Palynofacies and sea-level changes in the Middle Coniacian-Late Campanian (Late Cretaceous) of the East Coast Basin, New Zealand

A palynofacies analysis of four sections through the Paton and Herring Formations of the East Coast Basin in southern Marlborough indicates that the two formations were deposited on the inner to mid-shelf in a marine environment with conspicuous input of plant material from adjacent land area. The Paton Formation was deposited on the inner to mid-shelf under oxic conditions and in proximity to a river delta, possibly in a deltafront setting. Its lower part is clearly less marine than its upper part, pointing to an overall deepening trend with time. The deposition of the Herring Formation took place farther offshore, on the mid-shelf, in a mud-dominated environment under poorly oxygenated conditions at the sediment/water interface, following a landward shift of shoreline. A stratigraphic analysis of changes in palynofacies and lithology through the four sections allows a breakdown of the succession into seven depositional sequences, separated by unconformities or their correlative conformities. A regional sea-level curve for the Middle Coniacian-Upper Campanian in the East Coast Basin is proposed on the basis of the inferred sequences and chronostratigraphic control from dinoflagellate biostratigraphy. The sea-level cycles thus inferred for the East Coast Basin show a poor correlation with the re-scaled Haq cycle chart, suggesting that regional tectonics rather than eustasi controlled the East Coast Basin sequences.