Lithofacies and dynamics of a cool-water carbonate seaway: mid-Tertiary, Te Kuiti Group, New Zealand

Abstract

AbstractThe Waimai, Orahiri and Otorohanga limestones of the upper Eocene to lowermost Miocene Te Kuiti Group, North Island, New Zealand, provide examples of cool-water carbonate sedimentation within seaways. The limestones are dominated by grainstones and packstones, and contain abundant bryozoans, benthic foraminifers and echinoderm fragments, with only small amounts of siliciclastic material. Horizontally bedded and cross-bedded lithofacies represent sedimentation in wave-dominated and current-dominated settings, respectively; biostrome lithofacies are less abundant and tend to be associated with the current-generated deposits. The migration of dune fields and the associated biostromes generate laterally restricted cyclic alternations of lithofacies. Stratigraphic partitioning of cross-bedded and wave-dominated lithofacies demonstrate that the Te Kuiti seaway alternated between current-dominated, wave-dominated and mixed-energy conditions. Eustatically and/or tectonically produced changes in water depth had the most important influence, with current-dominated conditions prevailing when water depth was optimal to allow flow acceleration through the seaway. Wave-dominated or mixed-energy conditions prevailed when water depth was less or more than this optimum depth. Mixed-energy conditions were most prevalent in widest seaways. The controls on seaway sedimentation inferred have application to other carbonate and siliciclastic seaway successions.