Fossil echinoderms from the Triassic and Jurassic of Ireland

An overview is provided of fossil echinoderm taxa recovered from the Jurassic (Lias Group) and Triassic (Penarth Group) of Ireland. Despite limited outcrop and generally poor exposure, at least 12 species are recorded (6 crinoids, 2 echinoids, 3 ophiuroids and one asteroid), with significant new material recovered from an early Hettangian lagerstätte. The crinoid Isocrinus angulatus (Fraas, 1858), omitted from an earlier Palaeontographical Society Monograph on Lower Jurassic crinoids, is described based on articulated material.     

西藏海相三叠系-侏罗系界线及晚三叠世生物绝灭事件研究

1998—2004年间在西藏聂拉木、林周、墨竹工卡和洛扎等地进行的三叠系/侏罗系界线地层研究表明,西藏隆子县和洛扎县尚未发现具有连续菊石层序的三叠系/侏罗系界线地层剖面。拉萨以北地区广泛分布的火山岩时代确定为晚三叠世—早侏罗世早期,这有助于解释晚三叠世末期生物绝灭与晚三叠世岩浆侵入和大规模的火山活动有关,但T/J界线尚待精确限定。聂拉木县格米格剖面是特提斯地区唯一未曾“压缩”的三叠系/侏罗系界线地层剖面,具有瑞替阶MARSHI菊石带、赫塘阶Tibeticum、Callyphyllum和Pleuro-notum菊石带。格米格剖面三叠系/侏罗系界线碳稳定同位素曲线记录了晚三叠世瑞替阶末期(Marshi菊石带)突然的负偏移,它很有可能和晚三叠世末期的由超级温室效应所产生的生物绝灭事件相对应。     

东喜马拉雅地区晚三叠世—早侏罗世的菊石类

在东喜马拉雅范围以内的西藏康马、洛扎和隆子地区有国内首次发现的晚三叠世诺利期—早侏罗世Glyphidites、Phormedites、Epideroceras、Phricodoceras Uptonia等菊石。晚三叠世诺利期有Tibetites sp.、Anatibetites sp.、Glyphidites sp.、Cyrtopleurites sp.、Parajuvavites sp.、Sagenites sp.和Phormedites sp.。早侏罗世辛涅缪尔期有Arnioceras ceratoides、Angulaticeras sp.、Arnioceras sp.、Juraphyllites sp.、Epideroceras sp.以及普林斯巴赫期Phricodoceras cf.cornutum、Uptonia sp.、Galaticeras sp.、Gleviceras cf.paniceum等。东喜马拉雅地区的菊石动物群在晚三叠世—早侏罗世期间的幕式出现与海侵和沉积环境变深有关,代表受海平面变化控制的晚三叠世的诺利中期(Columbianus带)、早侏罗世的辛涅缪尔期(Semico-statum带)、以及普里斯巴赫早期(Jamestoni带)的全球性菊石动物群扩散和迁移。     

On the Unconformity between the Triassic and Jurassic in Weiyuan, Szechuan

To the north of the famous Tseliutsing salt district of central Szechuanthere exists a big dome-anticline, which is clearly shown in Tan and Lee's [1]Atlas for "Geology of Szechuan and Sikang." Since this anticline occupies thegreater part of the district of Weiyuan, it may be conveniently termed the     

Climate change on the Yucatan Peninsula during the Little Ice Age

We studied a 5.1-m sediment core from Aguada X'caamal (20° 36.6′N, 89° 42.9′W), a small sinkhole lake in northwest Yucatan, Mexico. Between 1400 and 1500 A.D., oxygen isotope ratios of ostracod and gastropod carbonate increased by an average of 2.2‰ and the benthic foraminifer Ammonia beccarii parkinsoniana appeared in the sediment profile, indicating a hydrologic change that included increased lake water salinity. Pollen from a core in nearby Cenote San José Chulchacá showed a decrease in mesic forest taxa during the same period. Oxygen isotopes of shell carbonate in sediment cores from Lakes Chichancanab (19° 53.0′N, 88° 46.0′W) and Salpeten (16° 58.6′N, 89° 40.5′W) to the south also increased in the mid-15th century, but less so than in Aguada X'caamal. Climate change in the 15th century is also supported by historical accounts of cold and famine described in Maya and Aztec chronicles. We conclude that climate became drier on the Yucatan Peninsula in the 15th century A.D. near the onset of the Little Ice Age (LIA). Comparison of results from the Yucatan Peninsula with other circum-Caribbean paleoclimate records indicates a coherent climate response for this region at the beginning of the LIA. At that time, sea surface temperatures cooled and aridity in the circum-Caribbean region increased.     

Onshore climate change during the Late Triassic marine inundation of the Central European Basin

Sedimentological, pedological and palynological evidence reveal radically increasing onshore humidity during the Rhaetian marine invasion of central Europe along the north-eastern margin of the Central European Basin (southern Sweden). Pre-Rhaetian aridity favoured the formation of Carnian redbeds with calcrete, which were succeeded by Norian hematite-cemented conglomerates, arkoses, arkosic wackestones, and smectititic mudstones deposited on braidplains and in lakes. Superimposed autochthonous coals and gleysols indicate the Rhaetian onset of year-round humidity. Chemically mature sandstones, kaolinitic mudstones and luvisols also formed at this time, influenced by a permanent vegetation cover which lowered soil pH and strongly intensified chemical weathering. The Rhaetian deposits accumulated in floodplain lakes repeatedly subjected to sediment infill, plant colonization and palaeosol development. The humidity shift resembles that contemporaneously recorded in the North Sea region.     

Climate change in lowland Central America during the late deglacial and early Holocene

The transition from arid glacial to moist early Holocene conditions represented a profound change in northern lowland Neotropical climate. Here we report a detailed record of changes in moisture availability during the latter part of this transition (～11 250 to 7500 cal. yr BP) inferred from sediment cores retrieved in Lake Petén Itzá, northern Guatemala. Pollen assemblages demonstrate that a mesic forest had been largely established by ～11 250 cal. yr BP, but sediment properties indicate that lake level was more than 35 m below modern stage. From 11 250 to 10 350 cal. yr BP, during the Preboreal period, lithologic changes in sediments from deep‐water cores (>50 m below modern water level) indicate several wet–dry cycles that suggest distinct changes in effective moisture. Four dry events (designated PBE1‐4) occurred centred at 11 200, 10 900, 10 700 and 10 400 cal. yr BP and correlate with similar variability observed in the Cariaco Basin titanium record and glacial meltwater pulses into the Gulf of Mexico. After 10 350 cal. yr BP, multiple sediment proxies suggest a shift to a more persistently moist early Holocene climate. Comparison of results from Lake Petén Itzá with other records from the circum‐Caribbean demonstrates a coherent climate response during the entire span of our record. Furthermore, lowland Neotropical climate during the late deglacial and early Holocene period appears to be tightly linked to climate change in the high‐latitude North Atlantic. We speculate that the observed changes in lowland Neotropical precipitation were related to the intensity of the annual cycle and associated displacements in the mean latitudinal position of the Intertropical Convergence Zone and Azores–Bermuda high‐pressure system. This mechanism operated on millennial‐to‐submillennial timescales and may have responded to changes in solar radiation, glacial meltwater, North Atlantic sea ice, and the Atlantic meridional overturning circulation (MOC). Copyright © 2005 John Wiley & Sons, Ltd.     

Extinction, survival and recovery of corals from the Triassic to Middle Jurassic time

Recognizing extinction events and determining their cause at the Triassic/Jurassic (T/J) transition and near the Pliensbachian–Toarcian (Lower Jurassic) boundary is a field of growing interest. We provide arguments for these events through a literature based new evaluation of coral diversity from Triassic to Dogger and a new palaeobiogeographical map. The T/J extinction of corals is clearly related to the breakdown of reef environments. Origination curves show that Hettangian (the lowest Jurassic stage) was not only a survival phase but already rather a recovery phase. Post-extinction evolution of reefs and their survival only in the northernmost margin of the Tethys support the hothouse hypothesis for the T/J extinction event. During Pliensbachian, many new taxa appear, but mostly solitary corals, not really framebuilders. Many of these taxa do not occur anymore during the following stages. The new increase in diversity is related to the development of Bajocian (Middle Jurassic) reefs.     

Climate change stressors in the Sahel

The Sahel is prone to climate stressors such as droughts, winds and floods. This study employs a systematic review approach to track the frequency with which these stressors are reported in the scientific peer reviewed literature, examining publishing trends to identify which stressors are most reported, documenting the spatial distribution of these stressors from a country and regional perspective, and assessing the role played by climatic and non-climatic drivers in causing the stressors. A total of (n = 388) reports of stressors were documented in (n = 164) peer reviewed articles. From a country perspective, Southern Niger records the highest number of reports on all three stressors (15.97%), followed by Ethiopia (11.85%) and Senegal (10.56%). Regionally, West African Sahel recorded the highest number of reports on all stressors (49.97%) followed by East African Sahel (29.89%) and Central African Sahel (12.11%) respectively. Droughts are observed to be the most frequently reported stressor (n = 219), followed by floods (n = 123) and winds (n = 46). The decade 1975–1985 recorded the highest reports of stressors (n = 207), while the decade 1997–2007 recorded (n = 80) and the decade 1986–1996 recorded (n = 52). While climatic drivers are dominant (52%), there is however an increasing attribution of the drivers of the stressors to non-climatic drivers (47%). The main weakness of this study is that it uses peer reviewed papers dwelling on climate stressors as a proxy for climate stressors in the Sahel and a lot more studies could be hiding in non-peer reviewed studies, underscoring that this work provides a general and baseline overview of the climate stressors in the region.     

Provenance change in the Irkutsk coal basin during the early and middle Jurassic: Geochemical and Sm-Nd isotope evidence

On the basis of the recently accepted chronostratigraphic chart, Jurassic sedimentation in the Irkutsk coal basin took place over a short time interval (~23 My), from the Pliensbachian (~191 Ma) to the Aalenian (~170 Ma). In this study, we present geochemical and Sm-Nd isotope data for sedimentary rocks of the Prisayan and Kuda formations and those in the upper course of the Angara River, which were deposited over an even shorter time interval (from ~174 to 170 Ma), as indicated by new data on biostratigraphy. Our results suggest that a greater contribution from Transbaikalia compared to that from the Siberian Platform during sediment deposition in the Irkutsk coal basin may reflect the onset of mountain building in Transbaikalia and reorganization of the river drainage network during the Middle Jurassic.     

Uppermost Triassic to Lower Jurassic sediments of the island of Ireland and its surrounding basins

The uppermost Triassic to Lower Jurassic interval has not been extensively studied across the island of Ireland. This paper seeks to redress that situation and presents a synthesis of records of the uppermost Triassic and Lower Jurassic from both onshore and offshore basins as well as describing the sedimentological characteristics of the main lithostratigraphical units encountered. Existing data have been supplemented with a re-examination and logging of some outcrops and the integration of data from recent hydrocarbon exploration wells and boreholes. The Late Triassic Penarth Group and Early Jurassic Lias Group can be recognised across the Republic of Ireland and Northern Ireland. In some onshore basins, almost 600 m of strata are recorded, however in offshore basins thicknesses in excess of two kilometres for the Lower Jurassic have now been recognised, although little detailed information is currently available. The transition from the Triassic to the Jurassic was a period of marked global sea-level rise and climatic change (warming) and this is reflected in the lithostratigraphical record of these sediments in the basins of Northern Ireland and offshore basins of the Republic of Ireland. In general, the sediments of this interval are thicker than those in Great Britain and have potential for detailed study of climatic and sea-level fluctuation.     

新疆吐-哈盆地三叠系和侏罗系含油砂体的形成条件

吐-哈盆地是位于天山造山带内的具复杂演化历史的中新生代叠合盆地,是典型的煤成烃陆相含油气盆地。盆地南带的前侏罗系 (三叠系 )油气藏其含油砂体的形成明显受沉积相、高地温和印支运动的影响,分布于盆地南部的扇三角洲砂体裙在印支运动中由于地层抬升而处于与盆地北部生烃中心接触良好的位置,并且具备了产生次生孔隙的动力学基础,从而及时接受了由于岩浆体热和印支构造热事件提供的热所形成的早成熟油,形成了该盆地第一套优质储油砂体。盆地北带的侏罗系油气藏其含油砂体以南物源辫状河三角洲相为主,次为北物源扇三角洲相,具有砂体层数多、上下叠置性强、原始物性好、与多层煤系烃源岩互层、烃类向南运移距离短的特点,形成以中侏罗统西山窑组、三间房组和七克台组为基础的第二、三、四套优质储油砂体。     

鄂尔多斯盆地三叠－侏罗系的成岩作用及其成藏成矿响应

鄂尔多斯盆地三叠-侏罗系的成岩作用显示出受周边活动带干扰的类克拉通型特征.来自北部老山的岩浆岩碎屑、铁镁质矿物及火山喷发的火山灰导致在同生.早期成岩阶段孔隙水中释放大量铁、镁、硅、铝等离子,从而析出大量蒙脱石和富铁的绿泥石、沸石类和硅质矿物;在上三叠统中夹有由火山灰成岩转变而成的多层斑脱岩;同时导致富铀碎屑的聚集和由于粘土矿物、褐煤等的吸附作用造成的铀离子的预富集.在中成岩阶段,石油生成并在粘土矿物放出大量孔隙水作为载体的情况下初次运移,有机溶液进入储层使铝硅酸盐矿物溶解产生次生孔隙;同时蒙脱石和伊利石对油和气的生成具有催化作用,显示出典型的有机-无机成岩成藏作用过程.中晚燕山运动是一次构造热事件,此时期发生的表生成岩阶段是鄂尔多斯盆地成藏成矿的重要时期,不但促进了三叠系油和古生界天然气的生成,而且提供了油气运聚成藏的动力学条件;另一方面,天然气向盆地北东向的大规模运移散失造成强还原环境,促使具备铀矿形成条件的东胜地区侏罗系中大型铀矿的形成,是典型的有机-无机成岩成矿作用的结果.     

班公湖—怒江构造带西段三叠纪—侏罗纪构造—沉积演化

班公湖－怒江构造带西段在大地构造位置上处于特提斯构造域东端，横跨班公湖－怒江断裂带。三叠纪－株罗纪期间，其构造－沉积演化经历了大陆初始裂谷（T）、原洋裂谷（J1）、残余弧后盆地（J2－J3）阶段。初始裂谷阶段的拉张是呈南断北超的半地堑式由东向西进行的，逐渐形成地堑式原洋裂谷盆地。中晚侏罗世，南部新特提斯洋壳开始北各俯冲,产生的区域挤压应力使原洋裂谷逐渐封闭，裂谷盆地的小洋壳表现出以南向俯冲为主的双向式腑冲，同时伴生区域热沉降，盆地具残余弧后盆地的性质。该阶段,羌南地区发育碳酸盐岩为主的稳定陆缘沉积，冈度斯－念青唐古拉板片北部则形成广泛南超的近源碎屑沉积。     

1971-2010年青藏高原冬季降雪气候变化及空间分布

利用青藏高原55个气象站1971-2011年冬季（12月-翌年2月）逐月降雪量资料分析了冬季降雪的气候特征,得到高原冬季降雪总体上呈现东部和南部多、西北部和雅鲁藏布江中段少雪的分布特征,相对变率分布与降雪的分布几乎相反且变率大,以30°N为界高原降雪存在南北反相的变化趋势即北部降雪有所增加而南部减少.用旋转经验正交函数REOF结合相关分析进行降雪分区的基础上,重点分析了近40 a来高原降雪的演变特征和长期气候趋势.结果表明：降雪分布清楚地反映了高原的地理特征和气候特点,即高原南部迎风坡、冷暖气流交汇处降雪多,而背风坡、北部降雪少;近40 a降雪呈现“少-多-少”趋势,1980-1990年代期间降雪明显偏多,大约1970年代中期发生了由少雪到多雪的突变现象,其中南部2个区分别在2007年和1988年出现了降雪减少的突变现象;降雪具有显著的准14 a年代际变化和准8 a周期变化,且存在年代际特征.     

亚洲高山区全新世中期气候及其影响下的冰川模拟

本文利用一个1 km分辨率冰盖模式和11个PMIP4全球气候模式,研究了全新世中期亚洲高山区气候和冰川的变化特征。多模式集合平均结果显示,(1)全新世中期亚洲高山区年平均温度较工业革命前期降低了约0.7 ℃,夏季气温升高约0.7 ℃,冬季气温降低约1.8 ℃,全新世中期年平均降水略微增加(0.5%),但夏季和冬季降水分别增加和减少了约16%;(2)全新世中期亚洲高山区冰川较工业革命前期整体显著退缩,面积减少了约13%,体积减小了约8%。在区域尺度上,全新世中期亚洲高山区北部冰川的面积(体积)减少了约58%(47%),西部冰川的面积(体积)减少了约26%(25%),而南部冰川的面积(体积)增加了约20%(39%);(3)全新世中期夏季升温主导亚洲高山区北部和西部冰川的退缩,而降水增多是亚洲高山区南部冰川扩张的首要控制因子。本研究有助于加深理解全新世中期亚洲高山区冰川的变化格局和驱动因子。     

再论塔里木盆地库车坳陷三叠纪-侏罗纪的海泛事件

多年来的油气源对比表明,塔里木盆地库车坳陷的油气来源于三叠系-侏罗系的湖相、湖沼相烃源岩,因而探讨三叠纪-侏罗纪湖盆曾否遭受过特提斯洋海水的海泛,不仅对古地理重建,而且对烃源岩及其生油气潜力评价都具有重要的意义.笔者在该坳陷三叠系-侏罗系湖相烃源岩的生烃母质中发现了大量的各类底栖宏观藻类化石,并获得了沉积地球化学证据.据此,并结合区域古构造-古地貌演变与全球、大区域海平面升降规律的综合判断,初步认为库车坳陷在三叠纪-侏罗纪曾多次受到过特提斯洋短暂海泛的影响,其中规模最大的是晚三叠世黄山街期晚期、早侏罗世阳霞期晚期和中侏罗世恰克马克期.海泛的原因,可能与特提斯洋海平面升高和库车坳陷湖盆区-陆源区地势缓坦的联合作用有关.由于海泛改善了生烃母质类型,从而使海泛层段的源岩氢指数等表征生烃能力的指标有一定提高.     

Climate change and groundwater resources in Myanmar

Myanmar is located in Southeast Asia within the Mekong River Basin. The estimated annual surface and groundwater potentials are 1 081 km3 and 494 km3, respectively. Based on geological conditions, 11 different types of aquifers have been classified in Myanmar. The recent alluvial formation, Irrawaddy formation, Upper Pegu Group and Plateau limestone formation are the major water-bearing geologic formations of the country. In Myanmar, 89% of the groundwater is used for agriculture, approximately 8% is used for domestic consumption, and 3% is used for industrial purposes. Climate change projections for Myanmar from 2001 to 2100 predict general increases in temperature, clear-sky days, rainfall variability and flooding risks and a greater occurrence and intensity of extreme weather events across the country. Additional technology and investments are required to achieve groundwater resource security in response to climate changes. In addition, methods of ensuring the sustainability of groundwater resources must be implemented via collaborations with other countries and international sources.