LetterU/Pb dating of a terminal Pliocene coral from the Indonesian Seaway
Highlights
► First ever U-Pb isochron for a coral of Pliocene age. ► First U-Pb age for coral from Indonesian region. ► U-Pb age supported by Sr chemostratigraphy, biostratigraphy and U-series. ► U-Pb age provides temporal constraints on topographic evolution of Timor.
Introduction
The tectonic opening and closing of oceanic pathways influence global thermohaline circulation (Berggren and Hollister, 1977), marine productivity (Schneider and Schmittner, 2006), and climate (Mudelsee and Raymo, 2005). Exhumed marine sequences in or adjacent to oceanic pathway systems (e.g., Central American seaway, Indonesian Seaway) provide opportunities to decipher tectonic, topographic, physical and chemical oceanographic pathway changes with relevance for marine faunal evolution (e.g. Jackson et al., 1996), salinity and temperature changes in adjacent oceans (e.g. Karas et al., 2009), major climate systems (e.g. von der Heydt and Dijkstra, 2011), and human evolution (Cane and Molnar, 2001). The ability to study these processes is partially limited by the difficulty in obtaining robust chronostratigraphy from marine sequences, due to factors including highly variable deposition rates, sediment reworking, lack of age-diagnostic fossils, lack of datable materials, and/or diagenetic alteration (Getty et al., 2001). U/Pb dating of detrital corals in exhumed marine sequences provides a novel and promising, albeit under-utilized, methodology to refine the chronostratigraphy of marine sequences under certain circumstances. Two prior successful attempts have been made in the Carribbean region, where U/Pb coral ages of 1.02 ± 0.07 Ma and 1.288 ± 0.034 Ma (Getty et al., 2001) and 5.52 ± 0.15 Ma (Denniston et al., 2008) were obtained. In this study, we make a first attempt to use U/Pb techniques to date pristine, detrital Platygyra corals from the syn-orogenic, marine Viqueque Megasequence (VM) presently exposed on the island of Timor in the eastern Indonesian region. Our results enable us to refine the chronostratigraphy of the VM and place finer temporal constraints on the onset of turbidite deposition and the emergence and vegetative colonization of the VM source region during a key time for IS evolution.
Section snippets
Geological setting
The NNE-directed voyage of the Australian continent at ~ 70 mm yr− 1 relative to the Sunda Shelf (DeMets et al., 1994, see Fig. 1A) resulted in collision of the leading continental margin with the Banda Arc by the Miocene to early Pliocene (Audley-Charles, 2011, Rutherford et al., 2001). Tectonic processes including the accretion of the Banda Arc to the Australian continental crust (Bock et al., 2003, Nugroho et al., 2009) and the detachment of the downgoing slab from the Australia Plate lead to
Stratigraphy and foraminiferal biostratigraphy of the Viqueque Megasequence
The relatively undeformed VM overlies structurally complex older units. The VM Type and Northern Cuha sections are exposed in the Cuha River on the northern limbs of WNW-striking synclines near the town of Viqueque (Fig. 2). The base of the Type section unconformably overlies the synorogenic mélange and contains mudstone clasts probably derived from the mélange matrix. The basal carbonate chalk has foraminiferal assemblages indicative of a Zone N18 age (5.2–5.6 Ma) (Batu Putih Formation; Haig
Screening
Coral sample TL07 (Fig. 2e) was extracted from the upper conglomerate, subsampled and screened for signs of diagenetic alteration following the methods of Denniston et al. (2008). X-ray diffraction (XRD) revealed 100% aragonitic composition and scanning electron microscopy (SEM) revealed a primary aragonitic skeleton with delicate growth structures, original porosity and minimal aragonitic cement and interstitial mud (Fig. 3a). Measurement of 234U/238U and 230Th/238U can be a powerful
Discussion
As demonstrated by Getty et al. (2001) and Denniston et al. (2008), the U/Pb dating of primary coral aragonite is possible providing the original coral U-series chemistry is retained and unaltered by weathering, diagenesis, and/or contaminants such as marine cement and deritus. Such preservation requires an unusual set of circumstances; the sample must have experienced little if any subaerial exposure, which would promote the calcification of aragonite, and limited burial, which would promote
Acknowledgments
This work has profited from discussions with David Haig, Myra Keep and Eujay McCartain at the University of Western Australia and Jamie Shulmeister at University of Queensland. We thank ENI Pty Ltd, the University of Canterbury, and the Royal Society of New Zealand Marsden Research Council (Fast-start grant M1137) for financial support. We thank the Secretariat for Energy and Natural Resources (SERN) in Dili for their continuing support for our research in Timor Leste and Joao Edmundo dos Reis,
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