Stratigraphic variation of sedimentary facies and architectual elements within channel complexes of the Mount Messenger Formation, Taranaki, New Zealand
Corbin, Nathan Andrew.
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This study establishes an architectural framework of sedimentary facies, event beds, and sedimentary bodies for channelized deep-water sandstone and siltstone deposits within the Lower Mount Messenger Formation (LMMF). Well exposed outcrops of the Late Miocene Mount Messenger Formation are present along the Taranaki coast of the North Island, New Zealand. These exposures provide an opportunity to study submarine channel complexes deposited within an inner basin-floor fan to base of slope setting. Sedimentary facies and architectural elements are described from the axis to the margin and overbank of channel complexes to show spatial and temporal variation of subaqueous flow properties operating at the time of deposition. Facies were placed into an architectural framework to show organized changes in the diversity and abundance of bodies across the LMMF. Thirty hydrodynamic facies were described from outcrop exposures. Each facies represents varying hydrodynamic processes and sediment sources present during deposition. Sediments in the LMMF are interpreted to represent deposition by high- and low-density turbidity currents, concentrated and hyperconcentrated density flows, en masse movements, and debris flows. Six channel complexes described from coastal and inland outcrops record the variation of sedimentary facies spatially and temporally throughout their evolution. Analysis of architectural elements and sedimentary facies across the LMMF indicates flows were weakly confined within the basal interval, and progressively became more confined up-dip. This is reflected by multilateral channels near the base, and multistory channels up-section. Minor flow transformations within subaqueous flows are inferred. The sediments within the LMMF reflect an overall temporal decrease in flow strength, flow frequency, and event bed thickness, and a temporal increase in flow variability up-section from the base. Channels were deposited within a 3.5 km wide channel belt with the uppermost channels confined to a 1.7 km wide master erosional channel south of the lowermost channels. Paleoflow was directed to the northwest with little variation between each successive channel complex.