Quaternary hinterland evolution of the active Banda Arc: Surface uplift and neotectonic deformation recorded by coral terraces at Kisar, Indonesia

Abstract

a b s t r a c tCoral terrace surveys and U-series ages of coral yield a surface uplift rate of $0.5 m/ka for Kisar Island, which is an emergent island in the hinterland of the active Banda arc-continent collision. Based on this rate, Kisar first emerged from the ocean as recently as $450 ka. These uplifted terraces are gently warped in a pattern of east-west striking folds. These folds are strike parallel to more developed thrust-related folds of similar wavelength imaged by a seismic reflection profile just offshore. This deformation shows that the emergence of Kisar is influenced by forearc closure along the south-dipping Kisar Thrust. However, the pinnacle shape of Kisar and the protrusion of its metamorphic rocks through the forearc basin sediments also suggest a component of extrusion along shear zones or active doming.Coral encrusts the island coast in many locations over 100 m above sea level. Terrace morphology and coral ages are best explained by recognizing major surfaces as mostly growth terraces and minor terraces as mostly erosional into older terraces. All reliable and referable coral U-series ages determined by MC-ICP-MS correlate with marine isotope stage (MIS) 5e (118-128 ka). The only unaltered coral samples are found below 6 m elevation; however an unaltered Tridacna (giant clam) shell in growth position at 95 m elevation yields a U-series age of 195 ± 31 ka, which corresponds to MIS 7. This age agrees with the bestfit uplift model for the island. Loose deposits of unaltered coral fragments found at elevations between 8 and 20 m yield U-series ages of <100 years and may represent paleotsunami deposits from previously undocumented tectonic activity in the region.

Human foraging responses to climate change; Here Sorot Entapa rockshelter on Kisar Island

“…Higher concentrations of Actinopterygii (bony fishes) remains coupled to a greater abundance of Carcharhinidae (requiem sharks) in Phase 2 compared to other occupation phases and indicates the intensiveness of the fishing activities by HSE inhabitants during this period. The south coast of Kisar has a steep drop off (Major et al 2013), coupled with the presence of a considerable sea channel between Kisar and Timor, presumably makes for rich near-shore fishing conditions. Intensive fishing activities at HSE are also supported by the presence of shell fish-hooks that have been recovered from most phases of occupation, with largest numbers recovered in Phases 2 and 3 (O'Connor et al 2019).…”

“…This is supported by the sedimentation rates and stratigraphy recorded at HSE; especially HSE-B; in which numerous dense ash and charcoal layers from human activities were identified ( Figure 3). Based on dating of coral in the sterile sand and coral unit underlying the occupation deposit at HSE (O'Connor et al 2019), combined with estimated uplift rates (Major et al 2013), it is predicted that the shelter would have been dry and available for occupation shortly after 45 ka (O'Connor et al 2019). However, the oldest possible date for human settlement at the shelter, based on radiocarbon dated age-depth models, suggests that HSE was not inhabited until around 16 ka (O'Connor et al 2019).…”

“…Kisar and other islands of the Lesser Sundas, such as Timor, Moa, Leti, Wetar, and Romang, formed as a result of the collision between the Australian and Eurasian Plates (Kadarusman et al 2010). Of these islands, Kisar is located on the border between the non-volcanic area of the Outer Banda Arc (that consists of the islands of Timor, Moa, and Leti) and the volcanic area that lies on the Inner Banda Arc (including Wetar, Romang, and Damar) (Kadarusman et al 2010;Major et al 2013).…”

“…Kisar's geology consists predominantly of metamorphic rocks surrounded by a series of limestone terraces formed as surrounding coral reefs were uplifted over time ( Figure 1; Major et al 2013). The island has undergone a tectonic uplift of about 0.5 m per 1000 years as the result of its geological location Veeh 1978, Major et al 2013).…”

Provenance of Permian–Triassic Gondwana Sequence units accreted to the Banda Arc in the Timor region: Constraints from zircon U–Pb and Hf isotopes

“…1). It is also exposed on the island of Kisar (Richardson and Blundell, 1996;Harris, 2006;Major et al, 2013) and likely on other outer-arc islands to the east based on lithological similarities (Kaneko et al, 2007). The Aileu Complex consists of a protolith of Permian-Triassic, and possibly Jurassic, psammite and limestone, and basalt, rhyolite, tuffaceous material and gabbroic and dioritic plutons (Berry and McDougall, 1986;Prasetyadi and Harris, 1996;Harris, 2011).…”