Provenance Analysis and Diagenesis Using Integrated SEM-Cathodoluminescence and Optical Microscopy for the Sandstones of the Pirispiki Formation, Kurdistan Region, Northern Iraq

Abstract

The paragenetic history and provenance of framework grains in marginal marine and deltaic sandstones of the Pirispiki Formation in two sections, (Ora and Kaista), northern Iraq were examined. This was achieved using an integrated approach employing scanning electron microscopy-cathodoluminescence (SEM-CL), and optical microscopy. The Pirispiki Formation is lithologically characterized by alternating layers of thin- and thick-bedded sandstones. These were intercalated with thin laminae of grey-black shale. Petrographic analysis revealed that the dominant detrital grains in the mature quartz arenite sandstone were monocrystalline quartz grains with undulose extinction. The diagenetic analysis of the sandstones documented several processes that occur in three distinct stages. The SEM-CL technique enabled the identification of two distinct quartz overgrowth phases. Quartz cementations are of two types, the earliest phase and the most significant by volume is the Q1 cement characterized by dark non-luminescence which led to the destruction of most of the primary pores and the healing of mechanically induced cracks. Q2 cement is formed after major compaction and is characterized by bright luminescence with sector zoning, revealing an intricate SEM-CL zonation. CL revealed five special textures within detrital quartz grains including healed fractures and zoning. The provenance of the detrital quartz grains indicated the dominance of plutonic and metamorphic sources, with trace amounts originating from volcanic sources. These were mostly derived from the Bitlis Massif Zone in Turkey.