CHARACTERISTICS OF THE ENVIRONMENTAL MAGNETIC RECORD OF A ~150 M SEDIMENT CORE: CLEAR LAKE, NORTHERN CALIFORNIA

We are studying the environmental magnetic record of a new ~150 meter drill core from Clear Lake, CA. The sediment of Clear Lake is believed to have been deposited fairly consistently without changes in source material, making it an ideal site to use environmental magnetism to study environmental change.

Data from measurements of anhysteretic remanent magnetization (ARM) and saturation isothermal remanent magnetization (SIRM) have provided information about the magnetic mineralogy of the sediments. Five noticeable intervals are present in the data, indicating that there may have been as many depositional regimes reflected by the Clear Lake sediments. The youngest sediments, located in the upper 20 meters of the core, comprise the first interval, which is characterized by relatively low magnetization intensity and coercivity values. The interval between 20 and 90 meters has higher magnetization intensity and coercivity values, and higher amplitude variations. Between 90 and 110 meters below lake floor, the sediments have more variable intensity values, with larger amplitude and inconsistent frequency variations. The sediments in the fourth interval, between 110 and 125 meters depth, have intensity values similar to the previous interval. The coercivity values, however, are slightly higher (reaching the highest of the whole core) and amplitudes of the variation is comparable to the first two intervals, but with higher frequency. The oldest sediments, from 125 meters to the end of the core, form the fifth interval and have the highest relative amplitudes and lowest frequency. Magnetization intensity, coercivity, and their relative variations of amplitude and frequency provide information about magnetic mineralogy and grain domain sizes.