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Field Location: Gateway, Colorado (click on link to see
Geologic Feature: Gateway Fan.
Necessary Background Information: None
Geologic Problem: What is the origin of the Gateway Fan?
Rock Units Exposed: Pennsylvanian to Permian coarse clastics shed from
the Uncompahgre Uplift.
Skills: Analysis of clastic sedimentary rocks (grain size,
composition, depositional environment, flow characteristics), introduction to
use of Brunton. Continue use of topographic maps. Refine methods
for planning a field study.
Other Questions to Consider: 1) What is the source of the rock
that makes up the Gateway Fan? 2) How does the character of beds within
the fan change with distance from the Uncompahgre? 3) What process or
processes were responsible for deposition of the rocks adjacent to the
Uncompahgre? 4) How do the light red and purple layers differ from one
another near the town of Gateway? Do they contain different sizes of
grains? Do they contain different sedimentary structures? 5)
Which sedimentary structures give information about the direction of flow of
the fluid that formed the structures? What directions of flow are
indicated by the different sedimentary structures?
Anticipated Outcomes: Identify cross lamination, cross bedding, pebble
imbrication, mudcracks, sole marks, and fluvial, mudflow and debris flow
deposits. Use a Brunton to determine paleocurrent orientations.
Plot data on topographic maps. Develop a plan for a field study.