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[dinosaur] A reminder that lithostratigraphy does not equal geochronology

The recent discussion about Quaesitosaurus is a good opportunity to remind 
people on the list:

Formations are lithostratigraphic units: bodies of rocks. Their boundaries 
represent when the environment shifted from one condition
to another. This shift is NOT going to happen everywhere at the same time: 
thus, the upper boundary of one formation will not
represent the same time period everywhere, and the lower boundary will 
similarly not represent the same time period everywhere.

Similarly, you will have different formations being deposited simultaneously in 
a region based on the local environment at any given
time. As the environments shift, the lateral boundaries between the two 
formations will move back and forth.

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu         Phone: 301-405-4084
Senior Lecturer, Vertebrate Paleontology
Office: Geology 4106, 8000 Regents Dr., College Park MD 20742
Dept. of Geology, University of Maryland
Phone: 301-405-6965
Fax: 301-314-9661              

Faculty Director, Science & Global Change Program, College Park Scholars
Office: Centreville 1216, 4243 Valley Dr., College Park MD 20742
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        8000 Regents Drive
                        University of Maryland
                        College Park, MD 20742-4211 USA