Analyzing Sandstone Samples from the Limon Basin: Investigating the Closure of the Central American Seaway

Despite its significance, the nature and timing of the closure of the Central American Seaway (CAS) is still poorly understood. Conflicting geological and palaeobiological and data mark the timing of the closure of the seaway from 25-13 Ma and 4-2.8 Ma, respectively. As the closure of the CAS marks the beginning of the Great American Biotic Interchange and initiated changes in global ocean circulation, ultimately leading to the last glacial maximum, determining its timing is of utmost importance. This discrepancy, along with new provenance data from the San Carlos Basin in Costa Rica (indicating closure from 8-6 Ma), suggests the need for further evaluation of additional basins in Central America (particularly Costa Rica) to confidently constrain the timing of CAS closure. Zircon morphological data from a sandstone sample from the Limón Basin suggest the presence of metamorphic zircons, which were likely derived from a more northern Central American source, indicating the presence of a prior marine corridor along the Costa Rica-Nicaragua border. Based on this data, we propose the existence of a northern branch of the CAS in the form of this marine corridor that remained open until 5.2-4.3 Ma, much earlier than most suggested ages from geological perspectives.