Geology Reference
In-Depth Information
functioning. Geology and biology merge in shallow,
tropical carbonate systems since ecology and
successional stages of biotic communities infl u-
ence the development of facies and vice versa
(Ginsburg, 1957; Toomey, 1981; Schlager, 2005).
While the environment (climate, tectonism,
eustasy, etc.) controls lateral dimensions and ver-
tical successional pattern (James, 1984; Wilgus
et al.
, 1989; Tucker & Wright, 1990; Wilkinson
et al.
, 1997, 2003; Lehrmann & Goldhammer, 1999;
Rankey, 2004; Schlager, 2005), ecology often defi nes
facies at a fi ner scale (Flügel, 2004).
In numerous previous studies, Markov chains
have shown that conditional probabilistic rela-
tionships (knowledge of an event/facies will
defi ne probability of a following event/facies)
exist among vertical facies successions (Krumbein,
1967; Krumbein & Greybull, 1967; Gingerich, 1969;
Doveton, 1971, 1994; Miall, 1973; Carle & Fogg,
1997; Wilkinson
et al.
, 1997, 2003; Lehrmann &
Rankey, 1999; Parks
et al.
, 2000; Davis, 2002).
Stages of ecological community and landscape
successions have Markovian properties (Pielou,
1969; Horn, 1975; Usher, 1979; Turner
et al.
, 2001;
Urban & Wallin, 2002), which can be expressed
using graphs (Roberts, 1976; Cantwell & Forman,
1993; Bunn
et al
., 2000; Urban & Keitt, 2001; Urban,
2005). Markov chains and graphs may therefore
emerge as useful quantitative tools for investiga-
tions into potential linkages between lateral and
temporal, ecological and sedimentological dynam-
ics in the tradition of comparative sedimentology
(Ginsburg, 1974).
There clearly exist relations between sedimen-
tological pattern and ecological pattern (Ginsburg,
1957). Landscape patterns result from ecological
and sedimentological processes that are intric-
ately linked and that feed back into each other
(Ginsburg & Shinn, 1994). The lateral aspects of
the present landscape can be effi ciently described
using remote sensing (Harris & Kowalik, 1994;
Rankey & Morgan, 2002; Rankey, 2004; Purkis &
Riegl, 2005; Purkis
et al.
, 2005; Hetzinger
et al.
,
2006) and vertical patterns can be obtained from
outcrop or core. In this study, we use satellite
images to describe recent facies patterns in the
Arabian Gulf, one of the classic carbonate ramp
settings (Kirkham, 1998). These facies (coral reefs,
grain shoals, hardgrounds, etc.) express quantifi -
able neighbourhood patterns (Purkis
et al.
, 2005)
and good understanding exists on ecological
(Riegl, 2002; Purkis & Riegl, 2005) and sedimen-
tological successions (Shinn, 1969; Uchupi
et al.
,
1996; Alsharhan & Kendall, 2003).
The horizontal Holocene facies pattern in the
Arabian Gulf will be compared with vertical out-
crop data from the Miocene (Badenian) Paratethys
in the Austrian Leitha Limestone, previously inter-
preted as a fossil equivalent of today's Arabian Gulf
(Riegl & Piller, 2000). The presence of comparable
facies frequencies and conditional transition prob-
abilities (i.e. the Markov property) in both systems
would suggest a quantitative link between the two
time-slices and between vertical and lateral suc-
cession of facies - since from Walther's Law it may
be deduced that one should exist (Doveton, 1994;
Parks
et al
., 2000; Elfeki & Dekking, 2001, 2005).
Using discrete mathematical tools the expres-
sion of a quantitative link of temporal and spatial
dynamics will be attempted in order to explore
whether the relationship among facies in a land-
scape can be reduced to a simple graph or matrix
encapsulating a model of the system's functioning
that can then be used to predict changes in the
spatial characteristics of facies through time, for
example in changing environments. The model
will be applied to investigate possible facies
change due to small-amplitude sea-level change.
REGIONAL SETTING
The Holocene sediments of the United Arab
Emirates (UAE) include shallow-water marine car-
bonates in one of the world's classic, modern car-
bonate systems (Kirkham, 1998). Our study area
was defi ned by the gently sloping bathymetry of the
Arabian homocline and highs produced primarily
by salt diapirism that form banks with well-defi ned
lateral facies successions (Purser & Seibold, 1973).
Coastal and near-shore sedimentology was shaped
by rapidly changing sea-level in the Pleistocene
and Holocene (Lambeck, 1996; Uchupi
et al.
, 1996;
Kirkham, 1998) and, in the shorter term, by wind
and waves. Daily afternoon breezes and especially
the prevailing (though largely seasonal) Shamal
winds infl uence the local wave-induced currents,
which in turn are a major factor in developing the
sedimentology of the coast and the offshore banks
(Kirkham, 1998; Sheppard
et al.
, 1992). The north-
west trending coastline of the UAE and the north-
ern edges of the banks are strongly infl uenced by
the Shamal, due to their oblique position to this
north wind and the lack of shelter from offshore
barriers. The shallow sea fl oor throughout the
study area lies above wave-base typical for Shamal
conditions - likely to extend to a depth of at least
20 m (Purser & Evans, 1973).
