Distinguishing storm or fire events in historic sediments Willy Amidon, Eric Butler
Introduction
• Lake sediments record past events
• Coring allows study of these records
Previous work
Brown (2000), Noren (2001) used long (6m) cores to reconstruct paleoclimate and environment
- identified coarse, inorganic sediment layers
- interpreted as storm events
OUR PURPOSE: Distinguish fire events from storm events
Goals
Use short cores (< 40cm) to:
• Quantify historic charcoal levels
• Identify historic/prehistoric boundary
• Interpret any “storm” layers found
• Refine lab techniques
Methods of analysis
• Visual logs
- Changes in color, density, grain size, debris
• Loss on Ignition (LOI)
- Identifies trends in organic carbon content
• Charcoal analysis
- Elemental analyzer quantifies elemental carbon (charcoal)
Coring method
• Gravity cores from canoe
• Extrude in the field
• Cores separated into 1 cm intervals
Sample preparation
• Dry samples & weigh
• Digest in nitric acid
- removes organic carbon
• Rinse & dry, weigh
• Elemental analyzer
- measures elemental carbon (charcoal)
Results
• Incomplete digestion (SY)
• Incomplete washing (SY, OG)
Alternate methods
• Visual log on OG core
• LOI on OG core
Results
• Correlation between LOI and organic material
• Suggests a storm/fire layer?
• May also represent logging
10 12 14 16 18 20
30
25
20
15
10
5
Loss-on-ignition (%)
Coming soon
• Elemental analysis on rewashed samples
- % charcoal content
• Hopeful correlation with LOI and visual log
- Does increase in charcoal correlate with decrease in LOI & color change?
Future work
• Apply procedure to longer cores
• Pb210 dating of macrofossils (wood chips)
• Analyze & compare more short cores
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