| The widely scattered paleo-mean sea-level indicators along the BohaiBay supply basic foundation for reconstructing of relative sea-level changein this area. During the past 20 years, scientists had built some relativesea-level curves in this area. However, they mixed all the impacting factorsto the elevation of paleo-mean sea-level indicators up when they built thiscurves. A spatial-temporary distribution of such seven indicators,corresponding with the regional predicted sea-level curve, is established tocalculate the subsidence of each indicator. Therefore, we can distinguish thecontributions of tectonics and sea-level change associated with glacio-andhydro-isostatic adjustment in the local area to the elevations of the indicators.Furthermore, with the results of stable isotopic analyses to the oyster shellsin the Biaokou reef and a paleo-earthquake trace in Dawuzhuang reef, wediscuss the tectonic subsidence during the buildup of the reef bodies. And wecompare the result to a strong paleo-earthquake event occurred in this areawith spatial distribution map and (14)~C dating ages. As proxies, the results ofoxygen and carbon isotopic analyses to the shells, lying on different verticalpositions in one section, have indicated tectonic movements and subsidencerecorded in the reef body while it was building up.The results of radiocarbon dating to the fifteen shells in the section 1 ofDawuzhaung oyster reef, which located in the Northwest Coast of Bohai Bay,show that the duration of this reef is about 1600 yrs (from ca. 7200?5600 calBP). The whole thick of this reef is about 4.5 meters. And if we calculatewith the mean building up rate of 1 cm/yr to this oyster reef, which is basedon both the analysis to stable isotopes of the live and fossil oyster shells andcount to the amount of concave up and concave down ridges on the hinge,the duration of it is only one-third of the results given by radiocarbon dating.The difference between of them is attributing to the horizontal layers in theoyster reef. Each of the horizontal layers lasts a relative long period of ca.200 yrs, which geo-environment is not suitable for oyster grows and its reefbuilds up. And we name this as chronic geo-environmental change recordedin the oyster reef during the middle Holocene on Northwest Coast of BohaiBay, China.Comparation between the time-space of horizental layers and normallayers in the Dawuzhuang reef body with the local paleo-enivronmentalcurve inferred from the peat cellulose has show that the interchanges ofhorizental with normal layers match the flunctuations of the regionalpaleo-environment change. That is the normal layers represent the warmerperiods and the horizental layers for the cooler periods.The sizes of oyster shells which compose the horizental layers in theDawuzhuang oyster reef are smaller than these in the normal layers. And theamounts of boring organisms in these smaller shells are more than to thebigger ones. It means that these small shells in the horizental layers are moreimpacted by the boring organisms than these bigger shells during they arealive. Experiments by Menzel et al., (1996) have showed that during periodsof drought and high salinity these boring orgainisms were the main cause ofreef depletion. Therefore, we think the smaller shells in the horizental layerswith more boring holes represent the high salinity. And the bigger ones inthe normal layers with less boring holes represent the low salinity. Therefore,the alternation of horizental layers with normal layers in the reef bodyrepresents the periodic changes of the water salinity which this reef hadlived. Above all, the low temperature as well as high salinity possiblly takesimportant role in the existance of the horizental layers in the reef body.The eight OSL dating results to the muddy sediments below and abovethe Dawuzhuang oyster reef body indicating not only the duration of thisreef body (~1200 yrs) but also the deposit rate of the deposit rates duringand before and after the reef buildup. Before the reef buildup (before 6200...
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