Deglacial to postglacial palaeoenvironments of the C eltic S ea: lacustrine conditions versus a continuous marine sequence
Deglacial to postglacial palaeoenvironments of the C eltic S ea: lacustrine conditions versus a continuous marine sequence
复制标题
凯尔特海冰消期到冰期后的古环境：湖泊条件与连续海洋序列
作者：
Furze M
最近对不列颠群岛最后一次冰川的研究使人们更好地了解了不列颠−爱尔兰冰盖(BIIS)从其南部最大值(锡利岛)向北退缩到凯尔特海和爱尔兰海的性质和时间。然而，凯尔特海陆架上的去冰川环境的性质、空中暴露的程度以及在冰川消退后英国和爱尔兰之间是否存在(或以其他方式)毗连的陆地联系仍然不明确。多代理研究基于对凯尔特深盆地(CDB)12个BGS可控震源的分析，试图解决这些问题。CDB岩心显示出全新世海相砂体向上富含贝壳的细化序列，位于剥蚀接触带上方，由层状泥浆切割而成，孤岩很少见。底泥中没有软体动物、有孔虫和海洋硅藻，但很少出现受损的淡水硅藻和有孔虫衬里。甲藻孢囊和其他非花粉孢粉孢囊体证明了不同的、环境不相容的植物区系，温带、北方和北极冰川海绵分类群共存。这样的多代理记录可以被解释为代表了退缩的冰缘，将海洋沉积物重新加工成湖盆。同样，同样的记录可以被解释为记录了以熔水输出和重新加工的微化石沉积为主的半封闭海洋海湾内的类似情况。由于这些岩心的组合与CDB外部已探明的冰海相层序形成了鲜明的对比，因此对层序更倾向于冰湖相解释，被魏氏晚期海侵层序截断，向上细化到完全海相条件。重新加工的稀有潮间带软体动物直接位于区域不整合之上，提供了最小的数据。13.9 。Ka BP要求开始大范围的海洋侵蚀。尽管暗示了冰湖条件，但CDB内部层状沉积物沉积的确切性质和时间，以及这对冰川消融后爱尔兰(PEN)岛国的影响，仍然难以捉摸。
Recent work on the last glaciation of the British Isles has led to an improved understanding of the nature and timing of the retreat of the British−Irish Ice Sheet (BIIS) from its southern maximum (Isles of Scilly), northwards into the Celtic and Irish seas. However, the nature of the deglacial environments across the Celtic Sea shelf, the extent of subaerial exposure and the existence (or otherwise) of a contiguous terrestrial linkage between Britain and Ireland following ice retreat remains ambiguous. Multiproxy research, based on analysis of 12 BGS vibrocores from the Celtic Deep Basin (CDB), seeks to address these issues. CDB cores exhibit a shell‐rich upward fining sequence of Holocene marine sand above an erosional contact cut in laminated muds with infrequent lonestones. Molluscs,in situForaminifera and marine diatoms are absent from the basal muds, but rare damaged freshwater diatoms and foraminiferal linings occur. Dinoflagellate cysts and other non‐pollen palynomorphs evidence diverse, environmentally incompatible floras with temperate, boreal and Arctic glaciomarine taxa co‐occurring. Such multiproxy records can be interpreted as representing a retreating ice margin, with reworking of marine sediments into a lacustrine basin. Equally, the same record may be interpreted as recording similar conditions within a semi‐enclosed marine embayment dominated by meltwater export and deposition of reworked microfossils. As assemblages from these cores contrast markedly with proven glaciomarine sequences from outside the CDB, a glaciolacustrine interpretation is favoured for the laminated sequence, truncated by a Late Weichselian transgressive sequence fining upwards into fully marine conditions. Reworked rare intertidal molluscs from immediately above the regional unconformity provide a minimum datec.13.9 cal. ka BP for commencement of widespread marine erosion. Although suggestive of glaciolacustrine conditions, the exact nature and timing of laminated sediment deposition within the CDB, and the implications this has on (pen)insularity of Ireland following deglaciation, remain elusive.