Download Geology of the Belly River Group

Alberta Geological Survey
4th Floor, Twin Atria Building
4999-98 Ave Edmonton, AB
www.ags.gov.ab.ca
Mapping the Belly River Group in Alberta
CANADA
As part of a new initiative to create a digital atlas of the near-surface
geology of Alberta, Alberta Geological Survey is undertaking a
regional study of the Belly River Group. The goal is to delineate
major stratigraphic surfaces within the Belly River Group at the
regional scale within approximately 500 m of the surface, where
stratigraphic data are often sparse or inconsistent. An accurate and
detailed geological framework of the near-surface bedrock is
U.S.A.
200 km
resources.
100 miles
Horseshoe Canyon (Khc),
St. Mary River (Ksm), upper
Wapiti (Kwt-u) formations
Klp
Bearpaw Formation (Kbp)
Ravenscrag
Iddesleigh
Section
Belly River Group (KBR); lower
Wapiti Formation (Kwt-l)
Oldman and Dinosaur Park formations
(undivided)
Foremost Formations
Judith R.
Pakowki (Kpa) and Lea Park (Klp) formations
49o
Simplified geological map showing the distribution of Belly River Group rocks
in Alberta and the location of wells and outcrop referred to on this poster.
Methods
Bow City structure
Picks were made on geophysical well logs using a series of closely
spaced, interlocking cross-sections. For the top of the Belly River
Group surface, a minimum of one well per township was used,
although in many areas data density greatly exceeds that number.
Approximately 550 townships were picked, with an average data
density of about 13 wells per township.
A bowl-shaped structure with a central uplift was identified in the
subsurface, several kilometres west of Bow City (Twps. 17-18,
Rges 17-18). The structure has little or no surface expression.
The diameter of the anomaly is approximately 8 km.
Wells with anomalous kelly bushing and ground-elevation data, as
well as directional wells, were culled from the data set.
Geostatistical methods identified regional and local statistical
outliers, which were either confirmed or removed. Where
anomalous structure was identified during preliminary modelling,
we increased data density to improve resolution.
Modelling Data
The modelled surface illustrates the regional structure on the top of
the Belly River Group in the Alberta Plains. The picks were
modelled in
software using the highly connected features
(least squares) method.
Targeted Fieldwork
Correlation uncertain
The Belly River Group comprises a westward-thickening, shallow to
nonmarine clastic succession of Campanian age situated within the
Western Canada Sedimentary Basin. In southern Alberta, the Belly
River Group is subdivided into the Foremost, Oldman, and Dinosaur
Park formations. Limited outcrop, rapid lateral facies changes, and
the heterolithic nature of the Belly River Group in east-central Alberta
hamper correlation with units exposed in southern Alberta. In
southeastern and eastern Alberta, there is a complex interfingering
between marginal to shallow-marine rocks of the Belly River Group
and marine siltstone and shale of the Lea Park Formation.
Iddesleigh section
(Dinosaur Provincial Park; T21-R10W4)
Measured Section
Bearpaw
Formation
Lethbridge
coal zone
Structure map of the top of the Belly River Group showing the bowl-shaped
Bow City structure. The surface is truncated at the approximate outcrop edge of
the top of the Belly River Group. Contour interval is 5 m.
Structure map of the top of the Belly River Group. Contour interval is 50 m.
Black outline shows the location of the Bow City structure.
Lower part of Iddesleigh section (right) showing the contact between the
Oldman Formation and the Dinosaur Park Formation (yellow dashed line).
Outcrop is approximately 40 m high.
The identification of the Bow City structure highlights the
sensitivity of the method used in this study and the existence of
undiscovered structural features within the shallow (0-500 m)
bedrock of Alberta. Continued mapping is needed to define
structural elements and to develop an accurate and internally
consistent geological framework for the shallow bedrock of Alberta.
Alberta Geological Survey staff performed targeted fieldwork on
representative sections to correlate outcrop sections with
geophysical well logs. A hand-held spectrometer was used to
create outcrop gamma-ray curves.
00/08-03-020-10W4/0
Geology of the Belly River Group
Low-angle reverse faults located approximately 120 km to the
east of the deformed belt have been mapped locally at the surface
along the Bow River north of the Bow City structure. Near the
central uplift, an outlier of Oldman Formation (undivided) rocks,
surrounded by overlying rocks of the Bearpaw Formation, has
been mapped previously.
metres above sea-level
Paul Glombick, Clastic Stratigrapher Christopher Banks, Clastic Stratigrapher
Ben Hathway, Clastic Stratigrapher
Duncan Hay, Clastic Stratigrapher
Shilong Mei, Geologist
Glen Prior, Geologist
The structure map for the top of the Belly River Group illustrates the
major structural elements in the southern Alberta segment of the
Western Canada Sedimentary Basin. The Belly River Group and
overlying strata have been eroded over most of southeastern
Alberta, where uplift along the Sweetgrass Arch has occurred.
Alberta Geological Survey has created an internally consistent,
high-resolution, three-dimensional geological surface, based on
an average data density of approximately 13 wells per township,
for the top of the Belly River Group in southeastern Alberta.
Stratigraphic knowledge obtained by geological measurement
of outcrop sections, supplemented by outcrop
gamma-ray logging, has been incorporated
into the subsurface interpretive work.