2008 Michigan Academy Meeting - Holocene alluvial fill in a small
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Transcript of 2008 Michigan Academy Meeting - Holocene alluvial fill in a small
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
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3.0
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0 10 20 30 40 50
mass Xlf (x 10-8 m3/kg)
Dep
th (
m)
0.0
0.5
1.0
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2.0
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3.0
3.5
0 5 10 15 20 25
% carbonates
0.0
0.5
1.0
1.5
2.0
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3.0
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0 5 10 15 20 25
% organic
0.0
0.5
1.0
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2.0
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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.