A presentation given at the 2008 Michigan Academy of Sciences Meeting

1. Welcome
Geological Sciences Section
2008 Meeting at Western Michigan University
Michigan Academy of Sciences
Arts, and Letters

2. Holocene alluvial fill in a small
tributary of the Grand River
Ottawa County, Michigan
Patrick M. Colgan
Grand Valley State University
Allendale, Michigan

3. Ottawa County
10 kilometers N
Michigan
Study
Grand site
Rapids

4. GVSU
Campus end
moraine
1 km

5. Little Mac Ravine
Grand River
N
500 meters

6. Grand River
ravine head
alluvial plain
alluvial fan
ravine head
ravine head
100 meters N

7. North to South Cross Section across GVSU Campus
diamicton
(basal till)
elevation (ft)
fine silty sand (lacustrine)
clay, silt and fine sand (lacustrine)
diamicton (basal till)? Marshall Sandstone
~ 480-510 feet
S distance (meters) N
vertical exaggeration ~16:1

8. coring
site
GV-9 GV-2
GV-5
N
100 meters

9. Environmental geology students in Little Mac Ravine.

10. Setting up the vibracoring tripod.

12. Preparing to recover a core

13. Environmental geology students sampling cores.

14. Wood in core GV-7 overlying unconformity

15. up
Silty and clay
gravel
and wood
Unconformity at ~1.85 meters depth in core GV-7

16. Core GV-2 Downstream Site
Lithology
Lithology m ass Xlf (x 10-8 m 3/kg) % organic % carbonates
Interpretation
00
coarser 0 10 20 30 40 50 0 5 10 15 20 25 0 5 10 15 20 25
0.0
0.0 0.0 0.0
0.5 0.5 0.5 0.5
0.5
Upper fill
1.0 1.0 1.0 1.0
1.0
1.5 180 ± 40 BP 1.5 1.5 1.5
Depth (m)
1.5
2.0 2.0 2.0 2.0
2.0
2.5 2.5 2.5
Lower fill
2.5
2.5
5070 ± 80 BP
3.0 3.0 3.0
3.0
3.0
3.5 3.5 3.5
3.5
3.5
Depth to unconformity is ~ 2.3 to 2.5 meters

17. Wood in core GV-2
Radiocarbon age:
5070 ± 80 BP
5920-5720 Cal BP

18. Core GV-5 Upstream Site
m ass Xlf (x 10-8 m 3/kg) % organic/%m oisture % carbonates
0 10 20 30 40 50 0 5 10 15 0 5 10 15 20 25
Interpretation
0.0 0.0 0.0
Upper fill
0.5 0.5 0.5
1.0 1.0 1.0
1.5 1.5 1.5
Depth (m)
2.0 2.0 2.0
Lower fill
2.5 2.5 2.5
3.0 3.0 3.0
3.5 3.5 3.5
Depth to unconformity is ~ 1.9 meters

19. Valley Side Site
Core GV-9
m ass Xlf (x 10-8 m 3/kg) % organic % carbonates
Interpretation
0 10 20 30 40 50 0 5 10 15 20 25 0 5 10 15 20 25
0.0 0.0 0.0
0.5 0.5 0.5
Upper fill
1.0 1.0 1.0
Depth (m)
1.5 1.5 1.5
Lower fill
2.0 2.0 2.0
2.5 2.5 2.5
Depth to unconformity is ~ 1.6 meters

20. 0.87 meters
Source: Anthony Rodriguez

21. Alluvial Fill Properties
• Upper Fill • Lower Fill
– Texture is variable – Texture is silt and clay
– Organic % is moderate – Organic % is low to
to high moderate
– Carbonate % is low – Carbonate % is high
– Massive and – Mainly massive to
laminated fines and finely laminated.
sorted sand and
gravel.

22. 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

23. 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.

24. 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.