Abstract

The drilling of the first West Timor well, the Amoseas Indonesia Banli-1, has confirmed the model of thin-skinned thrust tectonics as suggested from surface geologic data collected during four years of fieldwork, offshore seismic data, aeromagnetic data and gravity data. Extensive age-dating of surface rock exposures, coupled with structural field mapping, has shown that the surface structures are a series of thin-skinned, southward-directed, imbricate thrusts composed of Jurassic to Miocene-aged rocks. The major bedding-plane detachment surface for these thrusts is within a zone containing rocks of Middle Jurassic (Early Callovian to Mid Bathonian) age. The surface trace of these thrust sheets can be traced southwestward to tie into the marine seismic data south of desas Oebelo and Kolbano. This seismic data clearly images a series of extremely imbricated thrust sheets overlying a non-imbricated, gently deformed footwall of Jurassic and older rocks.

The Banli-1 well penetrated the southeast flank of a giant antiformal feature containing Jurassic to Miocene thrust slices that dip steeply (60 degrees) overlying the gently dipping (10 degrees of south dip) Jurassic to Triassic rocks. These footwall rocks are remarkably undeformed with consistent low dip, and have lithologies similar to coeval rocks of the Bonaparte Basin and Ashmore platform. These Tertiary-Triassic footwall rocks, farther to the south in the offshore, are located on the hangingwall of the Timor Trench subduction zone. They have, in turn, been thrust southward over a footwall of Tertiary-aged rocks contiguous with the Australian craton.