Uppermost Triassic Halstätt-like cephalopod limestone (Lilu Facies) and Foraminifera, Timor-Leste

Abstract

Ammonoid-rich wackestone beds forming a ca 2 m section between shallow-marine limestones of the Bandeira Group (Norian to possibly Rhaetian) and a wackestone–calcareous mudstone succession belonging to the Lower Jurassic Wailuli Group are recorded from the western part of Timor Leste. They are included in the Halstätt-like Lilu Facies of the Bandeira Group. Age-diagnostic involutinid foraminiferal species, not previously recorded from Timor, include Involutina liassica, Trocholina sp. ex. gr. Trocholina turris and Lamelliconus permodiscoides, which collectively indicate a Rhaetian age, possibly ranging down to the Sevatian. The conodont Norigondolella steinbergensis, recorded low in the section, is consistent with this age determination. The Lilu Facies was deposited at a water depth of a few tens of metres, as suggested by the presence of extensive cyanobacterial borings into shell fragments and the presence of microbial laminations including the presence of stromatolites and bacinellid-like fabrics. Among macrofossils, common ammonoids are present in the section, and marine reptile bones are conspicuous in the lower beds. Other biogenic components of the rock observed in acetate peels and thin sections are abundant echinoderm debris (including pentacrinoid columnal plates), bivalve fragments and micro-gastropods, rare siliceous sponge spicules, solitary corals, and brachiopod debris. In the studied region, a major drowning of a shallow-marine carbonate platform took place probably in the Rhaetian or possibly latest Norian. Similar ‘ammonitico rosso limestone’ interbedded with thick-bedded limestones of a shallow-marine carbonate platform is present in the uppermost Triassic of Seram. More detailed biostratigraphical comparisons and correlations of similar units in Timor and other nearby islands may indicate a general marine drowning of Late Triassic carbonate platforms, at least in the northern part of the East Gondwana Interior Rift system, during the Rhaetian or possibly latest Norian.

Keywords:

• Rhaetian
• upper Norian
• East Gondwanan Interior Rift
• involutinids
• carbonate platform drowning

Acknowledgements

We thank the local people and government authorities for permission to access the study area. Carlos Barros and Clementino Tailoco guided us to the study site. Joanico Pires, Elias da Silva, Lucia dos Santos, Edwin Mandela, Martalina Lousina, Bernardo de Araujo, and David Martins are thanked for assistance with field work and data development. Edilirio da Costa, Jonatas L. Mendonça, Venacio Boavida, Joao Pinto, Domingos Pereirra, and Bonifacio Andrade assisted with the logistics of field work, including driving. ISB is grateful to the Instituto do Petróleo e Geologia-Instituto Público (IPG), Timor-Leste, for providing funding and logistics for this study, and thanks his parents, Rosano Barros and Lourença dos Santos, who provided accommodation during the field work. Clément Tremblin photographed the conodonts and Manuel Rigo checked their identification. DWH and EM thank UWA; DWH is grateful to its Oceans Graduate School for providing facilities in support of his contribution while in retirement.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Isaias Santos Barros

Isaias Santos Barros [[email protected]], Instituto do Petróleo e Geologia - Instituto Público, Dili, Timor-Leste

David W. Haig

David W. Haig [[email protected]], Oceans Graduate School, The University of Western Australia, 35 Stirling Highway, Perth, Western Australia, 6009, Australia

Eujay McCartain

Eujay McCartain [[email protected]], School of Earth Sciences, The University of Western Australia, 35 Stirling Highway, Perth, Western Australia, 6009, Australia.