Quaternary sedimentology of the Rose Creek fan delta, Walker Lake, Nevada, USA, and implications to fan-delta facies models

The 3·2 km long Rose Creek fan delta of west‐central Nevada is prograding from an active rift margin into the 32 m deep Walker Lake. A case study of the forms, processes and facies of this fan delta reveals that the proximal and medial zones mainly are of sub‐aerial origin, and the distal zone is of lacustrine origin. Pebbly to bouldery rock‐avalanche mounds >100 m thick (Facies A) and muddy to bouldery debris flow levées 0·5 to 2·0 m thick (Facies B) dominate the proximal zone, whereas mostly matrix‐supported cobbly pebbly debris flow lobes 0·1 to 1·0 m thick (Facies C) typify the medial zone. Surficial pebble lags and gully fills (Facies D) are widespread in both zones but, in exposures, comprise only partings or lenticles between debris flow units. The distal fan delta mainly consists of lakeshore to lake‐bottom tracts formed by extensive wave reworking of debris flow facies. Nearshore deposits include erosional cobbly boulder lag beaches (Facies E), pebbly constructional beaches attached at headcuts or on barrier spits (Facies F), pebbly upper shoreface (Facies G) and sandy lower shoreface (Facies H) tracts positioned lakeward of the beach, and pebbly landward‐dipping foresets (Facies I) and backshore‐pond sand and mud (Facies J) present landward of the spits. Erosional lag beaches fringe the windward north side of the fan‐delta front, attached constructional beaches characterize the central zone, and southward‐elongating barrier spits typify the leeward south side, extending from the zone of greatest projection of the fan delta into the lake. Shoreline facies asymmetry results from largely unidirectional longshore drift caused by high fetch to the north and minimal fetch to the south, combined with the arcuate shape of the fan‐delta front. The spits overlie a platform deposited below common wave base consisting of south‐east‐trending cones of pebbly Gilbert foresets (Facies K) and sandy toesets (Facies L). Typically slumped silt and mud (Facies M) fringe both this platform and lower shoreface sand in deeper water. This case demonstrates facies types and patterns that are inconsistent with the widely promoted fan‐delta facies model having a front consisting of an apron of radially directed Gilbert foresets deposited where sub‐aerial flows enter the lake. The Rose Creek fan‐delta front instead features a sharp contact between sub‐aerial and lakeshore facies formed where waves erode, sort and redistribute heterogeneous debris flow sediment into the various shallow‐to‐deep lake facies. Gilbert foresets are present only in the lee of the fan delta where sediment moving by longshore drift reaches the brink of the spit front. This facies scenario results from the infrequency of fan‐building events versus nearly constant wind‐induced waves, a scenario that, in contrast to the popular Gilbert model, probably is the norm for fan deltas. The level of Walker Lake, and thus the position of wave reworking on the Rose Creek fan delta, fluctuated over a range of ～157 m during the last 18 kyr, producing complex interfingering between sub‐aerial and lakeshore facies across a 1700 m wide radial belt, typifying a wave‐modified, freestand lacustrine fan delta.     

Migration patterns of Neolithic settlements on the abandoned Yellow and Yangtze River deltas of China

Archaeological records of the Neolithic settlements on the eastern China coast between 35°N and 30°N, an area covering the abandoned Yellow River and the Yangtze River delta plains, reveal that Neolithic people moved from the Yellow River basin onto the northern coast for fishing, hunting and dry-land agriculture ~ 7000 yr ago. Marine transgression interrupted their activities on the low-lying (2-5 m in elevation) coastal wetlands between 6000 and 5000 yr ago, after which they reclaimed their land near the river mouths. Their migration routes on the southern Yangtze delta plain indicate another scenario: early Neolithic communities moved onto the plain for wet-rice cultivation. Despite relative sea-level rise from 7000 to 4000 yr ago, a large number of settlements were established on the lowlands between the eastern Chenier Ridges and the western Taihu Lake depression. The Chenier Ridges, with ~ 1.0 m higher topography than the adjacent coastal area, played a role in sheltering the Neolithic people. Subsequently, settlements waned considerably, possibly due to further marine inundation combined with cold climate. The present study shows that migration patterns of the Neolithic settlements are closely associated with a gradually rising sea level between 7000 and 4000 yr ago.     

基于图形数据差的居民地变化信息提取方法研究

作为空间数据库更新的一项关键内容,变化信息的提取直接关系着整个更新工作的效果。居民地是空间实体中变化频率较高的要素,成为空间数据库更新的关注重点。文中针对当前提取方法尚未关注空间实体具体变化的问题,提出一种基于图形数据差的居民地变化信息提取方法。根据图形数据差的分类,实现变化信息的归类,继而通过图形数据差的判别方法,达到居民地变化信息提取的目的。通过实验验证该方法的可行性和有效性。     

委内瑞拉卡拉高莱斯合同区储层沉积微相研究

以岩心分析和大量的测井，地震资料为基础，通过对各种沉积相标的分析，对委内瑞拉卡拉高莱斯合同含油层系的沉积相类型，微相组成以及主要沉积微相的特征进行研究，笔者认为该区海内库莱（Mercure)组和奥菲西纳（Oficina)组为一套海陆过渡环境的三角洲相沉积，储集层主要为三角洲平原分流河道砂体，三角洲前缘水下分流河道及与之同期伴生的河口坝，前缘席状砂砂体，其次，在小层划分，对比的基础上，根据测井，地城和生产动态资料，分析了合同区含油层系100余个小层的沉积微相的平面展布状况及沉积微相在纵向上的演化规律。     

论长江三角洲都市经济圈的形成及其核心城市上海的功能定位

加快形成长江三角洲都市经济圈及充分发挥上海的核心功能，不仅对于加快长江三角液地区经济的持续，快速，健康发展具有重要意义，而且也将对贯彻国家长江发展战略和西部大开发战略起到积极推动作用，通过分析形成长江三角洲都市经济，圈的理论基础和主要发展思路，从区域经济协调发展的角度，提出上海作为该地区的首位城市，应当在产业结构升级，区域 要素市场培育，综合交通运输网构建及区域经济一体化服务建设等四方面发挥核心城市的;功能。     

广东三水盆地第四纪网状河沉积特征

珠江三角洲西北部的三水盆地范围内发育典型的网状河体系。它们具有重复分叉合并、坡降低以及河道深且窄的特点，并且发育天然堤、河间湖泊和洼地等地貌单元。钻井资料显示，网状河的沉积记录以泛滥平原地区沉积的悬浮负载的细粒沉积物为主，由砂砾和砂组成的河道沉积物分布比较局限，呈较窄的带状，被包裹在细粒的泛滥平原积物之中。主干河道表现出较高侧向稳定性垂向继承性，形成了较厚的砂体。较小的分叉河道则容易发生决口改道，沉积了较薄的砂体。河间湖泊沉积主要为含植物碎片的灰黑色粉砂质淤泥，沼泽中植物遗体的堆积形成了泥炭层。晚更新世以来的构造沉降、全球海平面上升以及河流搬运物质的快速加积是珠江三角洲平原地区形成网状河体系的主要原因.     

鄂尔多斯盆地南部延安组水下分流河道型湖泊三角洲体系的沉积构成

采用过程沉积学和成因地层分析相结合的方法,在鄂尔多斯盆地南部延安组中识别出了一种新的湖泊三角洲沉积体系。它与普通河控型湖泊三角洲的主要区别是下三角洲平原部分不是由典型的分流河口坝和前三角洲沉积组成,而是由多分支的水下分流河道、水下决口扇和湖泊沉积组成。在边缘三角洲部分,时常受波浪作用的改造,并形成各种类型的湖滨沉积。本文比较详细地讨论了这类湖泊三角洲的沉积构成及其发育的边界条件。     

The formation of circular littoral cones from tube-fed pāhoehoe: Mauna Loa,Hawai'i

Pyroclastic cones along the southwest coast of Mauna Loa volcano, Hawai'i, have a common structure: (a) an early formed circular outer rim 200–400 m in diameter composed mostly of scoria and lapilli, and (b) one or more later-formed inner rims composed almost exclusively of dense spatter. The spatter activity locally fed short lava flows that ponded within the outer rims. Based on various lines of evidence, these cones are littoral in origin: relationships between the cones and associated flows; the degassed nature of the pyroclasts; and (although not unequivocal) the position of the cones relative to known eruptive vent locations on Mauna Loa. Additional support for the littoral interpretation comes from their similarity to (smaller) littoral cones that have been observed forming during the ongoing Kilauea eruption. The structure of these Mauna Loa cones, however, contrasts with that of standard Hawaiian littoral cones in that there is (or once was) a complete circle of pyroclastic deposits. Furthermore, they are large even though associated with tubefed phoehoe flows instead of 'a'. The following origin is proposed: An initial flow of tube-fed phoehoe into the ocean built a lava delta with a base of hyaloclastite. Collapse of an inland portion of the active tube into the underlying wet hyaloclastites or a water-filled void allowed sufficient mixing of water and liquid lava to generate strong explosions. These explosions broke through the top of the flow and built up the outer scoria/lapilli rims on the solid carapace of the lava delta. Eventually, the supply of water diminished, the explosions declined in intensity to spattering, and the initial rim was filled with spatter and lava.     

Quaternary changes in delivery and accumulation of organic matter in sediments of Lake Biwa, Japan

A 911-m-long sediment core from Lake Biwa, Japan, provides a record of organic matter delivery and accumulation in this large lake during a succession of tectonic and climatic changes dating back to the latest Pliocene. Sediments deposited since 430 ky are profundal; older sediments vary in setting between shallow-water and fluviodeltaic conditions, with occasional deep-water intervals. C/N ratios identify algal production as the dominant source of organic matter throughout the core, although the proportion of land-derived contributions episodically increases in the fluviodeltaic and shallow-water sediments. Rates of organic matter delivery and burial in lake sediments change in response to glacial-interglacial climate changes over the past 430 ky. Sediments deposited during interglacial intervals have organic carbon mass accumulation rates up to 9 times greater than those from glacial intervals, reflecting interglacial climates that were wetter than glacial climates. Algal production of organic matter increased during interglacial times because of greater wash-in of soil nutrients, and organic matter preservation was enhanced because of faster sedimentation rates.     

基于ESDA的长三角区域经济差异分析

区域经济发展不仅与区域自身相关,更受到周边区域的相互作用,基于此,本文引入ESDA技术(探索性空间数据分析)来分析区域经济差异。通过对长三角区域2001~2013年各市的人均GDP数据进行ESDA全局和局部自相关分析,描述了21世纪开始的13年以来长三角市域经济格局在空间上的分布及演化,并对空间格局成因进行了科学分析。结果表明:长三角地区表现出强的自相关,即相似城市间有显著的空间集聚特征,并且集聚特征逐年增强。然而,区域经济在空间分布上存在明显的不均衡,相离较远的地区差异还是很大,如上海、苏南地区与苏北、浙南地区。