2008 michigan academy meeting - holocene alluvial fill in a small
DESCRIPTION
A presentation given at the 2008 Michigan Academy of Sciences MeetingTRANSCRIPT
Welcome
Geological Sciences Section
2008 Meeting at Western Michigan University
Michigan Academy of Sciences
Arts, and Letters
Holocene alluvial fill in a small
tributary of the Grand River
Ottawa County, Michigan
Patrick M. Colgan
Grand Valley State University
Allendale, Michigan
Michigan
Ottawa County
10 kilometers N
Study
siteGrand
Rapids
1 km
end
moraine
GVSU
Campus
500 meters
N
Little Mac Ravine
Gra
nd R
iver
100 meters N
alluvial plain
Gra
nd R
iver
ravine head
ravine head
ravine head
alluvial fan
fine silty sand (lacustrine)
diamicton
(basal till)
Marshall Sandstone
~ 480-510 feet
clay, silt and fine sand (lacustrine)ele
vati
on
(ft
)
distance (meters)S N
vertical exaggeration ~16:1
North to South Cross Section across GVSU Campus
diamicton (basal till)?
100 meters
coring
site
GV-2
GV-5
GV-9
N
Environmental geology students in Little Mac Ravine.
Setting up the vibracoring tripod.
Preparing to recover a core
Environmental geology students sampling cores.
Wood in core GV-7 overlying unconformity
up
Unconformity at ~1.85 meters depth in core GV-7
Silty and claygravel
and wood
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 10 20 30 40 50
mass Xlf (x 10-8 m3/kg)
Dep
th (
m)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 5 10 15 20 25
% carbonates
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 5 10 15 20 25
% organic
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
Lithology
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
LithologyInterpretation
5070 ± 80 BP
Up
pe
r fi
llL
ow
er
fill
Core GV-2
Depth to unconformity is ~ 2.3 to 2.5 meters
180 ± 40 BP
Downstream Site
coarser
Wood in core GV-2
Radiocarbon age:
5070 ± 80 BP
5920-5720 Cal BP
Interpretation
Core GV-5
Up
pe
r fi
llL
ow
er
fill
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 10 20 30 40 50
mass Xlf (x 10-8 m3/kg)
Dep
th (
m)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 5 10 15 20 25
% carbonates
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 5 10 15
% organic/%moisture
Depth to unconformity is ~ 1.9 meters
Upstream Site
0.0
0.5
1.0
1.5
2.0
2.5
0 10 20 30 40 50
mass Xlf (x 10-8 m3/kg)D
ep
th (
m)
0.0
0.5
1.0
1.5
2.0
2.5
0 5 10 15 20 25
% carbonates
0.0
0.5
1.0
1.5
2.0
2.5
0 5 10 15 20 25
% organic Interpretation
Core GV-9
Up
pe
r fi
llL
ow
er
fill
Depth to unconformity is ~ 1.6 meters
Valley Side Site
Source: Anthony Rodriguez
0.87 meters
Alluvial Fill Properties
• Upper Fill
– Texture is variable
– Organic % is moderate
to high
– Carbonate % is low
– Massive and
laminated fines and
sorted sand and
gravel.
• Lower Fill
– Texture is silt and clay
– Organic % is low to
moderate
– Carbonate % is high
– Mainly massive to
finely laminated.
Radiocarbon Analyses From Alluvial Wood – Little Mac Ravine
Sample core analysis C-14 Age Calibrated Years
Beta-217917 stream C 180 ± 40 BP 290-260 Cal BP upper fill
(GVSU-1) exposure (1660-1680 AD)
wood near GV-1 220-140 Cal BP
(1730-1810 AD)
20-0 Cal BP
(1930-1950)
Beta- 235467 GV-7 C 190 ± 50 BP 310-60 Cal BP upper fill
(GVSU-4) (1640-1890 AD)
Wood 40-0 Cal BP
(1910-1950 AD)
Beta-231594 GV-3 AMS 320 ± 40 BP 480 to 310 Cal BP upper fill
(GVSU-3) (1470-1640 AD)
Wood
Beta-223048 GV-2 C 5070 ± 80 BP 5920-5720 Cal BP lower fill
(GVSU-2) (3960-3770 BC)
Wood
C = Conventional radiocarbon method
AMS = accelerator mass spectrometry method
Conclusions
• At least two alluvial fill units are present.
– Older fill - middle Holocene or older?
– Younger fill - Post-settlement ?
• Younger fill is from 0.5 to 2.5 meters thick
over most of the valley.
• Suggests a large change in sedimentation
rates since settlement.
Acknowledgements
• Thanks to the students in environmental
geology classes who helped with the field
and lab work.
• GVSU Geology students Rhiannon
Mulligan, Sarah Nagorsen and Anthony
Rodriguez who worked on research
projects in past geomorphology classes.