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

• Applicant: Professor Dr. Eberhard Gischler
• Subject Area: Palaeontology
• Term: from 2010 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 181603219

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.

• DFG Programme: Research Grants
• International Connection: USA
• Participating Persons: Professor Robert Ginsburg, Ph.D.; Professor Dr. Wolfgang Oschmann; Dr. Rainer Petschick