During the Palaeozoic era at least a few thousand kilometres of ocean floor were subducted, taking of the order of a hundred million years. Sediments were deposited in the ocean floor in the form of fans formed by turbidity currents off the side of a continental slope. The flow was in the northerly direction, indicating that the continental slope was to the south. These deposits occurred during the Ordovician period. The ocean floor was distant from the continental source of the sediment. Towards the end of this period there were isolated parts where no turbidity currents reached and only fine clay and animal organic and silica debris were deposited into oxygen-depleted deep water. This ocean basin has been called the Monaro Basin. To the north west was a volcanic chain of islands, the Macquarie arc, with an associated submarine trench.