Tephra distribution and sedimentation rates m the Bay of Plenty, New Zealand

Abstract

Abstract Sediment in the Bay of Plenty grades from dominantly sand near-shore to a green terrigenous sandy mud beyond the shelf edge. Cobbles, pebbles, and coarser sediments with considerable local textural variation occur on topographic highs. Nine rhyolitic tephras erupted from the Taupo Volcanic Zone are recorded from a series of piston cores taken from the Bay of Plenty. The tephras have been identified on the basis of stratigraphic position, dominant ferromagnesian mineralogy, and chemical analysis of their titanomagnetites. Radiocarbon dates of shell horizons found in some cores decrease in age with decreasing water depth. The shell beds and commonly associated pebble layers represent shallow water relict deposits which accumulated on the continental shelf during the late Pleistocene to early Holocene marine transgression. Rates of sedimentation on the continental shelf and slope have been estimated from the depth of burial of identified rhyolitic tephras and the radiocarbon ages of the shell beds a...