Sedimentology and taphonomy of a dinosaur bonebed from the Upper Cretaceous (Campanian) Judith River Formation of north central Montana

TL;DRAbstract

Excavations of the JDM Quarry north of Malta, Montana, have revealed a multi-individual pauspecific dinosaur bonebed.Over 1300 specimens have been removed from the quarry with over 90% of the material assignable to the Hadrosaur genus Brachylophosaurus.At least five individuals are present from two different age classes (adult and sub-adult).In addition to the vertebrate remains there is abundant plant material including a tree trunk which trends east-west.The bonebed lies within a sandstone body approximately 1.8 meters thick.The tan to brown sandstone is a friable, fine grained, quartz rich sandstone bounded above and below by gray mudstone.The sandstone body is dominated by trough cross-bedded sandstone in the lower 1.5 meter and ripple cross-lamination in the upper 0.3 meters suggesting lower flow regime conditions.The stratigraphic position of the bonebed suggests a nearshore depositional environment.

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