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 Unpublished MSc thesis, in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.
