Permo-Triassic successions of the Kekneno area, West Timor: implications for palaeogeography and basin evolution

Abstract

The Permo-Triassic succession of Kekneno, Timor, consists of mixed clastic and carbonate sediments, showing marked local variations in thickness and facies. Sedimentation occured in neritic to deep marine basin environments and was accompanied by fault controlled subsidence. The basin lay close to the northern margin of Gondwanaland but was partly enclosed by land areas to the east and north. Sandstones of the Timor succession are petrologically less mature than their equivalents in the Bonaparte Gulf Basin and the southern part of the Timor Sea, and also contain different heavy mineral assemblages. The implication is that the provenance area of the Kekneno sandstones was separate from the sandstones in the areas to the south. Uplifted carbonate platforms (e.g. the Sahul Platform) may have isolaetd the Kekneno Basin from the quartz rich sandstones which characterise some of the basins closer to the Australian hinterland. Palaeocurrent measurements from the Permo-Triassic sediments of Kekneno show several different flow trends through time. The most significant trends are north-south bimodal (earliest Permian), southeast (Early to Mid-Permian) and west-southwest (Middle to Late Triassic). These data, together with the abundance of terrestrially derived organic matter, suggest that emergent landmasses lay to the east and also to the north or northwest of Kekneno. Part of the northerly landmass may have been removed by Early to Mid-Permian rifting near the northern margin of Gondwanaland. Erosion of nearby shelf areas produced the sediments which infilled the Kekneno Basin. Slump folding and thick debris flows bear witness to active downfaulting of the basin margins, particularly in the Middle to Late Triassic.