障壁岛—潟湖沉积特征及模式:以美国普拉姆岛上更新统—全新统为例

Sedimentary characteristics and model of barrier island-lagoon: an example from the Upper Pleistocene-Holocene in Plum island, USA

普拉姆岛(Plum island)是美国东北部缅因湾最大的障壁海岸,岛内向陆一侧为新英格兰地区最大潟湖和沼泽区,它们是晚第四纪末次冰期冰川作用和冰后期海岸作用的沉积响应。通过普拉姆岛研究区上更新统—全新统160个钻孔描述,识别出8种沉积物:泥炭、冰川黏土、黏土、粉砂、细砂、中粗砂、砾、坠石。根据沉积物类型及其组合特征,结合沉积环境,共划分出8种沉积微相:障壁沙丘、滨岸沙、水下临滨沙、河道、潮汐水道、潟湖、潮坪、沼泽。研究区在晚第四纪末次冰盛期(MIS2)被劳伦斯蒂德冰盖(Laurentide Ice Sheet)覆盖,发育冰川地貌,冰川泥覆盖在基岩之上,形成底层沉积;冰后期(MIS1),冰盖消融,海平面发生变化,在冰川地貌鼓丘附近形成沙坝,最终沉积演化为障壁岛—潟湖环境,潟湖通过潮汐水道与广海相连通。

Plum island is the largest barrier island in the Gulf of Maine in the northeastern United States. On the continental side of Plum island are the largest lagoon and salt marsh in New England, which are the sedimentary responses to the late Quaternary glacial and coastal processes. Through the description of 160 boreholes in the Upper Pleistocence-Holocene the Plum island study area, eight types of sediments were identified: peat, glacial clay, clay, silt, fine sand, medium-coarse sand, gravel and dropstone. According to the characteristics of sediments and deposition phenomena, the sedimentary microfacies of Plum island can be divided into eight types: barrier dune, beachface deposits, offshore sand sheet deposits, salt marsh, fluvial channel, tidal inlet channel, lagoon and tidal flat. During the Last Glacial Maximum(MIS2),the study area was covered by the Laurentide Ice Sheet and glacial landform developed. Glacial clay accumulated above the bedrock and formed the basal deposits. During the Post-Glacial period(MIS1),the ice sheet melted and the sea level changed in New England, forming sand bars near the drumlins of the glacier landform, and finally evolving into a barrier island-lagoon environment. The lagoon was connected with the open sea through tidal inlet channels.