TREWIN, NIGEL H., Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen, Scotland

ABSTRACT: Quartz Cement Budget in the Tumblagooda Sandstone, Western Australia

The Tumblagooda Sandstone is a Late Silurian sandstone including facies of mixed fluvial and aeolian sandsheet origin. It is over 1 km thick in the type outcrop area and comprises quartz-rich medium-coarse grained redbed sandstones which are thought to rest unconformably on metamorphic basement. Mudrocks are only represented in the sequence by sparse mud-clasts within fluvial facies. Cementation in dominantly by quartz with minor illite and Fe-rich grain coatings. Fluvial facies have extensive quartz overgrowths (10-25% rock volume) and low fabric compaction due to net introduction of quartz. Aeolian facies show extensive quartz dissolution at grain contacts and only contain minor (up to 2%) quartz overgrowths. Point-count data gives compactional volume losses due to grain-to-grain di solution of up to 4% for fluvial and 10-19% for aeolian facies. Calculation of pre-cement porosity gives a range of 28-37% covering both facies. It is concluded that silica is generally conserved within the formation, being transferred from aeolian to fluvial facies with migration distances in the range of centimetres to tens of meters. Quartz cementation of fluvial sandstones was encouraged by relatively clean detrital grain surfaces, but grain coatings of clay and oxides on aeolian grains encouraged dissolution at grain contacts during burial. Macro-porosity values in the two facies are similar (Fluvial 2-13%; Aeolian 6-17%) but pore configuration and connectivity varies and would greatly affect the production potential of the major facies.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.