TRIASSIC-LOWER JURASSIC FORAMINIFERAL INDICES FOR BAHAMAN-TYPE CARBONATE-BANK LIMESTONES, CABLAC MOUNTAIN, EAST TIMOR

Abstract

Peloidal and oolitic limestones on Cablac Mountain in East Timor contain small calcite-cemented agglutinated and porcelaneous foraminifera that place these limestones in the Triassic or Lower Jurassic, in contrast to the Lower Miocene as previously mapped. An Early Jurassic (Sinemurian-Pliensbachian) age is indicated for some of the limestone by the presence of Meandrovoluta asiagoensis Fugagnoli and Rettori, Everticyclammina praevirguliana Fugagnoli and a palynomorph assemblage. The age of other limestones on the mountain is identified broadly as Late Triassic to Early Jurassic, based on the occurrence of Duotaxis metula Kristan. In basinal facies of the nearby Wai Luli Valley, Gsollbergella spiroloculiformis (Oraveczne Scheffer), palynomorphs, a brachiopod and halobiid bivalves indicate a Late Triassic (Carnian) age for a transported foraminiferal assemblage associated with peloids, ooids and Duotaxis and Siphovalvulina characteristic of carbonate-bank deposits. This occurrence suggests that carbonate banks were developed locally on submerged topographic highs in seas that flooded interior-rift basins in this part of Gondwana and that a complex facies array of deep-water muds, deltaic sands, and carbonate shoals were present in the basins. Taxonomic assessment of Triassic and Early Jurassic species previously placed in Tetrataxis suggests that these are better accommodated in Duotaxis , and some species placed in Trochammina are transferred to Siphovalvulina . The distinction between Duotaxis and Siphovalvulina , as now understood, rests on the shape of adult chambers.