渤海湾西北岸滨海湖埋藏牡蛎礁硅藻及其记录的古环境

对位于渤海湾西北岸平原的滨海湖埋藏牡蛎礁中各层牡蛎壳的泥质充填物做硅藻分析,整个牡蛎礁中海水砂质潮间带指标种标志种的Auliscus caelatus含量较高,为19%~42%,表明滨海湖礁体形成于潮间带环境。根据主要硅藻含量的变化,结合14C测年,自下而上将礁体发育期间的古环境分为3个带:I带为2 445~2 327 cal.aBP,礁体在向上建礁的过程中,海水作用逐渐减弱,潮间带特征愈加明显,为受河流影响较强且较为开放的潟湖潮间带环境;Ⅱ带咸水种硅藻Thalassionema nitzschioides的比例急剧增加;外洋指标种的Coscinodiscus spp.和Actinocyclus spp.急剧下降,表明在约2 327 cal.aBP,海岸带砂嘴闭合,形成较为封闭的潟湖内侧潮间带环境,且河流作用减弱导致潟湖的咸度明显增加;Ⅲ带为2 327~2 287 cal.aBP,由封闭的潟湖环境又转向较开放的潟湖潮间带环境。

DIATOM RECORDS OF THE BINHU BURIED OYSTER REEF,IN BINHAIHU,NORTHWEST BOHAI BAY AND PALEO-ENVIRONMENTAL IMPLICATIONS

The muddy sediments filling into the oyster shells in Binhaihu oyster reef of the northwest Bohai Bay were collected for diatom analysis. Auliscus caelatus, an indicator of intertidal zone environment, is as high as 19%~42% in the reef that suggested that the Binhaihu oyster reef was formed in an intertidal environment. Based on the diatoms and 14C dating, three zones were subdivided from the bottom to the top. The Zone I, formed during the period of 2 445~2 327 cal.aBP, was deposited in an open lagoon-intertidal environment with strong river influence. The marine influence decreased as the influence of intertidal zone increased upwards. In the Zone Ⅱ, which was formed around 2 327cal.aBP, marine species Thalassionema nitzschioides increased while oceanic species Coscinodiscus spp. and Actinocyclus spp. decreased, showing a closed inner lagoon-intertidal environment, and the salinity of lagoon was increased due to the decrease in river input. The Zone Ⅲ, formed 2 327~2 287 cal.aBP, was resulted of the change from a closed lagoon to an open lagoon-intertidal environment.