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Paleolimnologic Study of Redpath Lake, North Island, New Zealand

Joseph E. Carrasco Jr.1, Kathleen M. Marsaglia1, Mike Marden1, Matthew E. Kirby2, and Wayne G. Henderson2
1Geological Sciences, California State University, Northridge, 18111 Nordhoff Street, Northridge, CA 91330-8266, [email protected]
2Geological Sciences, California State University, Fullerton, P.O. Box 6850, Fullerton, CA 92834-6850

In June of 2007, a Landcare Research New Zealand terrace drilling program discovered a potential paleolake deposit (Redpath Paleolake) within the upper Waipaoa River catchment of North Island, New Zealand. This lake formed behind a local landslide dam that when breached resulted in the downcutting and exposure of lake sediments in a single stream bank. In January of 2008, eight meters of section along this bank (Redpath 1A) and a ten meter core (Redpath 3) from the original discovery well bore ~20 m northwest of the stream bank were measured, described, and photographed. Descriptions included color, sedimentary structures, bedding characteristics, organic matter content, grain size, and diagenetic features. These sections were sub-sampled at 1 cm to 2 cm intervals for laboratory analyses such as grain size analysis, mass magnetic susceptibility, loss on ignition 550° and 950°C, and smear slide petrography. Both stratigraphic sections are dominated by mud (~75%), locally laminated, and medium to thin sandy interbeds (~25%); these variations in sediment input perhaps reflect climatic, volcanic and/or tectonic events. Wood fragments yield maximum 14C ages of approximately 15,000 years B.P. for the sequence suggesting that the sediments fill a gap that has not been documented within the region, and is of importance to MARGINS Source-to-Sink modeling.

Key Words: paleolake, landslide, sediment, stream, MARGINS

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas