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

在该项目的第一阶段，在伯利兹中部沿海的五个地点收集了26个振动锤，从浅水泻湖（包括红树林沼泽、沼泽、洪泛平原、沙坑）及其周围回收第四纪沉积物。这些岩心正在进行沉积学、古生态学和年代学的研究，以了解沿海的发展，并将晚更新世至全新世期间的主要气旋记录在一起。沿海泻湖的特点是细粒度的背景沉积，因此粗粒度的事件沉积，如风暴床，可能会突出识别。过去几十年来大西洋飓风强度增加的原因尚不确定。因此，研究超越人类记录时间的更长时间序列的这一现象的历史是至关重要的。由于现有的全新世气旋档案远未完成，仅覆盖局部区域，并且也存在争议，因此探索额外的记录非常重要。对于这样的研究来说，伯利兹特别有趣，因为可以评估事件沉积对经典玛雅文明的可能影响，玛雅文明在公元800-1000年左右崩溃。到目前为止，已经分析了伯利兹4个沿海地区的22个岩心。更新世相通常构成岩心的基底，是带有黄色至红色斑点的坚硬壤土。上覆的全新世相包括富有机质泥质和粉砂、石英砂和泥炭/泥炭质沉积物。科尔森角和海牛泻湖泥质单元的壳层主要由耐盐双壳贝（Anomalocardia cuneimeris）主导。这一观察结果和尺寸-频率图表明贝壳是自然/泻湖沉积的。软体动物沿岩心的分布表明，在全新世海平面上升期间可能发生了相退化。Commerce Bight Lagoon的近岸潟湖岩心含有丰富的石英砂层，与细粒度沉积物和像Porites珊瑚这样的海洋生物交替存在。尽管薄石英砂层的起源尚不完全清楚，但珊瑚沉积物和1米厚的砂层被解释为在高能事件期间冲过砂障的结果。泥炭、软体动物壳和珊瑚骨架的放射性碳定年可以进行相比较，并指出了最大值。全新世沉积物年龄：~5.5 kyrs (Commerce Bight), ~6 kyrs BP (Colson Point), ~6.5 kyrs BP （Sapodilla, Manatee）。珊瑚事件层测年为~1.5和4.95 kyrs BP。相比之下，之前的研究发现，伯利兹海岸的风暴活动在距今1万年左右和距今4.5-2.5万年之间有所增加。在第三年，我们计划对五个地点之一的剩余7个核心进行分析，对结果进行整体解释，在两次会议上展示结果，并准备两份手稿发表。

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.