哥伦比亚OMBU区古近系Em组层序地层研究

综合利用地震、测井等地质资料,运用层序地层学方法和技术,建立了层序地层格架和对比模式,对研究区古近系Em组地层的发育展布特征以及沉积环境进行了研究。Em组顶底均为区域上的不整合面,内部划分为两期基准面升降体系域。构造运动和沉积物供应控制下的基准面升级使得沉积初期研究区发育辩状河-曲流河沉积体系,至晚期演变为曲流河沉积体系。     

河北海兴小山CK3孔磁性地层与第四纪火山活动记录*

基于对渤海湾西岸河北省海兴小山火山丘附近500 25 m 深CK3孔进行的磁性地层学研究,确认该钻孔揭示了吉尔伯特(Gilbert)极性时科奇蒂(Cochiti)亚时以来的地层,底部层位年龄约为4 38 Ma;结合 ¹⁴ C 测年和地层关系,可见本孔中所见4期火山活动分别发生在2.12 Ma、1.34 Ma、35～70 ka 和10～15 ka;与渤海湾滨海平原几个质量较高的钻孔古地磁研究成果对比显示,黄骅坳陷第四纪期间整体向NE方向倾斜,沉积物平均粒径变化与测井曲线有较好的对比关系和同步性。依据沉积物特征、沉积构造以及测井相、粒度分析资料综合分析,确定全孔揭露地层大多发育泛滥平原沉积,即使是分支间湾亚相也少见湖泊-湖沼相沉积,沉积物多呈氧化状态。晚更新世以来3期海侵地层皆为潮坪沉积,其底板埋深与整个渤海湾西岸所见相符,可以按海洋氧同位素分期划分。     

新疆乌夏地区白垩纪层序发育控制因素及演化模式

以层序地层学和沉积学为理论指导,综合运用岩芯、钻测井、地震等资料及井-震结合对比分析,对乌夏地区白垩系清水河组与呼图壁河组层序地层及沉积演化特征进行研究,在此基础上分析层序发育控制因素,并建立层序地层演化模式。结果表明:清水河组与呼图壁河组可划分为1个三级层序(KSQ1)和3个体系域,其沉积相类型包括辫状河、辫状河三角洲、曲流河三角洲和湖泊等;构造沉降与古气候为本区层序发育的主要控制因素。层序KSQ1低位体系域时期,研究区地形高差较大,气候炎热干旱,以辫状河相砂砾岩沉积为主,沉积范围局限在乌夏断褶带及其以南地区;水进体系域时期,发生大规模湖侵,沉积范围扩大,主要发育退积式辫状河三角洲、曲流河三角洲;高位体系域时期,转为半干旱气候条件,湖平面下降,发育大规模曲流河三角洲,以三角洲平原沉积为主。     

博格达山东北缘上二叠统沉积特征与沉积演化模式

通过对博格达山东北缘西大龙口剖面与水西沟剖面上二叠统进行详细观察和精细测量,详细分析了地层特征与沉积相特征,建立了沉积演化模式。结果表明:博格达山东北缘上二叠统自下而上发育泉子街组、梧桐沟组与锅底坑组;泉子街组沉积期,西大龙口剖面与水西沟剖面分别发育冲积扇、曲流河,冲积扇砂砾岩体内有大量的砂岩砾石与油页岩砾石,为博格达山周缘地区中二叠统红雁池组与芦草沟组被剥蚀后在山前沉积的产物;梧桐沟组沉积期,博格达山隆升为物源区,西大龙口剖面与水西沟剖面分别发育辫状河、曲流河,辫状河砂砾岩体内火山岩砾石较多;锅底坑组沉积期,西大龙口剖面与水西沟剖面主要发育曲流河泛滥平原,以紫红色粉砂质泥岩、泥岩为主。     

上新世以来北京平原NBT1孔记录的地层沉积及构造指示

磁性地层学结合宇宙成因核素、AMS 14 C测年为晚新生代可靠的长序地质年代框架建立提供了有效快捷手段。在北京平原东南部钻取的NBT1全取芯钻孔进行了详细的磁性地层学研究,400 m钻孔335 块样品识别出10个正极性和9个负极性时段,记录了布容(Brunhes)、松山(Matuyama)、高斯(Gauss)、吉尔伯特(Gilbert)极性时,孔底进入到4. 2 Ma的Gilbert负极性时。以岩性组合、26 Al/10 Be、AMS 14 C年代学为基础,结合测井沉积〖JP2〗相分析,判断钻孔上新世晚期地层底界位于319. 60 m,第四系下更新统、中更新统、上更新统底界分别位于214. 80 m、〖JP〗70. 60 m、59. 25 m。在上新世约4. 2~3. 5 Ma发育了6期明显的冲洪积扇的快速沉积过程,第四纪早更新世以曲流河沉积体系为主,中更新世以湖沼沉积为主,夹分支河道沉积,沉积厚度相对较薄,晚更新世以分支河道- 湖沼沉积为主,其顶部末次盛冰期浊黄橙色硬质黏土发育。钻孔包含了3个沉积速率较高（>150 m/Ma）的时期,分别为3. 58~3. 33 Ma、1. 945~1. 778 Ma和0. 126~0. 010 Ma,与上新世以来青藏高原隆升扩展及华北地区晚更新世构造活化在时间上具有一致性,揭示了华北地区的沉积构造演化对青藏高原隆升具有一定响应。     

羌塘盆地东部晚三叠世-侏罗纪构造-沉积演化

本文以野外实测剖面为基础,结合区域地质调查,通过地层学、岩石组合特征及沉积盆地分析,并综合区域构造演化背景及年代地层学等最新研究成果,对羌塘盆地东部上三叠统-侏罗系岩石组合、沉积类型和沉积相特征进行了对比研究,明确了羌塘盆地东部晚三叠世-侏罗纪的地层分布特征、沉积相类型、展布特征及构造-沉积演化过程。以区域性角度不整合为标志,将羌塘盆地东部上三叠统-侏罗系划分为2个构造层(卡尼阶-诺利阶构造层和瑞替阶-基默里阶构造层),并详细叙述了不同构造层内各地层的分布范围、厚度变化及岩性特征。研究区上三叠统-侏罗系以海陆过渡相和海相沉积为主,其中海陆过渡相包括三角洲相和潮坪-泻湖相,海相包括碳酸盐缓坡、蒸发台地、局限台地、滨海、浅海、半深海和深海相沉积。卡尼期主要发育滨海-浅海-半深海-深海相沉积(北羌塘坳陷)和滨浅海沉积(南羌塘坳陷)。诺利期早期以碳酸盐岩缓坡-混积陆棚沉积为主,诺利期晚期、赫塘期-巴柔期、卡洛期和基默里期主要发育潮坪-三角洲相沉积(北羌塘坳陷)和滨浅海沉积(南羌塘坳陷),巴通期和牛津期以蒸发台地-局限台地-混积陆棚沉积为主。沉积相东西向带状展布,东部低隆起是分割南北相带的重要构造单元,并在巴通期及牛津期为水下隆起,控制着羌塘东部局限台地、蒸发台地及台地边缘的分布。将区域构造背景与沉积记录相结合,总结出5个构造-沉积演化阶段:活动陆缘阶段(卡尼期,Ⅰ_1)、前陆盆地演化阶段(诺利期,Ⅰ_2)、裂陷-坳陷阶段(瑞替期-巴柔期,Ⅱ_1)、被动陆缘-坳陷阶段(巴通期-卡洛期,Ⅱ_2)和被动陆缘-坳陷阶段(牛津期-基默里期,Ⅱ_3)。     

甘肃疏勒河冲积扇发育特征及其对构造活动的响应

甘肃疏勒河冲积扇是面积达2400km²的一个巨型冲积扇,位于青藏高原北缘阿尔金断裂带东端。区域构造上该扇发育在阿尔金主断裂、三危山断裂和南截山断裂组成的阿尔金断裂带左旋走滑构造域。根据野外调查获得的沉积层序、地貌形态和构造变形等资料,该冲积扇可划分为老冲积扇和新冲积扇。老冲积扇扇顶紧靠阿尔金主断裂,由已显著构造变形的早更新统玉门砾岩组成;新冲积扇是在老冲积扇基础上发育的,扇顶已向下游移动到大坝附近,距阿尔金主断裂4km,主要由中更新统酒泉砾石和晚更新统戈壁砾石组成。疏勒河冲积扇发育对区域构造活动的响应主要表现为:1)在第四纪早期,阿尔金断裂的左旋走滑兼逆冲运动,导致了由玉门砾岩组成的疏勒河老冲积扇扇头被左旋错动约8km,同时扇体,尤其扇头明显褶皱隆升,扇顶向山外移动;2)此后随着阿尔金断裂继续作左旋走滑兼逆冲运动,老冲积扇扇头又被左旋错动了约2km,总共左旋位移了约10km,并且扇顶下移了约4km,形成新的冲积扇;3)在冲积扇内从早更新世至晚更新世沉积中心不断向下游移动,呈现向下游超覆沉积的特征,这也一定程度上反映了祁连山隆升、向外扩展和侵蚀作用显著     

帕米尔东北缘新生代隆升活动:来自奥依塔格剖面砾石统计的证据

砾岩相通常作为构造事件的标志,对探讨造山带隆升过程有着重要的意义.选取位于帕米尔构造带东北缘的奥依塔格剖面开展砾石统计分析.新生代不同时期砾石的统计结果显示,奥依塔格剖面砾石成分主要为火成岩和变质岩,这与帕米尔造山带岩性相符.其中,花岗岩砾石作为特征组分首次出现在上新统阿图什组底部.砾石主要为巨砾,且以长短轴比值为1~2的近圆状为主;砾石的磨圆度中等,绝大部分为次磨圆-次棱角状;分选中等-差.结合砾石所处地层的沉积环境和热年代学记录,认为帕米尔东北缘新生代可能存在3期构造隆升事件,包括渐新-中新世克孜洛依组沉积早期、中新世中期(安居安组中-上段和帕卡布拉克组下段沉积时期)和上新世以来(阿图什组下段沉积以来).      

秦岭构造带徽成盆地白垩纪-新生代构造应力场演化历史

沿凤-太断裂带发育的徽成盆地斜切秦岭构造带,成为东、西秦岭构造地貌的分界带。该盆地由上部成县群和下部东河群2套地层序列组成,之间为角度不整合接触。基于沉积地层序列、野外断层滑动矢量运动学分析和古构造应力场反演,结合上部成县群磁性地层学的研究结果和基性岩脉的年代测试结果,确定了该盆地2期伸展断陷成盆阶段和3期构造挤压改造的交替演化历史。认为下部盆地形成于早白垩世时期(107Ma之前),成盆应力场为NWW- SEE引张,与东西向勉略断裂带左旋走滑拉分作用有关,其中加积了一套河湖相砂砾岩沉积。该走滑盆地在沉积晚期遭受NW- SE向挤压应力作用,控盆边界断层发生反转,地层发生宽缓的褶皱变形,基性岩脉侵位其中(107Ma)。上部新生的断陷盆地很可能形成于早白垩世晚期-晚白垩世(自107Ma以来),受NW- SE引张作用,沿凤-太断裂带发生复活,其中堆积了一套河流相红色砂泥岩和砂砾岩沉积地层。该断陷盆地遭受2次挤压应力场的改造:早期NNW- SSE向挤压、晚期NNE- SSW向挤压,这两期挤压作用使控盆边界断裂(凤太断裂、勉略断裂)发生构造反转,地层陡倾,但盆地内部变形较弱。与区域构造演化历史对比,认为这两期挤压应力作用分别发生在白垩纪晚期与古近纪。     

新疆艾比湖东南缘K3孔晚新生代环境演化

新疆准格尔盆地艾比湖K3孔孔深500.8 m,岩心采取率80.4%。依据光释光(OSL)测年、磁性地层学、磁化率、微体古生物(介形类和有孔虫)、孢粉学和岩相学研究,确定了K3孔晚新生代以来的环境演化过程：该孔钻遇地层属于约4.2 Ma以来沉积,在约3.6～4.2 Ma时期此地是湖泊环境;大约自3.6 Ma以来,伴随着青藏高原快速隆升发生的哈密运动,该区沉积环境由半深湖和浅湖演变为滨湖和水下三角洲,研究区干旱化状况加剧;在约2.6～3.0 Ma的上新世末期,形成盆地边缘和冲积扇体系;2.6 Ma前后,在西域运动-盐水沟运动影响下,研究区是曲流河体系发育期;自“中更新革命”约0.8 Ma以来,全区干旱化状况与现代相近。4.2 Ma以来不连续的孢粉图示和介形类的分布,也显示了沉积动力和水体的复杂变化;构造-气候旋回控制了该地晚新生代环境演化。     

Multi-proxy evidence for late Holocene anthropogenic environmental changes at Bongpo marsh on the east coast of Korea

We present a multi-proxy record (pollen, microscopic charcoal, magnetic susceptibility, carbon-isotopic composition, total organic carbon [TOC], carbon/nitrogen [C/N] ratios, and particle size) of the late Holocene environmental change and human activities from Bongpo marsh on the east coast of Korea. Mutual interaction between the environment and humans during the late Holocene has not been properly investigated in Korea due to the lack of undisturbed samples with high sedimentation rates. In this study, the history of human responses to late Holocene environmental changes is clearly reconstructed using a multi-proxy paleoenvironmental approach that has not previously been applied in Korea. The evidence from Bongpo marsh indicates that 1) Bongpo marsh began to develop ca. 650 BC as a coastal lagoon was rapidly filled with organic matter, 2) agricultural disturbance around the study site remained slight until ca. AD 600, 3) full-scale intensive agriculture prevailed and the area of deforestation increased between ca. AD 600 and ca. AD 1870, and 4) the land use changed from lowland rice agriculture to upland cultivation when agricultural productivity declined after AD 1870, probably due to severe deforestation and the consequent heavy influx of clastic sediment on rice fields, as described in various historical documents.     

Alluvial geoarchaeology of an ephemeral stream: Implications for Holocene landscape change in the central part of the Ebro Depression,northeast Spain

La Virgen is an ephemeral tributary of the Ebro River in northeast Spain with a complex alluvial sequence. We analyzed alluvial stratigraphy to develop a model of Holocene fluvial evolution for La Virgen and infer causes of floodplain dynamics. Three alluvial terraces were mapped and described using a combination of geoarchaeological and geomorphological techniques. Stratigraphic ages were estimated using ¹⁴C dating and archaeological remains. Sedimentation in the valley floor commenced in the Neolithic period ca. 6000 BC and continued during the Bronze and Iron ages (ca. 1800–500 BC), the Iberian and Roman periods (ca. 500 BC–AD 500), and the Middle Ages (ca. AD 500–1500). The main terrace (N3) is 14m thick and predominantly composed of sand, silt, and clay that we believe are derived from local hillslopes and represent a long period of human‐induced soil erosion that intensified during the Bronze and Iron ages until the Late Roman period. © 2010 Wiley Periodicals, Inc.     

Speleothem evidence for late Holocene climate variability and floods in Southern Greece

We present stable isotope data (δ¹⁸O, δ¹³C) from a detrital rich stalagmite from Kapsia Cave, the Peloponnese, Greece. The cave is rich in archeological remains and there are reasons to believe that flooding of the cave has directly affected humans using the cave. Using a combination of U–Th and ¹⁴C dating to constrain a site-specific correction factor for (²³²Th/²³⁸U) detrital molar ratio, a linear age model was constructed. The age model shows that the stalagmite grew during the period from ca. 950 BC to ca. AD 830. The stable oxygen record from Kapsia indicates cyclical changes of close to 500 yr in precipitation amount, with rapid shifts towards wetter conditions followed by slowly developing aridity. Superimposed on this signal, wetter conditions are inferred around 850, 700, 500 and 400–100 BC, and around AD 160–300 and AD 770; and driest conditions are inferred to have occurred around 450 BC, AD 100–150 and AD 650. Detrital horizons in the stalagmite indicate that three major floods took place in the cave at 500 BC, 70 BC and AD 450. The stable carbon isotope record reflects changes in biological activity being a result of both climate and human activities.     

Quantitative inter‐annual and decadal June–July–August temperature variability ca. 570 BC to AD 120 (Iron Age–Roman Period) reconstructed from the varved sediments of Lake Silvaplana,Switzerland

Annually resolved June–July–August (JJA) temperatures from ca. 570 BC to AD 120 (±100 a; approximately 690 varve years) were quantified from biogenic silica and chironomids (Type II regression; Standard Major Axis calibration‐in‐time) preserved in the varved sediments of Lake Silvaplana, Switzerland. Using 30 a (climatology) moving averages and detrended standard deviations (mean–variability change, MVC), moving linear trends, change points and wavelets, reconstructed temperatures were partitioned into a warmer (+0.3°C; ca. 570–351 BC), cooler (?0.2°C; ca. 350–16 BC) and moderate period (+0.1°C; ca. 15 BC to AD 120) relative to the reconstruction average (10.9°C; reference AD 1950–2000 = 9.8°C). Warm and variable JJA temperatures at the Late Iron Age–Roman Period transition (approximately 50 BC to AD 100 in this region) and a cold anomaly around 470 BC (Early–Late Iron Age) were inferred. Inter‐annual and decadal temperature variability was greater from ca. 570 BC to AD 120 than the last millennium, whereas multi‐decadal and lower‐frequency temperature variability were comparable, as evident in wavelet plots. Using MVC plots of reconstructed JJA temperatures from ca. 570 BC to AD 120, we verified current trends and European climate model outputs for the 21st century, which suggest increased inter‐annual summer temperature variability and extremes in a generally warmer climate (heteroscedasticity; hotspot of variability). We compared these results to MVC plots of instrumental and reconstructed temperatures (from the same sediment core and proxies but a different study) from AD 1177 to AD 2000. Our reconstructed JJA temperatures from ca. 570 BC to AD 120 showed that inter‐annual JJA temperature variability increased rapidly above a threshold of ～10°C mean JJA temperature. This increase accelerated with continued warming up to >11.5°C. We suggest that the Roman Period serves with respect to inter‐annual variability as an analogue for warmer 21st‐century JJA temperatures in the Alps. Copyright © 2011 John Wiley & Sons, Ltd.     

Geomorphological records of a ‘flood-dominated regime’ in the Rhône Delta (France) between the 1st century BC and the 2nd century AD. What correlations with the catchment paleohydrology?

In the Rhône Delta, numerous paleoenvironmental indicators coming from geomorphology, sedimentology, paleoecology and archeology provide evidences of remarkable hydrological regime change at the beginning of the Roman Antiquity. A significant reinforcement in the Rhône Riverˈs competence is indicated by the increase in grain size of the sediments deposited in the floodplain, within the immediate proximity of the channel. Increase in the fluvial sediment yield is indicated by the increase in rate of sedimentation in the floodplain. Increase in water levels is indicated by the deposition of hydromorphous facies, the development of hydrophytic species, and the decrease in activity of terrestrial lombricoids in the floodplain. Numerous crevasse splays were formed by short-term avulsions of the Rhône River between the first century BC and the AD first century. Their frequency is related to an increase of Rhône River paleodischarge, which makes the channel network incapable of evacuating large volumes of water brought in by the river. The littoral zone experienced a phase of progradation between the AD 1st and the 3rd centuries, in relation to the increase of terrigenous deposits coming from the Rhône of Ulmet. The increase in solid discharge, in the flood-dominated regime (FDR) context, can be related to the overall increase in detrital output from the catchment. The Rhône Delta rather appears in phase with the northern Alps and Massif Central from the 1st century BC to the AD 1st century. The FDR at the beginning of the Christian era contrasts with the drought-dominated regime (DDR) and the reduction of torrential rainfall in the Mediterranean and south Alpine areas. These observations allow to confirm the hydroclimatic limit which could distinguish the southern part of the catchment (Provence, Durancian Alps) from the rest of the Rhône basin.     

Hydrological Variations and the Ancient Silk Road in the Northern Tarim Basin between Han and Sui Dynasties

The fluctuation pattern of China's civilization can be ascribed to climate change and historical geopolitical variations. The ancient Silk Road served as the most prosperous route connecting East Asia and Europe during Han Dynasty(206 BC–220 AD) and Sui-Tang Dynasties(581–907 AD), but was deserted in Wei, Jin, Northern and Southern dynasties(220–580 AD), of which the Tarim Basin was a key area. However, our understanding about the decline of the route during this period remains limited. Here, we present an ～7-year resolution record based on optically stimulated luminescence(OSL) age-depth model(ca. 120 BC–750 AD) from Luntai(LT) profile, about 5 km from the modern Tarim River, which fed the ancient oases, to assess the potential causes on the documented decline of the ancient Silk Road between Late Han and Sui dynasties. In this study, five episodes of hydrological change were identified by combining grain size, magnetic susceptibility, geochemistry and TOC/TN contents. Our reconstruction reveals that cold and wet climate dominated at 120 BC–50 AD and 550–750 AD, respectively, indicated by strong hydrodynamic conditions. Relatively warm and humid climate occurred at 120–550 AD, between Eastern Han and Sui-Tang dynasties, indicating a better and more suitable local environment. A comparison between the studied region and other areas of China demonstrates that the paleoclimatic variations in eastern and western China exhibit rough discrepancies, and the hydrological conditions in arid region is inconsistent with the decline of ancient Silk Road in the northern Tarim Basin. We suggest that political and societal factors are the key issues that caused the interruption of Silk Road during Wei, Jin, Northern and Southern dynasties, such as the co-occurrence of societal crises, turmoil and division in eastern China, rather than the deteriorating climatic condition in the northern Tarim basin.     

An assessment of changes in properties of steppe kurgan paleosoils in relation to prevailing climates over recent millennia

Comparative analysis of morphological and chemical properties of the soil chronosequence on Kastanozems soils in the steppe zone of the Russian Plain, which included paleosoils buried beneath kurgans erected ca. 2000 BC, AD 50, AD 200, and AD 1250 was performed to reconstruct the paleoenvironmental conditions in this archeologically important region. Paleoenvironmental dynamics were traced using the state of microbial communities of paleo and modern soils (including the dynamics of total and glucose-reactive biomass, and the abundance of microorganisms grown on selected media). We demonstrate that the share of the glucose-reactive microorganisms in the microbial community, the ecological–trophic structure, and oligotrophicity index might serve as indicators of the state of microbial communities and be used for paleoenvironmental reconstructions. The morphological–chemical and microbial properties confirm an arid period ca. 2000 BC, slightly wetter conditions ca. AD 50, and more humid conditions ca. AD 1250.     

Two decadally resolved records from north‐west European peat bogs show rapid climate changes associated with solar variability during the mid–late Holocene

Two ¹⁴C accelerator mass spectrometry (AMS) wiggle‐match dated peat sequences from Denmark and northern England record changes in mire surface wetness reconstructed using plant macrofossil and testate amoebae analyses. A number of significant mid–late Holocene climatic deteriorations (wet shifts) associated with declines in solar activity were recorded (at ca. 2150 cal. yr BC, 740 cal. yr BC, cal. yr AD 930, cal. yr AD 1020, cal. yr AD 1280–1300, cal. yr AD 1640 and cal. yr AD 1790–1830). The wet shifts identified from ca. cal. yr AD 930 are concurrent with or lag decreases in solar activity by 10–50 years. These changes are replicated by previous records from these and other sites in the region and the new records provide improved precision for the ages of these changes. The rapidly accumulating (up to 2–3 yr cm^?1, ～1310 yr old, 34 ¹⁴C dates) Danish profile offers an unprecedented high‐resolution record of climate change from a peat bog, and has effectively recorded a number of significant but short‐lived climate change events since ca. cal. yr AD 690. The longer time intervals between samples and the greater length of time resolved by each sample in the British site due to slower peat accumulation rates (up to 11 yr cm^?1, ～5250 yr old, 42 ¹⁴C dates) acted as a natural smoothing filter preventing the clear registration of some of the rapid climate change events. Not all the significant rises in water table registered in the peat bog archives of the British and Danish sites have been caused by solar forcing, and may be the result of other processes such as changes in other external forcing factors, the internal variability of the climate system or raised bog ecosystem. Copyright © 2008 John Wiley & Sons, Ltd.     

Geomorphological records of a ‘flood-dominated regime’ in the Rhône Delta (France) between the 1st century BC and the 2nd century AD. What correlations with the catchment paleohydrology?

Abstract

In the Rhône Delta, numerous paleoenvironmental indicators coming from geomorphology, sedimentology, paleoecology and archeology provide evidences of remarkable hydrological regime change at the beginning of the Roman Antiquity. A significant reinforcement in the Rhône River's competence is indicated by the increase in grain size of the sediments deposited in the floodplain, within the immediate proximity of the channel. Increase in the fluvial sediment yield is indicated by the increase in rate of sedimentation in the floodplain. Increase in water levels is indicated by the deposition of hydromorphous facies, the development of hydrophytic species, and the decrease in activity of terrestrial lombricoids in the floodplain. Numerous crevasse splays were formed by short-term avulsions of the Rhône River between the first century BC and the AD first century. Their frequency is related to an increase of Rhône River paleodischarge, which makes the channel network incapable of evacuating large volumes of water brought in by the river. The littoral zone experienced a phase of progradation between the AD 1st and the 3rd centuries, in relation to the increase of terrigenous deposits coming from the Rhône of Ulmet. The increase in solid discharge, in the flood-dominated regime (FDR) context, can be related to the overall increase in detrital output from the catchment. The Rhône Delta rather appears in phase with the northern Alps and Massif Central from the 1st century BC to the AD 1st century. The FDR at the beginning of the Christian era contrasts with the drought-dominated regime (DDR) and the reduction of torrential rainfall in the Mediterranean and south Alpine areas. These observations allow to confirm the hydroclimatic limit which could distinguish the southern part of the catchment (Provence, Durancian Alps) from the rest of the Rhône basin. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.     

公元前602年至公元11年黄河下游冲积平原沉积特征分析

根据钻孔中沉积物性状的详细描述、样品粒度分析资料,结合已有黄河下游历史变迁及沉积物测年成果,分析了公元前602年到公元11年黄河下游冲积平原的沉积特征和沉积环境的变化。发现可以利用沉积物颜色、组成、粒度组成变化比较准确地确定研究区公元前602年的古地面,砂粘比Kd值是确定界线的很好指标。公元前602年以后的黄河冲积平原沉积物以浅黄色、黄色、棕色砂质亚沙土和粉质亚粘土为主,少量粉质亚沙土,平均粒度范围为331～612Φ,分选较差,偏度多为正偏或极正偏,峰态为窄峰、很窄和中等峰态。总体上由上游到下游平均粒径逐渐变细,标准离差增大,峰度减小,即水动力减弱,分选程度降低。对比分析发现,古黄河冲积平原沉积与现代黄河河漫滩沉积样品相比粒径明显偏细。钻孔Kd值随深度的变化揭示,从公元前602年到公元11年,黄河下游冲积平原沉积环境的水动力条件发生了两次明显的强弱变化。