Spatially distributed modelling of soil erosion and sediment yield at regional scales in Spain

Initiated by the need to quantify erosion rates and the impacts of global changes on erosion, several attempts have been made to apply erosion models at regional scales. However, these models have often been directed towards on-site soil erosion estimates, emphasising sheet and rill erosion processes, and disregarding gully erosion, channel erosion and sediment transport. These models are therefore of limited use for the assessment of sediment yield, off-site impacts of erosion, and for the development of environmental management to control these impacts at regional scale. This study analyses and compares three spatially distributed models for the prediction of soil erosion and/or sediment yield at regional scales: the WATEM-SEDEM model that is based on the empirical Revised Universal Soil Loss Equation (RUSLE) in combination with a sediment transport equation, the physics-based Pan European Soil Erosion Risk Assessment model (PESERA), and a newly developed Spatially Distributed Scoring model (SPADS). The three models were applied to 61 Spanish drainage basins and model predictions were evaluated against data on measured reservoir sedimentation rates. Global data sets on land use, climate, elevation and soil characteristics were used as model input for WATEM-SEDEM and SPADS, whereas published soil erosion estimates of PESERA at 1 km² resolution were used directly. SPADS and WATEM-SEDEM provided best results after separate calibration for basins with a Sediment Delivery Ratio (SDR) higher than 5% and those with an SDR lower than 5%. In this way, SPADS explained 67% of variation in sediment yield, while WATEM-SEDEM explained 48% of the variation. PESERA represents a promising alternative to the use of empirical models at the regional scale as it can be applied to very diverse environments with little calibration. However, PESERA provides soil erosion rates and not sediment yield estimates. For most basins PESERA soil erosion rates vary between fifty and close to zero percent of total sediment yield. Two major factors may explain this discrepancy between modelled soil erosion rates and measured sediment yield. First, it may be that PESERA underestimates soil erosion under Mediterranean conditions, although PESERA soil erosion rates are of the same order of magnitude as erosion rates measured in erosion plot studies. Second, gully-, river channel erosion and sediment transport processes may be much more important than sheet- and rill erosion for regional scale sediment yield in these environments. These issues therefore require further attention in future model development. Although spatially lumped models provide better predictions of sediment yield at the basin scale, and while validation of the predicted spatial patterns of sources and sinks of sediment requires further research, spatially distributed models are expected to be of value to support management decisions regarding the assessment of on-site and off-site impacts of erosion at the regional scale.     

Distribution Characteristics of Effective Source Rocks and Their Control on Hydrocarbon Accumulation: A Case Study from the Dongying Sag, Eastern China

The exploration conducted in the Bohai Bay basin, eastern China has demonstrated that the abundant petroleum resources have close affinities to the hydrocarbon kitchen with rich organic matter. A number of oil-generating associations with various characteristics of organic geochemistry and assemblages of multiple reservoir facies are developed due to the multi-center sedimentation, multi-source supply and multi-cycle evolution of filling, which have resulted in the formation of multiple oil and gas accumulation zones of various layers and trap styles. Among them the Paleogene Shahejie Formation is the most important hydrocarbon accumulation combination in the Dongying sag. Heretofore, its proved reserve has reached nearly 1.8×109t, which accounts for more than 90% of the total proved reserves of the Dongying sag. Based on previous studies, more than 600 source rock samples and 186 crude oil samples of the Shahejie Formation, collected from 30 oilfields, have been treated with organic geochemical testing     

Late Holocene environmental changes and anthropogenic impact in Dee Why Lagoon,New South Wales

Late Holocene environmental changes were examined in Dee Why Lagoon, New South Wales, based on the sedimentological, geochemical and geochronological analysis of six cores collected from the fluvial delta and lagoon basin. The lagoon formed about 7300–7200?cal yr BP, following the post-glacial marine transgression and establishment of a sand barrier. Infilling of the lagoon occurred at a rate of 0.09–0.15?mm/yr until about 3300–3200?cal yr BP, when the barrier closed, resulting in mostly freshwater conditions, as evidenced by a change from pyrite-rich units to sediment containing little sulfur and a lack of foraminifera. Sedimentation rates increased to 0.23 then 0.43?mm/yr until about 100?years ago. Post-European land clearance led to an increase in sedimentation rates to 1.0–1.3?mm/yr on the fluvial delta, which are lower than those from other wave-dominated estuaries in New South Wales as well as those estimated by previous studies in Dee Why Lagoon. Our study shows that the fluvial delta started forming much earlier than originally thought, based on results of radiometric dating, and confirmed using sedimentological and geochemical data, as well as a critical examination of historic aerial photographs. Human impact has resulted in an increase in heavy metal (Cu, Pb, Zn) and metalloid (As) concentrations in the recent sediment, most likely attributed to stormwater discharge. Pb and As concentrations are above the ANZECC high sediment quality guideline values at the site closest to the stormwater outlet, with As-based pesticides one of the possible sources. Using the mean enrichment quotient, which is based on normalised Cu, Pb and Zn concentrations over their normalised background concentrations, we show that the surface sediments in Dee Why Lagoon are severely enriched, reflecting the recent anthropogenic impact that has also led to an increase in sedimentation rates.     

盐分对黏性土的沉积特性与表面电位影响研究

为了明晰黏土矿物和盐分浓度在沉积过程中所起的作用及物理机制,选取高岭土、膨润土及两者组成的混合土进行粒径分析试验、沉积试验和Zeta电位测试。结果显示,盐分环境下高岭土和膨润土的平均粒径增大,部分黏粒组向粉粒组转化。高岭土在蒸馏水环境下和盐水环境下,最终都形成土-水的稳定分界面,但是絮凝稳定时间在盐分环境下更短。膨润土在蒸馏水环境下处于稳定的分散体系中,在盐水环境下迅速絮凝沉积。混合土在蒸馏水环境下,上部澄清层和下部沉淀层之间存在土颗粒的悬浮层,且该层的高度最终稳定;盐水环境下,混合土则迅速的发生土水分离。随着NaCl浓度增加,膨润土和高岭土的Zeta电位绝对值降低,因此胶粒组的絮凝行为对平均粒径产生影响,进而影响其沉积特性。     

Stratigraphic architecture of Solander Basin records Southern Ocean currents and subduction initiation beneath southwest New Zealand

Solander Basin is characterized by subduction initiation at the Pacific‐Australia plate boundary, where high biological productivity is found at the northern edge of the Antarctic Circumpolar Current. Sedimentary architecture results from tectonic influences on accommodation space, sediment supply and ocean currents (via physiography); and climate influence on ocean currents and biological productivity. We present the first seismic‐stratigraphic analysis of Solander Basin based on high‐fold seismic‐reflection data (voyage MGL1803, SISIE). Solander Trough physiography formed by Eocene rifting, but basinal strata are mostly younger than ca. 17 Ma, when we infer Puysegur Ridge formed and sheltered Solander Basin from bottom currents, and mountain growth onshore increased sediment supply. Initial inversion on the Tauru Fault started at ca. 15 Ma, but reverse faulting from 12 to ca. 8 Ma on both the Tauru and Parara Faults was likely associated with reorganization and formation of the subduction thrust. The new seabed topography forced sediment pathways to become channelized at low points or antecedent gorges. Since 5 Ma, southern Puysegur Ridge and Fiordland mountains spread out towards the east and Solander Anticline grew in response to ongoing subduction and growth of a slab. Solander Basin had high sedimentation rates because (1) it is sheltered from bottom currents by Puysegur Ridge; and (2) it has a mountainous land area that supplies sediment to its northern end. Sedimentary architecture is asymmetric due to the Subtropical Front, which moves pelagic and hemi‐pelagic sediment, including dilute parts of gravity flows, eastward and accretes contourites to the shelf south of Stewart Island. Levees, scours, drifts and ridges of folded sediment characterize western Solander Basin, whereas hemi‐pelagic drape and secondary gravity flows are found east of the meandering axial Solander Channel. The high‐resolution record of climate and tectonics that Solander Basin contains may yield excellent sites for future scientific ocean drilling.     

Detrital zircon and apatite constraints on depositional ages,sedimentation rates and provenance: Pliocene Productive Series,South Caspian Basin,Azerbaijan

We used detrital zircon U/Pb geochronology and apatite (U–Th–Sm)/He thermochronology to better constrain depositional ages and sedimentation rates for the Pliocene Productive Series in Azerbaijan. U/Pb analysis of 1,379 detrital zircon grains and (U–Th–Sm)/He analysis of 57 apatite grains—from Kirmaky Valley and Yasamal Valley onshore sections, Absheron Peninsula—yielded two distinct sub‐populations: “young” Neogene grains and “old” Mesozoic, Palaeozoic and Proterozoic/Archean grains. The large numbers of Neogene age grains (around 10% of all grain ages) provided a new absolute age constraint on the maximum depositional age of the Lower Productive Series of 4.0 Myr. These “young” Neogene zircon grains most likely originated from volcanic ash falls sourced from the Lesser Caucasus or Talesh Mountains. In this paper we propose a timescale scenario using the maximum depositional age of the Productive Series from detrital zircon grain U/Pb constraints. Potential consequences and limitations of using apatite (U–Th–Sm)/He dating method in estimating maximum depositional ages are also discussed. These new age constraints for the Lower Productive Series gave much faster sedimentation rates than previously estimated: 1.3 km/Myr in the South Caspian Basin margin outcrops and up to 3.9 km/Myr in the basin centre. The sedimentation rates are one of the highest in comparison to other sedimentary basins and coeval to global increase in sedimentation rates 2–4 Myr. The older group of detrital zircon grains constitutes the majority of grains in all sample sets (~80%). These older ages are inferred to reflect the provenance of the Productive Series sediment. This sediment is interpreted to have been derived from the Proterozoic and Archean crystalline basement rocks and Phanerozoic cover of the East European Craton, Proterozoic/Palaeozoic rocks of the Ural Mountains and Mesozoic sedimentary rocks of the Greater Caucasus. This sediment was likely supplied from northerly sourced drainage that emptied into the South Caspian Basin.     

陕西左家庄金矿床特征

左家庄金矿矿质来源于近矿地层,成矿热液为同生沉积建造水,硫化物石英脉的形成是含矿热液流体沿左旋剪切扭动构造隐蔽面充填的结果.对其主要载金矿物黄铁矿的热电性测定,表明黄铁矿为空穴型导电,该矿床剥蚀程度不大,属上部出露.     

梵净山地区板溪群红子溪组钙质岩系中大理岩透镜体成因探讨

梵净山地区板溪群红子溪组钙质岩系中广泛发育大理岩透镜体。形成此岩系的控制因素可能为振荡频繁的构造运动或气候条件。通过仔细观察,发现大理岩透镜体有条带状、似层状断续产出2种,初步认为透镜体是成岩过程中差异性压实作用的产物,不是某种环境沉积的透镜体。     

Geochemistry of Sedimentation and Diagenesis in Qixia Formation (Early Permian) of Badong,Hubei Province, China: Implications for T-R Cycle Interpretation

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内蒙古呼伦湖表层沉积物的矿物组成和沉积速率

呼伦湖表层沉积物的取样和分析表明,沉积物主要由碎屑矿物和自生碳酸盐矿物组成。碳酸盐含量为10％—18％。碳酸盐沉积作用与湖水的较高含盐量和碳酸盐过饱和度有关。湖泊中心HL8号柱样的~(210)Pb测定结果是,10cm以上平均沉积速率0.25cm/a,10—12cm为0.05cm/a。60年代开始随湖泊水位上涨沉积物输入量迅速加大。