EVOLUTION OF A LOWER SLOPE SUBMARINE CHANNEL FAIRWAY WITHIN THE MOUNT MESSENGER FORMATION, TARANAKI, NEW ZEALAND

Continuous coastal and inland outcrops of the Mount Messenger Formation in Taranaki, New Zealand expose a 6 kilometer-wide lower slope submarine channel fairway in a fine-grained, sand-dominated deep-marine system. These outcrops provide an opportunity to study the dynamic evolution of submarine channelform bodies. Quantitative analyses of facies and event beds as well as dimensional measurements of surface length, geometry, and thickness define a hierarchical framework of sedimentary bodies. This hierarchy includes elementary bodies, composite bodies, and channel complexes which record the modulation of these attributes throughout the evolution of the channel fairway.

Sandstone bodies are subdivided into channel complexes W1 through W3. Mass transport deposits (MTDs) form cycle boundaries between each complex and influence channel placement within the fairway. MTDs vary in size, composition, and strain manifestation which affect the architectural evolution of each successive complex.

Complex W1 is subdivided into W1A and W1B due to a channel avulsion event. W1A is composed of a maximum of two composite bodies and ten elementary bodies while W1B is composed of a maximum of three composite bodies and nine elementary bodies. Similar to W1, W2 and W3 are offset by an avulsion event. W2 is composed of a maximum of two composite bodies and seven elementary bodies. W3 is composed of a maximum of three composite bodies and 14 elementary bodies. Aspect ratio measurements show an evolution from multistory/multilateral (W1) to multilateral (W2) to multistory (W3) stacking pattern. Additionally, process facies show a general fining upward sequence within each complex. Channel complexes are composed of mud-intraclast conglomerate, thick-bedded sandstone, thin-bedded sandstone interbedded with siltstone, and topped by siltstone or mudstone. Silt dominated thin beds above W3 mark the top of the channel fairway. This change to a silt-dominated system indicates a shift or a shut-down of coarse clastic sedimentation within the channel fairway.