Spatial patterns of deformation and paleoslope estimation within the marginal and central portions of a basin-floor mass-transport deposit, Taranaki Basin, New Zealand

Abstract

This study describes the character of submarine mass movement and associated deformation as revealed by an exceptionally well-exposed portion of a seismic-scale masstransport deposit (MTD) within the upper Miocene Mohakatino Formation (Taranaki Basin, New Zealand). The North Awakino MTD is at least 55 m thick and crops out along the northern Taranaki coastline for ~11 km in wave-cut platforms and in cliffs as much as 100 m high. Spectacular softsediment deformation features are developed in remobilized sediment gravity fl ow deposits that initially accumulated within a lowgradient intraslope basin. Sedimentary facies within the North Awakino MTD comprise laterally extensive, thick-to thin-bedded volcaniclastic sandstone and mudstone. Distinct postdepositional deformation styles are associated with bedding type: folds developed in thick-bedded sandstone are larger (fold heights to tens of meters) and more laterally continuous (to 1 km) than those developed in thinner bedded facies.Regional geologic relationships suggest that nearly the full width of the North Awakino MTD is exposed in outcrop, providing a rare opportunity to observe lateral relationships between the marginal and central portions of the MTD. We conducted a rigorous paleoslope analysis of slump fold, fault, and bedding orientations using both existing and newly proposed methodologies. Separate analysis of seven subregions within the North Awakino MTD reveals that the predicted MTD transport direction varies widely along the outcrop extent. Most notably, slump folds and faults within the inferred margins have mean orientations that are suborthogonal to those within the central portions of the MTD. This relationship is hypothesized to be a consequence of edge effects that may be related to lateral compression along the margins of the MTD. Our analysis demonstrates the importance of accounting for spatial hetero geneity in slump structure orientations when determining the paleoslope orientation through kinematic analysis. Our inference of west-directed translation suggests that the North Awakino MTD formed in response to a local change in the bathymetric slope orientation that was likely the result of tectonically induced basin deformation.

Strain analysis of a seismically imaged mass‐transport complex, offshore Uruguay

“…well penetration) is available. Although we are confident that the contractional domain of the MTCs is composed of a thrust-cored fold system, we recognise that an alternative 616 | EAGE STEVENTON ET al. interpretation of shortening by near-isoclinal folding model, is also plausible (see Sharman et al, 2015). Invoking the latter model for Section 1 shows that the apparent shortening increases significantly, from 18% to 43% and 26% to 54%, for H3 c and H3 c-f respectively ( Table 2).…”

“…However, as noted in field examples, downdip shortening could be accommodated by the formation of isoclinal folds rather than discrete thrusts (e.g. Sharman, Graham, Masalimova, Shumaker, & King, ) (see Supporting Information Figure S4). In this case, there is no discrete thrust fault, and reverse heave cannot be calculated; thus, the magnitude of shortening equals the difference between the original and folded line lengths.…”

Refined depositional history and dating of the Tongaporutuan reference section, north Taranaki, New Zealand: new volcanic ash U–Pb zircon ages, biostratigraphy and sedimentation rates

“…The higher sedimentation rates are compatible with the interpreted slope and base-of-slope paleo-environments and overall progradation of the depositional system (King et al 1993. High sedimentation rates likely contributed to slope destabilisation and mass wasting commonly observed within middlelate Miocene Taranaki Basin deposits (Utley 1987;Nodder et al 1990;King et al 1993King et al , 2011Browne et al 2006;Sharman et al 2015). It is possibly no coincidence that the largest mass-transport interval within the studied succession lies just beneath the inferred change in sedimentation rates.…”

“…The Mohakatino Formation is dominated by volcaniclastic sandstone and mudstone re-worked by turbidity currents and submarine landslides from eruptive detritus derived from a coeval volcanic arc located offshore, to the northwest of the present-day coastline (e. g. Nodder et al 1990;King et al 1993;Giba et al 2013;Sharman et al 2015). The overlying formations consist of siliciclastic sediments derived from the eastern and/ or southern hinterlands of the basin.…”

“…Intervals of mass-transport deposits, at bed-to seismic-scale, occur throughout the depositional succession (King et al 1993(King et al , 2011Browne et al 2006;Sharman et al 2015).…”