REGIONAL PHOTOGEOLOGY OF THE IPSWICH BASIN-ESK TROUGH, QUEENSLAND

The Ipswich Basin-Esk Trough Area of south-eastern Queensland was mapped photogeologically with the main emphasis on extending a uniform Jurassic sequence from the Surat Basin located to the west into the area under discussion. The photogeologic units are correlated with the Jurassic Hutton, Evergreen and Precipice formations. The remaining photogeologic units within the Ipswich Basin-Esk Trough Area are correlated with the previously established stratigraphic nomenclature. The structural interpretation agrees regionally with the basic tectonic framework as summarised by Hill (1961). The northern part of the Esk Trough is interpreted to be a westward tilted, compressed fault block. The resulting regional surface structure of the Esk Trough consists of two main synclines separated by a fault zone. The Triassic Esk Trough is unconformably overlapped to the south by the Jurassic rock sequence of the Ipswich Basin. The nature and southern extent of the Esk Trough under the Ipswich Basin is not known. The steeply dipping Mesozoic sequence located immediately west of the town of Ipswich and the asymmetric, faulted, South Moreton Anticline are both on trend with the eastern boundary of the Esk Trough and probably are tectonically related to it. An alignment of igneous intrusives in the south-western part of the Ipswich Basin may be controlled by a southerly trending surface extension of the tectonic line forming the west edge of the Esk Trough.