Ordovician radiometric dating
Incomplete shells and opercula of Teiichispira kobayashi were discovered in the Gap Creek formation, as well as internal molds of Ecculiomphalus cf. The Emanuel formation and Gap Creek formation are only two Ordovician localities in which a diverse number of trilobite species have been found. Elsevier Scientific Publishing Company, Amsterdam, pp.
Trilobites are an extinct form of arthropods that disappeared about 230 million years ago.
The Ordovician period of the Paleozoic Era is an interval exhibiting increased animal diversity and an abundance of marine life.
One of the many significant fossil sites from this time is the shallow Canning Basin in northwestern Australia (180 miles south-east of the present day city of Derby).
Although the environment today is desert, evidence suggests that the basin was a deep water marine environment of high faunal diversity during the Ordovician period.
A great diversity of fossil gastropods has been uncovered in the Canning Basin.
This formation (594 meters thick) is primarily composed of light grey limestone, green-grey shale, and a base of sandy dolomite.
The age of the fossils found in the Emanuel formation were determined using potassium-argon and uranium radiometric dating.
In the Emanuel formation alone, 130 specimens were uncovered which include six different species in five different genera. H., 1996, Global Events and Event Stratigraphy in the Phanerozoic, Springer-Verlay, New York, pp.
Present day gastropods, including slugs and snails, have the defining characteristic of torsion (developmental twisting) which results in the rotation of the visceral mass and the mantle on the foot. canningense and four of Seelya emanuelensis were found in the Canning Basin, both of which have not been found anywhere else.
The Gap Creek formation has a break in its strata due to a relatively rapid rise in sea level.