Mr Oatley joined the board as a Non-Executive Director and Chairman of the Remuneration Committee in July 2018.
He is also currently a Non-Executive Director of Wates Group Limited and Centurion Group Limited and previously in his career was Chief Executive of Cape plc and Hamworthy plc.
A spokesperson said: "Subsequent to the departure of the previous Chairman on 24 March 2020, it has become clear that the search for a permanent replacement may take significantly longer than previously anticipated.
"The Board believes that it is essential to have a Chairman in place given the current challenging market environment and the need to secure a long-term financing position for the Group, and has accordingly asked Joe to assume the role while continuing to search for a longer-term replacement.
Peter Slabbert, Senior Independent Non-Executive Director, said: "Joe has made a considerable contribution to the Board to date and will provide strong leadership during a difficult time until a longer-term replacement can be found".