Introduction

Abstract

Portuguese Timor forms the eastern half of Timor which is the largest of the Lesser Sunda Islands. Timor is that island of the Indonesian Archipelago nearest to Australia, being separated from the Sahul Shelf by only 120 km (75 miles). The geology of Timor is therefore particularly relevant to the problems of the geological relationships between Asia and Australia. This Memoir deals mainly with the stratigraphy and structure of Portuguese Timor, an area of 16000 km2 (7500 square miles). It is based upon 28 months of field mapping and three years of laboratory studies, mainly petrography and geochemistry. Two-thirds of the area was mapped on a scale of 1:40000 and the remainder on 1:100000. This detailed reconnaissance is supported by the palaeontological reports of several specialists. Twenty-four formations are distinguished, four of which are wholly allochthonous. The autochthonous formations range in age from Lower Permian to Recent, and make up a section of 8000m thickness. Of the wholly allochthonous formations one is pre-Permian, two are Permian, and the other a mid-Miocene gravity slide deposit. Four separate periods of folding are recognized, two of which, the Timorean and the Ramelauean, are of major importance and were accompanied by large-scale overthrusting. Two unconformities in the Lower Tertiary are recognized but no associated folding can be distinguished. Immediately following both the Timorean and Ramelauean orogenies there were periods of uplift. The geological history of Portuguese Timor is described, and in broad terms an attempt is made to correlate events in eastern Timor with those in western Timor, the other islands of the Indonesian Archipelago, New Guinea, and northern Australia. A regional tectonic sequence emerges. The seepages of petroleum and natural gas are described and their origin briefly discussed. © 1968 Geological Society of London.