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Microbial structures and dinosaur trackways from a Cretaceous coastal environment (Dakota Group, Colorado, U.S.A.)

Nora Noffke, James Hagadorn and Sam Bartlett
Microbial structures and dinosaur trackways from a Cretaceous coastal environment (Dakota Group, Colorado, U.S.A.)
Journal of Sedimentary Research (November 2019) 89 (11): 1096-1108

Abstract

Microbially induced sedimentary structures may help preserve unique glimpses of ancient shoreline habitats, but are little known from Mesozoic epicontinental settings. To help fill this knowledge gap, we describe a diverse suite of microbial structures from the Upper Cretaceous "J" Sandstone (South Platte Formation, Dakota Group) that are spectacularly exposed at Dinosaur Ridge in Morrison, Colorado, USA. Structures include "tattered" bed surfaces and ferruginous sand chips in supratidal flat facies. A large over-flip structure is preserved in a channel locally known as Crocodile Creek. In upper-intertidal facies, multidirectional ripple marks occur. Perhaps the most well-known microbial structures are exposed on extensive bedding surfaces known as "Slimy Beach," where lower supratidal-flat facies are dominated by decimeter-scale erosional remnants and pockets. Morphologies and superposition of the structures allows identification of three generations of erosional pockets. Generation A of these erosional pockets exhibit size similarities to ornithomimid, sauropod, and ornithopod dinosaur tracks from adjacent bedding planes, raising the question of whether initial disturbance of the mat-bound surface could have been from track making. Generation B erosional pockets are older and record continuous erosion of the initial pockets until they were eventually overgrown and sealed by microbial mats. Generation C pockets are the oldest ones, exposing wide areas of barren sediment that could not be overgrown by microbial mats anymore. In concert, the microbial structures point to seasonally variable meteorological conditions along the coastline of the Western Interior Seaway and indicate that the "Slimy Beach" bedding plane represents a multi-year record of dinosaur locomotion.


ISSN: 1527-1404
EISSN: 1938-3681
Serial Title: Journal of Sedimentary Research
Serial Volume: 89
Serial Issue: 11
Title: Microbial structures and dinosaur trackways from a Cretaceous coastal environment (Dakota Group, Colorado, U.S.A.)
Affiliation: Old Dominion University, Department of Ocean, Earth and Atmospheric Sciences, Norfolk, VA, United States
Pages: 1096-1108
Published: 201911
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 56
Accession Number: 2020-001094
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects.
N39°39'13" - N39°39'13", W105°11'28" - W105°11'28"
Secondary Affiliation: Denver Museum of Nature and Science, USA, United StatesFriends of Dinosaur Ridge, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 2020
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