小凌河下游晚全新世地层与环境

Late Holocene Stratigraphy and Environment in the lower Reach of Xiaolinghe River

作为从出山口至入海河口直线距离仅约20 km的短途河流,小凌河下游地区及相邻潮间带表层发育了砾石质冲洪积扇、曲流河道滞留相-点状砂坝-泛滥平原与洼地、贝壳砾石海滩、盐沼、开放潮坪下部与中上部等一系列沉积环境。通过沉积地层学、年代地层学及新构造等方面的综合研究,1)将中、晚全新世地层划分为7个年代地层单元,2)发现了夏-西周、元末-明初两道年龄分别约为2 050～650 BC和1 350 AD的古海岸线,3)确立了春秋、中唐-北宋初、"小冰期"结束以来3次小凌河沉积期,最有可能发育的时间进一步限定在约650～400 BC(第1期)、约700～1 000 A(D第2期)和1 850 AD以来(第3期),4)提出了NW向与NE向构造加剧小凌河下游曲流发育的假说。

Despite of a short distance of ca. 20 krn from the hill-plain junction to the estuary, the lower reach of Xiaolinghe River has developed a series of depositional environments, including pebbely alluvial fan, channel lag, channel bars, floodplain and depressions, salt marshes and open tidal flats, etc. Based on the multidisciplinary studies dealing with sedimentology, chronology and neotectonics, the authors make contribution that （1） The midto late-Holocene strata are divided into 7 chronostratigraphical units. （2） Determined the palaeo shorelines of the Xia-West Zhou, ca. 2 050 - 650 BC, and the Late Yuan-Beginning Ming, ca. 1 350 AD. （3） Three accumulation episodes of Xiaolinghe River were the Spring-Autumn, the Mid Tang-Early Song and the post-Little Ice Age, respectively. Most probably, they can be further limited to the ca. 650 - 400 BC （Episode 1）, ca. 700- 1 000 AD （Episode 2） and since 1 850 AD （Episode 3）. （4） A hypothesis ofneotecno-driven-meandering-process indicates the existing sinuosity would be greatly enhanced by the NE and NW lineament-structure.