Tectonically‐driven seabed rise and fall controlling temperate carbonate systems in a tide‐dominated multiple‐strait system: the example of unconformity‐bounded Neogene limestones (Northern Hawke's Bay, New Zealand)

ABSTRACT Internal structures of Neogene coquina limestones in northern Hawke's Bay include small‐ to large‐scale cross‐beds, which are interpreted as the foresets of subaqueous dunes produced by strong tidal currents flowing in constricted straits between elongated submarine ridges. Analysis of the stratigraphic architecture of the studied deposits reveals a tectonic origin for the development of barnacle‐ and mollusc‐dominated heterozoan carbonate depositional systems. Late Miocene to Late Pliocene limestone sheets across the study area are characteristically floored by an angular unconformity indicating that the onset of carbonate production was preceded by the tilting and folding of the underlying strata. Conversely, limestones are sharply overlain by deep‐water siliciclastics recording the submergence and termination of heterozoan carbonate production. Shallow‐water carbonates formed and accumulated in a morphostructurally‐controlled multiple‐strait system that developped following regional tectonic deformation and uplift. As such, carbonate production is associated with relative sea level fall. These conditions brought the seabed to tidal influence where heterozoan organisms could flourish. By contrast, regional tectonic subsidence led to relative sea level rise and rapid seabed drop, resulting in termination of the multiple‐strait system and shut down of carbonate factories.