The 2.77–2.63 Ga Fortescue Group is a well-preserved, thick (0.5–6 km) succession of continental flood basalts and interbedded sedimentary rocks deposited unconformably on basement granite-greenstone crust of the Pilbara Craton, Western Australia. Together with the contemporaneous Ventersdorp basalts in South Africa, the volcanic rocks are the oldest known continental flood basalts (trapps). The 2.63–2.45 Ga Hamersley Group, containing thick deposits of banded iron formation, conformably overlies the group. Sedimentary rocks of the Fortescue Group contain several horizons of stromatolitic carbonates, deposited in freshwater lacustrine environments. Controversial filaments showing septa have also been observed and related to septate microbial microfossils.