Alluvial Fan
Formation and Sedimentation Rates
OBJECTIVE:
To determine rates of sedimentation, within the CNR
alluvial fan, for the past 10,000 years based on volume and three dimensional
extent of four separate sedimentary units.
DESCRIPTION:
Background:
The CNR alluvial fan in the Tiger Hills, south central
Manitoba, is one of four locations being investigated by a multidisciplinary
project, the Study of Cultural Adaptations in the Canadian Prairie Ecozone
(SCAPE). SCAPE is concerned with
studying the natural and physical environment, the cultural landscape, and the
use of the environment by human groups in ecologically diverse areas in the
Canadian Prairie. The goals of the
project are to identify environmental and geomorphological processes contributing
to the ecological complexity of the research localities through time. Results
of previous SCAPE research indicate sedimentary deposits suitable for
preservation of post-glacial paleoenvironmental signals are scarce in the Tiger
Hills. With the lack of
late-Pleistocene (13,000-10,000 yrs. BP)/early-Holocene (10,000-7,500 yrs. BP)
sediment is a paucity of Paleoindian and early archaic well-stratified
archaeological sites dating from the period between 10000 and 5000 BP. Without a stratigraphic record little can be
discerned about the Late Pleistocene and early Holocene environment. It is most likely that the only locations in
which a full Holocene stratigraphic record for the Tiger Hills may exist, is
within alluvial fans located in the Pembina Trench, on the southern margin of
the Tiger Hills. In the summer of 2001
sixteen 7cm Geoprobe cores were taken from the CNR alluvial fan arranged in
three transects radiating from an arbitrary datum near the fan apex. By
identifying periods of fan stability, indicated by buried soils, and
instability, identified as general stratigraphic units, one may be able to
estimate sedimentation rates across the fan surface based on relative
correlation of soils to a regional temporal framework of landscape stability
and instability.
Study
Area:
The CNR alluvial fan is located along the south-facing
slope, of the north side, of the Pembina Trench, that comprises
the southern boundary of The Tiger Hills end moraine complex (Tw. 6 & 7 N.,
R. 17 & 18), south central Manitoba. The alluvial fan is a low angle fan,
with a slope of >1 degree. The fan
is ~ 500 m across and is fed by an active trunk stream, which drains the upland
area of the Tiger Hills. The
Tiger Hills are a forested upland, composed of hummocky end moraine and related
terminal Late-Pleistocene landforms.
The Pembina Trench is one of several large, deeply incised,
late-Pleistocene meltwater channels that occur within the Canadian prairies and
facilitated the catastrophic drainage of several glacial lakes into Glacial
Lake Agassiz.
Proposed
Tasks:
The first task is to interpolate the modern fan surface
from differential GPS points.
Measurements will be made concerning fan surficial area, volume, slope
and probable extent of the fan. Using
the present fan surface and depth measurement of buried soils past stable fan
surfaces will be interpolated. The top
and bottom extents of each statigraphic unit will be interpolated from the
cores and the theoretical edge of the fan defined previously. Volume will be
calculated from the resulting coverages of each stratigraphic unit. Spatial extent will be displayed to help
identify possible patterns of autocyclic switching. Rates of sedimentation will then be calculated across the fan
using buried soils as indicators of periods of negligible sedimentation.
Justin
Rogers: Saab93@msn.com