Stratigraphy is a sub-discipline of geology that is concerned with the correlation of rock strata. A number of approaches can be utlized, drawing on palaeontology, sedimentological evidence for sea level change, geochemical proxies, direct dating of rocks, as well as geophysical correlation of well logs and seismic data. Stratigraphy is of fundamental importance to the petroleum industry for correlation of petroleum reservoirs, but is equally important to academic problems and field mapping.