共查询到20条相似文献，搜索用时 78 毫秒
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《地质学报》1936,15(1):17-21
In the lamented death of Dr.V.K.Ting on January 5th,1936,atthe age of 49,China suffered an irredeemable loss.He may be called thefounder of the science of geology in China,and it was in geological field workthat his contribution was especially great.After his graduation from the Uni-versity of Glasgow he made his way back from Europe to China in 1912 by 相似文献
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ABSTRACT Thirty clay-rich horizons from the Wenlock and Ludlow Series of the Welsh Borderland were analysed to investigate their mineralogy and possible origins. Two mineralogical assemblages were determined: an assemblage of illite-smectite and kaolinite of volcanic origin which was associated in many samples with an assemblage of illite and chlorite of detrital origin. Immobile chemical discriminants (Zr/TiO2 versus Nb/Y) infer an originally rhyolitic ash composition with a possible temporal progression, from the Wenlock to Ludlow, to more differentiated compositions. The thin nature of the bentonites and lack of juxtaposed subduction related calc-alkaline magmatism suggests that the tuffs were derived from distant explosive eruptions from volcanic centres, possibly in NE Europe. 相似文献
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Iacopo Cavicchini H. Cecilia Heyworth Christopher J. Duffin Claudia Hildebrandt Michael J. Benton 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(2):144-158
Rhaetian bone beds have been described from many locations in south-west England, around Bristol. One site that has never been reported is Stowey Quarry, some 13?km south of Bristol. This quarry yielded Lias, and revealed thin Rhaetian units in the quarry floor, including two bone beds, the basal Rhaetian bone bed, and a second, higher bone bed, also within the Westbury Formation. The fossil fauna of both includes elements typical of Rhaetian bone beds elsewhere, but showing differences in faunal composition between the two. The basal bone bed yielded more specimens and more species, with three taxa (Sargodon tomicus, Rhomphaiodon minor and Hybodus cloacinus) exclusive to this bed and eleven identified in total. Severnichthys acuminatus accounts for more than 50% of the countable teeth from the basal bone bed, followed by Gyrolepis albertii with 20%, Lissodus minimus with 14% and Rhomphaiodon minor with 9%. The basal bone bed, as ever, is dominated by chondrichthyans, whereas the upper bone bed is dominated by osteichthyans, which form 90% of the non-dental remains. The only unique taxon is Dapedium, and Gyrolepis albertii is the most abundant species with 45% of countable teeth, followed by Severnichthys acuminatus with 38% and Duffinselache holwellensis with 11%. These faunal differences, and the equally good condition of specimens between both samples confirms that the upper bone bed is independent of the basal bone bed, and is not a reworked subsample. 相似文献
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Emanuel J.M. Willemse David C.P. Peacock Atilla Aydin 《Journal of Structural Geology》1997,19(12):1461-1477
Small-scale structures along strike-slip fault zones in limestones exposed around the Bristol Channel, U.K., suggest that pressure solution plays a key role during fault nucleation and growth. Incipient shear zones consist of enéchelon veins. The first generation of solution seams form due to bending of the intact rock (bridge) between overlapping veins. As the bridge rotates, slip occurs along the seams, linking the veins, causing cm-scale calcite-filled pull-apart structures to form and allowing fault displacement to increase. A second generation of solution seams forms at the tip of the sliding seams. As displacement increases further, causing larger rotation, slip also can occur along these second-generation solution seams, producing the third generation of solution seams as well as tail cracks (pinnate veins) at their tips. These three generations of solution seams all contribute to the formation of individual fault segments. Fourth and fifth generations of solution seams occur within larger-scale contractional oversteps between side-stepping fault segments. The oversteps are breached by slip along these localized solution seams, eventually leading to the formation of a distinct through-going fault with several metres of displacement.The initial enéchelon veins, solution seams of various generations and tail cracks progressively fragment the fault-zone material as fault slip accumulates. Slip planes nucleate on these pre-existing discontinuities, principally along the clay-enriched, weaker solution seams. This can be observed at a variety of scales and suggests that Mode II shear fracturing does not occur as a primary fracture mechanism, but only as a macroscopic phenomenon following Mode I (veins and tail cracks) and anti-mode I (solution seams) deformation. It appears that solution seams can play a similar role to microcracks in localizing a through-going slip plane. This micromechanical model of faulting may be applicable to some other faults and shear zones in host rocks which are prone to pressure solution. 相似文献
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