Geometries, Structures and Petrography of Tumey Injection Complex, California (USA)

Abstract

The understanding of stratigraphic, structural and petrographic features characterizing outcropping sandstone intrusions is fundamental for the study of sand injection complexes. Their mutual relationships may strongly help in the discovery and development of oil-bearing sandstone intrusions reservoirs. The Tumey Injection Complex (TIC) is a large sand injection complex intruding 350 meters of deep marine deposits of the Kreyenhagen Formation (Eocene) in Central California and extending laterally for over four kilometres. From the base to the top this formation consists of thin-bedded brown mudstones and shales alternating with two main levels of lithic sandstones. The sequence passes upward to biosiliceous mudstones which are erosively overlain by other level of sandstone with shales on the top. A detailed geological mapping supported by stratigraphic, structural and petrographic analysis allowed understanding the relationships between the depositional units and injections along different measured logs. The TIC is made by (1) host hydrofractured mudstones and shales, (2) depositional, locally remobilized, lithic sandstones (parent units), (3) an interconnected network of sills and dykes and (4) injection breccias developed in the base of the biosiliceous mudstones. The parent units consist of amalgamated channelized lithic sandstones bodies containing preserved sedimentary structures and mudstone clasts. These sandstones have been modified by liquefaction and fluidization processes promoted by overpressured fluids feeding the uppermost intrusions net. The sills are structurally controlled by bedding whereas the dykes by a NW-SE oriented fracture system probably driven by NE-SW stresses. The injection network shows a range of geometries like multi-layered sills, stepped dykes and saucer shape intrusions. The depositional and injected sandstones have the same composition (lithic) and a provenance signature of recycled orogeny. They differ from the sandstones of the underlying formations which show a different mineral assemblage and a provenance from a dissected magmatic arc. This data attests that the parent units of the TIC are the sandstones of the Kreyenhagen Formation. The TIC is a sand injection complex intruded in host mudstones producing a range of structures and features and it can be used as an analogous for subsurface intrusive traps containing oil and gas.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017