USNM 16002g, Tinu Formation, Oaxaca, Mexico - Robison and Pantoja-Alor 1968 (Ordovician of Mexico)

Where: Oaxaca, Mexico (17.0° N, 96.6° W: paleocoordinates 16.8° S, 105.5° W)

• outcrop-level geographic resolution

When: Saukia zone, lower Member (Tinu Formation), Tremadoc (485.4 - 477.7 Ma)

• fauna are from the lower 60 meters of the formation

• member-level stratigraphic resolution

Environment/lithology: shelly/skeletal limestone and shale

• General for fossiliferous portion of member: Interbedded thin to medium bedded dark fossiliferous (bioclastic/skeletal) limestone and thin to medium beds of light, generally unfossiliferous shale.

Collection methods: The fauna correlate (approximately) with the North American Saukia Zone (Late Cambrian), and with the lower Tremadoc of Europe and South America. However, probably less than 20% of the trilobite genera from the Tinu Formation have been reported from rocks either younger or older than the Tremadoc. On an end note, Robison talks of the differing opinions on the relative age placement of the Saukia Zone fauna. Conclusions are that the European Saukia Zone and those found in Mexico have an age of Early Ordovician and not Late Cambrian as determied for the "North American Saukia Zone".

Primary reference: R. A. Robison and J. Pantoja-Alor. 1968. Tremadocian trilobites from the Nochixtlan Region, Oaxaca, Mexico. Journal of Paleontology 42(3):767-800 [M. Patzkowsky/P. Borkow]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 9849: authorized by Mark Patzkowsky, entered by Phil Borkow on 24.01.2001

Creative Commons license: CC BY (attribution)

Taxonomic list

• The taxonomic list only includes trilobites and fauna important for future biostratigraphy: cephalopods (16000_), conodonts (16000_,16001_,16002_), gastropods (16001_, 16002_). The section of study also includes echinoderms, sponges, ostracodes, and problematica, but there placement in the individual collections is not documented.
 Asaphida - Asaphidae
Asaphellus communis Robison and Pantoja-Alor 1968 trilobite
 Ptychopariida - Shumardiidae
Shumardia ctenata n. sp. Robison and Pantoja-Alor 1968 trilobite
4 pygidia
Shumardia alata n. sp. Robison and Pantoja-Alor 1968 trilobite
10 pygidia and 100 cranidia