Quartz-dominated Cenozoic gravels in southeastern Australia: where did all the quartz come from?

Upper Cenozoic fluvial gravels in the Canberra region are quartz-dominated (>95 vol% quartz), whereas modern bedload sediments contain less than 50 vol% quartz and a range of lithologies that broadly reflect the catchment geology. Potential reasons for the compositional difference include changes in catchment geology, sediment transport distance, post-depositional weathering and regolith history. Breakage of unsound clasts during transport does not explain the difference because sediment transport distances in the Cenozoic were similar to today. Post-depositional weathering of less resistant clasts is ruled out because the Cenozoic gravels are clast-supported and preserve original bedding. During much of the Cenozoic, rainfall was significantly higher than the present, and rainforest species were present in the local and regional vegetation. Weathering regimes were likely very different from today, and deep weathering of catchment lithologies may have favoured the supply of quartz-rich gravelly sediment to the river systems.     

云南一条新的生物地理线

云南南部与东南部热带地区在地理上接近,具有类似的热带季风气候和热带雨林植被,它们的植物区系均以热带成分占优势,在现代植物区系分区上都属于热带亚洲或印度—马来西亚植物区系。研究发现在云南东南部植物区系中具有丰富的东亚植物区系的代表成分,如木兰科、山茱萸科、菝葜科、茶科、安息香科、山矾科、忍冬科、冬青科、卫矛科等,意味着它...     

深水块状砂岩沉积特征及其成因机制探讨:以鄂尔多斯盆地东南缘上三叠统长6油层组为例

近几年对鄂尔多斯盆地东南部延长组的石油勘探取得了重要突破,发现了多口达工业油流的油井.盆地东南部紧邻晚三叠世鄂尔多斯盆地湖盆沉积中心,在湖退背景下全盆广泛发育长6厚层砂体,目前已成为油气勘探的主要目标.依据岩心、露头观察等识别出长6沉积类型具有重力流沉积的特征,并认为盆地东南部长6沉积期广泛发育的深水块状砂岩属于受东北...     

云南省开远地区沉积型锰矿找矿前景分析

云南省开远地区位于南盘江克拉通盆地内,是滇东南地区传统的优质富锰矿产区。通过对云南省开远地区沉积型锰矿地质特征以及区内典型锰矿床研究,结合研究区遥感矿化蚀变信息特征、水系沉积物地球化学特征,系统总结了区内含锰岩系法郎组的成矿特征及找矿标志,在研究区内圈出了两个锰矿找矿远景区,通过地表山地工程验证,取得了较好的找矿成果,为在区内寻找锰矿指明了方向。     

阿尔金断裂带东南缘含油气盆地群的形成演化

沿阿尔金断裂带东南侧发育六个中、新生代的含油气盆地，盆地的边缘或盆地内部发育一系列的近东西走向、与阿尔金断裂锐角相交的断裂，该组断裂对盆地的隆坳格局和地层分布具有控制作用，盆地具有箕状结构或不对称结构特点。沿阿尔金断裂带方向，保罗系、白垩系、古近系、新近系的厚度和沉积特征在时空上呈有规律性变化，显示了阿尔金断裂带时、空活动的差异性。根据侏罗纪盆地在阿尔金断裂带两侧的展布特征和柴达木盆地西部发育的鼻状构造及其沉积演化特征，推断阿尔金断裂带中、新生代经历了多期不同方向的走滑运动。     

使用有序样品聚类分析法划分东南沿海地震活跃幕

在对东南沿海地震带空间分布的边界重新做界定的基础上,对该带二十世纪以来地震活跃幕的分段进行了探讨。主要使用了有序样品聚类分析中的离差平方和法、最优分割法,再结合地震学应变能释放水平进行划分。并以离差平方和法中的误差函数的参数变化为标准对划分的结果进行了判定及F值检验,认为该带划分成四个活跃幕较为合理。     

藏东南峡谷地区不同下垫面地表通量变化特征及其与降水的关系

利用藏东南峡谷地区排龙站、丹卡站、卡布站、墨脱站四个站点2018年11月至2019年10月的涡动协方差仪观测资料,分析藏东南峡谷地区不同位置入口、中段和末端地表通量变化的特征及其与局地降水的关系.研究表明:地表通量月平均日变化特征为夜间潜热通量大于感热通量,日间呈单峰变化特征.排龙站和丹卡站感热11月至次年4月较强,5...     

Salt Marsh Dieback: An overview of recent events in the US

This paper provides an overview of the marsh dieback events that have been observed along the east and gulf coasts of the U.S. over the past decade. It is likely that some of the recently reported changes in marsh vegetation were affected by physical or biotic disturbances that are known to generate bare areas, such as overgrazing or wrack smothering. Other areas may be experiencing a state change such as that caused by long-term changes in sea level. However, sites in many areas are not readily explained by these causes and are considered to have experienced “sudden dieback.” In such cases, there are observations that the above-ground plant material thinned or browned or, in some cases, failed to re-emerge in the spring; the dieback occurred over a period of months and usually affected multiple sites within the area; and there is evidence that these events are transient (through successful transplants or natural regrowth/recovery), although some areas take years to recover. We explored the potential linkage of dieback with drought (as characterized by the Palmer Severity Drought Index), and found that there is evidence for an association in the southeast (GA and SC) and the Gulf (LA), but not in the mid-Atlantic (DE, VA) or northeast (ME, RI, CT). We also review the evidence for potential causes of sudden dieback, including changes in soil chemistry, fungal pathogens, top–down consumer controls, and multiple stressors. There is currently no single explanation that can be applied to recent dieback. We highlight the need for the development of improved diagnostics that will allow us to better classify dieback areas and provide evidence for (or against) potential causes.     

腾格里沙漠东南缘荒漠植被盖度月变化特征及生态恢复

 研究表明:封育区植被盖度一年四季大于未封育区,在正常年份的生长季内前者植被盖度为17.89%~29.39%,后者为11.60%~16.05%。封育区和未封育区150 m样线上的灌木植物在70~90株(丛)和60~70株（丛）之间,基本保持稳定;草本植物个体数月变化则显著,未封育区从4月份以后数量递增, 7、8月显著增加,8月底达到最大值,而封育区则表现为4、 5月增加,6月减少,7、8、9月线性增加,达到最大值,且未封育区草本植物的数量少于封育区。未封育区由于植被盖度低,灌丛分布不均匀,沙面裸露多,地面风沙流活动强烈,白刺沙包风蚀严重;而封育区植被盖度较大,灌丛分布较均匀,风沙流活动弱,白刺沙包稳定,形成了较为稳定的自然植被生态系统。试验表明,在当地气候和地理条件下,通过封育或避免人为干预,荒漠区生态植被的自然恢复,可大大增加防风固沙能力,改善当地的生态环境。