河流对0.8 Ma B.P.环境突变事件的地貌响应研究

以兰州盆地0.8 Ma B.P.阶地为例证,运用古地磁测年方法,通过收集相关文献,分析讨论了0.8 Ma B.P.阶地与0.8 Ma B.P.环境突变事件的联系。结果表明：① 0.8 Ma B.P.环境突变事件主要表现在气候转型、构造运动等方面,具有群发性和全球性特点;② 兰州盆地以及其他区域0.8 Ma B.P.阶地存在的证据,表明河流在0.8 Ma B.P. 前后普遍发生过一次下切事件;③ 0.8 Ma B.P.阶地是河流对0.8 Ma B.P.环境突变事件的地貌响应,构造运动为提供了下切驱动力,而气候变化则控制了下切时间。     

Foraminiferal stratigraphy of raised marine deposits, representing isotope stage 5, Prins Karls Forland, western Svalbard

Two raised marine sequences from Prins Karls Forland, western Svalbard, interpreted to have been deposited during part of isotope substage 5e (Eemian) and substage 5a, were studied for foraminifera content. Time constraints are given by ¹⁴C ages, infrared stimulated luminescence age estimates and amino acid ratios in subfossil marine molluscs. A diamicton (unit B) separates the two marine sequences and reflects an advancement of local glaciers sometime late in isotope stage 5. The two marine sequences contain diverse benthic foraminiferal faunas, indicating periods of a relatively warm and seasonally ice-free marine shelf environment. Compared to the lowermost sequence (unit A), the upper marine sequence (unit C) seems to reflect a more shallow environment that could have resulted from the global lowering of the sea level towards the end of isotope stage 5. Our results further emphasise the problem of biostratigraphic distinction between interglacial and interstadial deposits at high latitudes, with temperature conditions for substage 5a close to those of substage 5e and present conditions.     

Alluvial terraces on the Ionian coast of northern Calabria, southern Italy: Implications for tectonic and sea level controls

In this paper we present the results of an integrated geomorphological, pedological and stratigraphical study carried out along the Ionian coast of northern Calabria (southern Italy). This area is characterised by the occurrence of five orders of alluvial terraces that are striking features of the landscape, where large and steep catchments debouch from the mountain front to the hilly coastal belt.Field investigations indicate that the deposits of all five terraces are suggestive of shallow gravel-bed braided streams.On the basis of the age of the Pleistocene substratum and morphostratigraphic correlation with marine terraces cropping out in the nearby areas, each order has been associated to specific marine oxygen isotope stages.Consequently, we focused on the interplay of allocyclic factors influencing stream aggradation/degradation. Soil features and other climatic proxies suggest that climate didn't play an important role with respect to tectonic and base-level changes in controlling fluvial dynamics.In particular, we recognised that during the middle Pleistocene the study area experienced a period of subaerial landscape modelling, as suggested by the thick and complex alluvial sequence of the highest terrace (T1). The onset of regional uplift marks a change in the geomorphic scenario, with tectonic and eustatically driven changes in base-level working together in causing switches in fluvial aggradational/erosional phases (T2–T5 terraces). Because of the uplift, river dissection occurred during phases of sea level fall, whereas aggradation phases occurred during periods of climate amelioration (sea level rise) just before highstands were attained.As a consequence, the stepped terraces in the study area reflect the interplay between tectonics (uplift) and sea level changes, in which terraces define episodes of relative sea level fall during the late Quaternary.     

Geomorphic evidence of major sea-level fluctuations during marine isotope substage-5e, Cape Cuvier, Western Australia

A detailed geomorphologic and morphostratigraphic investigation of raised marine terraces at Cape Cuvier, Western Australia, reveals two morphologically distinct units. A lower, well-developed accretional reef terrace between 3 and 5.5 m above MLWS (mean low-water springs; hereafter denoted as “+”) represents an extended interval of stable sea level. An upper erosional terrace and incipient coralgal rim between + 8.5 to 10.5 m represents a brief sea-level stillstand at this higher elevation. These features suggest the lower and upper terraces developed during discrete sea-level events. In an attempt to better define the timing of emplacement of each marine unit, 20 coral samples collected along vertical and lateral reef growth axis from both terraces were analysed with U-series dating. Unfortunately, all coral samples exhibited elevated δ²³⁴U_initial values, suggesting that pervasive uptake of ²³⁴U-enriched uranium and ²³⁰Th thorium had occurred. Despite the shortcomings of absolute dating, a succession of events can be resolved though morphostratigraphic relationships. Comparison of the facies relationships, coral growth, and morphostratigraphic features between the lower and upper terraces indicates that an early to mid MIS 5e stillstand at + 3 to 5 m was followed by a late rise to + 8.5 to 10.5 m. This agrees with an emerging global view of MIS 5e sea-level history derived from stable carbonate platforms, rejecting the hypothesis that these higher sea-level benchmarks are an artefact of localized tectonic processes.     

Longitudinal profile evolution of valleys on coastal terraces under the compound influence of eustasy, tectonism and marine erosion

On the coast of Tosa Bay, Southwestern Japan, there is a wide coastal terrace which was formed in the Last Interglacial and has been uplifted to altitudes of 150–200 m above the present sea level by crustal movement. Many valleys dissect the terrace surface with upwardly convex profiles in downstream reaches. Numerical simulations were conducted to investigate the development of longitudinal profiles of the valleys under the influence of baselevel change and marine erosion. The basic equation used for the calculation had been derived theoretically from the hydraulic mechanism of river erosion. The independent variables are the gradient and curvature of the valley floor and the distance from the divide (drainage area per unit basin width). The parameter in the sediment transport equation is determined based on the results of laboratory experiments. A time sequence of seashore migration which has been caused by marine erosion and relative sea level change due to crustal uplift and glacial eustasy since the Last Interglacial was given as a boundary condition. Numerical calculations were conducted using a finite difference method, starting from 125000 years ago when the shoreline was located at the upper end of the terrace surface, and progressive changes in the valley profiles over time were simulated. The present profiles obtained from the calculation fit quite closely to actual valley profiles, which demonstrates the validity of the equation, and at the same time suggests a formation process for wide coastal terraces.     

香港地区晚第四纪环境的几个问题

香港的“潜在”植物区系及顶极植被与爪哇及印度相似。香港的红树林组成逊于海南但胜于闽南。Ｑ３＾２海相层中有现今仅见于海南的陆均松和海松。Ｑ４海相层中有红茄冬、角果木、榄李，而现今仅见榄李。中全新世香港有海滩岩发育。上述现象表明香港属于热带北部，历史上热带性比今更强。香港及邻近海域１１个剖面揭示Ｑ３＾１以来有３个海相层，经历３次重大的海陆变迁。据验潮记录，近三四十年海平面上升率为１．６４±０．２５ｍｍ     

The sedimentary and geochemical record of Neogene-Quaternary water bodies in the Dead Sea Basin - inferences for the regional paleoclimatic history

Several waterbodies occupied the tectonic depressions along the Dead Sea transform during the NeogeneQuaternary. The earliest of these water bodies was the marine Sedom lagoon, which produced the SedomDead Sea brine. After the disconnection of the Sedom lagoon from the open sea several lakes were developed in the Dead Sea basinJordan Valley. Lake Amora (Samra) that existed from early to late Pleistocene, Lake Lisan (~ 70–15 kyr B.P.), and the Holocene Dead Sea. The lacustrine water bodies in the Dead Sea basin behave as amplifier lakes whose size and depth reflect the changing climatic conditions in the region. Lake level and limnological conditions of Lake Amora are not yet known, nevertheless, the lake probably extended over a large part of the Dead Sea basin-Jordan Valley. Lake Lisan level changed between ~ 330 and ~ 150 meters below sea level (m b.s.l.). Its maximum elevation was reached at ~ 27–23 kyr B.P. during marine isotope stage 2. Its minimum elevation was reached at ~ 47–43 kyr during marine isotope stage 3. Lake Lisan began to recede at ~ 17–15 kyr B.P. and at 12–11 kyr B.P. the postLisan water body declined to its minimum level. During most of the Holocene the lake (paleoDead Sea) stabilized at ~ 400 m b.s.l.The limnological evolution of water bodies in the Dead Sea basin reflects the climatic conditions in the region during the late Pleistocene, which fluctuated between wetter and drier periods. During Lisan time these fluctuations appear to be modulated by the cold and warm cycles, respectively in the northern Hemisphere. This relation is less obvious in the postLisan water body, where the strongest lake drop appears to occur during the Younger Dryas cold event.     

Marine Terraces and Quaternary Tectonism,Northwest Baja California,Mexico

Deformed marine terraces provide excellent measures of Quaternary tectonism along 400 km of the Pacific coast of Baja California between Ensenada and Punta Blanca. The nature and magnitude of deformation are well expressed by the present elevation of the marine limit, of Upper Pliocene or Lower Pleistocene age, which has been upwarped to 345m, 357m, and at least 195m in three separate localities, while occurring at lower levels elsewhere. Multiple terraces are found below this marine limit where appreciable uplift has occurred. Where relative subsidence has prevailed, fewer broader terraces or thick alluvial and eolian deposits occur. Terraces are further dislocated by NW-SE strike-slip faulting and by normal faults that trend NE-SW across the coast. Folding and faulting are less significant on the younger terraces than on the older features, and negligible for the Sangamonian terrace, except close to major faults. Crustal movements revealed by these terraces, and by similar features in southern California, Baja California Sur, and around the Gulf of California, are interpreted in terms of plate tectonics. Over the past 5 million years, the Peninsular Ranges have been carried northwestwards away from mainland Mexico, at an average rate of 6cm/yr, on the dis located limb of a spreading sea floor associated with the East Pacific Rise now found beneath the Gulf of California. The Pacific coast of the Peninsular Ranges comprises several discrete crustal slivers which, on the evidence of the marine terraces, have been warped and dislocated in response to tec tonic forces associated with rafting and subsequent crowding against transverse structures to the north. Uplift rates range as high as 1.0m/1000 yrs locally but are generally less, and are much less than rates found in the Transverse Ranges farther north. As in the latter province, basins typified by net sub sidence during Quaternary time are also found.     

台湾西北部海岸阶地的研究

海岸阶地的形成通常是海准面变动、地壳变动或两者共同作用之结果．研究海阶不仅可印证推论古气候、往昔海准面变化及地壳变动状况,更可藉以了解各区域间变动的差异,全盘了解大地构造的意义,而且小规模的海阶变动,时常与地震活动伴生,因此,研究海阶更可作为判读地震周期的依据之一,所以,世界各地位于地壳活动带的国家对于海阶的型态与演育...     

台湾西北部海岸阶地的研究

海岸阶地的形成通常是海准面变动、地壳变动或两者共同作用之结果．研究海阶不仅可印证推论古气候、往昔海准面变化及地壳变动状况,更可藉以了解各区域间变动的差异,全盘了解大地构造的意义,而且小规模的海阶变动,时常与地震活动伴生,因此,研究海阶更可作为判读地震周期的依据之一,所以,世界各地位于地壳活动带的国家对于海阶的型态与演育过程均作详细的调查及研究．本研究以淡水河以南至大安溪以北之海阶作为研究范围,发现台湾西北部位于观音山北部沿海、新竹山子顶沿海、客雅溪口南岸、后龙溪口南岸等4个地区,都有零星的海阶分布．经过阶地分布、地形特征与阶序对比,并利用世界海阶对比基图求出该地区的地壳隆升率与海阶可能形成的年代,藉以了解各区域间变动的差异．台湾西北部海岸地区的海阶大致上可划分为高位及低位2群阶：也,高位海阶分布的高度在15～275m之间,阶面覆盖着红壤层,为晚更新世时所造成;低位海阶分布的范围与高度较小,在海滩与高位阶地末端阶崖之间,沿着海岸成带状分布,阶面无红壤掩覆,海拔大多在10m以下．低位海阶构成的物质多以砾石及砂为主,属全新世海阶,即第四纪最后一次冰期结束后,近1万年以来全球高海水位时期所形成．利用海阶对比基图与已有的定年数据,辅以地形地貌及堆积物特征比较,获得各段阶地之平均隆升率,观音山北部沿海、客雅溪口南岸、后龙溪口南岸3个地区,经过比对,分别是2．1mm／a、2．2mm／a、2．15mm／a,数值相近,显示该区之地盘隆升率及海准面变动状况大致相同;仅新竹山子顶沿海地盘隆升率较小,为1．4mm／a．此表示,台湾岛的海阶变化不仅受到海准面变动的影响,尚受到区域性地壳隆升的控制．     

青藏高原东北部甘加盆地古梯田地层与年代初探

梯田是人类几千年来利用和改造自然能力的象征,在人类社会发展中发挥了重要的作用。甘加盆地位于青藏高原东北部甘肃省夏河县,盆地内的丘陵、山麓地带分布大面积的层状梯形景观,疑似弃耕的古代梯田。本文在实地考察的基础上,基于卫星遥感资料,通过GIS手段分析发现古梯田面积为42.2 km²（约63000亩）,主要分布在盆地内央曲河及其支流两侧海拔2936~3326 m间的山坡上。通过对3个古梯田剖面样品的磁化率、总有机碳/氮（TOC、TN）含量、孢粉、粒度等环境代用指标分析,同时对比具有准确年代控制的自然剖面磁化率与粒度。研究结果显示：梯田开垦于晚全新世（距今3000 a）古土壤,梯田剖面顶部25~35 cm不同于自然剖面而呈均一化的指标证实了耕作层的存在（距今约1000 a以下层位）;但耕作层之上TOC、TN含量的增多,以及梯田剖面与自然剖面整体一致的指标变化趋势说明了梯田被短期利用后长期废弃;结合历史文献资料推断夏河古梯田是在北宋“弓箭手屯田”制度（1074—1125年）下开垦的;气候重建资料显示该时段温度较高、降水增加,整体有益于农业生产。本文提供了过去人类社会适应气候变化的典型案例。     

珠江三角洲晚第四纪地层、海平面变化 与构造运动的关系

在回顾南海北部海岸和陆架地层证据的基础上,梳理了珠江三角洲晚第四纪演变历史。结果显示：1）本区晚第四纪地层拥有2套海相沉积,上（新）海相层是当前间冰期（或10.5 ka B.P.以来）高海平面期间形成的沉积物,而下（老）海相层最可能是末次间冰期（126―120 ka B.P.）高海平面阶段留下的沉积物;2）老海相层顶面埋深在三角洲盆地内至少比现今海平面低10~15 m,在珠江口一带则低于20 m,这说明珠江三角洲盆地存在构造沉降,因为2次间冰期的海平面高度是相近的;3）在新生代欧亚板块大陆向东南伸展的构造格局下,南海北部陆架和海岸带经历长期连续的沉降,而长期平均沉降率在0.12 mm/a左右,明显低于GPS测出的现代沉降率;4）在这种板块运动基础上,晚第四纪断裂活动增强了三角洲盆地的沉降,为2次海侵提供了可容沉积空间。     

禹门口南黄河东岸沙丘初步研究

在禹门口南山西省河津、万荣县境内黄河阶地上发育了一些固定、半固定沙丘,注入黄河的汾河将这些沙丘分成了南北两部分。北部的沙丘多在海拔400m左右,高出现代黄河约35m,位于黄河的第二级阶地上,由两条南北向的沙垄和两垄之间分布的抛物线形沙丘构成特殊的景观。这些抛物线形沙丘一般高度约7~8m,背风面突出,迎风坡坡度一般为15°~20°,背风坡坡度一般大于40°。风沙堆积下伏的河流堆积物的¹⁴C年龄为26.40±0.8kaBP,表明沙丘形成于距今26ka以来。南部沙丘海拔高度近500m,高出现代黄河水面150m,覆盖于黄河第三级阶地之上。一个天然剖面揭示,第三阶地的底部为黄色中粗砂与灰绿色粉砂粘土互层,中部为灰黄色黄土,顶部为黄色风沙层。在黄土地层中可以识别出S₁古土壤和位于风沙堆积下面的可能为L₁SS₁的弱成土层。由此推断风沙堆积于距今3万a以来。黄河阶地上的沙丘是在特殊的地区和特定的时期;强大的风力、丰富的沙源和气候变干条件下形成的。虽然东岸沙丘已是固定、半固定沙丘,但沙化仍然是该地区的一个问题。由于3~4a前开始在丘前洼地栽种苹果树,破坏了下风向沙丘迎风面的植被,造成了原来已固定沙丘的活化,在沙丘顶部生成了新的小抛物线形沙丘,高度大于1 m。沙丘上裸露的树根指示表土已被侵蚀0.3 m。南部沙丘区的风蚀作用也很强,例如,万荣县裴庄乡西范村北一片柿树林的树根由于风蚀已经裸露1.2 m。     

云南大理点苍山地区更新世晚期沉积地层的ESR测年研究

本文采用电于自旋共振（ESR）方法测定了云南点苍山地区更新世晚期沉积地层的形成年代。测年结果显示；（1）点苍山地区冰川沉积物的ESR年龄均小于140．35KaBP，说明该地区的第四纪冰川作用最早出现于中更新世晚期，主要发生于晚更新世；（2）点苍山西麓平坡附近最高一级基座阶地的堆积时代为184．3KaBP，证明西洱河阶地系列为中更新世以来的产物；（3）点苍山东侧白雀寺地区深3．7m处的褐红色地展形成的ESR年龄为12218KaBP，揭示出该地层形成于深海氧同位素5e阶段所代表的一个温热气候时期。     

Geomorphology and tectonics of uplifted coasts: New chronostratigraphical constraints for the Quaternary evolution of Tyrrhenian North Calabria (southern Italy)

The Tyrrhenian coastal sector of North Calabria, stretching between Torre S. Nicola and the Lao river, belongs to the inner extensional sector of the Neogene Apennines thrust belt. It is characterised by a stair of Quaternary marine and fluvial terraces representing the geomorphic response to the interaction between the Quaternary sea level fluctuations and the regional trend of tectonic uplift experienced by the margins of the Tyrrhenian back-arc basin. Since the last century, several authors studied the North Calabria coasts, where the flight of terraces preserves significant marine and continental successions, and proposed several paleo-geomorphological and tectonic reconstructions. In this paper we present a new stratigraphic and morphostructural setting of the North Calabria coasts based on both chronostratigraphical constraints obtained from marine deposits and detailed geomorphological analysis. A ten order stair of marine terraces, stepping between 240 and 0 m a.s.l., was recognized and time-constrained by the age of the Fornaci S. Nicola marine succession which was ascribed by integrated paleoecological, biostratigraphical and paleomagentic analyses to the early Middle Pleistocene (MIS 19–15). In particular, the 240, 200 and 160 m a.s.l. high strandlines were ascribed to the Early Pleistocene and the ones between 100 and 15 m a.s.l. to the Middle Pleistocene. The total amount of the vertical motion experienced by the studied area was estimated, and evaluation of the average rates of uplift for the Middle and Late Pleistocene times were also given. Considering the elevation a.s.l. of the oldest terraces, a tectonic uplift of at least 240 m was calculated for the North Calabria coasts since the Early Pleistocene times, 100 m of which gained from the beginning of the Middle Pleistocene. On the other hand, the 8-m high Late Pleistocene strandlines display a negligible vertical displacement affecting the area during the last 130 ka. The entire staircase of terraces preserves a record of slowing down in the rate of uplift, which attained an average value of 0.15 mm/year during the Middle Pleistocene.     

大同-阳原盆地古泥河湾湖的岸线变化

本文通过大同-阳原盆地古湖岸线遗迹的分析,阐述第四纪古泥河湾湖的出现、发展和消亡,指出湖泊变迁是构造运动和气候变化等因素共同作用的结果,构造运动是主要因素。     

南极洲维斯特福尔德丘陵与菲尔德斯半岛冰缘地貌的比较研究

东南极大陆沿岸的维斯特福尔德丘陵(68°22'～68°40'S,77°55'～78°30'E)和西南极乔治王岛南端的菲尔德斯半岛(62°08'～62°20'S,58°45'～58°58'W)的气候条件不同。前者属于极地大陆性气候,气温低,冬季严寒,干燥、风大,夏季较短;后者属于极地海洋性气候,气温不很低,湿润、风小,夏季较长。因此,两地的冰缘地貌的组合类型及其发育过程存在明显的差异。前者冰缘地貌单一,发展速度较慢;后者冰缘地貌复杂多样,发展速度较快。 本文根据实地观测资料,对极地大陆型和极地海洋型两类冰缘地貌作一些比较,并且提出,年冻融日数是决定冰缘作用强弱的最重要指标。     

台湾海峡北部两侧海阶之研究

海岸阶地的形成是海平面变动、地壳变动或两者共同作用之结果．研究海阶不仅可印证推论古气候、往昔海平面变化及地壳变动状况,更可藉以了解各区域间变动的差异,全盘了解大地构造的意义,同时,小规模的海阶变动,常与地震活动伴生,研究海阶可作为判读地震周期的依据之一,所以,世界各地位于地壳活动带的国家对于海阶的形态与演育过程均作详细的调查及研究．位于台湾海峡北部两侧的台湾西北部以及马祖、金门等海岸地区,都有海阶的分布．透过阶地分布、地形特征与阶序对比,同时,利用世界海阶对比基图找出该地区的地壳隆升率与海阶可能形成的年代,并藉以了解各区域间变动的差异．前述地区的海阶大致上可分成高位与低位2群,高位海阶分布的高度在15～275m之间,上覆红壤层,为晚更新世时期产物;低位海阶分布的范围较小,高度较矮,大部分分布于海滩与高位阶地末端阶崖问,沿着海岸呈带状分布,阶面大多无红壤层覆盖,海拔在10m以下．组成的物质多以砾石及砂为主,属于全新世时期的产物,即近1万年以来全球高海水位时期（第四纪最后一次冰期结束后）所形成．利用海阶对比基图与已有的定年数据,辅以地形地貌及堆积物特征比较,获得各段阶地之平均隆升率,台湾西北部之观音山北部沿海、客雅溪口南岸、后龙溪口南岸3个地区,分别是2．1mm／a、2．2mm／a、2．15mm／a,数值相近,显示该区之地盘隆升率及海平面变动状况大致相同;仅新竹山子顶沿海地盘隆升率较小,为1．4mm／a．此表示,台湾岛的海阶变化不仅受到海平面变动的影响,尚受到区域性地壳隆升的控制．马祖与金门地区的隆升率则分别为1．6mm／a、1．3mm／a,由于该区仅受新华夏断裂构造的控制,因此,其活动的幅度相对而言较台湾为小．     

New constraints on the late Cenozoic incision history of the New River, Virginia

The New River crosses three physiogeologic provinces of the ancient, tectonically quiescent Appalachian orogen and is ideally situated to record variability in fluvial erosion rates over the late Cenozoic. Active erosion features on resistant bedrock that floors the river at prominent knickpoints demonstrate that the river is currently incising toward base level. However, thick sequences of alluvial fill and fluvial terraces cut into this fill record an incision history for the river that includes several periods of stalled downcutting and aggradation. We used cosmogenic ¹⁰Be exposure dating, aided by mapping and sedimentological examination of terrace deposits, to constrain the timing of events in this history. ¹⁰Be concentration depth profiles were used to help account for variables such as cosmogenic inheritance and terrace bioturbation. Fill-cut and strath terraces at elevations 10, 20, and 50 m above the modern river yield model cosmogenic exposure ages of 130, 600, and 600–950 ka, respectively, but uncertainties on these ages are not well constrained. These results provide the first direct constraint on the history of alluvial aggradation and incision events recorded by New River terrace deposits. The exposure ages yield a long-term average incision rate of 43 m/my, which is comparable to rates measured elsewhere in the Appalachians. During specific intervals over the last 1 Ma, however, the New River's incision rate reached 100 m/my. Modern erosion rates on bedrock at a prominent knickpoint are between 28 and 87 m/my, in good agreement with rates calculated between terrace abandonment events and significantly faster than 2 m/my rates of surface erosion from ancient terrace remnants. Fluctuations between aggradation and rapid incision operate on timescales of 10⁴− 10⁵ year, similar to those of late Cenozoic climate variations, though uncertainties in model ages preclude direct correlation of these fluctuations to specific climate change events. These second-order fluctuations appear within a longer-term signal of dominant aggradation (until 2 Ma) followed by dominant incision. A similar signal is observed on other Appalachian rivers and may be the result of sediment supply fluctuations driven by the increased frequency of climate changes in the late Cenozoic.