Mass flow deposits on a mid-Tertiary carbonate shelf, southern New Zealand

Abstract

Sheet-like and channel-filling conglomerates and pebbly biomicrudites occur within a sequence of cross-stratified shallow-water bioclastic limestones, the Forest Hill Formation of Late Oligocene to Early Miocene age. The largest channel, 50 m wide, 9 m deep, and at least 1.2 km long, is infilled with four separate conglomerate units of pebble-to boulder-sized limestone lithoclasts in a sparse muddy matrix (biomicrudite). Both the conglomerates and associated pebbly biomicrudites possess features characteristic of high concentration mass flows -both of laminar flow (preferred clast orientation, inverse grading or massive bedding) and of turbulent flow (normal coarse-tail or distribution grading and stratification). Clast imbrication (a-or b-axes) is suggestive of gradual deposition. Some flows travelled far enough to allow both vertical and horizontal differentiation of the coarse sediment. Facies models which have been proposed for conglomerates of deep water (turbidite) association can also be applied to the small-scale neritic conglomerates. Formation and remobilisation of such coarse grained facies in a shelf setting is attributed to eustatic sea-level changes and/or to local tectonism. ] H i "Southland KEY Late Cret.-Holoc. strata incl. Oligo-Mioc 1st. Murihiku terrane TJ Brook Street terr " undiff. Palaeozoic %

Submarine lobes and feeder channels of redeposited, temperate carbonate and mixed siliciclastic‐carbonate platform deposits (Vera Basin, Almería, southern Spain)

“…8. not relate to a major exposure event as in the case described by Hyden (1980) of channel-®lling conglomerates occurring within cross-strati®ed, inner-shelf bioclastic limestones in the Neogene of New Zealand. The possibility does exist for them being subaerial, in this case corresponding to¯uvial courses crossing the inner platform during precession-induced, eustatic sea-level falls.…”

Channels across continental shelves: Corequisites of canyon-fan systems and potential petroleum conduits

“…Although associated with general Plio-Pleistocene progradation and possibly influenced by a glacial low sealevel stand and/or tectonism, the initiating cause for the shelf channels found onshore may have been solely retrogressive mass failures up the shelf gradient from a canyon generated from prevailing southnorth alongshelf currents (cf. Herzer 1979 Lewis et al 1980, Osborne 1981, in Early Oligocene mid-or inner-shelf sandstones at Nelson (D. W. Lewis 1980), and in Late Oligocene-Early Miocene shallow-water bioclastic limestones of central Southland (Hyden 1980). Recent preliminary re-investigation of mass-flow deposits in Eocene mudstones of the transgressive succession at Greymouth (Omotomotu Formation; Gage 1952) and north of Westport (Torea Breccia; Laird & Hope 1968) suggests that they also represent shelf channel fillings.…”

“…In the Oligocene deposits at Nelson, intermittent stormgenerated currents cut and filled the channels. In the Southland sequence studied by Hyden (1980), evidence is more equivocal concerning the initiating cause(s). In all examples, individual channels Early Pleistocene sequence at Motunau (Fig.…”