Early Cretaceous subsidence of the Naturaliste Plateau defined by a new record of volcaniclastic-rich sequence at IODP Site U1513

Abstract

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Evolution of the Southwest Australian Rifted Continental Margin During Breakup of East Gondwana: Results From International Ocean Discovery Program Expedition 369

“…The onset of seafloor spreading west of the Naturaliste Plateau (the Naturaliste Plateau breakup event) occurred during deposition of the upper part of lithostratigraphic unit V. We associate this breakup event with a conformable upward transition from clayey siltstone (subunit 3) to silty claystone (subunit 2) and corresponding decreases in the abundance of fossils, bioturbation, and volcanic material (Huber et al, 2019a(Huber et al, , 2019bLee et al, 2020). Benthic foraminifera indicate deepening of the seafloor from neritic to upper bathyal depths during this interval, followed by subsidence to at least middle bathyal water depth during Aptian time between deposition of unit V and the marine claystones of unit IV.…”

“…A prominent reflector from the boundary between lithostratigraphic units IIc and IIb at Site U1515 can be traced into the western Mentelle Basin, where it manifests as an undated unconformity below the basalt flows at the top of the faulted synrift strata (Figure 3c). glauconite, pyrite, shell fragments, plant debris, and abundant volcanic mineral grains and clasts (lithostratigraphic unit V) (Huber et al, 2019a(Huber et al, , 2019bLee et al, 2020). A similar lithostratigraphic unit, rich in volcanic clasts and with a ferruginous detrital claystone at its base, was encountered at nearby DSDP Site 258 (Davies et al, 1974).…”

“…Unit II is underlain by a 209 m thick Cenomanian through Albian clay and claystone deposited in middle bathyal to bathyal water depths (lithostratigraphic unit III, 22 m thick; and unit IV, 187 m thick). The clay and claystone beds conformably overlie a 235 m thick lithic‐rich clayey siltstone and sandstone interval ranging from early Aptian to earliest Hauterivian in age that contains glauconite, pyrite, shell fragments, plant debris, and abundant volcanic mineral grains and clasts (lithostratigraphic unit V) (Huber et al., 2019a, 2019b; Lee et al., 2020). A similar lithostratigraphic unit, rich in volcanic clasts and with a ferruginous detrital claystone at its base, was encountered at nearby DSDP Site 258 (Davies et al., 1974).…”

“…Benthic foraminifera indicate water depths increased only slightly during this time, from neritic to upper bathyal (Lee et al., 2020). The amount of tectonic subsidence, S t , during this period is estimated from the change in the depth to the base of the unit after correcting for sediment and water loading (Steckler & Watts, 1978): where T u is the uncompacted thickness of the unit (273 m: Lee et al., 2020 supplemental data), ΔSL and ΔSF respectively are the changes in eustatic sea level (60 m; Haq, 2014) and seafloor depth that occurred during deposition of the unit, and ρ m , ρ s , and ρ w are the densities of the mantle, sediments, and water, respectively. ΔSF is nominally estimated to be 300 m (the distance between the midpoints of the neritic and upper bathyal depth ranges), with a maximum of 600 m (innermost neritic to lowermost upper bathyal).…”

“…M5n and M3n (126-124 Ma). The overlying epiclastic sequence of unit V contains volcanic mineral grains and lithic fragments interpreted to be eroded from volcanic rocks on the Naturaliste Plateau or perhaps further south on the conjugate Antarctica margin, which were reworked and deposited in shallow marine to upper bathyal conditions (Lee et al, 2020) as the Perth Abyssal Plain spreading center migrated westward along the northern margin of the plateau. A similar interpretation was made of the volcaniclastic strata encountered at nearby DSDP Site 258 (Davies et al, 1974).…”