Cool-water shell bed taphofacies from Miocene-Pliocene shelf sequences in New Zealand: utility of taphofacies in sequence stratigraphic analysis

Abstract

AbstractAn investigation of the taphonomy, palaeoecology and stratigraphy of cool-water skeletal concentrations (shell beds) of the Matemateaonga Formation (Late Miocene-Early Pliocene) of Wanganui Basin, New Zealand, has provided the basis for the classification of taphofacies presented here. Two taphofacies described from transgressive systems tracts include the amalgamated shell bed and sediment starved shell bed taphofacies, representing skeletal concentration dominated by wave and current agitation, and sediment starvation, respectively. A further five taphofacies described from highstand and regressive systems tracts exhibit a gradient of sedimentological, taphonomic and palaeoecological properties that result from variation in storm event and fair-weather wave processes across the palaeoshelf bathymetric gradient. A principal components analysis of semi-quantitative data (53 observations) from sequences in Manutahi-1 well core demonstrates that taphonomic properties may be limited to particular systems tracts in some cases, but can also be repeated in different system tracts where the depositional environments are similar. Taphofacies, which are contained within siliciclastic-dominated portions of sequences (highstand and regressive systems tracts) possess little direct relevance to sequence stratigraphic analyses, but do provide valuable information on environmental conditions, in particular, depth relative to storm and fair-weather wave base, and proximity to shoreline.