Clowes, Emma; (1997) Micropalaeontological analysis of the Kolbano sequence (Jurassic to Pliocene), West Timor, and its Radiolarian fauna. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This project comprises a study of the stratigraphy of the Kolbano sequence of West Timor and an investigation of its Lower Cretaceous radiolarian fauna. Using age data obtained from microfossils (primarily Radiolaria and calcareous nannofossils) and detailed lithological descriptions from fieldwork in the Kolbano area, the stratigraphy of the Kolbano sequence is clearly defined. Where necessary existing stratigraphies have been modified. The radiolarian bearing sediments of the Lower Cretaceous Nakfunu Formation have been divided into two facies; a more proximal facies (the Oinlasi member) comprising sequences of distal, turbiditic radiolarian sands and a more distal facies (the Tuke member) comprising fine grained radiolarian mudstones and claystones with occasional bedded cherts. A new formational name, the Latan Formation, is proposed to describe a sequence of Tertiary (Paleocene-Miocene) massively-bedded and occasionally slumped pink and white limestones and a sequence of well-bedded brown calcareous mudstones. The depositional environments of the lithologies comprising the Kolbano sequence are discussed. Over 400 samples were collected in the field. 212 samples (largely from the Upper Cretaceous and Tertiary limestone formations) have been analysed and dated using calcareous nannofossils. A total of 178 samples from the Lower Cretaceous Nakfunu Formation were processed for Radiolaria from which 32 key samples were selected for dating purposes and for the documentation of the radiolarian fauna for which full synonomy is given. The Nakfunu Formation has been dated as ranging in age from the late Valanginian to the late Aptian/early Albian using published age ranges of the Radiolaria. The structural complexity of the Kolbano sequence (formed as an accretionary wedge during the collision between Australian continental crust and the Banda volcanic forearc in the Pliocene) made it unsuitable for the development of a radiolarian biostratigraphic scheme. The radiolarian fauna was found to consist of a mixed assemblage of species widely reported from Tethys and species which have, to date, only been reported from southerly high latitude localities. Non Tethyan forms were found to be particularly abundant during the late Valanginian-Barremian. The radiolarian faunas are compared with those from other high latitude sites and the implications for palaeobiogeography and palaeoceanographic circulation patterns in the Lower Cretaceous is briefly discussed.

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