Arthrophycus alleghaniensis Harlan, 1831 in the Tianguá Formation, Brazil (Silurian of the Parnaíba Basin)

Abstract

This study deals with the Arthrophycus ichnogenus and its associates, recorded in Silurian deposits of the Tianguá Formation, Serra Grande Group of the Parnaíba Basin. The methodology used in the field followed traditional procedures of geology observation and the presence of fossils in outcrops, also including specific paleoichnological details. Samples collected in the field are deposited in the scientific collection of the Dom José Museum, in Sobral-CE. The Arthrophycus alleghaniensis ichnospecies is preserved in its typical form of bundle or isolated excavations, always endowed with transverse rings. The presence of Arthrophycus in rocks of the Tianguá Formation associated with an ichnofossiliferous assembly composed of Arenicolites, Didymaulichnus and Cruziana infers a shallow marine paleoenvironment. The hummocky cross stratification indicates deposition in an area dominated by storm wave action and links the ichnofauna of the Tianguá Formation to the Cruziana ichnofacies. This record, so far unpublished for the Silurian deposits of the Parnaíba basin, reinforces the preferential stratigraphic distribution of Arthrophycus to the lower Paleozoic and expands the paleobiogeographic distribution of the ichnogenus in South America.