RE: Portlandian

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: Mike Keesey [mailto:tmk@dinosaur.umbc.edu]
> Anyone know what time period "Portlandian" refers to? (Or is it a time
> period?)
>

The Portlandian Stage is part of an alternative English geochronology for
the Late Jurassic-Early Cretaceous system.

The International system goes: Kimmeridgian - Tithonian - Berriasian -
Valanginian, with the J-K boundary at the base of the Berriasian.

The alternative English system goes: Lower Kimmeridigian (= Kimmeridgian in
the International system), Upper Kimmeridgian ( = Lower, Middle, and part of
the Upper Tithonian), Portlandian ( = rest of Upper Tithonian and Lower
Berriasian), Ryanzanian (= Middle and Upper Berriasian, and lowermost
Valanginian), and Valangianian.  The J-K boundary is at the top of the
Portlandian.

To make matters worse, the Russians sometimes use the term Volgian for a
unit equivalent to the Tithonian and Lower Berriasian of the International
system (or the Upper Kimmeridgian and  Portlandian of the English).

Fun, huh?

Happy New Year, folks!

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-314-7843