[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Forthcoming Cretaceous Research articles


The following are posted on the Forthcoming Papers section of Cretaceous
Research. I don't think these have been mentioned on the list yet:

Dinosaur remains from the Lower Cretaceous of the Chubut Group, Argentina

Oliver W. M. Rauhut, Gerardo Cladera, Patricia Vickers-Rich and Thomas H.

Some fragmentary dinosaur remains from the uppermost Hauterivian?Barremian
La Paloma Member of the Cerro Barcino Formation of northern Chubut,
Argentina are described. Together with the fauna from the La Amarga
Formation of Neuquén, Argentina, this material represent the oldest known
Cretaceous dinosaur fauna from South America. It includes remains of a
probable titanosaurian sauropod and an abelisaurian, probable abelisaurid,
theropod. This is the oldest record of titanosaurs from South America and
the oldest record of abelisaurids globally. The presence of both
small-bodied noasaurids in the La Amarga Formation and medium-sized?large
abelisaurids in the Cerro Barcino Formation, in the middle Lower Cretaceous
of Argentina, indicates that abelisaurian diversification began well before
the final fragmentation of Gondwana. Whereas this explains the wide
distribution of abelisaurs in the Late Cretaceous, reasons other than
vicariance must be invoked for their apparent absence in the `middle'
Cretaceous of Africa.


Depositional environments and processes in Upper Cretaceous nonmarine and
marine sediments, Ocean Point dinosaur locality, North Slope, Alaska

R. Lawrence Phillips

A 178-m-thick stratigraphic section exposed along the lower Colville River
in northern Alaska, near Ocean Point, represents the uppermost part of a
1500 m Upper Cretaceous stratigraphic section. Strata exposed at Ocean Point
are assigned to the Prince Creek and Schrader Bluff formations. Three major
depositional environments are identified consisting, in ascending order, of
floodplain, interdistributary-bay, and shallow-marine shelf.

Nonmarine strata, comprising the lower 140 m of this section, consist of
fluvial distributaries, overbank sediments, tephra beds, organic-rich beds,
and vertebrate remains. Tephras yield isotopic ages between 68 and 72.9 Ma,
generally consistent with paleontologic ages of late Campanian?Maastrichtian
determined from dinosaur remains, pollen, foraminifers, and ostracodes.

Meandering low-energy rivers on a low-gradient, low-relief floodplain
carried a suspended-sediment load. The rivers formed multistoried channel
deposits (channels to 10 m deep) as well as solitary channel deposits
(channels 2?5 m deep). Extensive overbank deposits resulting from episodic
flooding formed fining-upward strata on the floodplain. The fining-upward
strata are interbedded with tephra and beds of organic-rich sediment.
Vertical-accretion deposits containing abundant roots indicate a sheet flood
origin for many beds. Vertebrate and nonmarine invertebrate fossils along
with plant debris were locally concentrated in the floodplain sediment.
Deciduous conifers as well as abundant wetland plants, such as ferns,
horsetails, and mosses, covered the coastal plain. Dinosaur skeletal remains
have been found concentrated in floodplain sediments in organic-rich bone
beds and as isolated bones in fluvial channel deposits in at least nine
separate horizons within a 100-m-thick interval. Arenaceous foraminifers in
some organic-rich beds and shallow fluvial distributaries indicate a lower
coastal plain environment with marginal marine (bay) influence.

Marginal marine strata representing interdistributary bay deposits overlie
the nonmarine beds and comprise about 15 m of section. Extensive vegetated
sand flats, shoals, and shallow channels overlain by shallow bay deposits
(less than 7 m deep), containing storm-generated strata characterize the
marginal marine beds. Abundant bioturbation and roots characterize the
stratigraphic lowest bay deposits; bioturbated sediment, pelecypods,
barnacles, and benthic microfossils are found in the overlying bay storm
deposits. The sediments abruptly change upward from hummocky
cross-stratified bay deposits to a muddy marsh deposit containing shallow
organic-rich channels to prograding nonmarine to marginal marine beds.

Transgressive, abundantly fossiliferous shallow-marine strata more than 13 m
thick comprise the uppermost exposures at Ocean Point. The marine beds
overlie nonmarine and bay strata and represent an environment dominated
episodically by storms. The age of the marginal marine and marine beds is
late Maastrichtian based on pollen.


Environments of Mid-Cretaceous Saharan dinosaurs

Dale A. Russell, and Michael A. Paeslerb

Recent studies of the oceanic record suggest that the Earth was a global
greenhouse during middle Cretaceous time. A review of topographic,
sedimentary and biologic data pertaining to terrestrial mid-Cretaceous
equatorial environments broadly supports the climatic inferences of marine
studies. In particular, analyses of widely-occurring low latitude Saharan
sediments support the Cretaceous greenhouse hypothesis. In comparison to
marine ecosystems, terrestrial ecosystems respond more sensitively to
atmospherically transported heat and nutrients because of the more tenuous
presence of the hydrosphere on land. Indeed, the morphologies of terrestrial
biota suggest that: (1) equatorial mid-Cretaceous climates were episodic
rather than seasonal; (2) convective storms although infrequent were
violent; and (3) a moist intertropical convergence zone was absent.
Cretaceous atmospheric dynamics apparently differed importantly from those
of the present. Circumstantial evidence suggests that (1) higher atmospheric
carbon dioxide levels probably stimulated the emission of other greenhouse
gases; and (2) higher humidity levels reduced diurnal temperature variations
but impaired evaporative thermoregulatory mechanisms. That terrestrial
ecosystems withstood greenhouse conditions in low latitudes as well as they
did underscores the adaptability of terrestrial life. Analogies for future
environmental stresses and responses, whether anthropogenic or resulting
from other causes, might be found in the terrestrial record of the
Cretaceous equatorial zone.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796