SEDIMENTS FORMING THE BED AND BANKS OF THE LOWER MISSISSIPPI RIVER AND THEIR EFFECT ON RIVER MIGRATION

Physiographic features and depositional history of the sediments forming the bed and banks of the lower 200 miles of the Mississippi River are summarized. From mile 200- 160 the river is scouring into coarse substratum sands, between miles 160 and 80 into Pleistocene clays, and between mile 80 and 0 chiefly into prodelta and interdistributary clays. Point-bar accretion averages 500 acres per river mile in the uppermost segment, 200 acres per river mile in the middle segment, and 30 acres per river mile in the lower- most segment. The occurrence of bends caused by faulting or formed during seaward growth of the delta, and the occasional existence of coarse materials in the path of the stream are significant factors in the initiation of meanders. The composition of the bed and banks, and the length of channel occupation are important in the rate and extent of migration. Migration of the river between miles 0 and.160 has been and should continue to be very slow.     

加勒比板块边缘中新生代构造古地理特征及演化

加勒比板块边缘带包括西缘中美洲古陆块及火山岛弧、北缘大安的列斯岛弧带、东缘小安的列斯岛弧带和南缘南美板块北部4个部分,其沉积充填特征存在明显差异。加勒比板块边缘接受沉积时间由西向东逐渐变晚,其中中美洲古陆块以碳酸盐岩及火山碎屑岩充填为主,大安的列斯岛弧带及南美板块北部地区以碳酸盐岩—碎屑岩混合沉积充填为特征,中美洲火山岛弧带与东缘小安的列斯岛弧带以火山碎屑岩充填为主,造成这种沉积充填差异的主要原因是构造演化控制下的加勒比地区的古地理特征不同。加勒比板块及其周缘地区的构造古地理演化共经历4个阶段:(1)侏罗纪裂谷期,泛大陆的裂解使得南、北美板块边缘发育裂谷相;(2)白垩纪被动陆缘期,古加勒比海槽的进一步打开使得南、北美板块边缘发育被动大陆边缘浅海相;(3)晚白垩世—始新世碰撞造山期,加勒比板块与南、北美板块的碰撞拼合作用使得加勒比板块南、北缘均从海相转变为碰撞造山陆相;(4)始新世以来的分异期,随着古加勒比海槽的消亡和北缘碰撞拼合的结束,加勒比板块东缘及西缘的火山岛弧带进一步发育,而北缘及南缘继续发育陆相沉积。     

Evaluation,repair and stabilization of the boling sinkhole

Abrupt ground subsidence occurred along FM 442, approximately 3 miles east of Boling, in Wharton County, Texas, in August 1983 The subsidence created a depression of approximately 250 feet in diameter with a maximum depth of about 25 feet. Roadway collapse, pavement breakage, and inundation of the sinkhole by subsurface waters forced the closure of FM 442 to thru-traffic The vicinity of the sinkhole is underlain, by alluvial deposits of the Colorado River drainage basin and unconsolidated Miocene, Pliocene, and Pleistocene sediments to a depth of about 500 feet. The sediments consist largely of sand, silts, clays, and gravels. The Boling Salt Dome and its associated caprock occur directly beneath the section of unconsolidated sediments Major and minor axes of the dome are about 5 miles and 35 miles, respectively, and the sinkhole occurred approximately 1 mile east-northeast of the dome's center An investigation was conducted in the immediate area of the sinkhole to determine the cause of the subsidence and also to determine the feasibility of dewatering the sinkhole Four monitoring wells were installed around the perimeter to evaluate the potential recharge from shallow sand units Two 300-foot holes were drilled and geophysically logged to determine the stratigraphy adjacent to the sinkhole, and two slope indicators were installed in order to evaluate further earth movements A total of six million gallons of saline water were removed and disposed of from the sinkhole Based on information provided by the geologic and dewatering investigation, the Texas State Department of Highways and Public Transportation elected to fill the existing sinkhole and reconstruct the roadway A total of 3,500 cubic yards of rock borrow and 26,000 cubic yards of soil borrow were placed in the depression Construction began in February 1984, and the roadway was completed in May A monitoring program to evaluate subsequent earth movements will continue into 1985     

Neogene echinoids from the Cayman Islands,West Indies: regional implications

The first fossil echinoids are recorded from the Cayman Islands. A regular echinoid, Arbacia? sp., the spatangoids Brissus sp. cf. B. oblongus Wright and Schizaster sp. cf. S. americanus (Clark), and the clypeasteroid Clypeaster sp. are from the Middle Miocene Cayman Formation. Test fragments of the mellitid clypeasteroid, Leodia sexiesperforata (Leske), are from the Late Pleistocene Ironshore Formation. Miocene echinoids are preserved as (mainly internal) moulds; hence, all species are left in open nomenclature because of uncertainties regarding test architecture. All Miocene taxa are recorded from single specimens apart from the 27 assigned to Brissus. Schizaster sp. cf. S. americanus (Clark) is compared to a species from the Oligocene of the south‐east USA. Brissus sp. cf. B. oblongus is close in gross morphology to a taxon from the Miocene of Malta. Leodia sexiesperforata is identified from fragments with confidence, being the only extant Antillean sand dollar with elongate ambulacral petals that is limited to carbonate substrates. The Miocene echinoids of Grand Cayman, although of limited diversity, are mainly comprised of genera common in comparable mid‐Cenozoic carbonate environments. Copyright © 2015 John Wiley & Sons, Ltd.     

黄河源区第四纪地质研究的新进展

通过对黄河源区的钻孔、自然露头的研究, 建立了黄河源区的第四纪地层层序。第四纪地层可划分为下更新统、中更新统、上更新统和全新统。下更新统为河湖相沉积; 中更新统主要有湖积物、冰碛物和冰水沉积物; 上更新统主要有湖积物、冰碛物、冰水沉积物、洪积物和河流沉积物; 全新统主要由河流沉积物、洪积物和湖积物构成。黄河源区的冰期可划分为3期, 即末次冰期、倒数第二次冰期、倒数第三次冰期, 末次冰期又可分为2个冰阶。黄河源区的湖泊演化可划分为早更新世、中更新世和晚更新世—全新世3个阶段: 早更新世的湖泊范围小; 中更新世的湖泊范围明显扩大, 在位置上也较早更新世的湖泊南移; 晚更新世的湖泊经历了两次的扩张—收缩变化, 到了全新世, 除现今还发育的几个湖泊外, 大多数地区的湖水已退出, 基本上转变为河流环境。在晚更新世末期到全新世初期, 封闭黄河源区的多石峡被切开, 湖水外泄, 现今的黄河形成了, 同时发生了袭夺长江水系的水流。     

周口店地区第四纪哺乳动物群的演化与环境变迁探讨

讨论了Ａｌｉｌｅｐｕｓａｎｎｅｃｔｅｎｓ、ＨｙｐｏｌａｇｕｓｂｒａｃｈｙｐｕｓＬｅｐｕｓｓｐ．、Ｓｃｉｕｒｏｔａｍｉａｓｐｒａｅｃｏｘ、ＡｌｌｏｃｒｉｃｅｔｕｓｔｅｉｌｈａｒｄｉＣｒｉｃｅｔｉｎｕｓｖａｒｉａｎｓ、Ｈｙｐｅｒａｃｒｉｕｓｙｅｎｓｈａｎｅｎｓｉｓ、Ａｌｌｏｐｈａｉｏｍｙｓｃｆ．ｐｌｉｏｃａｅｎｉｃｕｓ、Ｐｒｏｅｄｒｏｍｙｓｃｆ．ｂｅｄｆｏｒｄｉ、Ｃｈａｒｄｉｎｏｍｙｓｎｉｈｅｗａｎｉｃｕｓ、Ｍｕｓｃｆ．ｍｕｓｃｕｌｕｓ和Ａｐｏｄｅｍｕｓｄｏｍｉｎａｎｓ的地史分布。根据哺乳动物群的分析与对比，得出第１８地点为早更新世早期，第１２地点、东洞地点为早更新世中期，第９地点、西洞地点为早更新世晚期，第１３地点为早更新世末期至中更新世初期，第１、２、５、６、１１、１０、２１、２３及上店洞地点为中更新世，新洞为中更新世晚期至晚更新世早期，东岭子洞为晚更新世，山顶洞为晚更新世晚期。还讨论了周口店地区一些主要第四纪哺乳动物群的生态类型特点，第四纪的气候波动及生态环境变迁。     

Biostratigraphic correlation of Pleistocene marine deposits and sea levels,Atlantic coastal plain of the southeastern United States

Marine ostracodes from 50 localities were studied to determine the age and elevation of Pleistocene sea levels in the Atlantic coastal plain from Maryland to northern Florida. Using ostracode taxon and concurrent ranges, published planktic biostratigraphic, paleomagnetic, and radiometric data, ostracode assemblage zones representing early (1.8-1.0 my), middle (0.7-0.4 my), and late (0.3-0.01 my) Pleistocene deposition were recognized and used as a basis for correlation. Ostracode biofacies signifying lagoonal, oyster bank, estuarine, open sound, and inner sublittoral environments provided estimated ranges of paleodepths for each locality. From these data the following minimum and maximum Pleistocene sea-level estimates were determined for the southeastern coastal plain: late Pleistocene, 2–10 m from Maryland to northern Florida; middle Pleistocene, 6–15 m in northern South Carolina; early Pleistocene, 4–22 m in central North Carolina, 13–35 m in southern North Carolina, and 6–27 m in South Carolina. Climatically induced glacio-eustatic sea-level fluctuations adequately account for the late Pleistocene sea-level data, but other factors, possibly differential crustal uplift, may have complicated the early Pleistocene record.     

江西九江中更新世红土物质来源研究

华南地区广泛分布中更新世红土。目前, 对其物质来源尚有争议。九江红土剖面的沉积时代已得到很好限定, 同时由于其沉积连续、地层出露较好, 是开展中更新世红土物质来源研究的理想剖面。通过对九江中更新世红土2件碎屑锆石样品的分析, 共获得177颗谐和锆石U-Pb年龄, 主要峰值集中在新元古代(816 Ma、801 Ma和991 Ma)、古元古代(2019 Ma、2022 Ma和2481 Ma)和新太古代(2502 Ma), 并具有不显著的中生代峰值(135 Ma)。将其与潜在远源和近源物源区的锆石U-Pb年龄组成进行对比, 结果发现中国北方戈壁、沙漠和黄土高原、塔里木盆地、华北平原并不是九江中更新世红土的主要源区。庐山北麓早更新世发育的洪积扇为九江中更新世红土发育提供了充足物质。九江中更新世红土和九江晚更新世黄土的碎屑锆石U-Pb年龄组成存在明显差别, 后者主要来自长江河漫滩的碎屑物质。不同的气候条件主导了九江地区红土和黄土的发育, 二者都受控于青藏高原构造隆升产生的环境变化。     

许家窑组及许家窑文化层年代问题的磁性地层学证据

许家窑文化遗址的发现将传统上被认为是早更新世前后的泥河湾层的年代范围推至晚更新世 ,由此建立的许家窑组被确认为我国北方晚更新世湖相沉积的标准地层。近几年对包含许家窑文化层在内的泥河湾层用高分辨率磁性地层学方法研究结果表明 ,在文化层以下 3m处发现了厚度达 6 m以上且分布连续的反向极性带 (未见底 ) ,综合分析认为 ,该反向极性带为松山反向极性带。这一发现否定了在文化层以下 4— 5 m处存在布莱克反向极性偏移的报道。根据松山反向极性时的结束时间为距今 78万年及泥河湾层的沉积速率推算 ,许家窑泥河湾层的年代范围应为早更新世晚期至中更新世 ,而许家窑文化层应为中更新世早期。由此可见 ,泥河湾层的年代范围及分组方案尚需用多种手段进一步研究才能定论     

Pleistocene movements in the Gregory Rift Valley

Summary The Tertiary and post-Tertiary chronology of faulting in the Gregory Rift Valley is discussed with particular reference to areas where Middle Pleistocene deposits have been mapped. It is concluded that while strong faulting occurred at the end of the Middle Pleistocene period, the main faulting was earlier. At least three pre-Middle Pleistocene phases of faulting are recognised; the maximum movements probably occurred in late Pliocene or earliest Pleistocene times.     

化学风化指数和磁化率对洞庭盆地第四纪古气候变化的响应

在安乡凹陷东南部两护村新施工揭穿第四系的ZKC1孔,孔内第四系为河流和湖泊沉积,地层组成自下而上依次为上新世—早更新世华田组、早更新世汨罗组、中更新世早期—中期洞庭湖组、晚更新世坡头组以及全新统等。对钻孔岩心进行了系统的主量元素及磁化率分析,进而从陆相沉积物化学风化指数(CWI)与温度和湿度正相关、磁化率与温度和湿度负相关的理论出发,探讨洞庭盆地第四纪气候演变。结合其他资料,CWI曲线特征指示洞庭盆地第四纪气候演变过程:早更新世为冷干→暖湿→冷干→暖湿,中更新世为冷干→暖湿→冷干—温湿→暖湿,晚更新世为寒冷→温湿→寒冷,全新世总体为温湿-暖湿。这一结论与ZKC1孔孢粉组合特征反映的气候演变过程及中国东部第四纪气候演化基本吻合,说明沉积物CWI对第四纪气候演变具有较好的响应。变化曲线及相关系数(-0.32)表明磁化率值与CWI值呈较明显的负相关,暗示温度和湿度对磁化率具有明显的控制作用。但可能受盆地升降等因素的影响叠加,磁化率曲线未能如CWI一样明确反映出第四纪气候的阶段性变化。     

河北省唐山地区古滦河冲积扇第四纪以来演化与变迁

古滦河冲积扇研究的关注点更多在全新世,对其更新世的演化与变迁一直没有进行过系统研究。根据古滦河冲积扇上PZK10、PZK20钻孔的磁性地层学、年代地层学、沉积学、测井沉积学、岩芯色度分析等,对古滦河冲积平原的第四纪三维地质结构、冲积扇体的规模以及迁移规律进行综合研究,结果表明：PZK10孔揭露了上新世时沉积的巨厚洪积成因“泥包砾”地层,早更新世时发育两个冲积扇-湖相旋回,中更新世时发育辫状河沉积,晚更新世发育湖相、冲积扇相、辫状河相沉积。PZK20孔上新世沉积了一套巨厚“泥包砾”层,早更新世为扇前平原-辫状河相沉积,中更新世为辫状河-冲积扇相沉积,晚更新世为辫状河沉积。古滦河发育两期冲积扇,第一期为早更新世早期,在沙流河镇一带出山口形成的规模较大的冲积扇;第二期为早更新世中期,古滦河在现今丘庄水库一带发生分流,在丰润区一带出山口形成的冲积扇。中更新世,第一期冲积扇开始萎缩,第二期冲积扇继续发育,形成巨厚砾石层;晚更新世,古滦河在迁西县城以北发生袭夺,东流迁移出研究区,在西峡口进入迁安盆地,形成以西峡口为顶点的冲积扇。     

大兴安岭哈拉哈河-绰尔河第四纪火山分期: K-Ar年代学与火山地质特征

大兴安岭中部哈拉哈河-绰尔河第四纪火山区分布有34座火山,这些火山总体呈北东向带状分布,火山岩分布面积约400 km2,岩性主要为碱性橄榄玄武岩.根据火山地质特征,结合火山岩K-Ar测年结果,哈拉哈河-绰尔河第四纪火山可进一步划分为早、中、晚更新世和全新世4期.早更新世火山岩,由于被后期火山岩覆盖,主要分布于火山区周边和出露在河谷中.中更新世火山活动最强,不论火山数量(27座)还是熔岩流规模都超过该区第四纪火山的一半以上.晚更新世时期火山活动趋弱,火山活动范围缩小,只局限于小范围区域.全新世火山活动又进入新的高峰期,强爆破式喷发和规模宏大的熔岩流,以及保存完好的熔岩流地貌是全新世火山之特点.     

朝鲜北部及其邻区的新构造运动和现代地形构造的形成

朝鲜北部及其邻区的第四系更新统(Q_1)由玄武岩和碎屑岩互层组成。下更新统玄武岩是在新第三纪上新世广而平坦的侵蚀面上形成的台地型玄武岩。朝鲜北部及其邻区的地形构造是通过下更新统沉积以后发生的新构造运动形成的。朝鲜下更新统和上更新统中的沉积矿产(特别是砂金矿床)普查、开发远景很大。     

黄河源区黄河袭夺长江水系之初探

对黄河源区的河流地貌研究表明,该区共发育三级阶地,其中第一、第二级阶地形成于晚更新世的末期至全新世,而第三级阶地形成于晚更新世晚期。在晚更新世晚期,多石峡被切开,黄河源区晚更新世湖泊消失,现今黄河形成。随着现今黄河的形成和晚更新世湖泊的消失,南岸支流之一的多曲向南溯源侵蚀加强,并穿越巴颜喀拉山,夺取了巴颜喀拉山南侧原属于长江流域的贝敏曲和洛曲,使分水岭向南推进了25km,袭夺的时间为晚更新世末期。     

Quaternary marine transgressions and paleoclimate in the Yangtze River delta region

Eight marine transgressions have been recognized from more than 30 deep drill holes (ca. 300 m deep) through Quaternary sequences in the Yangtze River delta region. These are, in ascending order, the Rugao and Zhoupe transgressions (early Pleistocene); the Shanghai, Jiading, and Wangdian transgressions in the middle Pleistocene; the Jiangyin and Gehu transgressions in the late Pleistocene; and the Zhenjiang transgression in the Holocene. The transgressions correspond to warm periods and regressions to cold periods. The younger transgressions were not only of shorter duartion, but also of larger magnitude. The findings verify that there were five moderately warm periods during the early to middle Pleistocene and two very warm periods during the late Pleistocene in the Yangtze River delta region.     

松嫩平原东部中、晚更新世地层界限：光释光年龄及元素变化

松辽平原东部受第四纪差异性构造活动影响,形成特殊的更新世沉积地层。由于第四纪划分方案和地域差异,松辽平原东部中、晚更新世界限仍处于不确定状态。通过黑龙江省方正剖面的研究、中更新统顶部(149.6±10.4) ka光释光年龄和主要氧化物、微量元素、稀土元素分析以及区域剖面对比,认为将松辽盆地东缘中、晚更新世的界限年龄置于140 ka更适合地层实际情况。中更新世地层以河湖相、河流相和洪积相沉积物为主,完整的晚更新世地层应该包括下部的沼泽漫滩相黏土、亚黏土和上部亚砂土、黄土沉积。黑龙江省荒山剖面哈尔滨组下部可能由于相变而缺少沼泽漫滩相的沉积物。方正剖面与榆树东岗组剖面地层可以对比。中、晚更新世沉积环境发生了明显变化,主要氧化物、微量元素和稀土元素含量在中、晚更新世的地层界限处都发生了明显的突变。     

川西凹陷地区更新统砾石层沉积成因探讨

笔者通过野外地质调查和相关资料,从宏观形态和沉积特征多方面对川西凹陷地区的更新统砾石层的成因进行综合分析.发现各时期更新统砾石层平面上均呈扇状,具多级阶地.各砾石层的岩性结构柱、基本层序、砾石的组构特征均表现为河流相冲洪积成因.并通过ESR和孢粉、充填序列和地貌标志探讨了区内各更新统砾石层的沉积时代、古气候特征.综合研究表明区内存在4套不同特征的更新统砾石层,它们不仅在空间位置上存在密切联系,而且在沉积特征和形成时代上也具继承性.沉积环境均为温暖潮湿热环境下,出龙门山的古青衣江在盆地中不同时期、不同位置的沉积响应.并反演古青衣江水系在前陆盆地中不同时期的迁移及变化规律.     

洞庭盆地澧县凹陷第四纪沉积特征与古地理演化

澧县凹陷内第四系厚度达200m左右,由早更新世-中更新世中期沉积和全新统组成。早更新世-中更新世中期沉积除顶部为粘土外,主体为砾石层,在凹陷中央夹粉砂、细砂和少量粘土。全新统分布于凹陷南部,为湖冲积粘土。早更新世澧县凹陷区断陷沉降,于河道和冲积扇环境下接受沉积;中更新世凹陷逐渐扩张,沉积范围扩展至凹陷外缘,凹陷主体部位自边缘向中央依次为冲积扇和扇前浅湖环境。中更新世中后期因盆地扩张,自凹陷中央至边缘地带均为静水湖泊环境。中更新世晚期至晚更新世,凹陷及周缘因构造抬升而遭受剥蚀而缺失沉积。全新世凹陷南部受澧水及区域湖面上升影响而发育湖冲积沉积。     

Quaternary Stratigraphic Division and Paleoenvironmental Evolution Observed from Core LZK1 on Hengsha Island, Shanghai

The Quaternary sediments in the Yangtze delta are loose and lack precise stratification marks in the lithology. Moreover, due to the limitations of dating methods, it is difficult for Quaternary cores to deliver accurate age constraints. Thus, it is a challenge to establish the Quaternary stratigraphic framework. Gravity core LZK1 was drilled on Hengsha Island, Shanghai, in the Yangtze delta, in 2012. The core was terminated at 403.83 m below the local land surface, the uppermost 291.2 m comprising a thick sequence of Quaternary sediments. This study investigated the stratigraphic subdivision and paleoenvironmental change of the Quaternary sediments. From bottom to top, the Quaternary stratigraphic sequence can be subdivided into the lower Pleistocene Anting Formation, Middle Pleistocene Jiading Formation, Upper Pleistocene Chuansha Formation and Nanhui Formation, Holocene Loutang Formation, Shanghai Formation, and Rudong Formation. According to this study, the Hengsha Island area was dominated by a freshwater lacustrine environment during the early Pleistocene, an alternation of shallow lake and shore lake environment during the Middle Pleistocene, a delta plain to lagoonal environment during the early Upper Pleistocene, a fluvial channel to floodplain environment from the LGM (Last Glacial Maximum) to the end of the Upper Pleistocene, and a delta environment during the Holocene.