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An Environmental Reconstruction of the Tekapo Formation using Facies Analysis

Sarah Mager
Department of Geography, University of Otago, Dunedin, New Zealand

 
Abstract

One of the fundamental tools used to reconstruct ancient environments is facies analysis. Facies analysis has been applied in vastly contrasting ways and there are no widely used guidelines that describe the intellectual process or research strategy for environmental reconstruction’s using facies models. Therefore, there is a need to develop a framework that describes how to complete facies analysis in a practical and scientific manner. The problems associated with varying quality of facies analysis can at least be partially solved by implementing a "best practice". In particular, using a deductive framework facilitates the development of multiple working hypotheses by consulting previous interpretations and observations of contemporary processes. The last step of the proposed “best practice” is to evaluate the facies model. The evaluation framework that is proposed is a qualitative process to form a structured review process of facies analysis. This framework is designed specifically to identify the important components of a rigorous scientific approach to reconstructing ancient environments based of facies and landform associations. An environmental reconstruction of the Tekapo moraine was used as a case study to develop the current best practice and evaluation scheme.

The reconstruction of the Tekapo Formation moraine identified twenty facies, and five facies associations. These associations are: delta foresets and bottomesets, sediment density flows, ice-contact lake sediments with ice-rafted debris and resedimentation, and outwash gravels. These associations are intimately related to the landform development in this area. The Tekapo Formation moraine is formed by the downwasting of the ice surface that exposes englacial conduits to form thermokarst lakes. These thermokarst lakes enlarge and coalesce to form a large supraglacial lake. As downwasting continues the draining river downcuts the ice-cored moraine which lowers the lake level. This exposes lake-bottom sediments and shorelines that are deposited against ice-cored moraine. As the ice-cored moraine melts, these lake sediments are deposited against the outwash head and form a ridge of material.

 
Reference

Mager, S. 1999. An environmental reconstruction of the Tekapo formation using facies analysis. Unpublished MSc thesis, in Geography, at the University of Otago, Dunedin, New Zealand. 145 pp.

© 2009 Department of Geography, University of Otago, Dunedin, New Zealand