Geology Reference
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Fig. 8. Cropped photographs and
grey-scale traces of a portion of an out-
crop of the Kope Formation, Ordovician,
northern Kentucky, USA. On the right
is a 1-m-wide scan of the outcrop. To
the left of the fi eld photograph is the
grey-scale trace averaged over each hor-
izontal row of pixels. Farthest left is a
composite of a 2-cm-wide scan through
the centre of the 1-m-wide photograph
and the grey-scale trace derived from
that image. Note the signifi cant degree
of smoothing in the 1 m grey-scale
relative to the 2 cm trace.
2 cm Grey-scale Scan
1 m Grey-scale Scan
selected such that horizontal rows of pixels are
parallel to bedding, then it is possible to evaluate
the grey-scale character of the outcrop at different
width scales.
In order to evaluate the effects of lateral aver aging
along beds, high-resolution fi eld photographs of
the Ordovician Kope and Bellview formations of
northern Kentucky were analysed (Figs 8 and 9).
Limestones of the Kope and Bellview formations
were deposited on a shallow storm-dominated
mixed siliciclastic-carbonate ramp. These rocks
are part of the well-known Cincinnatian Series
and have been studied extensively by a number
of workers (Tobin & Pryor, 1981; Jennette & Pryor,
1993; Holland et al ., 1997). The Kope and Bellview
formations are well-suited for photographic
analysis because outcrops along the Alexandria-
Ashland highway present a series of horizontally
bedded exposures that are readily measured and
photographed at high resolution with minimal
outcrop step-back. Additionally, the interbedded
limestone-shale stratigraphy presents perhaps a
less complex lithological setting than other per-
itidal or subtidal carbonate sequences (Wilkinson
et al ., 1997; Cozzi et al. , 2005) and, as such, is
better suited to grey-scale analysis.
The Kope Formation consists of a series of
fossil-rich beds ranging from pure grainstones to
packstones and wackestones interbedded with
fossiliferous shale. Drummond & Sheets (2001)
identifi ed the presence of stratigraphic organiza-
tion within the Kope composite reference section
of Holland et al . (1997) in the form of stratigraphic
clustering of grainstone and packstone beds.
As illustrated in Fig. 8, the Kope Formation is
relatively shale-rich with prominent ledge-
forming grainstone beds and small local scree
cones. A fi eld photograph of the Kope Formation
was cropped to two sizes; in the fi rst example,
the width of the fi eld of view is approximately 1 m
while the second consists of approximately 2 cm
taken from the centre of the 1 m image. Figure 8
illustrates 2.51 m of the stratigraphic section with a
pixel scale of 0.71 mm. Using the shareware Scion
Image, these cropped images were subjected to
grey-scale analysis. Due to the averaging of pixel
values across the wider row, the 1 m wide image
produces a smoother grey-scale trace than does
the 2 cm wide image. Both of the traces, however,
display a great deal of similarity in their gross
geometry (Fig. 8). Specifi c variations between the
shape of the traces is due to a combination of lat-
eral lithological variation and increased inclusion
of stratigraphic 'noise' in the form of differential
weathering, scree cover and vegetation when
wider images are used.
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