Abstract

The southern flank of the Central Range, Irian Jaya is formed by over 5000 m of platform sediments, overlying the northern margin of Australian Continental Crust. Thick, predominantly arenaceous and argillaceous rocks of Paleozoic to Mesozoic age are overlain by approximately 2000 m of the Tertiary New Guinea Limestone Group. The sequences have been exposed by uplift early in the orogeny that formed the Central Range.

A petrographic study and a scanning electron microscope (SEM) investigation were carried out on some selected outcrop samples of Paleozoic to Mesozoic sandstones. The study revealed diagenetic features which may affect reservoir rock potential. The use of the SEM also enabled a study of the geometry of primary and secondary porosity of the sandstones.

Most sandstones of the Paleozoic Aiduna Formation are characterized by well developed quartz overgrowths, and the pore spaces have been filled by authigenic silica cement during the diagenetic regime stage. Micro-intergranular pore textures are identified as the result of cement dissolution. Authigenic cements, particularly carbonates, were developed within the sandstones of the Mesozoic Tipuma Formation and Kembelangan Group without extensive quartz overgrowths. Nevertheless, secondary intergranular and intracement pore textures appear to be common. It is suggested that several sandstone horizons in the Mesozoic sequences possibly are good reservoir rocks.