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Carnian/Norian boundary at Berlin-Ichthyosaur State Park (Upper Triassic, Nevada)



Ben Creisler
bcreisler@gmail.com

A new online paper:


Marco Balini, James F. Jenks, Riccardo Martin, Christopher A.
McRoberts, Michael J. Orchard & Norman J. Silberling (2014)
The Carnian/Norian boundary succession at Berlin-Ichthyosaur State
Park (Upper Triassic, central Nevada, USA).
Paläontologische Zeitschrift (advance online publication)
DOI: 10.1007/s12542-014-0244-2
http://link.springer.com/article/10.1007/s12542-014-0244-2


The Upper Carnian-Lower Norian (Upper Triassic) Luning Formation at
Berlin-Ichthyosaur State Park (BISP) in central NV (USA) has been
sampled using for the first time the bed-by-bed approach for
ammonoids, pelagic bivalves, and conodonts, more than 60 years after
its first description by Silberling (U.S. Geological Survey
Professional Paper 322: 1–63, 1959). BISP is historically important
for the definition of the uppermost Carnian of the North American
Triassic chronostratigraphic scale and is known worldwide as one of
the most important ichthyosaur Fossil-Lagerstätte because of its
extraordinary record of 37 articulated, large-sized specimens of
Shonisaurus popularis. Nearly 190 ammonoids were collected from two
stratigraphic sections, documenting all the latest Carnian to Early
Norian ammonoid faunas previously described by Silberling. Halobiids
were collected from five levels, and the first report of conodonts
from BISP includes faunas from 13 levels. The ~340-m thick Brick Pile
section, the most complete in the study area, includes the uppermost
Carnian Macrolobatus Zone, which provides conodont faunas of the lower
primitia zone and Halobia septentrionalis. The 200-m thick lowermost
Norian Kerri Zone, which begins 52 m above the Macrolobatus Zone,
yields conodonts of the upper primitia zone in its lower part,
together with H. cf. beyrichi and H. cf. selwyni. The
ichthyosaur-bearing interval, whose stratigraphic position has been
interpreted quite differently by previous authors, is documented in
the uppermost Carnian Macrolobatus Zone and is characterized by rich
Tropites-dominated ammonoid faunas and by the onset of Halobia. All
models proposed by various workers to explain the unusual ichthyosaur
record are discussed and an additional explanation for the main
ichthyosaur-bearing bed is proposed. The new hypothesis is that a
harmful algal bloom (HAB) may have been the trigger for the mass
mortality recorded in this level. Although the C/N boundary in the
Brick Pile section lies within a 52 m interval that presently lacks
paleontologic data, this succession is included in a small group of
sections that are expected to contribute to the definition of the GSSP
of the Norian stage. Correlation of the Brick Pile section with the
best Carnian/Norian sections in northeastern British Columbia is
discussed. Compared to the British Columbia Juvavites Cove and the
GSSP candidate Black Bear Ridge sections, the Brick Pile section
exhibits an ammonoid and Halobia record that is slightly more similar
to that of the Tethyan sections. Correlation of the Brick Pile section
with the second GSSP candidate Pizzo Mondello (Sicily, Italy) well
demonstrates the significant problems encountered in calibration of
the Tethyan and North American scales.