PALEOENVIRONMENTAL SIGNIFICANCE OF SEDIMENT CHARACTERISTICS AND MAGNETIC FABRICS PRESERVED BY POST-GLACIAL DEPOSITS OF SENECA LAKE, NY
During the warmer Early to mid-Middle Holocene (10-6 ka cal yr BP), the mean grain size (7.3φ), % sand (up to 4.8%), carbonate concentration (10-42%), and bulk magnetic susceptibility (6 x 10-4SI units) are all at their highest and show decreasing trends upcore. The organic matter concentration is low (2%) and increases upcore. Well-defined magnetic fabrics occur during this warm interval: a high degree of anisotropy (P'), which records the degree of alignment of magnetic grains (1.02-1.06) and oblateness (T), which reflects the shape of the magnetic ellipsoid (0.40-0.95). The relatively cooler late Middle Holocene and Late Holocene (6 ka cal yr BP and present) is characterized by a smaller mean grain size (8.1φ), less sand (<1%), lower carbonate (4%), slightly lower bulk magnetic susceptibility (4 x 10-4 SI units), and higher organic matter concentrations (3-6.9%). The cold period is distinguished by a small degree of anisotropy (P': 1.006-1.035) and anomalous shape factors (T: 0.2- -0.624). Results suggest a strong relationship among magnetic fabrics, sediment characteristics and climate. The abrupt change in both sediment and magnetic properties may result from a decrease in the current strength during the Holocene. Increased effects of bioturbation or diagenetic dissolution of magnetite grains on development of anomalous magnetic fabrics cannot be ruled out for the Late Holocene. Petrographic analysis supports bioturbation as the cause of anomalous fabrics.