Holocene relative sea‐level changes in Harris,Outer Hebrides,Scotland, UK     

Jason T. Jordan  David E. Smith  Sue Dawson  Alastair G. Dawson 《第四纪科学杂志》2010,25(2):115-134

Evidence for relative sea‐level changes during the middle and late Holocene is examined from two locations on the Atlantic coast of Harris, Outer Hebrides, Scotland, using morphological mapping and survey, stratigraphical, grain size and diatom analysis, and radiocarbon dating. The earliest event identified is a marine flood, which occurred after 7982–8348 cal. a (7370 ± 80 ¹⁴C a) BP, when the sea crossed a threshold lying at ?0.08 m Ordnance Datum Newlyn (OD) (?2.17 m mean high water springs (MHWS)) before withdrawing. This could have been due to a storm or to the Holocene Storegga Slide tsunami. By 6407–6122 cal. a (5500 ± 60 ¹⁴C a) BP, relative sea levels had begun to fall from a sandflat surface with an indicated MHWS level of between 0.08 and ?1.96 m (?2.01 to ?4.05 m). This fall reached between ?0.30 and ?2.35 m (?2.39 to ?4.44 m) after 5841–5050 cal. a (4760 ± 130 ¹⁴C a) BP, but was succeeded by a relative sea‐level rise which reached between 0.54 and ?1.57 m (?1.55 to ?3.66 m) by 5450–4861 cal. a (4500 ± 100 ¹⁴C a) BP. This rise continued, possibly with an interruption, until a second sandflat surface was reached between 2.34 and ?0.26 m (0.25 to ?2.35 m) between 2952–3375 cal. a (3000 ± 80 ¹⁴C a) and 1948–2325 cal. a (2130 ± 70 ¹⁴C a) BP, before present levels were reached. The regressive episode from the earliest sandflat is correlated with the abandonment of the Main Postglacial Shoreline. It is maintained that the fluctuations in relative sea level recorded can be correlated with similar events elsewhere on the periphery of the glacio‐isostatic centre and may therefore reflect secular changes in nearshore sea surface levels. Despite published evidence from trim lines of differential ice sheet loading across the area, no evidence of variations in uplift between the locations concerned could be found. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

中国东部岩石圈热状态与流变学强度特征   总被引：10，自引：1，他引：9  

汪洋  程素华 《大地构造与成矿学》2011,35(1):12-23

根据均衡原理制约的地热计算得到中国东部岩石圈的温度分布状态,以40、70、100km和莫霍面深度等温线图以及600°C、1100°C等温面深度的形式表示.同时计算了以1350°C等温面深度表示的中国东部的热岩石圈厚度.结果显示:在扬子克拉通西部四川盆地之下存在160～200km厚的岩石圈根,但在整个华北克拉通之下缺失岩...  相似文献   

Connectivity between the western and eastern limbs of the Bushveld Complex   总被引：1，自引：0，他引：1  

R. G. Cawthorn  S. J. Webb 《Tectonophysics》2001,330(3-4):195-209

The mafic layered rocks of the Bushveld Complex are 6–8 km thick and crop out over an area of 65,000 km². Previous interpretations of the Bouguer gravity anomalies suggested that the intrusion consisted of two totally separate bodies. However, the mafic sequences in these arcuate western and eastern limbs are remarkably similar, with at least six petrologically distinctive layers and sequences being recognisable in both limbs. Such similarity of sequences in two totally discrete bodies 200–300 km apart is petrologically implausible, and it is suggested that they formed within a single lopolithic intrusion.

All previous Bouguer gravity models failed to consider the isostatic response of the crust to emplacement of this huge mass of mafic magma. Isostatic adjustment as a result of this intrusion would have caused the base of the crust to be depressed by as much as 6 km. With this revised whole crustal model, it becomes possible to construct a gravity model, consistent with observed data, which includes a 6 km-thick sequence of mafic rocks connecting the western and eastern limbs of the Bushveld Complex. The exact depth at which the mafic rocks of the Bushveld Complex lie in the centre of the structure cannot be constrained by the gravity data.

Such a first-order model is an approximation, because there have been subsequent deformation and structural readjustments in the crust, some of them probably related to the emplacement of the Bushveld Complex. Specifically, the observed geometry of the rocks around the Crocodile River, Dennilton, Marble Hall and Malope Domes suggests that major upwarping of the crust occurred on a variety of scales, triggered by emplacement of the Bushveld Complex.  相似文献   

Early Cenozoic rapid flight enigma of the Indian subcontinent resolved: Roles of topographic top loading and subcrustal erosion   总被引：1，自引：1，他引：0  

Muthuvairavasamy Ramkumar  David Menier  Manoj Mathew  M. Santosh  Numair A. Siddiqui 《地学前缘(英文版)》2017,8(1):15-23

Intrinsic magmatic processes are considered as critical operators of plate movements. Here we demonstrate the role of extrinsic processes consequent to intrinsic processes as a catalyst for anomalous rapid plate movement. The rapid and accelerated flight of the Indian subcontinent since Deccan volcanism until its collision with Eurasia remains as one of the geological conundrums. Data on seismic tomography, peninsular geomorphology and inferences on continuum of subcrustal structures are utilized to address this enigma. We propose geomorphic isostasy as the mechanism that has driven this fastest drift ever recorded in geological history. It was initiated by sudden instability after the Deccan volcanism and resultant extensive accumulation of lava pile over continental lithosphere of northern India, northern-eastern tilt due to crustal thickness heterogeneity and subcrustal thermal stratification. The drift was sustained by Carlsberg and Central Indian ridge-push until collision and sediment top loading at northeast thenceforth. These inferences and geomorphic isostasy as a catalytic mechanism necessitate variability of drift rates as integral inputs for any continental scale modeling.  相似文献   

A global isostatic gravity model of the Earth   总被引：3，自引：0，他引：3  

Mikhail K. Kaban  Peter Schwintzer  & Sergey A. Tikhotsky 《Geophysical Journal International》1999,136(3):519-536

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珠穆朗玛峰重力值的推估──兼论推估方法的基本原理          下载免费PDF全文

张赤军 《极地研究》2001,13(4):273-282

在山区 ,尤其是在有全球第三极之称的喜马拉雅山区 ,当相邻点间距不大时 ,如何利用这些点上的重力与地形 (高程 )数据推估待求点的重力值 ,这对难以攀登和不能用仪器观测的山峰很有意义。研究指出 ,在地形负荷的波长很短时 ,具有一定强度的地壳足以能够支撑这种负荷 ,因此 ,不能用Airy Heiskanen和Pratt Hayford局部补偿模型作重力推估 ;由于空间异常主要受地形起伏制约 ,因此借助于邻近重力点的地形 (高程 )作推估会得到满意的结果。基于这一思路 ,我们采用了 4种有关公式 ,有效地推估了第三极之巅珠穆朗玛峰顶上的重力值 ,该值为(976 970± 7)× 1 0 - 5m·s- 2 。这一结果为精确推求珠峰大地水准面和正高提供了必要的数据 ,若用均衡的方法来推估 ,则可能相差近 1 0 0× 1 0 - 5m·s- 2 。  相似文献   

滇西试验场区地壳的试验均衡研究   总被引：1，自引：1，他引：0  

申重阳  甘家思  徐菊生  朱思林 《大地测量与地球动力学》1994,(4)

本文利用滇西试验场区最新完全布格重力异常和地形高资料，采用设置虚拟数区和边界限定、消除趋势项、低道滤波等预处理措施，按试验均衡理论，计算了该区地壳的均衡响应函数及试验均衡异常；结合文献［１］的研究结果，对其均衡异常分布特征、区域构造运动机制、活动断裂与强震展布间的关系进行了研究；结果表明：１）该区均衡响应函数值高于美国、加拿大及我国华北等地区，其地壳处于亚均衡状态；２）区内各部位的均衡状态并不均一，且异常幅值大小多与地壳的相对隆起或沉降相关；３）红河断裂带两侧均衡异常值差异明显，全区均衡异常的展布同活动断裂与强震分布有较密切的联系。  相似文献   

Relative sea‐level change and postglacial isostatic adjustment along the coast of south Devon,United Kingdom     

Anthony C. Massey  W. Roland Gehrels  Dan J. Charman  Glenn A. Milne  W. Richard Peltier  Kurt Lambeck  Katherine A. Selby 《第四纪科学杂志》2008,23(5):415-433

Previous sea‐level studies suggest that southwest Britain has the fastest subsiding coastline in the United Kingdom, but tide‐gauge data, GPS and gravity measurements and geophysical models show little evidence of anomalous subsidence in this region. In this paper we present 15 new sea‐level index points from four coastal barrier systems in south Devon. Eight are from compaction‐free basal sediments and others were corrected for autocompaction. Our data suggest that relative sea level along the south Devon coastline has risen by 21 ± 4 m during the past 9000 years. Sea‐level rise slowed during the middle and late Holocene and a rise of 8 ± 1 m has occurred since ca. 7000 cal. yr BP. Anomalous ages for many rejected points are attributed to sediment reworking during barrier transgression. The relative sea‐level history during the early and middle Holocene shows a good fit with geophysical model predictions, but the geological and modelled data diverge in the later Holocene. Unlike the geophysical models, sea‐level index points cannot differentiate between late Holocene relative sea‐level histories of south Devon and southwest Cornwall. It is suggested that this discrepancy can be resolved by obtaining additional high‐quality sea‐level index points covering the past 4000 years. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

On post-glacial sea level: I. General theory   总被引：3，自引：0，他引：3  

Jerry X. Mitrovica  Glenn A. Milne 《Geophysical Journal International》2003,154(2):253-267

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局部热膨胀产生的重力异常及其构造意义     

杨学祥  杨文瑛 《大地测量与地球动力学》1995,(1)

地热梯度的增加不仅引起地壳的体积变化，而且使地壳的荷载发生变化。定量计算表明，在均衡深度以上，局部地壳地热梯度的增加将产生重力负异常。随之而来的地壳均衡运动会造成２ｋｍ左右的地壳上升，用以补偿膨胀后地壳的质量亏损。  相似文献