs of DEM56kyrBP and DEM65kyrBP were reconstructed, using seismic stratigraphy, sedimentology, and back-stripping methods. Geostatistical and geometric models of clinoforms and delta geometry, as well as the courses of the reconstructed paleo-distributary channels and paleo-river valleys, supported the interpretation that most delta sediment could be regarded as erosional products from Hainan Island. We hypothesized that an intensification of sediment supply outpaced SL rise during the Marine Isotopic Stages 4/3 transition, resulting in a normal regression during the formation of the Hainan delta. Morphodynamic modeling and meteorological data reanalysis further supported our interpretation that shifts in the Asian Monsoon system—combined with local meteorological effects on Hainan Island and with global SL changes—were the main drivers for the sediment source-to-sink systems at the NW SCS continental margin, during the LGC.

Sedimentary Facies and Depositional Environment of Long Sediment Cores from the Nakdong Incised-valley Fills, Southeastern Korea

Hong, S.-H.; Chun, S.S.; Kim, J.-C.; Lee, G.-S.; Yoon, H.-H., and Yoo, D.-G., 2020. Sedimentary facies and depositional environment of long sediment cores from the Nakdong incised valley fills, southeastern Korea. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 511–515. Coconut Creek (Florida), ISSN 0749-0208.Two deep-drilled cores were obtained from the Nakdong River delta in 2016. Based on the sediment structure, composition and texture, the deposits can be divided into four depositional units: I) fluvial sediments, II) estuarine sediments, III) coastal sediments, and IV) delta sediments. The lowermost Unit I is about 25 m thick and comprised clast-supported gravel and massive sand. The age dates of the upper part of Unit 1 is 49.7 ± 5.3 ka. Unit II consists of thin silt laminations that vary rhythmically in thickness, suggesting tidal influences in the estuarine environment. The age dates of this unit range from 10.9 ± 0.18 to 9.6 ± 0.11. Unit III is composed of cross-bedded sand, which contains peat materials and shell fragments and is interpreted to rapidly deposited sand bars in coastal environment. The age of Unit III had 9.7 ± 0.18 ka. Unit IV is composed of extremely bioturbated sandy mud and cross-laminated sand. The age dates of Unit IV ranges from 7.4 ± 0.5 to 0.8 ± 0.09 ka, the deposits belonging to the Holocene. These results indicate that depositional units in the study area consists of fluvial deposits of forced regression formed during the MIS 3, estuarine to tidal flat deposits during deglacial transgression, prograding delta deposits during postglacial periods.

Refined chronostratigraphy of a late Quaternary Sedimentary sequence from the Yangtze River delta based on K-feldspar luminescence dating

Dating of sediments in the tidal-dominated Yangtze River delta remains a challenge because of extremely complicated processes during sediment transport and deposition in such a fluvial-marine transition zone. To better understand the late Quaternary sedimentary history of the Yangtze River delta, we explore the applicability of K-feldspar luminescence dating techniques to deposits through a case study on a 60-m-long borehole core (YZ07) in the delta and then establish a spanning ~50,000-year-long chronological sequence. A series of luminescence pre-tests, including dose recovery tests and determination of residual dose and fading rates, were implemented using the modified single-aliquot-regenerative dose (SAR) protocol for post-infrared (IR) IR stimulated luminescence (IRSL) measured at 150 °C after prior IRSL at 50 °C (pIRIR150), respectively. Luminescence characteristics of the prior IRSL (IR50) and pIRIR150 were then analyzed to check their validity. Two fading-correction models were utilized to correct apparent ages obtained from IR50 and pIRIR150 signals. The newly obtained K-feldspar luminescence ages were compared with quartz OSL ages and 14C ages. Our results indicate that most of ages derived from pIRIR150 signals were overestimated due to incomplete bleaching; in contrast, the fading-corrected ages from IR50 measured in pIRIR150 protocol are robust as they are consistent with quartz OSL ages and 14C ages as well as the stratigraphy. Additionally, IR50 ages are characterized by negligible residual dose, and thus used for defining chronology of the investigated sequence over the past 50 ka. In combination with sedimentological and paleontological analyses of core YZ07, we find that fluvial to tide-influenced fluvial deposits were emplaced during the period 30–50 ka, which were then overlain by post-glacial tidal-river (13–11.5 ka), and Holocene estuarine-shelf, delta system, and tidal flat deposits in the Yangtze River delta. Together with other chronostratigraphy from the selected cores, we confirm the existence of Marine Isotope Stage (MIS) 3 depositional units along the marginal coast of the Yangtze River delta in relation to the interstadial sea-level highstand. Our stratigraphic correlation based on the refined chronology reveals offshore transition of the MIS 3 unit into facies deposited in deeper and offshore marine environments.

Detection of subsidence in the Ebro Delta plain using DInSAR: analysis of the measurements and the factors that control the phenomenon

Abstract. The Ebro Delta is a highly vulnerable Mediterranean coastal ecosystems located on the northern Mediterranean coast of Spain. Determining its subsidence rate and sources is a key issue for the present and future management of this area. Differential Interferometry Synthetic Aperture Radar (DInSAR) compared with the contribution to subsidence of the compaction of delta's sediments and the lithosphere's deformation, indicated a general Ebro Delta subsidence ranging from <1 to ∼ 2.3 mm yr−1. Subsidence is determined to be mainly driven by natural sediment compaction (∼ 76 %), with areas strongly influenced by local processes associated to their sedimentary distribution and composition, or external factors such as sea level rise.

A shallow compaction model for Holocene Mississippi Delta sediments

Abstract. The extensive loss of land elevation and the consequent exposure to flood hazards are seriously threatening the long-term survival of the Mississippi Delta. Shallow compaction of the top soil is one of the major components contributing to the relative sea level rise. In the last decades, more subsidence measurements have become available and recent studies demonstrate that compaction of Holocene strata is dominant. Here we propose a novel application aimed at modeling the present-day shallow compaction due to consolidation processes in the top soil. Soil compaction is properly computed and accounts for the large soil grain motion and the delayed dissipation of pore-water overpressure. The grain motion is described by means of a Lagrangian approach with an adaptive mesh where the grid nodes follows the accretion/compaction processes. Model calibration is obtained from stratigraphic and geochrology information collected at the Myrtle Grove Subsidence Superstation, where a nearly 40 m-deep sediment core that penetrates the entire Holocene succession allows testing model results over long (millennial) timescales. Model validation with available observations from rod surface-elevation table – marker horizon (RSET-MH) data enables the model to predict future scenarios.

Characteristics and controlling factors of Chang 8 Reserviorof the Jiyuan Area in the Ordos Basin

By analyzing the thin sections and physical property,the petrology feature and pore characteristics of the Chang 8 Formation in the Jiyuan Area,the microscopic reservoir pore structure characteristics,characteristics of porosity and permeability are studied and the reservoir performance′s main influencing factors were analyzed.The results suggest that delta sediments are the main deposits in the Chang 7 Formation,and delta front underwater distributary channel sand is the main reservoir.The lithological characteristics mainly include fine-grained lithic feldspathic sandstone and feldspathic detritus sandstone,with low compositional maturity and middle textural maturity.Granular pore and secondary feldspar-dissolution pore are the main pore types.Pore throat presents fine pore fine throat with poor sorting and high micro-heterogeneity.The Chang 7 reservior has low permeability of which the porosity is below 9.448%and the permeability is less than 0.685×10-3μm 2.The reservoir characteristics are influenced by deposition and diagenesis primarily.Sedimentary facies zone controlled development and distribution of reservoir.Besides,compaction and cementation lead to porosity decreased,but the dissolution improves the reservoir propert.

Pore size distribution in the tight sandstone reservoir of the Ordos Basin, China and their differential origin

The micro-nano pore throat system widely developed in tight sandstone is the essential difference between tight sandstone reservoir and conventional sandstone reservoir; it is also the main factor affecting the seepage characteristics and development effect of tight sandstone reservoir. This thesis analyzed the pore-throat types and distributions of the Chang 6 and the Chang 7 reservoirs in the Jiyuan area of the Ordos Basin and discussed the original causes by cast section, SEM, and constant-rate mercury injection. The results showed that the pore type of the Chang 6 reservoir is predominantly residual intergranular pores wherein the throat is mostly compacted. The pore of Chang 6 is more developed than the throat. The pore type of the Chang 7 reservoir is mainly feldspar solution pores, whereas its throat is mostly dissolution. The throat of Chang 7 is more developed than pore. The pore radius distribution range and the average value of the Chang 6 reservoir are similar to those of the Chang 7 reservoir. The distribution range and average value of the throat radius of the Chang 6 reservoir are obviously larger than that of the Chang 7 reservoir. Meanwhile, the physical property of the Chang 6 reservoir is better than that of the Chang 7 reservoir. The Chang 6 reservoir is located in delta sedimentary with shallow burial depth. The high chlorite membrane content and low compaction strength of the Chang 6 reservoir make it more conducive to maintaining the original sedimentary pore space; the dissolution further enlarges the pore space. The Chang 7 reservoir is located in a semi-deep lake sedimentary with large burial depth. The compaction and cementation of the Chang 7 reservoir are strong, and the original sedimentary pore space is massively compressed. Although dissolution strongly occurs in the later stage, the connectivity and seepage capacity of the throat of dissolution origin are lower than those of compaction origin. Dissolution can increase reservoir space; nevertheless, it cannot significantly improve seepage capacity. Therefore, there is a significant difference in permeability of the two successive layers.

Causes of Oil Accumulation of Isolated Bars in Lacustrine Delta

After over 20 years of development in Daqingzijiang Oilfield, isolated sand bodies under the delta front and pro-delta in the Qingshankou Formation(qn)have become important oil and gas reservoir bodies. However, the cause for large amounts of isolated bar sand bodies in the lake-basin delta sediment system has not been reported in China. This article, through core observation, reveals plenty of evidence that there storm waves once existed. Combined with paleogeography and hydrodynamic force analysis, it describes the transformation effect of waves on delta sand bodies and on the formation mechanism of bar sand bodies. Based on a study on paleogeomorphology and the statistics of sand body distribution, we consider ‘Storm waves conveying sand’ and ‘landform controlling sand’ as the cause and distribution model of the delta’s isolated bar sand body formation. We also think that the superposition of multiple bar sand bodies is the direct cause of the strong anisotropy in reservoirs and the complex relationship between oil and water in reservoirs. Most of these sand bodies have formed into lenticular lithologic hydrocarbon accumulations. On the basis of this integrated study on hydrocarbon accumulation, we set up an accumulation model of lenticular hydrocarbon accumulation involving the variables ‘Surrounded by source rocks to generate hydrocarbon’, ‘Driven by pressure difference’, ‘Migration through multi pathways’ and ‘Accumulation by filtering water’.

Rapid consolidation characteristics of Yellow River-derived sediment: Geotechnical characterization and its implications for the deltaic geomorphic evolution

The Yellow River, which presently discharges into the western Bohai Sea, has been widely recognized as having one of the highest sediment loads on Earth. Understanding the consolidation characteristics of Yellow River-derived sediments is critical for improving our knowledge of the riverine sediment transport, depositional processes, and evolution of the Yellow River Delta morphology. In this study, we conducted in situ experiments from 2004 to 2008 at an abandoned subaqueous delta lobe (Diaokou lobe) in order to investigate the consolidation process of the sediments. Our results show that the initial consolidation of Yellow River-derived sediment is a rapid process when the excess pore-water pressure caused by sediment aggradation can completely dissipate in ~1500 min. The change in the physical and geotechnical properties during the consolidation endows the sediments with a certain shear strength. However, due to the hydrodynamic conditions, the distribution of the sediment strength is both temporally and spatially inhomogeneous. Furthermore, a hard layer can develop at the depths of 10–30 cm and the adjacent layer can become a potential sliding surface. This study offers some insight into the formation and evolution processes of the Yellow River Delta's sedimentary and geomorphic forms.

Provenance of the uppermost clastic rocks of the Lower Cretaceous Kezilesu Group from the Ulugqat Basin, Xinjiang, NW China and its tectonic implications: Insights from sedimentary records and detrital zircon U–Pb geochronology

The Ulugqat Basin is located at the juncture of the Tarim Basin, the western Tianshan Orogen of the Central Asian Orogenic Belt, and the Pamir salient of the Tethys domain. A comprehensive provenance study using sedimentology, petrology, and detrital zircon U–Pb geochronology was carried out on the clastic rocks of the fifth member of the Lower Cretaceous Kezilesu Group from the Ulugqat Basin, aiming to better understand the nature of its relationships with the neighbouring tectonic units as well as the formation of sandstone‐hosted Zn–Pb mineralization. The fifth member consists of conglomerate, gravelly sandstone, sandstone, and mudstone interbeds, and is interpreted as alluvial fan–braid river–braid river delta sediments. The conglomerate and gravelly sandstone contain different kinds of lithic fragments, including phyllite, quartzite, chert, chalcedony, and some felsic igneous rocks, with low compositional maturities. The detrital zircon U–Pb ages of sandstone from the uppermost part of the fifth member range widely from 229.7 to 2,984.9 Ma, concentratedly distributed in five groups: 230–300, 390–480, 750–880, 1,600–2,200, and 2,300–3,000 Ma. The identified palaeocurrent directions, heavy mineral assemblages, specific provenance indicators, and distributions of detrital zircon U–Pb ages all indicate that these clastic rocks are probably sourced from the South Tianshan Orogen to the north, rather than the Pamir salient, probably involving the Proterozoic Aksu metamorphic rocks, Palaeozoic sedimentary rocks, Late Carboniferous–Early Permian alkali granite, and some mafic/ultramafic rocks of ophiolitic mélange. This interpretation is consistent with a late Early Cretaceous uplifting of the South Tianshan Orogen according to previous low‐temperature thermochronological data sets. The thick deposition of these Lower Cretaceous clastic rocks and associated uplifting of the South Tianshan Orogen are interpreted to be related to the coeval collision of the Karakoram–Lhasa Block with the southern Asian margin.

The study on the modern sedimentary system of Buha River Delta in Qinghai Lake

Qinghai Lake forming in the Miocene is the largest faulted brackish lake in China. Different researchers conducted comprehensive study via multidisciplinary methods between 1960 and 1970, but modern sedimentary researchers mostly focus on a single facies instead of trying to systemically understand the sedimentary systems of Qinghai Lake and its surrounding areas. Based on observation of outcrop and bathymetry, remote sensing imagery, and meteorological data, the combined research of the modern sedimentary systems in Buha River of Qinghai Lake is conducted, assisted by mechanical analysis and geochemical test. The theory of “source‐to‐sink” system is presented in this study. Based on sedimentary facies analysis in single sites and linear “source‐to‐sink” sedimentary system are well built. The delta of Buha River develops underwater distributary, underwater natural levee, mouth bar, sheet sand, and delta front slope. The control factors of Buha River Delta sedimentary systems include provenance lithology, topography, drainage, vegetational species, plant coverage, wave, coastal current, and lake level fluctuation.

Effects of Upward Seepage on the Resuspension of Consolidated Silty Sediments in the Yellow River Delta

Zhang, S.; Jia, Y.; Lu, F.; Zhang, Y.; Zhang, S., and Peng, Z., 2020. Effects of upward seepage on the resuspension of consolidated silty sediments in the Yellow River Delta. Journal of Coastal Research, 36(2), 372–381. Coconut Creek (Florida), ISSN 0749-0208.Strong seepage flows in coastal zones could significantly change seabed properties, even leading to seepage failure. With respect to the effect of seepage flows on sediment resuspension, available literature has presented conflicting results, indicating that the influence appears to vary for different locations. In the present study, a seepage-scouring, annular flume was designed and employed to evaluate the influence of a sequence of seepage gradients on the resuspension of silts derived from the Yellow River Delta. The experimental results indicated that upward seepage slightly increases the suspended sediment concentration (SSC) level by 4.9–11.1% before the occurrence of seepage failure; however, the occurrence of seepage failure dramatically increases the SSC by at least 64% by pumping massive sediments out of the seabed into the overlying water column. Strong seepage flow and the resultant loss of sediments from the internal seabed are potential mechanisms for the formation of numerous collapse depressions in the Yellow River Delta.

Seismic interpretation and structural restoration of the Heligoland glaciotectonic thrust-fault complex: Implications for multiple deformation during (pre-)Elsterian to Warthian ice advances into the southern North Sea Basin

Despite a long history of research, the locations of former ice-margins in the North Sea Basin are still uncertain. In this study, we present new palaeogeographic reconstructions of (pre-) Elsterian and Warthian ice-margins in the southeastern North Sea Basin, which were previously unknown. The reconstructions are based on the integration of palaeo-ice flow data derived from glaciotectonic thrusts, tunnel valleys and mega-scale glacial lineations. We focus on a huge glaciotectonic thrust complex located about 10 km north of Heligoland and 50 km west of the North Frisian coast of Schleswig-Holstein (Northern Germany). Multi-channel high-resolution 2D seismic reflection data show a thrust-fault complex in the upper 300 ms TWT (ca. 240 m) of seismic data. This thrust-fault complex consists of mainly Neogene delta sediments, covers an area of 350 km2, and forms part of a large belt of glaciotectonic complexes that stretches from offshore Denmark via northern Germany to Poland. The deformation front of the Heligoland glaciotectonic complex trends approximately NNE-SSW. The total length of the glaciotectonic thrust complex is approximately 15 km. The thrust faults share a common detachment surface, located at a depth of 250–300 ms (TWT) (200–240 m) below sea level. The detachment surface most probably formed at a pronounced rheological boundary between Upper Miocene fine-grained pro-delta deposits and coarser-grained delta-front deposits, although we cannot rule out that deep permafrost in the glacier foreland played a role for the location of this detachment surface. Restored cross-sections reveal the shortening of the complex along the detachment to have been on average 23% (ranging from ca. 16%–50%). The determined ice movement direction from east-southeast to southeast suggests deformation by an ice advance from the Baltic region. The chronospatial relationship of the thrust-fault complex and adjacent northwest-southeast to northeast-southwest trending Elsterian tunnel valleys implies a pre-Elsterian (MIS 16?) age of the glaciotectonic complex. However, the age of these Elsterian tunnel valleys is poorly constrained and the glaciotectonic complex of Heligoland may also have been formed during an early Elsterian ice advance into the southeastern North Sea Basin. The glaciotectonic complex underwent further shortening and the Elsterian tunnel-valley fills that were incised into the glaciotectonic complex were partly deformed during the Saalian Drenthe and Warthe (1) ice advances.

Response of sedimentation processes in the Minjiang River subaqueous delta to anthropogenic activities in the river basin

Sedimentary processes in the subaqueous deltas of small mountainous rivers are very sensitive to environmental variation within the river basin and hydrodynamic conditions near the estuarine environment. Through radiometric dating and sediment grain size analysis of core sediments collected in the subaqueous delta area of the Minjiang River (MJR), we studied the sedimentary processes in this area since the 1950s and revealed their responses to human activities within the MJR basin. The dry density of core sediments in the MJR subaqueous delta varied from 0.81 to 1.32 g/cm3. The mean sedimentation rate was 0.61 cm/yr (0.68 g/cm2⋅yr) before 1963, and has increased to 1.04 cm/yr (1.05 g/cm2⋅yr) between 1963 and 1986, and then decreased to 0.46 cm/yr (0.41 g/cm2⋅yr) between 1986 and 2014. The core sediments were composed primarily of silt, and the main sediment type was clayey silt; the mean grain size varied from 5.1 to 22.3 μm, with a mean value of 10.3 μm. With increasing anthropogenic activity within the MJR catchment, the land use pattern changed markedly. Soil erosion intensified, and the sediment flux discharged by the MJR to the sea clearly increased; consequently, the sedimentation rate in the subaqueous delta also increased. However, owing to dam construction, large quantities of sediment were trapped within reservoirs, decreasing the sediment flux discharged by the MJR to the sea, affecting the sedimentation rate in the subaqueous delta and also changing the sediment frequency curve from a bimodal pattern to a single-peak pattern.

Method for Estimating Sediment Mass Movement from Delta Recutting: A Case Study Using Single Beam Sonar in Deer Creek Reservoir

The recutting of delta sediments typically occurs during reservoir drawdown in the summer months. It can affect various reservoir processes and can impact water quality because of resuspending nutrients during warm periods supports phytoplankton growth. Quantifying this sediment movement is a key element for evaluating the life and quality of a reservoir. This study targets reservoirs in the intermountain region of the U.S. These reservoirs are filled in the spring, then drawdown through the summer to provide irrigation water. Incoming sediment loads are generally restricted to spring high flows, with little new sediment entering the reservoirs during the remainder of the year. As the reservoirs undergo drawdown, the sediment deposited in the delta region during spring flows is re-cut from the exposed delta and moved into submerged delta region. The majority of flow and sediment movement both above and below the water surface occurs in channels cut into the sediments during spring deposition. During recutting, channels in the exposed sediments often move, but the submerged channels are more stationary. Traditional single-beam sonar surveys are performed on a grid and changes are used to quantify sediment movements. This approach is not applicable to delta recutting as the grid resolution is not sufficient to resolve the relevant changes that occur in the narrow excised flow channels. This study explores the ability to quantify and monitor sediment mass movement in Deer Creek Reservoir (DCR) using a single beam sonar. Our method uses surveyed cross-sections across the flow channels. It is difficult to position boat passes exactly on previous survey lines, and small location differences in an up-stream or down-stream location can be significant because of the slope of the channel. To address this, we surveyed each line in two directions, then interpolated both the position and elevation data. We performed periodic surveys over a two-month period. We were able to document and quantify both sediment deposition and erosion areas. As expected, sediment movement was from the inlet areas toward the reservoir. The data showed both deposition and erosion depending on the distance from the reservoir head, which changed over the survey period. This method can be used to quantify sediment recutting and resuspension that can affect nutrient loads during critical warm, low-reservoir conditions, but is difficult to implement accurately.

Slowing rates of regional exhumation in the western Himalaya: fission track evidence from the Indus Fan

AbstractWe use apatite fission track ages from sediments recovered by the International Ocean Discovery Program in the Laxmi Basin, Arabian Sea, to constrain exhumation rates in the western Himalaya and Karakoram since 15.5 Ma. With the exception of a Triassic population in the youngest 0.93 Ma samples supplied from western Peninsular India, apatite fission track ages are overwhelmingly Cenozoic, largely <25 Ma, consistent with both a Himalaya–Karakoram source and rapid erosion. Comparison of the minimum cooling age of each sample with depositional age (lag time) indicates an acceleration in exhumation between 7.8 and 7.0 Ma, with lag times shortening from ∼6.0 Myr at 8.5–7.8 Ma to being within error of zero between 7.0 and 5.7 Ma. Sediment supply at 7.0–5.7 Ma was largely from the Karakoram, and to a lesser extent the Himalaya, based on U–Pb zircon ages from the same samples. This time coincides with a period of drying in the Himalayan foreland caused by weaker summer monsoons and Westerly winds. It also correlates with a shift of erosion away from the Karakoram, Kohistan and the Tethyan Himalaya towards more erosion of the Lesser and Greater Himalaya and Nanga Parbat, as shown by zircon U–Pb provenance data, and especially after 5.7 Ma based on Nd isotope data. Samples younger than 5.7 Ma have lag times of ∼4.5 Myr, similar to Holocene Indus delta sediments.

Assessing the carbon assimilation and production of benthic archaeal lipid biomarkers using lipid-RIP

Abstract Distributional patterns of intact polar lipids (IPLs) suggest that archaea are abundant in marine subsurface sediments. However, the production of archaeal lipids remains largely unresolved. We performed a lipid radioisotope probing (lipid-RIP) experiment using 14C-bicarbonate and 2-14C-acetate with surface and methanogenic marine sediments from the Rhone delta (Mediterranean Sea) to investigate mechanisms of carbon assimilation and to assess biomass production of benthic archaea. The direct determination of carbon assimilation rates into diagnostic IPLs in the experiments with 14C-bicarbonate were up to 9 times higher than in the incubations with 2-14C-acetate, implying that autotrophy is an important carbon pathway for the benthic archaea in the Rhone delta sediments. Production rates of polyglycosidic archaeols (AR) were one to two orders of magnitude higher than those of mono- and polyglycosidic glycerol dialkyl glycerol tetraethers (GDGTs), suggesting that the former IPLs are good biomarkers for active benthic archaea in marine sediments. In contrast, the low production rates of the monoglycosidic AR and GDGTs, indicate that a large fraction of these IPLs may represent fossil sedimentary remains from the water column. Unexpectedly, the lipid production rates of AR and GDGT core lipids (CLs) were similar to those of polyglycosidic IPLs. Considering the relatively short period of incubation (21 days), this suggests that CLs may be actively synthesized by benthic archaea in marine sediments and are not exclusively formed from the degradation of IPL precursors.

Effect of Sediment Load Boundary Conditions in Predicting Sediment Delta of Tarbela Reservoir in Pakistan

Setting precise sediment load boundary conditions plays a central role in robust modeling of sedimentation in reservoirs. In the presented study, we modeled sediment transport in Tarbela Reservoir using sediment rating curves (SRC) and wavelet artificial neural networks (WA-ANNs) for setting sediment load boundary conditions in the HEC-RAS 1D numerical model. The reconstruction performance of SRC for finding the missing sediment sampling data was at R2 = 0.655 and NSE = 0.635. The same performance using WA-ANNs was at R2 = 0.771 and NSE = 0.771. As the WA-ANNs have better ability to model non-linear sediment transport behavior in the Upper Indus River, the reconstructed missing suspended sediment load data were more accurate. Therefore, using more accurately-reconstructed sediment load boundary conditions in HEC-RAS, the model was better morphodynamically calibrated with R2 = 0.980 and NSE = 0.979. Using SRC-based sediment load boundary conditions, the HEC-RAS model was calibrated with R2 = 0.959 and NSE = 0.943. Both models validated the delta movement in the Tarbela Reservoir with R2 = 0.968, NSE = 0.959 and R2 = 0.950, NSE = 0.893 using WA-ANN and SRC estimates, respectively. Unlike SRC, WA-ANN-based boundary conditions provided stable simulations in HEC-RAS. In addition, WA-ANN-predicted sediment load also suggested a decrease in supply of sediment significantly to the Tarbela Reservoir in the future due to intra-annual shifting of flows from summer to pre- and post-winter. Therefore, our future predictions also suggested the stability of the sediment delta. As the WA-ANN-based sediment load boundary conditions precisely represented the physics of sediment transport, the modeling concept could very likely be used to study bed level changes in reservoirs/rivers elsewhere in the world.