Abstract Three-dimensional (3D) seismic data reveal the complex interplay between the surface topography of a c. 4405 km 3 mass transport deposit (MTD) and overlying sedimentary packages over approximately the last two million years. The data image part of the Pleistocene to recent shelf to slope to basin-floor Giant Foresets Formation in offshore western New Zealand. The MTD created substantive topographic relief and rugosity at the contemporaneous seabed, formed by the presence of a shallow basal detachment surface, and very large (up to 200 m high) intact slide blocks, respectively. Sediments were initially deflected away from high-relief MTD topography and confined in low areas. With time, the MTD was progressively healed by a series of broadly offset-stacked and increasingly unconfined packages comprised of many channel bodies and their distributary complexes. Positive topography formed by the channels and their distributary complexes further modified the seafloor and influenced the location of subsequent sediment deposition. Channel sinuosity increased over time, interpreted as the result of topographic healing and reduced seafloor gradients. The rate of sediment supply is likely to have been non-uniform, reflecting tectonic pulses across the region. Sediments were routed into deep water via slope-confined channels that originated shortly before emplacement of the MTD.

ABSTRACT We combined sand petrofacies with lithofacies to characterize sedimentation within unconformity-bounded sequences at Integrated Ocean Drilling Program (IODP) Expedition 317 sites drilled across the Canterbury shelf to the slope, located off the east coast of the South Island, New Zealand. Differentiation of the relative influence of along- and across-shelf sand supply in this system is made possible by the unique aspects of the onshore geology. Northern rivers draining mainly Torlesse composite terrane lithologies are dominated by lower-grade metamorphic lithic fragments, whereas central rivers, draining the Torlesse to schist (semi-schist) transition (Haast/Otago Schist), contain more higher-grade metamorphic lithic fragments, and the southern rivers contain sand that is quartzofeldspathic and mica rich, having been derived predominantly from coarse schist. Differences are documented in onshore river sand that allow for the provenance classification of 38 offshore sand samples from IODP Expedition 317 cores into four provenance groups based on their likely bedrock sources: (1) Torlesse, (2) Torlesse-schist transition, (3) schist, or (4) mixed. The distribution of sand composition in the 0–0.62 Ma sections of the shelf and slope sites indicates a dynamic system where shore-parallel and shore-perpendicular processes alternated on the shelf, and shore-perpendicular processes dominated at the slope site. When sand compositions are placed in a sequence-stratigraphic context, they indicate an evolving paleogeography through time. Significant sand provenance shifts are linked to falling sea level, with Torlesse-schist transition compositions characteristic of regressive systems tracts. Torlesse compositions are supplied to the sites during falling sea level and sea-level lowstands, when fluvial and coastal geomorphology promotes influx from the north. Mixed compositions characteristic of transgressive systems tracts are likely products of littoral- and shelf-current mixing and potential influx of schist detritus from the south.

Abstract In north Taranaki, New Zealand, spectacular examples of deep-water mass-transport deposits (MTDs) are exposed in coastal cliffs and imaged in nearby offshore seismic reflection data. The MTDs are Late Miocene (Tortonian) in age, and lie within successively overlying successions of volcaniclastic sandstone-dominated basin-floor turbidites (Mohakatino Formation), epiclastic sandstone- and siltstone-dominated basin-floor turbidites (Mount Messenger Formation), and siltstone-dominated slope deposits (Urenui Formation). Seismic-scale MTDs are exposed north of Awakino River and also between the Mohakatino and Tongaporutu river mouths. These MTDs incorporate a range of original deep-water lithofacies that subsequently have been dramatically deformed into highly chaotic packages during re-emplacement in mid-bathyal to lower bathyal water depths near to or beyond the base of slope. There does not appear to be any stratigraphic or lithologic control on the types of beds incorporated into these particular MTDs, and the deformed strata are potentially derived from several original submarine-fan depositional units. These seismic-scale MTDs are in places at least 50 m thick and appear to extend for a few kilometers, although lateral stratigraphic correlation is made difficult by the complex MTD deformation and by postdepositional normal faulting. It is possible that two different MTDs are represented in the outcrop section between Mohakatino and Tongaporutu, and together they may form a larger composite MTD or mass-transport complex. At least two large MTD successions are revealed on seismic reflection profiles located offshore, relatively near to the coastal outcrop section. They extend for several tens of kilometers in length, and are up to 330 m (250 ms two-way travel time (TWTT) thick. These MTDs are in approximately the same stratigraphic interval as those in outcrop (Mohakatino and lower Mount Messenger Formations). At least one of these MTDs extrapolates up structural dip to where an MTD is exposed onshore, but an absolute correlation between the two MTDs is precluded by the lack of seismic data in the intervening coastal transition zone. MTD intervals equivalent to those exposed are also imaged in high-resolution behind-outcrop seismic reflection lines, and are recorded by anomalous biostratigraphic signatures in the nearby Pukearuhe-1 exploration well. Siltstone-dominated MTDs of subseismic scale (up to 15 m thick) are evident in central parts of the outcrop section, within fine-grained intervals near the tops of inner-fan depositional cycles. They are also present in southern parts of the section (retrogradational and progradational slope), within fine-grained intervals that lie stratigraphically close beneath incised slope channels infilled with sandstone. Whilst these MTDs are only 5-15 m thick, they could thicken away from the outcrop transect. The magnitude and styles of deformation within the various exposed MTDs may reflect differing transportation processes or triggering mechanisms. The larger, seismic-scale MTDs appear to be the product of massive slope failure and downslope translation of strata, or relatively local tectonic movement of the sea bed. The ordered stratigraphic position of the sub-seismic-scale MTDs near the tops of inferred depositional cycles suggests that changes in relative base level may have controlled their development.

Abstract Late Miocene Mount Messenger Formation exposures in north Taranaki, New Zealand, demonstrate contrasting styles of deepwater basin-floor fan and slope fan development. Some of these attributes may have analogs in subsurface thin-bedded, deepwater reservoirs. Basin-floor fan settings are characterized by thick-bedded sandstone litho-facies (central lobe) and thin-bedded sandstone/siltstone lithofacies (lobe fringe). The thick- and thin-bedded sandstones were deposited by high-density mass flows. Stratigraphically higher slope fan units are invariably thin bedded. They display scouring at various scales and well-developed sedimentary structures that are indicative of deposition by turbidity flows. The slope fan depositional settings include individual and nested channels, and vertically stacked and shingled levee complexes.

A unique section through late Miocene basin floor fan, channel-levee complex, and prograding complex units of several lowstand systems tracts, occurs in the coastal region of north Taranaki, New Zealand. Strata dip gently and are superbly exposed in coastal cliffs as much as 200 m high. The overall succession exposed along the coast is progradational. The major controls on sedimentation were relative changes in sea-level (base-level changes), influenced by high rates of sediment supply. Broad intervals dominated by one or other lowstand systems tract component are identified in outcrop, and can be correlated into the subsurface using seismic reflection profiles and SP logs. Exposed basin floor fan and channel-levee successions within the Mount Messenger Formation form the basis of the present study. Five distinct sequences are recognized. Relatively thick, fine-grained intervals constitute the upper portions of individual sequences. Paleobathymetric deepening trends and high gamma-ray counts have been recorded in some of these intervals. Sequence boundaries occur as erosional contacts. The basin floor fan (lowstand fan) units comprise meterthick massive and convolute-bedded sandstone with minor mudstone, and thin-bedded massive sandstone, horizontal and ripple-laminated sandstone, and mudstone. More proximal early lowstand (basin floor fan equivalent) lithofacies include conglomerate and thick-bedded sandstone, within nested channels that erode as much as 30 m into underlying strata. Channels almost invariably occur above slumped intervals, and we suggest that retrogressive slumping created sea-floor topographic depressions within which the channels preferentially formed. Channel-levee complexes are characterized by interleaving packages of thin-bedded siltstone and sandstone. Levee overbank siltstone is prevalent in lower, more distal parts of channel-levee complexes. In upper, more proximal parts, coalescing channelized units are common, and within these, welldeveloped Bouma sequences and climbing ripple-laminated sandstones are particularly distinctive. Thick-bedded sandstones (basin floor fan) have lowest outcrop gamma ray values, of about 125 counts per second (cps). Sandstone gamma ray values generally range up to 180–190 cps, both in the basin floor fan and channel-levee lithofacies. Mudstone gamma ray counts are generally higher (up to 250 cps), though there is considerable overlap with sandstone values, particularly in thin-bedded lithofacies. Sandstone permeabilities measured in outcrop are mainly in the range 100mD–800mD. Thick-bedded sandstones have the highest permeabilities, demonstrating a primary facies control on reservoir quality.