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2008 Michigan Academy Meeting - Holocene alluvial fill in a small
- 1. Welcome Geological SciencesSection 2008 Meeting at Western Michigan University Michigan Academy of Sciences Arts, and Letters
- 2. Holocene alluvial fillin 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 SouthCross 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 studentsin Little Mac Ravine.
- 10. Setting up thevibracoring tripod.
- 12. Preparing to recovera core
- 13. Environmental geology studentssampling cores.
- 14. Wood in coreGV-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 coreGV-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 CoreGV-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: AnthonyRodriguez
- 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 FromAlluvial 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 leasttwo 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 tothe 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.