Abstract
In the Central Valley of Costa Rica exists a principal sandy- quartz sequence (Middle Miocene to Upper Miocene). Occasionally this rocks are inter-bedded with coal seams (lignite 0.3 to 1 m thick) and silstones very riches in organic matter.
The new data and reinterpretation of the sequences, permitted defined the sedimentary facies: Silicoclastic Platform (mixed facies), Open Bay Facies, Bar Facies (bar front (middle shoreface) and upper shoreface).
Those facies represent a Strand Plain, generated by Miocene inter-ceanic currents, through the channel genetic related with the Sinistral Costa Rica Transcurrent Fault System. That fault, has segmented the national territory and generated the pull-apart Basin in the Central Valley. The rapidly susidence accumulated thick shallow deposits.