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31.
The Paleogene sections of Kutch are the reference for the regional chronostratigraphic units of India. The ages of these dominantly shallow marine carbonates are mainly based on larger benthic foraminifera (LBF). The taxonomic revisions of the LBF and the progressively refined shallow benthic zonations (SBZ) have necessitated the present study on updating the stratigraphy of the area. The sedimentation in Kutch commenced with the deposition of volcaniclastics in terrestrial environments in the Paleocene. The marine transgression in SBZ 5/6 deposited finer clastics and carbonates, designated as Naredi Formation, in early Eocene. There is no evidence of marine Paleocene in Kutch. A major hiatus spanning SBZ 12 to SBZ 16 was followed by the development of a carbonate platform and deposition of Harudi Formation – Fulra Limestone during the Bartonian, SBZ 17. The hiatus corresponds to a widespread stratigraphic break in Pakistan and India to Australia, referred as the ‘Lutetian Gap.’ The Maniyara Fort Formation is assigned to SBZ 22 B and SBZ 23, and its age is revised to Chattian. Climate played a major role in building up of the Paleogene stratigraphic succession of Kutch, the carbonates formed during the warming intervals and the stratigraphic gaps were in the intervening cooling periods. 相似文献
32.
Many tafoni occur on the faces of marine cliffs on three uplifted shore platforms with different altitudes and with known ages of emergence. The mean value of the ten largest depths of tafoni, D (cm), was obtained and the period of their formation, t (years), was estimated. The relationship between the two variables was found to be D = 20·3 × (1?e?0.005t). 相似文献
33.
地球物理测井是利用各种现代物理学的方法(包括电学、声学、核物理、热学、光学、磁学、力学等)对储层空间的油气水特性、沉积环境、地层层序、构造地质等现象进行定量研究,逐步形成的一门理论性、实用性很强的边缘学科.海洋测井作业环境更为特殊而复杂,不但投资大、作业风险大,而且具有技术高度密集、技术难度大的特点.发展海洋石油勘探事业,必须加强对海洋测井技术的研究,利用现代高新科学技术,开拓海洋测井新领域,为海洋石油勘探提供更丰富、更准确的地质信息. 相似文献
34.
Measurements were made of the water content in coastal rocks, by simulating tidal oscillations in the laboratory, and by field measurement in eastern Canada. If rapid freezing takes place upon exposure to the air, saturation levels may be high enough to permit frost weathering in fine grained rocks in the lower portions of the intertidal zone. Near the high tidal level, however, it may be dependent upon a supply of water from the ice foot and from melting snow. If freezing is slow, frost action may be inhibited by desorption of the rocks while they are exposed by the ebb tide. There was no evidence of a level of permanent sea water saturation within the intertidal zone. Ambient temperature and humidity may affect the rate of rock desorption. 相似文献
35.
Gordon E. Bigelow 《地球表面变化过程与地形》1984,9(4):383-390
Tumbler simulations of abrasion processes affecting rocks on basaltic marine benches have clarified the effects of mass and volume of rock fragments on their rate of wear. Several experiments indicate that rate of basalt wear increases with mass in the interval 1 g to 8 g, but is not related to volume of fragments abraded in seawater. Relatively small quantities of rock flour suspended in the immersant seawater substantially reduced the rate of basalt wear. Basalt and calcareous beachrock responded differently in systems with both rock types tumbling together. Examination of the cuttings from these low-energy encounters suggests that abrasion on elevated benches along exposed seacoasts reduces virtually all clastic material to particles of silt size or smaller, producing essentially no sand. 相似文献
36.
37.
A. S. Trenhaile 《地球表面变化过程与地形》2001,26(10):1103-1128
A mathematical model was used to investigate the effect of glacially induced fluctuations in sea level on the evolution of wave‐cut shore platforms and erosional continental shelves during the Quaternary. The model used two deep‐water wave sets, which were used to calculate breaker height and depth, and the force of the waves at the waterline, according to the width and bottom roughness of the surf zone and the gradient of the submarine slope. The model also incorporated an erosional threshold related to the strength of the rocks, the number of hours each year in which the water level is at each intertidal elevation and the amount and persistence of the debris at the cliff foot. Most runs were made using a sea level model that consisted of 26 glacial cycles from 2 million to 0·9 million years ago, and nine, of approximately twice the amplitude and wavelength, in the last 0·9 million years. The model emphasized the dynamic association between the contemporary intertidal platform and the continental shelf. Both surfaces trend towards a state of static equilibrium under oscillating sea level conditions, when attenuated waves are unable to continue eroding the rock. If there has not been enough time to reduce the gradient of the shallower portions of the continental shelf, however, intertidal shore platforms can be in a temporary, though possibly long‐lasting, state of dynamic equilibrium. The model suggests that most platforms are, at least in part, inherited from one, or in many cases more, interglacial stages when sea level was similar to today's. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
38.
During the early Middle Devonian in South China, an extensive carbonate platform was broken up through extension to create a complex pattern of platforms, and interplatform basins. In Givetian and Frasnian carbonate successions, five depositional facies, including peritidal, restricted shallow subtidal, semi‐restricted subtidal, intermediate subtidal and deep subtidal facies, and 18 lithofacies units are recognized from measured sections on three isolated platforms. These deposits are arranged into metre‐scale, upward‐shallowing peritidal and subtidal cycles. Nine third‐order sequences are identified from changes in cycle stacking patterns, vertical facies changes and the stratigraphic distribution of subaerial exposure indicators. These sequences mostly consist of a lower transgressive part and an upper regressive part. Transgressive packages are dominated by thicker‐than‐average subtidal cycles, and regressive packages by thinner‐than‐average peritidal cycles. Sequence boundaries are transitional zones composed of stacked, high‐frequency, thinner‐than‐average cycles with upward‐increasing intensity of subaerial exposure, rather than individual, laterally traceable surfaces. These sequences can be further grouped into catch‐up and keep‐up sequence sets from the long‐term (second‐order) changes in accommodation and vertical facies changes. Catch‐up sequences are characterized by relatively thick cycle packages with a high percentage of intermediate to shallow subtidal facies, and even deep subtidal facies locally within some individual sequences, recording long‐term accommodation gain. Keep‐up sequences are characterized by relatively thin cycle packages with a high percentage of peritidal facies within sequences, recording long‐term accommodation loss. Correlation of long‐term accommodation changes expressed by Fischer plots reveals that during the late Givetian to early Frasnian increased accommodation loss on platforms coincided with increased accommodation gain in interplatform basins. This suggests that movement on faults resulted in the relative uplift of platforms and subsidence of interplatform basins. In the early Frasnian, extensive siliceous deposits in most interplatform basins and megabreccias at basin margins correspond to exposure disconformities on platforms. 相似文献
39.
Tsunami deposits in the geological record 总被引:2,自引:0,他引:2
A review is presented here of tsunami deposits in the geological record. It begins with a discussion of the relationships between the processes of tsunami generation and propagation and the sedimentary responses. This is followed by a consideration of the sedimentary processes associated with the passage of tsunami waves across coastlines. Attention is also given to the sedimentary processes associated with tsunami-triggered gravity backwash flows and comparisons are made with turbidity current action. We observe that despite sedimentary evidence for recent tsunamiites, geological research on ancient tsunamis has not identified stratigraphic units associated with onshore tsunami sedimentation. Equally, it is noted that nearly all published studies of sedimentary processes associated with modern tsunamis have not considered patterns of sediment transport and deposition in the offshore zone. 相似文献
40.
在对2005年广东珠江口-东平近海海域实测浅地层声学剖面资料进行地质解释的基础上,划分出八个地震相单元(亚单元),建立了调查区浅地层的沉积格架。对调查区内发育的沙脊、潮沟充填沉积体、浅海沙席和沙波等海底砂质地质体,以及埋藏潮流沙脊、大型充填潮沟和埋藏古河道等地质体的特征有了较深入的了解。对砂矿赋存条件、砂体厚度及物源供给等因素进行了讨论。 相似文献