The Cambrian and Ordovician Systems in the Pacific Area : (II)

Abstract

In South America the Guiana and Brazil shields on the east side are separated from each other by the Amazonas basin. In the west side of the continent the Andean mountain system provided with the Pampean highland on its east side extends from Venezuela to Chile and the fossiliferous Cambro-Ordovician formation is extensively distirubuted in the east side of the mountain system.
The history of research in the Cambro-Ordovician biostratigraphy is here summarized. An Olenellian species, two Albertan faunules and a few Croixian genera are known of the Andean Cambrian fauna. Now various graptolites are known there from Tremadocian to Ludlovian. In 1937 I have published a study on “the Cambro-Ordovician shelly fauna of South America”. Our knowledge was considerably improved by Harrington and Leanza's “Ordovician Trilobites of Argentina” 1957, particularly in the Lower Ordovician part. A few Ashgillian trilobites were discovered at length in the San Juan area by Baldis and Blasco (1975) and thus the six ages of the Ordovician period are all documented. Finally, brief notes are appended on the history of the Andean belt in the Palaeozoic and later pe-riods with reference to other arears.