“Leonardo,” a Mummified Brachylophosaurus (Ornithischia: Hadrosauridae) from the Judith River Formation of Montana

2018 ◽  
pp. 117-134 ◽  
Author(s):  
Nate L. Murphy ◽  
David Trexler ◽  
Mark Thompson
Keyword(s):  
Judith River Formation

Isotaphonomy in concept and practice: an exploration of vertebrate microfossil bonebeds in the Upper Cretaceous (Campanian) Judith River Formation, north-central Montana

Paleobiology ◽  
2017 ◽  
Vol 43 (2) ◽  
pp. 248-273 ◽  
Author(s):  
Raymond R. Rogers ◽  
Matthew T. Carrano ◽  
Kristina A. Curry Rogers ◽  
Magaly Perez ◽  
Anik K. Regan
Keyword(s):  
Upper Cretaceous ◽  
Statistical Tests ◽  
Sampling Strategies ◽  
North Central ◽  
Wetland Ecosystems ◽  
Future Studies ◽  
Size And Shape ◽  
Definition Of ◽  
Central Montana ◽  
Judith River Formation

AbstractVertebrate microfossil bonebeds (VMBs)—localized concentrations of small resilient vertebrate hard parts—are commonly studied to recover otherwise rarely found small-bodied taxa, and to document relative taxonomic abundance and species richness in ancient vertebrate communities. Analyses of taphonomic comparability among VMBs have often found significant differences in size and shape distributions, and thus considered them to be non-isotaphonomic. Such outcomes of “strict” statistical tests of isotaphonomy suggest discouraging limits on the potential for broad, comparative paleoecological reconstruction using VMBs. Yet it is not surprising that sensitive statistical tests highlight variations among VMB sites, especially given the general lack of clarity with regard to the definition of “strict” isotaphonomic comparability. We rigorously sampled and compared six VMB localities representing two distinct paleoenvironments (channel and pond/lake) of the Upper Cretaceous Judith River Formation to evaluate biases related to sampling strategies and depositional context. Few defining distinctions in bioclast size and shape are evident in surface collections, and most site-to-site comparisons of sieved collections are indistinguishable (p≤0.003). These results provide a strong case for taphonomic equivalence among the majority of Judith River VMBs, and bode well for future studies of paleoecology, particularly in relation to investigations of faunal membership and community structure in Late Cretaceous wetland ecosystems. The taphonomic comparability of pond/lake and channel-hosted VMBs in the Judith River Formation is also consistent with a formative model that contends that channel-hosted VMBs were reworked from pre-existing pond/lake assemblages, and thus share taphonomic history.

40Ar/39Ar age and correlation of the nonmarine Two Medicine Formation (Upper Cretaceous), northwestern Montana, U.S.A.

1993 ◽  
Vol 30 (5) ◽  
pp. 1066-1075 ◽  
Author(s):  
Raymond R. Rogers ◽  
Carl C. Swisher III ◽  
John R. Horner
Keyword(s):  
Total Duration ◽  
Direct Determination ◽  
Regional Correlation ◽  
New Radio ◽  
Northwestern Montana ◽  
Judith River Formation ◽  
First Time ◽  
Provincial Park ◽  
Ammonite Zones

The age of the nonmarine Two Medicine Formation of northwestern Montana is currently based upon correlations with K–Ar-dated Western Interior ammonite zones. 40Ar/39Ar dating of biotite and plagioclase separated from four bentonites and one crystal-rich tuff permits for the first time direct determination of the age of Two Medicine strata. Biotite and plagioclase from a bentonite 10 m below the top of the Two Medicine Formation yield concordant 40Ar/39Ar ages of 74 Ma, while biotite and plagioclase from two bentonites and a crystal-rich tuff from approximately 100 m above the base of the formation cluster in age around 80 Ma. The total duration of Two Medicine deposition is estimated using these new radio-isotopic ages via extrapolation of an average rock accumulation rate.The new 40Ar/39Ar ages facilitate regional correlation of the dinosaur-dominated paleofauna recovered from the Two Medicine Formation, and help constrain the timing of the Claggett and Bearpaw transgressions. The ages support correlation of the richly fossiliferous upper lithofacies suite of the Two Medicine Formation with exposures of the Judith River Formation in Dinosaur Provincial Park, Alberta, Canada. Radioisotopically dated exposures of the Judith River Formation within Montana that include important Judithian "age" mammal localities correlate approximately with middle and lower parts of the middle lithofacies suite of the Two Medicine Formation. The new 40Ar/39Ar ages further indicate that the transgressions of the Claggett and Bearpaw seas culminated within northwestern Montana at ca. 79.6 and 74.0 Ma, respectively.

The Denholm landslide, Saskatchewan. Part I: Geology

1983 ◽  
Vol 20 (2) ◽  
pp. 197-207 ◽  
Author(s):  
E. A. Christiansen
Keyword(s):  
Shear Zone ◽  
Radiocarbon Dating ◽  
Upper Cretaceous ◽  
Average Rate ◽  
Surface Expression ◽  
Recent Time ◽  
Displacement Rate ◽  
The North ◽  
Colorado Group ◽  
Judith River Formation

The Denholm landslide, whose surface is composed of scarps, ridges, and elongated depressions, is 160 m high, 2000 m wide, and up to 100 m thick. The shear zone is in silty, montomorillonitic clay of the upper part of the Lea Park Formation and Upper Colorado Group unit. The Upper Cretaceous Judith River Formation and the Quaternary Empress, Sutherland, and Saskatoon groups were affected by the landslide. Although these sediments were fractured and gravity faulted by tension when the landslide moved, they can be readily traced through the landslide, particularly the upper part. The scarps (gravity faults), ridges (horsts), and elongated depressions (grabens) are the surface expression of tension resulting from the stretching of beds during the landslide.The movement of the landslide is thought to have started when the North Saskatchewan spillway eroded to the level of the present shear zone about 11 000 years ago (established by radiocarbon dating) and is believed to have stopped in recent time. During this time, it moved about 390 m across the North Saskatchewan River alluvium at an average rate of 35 mm per year. As the landslide moved across the valley, it encountered deposition of alluvium at an average rate of about 2.4 mm per year which resulted in the curved shear zone on the alluvium. Keywords: retrogressive landslide, shale-alluvium, displacement, rate, age.

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