青藏高原东缘中更新世伸展作用及其新构造意义

基于区域TM遥感影像资料解译和野外构造地貌调查以及晚第四纪沉积物光释光测年分析,论述了青藏高原东缘复杂地貌边界带晚第四纪伸展构造及其构造地貌特征。结果显示,伸展构造主要见于下列几个构造带:沿南北走向的安宁河谷地、大凉山构造带、若尔盖盆地、岷江断裂带等。其典型的地貌特征表现为充填晚第四纪沉积物的狭窄河谷。根据盆地沉积物的地层时代和年龄推断,正断作用主要发生在中更新世时期,大约起始于早更新世末期(1.2～0.9Ma),结束于中更新世晚期(100～200ka)。晚更新世以来,构造体制转化为走滑—逆冲机制。青藏东缘中更新世伸展构造作用可能与该地貌边界带晚新生代造山后的高原垮塌有关。     

青海格尔木早更新世昆仑河砾岩的发现及其地质意义

昆仑河发源于昆仑山,是格尔木河的重要支流之一。前人所报道的新近纪与第四纪地层,主要集中于昆仑山垭口地区,而在昆仑河—格尔木河谷地中,只有中更新世以来的最新地层,从而提出了发生于1.1~0.6 Ma BP间的“昆仑—黄河运动”的概念。然而在昆仑河谷中发现了厚达20 m的钙质胶结的河流相砾石层(昆仑河砾岩),其分布、特征及其与纳赤台沟组、三岔河组和低阶地沉积等上覆地层的不整合接触关系,以及ESR法测定的该砾石层2个钙质胶结物样品的年龄(分别为1 042 ± 104 ka BP与1 269 ± 126 ka BP)均表明,早在距今1.27~1.42 Ma之前昆仑河—格尔木河河谷已经形成,而且已深切到现今的谷底。此后河谷内的多次切割与堆积,不应是构造运动的结果,而可能是冰期与间冰期气候变化所引起的侵蚀与搬运能力变化造成的。同样,昆仑山相对于柴达木盆地的强烈隆升至少应发生于距今1.27~1.42 Ma之前。      

洞庭盆地中更新世洞庭湖组砾石特征及其意义

对位于洞庭盆地安乡凹陷东南部的两护村ZKC1孔中更新世洞庭湖组砾石层进行了粒度和砾态的统计分析.结果表明,砾石的粒度变化反映出2个较大尺度的由大→小的旋回,早旋回由洞庭湖组下段砂砾层组成,晚旋回由洞庭湖组中段上部的砂砾层组成,反映出中更新世早-中期安乡凹陷的两次由慢→快的幕式沉降过程.在上述2个大的粒度旋回之上,叠加有多个更小尺度的砾石粗、细变化,主要与气候干湿的频繁波动有关.洞庭湖组中段顶部砾石的磨圆度明显偏低,反映其沉积时期盆地沉降和周缘隆起区抬升活动的增强.     

The North of Eastern Siberia: Refuge of Mammoth Fauna in the Holocene

The global climate changings at the end of Pleistocene led to extinction of the typical representatives of Mammoth fauna–mammoth, woolly rhinoceros, wild horse, bison, muskox, cave lion, etc.–on the huge territories of Northern Eurasia. Undoubtedly the Mammoth fauna underwent pressure from the Upper Paleolithic Man, whose hunting activity also could play the role in decreasing the number of mammoths and other representatives of megafauna (large mammals). Archaeological data testify that the typical representatives of Mammoth fauna were the Man's hunting objects only till the end of the Pleistocene. Their bone remains are not usually found on the settlements of Mesolithic Man. Formerly it was supposed that the megafauna of ‘Mammoth complex’ was extinct by the beginning of Holocene. Nevertheless the latest data testify that the global extinction of the Mammoth fauna was sufficiently delayed in the north of Eastern Siberia. In the 1990s some radiocarbon data testified that the mammoths on the Wrangel Island existed for a long time during the Holocene from 8000 till 3700 y. BP. The present radiocarbon data show that wild horses inhabited the north of Eastern Siberia (the lower stream of the Enissey river, the Novosibirskie Islands, the East Siberian sea-shore) 3000–2000 y. BP. Musk-oxen lived on the Taimyr Peninsula and the Lena River delta about 3000 y. BP. Some bison remains from Eastern Siberia belong to the Holocene. The following circumstances could promote the process of preservation of the Mammoth fauna representatives. The cool and dry climate of this region promotes the maintenance of steppe associations – habitats of those mammals. The Late Paleolithic and Mesolithic settlements are not found in the Arctic zone of Eastern Siberia from the Taimyr Peninsula to a lower stream of the Yana River; they are very rare in the basins of the Indigirka and Kolyma Rivers. So, the small number of the Stone Age hunting tribes on the North of Eastern Siberia was another factor in the long-term preservation of some Mammoth fauna representatives.     

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.     

福建晚更新世海侵问题探讨

福建沿海在晚更新世大约距今90—80ka、70—60ka、44—39ka和34—20ka期间分别发生过4次海侵。最末一次海侵(距今34—20Ka)期间有过明显的海面下降波动,时间大约在距今28ka前后。     

新石器晚期颍河上游旱作农业的多元化特征

用王城岗遗址地层中炭化作物种子、植物花粉的分选鉴定结果,讨论了颍河上游地区龙山文化晚期至二里岗文化时期(约4.2~3.3 kaBP)的气候背景、作物类型和农业活动对环境的影响。结果显示,粟、黍种子数目一直占绝对优势,小麦种子在二里岗时期出现并逐渐走强;由于土地承载力和气候条件限制,王城岗地区的早期农业自龙山晚期后加速了多元化的进程,逐渐形成了以粟、黍、麦、豆为主,水稻、高粱、荞麦、稗子为辅,兼有果实采集的多样化农业生产。小麦的引入表明,本区早期农业与西部地区文化交流是主体,同时促进了颍河上游早期农业的多元化,巩固了史前社会可持续发展的物质基础。     

Study of stable isotopes for highly deformed aquifers in the Hsinchu-Miaoli area, Taiwan

This study was based on the analysis of isotopic compositions of hydrogen and oxygen in samples from precipitation, groundwater and stream water. In addition, parts of groundwater samples were dated by carbon-14 and tritium. These data are integrated to provide other views of the hydrologic cycle in the Hsinchu-Miaoli groundwater district. The groundwater district is principally composed of Pleistocene and Holocene aquifers. The Pleistocene aquifers are highly deformed by folding and faults into small sub-districts with areas of only tens of square kilometers. These aquifers are exclusively recharged by local precipitation. The Holocene aquifers cover narrow creek valleys, only tens of meters in thickness. The local meteoric water line (LMWL), constructed from rainfall samples in the Hsinchu Science Park, is described by the equation δD=8.02δ¹⁸O+10.16, which agrees with the global meteoric water line. In addition, the precipitation isotopic compositions can be categorized into two distinct end members: typhoon type and monsoon type. The groundwater isotopic compositions are perfectly located on an LMWL and can be considered a mixture of precipitations. Based on the mass balance of isotopic compositions of oxygen and hydrogen, infiltration is more active in the rainy season with depleted isotopic compositions. The amount of infiltration during May–September is roughly estimated to comprise at least 55% of the whole year’s recharge. The isotopic compositions of stream water are expressed by a regression equation: δD=7.61δ¹⁸O+9.62, which is similar to the LMWL. Although precipitation isotopic compositions are depleted during summer time, the isotopic compositions contrarily show an enriched trend in the upstream area. This is explained by the opposite altitude effect on isotopic compositions for typhoon-related precipitations.     

Geomorphological,stratigraphic and geochronological evidence of fast Pleistocene coastal uplift in the westernmost part of the Corinth Gulf Rift (Greece)

Rapid extension and active normal faulting in the western extremity of the Corinth Gulf are accompanied by fast coastal uplift. We investigate Pleistocene uplift west of Aigion, by attempting to date remains of marine terraces and sedimentary sequences by calcareous nannoplankton and U‐series analyses. Net uplift initiated recently, due to abandonment of an older rift‐bounding fault zone and increase in activity on the presently active, coastal fault zone. This change apparently coincides with an abrupt slow down (or, termination) of secondary fault block tilting within the broader hangingwall block of the older zone, indicated by an angular unconformity that dates in the early part of MIS10 (∼390–350 ka BP, preferably, in the earlier part of this period). Net uplift driven by the coastal zone resulted in the formation of MIS9c (330 ka) and younger terraces. The formation of the unconformity and the initiation of net uplift coincide temporally with a ∼300–400 ka unconformity recognized by recent studies in a wide area offshore Aigion i.e. they could be part of an evolutionary event that affected the entire western part of the Corinth Rift or, a large area therein. Uplift rate estimates at four locations are discussed with reference to the morphotectonic context of differential uplift of secondary fault blocks, and the context of possible increase in uplift rate with time. The most reliable and most useful estimate for uplift rate at the longitude of the studied transect is 1.74–1.85 mm/year (time‐averaged estimate for the last ∼240 ka, based on calcareous nannoplankton and sequence‐stratigraphic interpretation). Copyright © 2009 John Wiley & Sons, Ltd.