Coastal lagoons as archives of event deposits, Belize, Caribbean Sea

在该项目的第一阶段，在伯利兹中部海岸沿着的五个地点采集了26个振动岩心，以从浅泻湖（包括红树林沼泽、沼泽、洪泛平原、沙嘴）及其周围回收第四纪沉积物。正在对这些岩芯进行沉积学、古生态学和年代学研究，以了解海岸的发展情况，并将晚更新世至全新世期间主要气旋的全新世记录放在一起。沿海泻湖的特点是细粒背景沉积，使粗粒事件沉积，如风暴床，可能脱颖而出的识别。过去几十年大西洋飓风强度增加的原因尚不确定。因此，研究这一现象在人类记录时间之外的更长时间序列中的历史至关重要。由于现存的全新世气旋档案远不完整，只覆盖局部地区，而且也有争议，因此探索更多的记录是很重要的。伯利兹对这样一项研究特别感兴趣，因为可以评估事件沉积对公元800-1000年左右崩溃的经典玛雅文明的可能影响。到目前为止，已经分析了来自伯利兹4个沿海地区的22个岩心。更新世相，通常形成岩芯的基底，是硬壤土，带有黄色到红色的污点。上覆全新世相包括富含有机物的泥灰岩泥和粉砂、石英砂和泥炭/泥炭质沉积物。壳层内的泥泞单位的科尔森点和海牛泻湖主要是由耐盐双壳类Anomalocardia cuneimeris。这一观察和大小频率图表明，原地/泻湖沉积的贝壳。软体动物分布沿着的核心表明可能发生在全新世海平面上升相的退积。商业湾泻湖的近岸泻湖岩心含有丰富的石英砂层，与细粒沉积物和海洋生物（如滨珊瑚）交替。而薄石英砂层的起源尚不完全清楚，珊瑚沉积物和1米厚的砂层被解释为在高能量事件期间过洗桑迪屏障的结果。泥炭、软体动物壳和珊瑚骨骼的放射性碳年代测定允许相对比，并表明最大。全新世沉积物的年龄约为5.5 kyrs（Commerce Bight）、约6 kyrs BP（Colson Point）、约6.5 kyrs BP（Sapodilla、Manatee）。珊瑚事件层的年代约为1.5和4.95 kyrs BP。相比之下，以前的研究发现，沿着伯利兹海岸的风暴活动在大约1 kyrs BP和4.5-2.5 kyrs BP之间增加。第三年，我们计划分析五个地点之一的剩余7个岩心，对结果进行全面解释，在两次会议上介绍结果，并准备两份手稿供出版。

During the first phase of this project, 26 vibracores at five locations were collected along the coast of central Belize recovering Quaternary deposits from and around shallow lagoons (including mangrove swamps, marshes, floodplains, sand spits). The cores are being studied sedimentologically, paleoecologically, and chronologically in order to understand the coastal development and to put together a Holocene record of major cyclones during the late Pleistocene to Holocene. Coastal lagoons are characterized by fine-grained background sedimentation so that coarse-grained event deposits, such as storm beds, potentially stand out for identification. The reasons for the increase in hurricane intensity in the Atlantic over the past few decades are uncertain. Therefore, it is crucial to study the history of the phenomenon in longer time series that go beyond the time of human recording. Because existing Holocene cyclone archives are far from complete, cover only local areas, and are also controversial it is important that additional records be explored. Belize is especially interesting for such a study because the possible influence of event sedimentation on the classic Maya civilization, which collapsed around AD 800-1000, can be evaluated. So far, 22 cores from 4 coastal locations in Belize have been analyzed. Pleistocene facies, that usually form the base in cores, are stiff loams with yellow to reddish stain. Overlying Holocene facies include organic-rich marly muds and silts, quartz sands and peat/peaty sediments. Shell layers within the muddy units of Colson Point and Manatee Lagoons are mostly dominated by the salinity-tolerant bivalve Anomalocardia cuneimeris. This observation and size-frequency diagrams suggest autochthonous/ lagoonal deposition of the shells. Mollusk distribution along the cores indicates retrogradation of facies that may have occurred during Holocene sea-level rise. Nearshore lagoonal cores from Commerce Bight Lagoon contain abundant quartz sand layers alternating with finer grained sediments and marine organisms like Porites corals. Whereas the origin of thin quartz sand layers is not entirely clear as yet, coral deposits and a 1-m-thick sand layer are interpreted as the result of overwash across sandy barriers during high-energy events. Radiocarbon dating of peat, mollusc shells and coral skeletons allows facies correlation and indicates a max. age of Holocene sediments of ~5.5 kyrs (Commerce Bight), ~6 kyrs BP (Colson Point), ~6.5 kyrs BP (Sapodilla, Manatee). Coral event layers were dated as ~1.5 and 4.95 kyrs BP. For comparison, previous studies found increased storm activity along the Belize coast around 1 kyr BP and from 4.5-2.5 kyrs BP. For the third year, we plan to analyze the remaining 7 cores from one of the five location, to make an overall interpretation of the results, to present the results on two conferences, and to prepare two manuscripts for publication.