Palynology of theAcacia-bearing beds in the Komako district, Pohangina Valley, North Island, New Zealand

Abstract

In the Pohangina Valley, north of Ashhurst, upper Nukumaruan—Okehuan sediments, underlain by limestones, mudstones, and sandstones and overlain by sands containing marine fossils, contain pollen of Acacia (represented by its form genus Acaciapollenites) throughout a minimum thickness of 90 m. Ecologically the pollen assemblages consist of coastal swamp sedges together with scrub and grassland species. Inference of a coastal environment is supported by the presence of dinoflagellate cysts of Spiniferites. Tree pollen is relatively rare and trees may have been restricted to the surrounding hills (Ruahine Range). The presence of Acacia and the paucity of tree pollen indicate dry, cool to mild conditions. It is suspected that such conditions extended well north of the study area during late Nukumaruan—Okehuan time. Acacia appeared in New Zealand during the Pliocene, became prominent in the late Pliocene-early Pleistocene, and then became extinct. Acacia may form a stratigraphically useful index fossil of dry, cool to mild coastal environments for the northern part of the North Island of New Zealand, during the Nukumaruan and Okehuan and perhaps during the Hautawan. Acacia probably migrated to New Zealand from Australia by chance transoceanic dispersal, not via land bridges.