THE GULF OF CARPENTARIA AS A MODERN TECTONIC AND EUSTATIC ANALOGUE FOR THE ILLINOIS BASIN DURING THE PENNSYLVANIAN

The Gulf of Carpentaria is a shallow, flat-floored epicontinental sea that lies on the Australian Plate between Northern Australia and the Island of New Guinea. The Gulf is approximately 900 km by 600 km and is separated from the Coral Sea on the northeastern side by the 12 m deep Torres Strait and from the Arafura Sea on the northwestern side by the Arafura Sill, which lies about 53 m below sea level. The maximum water depth is about 70 m, and the bottom gradient below 50 m is about 1:13000. During the Quaternary, the basin was subaerially exposed a number of times and seismic sections show at least 10 reflections that extend across the basin, all of which also have channels associated with them. Pedogenesis has been recognized in piston cores beneath 1 m of bottom sediments that are approximately 35,000 years old.

The present day extent of Pennsylvanian age strata in the Illinois Basin is approximately 600 km by 300 km, one-third the area of the Gulf of Carpentaria. The dip of the coal-bearing strata in the center of the Basin can be measured in meters per kilometer. There have been more than 50 oscillations (cyclothems) identified in Middle and Upper Pennsylvanian strata in the Illinois Basin, most of which involved transitions from marine to non-marine conditions and included pedogenesis (underclays) and coal formation. These oscillations occurred at a time of eustasy resulting from Gondwana glaciation. Major coal beds and associated underclays can be mapped throughout the Basin and they commonly have extensive channels associated with them.

The Gulf of Carpentaria is a tectonic and eustatic analogue for the Illinois Basin. However, it is not a complete analogue in that during the Quaternary it lacked the climate necessary to develop the peat precursors to mineable coals.