Portal de Periódicos da CAPES

Mass-emplaced siliciclastic-volcaniclastic-carbonate sediments in Middle Miocene shelf-to-slope environments at Waikawau, northern Taranaki, and some implications for Taranaki Basin development

1990; Taylor & Francis; Volume: 33; Issue: 4 Linguagem: Inglês

10.1080/00288306.1990.10421378

1175-8791

Scott D. Nodder, Campbell S. Nelson, Peter J.J. Kamp,

Geological and Geophysical Studies

Abstract The Middle Miocene (Altonian-Waiauan) sequence at Waikawau (Mokau-Mohakatino Groups), totalling c. 350 m thick, sits directly on Mesozoic basement rocks or rarely on local Oligocene Te Kuiti Group. It comprises four newly defined formations. Nukuhakari Formation is dominated by hemipelagic slope mudstones and some turbidites; Tirua Formation comprises redeposited calcareous sandstone/sandy limestone sheets, frequently thoroughly bioturbated, formed in broad, shallow channels on an upper to mid-continental slope carbonate apron; Ngarupupu Formation consists of variably volcaniclastic sandstones and mudstones deposited from sediment gravity flows on the mid- to outer regions of deep-marine, coalescing, volcaniclastic fan-aprons; and Waikaretu Formation is dominated by fine nonvolcaniclastic sandstones deposited by sand-rich, high-concentration turbidity currents at bathyal depths. Two petrofacies occur, suggesting two distinct sediment provenances: Nukuhakari and Waikaretu Formations have a Mesozoic basement source (quartz-rich), and Ngarupupu and Tirua Formations have a dominantly andesitic volcanic source (quartz-poor). Sedimentation in the Waikawau depocentre occurred mainly at upper to mid-slope depths, bound to the east by emergent basement rocks (Herangi High) and to the west by (now-buried) active volcanic massifs ("Mohakatino volcanics"). Tectonic and structural controls were influential throughout the depositional history of the basin, with erosion of basement blocks supplying most sediment for Nukuhakari and Waikaretu Formations. Volcanism began in the early Waiauan and affected sedimentation in the calciclastic Tirua and volcaniclastic Ngarupupu Formations, overwhelming the quartz rich basement provenance. The thin (c. 7 m) Te Kuiti Group succession onshore beneath the Waikawau sequence contrasts with the much greater thickness (c. 1 km) of Oligocene sediments offshore in Taranaki Basin. This suggests either major Oligocene subvertical faulting near the present coastline, or, more probably, subsequent Early Miocene juxtapositioning of basin margin and basin axis sequences by westward-directed horizontal shortening, involving basement overthrusting. During the Late Oligocene — Early Miocene, the Waikawau region was mildly uplifted, with consequent erosion of most of the Oligocene succession. During the Middle Miocene, both sides of the Taranaki Fault rapidly subsided to slope depths, and during the Late Miocene, the eastern side was uplifted more than 1 km, probably by reverse movement The dominance of mass-emplaced facies indicates comparable redeposited facies may be generally widespread in Middle Miocene sequences in northern Taranaki Basin.