New Zealand Journal of Geology and Geophysics abstracts
Grain-size characteristics for distinguishing basin floor fan and
slope fan depositional settings: outcrop and subsurface examples from
the late Miocene Mount Messenger Formation, New Zealand
Greg H. Browne
Peter R. King
Karen E. Higgs
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
g.browne@gns.cri.nz
Roger M. Slatt
School of Geology and Geophysics
University of Oklahoma
Norman, Oklahoma, USA 73019
Abstract An outcrop section of late
Miocene deep-water sediments of the Mount Messenger Formation in
Taranaki, New Zealand, displays distinctive physical sedimentary
features that allow differentiation of basin floor and slope fan
depositional units. Sandstone grain-size characteristics have been
examined in this study to differentiate these two types of deep-water
deposits. Outcrop data indicate that basin floor fan sandstones are
relatively sand rich in comparison to silt-rich slope fan sandstones.
Both basin floor and slope fan sandstones show better sorting with
increasing grain size, though cross-plots show the nature of this
relationship differs slightly for basin floor and slope fan samples.
These relationships appear to hold for both outcrop and subsurface
sandstone samples from the formation. This finding is unexpected given
the c. 600 m stratigraphic thickness of the formation,
representing several million years of depositional history, and implies
a uniform sediment texture was supplied to the basin through time.
The differentiation of basin floor fan and slope fan
deposits is significant especially in subsurface settings involving
petroleum well data. Hydrocarbon exploration strategies will vary
markedly for basin floor fan versus slope fan reservoirs, making such
differentiation of lithofacies types important to optimise hydrocarbon
discovery. With subsurface data, the interpretation of these two
reservoir sandstone lithofacies is often difficult to make. The
grain-size changes appear to mimic the contrasting depositional
mechanisms operative in these two deep-water settings.
Keywords Mount Messenger Formation;
deep-water sedimentation; bathyal; basin floor fan; slope fan;
paleoenvironment; grain-size analysis; thin section petrography
G03023; Received 6 August 2003; accepted 17 August 2004; Online
publication date 25 May 2005
New Zealand Journal of Geology & Geophysics, 2005, Vol. 48:
213–227
0028–8306/05/4802–0213© The Royal Society of New Zealand 2005
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