However, during the Ordovician period, the brachiopod fauna changed greatly. This resulted in large differences between brachiopods from the Early and Late Ordovician. This formation (594 meters thick) is primarily composed of light grey limestone, green-grey shale, and a base of sandy dolomite.
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.
In addition, the shallow portion of the basin endured turbulent tides, as evidenced by observing erosional evidence and the poor preservation of gastropod shells found in the Canning Basin.
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.
Such sea level changes had a profound effect on fauna in the early Ordovician period. Ordovician sea level changes can be traced in the Canning Basin strata with the appearance of condensed marine fossil sections.
A great diversity of fossil gastropods has been uncovered in the Canning Basin.
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 abundance of trilobite fossils in these two formations may be associated with highly favorable Ordovician environmental conditions.
The Emanuel and Gap Creek formations are important because of the high faunal diversity that their microfossils represent during the Ordovician period. Evolutionary Crisis of the Ashgill Graptolites, pp. Global Carbon Isotopic Events Associated with Mass Extinction and Glaciation in the late Ordovician, pp.
They had hard outer skeletons, jointed legs, and oval segmented bodies. A., Hints, L., Meidla, T., Paleogeography Paleoclimatology Paleoecology, 1997.