Mechanisms of low-frequency sea level fluctuations in the Hangzhou Bay

-low-frequency sea level fluctuations in the Hangzhou Bay in winter and summer, 1973-1974 are analyzed in this paper. The established multi-spectrum response models effectively identify the different dynamical factors and their contributions to the low-frequency sea level fluctuations inside the bay. The results show that the Ekman transport due to longshore winds is the major mechanism to induce the sea level fluctuations, more important than the frictional effect of local winds. There also exists obviously the influental effect of the free fluctuations of the continental shelf. In addition ,a simple estimation suggests that the remarkable sea level fluctuation of 0. 4 d-1 in the bay is related to the resonance of the Huanghai Sea and the Bohai Sea (taken as a single bay).

Paleocommunity Replacements of Benthic Brachiopod in the Middle-Upper Devonian in the Longmenshan Area,Southwestern China:Responses to Sea Level Fluctuations

Twelve paleocommunities dominated by benthic brachiopod are recognized in the Givetian-Frasnian stages of the Devonian in the Longmenshan area, southwestern China, in which two kinds of brachiopod community replacement are classified. One is the abrupt replacement, represented by abrupt alternation between the Leiorhynchus community and Zhonghuacoelia-Striatopugnax community in the Frasnian Tuqiaozi Formation. The other is the gradual one, developed in the Givetian Guanwushan Formation, which had been completed by the shift of the Independatrypa lemma-Uncinulus heterocostellis-Emanuella takwanensis community via the Sinospongophyllum irregulare-Pseudomicroplasma fongi community to the Clathrocoilona spissa-Hexagonaria composite reef community. According to analyses of the paleocommunities, either the abrupt or gradual paleocommunity replacement of the Middle-Upper Devonian in the Longmenshan area is suggested as a response to the 5th-order sea level fluctuation due to the replacements of the paleocommunities in a tracts-system of depositional sequence. It is supposed that changes of paleocommunity diversity, one of the results of paleocommunity replacement, are depended on the range and magnitude of sea level fluctuation, but there is not a linear relationship between them. Furthermore, a suggestion is proposed that the concept of paleocommunity succession seem to be abandoned in the paleocommunity analysis because it almost never be practiced to recover the information of community succession in the geological record at present.

Tertiary and Quaternary Marine Terraces and Planation Surfaces of Northern Oman:Interaction of Flexural Bulge Migration Associated with the Arabian-Eurasian Collision and Eustatic Sea Level Changes

The northeastern Arabian passive margin is being subducted beneath the Zagros and Makran of Iran. A flexural bulge related to the weight of the Makran has migrated at 4 cm/a through the previously uplifted Hajar Mountains of Oman as this active convergence and collision between Arabia and Eurasia progresses, adding approximately another 500 meters of relief, and forming a series of uplifted marine terraces, alluvial terraces, and planation surfaces that record the passage of the bulge. We use a combination of field studies, remote sensing and GIS to map and better-understand these terraces, and elucidate how the tectonics of bulge migration, down-to-trench normal faulting, and eustatic sea level changes have interacted to produce the extant geomorphic features on the inner slope of the flexural bulge as it sinks into the foredeep of the Gulf of Oman. We speculate those terraces that were uplifted on the outer slope of the forebulge as it initially migrated through the passive margin （affected by ophiolite obduction in the Cretaceous） 3.75-7.5 Ma ago are now sinking on the inner slope of the forebulge （corresponding to the outer trench slope in the foredeep）, and have been partly covered by Quaternary marine terraces related to a Weichselian sea level high stand. Both the Tertiary and Quaternary terraces are cut by faults related to the active collision, confirming that there is a significant risk of moderate earthquakes in the region.