Pii: S1367-9120(00)00010-9
نویسندگان
چکیده
The Ordovician System, cropping out in southern and west-central Jordan, consists entirely of a 750 m thick clastic sequence that can be subdivided into six formations. The lower Disi Formation starts conformably above the Late Cambrian Umm Ishrin Formation. According to Cruziana furcifera occurring in the upper third of the Disi Formation, an Early Ordovician age is con®rmed. The Disi Formation, consisting mainly of downstream accretion (DA) ̄uvial architectural element, was deposited in a proximal braidplain ̄owing N±NE from the southerly-located Arabian±Nubian Shield towards the Tethys Seaway. The braidplain depositional environment evolved into a braidplain-dominated delta through the middle and upper parts of the Disi Formation and the lower part of the overlying Um Saham Formation. The delta was replaced by siliciclastic tidal ̄ats, that in turn evolved into an upper to lower shoreface environment through the upper part of the Um Saham Formation. The depositional environment attained the maximum bathymetric depth during the deposition of the lower and central parts of the third unit, the Hiswa Formation, where offshore graptolite-rich mudstone with intercalated hummocky cross-strati®ed tempestites were deposited. The Tethys Seaway regressed back through the upper part of the Hiswa Formation promoting a resumption of the lower±upper shoreface sedimentation. Oscillation between the lower to upper shoreface depositional environment characterized the entire fourth unit, the Dubaydib Formation, as well as the Tubeiylliat Sandstone Member of the ®fth unit, the Mudawwara Formation. The depositional history of the Ordovician sequence was terminated by a glacio ̄uvial regime that ®nally was gradually replaced by a shoreface depositional environment throughout the last unit, the Ammar Formation. q 2001 Elsevier Science Ltd. All rights reserved.
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Pii: S1367-9120(00)00019-5
Precise zonation of the territory of China has been performed based on the active known faults, type of faulting and seismicity level. One hundred and forty seven seismogenic regions were de®ned, forming 10 larger seismic areas, and the seismotectonic characteristics in each one of them were investigated in detail. After checking for data accuracy and completeness of the shallow earthquakes (h ...
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We improve previous lower bounds on the number of simple polygonizations, and other kinds of crossing-free subgraphs, of a set of N points in the plane by analyzing a suitable configuration. We also prove that the number of crossing-free perfect matchings and spanning trees is minimum when the points are in convex position. 2000 Elsevier Science B.V. All rights reserved.
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The moderate magnitude Chamoli earthquake, which occurred on 29 March, 1999 in the Alkananda river valley region of Garhwal Himalaya, caused considerable loss to human life and property. From a systematic ®eld survey of the damage, conducted for ®ve continuous days immediately after the earthquake, the following could be noted: (i) The consequences of the damage are most pronounced near the Mai...
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