Eujay McCartain

Carbonate pelagites in the post-Gondwana succession (Cretaceous – Neogene) of East Timor

In East Timor the upper parts of the Permian to Middle Jurassic Gondwana Megasequence are structurally juxtaposed against indurated carbonate pelagites of Early Cretaceous (Aptian) to early Late Miocene age. The pelagites probably represent a thin (several hundred metres thick) succession that was deposited at middle to lower bathyal water depths unconformably above the Gondwana succession after continental breakup. The widespread occurrence of pelagites, lack of turbidites at least in the post-Albian succession, association with upper parts of the Gondwana Megasequence and with Upper Jurassic shales of Australian affinity, and stratigraphic correspondence with adjacent Australian basins suggest that these sediments were deposited on a middle bathyal continental terrace similar to the present-day Exmouth Plateau. Evidence of chaotic soft-sediment mixing affecting units as young as early Late Miocene and analogy to present-day coeval successions on undeformed continental terraces suggest that the carbonate pelagites were friable chalk or ooze prior to deformation. Cementation, stylolitisation, and vein formation took place after the early Late Miocene (i.e. after 10.9 – 9.8 Ma GTS2004). Overlying the deformed succession is the Pliocene – Pleistocene Viqueque Megasequence (planktonic foraminiferal Zones N18 – N23) with a thin basal unit of friable chalk (30 m thick in the type area) that was deposited at middle to lower bathyal water depths similar to the older carbonate pelagites. The basal chalk ranges from zone N18 through N20 (Early to Middle Pliocene) and suggests a quiet tectonic interval, although the first indication of distal turbiditic deposition, presumably to the north, lies in the 4.2 – 3.35 Ma GTS2004 interval. Proximal turbidite deposition commenced at around 3.35 Ma GTS2004 with clasts sourced from an emerging Timor island to the north. The basal unit of the Viqueque Megasequence together with the older carbonate pelagite succession suggests that a middle bathyal continental terrace setting continued in this region, at least on the southern side of Timor, from the Cretaceous – Paleogene to the Late Miocene and Early Pliocene. The soft-sediment mixing, probably induced by tectonism, in the deformed pelagites, and the Bobonaro Mélange beneath the relatively undeformed type section of the Viqueque Megasequence suggest that during part of the Late Miocene (9.8 – 5.6 Ma GTS2004), tectonic mobilisation of sedimentary units took place, and mud volcanoes erupted on the seafloor. The Timor highlands were emergent from about 3.35 Ma GTS2004 (Middle Pliocene) as the deformation front moved from the north. The Timor Trough developed as a gentle downwarp from a pre-existing continental terrace that had been located in the middle bathyal zone since the late Early Cretaceous.

Latest Carboniferous (late Gzhelian) fusulinids from Timor Leste and their paleobiogeographic affinities

Abstract An uppermost Gzhelian bioherm discovered in the central highlands of Timor Leste contains abundant foraminifera belonging to 17 genera. Representatives of the families Biseriamminidae, Biwaellidae, Bradyinidae, Cornuspiridae, Lasiodiscidae, Palaeotextulariidae, Pseudotaxidae, Ozawainellidae, Schubertellidae, Schwagerinidae, Staffellidae and Textrataxidae are present, including 21 species referred to known types and 12 species left in open nomenclature. Two new Schwagerina species are described: Schwagerina timorensis new species, and Schwagerina maubissensis new species. The assemblage belongs to the uppermost Gzhelian Schwagerina robusta–Ultradaixina bosbytauensis Zone although a possible lowest Asselian correlation cannot be excluded (the name Ultradaixina is controversial and sometimes synonymized as Bosbytauella. The case to resolve this issue has been submitted to the Bulletin of Zoological Nomenclature). The bioherm is the oldest carbonate unit so far recorded from the Maubisse Formation and the oldest sedimentary unit biostratigraphically dated in Timor. This discovery has implications for the latest Carboniferous–earliest Permian climate history of Timor that lay in the northern part of the north-south East Gondwana rift system along which the western margin of Australia later developed. The highest peak in fusulinid diversity within the Pennsylvanian–Cisuralian interval and a major marine transgression documented in many regions in Northern Pangaea took place during the latest Gzhelian to earliest Asselian and evidence for this is now extended to southern Pangaea. Cluster analysis, using the Jaccard similarity index at species level, of late Gzhelian fusulinids from 16 regions has been performed. This shows that the Timor fauna is most closely related to faunas from South China and the Changning-Menlian region of Yunnan (China). The assemblages here are distinct from those of three biogeographic regions (Arctic, Uralo-Asian and Irano-Taurids) recognized within the Tropical belt.