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Detailed 2000 Year Climate Record in the Mixed Carbonate/Siliciclastic Belize Central Shelf Lagoon


Although the mixed carbonate/siliciclastic Belize Central Shelf Lagoon is not anoxic, it has been used as a potential analogue for the depositional sedimentary environment of the Eagle Ford Shales. Moreover, mixed shelfal sediment also can be excellent archives for the weathering rates in the adjacent hinterland, highly influenced by precipitation variability, and therefore climate fluctuations. The main purpose of this research program focuses on the late Holocene mixed sediment partially filling the Rhomboid Reef lagoons, English Caye Channel, and the central shelf lagoon. The Belize climate is described as subtropical, highly influenced by the seasonal migration of the Intertropical Conversion Zone (ITCZ), triggering alternating winter dry and summer wet seasons. In the late Holocene, the ITZC has been reported to have reached higher latitudes during the Medieval Warm Period (MWP) producing high precipitation on the Yucatan Peninsula, contrasting with periods when the ITCZ remained in low latitudes, generating years of low precipitation and even dramatic droughts, as during the Little Ice Age and the couple of centuries just preceding the MWP, corresponding to the Mayan Terminal Classic Collapse. Nine vibrocores and two gravity cores were retrieved from the Belize Central Shelf Lagoon. Their timeframe was established by dating, via radiocarbon, intact non-transported macro (bivalves) and micro (benthic foraminifera, Quinqueloculina) fossils. Carbonate content values were determined by carbonate bomb and element (Ti, Si, K, Fe, Al, and Sr) counts via XRF scans. Values of carbonate content in the cores from the Rhomboid lagoons vary from 84 to 90%, in the cores from English Caye Channel from 44 to 75%, and in the cores from the Central Shelf Lagoon from 44 to 64%. As expected, the highest strontium counts (3600–4000) are observed in cores located in the Rhomboid Reefs lagoon surrounded by continuous reefal rims. Three of the nine cores, with well-constrained radiocarbon timeframes, display detailed climatic records for the last 2000 years. The 800–950 A.D. interval preceding the MWP is characterized by a sudden decrease in Ti, Si, and K counts, related to a severe drought and overall low sedimentation rates which correspond rather well with the Mayan Terminal Classic collapse. Systematic high Ti, Si, and K counts are observed during the MWP (950–1300 A.D.), while during the Little Ice Age (1300–1800 A.D.) these element counts reach minimum values.