Neogene Calcareous Nannofossils from Sites 811 and 819 through 825, offshore Northeastern Australia

Abstract

Calcareous nannofossils are generally abundant at the Queensland Trough transect sites (811 and 819 through 825) of Leg 133, and they provide the primary means of dating the Neogene sediments. Sites 819 through 821 to the east of the Great Barrier Reef yielded abundant, moderately preserved Pleistocene nannofossils. The sections are biostratigraphically complete, except for a very condensed interval or a hiatus in the middle Pleistocene section at Site 819. A similar hiatus has been identified at Site 822, where abundant, well-preserved upper Pliocene through Holocene nannofossils were recovered. Abundant and well-preserved nannofossils at Site 823 provide a fairly high-resolution biostratigraphy for the upper Miocene-Holocene sediments recovered, which is remarkable for this turbidite-ridden sequence. Calcareous nannofossils diminish as preservation deteriorates abruptly downhole at Sites 811, 824, and 825 on the Queensland Plateau, and the nannofossil biostratigraphy for the Pliocene and Miocene intervals is only marginally useful. Preservation of calcareous nannofossils varies greatly among different sites and is controlled by the amount of clay and bank-derived metastable aragonite and high-magnesium calcite in the sediments. Strong dissolution of upper Pleistocene calcareous nannofossils deposited in relatively shallow water and buried at shallow depth is documented for the first time.