Trace Fossils

PaleontologyGeology 331

Characteristics of Trace Fossils that make them valuable in Paleoecology• Long Time Range – allows rocks of widely

different ages to be compared.• Narrow Facies Range – most trace fossils

are found in their preferred environment.• No Secondary Displacement – can not be

transported like body fossils.

The behavioral classification of trace fossils, showing the major categories, and some typical examples of each. Illustrated ichnogenera are: 1, Cruziana; 2, Anomoepus; 3, Cosmorhaphe; 4, Paleodicyton; 5, Phycosiphon; 6, Zoophycos; 7, Thalassinoides; 8, Ophiomorpha; 9, Diplocraterion; 10, Gastrochaenolites; 11, Asteriacites; 12, Rusophycus. (Based on Ekdale et al. 1984.)

Cubichnia = RestingRepichnia = CrawlingPascichnia = GrazingAgrichnia = FarmingFodinichnia = Deposit FeedingDwelling = DomichniaFugichnia = Escape

Terminology for trace fossil preservation, depending on the relationship of the trace to sediment horizons. (Based on Ekdale et al. 1984.)

One trace fossil may be produced by many different organisms. Here, all the traces are resting impressions, cubichnia, of the ichnogenus Rusophycus, produced by (a) the polychaete worm Aphrodite, (b) a nassid snail, (c) a notostracan branchiopod shrimp, and (d) a trilobite. (Based on Ekdale et al. 1984.)

Freshwater

Hardgrounds and

Firmgrounds and

Shoreface

Marine

Soft marine sediments

Ichnofacies

Skolithos burrows, Miss., WV. Skolithos Ichnfacies

Formation clues: Skolithosburrows in Aladdin Sandstone,

Black Hills, SD

Skolithos trace fossils in the Cambrian of Wyoming

Arenicola, sediment casings, and it’s burrow opening

Ophiomorphagallery of burrows.

Eocene of Mississippi.

SkolithosIchnofacies

Callianassaor Ghost Shrimp

Callianassa shrimp mounds: origin of Ophiomorpha. Tidal flat, Florida Keys.

Trilobite traces, Cruziana Ichnofacies

Rusophycus, resting Cruziana, crawling

Diplichnites, walking

Arthrophycus, Silurian. Cruziana Ichnofacies

Polychaete worm

Palaeophycus, Mississippian. Cruziana Ichnofacies

Olivellites, Pennsylvanian, WV. Cruziana Ichnofacies

Rhizocorallium, Penn. WV. Cruziana Ichnofacies

Bioturbation from abundant trace fossils, Cruziana Ichnofacies,

Ordovician dolomite, Wyoming

Zoophycos, Miss., KY. Zoophycos Ichnofacies. Underside of bed.

Zoophycos

Turbidite beds in Kentucky

Escape structure, Mississippian turbidite, KY

Helminthoidea, Tertiary. Nereites Ichnofacies

Paleodictyon, Nereites Ichnofacies

Psuedofossils: Load casts, Miss., WV.

Cambrian Substrate Revolution

Ichnofabric indices for different sedimentary/ichnofacies settings. These diagrams show the proportions of sediment reworked by bioturbation, as seen in vertical section and numbered from top to bottom: 1 (no bioturbation) to 5 (intensely bioturbated). (Courtesy of Mary Droser and Duncan McIlroy.)