Paleotempestology Lab protocol

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Louisiana State University *

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2020

Subject

Geology

Date

Apr 3, 2024

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docx

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2

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Paleotempestology and Loss on Ignition Analysis A. Purpose To determine storm layers in a sediment core using loss on ignition analysis. B. Introduction Paleotempestology is a young field of science that studies past hurricane activities by means of geological and archival techniques. It is important to look to the past for long-term perspectives on hurricane activity since observational records of hurricanes only go back about 150 years. Long term perspectives are vital to accurately determine risk assessment. Paleotempestology research seeks to answer questions such as: What is the probability for a location to be hit by a catastrophic hurricane? How do probabilities change over time? How are the long term changes related to global climate change? There are multiple proxies to be used in paleotempestology with some including studying overwash sand layers, pollen, diatoms, dinoflagellates, phytoliths and microscopic charcoal. The principal approach is the detection or identification of overwash deposits in back barrier lake and marsh sediments. As a storm approaches land, overwash occurs, toppling beach sand dunes and depositing these sands in the coastal lake behind the dunes. This can lead to changes in water, organic material, and carbonate concentrations as well as alter grainsize distribution (discussed in previous lab). Loss-on-ignition Analysis (LOI) is one of the many proxies used to find likely storm layers within a sediment core. LOI describes the process of measuring the loss of weight over a series of burning off materials in a sample. To determine storm layering, scientists are interested in water, organic materials, and carbonate concentrations within a given sample. After retrieving a core at the study location, it can then be cut to isolate depths and create a set of samples that can be used to study the depth profile of water, organic materials, and carbonate concentrations. After preforming LOI at each interval, scientists can then identify “spikes” or notable events that to be further study and used to identify historical storm events. For example, sand layers have a lower water content and organic matter content than lake muds. The specific process of LOI consists of the burning of a sample at 105° C, 550° C, and 1000° C in order to determine water, organic, and carbonate concentration, respectively. X-ray fluorescence can be used to measure concentrations of chemical elements like strontium (Sr) and chlorine (Cl)/bromine (Br) which can be used as marine indicators. 1
Paleotempestology and Loss on Ignition Analysis C. Calculations 1. Use the given data to create columns for % water, % organic, and % carbonate. (15 pts) 2. Create a graph for each column with depth and % on the axes. (15 pts) D. Questions 1. What is the ideal kind of location to do research on paleotempestology? Why? (10 pts) 2. Describe LOI. Why do we look at the 3 specific concentrations described? (10 pts) 3. What are the temperatures that burn off the 3 materials determined using LOI? (6pts) 4. What are 4 methods of taking a core? (4pts) 5. Looking at the graphs you created using the provided excel data, are there any probable storm layers? If so, at what intervals? (10 pts) 6. Identify possible storm layers in the provided LOI/XRF charts. Highlight/circle them on the graphs and attach photos of them. (10 pts) 7. Suppose the topmost storm layer was deposited in 2012 from Lake Pontchartrain area. Use https://coast.noaa.gov/hurricanes/#map=4/32/-80 to determine which hurricane was likely responsible for the deposition. (10 pts) 8. Describe the basic principle of Palynology (Pollen Analysis) discussed in class. (10pts) - Can use outside resources for additional help. - One or more paragraphs are needed to accurately explain. 2
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