The Mountain Geologist

• Year: 2004
• Title: The Mountain Geologist
• Author: Rocky Mountain Association of Geologists
• Description: October 2004, Volume 41, Number 4
• Publications - Doc Type: Other

Peter E. Barkmann
Aquifer Terminology
8000 DAWSON
BUTTE
7000 Dawson Aquifer
Denver Aquifer
J.: J
Arapahoe Aquifer
600©
-
E.1
cc
1 1 — - --
w 5000 _
4000
A
Figure 2. A. The principal aquifers of the Denver Basin aquifer system consist of interbedded sandstone, conglomerate and shale that have
been subdivided into four principal aquifers separated by specific shale beds identified in geophysical logs. B. Recent stratigraphic inter-
pretations of the Denver Basin subdivide the synorogenic sediments into two primary units, D1 and D2. Detailed analysis of geophysical
logs from hundreds of water wells further reveals great lateral variability in the sediments with coarser grains near the sediment source to
the west grading to finer - grained shaly sediments across the basin to the east. From Raynolds, 2002.
in. the characteristics of the sediments filling the basin.
Generally, the coarser - grained sediments found closer to
the source on the west give way eastward across the Basin
to finer- grained, shale- dominated sediments (Raynolds,
2002). Figure 2B illustrates this horizontal variability. This
relationship is also apparent in net saturated sand and
transmissivity maps of the Basin (Topper et al., 2003)• Fur-
thermore, detailed paleontological work combined with
The Rocky Mountain Association of Geologists 172
mapping of well - developed soil horizons (paleosols)
within the sedimentary package in the years following the
statutory definition of the Denver Basin aquifers has led to
a new interpretation delineating the synorogenic sequence
into two primary sedimentary packages identified as the
D1 and D2 sequences (Raynolds, 2002).
Two critical characteristics influencing the hydrologic
behavior of the aquifer system are the relative proportion