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SEDIMENT ANALYSIS USED TO PRODUCE A PALEOCLIMATIC RECORD FOR THE SAN JUAN, COLORADO REGION Jacob E. Buettner Dr. Bryan Shuman & Jeremiah Marsicek Geology and Geophysics PROPOSED RESEARCH PROJECT Dr. Bryan Shuman, Jeremiah Marsicek, Zackie Salmon & Susan Stoddard The Rocky Mountain region has a mid- latitude steppe climate and has wet and dry season variability. The region is reliant on snow pack from the high mountains to supply water to rivers and watersheds. To understand current and future climate, watershed, and snow pack variations we look to the past. Small lakes with no inlet or outlet source, other than snowpack melt, provide a past climatic or precipitation gage record for a given region. The purpose of this study is to establish a moisture-level record for the San Juan, CO region using grain size and sediment density analyses of lake bed sediments from Little Molas Lake, CO. This lake was selected because it has no inlet or outlet stream, and so acts as a precipitation gage for the past ~11,000 years (lakes history). The objective of this project is to identify water availability during the last ~11,000 years in the San Juan, Colorado region. Methods will include grain size (% sand content; steps below) and sediment density analyses of lake bed sediments for use in producing a moisture availability record. Dense, sandy intervals represent periods of low water, and less dense, silty sediments (mainly organic) will represent high stands. 1 cm 3 subsamples of sediment will be removed at contiguous intervals throughout the core for analysis. Step 1: The 1 cm 3 will be weighed, burned at 110 C and 550 C, to evaporate water and burn off organic matter, respectively, and then reweighed to obtain the percent water and percent organic matter contained in the sediment sample. Step 2: The 1 cm 3 cooked sample will be screened using a 63 micron sieve. If the sediment goes through the sieve it, then by definition it is not sand. The sediment contained in the sieve, sand, will then be weighed and burned at 550 C to remove any large organic material, and weighed again. Step 3: Intervals that show evident change in sediment type (i.e. silt to sand) will then have one milligram of charcoal removed to date the time of the change. The importance of this study is to analyze and understand the past water availability in the Rocky Mountain region to help inform future trends. Water availability is a critical issue in the Rocky Mountain region and for the rivers that are fed from the Rocky Mountain watersheds. Understanding past trends in water availability and possibly what drove them can help forecast potential trends of future water availability. Ultimately, this data can assist in implementing proper water management systems for the future. Methods for Analysis Introduction Statement of the Problem Objective Importance Acknowledgements North South Cross Section of Little Molas Lake Arial view of Little Molas LakeScenic view of Little Molas Lake From Google Maps: Topographic View Core sample from Hidden Lake Colorado; It shows a portion of the sediment record