Field Trips 2021 Cretaceous Trackways and the Boulder-Weld Allochthon

2021 Colorado Scientific Society Fall Field Trip

On Saturday, September 25th and Saturday, October 2nd, 2021

Toe Thrusts and Turtle Toes – Trackways and Tectonics of the Boulder-Weld Allochthon

Boulder Open Space and Mountain Parks, Cherryvale and White Rocks Properties

Trip Leaders: Sue Hirschfeld, Beth Simmons, Bruce Trudgill, Bob Raynolds and Ned Sterne

turtle toes
turtle toes

The field trip highlighted the recent discovery at Cherryvale of dinosaur and non-dinosaur fossil tracks in floodplain deposits of the Laramie Formation, as laid down along the shoreline of the retreating Western Interior Seaway at 68-69 Ma. The trackways occur among the historical workings of the Boulder-Weld coal field, which date as far back as 1859.

toe thrust
Bob Raynolds on a toe thrust

The field trip also featured new structural interpretations of the Boulder-Weld Allochthon, the 216 mi2 remnant of a once larger feature, that moved east up to two miles from the flank of the Front Range into the western part of the Denver Basin. Excellent outcrop exposures and subsurface well control in the Cherryvale and White Rocks areas reveal thrust and normal faults developed above the basal decollement of the allochthon as it ramped 900 feet up-section between bedding-parallel detachments in the Upper Transition Member of the Pierre Shale.

This one-day field trip was on Saturday September 25th and repeated on Saturday October 2nd.

  • The field trips started at 8:30 a.m. at Eldorado Park and Ride at the junction of Marshall Road (Colo. 170) and Colo. 93, south of Boulder. They ended at 4:00 p.m. in the Heatherwood neighborhood east of Boulder.
  • Carpooling is encouraged for access from Cherryvale Road. There isn’t enough parking for everyone to come in their own car.
  • The trip requires walking on unimproved social trails over gently rolling terrain with a few short steep grades.
  • Note: The White Rocks area we visited in the afternoon is protected City of Boulder open space.  Access is restricted to small groups who have pre-registered with the City of Boulder Open Space and Mountain Parks.

Flyer about 2021 CSS Fall_Field_Trip, Cretaceous_Tracks_and_Boulder_Weld_allochthon

Papers about the the Cherryvale tracksite and the Boulder-Weld allochthon

These articles have more information about the Cherryvale tracksite and the Boulder-Weld allochthon.

A New Dinosaur Track Locality in the Late Cretaceous (Maastrichtian) Laramie Formation of Colorado (12 MB) by Martin Lockley, Beth Simmons, and Sue Hirschfeld

The Non-Dinosaur Tracks at the Late Cretaceous Cherryvale Tracksite, Colorado (14 MB) by Sue Ellen Hirschfeld and Beth Simmons

2019 Year End Report on Geology of White Rocks Open Space (14 MB) by Edward J. (Ned) Sterne and Robert G. Raynolds

Structure and genesis of the Boulder-Weld allochthon, Denver Basin, Colorado – Gravity slide or Laramide thrust sheet? (6 MB) by Edward J. (Ned) Sterne

These White Rocks posters (4 MB) by Ned Sterne show more details about the Boulder-Weld allochthon.

Pictures of field trip to see Cretaceous tracks above Marshall and Boulder-Weld allochthon at White Rocks on Oct. 2, 2021 by Lewis Kleinhans.

Lewis Kleinhans’ pictures include:

Saurexallopus track above Cherryvale Road, near Marshall. See Lockley, Simmons, and Hirschfeld, 2018 (above).
Saurexallopus track with three slender toes above Cherryvale Road, near Marshall. See Lockley, Simmons, and Hirschfeld, 2018 (above).
Big fault slickenline in White Rocks. See Ned Sterne's White Rocks posters (above).
Big fault slickenline in White Rocks. See Ned Sterne’s White Rocks posters (above).

For a higher resolution image of above image, see: Big fault slickenlines (large).

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