Stratigraphic Revision of a Lower Triassic Shale Unit Previously Placed in the Upper Jurassic, East Gondwana Interior Rift Association, Eastern Timor-Leste

Due to structural complexity, great efforts must be invested in reconstructing the tectonostratigraphic framework of rock successions older than late Miocene in the Timor-Leste orogenic belt. In some previous studies, lithostratigraphic units have been proposed without age control and this has led to significant miscorrelations. Based on recent geological mapping by the Instituto de Geociências de Timor-Leste in the Tchinver River area in eastern Timor-Leste, a shale unit previously considered to belong to the Upper Jurassic is shown to be Lower Triassic. The unit consists of a varied-coloured shale succession that contains rare bivalves ( Claraia spp.), very rare probable ophiceratid ammonoids, and abundant palynomorphs dominated by Michrystridium and Veryhachium acritarchs. The presence of Claraia with affinities to either C . griesbachi or C . wangi indicates that the shale containing these macrofossils lies within the Induan (lowest Triassic) Stage. The palynomorphs are attributed to the Induan-lower Olenekian (Lower Triassic) Kraeuselisporites saeptatus Spore-Pollen Zone. Lithologically and biostratigraphically the shale is similar to the type section of the Baharedu beds. The shale was previously described as the Tchinver Shale with very little detail and attributed, without any age control, to the Upper Jurassic. In Timor-Leste, the name “Tchinver Shale” should be discontinued in formal stratigraphic schemes. The shale unit, now placed in the Baharedu beds, belongs to the East Gondwana Interior Rift Association and correlates with coeval shale units in Western Australian basins to the east and south.