New Mexico Geological Society Annual Spring Meeting — Abstracts

Sedimentology, carbon isotope data, percent organic carbon, and an Ar/Ar date of 552 + 3 ka for 78 m depth have been used independently to suggest that 80 m of lacustrine sediment was deposited during glacial terminations VI (522 ka) and V (424 ka). In this study, alternating patterns of rock magnetic properties with depth (specimens taken at a minimum of 20 cm) are used as a proxy for climatically controlled changes in lithology. These combined results contribute to a mid-Pleistocene climatic model for Northern New Mexico.

Alternating field (AF) demagnetization response yields positive inclination vectors through most of the core, consistent with Brunhes normal polarity. Three short intervals of negative inclination may partially record geomagnetic polarity events at ~410 ka, ~535 ka, and ~565 ka (Big Lost excursion). Remanence in these sediments is carried by multidomain and pseudo-single domain ferrimagnetic particles as shown by rock magnetic data. Paleomagnetic and rock magnetic data all record higher intensity values during glacial times (NRM from ~0.1 mAm, ARM from ~8 mAm, SIRM from ~500, and susceptibility from ~1E-4) and lower intensity values during interglacial times (NRM from ~0.2 mAm, ARM from ~4 mAm, SIRM from ~100, and susceptibility from ~6E-5). This alternating pattern may be due to a combination of an increase in terrigenous sediment during glacial times, or a change in oxidation state. An anomalous interval of high magnetic susceptibility is recorded between ~40 and ~45 m depth and is most likely due to diagenetic or biologic alteration of ferrimagnetic particles.