Clay Mineralogy Constraining the MIDDLE – Miocene Climatic Optimum In Panama

The Middle Miocene Climatic Optimum (MMCO) is the warmest peak of the Neogene with global mean temperatures approximately 6 °C above those of present day. Such a peak should be identified by differential weathering conditions before and after the MMCO. Clay mineralogical analysis can be used as a marker of climatic conditions, as different clay minerals are formed depending on the prevailing precipitation and temperature values. Sedimentary sequences within the Culebra and Cucaracha Formations of the Panama Canal basin may contain the record of this peak. The Culebra Formation consists of mostly carbonaceous mudstones at the bottom and towards the top the amount of sandstone increases. The Cucaracha Formation is composed of reddish to grayish mudstone and claystone representing paleosols with some conglomerates and tuffaceous layers. Its depositional environment is interpreted as a deltaic plain with fluvial channels, mangroves, and flood plains. The contact between Culebra and Cucaracha formations is abrupt, easily recognizable by a color change, it is of regional extent, and could be used to unravel stratigraphic relations in the Panama Canal basin. This study represents an untried approach to pinpoint the MMCO in the tropics, using clay mineralogy to infer paleoclimates. The advantage of using this technique in the Panama Canal basin is that the source areas are homogeneous – basic and intermediate rocks - and the thickness of the sedimentary pile is less than 1000m, thus having minimal diagenetic processes. Additionally, a detailed stratigraphy and sandstone modal analyses will be carried out. Age constraints will be assessed using U/Pb in zircons from tuff layers in the Cucaracha Formation, further calibrated with a palynological zonation.This study will provide an additional data source that may improve understanding of the Middle – Miocene Climatic Optimum in the Neotropics.