Maastrichtian to Paleocene dinocysts from the Clarence Valley, South Island, New Zealand

Abstract

A palynological study of uppermost Maastrichtian to lower Paleocene marine strata from two stratigraphic sections in the Clarence Valley, Marlborough, New Zealand, revealed diverse organic-walled dinoflagellate cyst (dinocyst) assemblages. One hundred and twelve samples were investigated and 86 dinocyst species were identified, from the two sections studied: Branch and Mead streams. Nine new species are described herein: Cerodinium nielsii, Impagidinium agremon, I. cavea, I. crouchiae, I. hannahii, Lejeunecysta kammae, Pyxidinopsis epakros, P. everriculum and P. meadensis. Stratigraphic correlations are achieved using nine new index species and eight cyst acme intervals, named A to H, integrated with foraminiferal datums and the radiolarian zonation for the South Pacific. The first occurrence of Carpatella septata combined with a high relative abundance of Diconidinium martianum characterizes the interval directly below the Cretaceous–Paleogene (K–Pg) boundary or uppermost part of the Manumiella druggii Zone. Based on the results from both sections, the earliest Paleocene Trithyrodinium evittii Zone is subdivided into the following intervals: Senoniasphaera inornata, Carpatella cornuta, Cassidium fragile and Cerodinium striatum subzones. The following dinocyst species first appear at or near the top of the T. evittii Zone: Alterbidinium pentaradiatum, Glaphyrocysta perforata, Habibacysta sp. cf. H. tectata, Kallosphaeridium brevibarbatum, Lejeunecysta kammae, Pyxidinopsis sp. cf. P. waipawaensis, Spiniferella cornuta and Tectatodinium meandriforme. The boundary between the T. evittii and the overlying Palaeocystodinium golzowense Zone was recorded only in the Mead Stream section where it is dated to ca 64.0 Ma. A high relative abundance of Isabelidinium cingulatum succeeded by the first occurrence of Isabelidinium bakeri, Deflandrea foveolata and D. delineata characterizes the lower to middle part of the early Paleocene P. golzowense Zone. The last consistent occurrence of P. pyrophorum is recorded within the upper part of radiolarian Zone RP3 corresponding to the middle part of the early Paleocene calcareous nannoplankton Zone NP3 (Early Teurian) or ca 63.7 Ma. The K–Pg boundary is not characterized by a mass extinction of dinoflagellates in the New Zealand sections. Instead, there is a marked change in cyst associations directly above the boundary and several new species appear in the lowermost Paleocene. Several typical latest Maastrichtian taxa have their last occurrences within the lowermost Paleocene corresponding to an interval of ca 0.5–0.7 Myrs after the K–Pg boundary.