Resistance of salt marsh substrates to near-instantaneous hydrodynamic forcing

Salt marshes deliver vital ecosystem services by providing habitats, storing pollutants and atmospheric carbon, and reducing flood and erosion risk in the coastal hinterland. Net losses in salt marsh areas, both modelled globally and measured regionally, are therefore of concern. Amongst other controls, the persistence of salt marshes in any one location depends on the ability of their substrates to resist hydrodynamic forcing at the marsh front, along creek margins and on the vegetated surface. Where relative sea level is rising, marsh elevation must keep pace with sea-level rise and landward expansion may be required to compensate for areal loss at exposed margins. This paper reviews current understanding of marsh substrate resistance to the near-instantaneous (seconds to hours) forcing induced by hydrodynamic processes. It outlines how variability in substrate properties may affect marsh substrate stability, explores current understanding of the interactions between substrate properties and erosion processes, and how the cumulative impact of these interactions may affect marsh stability over annual to decadal timescales. Whilst important advances have been made in understanding how specific soil properties affect near-instantaneous marsh substrate stability, less is known about how these properties interact and alter bulk substrate resistance to hydrodynamic forcing. Future research requires a more systematic approach to quantifying biological and sedimentological marsh substrate properties. These properties must then be linked to specific observable erosion processes, particularly at the marsh front and along creek banks. A better understanding of the intrinsic dynamics and processes acting on, and within, salt marsh substrates will facilitate improved prediction of marsh evolution under future hydrodynamic forcing scenarios. Notwithstanding the additional complications that arise from morphodynamic feedbacks, this would allow us to more accurately model the future potential protection from flooding and erosion afforded by marshes, while also increasing the effectiveness of salt marsh restoration and recreation schemes. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

Laboratory simulation of salt weathering under moderate ageing conditions: Implications for the deterioration of sandstone heritage in temperate climates

Salt weathering is a significant process affecting the deterioration and conservation of stone-built heritage in many locations and environments. While much research has focused on the impact of salt weathering under arid or coastal conditions with characteristic climatic conditions and salt types, many sites found to be experiencing salt-induced deterioration, such as sandstone rock-hewn cave temples in Gansu Province, China and sandstone buildings in the northern UK, experience high humidities, moderate temperature ranges, and different salt types. To evaluate the impact of salt weathering on sandstone-built heritage under such mild humid environmental conditions, a lab simulation experiment was designed. The experiment was carried out on three types of sandstone (used in the northern UK and Gansu Province, China) and utilized a realistic diurnal humidity and temperature cycle (85% RH/16°C + 60% RH/22°C), and three widespread damaging salts, that is, Na₂SO₄, MgSO₄, and the mixture of Na₂SO₄–MgSO₄. The nature and extent of deterioration was monitored by photography, weight loss, and the changes in petrophysical properties measured using hardness, ultrasonic pulse velocity (P-wave velocity), water absorption coefficient by capillarity, open porosity, and apparent density. All three sandstones were found to be susceptible to MgSO₄ and the mixture of Na₂SO₄–MgSO₄, but weakly affected by Na₂SO₄ under mild humid environmental conditions.     

Formation,mechanism and significance of alluvial-dammed lakes in Golmud River catchment,north-eastern Qinghai-Tibetan Plateau

This study investigated a series of dammed lakes and downstream-adjacent alluvial fans in the upstream to middle reaches of the Golmud River in the eastern Kunlun Mountain, on the north-eastern Qinghai-Tibetan Plateau (QTP). An optically stimulated luminescence (OSL) chronology shows the sediments of five dammed lakes developed from c. 45–40, 30–25, 18–14, and 12–8 ka, corresponding to MIS 3b, late MIS 3a, Last Deglaciation, and early Holocene, respectively. The remote sensing data show these dammed lakes have a total area of 109.4 km², with the lake volume of more than 4.0 km³. Symmetric alluvial fans from north–south tributary valleys produced OSL ages of c. 61–52, 42–31, 26–20, and 16–10 ka, corresponding to glaciation periods: the MIS 3c and MIS 3a, MIS 2, and the Last Deglaciation. This suggests that glacial activity is responsible for the alluvial fan development, where dammed rivers occurred first, but lake formation did not take place synchronously until later periods of strong hydrologic activity, resulting from northward intrusions of the Indian summer monsoon (ISM) or glacier melt. Thus, the blocking pattern is that river valleys were dammed during periods of glacial activity and lakes formed during wet periods. The lake formation and subsequent drainage may have resulted in: (i) impeded headwater incision and strengthening of downstream dissection; (ii) enriched the halite and potash in the distal Qarhan Salt Lake through hydrologic and hydrochemical processes of abundant water input, the salt lake expansion, salt redissolution from playa and final resedimentation during later dry periods. The alluvial-dammed lake pattern in the mountain-basin systems of eastern Kunlun Mountain offers a model for assessing the linkages between monsoon dynamics, geomorphic processes and distal salt lake evolutions in other arid regions.     

察尔汗盐湖别勒滩西北边缘浅层晶间卤水Li含量分布特征的研究

别勒滩位于察尔汗盐湖西部边缘地区,与东台吉乃尔盐湖接壤,同处柴达木盆地拗陷中心,在整个柴达木盆地盐湖中也是Li元素相对富集的地段之一。该地段在距北岸10 km的范围内,Li平均含量为0.594 g/L,最高可达1.225 g/L,与东台吉乃尔盐湖晶间卤水中Li含量很接近,但Mg/Li比值高出东台吉乃尔盐湖2³倍。该地段Li的水平分布大致可划分为3个区域:Ⅰ区Li含量为1.03倍。该地段Li的水平分布大致可划分为3个区域:Ⅰ区Li含量为1.0¹.2 g/L;Ⅱ区Li含量为0.41.2 g/L;Ⅱ区Li含量为0.4⁰.6 g/L;Ⅲ区Li含量为0.20.6 g/L;Ⅲ区Li含量为0.2⁰.3 g/L,其变化趋势是由北向南逐渐降低。别勒滩干盐湖底部盐层形成于距今25 000 a,上部盐层成盐期大约距今15 000 a。别勒滩西部边缘的涩聂湖是在大约距今10 000 a左右形成的新的具有表面卤水的全新世盐湖,该湖也是别勒滩区段主要物质来源的汇集区和补给区。     

马海钾矿第四纪沉积特征及盐湖演化

本文研究了马海盆地更新统一全新统含盐岩系分层沉积特征。下更新统:化学沉积中心与沉降中心一致,以石膏、石盐为主的盐层赋存于该统顶部。中更新统:盐层层数多,分布面积较下统增大。上更新统:含盐岩系范围小,盐类沉积丰富,盐矿物种类多,形成杂卤石、钾石盐为主的钾矿层。全新统:含盐率较高,有石盐相、钾石盐-光卤石相,缺失硫酸盐相。马海盐湖的演化历经湖盆形成期、湖盆封闭过渡期、湖盆封闭期、湖盆干化期四个时期。相应盐类沉积阶段为盐类聚集阶段、石盐沉积阶段、钠镁硫酸盐沉积阶段、钾镁盐沉积阶段。     

陕北盐盆马五6亚期构造分异对成钾区位的控制

本文以16口钻井资料为基础,通过井震联合标定解释,获取累计5595km二维地震剖面的速度等特征物性参数,利用变速成图方法,初步编制出陕北奥陶纪盐盆主要含钾层段——马家沟组五段六亚段盐系等厚图,并进行相应的构造分异解析。提出在陕北盐盆奥陶系马家沟组五段六亚段沉积期,盆底总体表现为"两坳夹一隆"的构造样式,其中厚度大于150m的成盐凹陷主要有5个。西部盐坳的发现、东二盐凹被进一步分解为东、西2个次级盐洼、以及"两坳夹一隆"构造样式的提出,系本次研究取得的新进展和认识,表明陕北盐盆并非是一个"平底锅",其内部存在多个受同沉积断裂控制的、相对活动的次级盐凹,这些次级盐凹将有利于富钾卤水的汇聚,为可能的大规模海相钾盐成矿提供了足够的可容空间和有利的构造区位。     

四川盐源盐矿成盐成钾分析预测

四川盐源盆地盐矿成盐于早、中三叠世时期,区域构造复杂,经历多期次的构造变动与演化,在成盐后经历了种种的基底反复变动后形成盐矿底辟构造。以前在该区域做过多方面的研究工作,其中包括三叠纪岩相古地理及生物古地理、三叠系地层、区域古构造演化及水化学分析、物探、钻探等勘探工程。通过这些工作可以证实,盐源盆地在早、中三叠世,经历了蒸发岩盆地的发育阶段。盆地不仅发育有石膏夹层,而且保存有石盐层及含盐卤水层,但有盐无钾。通过对上覆的陆相古近纪和新近纪盆地中出现的三叠系岩盐层和盐丘的研究发现,它们与基底为含盐的海相蒸发岩有一定的内在联系,尽管还不能确定其盐、钾资源前景,但可以确定该区域有成钾盐矿藏的条件和可能,因此,该盆地有可能成为深入研究成盐找钾的重点地区。     

Origin of aragonite in a continental saline seep,north Queensland

Aragonite, low‐magnesian calcite, gypsum and halite were identified by X‐ray diffraction and electron microbeam techniques in mineral precipitates near a salt seep 50 km southwest of Charters Towers in north Queensland. The chemistry of water from the creek and from the groundwater at the salt seep shows that Mg:Ca ratios are greater than or equal to 1.5 throughout the year. The formation of halite and gypsum is due to evaporative concentration of the water at the seep and that of the carbonates, in particular aragonite, is probably due to a combination of evaporation and photosynthetic activity by diatoms.     

渤海海冰断裂韧度试验

海冰的断裂韧度是近海结构冰荷载分析的重要参数,也是影响海冰断裂、重叠和堆积等动力行为的主要力学特性。2011—2012年冬季现场采集了渤海莱州湾的海冰试样,在室内低温环境下通过三点弯曲试验测得了不同温度、盐度和加载速率下的海冰断裂韧度K_IC。结果表明,卤水体积(温度和盐度)和加载速率对K_IC的影响比较显著。随温度和加载速率的降低,K_IC值均会增大,且与卤水体积的平方根呈负指数关系。为极限破坏状态下海冰的断裂过程和冰荷载分析的参数选用提供了依据。     

CY-1钻孔盐水泥浆护壁技术

CY-1钻孔是河北沧县盐矿深部勘探的第一钻,在钻探施工中,泥浆护壁是遇到的技术难题之一。针对工区施工条件采用了分段泥浆转换方案,确保了施工安全及质量。实践表明,该钻孔泥浆护壁方法技术路线可行,实现了顺利取心,为沧州地区深部盐矿勘探积累了经验。详细介绍了该孔盐水泥浆护壁技术。