"Tertiary Dinosaurs" in the Nanxiong Basin are reworked from the Cretaceous

[Jose Ignacio Ruiz-Omeñaca <jigruiz@unizar.es>]

The Journal of Geology Volume 112, Number 1 (January 2004) is now available at 
http://www.journals.uchicago.edu/cgi-bin/contents?JG+v112n1

and includes this GEOLOGICAL NOTE:

Brenda J. Buck, Andrew D. Hanson, Richard A. Hengst, and Hu Shu-sheng. 2004. 
"Tertiary Dinosaurs" in the Nanxiong Basin, Southern China, are reworked from 
the Cretaceous. The Journal of Geology 112, 111-118 [ 
http://www.journals.uchicago.edu/cgi-bin/resolve?JG112107 ]

ABSTRACT: The Nanxiong and Shanghu Formations of southeastern China span the KT 
boundary interval and preserve an important paleontological record. A 1285-m 
section across the KT boundary was measured, and lithological units were 
documented and sampled. Strata were deposited in alluvial fan/playa mudflat 
environments in a highly seasonal, semiarid climate. Previous workers placed 
the KT boundary at the Nanxiong/Shanghu formational contact. The uppermost 
Nanxiong and lowermost Shanghu Formations contain an assemblage of dinosaur egg 
fragments and  Tertiary fossils, which led to the notion that dinosaurs 
survived into the Paleocene. On the basis of our results, we argue that the 
mixed KT assemblage is a result of debris flows reworking Cretaceous fossils. 
Depositionalenvironments and paleoclimate did not change significantly across 
the KT boundary.

On page 116, Buck et al say:

"Zhao et al. (2002) cite the presence of intact egg nests below the 
controversial interval. They also state that two clutches of eggs occur in the 
controversial interval. The presence of intact dinosaur egg nests in this 
interval would weaken our interpretation. However, detailed descriptions of 
stratigraphic location, egg geometries, and the sedimentology of encasing 
materials are lacking. Zhao et al. (2002) state that eggs and fragments occur 
as  heaps throughout the Nanxiong Formation. We, too, observed concentrations 
of eggshells within the mudflow deposits in the controversial interval but saw 
no intact nests or eggs. Therefore, until more detailed descriptions are 
published, all of these egg occurrences can more easily be ascribed to debris 
flow and mudflow processes than they can to Tertiary dinosaurs. We believe that 
eggs that have been cited as being Tertiary are, in fact, reworked Cretaceous 
fossils now contained within Tertiary pollen-bearing mud and debris flows."

I think that eggs and eggshells are no easily reworkables because of its 
fragility.

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Jose Ignacio Ruiz-Omeñaca
Departamento de Ciencias de la Tierra
Area de Paleontologia
Universidad de Zaragoza
E-50009 ZARAGOZA, SPAIN

tel: (+34) 976 761000 ext. 3160
fax: (+34) 976 761106
e-mail: jigruiz@unizar.es
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