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Seismic and sequence stratigraphic architecture of the central western continental margin of India (between Coondapur and south of Mangalore) has been investigated with shallow seismic data. Seismic stratigraphic analysis defined nine seismic units, that are configured in a major type-1 depositional sequence possibly related to fourth-order eustatic sea-level changes, comprising regressive, lowstand, transgressive and highstand systems tracts. The late-Quaternary evolution of the continental margin took place under the influence of an asymmetric relative fourth-order sea-level cycle punctuated by higher frequency cycles. These cycles of minor order were characterised by rapid sea-level rises and gradual sea-level falls that generated depositional sequences spanning different time scales. During the regressive periods, dipping strata were developed, while erosional surfaces and incised valleys were formed during the lowstands of sea level. Terraces, v-shaped depressions, lagoon-like structures observed on the outer continental shelf are the result of the transgressive period. In the study area we have recognised a complex erosional surface that records a long time span during the relative sea-level fall (regressive period) and the following sea-level lowstand and has been reworked during the last transgression. We also infer that sedimentation processes changed from siliciclastic sedimentation to carbonate sedimentation and again to siliciclastic sedimentation, marking an important phase in the late-Quaternary evolution of the western continental shelf of India. We attribute this to an abrupt climate change at the end of the oxygen isotope stage 2, between the Last Glacial Maximum and the Bølling-Allerod event (14?000 yr BP). This sensitive climate change (warming) favoured the formation of reefs at various depths on the shelf, besides the development of Fifty Fathom Flat, a carbonate platform on the outer shelf off Bombay developed prior to 8300 yr BP. The highstand systems tracts were deposited after the sea level reached its present position. 相似文献
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昭通-鲁甸断裂晚第四纪活动及其构造意义 总被引：12，自引：7，他引：5
昭通-鲁甸断裂带主要由昭通-鲁甸、洒渔河和龙树3条右阶斜列的断裂组成。总体走向40°~60°,洒渔河和龙树断裂倾向SE,昭通-鲁甸断裂倾向NW,它们共同构成几何结构复杂的逆冲断裂系。野外考察表明:沿断裂表现为平直的断层槽地、定向排列的断层三角面、断层陡坎等地貌;大桥边、北闸镇、光明村等地断错了晚更新世—全新世地层;龙树河Ⅰ级阶地上发育高0.5~2.0m的断层陡坎。表明其最新活动时代为晚更新世—全新世,运动性质以逆冲运动为主兼有右旋走滑分量。此外,在NE向断裂间穿插发育的一些NW向断裂,同样表现出晚第四纪活动特征。在2014年鲁甸M6.5地震震区产生了NE和NW向地裂缝和地形反坎等地表形变,与NE和NW向断裂展布基本一致,反映了断裂的新活动特征。由于块体远程变形响应与能量交换传递,在川滇块体东侧形成了凉山次级活动块体,昭通-鲁甸断裂带位于凉山次级活动块体SE向运动的前缘部位。它独特的地理位置和复杂的断裂几何结构成为凉山次级块体构造变形的主要承载体之一,吸收、调节块体SE向运动应变,并构成了凉山次级活动块体的南部边界。从区域构造部位和运动特征分析,昭通-鲁甸断裂带之于凉山次级块体,正如龙门山断裂带之于巴颜喀拉块体。昭通-鲁甸断裂带在活动块体边界和区域构造格架划分上具有重要的构造意义,同时也是滇东北地区重要的地震构造。 相似文献
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龙门山断裂带晚第四纪活动性分段的初步研究 总被引：21，自引：3，他引：21
NE向展布于松潘-甘孜造山带与扬子陆块之间的龙门山断裂带,是由后山断裂等4条主干断裂及其控制的冲断构造岩片组成的具前展式发育特点的推覆构造带。它形成于印支运动,此后多次活动,第四纪以来活动强烈,但不同地段活动程度具有明显的非均一性。根据地貌、地质构造、布格重力异常和地震活动等资料的综合分析研究认为:1)以位于虎牙—北川—安县一线的近SN向虎牙断裂和擂东断裂为界划分出断裂带西南段和东北段,其活动性迥然不同,西南段晚更新世以来活动强烈,中小地震频繁;东北段第四纪活动微弱,仅偶有小震分布。2)在青藏高原被挤压隆升和块体侧向滑移的作用下,川青地块向SEE滑动,使它东缘发育的岷山隆起与被其截切的龙门山断裂带西南段一起构成了川青地块东部的活动边界,而龙门山断裂带东北段则被遗弃 相似文献
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发育在褶皱区的河流阶地作为一种发育广泛、易于定年的被动变形的地貌标志物,已越来越多地被应用到活动逆断层相关褶皱晚第四纪变形的研究中;结合前生长地层和生长地层,可限定褶皱缩短总量和变形起始时间等参数,恢复从开始生长至晚第四纪以来完整的生长演化历史。文中对正弦曲线状和尖棱状弯滑褶皱模型、经典断弯褶皱模型和纯剪切断顶褶皱模型进行了总结和讨论。这些模型的提出为限定褶皱变形提供了很好的方法,但不能完全概括自然界中的褶皱模型,这就需要更多的野外地质、数值模拟和实验模拟工作。 相似文献
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2013年8月31日5.9级地震的震中地区位于川滇菱形块体西北边界附近,地质构造复杂,近SN向的金沙江断裂带与NW向的德钦-中甸-大具断裂在此交会。野外地质、地貌调查结果表明,金沙江断裂带的曾大同断裂、里甫-日雨断裂带、郎中断裂、古学断裂等晚更新世—全新世表现出明显的活动迹象,运动性质以右旋走滑为主,兼有逆冲滑动分量,其全新世右旋水平滑动速率为3.5~4.3mm/a,垂直滑动速率为0.9~1.1mm/a。德钦-中甸-大具断裂具明显的右旋走滑兼正断性质,最新活动时代为晚更新世—全新世,水平滑动速率为1.7~2.0mm/a,垂直滑动速率为0.6~0.7mm/a。该断裂与金沙江断裂带一起,共同构成了川滇菱形块体的西北边界。它是青藏高原EW向伸展作用下的一条重要的右旋走滑断裂,起着调节高原物质向SE运动的作用。据地震烈度等震线长轴方向、震源机制解资料和滑坡崩塌体展布位置分析认为,2013年奔子栏M5.9地震的发生与德钦-中甸-大具断裂的活动密切相关。 相似文献
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LATE-QUATERNARY GEOLOGICAL EVIDENCE OF JIANQUANZI-BARKOL SINISTRAL FAULT SYSTEM IN EASTERNMOST TIENSHAN 
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下载免费PDF全文 As we all know, Eastern Tienshan and Altaid in central Asia accommodate~10mm/a crustal shortening, accounting for 1/4 shortening between India and Eurasia(~40mm/a). A substantial portion of these deformations was absorbed in Altaid in the north through a combination of right-lateral strike-slip and counterclockwise vertical axis rotation of crustal blocks, but how the crustal deformation was accommodated in Eastern Tienshan is still in debate. Based on the field investigation in Jianquanzi, Barkol Tagh and Karlik Tagh in Eastern Tienshan in recent years, we identified a sinistral strike-slip fault system mapped in Eastern Tienshan. From west to east, the Jianquanzi-Tuolaiquan Fault(JTF), South Barkol Basin Fault (SBF) and Central Karliktagh Fault(CKF)constitute the tectonic frame of this large-scale fault system, which plays an important role in adjusting the strain distribution during the process of orogening in Eastern Tienshan in Quaternary even since Ceonozoic era. The fault system displays different late-Quaternary characteristics when its orientation changes with regional tectonic principal stress(NE). Specifically, the EW-trending JTF exhibits sinistral slip with little vertical component which can extend to Xiongkuer segment on EW-NW-trending SBF. The EW-NW SBF displays sinistral slip from east of Luobaoquanto, Barkol County and reverse slip with little horizontal component at east of Barkol County. In easternmost, the WNW-EW trending CKF shows sinistral slip with no obvious vertical motion. This fault system's activity coupled in the orogenic process of easternmost Tienshan, adjusting and accommodating a portion of deformation included in the orogenic process, and in turn we suggest that the deformation associated with range front fault in the orogen root may not be the only decisive way of deformation releasing. 相似文献
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Kun Qi Chenglin Gong Jinyu Zhang Katrine Juul Andresen Zhenkui Jin 《Basin Research》2023,35(2):842-864
As one of the most important forcing factors, relative sea-level changes exert a major influence on the building of shelf-margin clinothems. However, it is still not well understood how these changes control the growth of shelf edges and the condition of sediments transporting into deep water, especially over the individual-clinothem scale of several 100 ky. On the late-Quaternary Pearl River margin, there are two distinct shelf-margin clinothems: SQ3 and SQ4. They have different shelf-edge trajectories (slight rising vs. steep rising) and different styles of deep-water deposition (fan lobes consisting mainly of MTDs vs. fan lobes consisting mainly of turbidites). This work takes those SQ3 and SQ4 as study objects and runs a total of 136 experiments from the Dionisos stratigraphic forward model to investigate how relative sea-level changes control the trajectories of shelf edges and the volumes of MTDs in deep water over the individual-clinothem scale. Our quantitative results suggest that under the geological background of high sediment supply on the late-Quaternary Pearl River margin, the duration of highstand systems tracts (HST) relative to lowstand systems tracts (LST) or forced regressive systems tracts (FST) has a significant influence on the building of individual shelf-margin clinothems. If the relative duration of HST is either very short or very long, slight-rising shelf-edge trajectories and large-volume MTDs would be formed, whereas if the relative duration of HST is comparable with LST or FST, steep-rising shelf-edge trajectories and limited MTDs would be formed. Through the constrains of the model set to the real geological condition of the SQ3 and SQ4 clinothems, it is found that SQ3 was caused by the quite long relative duration of HST, which made highstand deltaic systems advance over the pre-existing shelf-slope break, leading to significant accretion and instability of the shelf edge and thus, giving rise to the formation of slight-rising shelf-edge trajectories and fan lobes with high MTDs contents. SQ4, however, formed as a result of the comparable durations of HST, LST, and FST, which made highstand deltaic systems advance to but not beyond the previous shelf-slope break allowing the subsequent FST to be directly perched on the clinoform slope. Such building processes did not drive pronounced accretion and instability of the shelf edge and thus, caused the formation of steep-rising shelf-edge trajectories and fan lobes with low MTDs contents. 相似文献
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帕米尔-天山对冲带明尧勒背斜西南倾伏端晚第四纪褶皱变形 总被引：1，自引：1，他引：0
褶皱在三维空间的生长包括横向缩短、垂向隆升和侧向扩展.沿褶皱走向不同位置这3个分量的比重是不同的:在背斜中段以缩短和隆升为主;靠近背斜端部,在缩短和隆升的同时也会发生强烈的侧向扩展.前人研究主要集中在褶皱中段,对端部这一相对独特的构造位置研究较少.那么褶皱端部是如何生长变形的,与褶皱中段有何不同,伴随褶皱生长同步变形的河流阶地具有怎样的发育特征?对帕米尔-天山对冲带明尧勒背斜西南倾伏端的研究表明,研究区内的4期河流阶地在垂直褶皱轴向上均发生了强烈反向掀斜,越老的阶地面掀斜角度越大,背斜在西南端的生长是以翼旋转机制进行的.据T2b,T3b,T4a的细颗粒石英光释光年龄及下伏基岩的磁性地层年龄可得46°等斜岩区在距今约0.35Ma、(93.9±18.7)ka、(82.6±16.5)ka和(19.4±2.9) ka时期旋转角度大致呈抛物线曲线函数递减,平均旋转速率依次为＞(0.13±0.01)°/ka、(0.08±0.02)°/ka、(0.05±0.01)°/ka和(0.04±0.01)°/ka,呈明显减小趋势,但该等斜岩区吸收的缩短速率大致保持恒定.河流阶地在发生掀斜和抬升变形的同时,也发生了向西的侧向扩展变形:由东向西,T3a和T4a阶地面上冲沟密度、宽度和下切深度明显减小,阶地拔河高度、陡坎高度和旋转角度也呈减小趋势,这些均反映了背斜向西的侧向扩展.据喀浪勾律克河谷和背斜西南剖面的磁性地层年代学结果,背斜向西侧向加长的速率恒定为16.0 ～ 16.8mm/a. 相似文献
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Mary E. Edwards Nancy H. Bigelow Bruce P. Finney Wendy R. Eisner 《Journal of Paleolimnology》2000,24(1):55-68
We investigated whether techniques developed to evaluate qualitative lake-level changes in the temperate zone can be used in sub-arctic and arctic Alaska. We focused on aquatic pollen records and sediment properties (loss-on-ignition and magnetic susceptibility) from centrally-located sediment-surface samples and cores, as these are the most commonly reported data in the literature. Modern aquatic pollen values are generally low (< 5%) and may be zero, even in lakes with abundant aquatic macrophytes. Greater diversity and higher values of aquatic pollen are likely at depths < 5 m, but pollen is found in depths up to 15 m. It is absent at depths > 20 m. Spores of Isoetes and Equisetum and Pediastrum cell-nets, when present, tend to be widely distributed, even in deep water. At Birch Lake, interior Alaska, trends in aquatic taxa and sediment characteristics for the last ca. 12,000 14C yrs recorded in a single, deep-water core reflect the same water-level changes as do transect-based lake-level reconstructions - if modern distributional characteristics of pollen and spores are taken into account. The lake rose from extremely low levels at ca. 12,000 14C yr B.P. After a period of fluctuation, it rose to a relatively high level by ca. 8000 14C yr B.P. and then stabilized. A preliminary survey of aquatic pollen trends from other lake-sediment records suggests that the period ca. 11,000-8000 14C yr B.P. may have seen relatively low lake levels in north-western and interior Alaska and high levels thereafter. Changes in aquatic pollen and sediments are evident in north-eastern interior lakes at the same time, but they are more difficult to interpret. Aquatic pollen productivity in Alaskan lakes may partly depend on factors other than water depth (e.g. temperature, pH, nutrient status, or length of the ice-free season). An Alaska-wide reconstruction of late-Quaternary lake levels based on extant single-core data would be best done after further study of contributing factors that may control sediment properties and aquatic pollen distribution. 相似文献
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西南天山迈丹断裂东段晚第四纪活动的发现及构造意义 总被引：1，自引：0，他引：1
利用详细的遥感影像解译、实地调查、探槽开挖以及释光年代学测定的方法对西南天山山前的迈丹断裂东段进行研究,获得了该断裂晚第四纪以来活动的可靠证据。迈丹断裂东段是一条由多条次级断裂组成的复杂断裂带,最大宽度可达17km,晚第四纪以来的活动断错了山前各级地貌面和阶地。探槽开挖表明,断裂在全新世期间曾发生过断错地表的强震事件,造成的垂直位错量在2m以上。迈丹断裂晚第四纪以来活动表明,西南天山地区的构造变形并不完全集中在推覆体前缘新生的逆断裂-背斜带上,天山根部断裂也吸收了一部分构造变形。这一构造变形模式与已知的北天山前展式的构造变形样式具有明显差异,柯坪推覆体并不完全遵从断裂新活动不断向盆地方向扩展的特点,推覆体前缘新生断裂和根部断裂都有较强的活动,可能是一种无序或反序的构造变形样式。此类构造,其发震构造模型的建立及强震危险性预测给我们带来新的挑战。 相似文献
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