FACIES AND DEPOSITIONAL PROCESSES IN AN UPPER JURASSIC TO LOWER CRETACEOUS PELAGIC SEDIMENTARY SEQUENCE, ANTARCTICA

The Nordenskjold Formation (?Oxfordian-Berriasian age) is exposed on t he east coast of the Antarctic Peninsula, where it consists of interbe dded ash layers and biosiliceous mudstones which accumulated under ana erobic to dysaerobic bottom waters. The mudstones were deposited by pe lagic settling and the ash layers by pelagic settling from suspension or as fallout from subaerial eruption columns. The lower part of the s uccession accumulated in a basinal setting under anaerobic bottom wate rs and is characterized by parallel bedding. Mudstones deposited in th is setting preserve abundant zooplankton faecel pellets. Compaction of these pellets has given rise to a bedding parallel fissility. The upp er part of the succession accumulated under dysaerobic bottom waters i n a slope setting. The sequence is wavy bedded and contains abundant e vidence of post-depositional sediment instability and resedimentation, much of which was caused by tectonic activity. Discrete slide masses are absent from the slope sequence and it appears that slope processes were dominated by creep. Examination of the mudstones shows that as l evels of dissolved oxygen in bottom waters increase, pelleted mudstone s give way to structureless mudstones before visible bioturbation is n oted.