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. Henderson^2
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