Triassic pelagic deposits of Timor: palaeogeographic and sea-level implications

In West Timer, Triassic deposits are found in the Parautochthonous Complex, as well as in the Allochthonous series of Sonnebait. A detailed biostratig raphic investigation integrating field observations and facies analysis, al lowed the reconstruction of a synthetic lithostratigraphic succession for t he Upper Triassic, a stratigraphic transition from Carnian shales to Upper Norian-Rhaetian limestones is also shown by this study. The fossil content predominantly originates from an open marine environment; lithostratigraphi c Units A-E are dated on the basis of radiolaria and palynomorphs, and Unit H, on ammonites and conodonts. The presence of pelagic bioclasts, together with normal grading, horizontal laminations, and current ripples, is indic ative of a distal slope to basin environment. The ammonite rich condensed l imestone of Unit H was deposited on a 'pelagic carbonate plateau' exposed t o storms and currents. The organic facies have been used as criteria for bi ostratigraphy, palaeoenvironmental interpretation, and sequence stratigraph y. The palaeontological analysis of the Triassic succession of West Timer i s based on the investigation of radiolaria and palynomorphs, in the marls a nd limestones of Units A-E, and also on ammonites and conodonts in the cond ensed limestone of Unit H. Units A and B are Carnian (Cordevolian) in age, based on the occurrence of the palynomorph Camerosporites secatus, associat ed with 'Lueckisporites' cf. singhii, Vallasporites ignacii, Patinosporites densus and Partitisporites novimundanus. Unit C is considered as Norian, o n the basis of a relatively high percentage of Gliscopollis meyeriana and G ranuloperculatipollis rudis. Unit D contains significant palynomorphs and r adiolaria; the organic facies, characterized by marine elements, is dominat ed by the Norian dinocysts Heibergella salebrosacea and Heibergella aculeat a; the radiolaria confirm the Norian age. They range from the lowermost Nor ian to the lower Upper Norian. Unit E also contains radiolaria, associated in the upper part with the well-known marker of the Upper Norian, Monotis s alinaria. For Unit E, the radiolaria attest to a Lower to Upper Norian age based on the occurrence of Capnodoce and abundant Capnuchosphaera; the uppe r part is Upper Norian to Rhaetian based on the presence of Livarella valid a. Finally, the blocks of condensed limestone with ammonites and conodonts of Unit H allowed the reconstruction of a synthetic stratigraphic successio n of Upper Carnian to Upper Norian age. Our stratigraphic data lead to the suggestion that the Allochthonous complex, classically interpreted as a tec tonic melange of the accretionary prism of the island Arc of Banda. is a te ctonically dismembered part of a Triassic lithostratigraphic succession. (C ) 2000 Elsevier Science B.V. All rights reserved.