How marine fossils got to inland Australia

How marine fossils got to inland Australia

The inland sea occupied the last two stages of the Early (half of) Cretaceous
time. It is illustrated by two wall maps: greatest extent, and when the rocks
now outcropping at Richmond were sea floor. It was most wide-spread late
in the older stage (Albian Stage), and most restricted very late in the Aptian
Stage and into the next stage (Albian Stage). Renewed flooding of the inland
sea was only through the Gulf of Carpenteria from the open ocean during
middle and Upper Albian.

Normal sea-water was renewed through a broad strait between the Mt Isa/
Cloncurry block of old metamorphic rocks and the Georgetown block of old
metamorphic rocks. The northern area of the inland sea shows a rich fauna
as a result of its position in the path of clean seawater. Richmond Shire has
exposures of the oldest to the youngest of these marine rocks.

The floor of the inland sea formed the "roof' of the aquifer (water-carrying beds)
of the Great Artesian Basin. The non-marine beds of the aquifer project from below the marine beds in the North-east of the Shire, making it an intake area. The marine beds follow in sequence from north to south, finishing, with the filling of the inland sea at the end of Early Cretaceous time.

The non-marine rocks of the Winton Formation are preserved in the south of the Shire, here they are the oldest of the late Cretaceous beds, the earliest part of the Cenomanian Stage.

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