RE: Age Abstractions

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

> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu]On Behalf Of
> Jeff Hecht
>
> It's curious that the coauthors of previous papers that Roberto cited have 
> vanished.
>Perhaps there's a message there?
>
Probably because the co-authors eventually had a different interpretation of 
the evidence (referenced by Roberto):
http://gsa.confex.com/gsa/2003RM/finalprogram/abstract_47695.htm

NO PALEOCENE DINOSAURS IN THE SAN JUAN BASIN, NEW MEXICO
SULLIVAN, Robert M., Section of Paleontology and Geology, The State Museum of 
Pennsylvania, 300 North Street, Harrisburg, PA
17120-1026, rsullivan@state.pa.us, LUCAS, Spencer G., New Mexico Museum of Nat 
History, Albuquerque, NM 87104, and BRAMAN, Dennis,
Royal Tyrrell Museum of Palaeontology, Box 7500, Drumheller, AB T0J 0Y0, Canada
Until recently, the age of the upper part of the Kirtland Formation (De-na-zin 
and Naashoibito members) has been somewhat
problematic. Although 40Ar/39Ar dating has firmly established the age of the 
De-na-zin Member at 73.37-73.04 Ma (late Campanian),
the age of the overlying Naashoibito Member remains contentious. Some dinosaur 
taxa formerly cited as from the Naashoibito Member
(such as "Kritosaurus," Parasaurolophus and Pentaceratops) are actually from 
the underlying De-na-zin Member. Few diagnostic
dinosaur genera are known from the Naashoibito Member, and some (especially 
Torosaurus and Tyrannosaurus) rest on problematic
identifications. No radioisotopic dates are available, and only three mammal 
species have been identified from this unit. The
possible age ranges from late Campanian to late Maastrichtian, and an early 
Maastrichtian age is most likely Recent sampling of a
lignite at the top of the De-na zin Member at Barrel Springs has yielded 
conflicting palynomorph data. Fassett maintains that the
palynomorphs Momipites tenuipolis and Brevicolporites colpella indicate a 
Paleocene age for this lignite and the overlying
Naashoibito Member, which locally contains numerous (non-reworked) dinosaur 
fossils. We sampled this same lignite and did not
recover any Paleocene palynomorphs, but instead found Proteacidites retusus, P. 
thalmanni and Tricolpites microreticulatus, taxa
that are only known from the Campanian and Maaastrichtian. The presence of 
Pandaniidites typicus and Umoideipites krempi further
restrict the age of the sample to Maastrichtian. No taxa restricted to the 
Paleocene were recovered, although several species that
span the K/T boundary are also present. The suggestion of a Paleocene age for 
this lignite is also inconsistent with the presence of
numerous non-reworked dinosaur remains in overlying strata. A hadrosaur femur 
from the Ojo Alamo Sandstone near Farmington,
apparently stratigraphically above Paleocene palynomorphs, is arguably 
reworked. We conclude there is no convincing evidence of
Paleocene dinosaurs in the San Juan Basin.


                Thomas R. Holtz, Jr.
        Senior Lecturer, Vertebrate Paleontology
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
        Mailing Address:
                Building 237, Room 1117
                College Park, MD  20742

http://www.geol.umd.edu/~tholtz/
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796


> -----Original Message-----

> At 5:12 PM -0700 6/19/07, Jerry D. Harris wrote:
> >OK, so it's just an abstract (so far, not counting all that's been published 
> >on the topic previously), but:
> >
> >Fassett, J.E. 2007. The documentation of in-place dinosaur fossils in the 
> >Paleocene Ojo Alamo Sandstone and Animas
> Formation in the San Juan Basin of New Mexico and Colorado mandates a 
> paradigm shift: dinosaurs can no longer be thought
> of as absolute index fossils for end-Cretaceous strata in the Western 
> Interior of North America. New Mexico Geology 29(2):56.
> >
> >ABSTRACT: Extensive geochronologic studies of the rocks adjacent to the 
> >Cretaceous-Tertiary (K-T) interface in the San
> Juan Basin have now provided compelling data attesting to the Paleocene age 
> of the dinosaur-bearing Ojo Alamo Sandstone
> in New Mexico and the Animas Formation in Colorado. These data consist of 
> radiometric age determinations for Cretaceous
> strata underlying the K-T interface and palynologic, paleomagnetic, and 
> geochemical evidence attesting to the Paleocene
> age of the strata above the K-T interface. The identification of the 
> paleomagnetic normal interval - C29n - in the
> dinosaur-bearing lower part of the Ojo Alamo Sandstone in the southern San 
> Juan Basin at multiple localities allows for
> the precise dating of the last occurrence of Paleocene dinosaurs at the top 
> of chron C29n at 64.432 Ma.
> >    The conventional wisdom (entrenched dogma) among most geologists, and 
> > especially among vertebrate paleontologists
> has been, for more than 100 years, that all dinosaurs became extinct at the 
> end of the Cretaceous. Thus, dinosaur bone
> found in place in a formation provided indisputable evidence that the 
> formation was Cretaceous in age. Now, with the
> discovery of Paleocene dinosaurs, the paradigm of Cretaceous-only dinosaurs 
> must shift. Let us hope that this
> paradigm-shift will be a smooth and placid lateral-slip along planar fault 
> blocks rather than a grumbling, rumbling,
> herky-jerky sliding of jagged-edged, opposing sides past each other. Science 
> must always be conservative and accept such
> paradigm shifts only on the basis of the most solid evidence, however, when 
> the data do finally speak, the shift must be
> accepted by all of us who follow the data in the noble pursuit of finding out 
> how the world was made.
> >
> >
> >I'd've thought he'd put out a press release...?!?
> >
>
> --
> Jeff Hecht, science & technology writer
> jeff@jeffhecht.com  http://www.jeffhecht.com
> 525 Auburn St., Auburndale, MA 02466 USA
> v. 617-965-3834; fax 617-332-4760
>