Petrographic and geochemical study of Jurassic dolostones from Lebanon: Evidence for superimposed diagenetic events

The Jurassic rock sequence in Lebanon is characterized by pervasive dolomitization (thickness > 1000 m). Two distinct dolostones are recognized within this rock succession: fine-to-medium crystalline seepage-reflux grey dolostone and coarse-crystalline hydrothermal beige dolostone. In this contribution, field, petrographic, and geochemical investigations on a dolostone ‘tongue’, occurring in Late Jurassic carbonates in central Lebanon, are discussed. The dolostone ‘tongue’ consists predominantly of the beige Late Jurassic hydrothermal dolostones. During and/or after the deposition of the overlying continental sandstones (Early Cretaceous), meteoric water percolated through the sand layers and into the underlying beige dolostones. This resulted first in dolomite intracrystalline dissolution, and then in the precipitation of oxides/hydroxides within the pore space. Finally, the precipitation of ferroan dolomite cement — from reduced fluids during a new stage of burial — took place. This study attempts to explain how superimposed diagenetic events result in a single pervasive dolostone body.