Geology Reference
In-Depth Information
for ~7 km and ~1.5 km offshore, a region with a
typical depth of 8 m beneath lowest astronom-
ical tide (mean slope angle 0.5°). Previous studies
(Riegl, 1999, 2002; Riegl
et al.
, 2001) had identi-
fi ed coral carpets (= biostromes), areas covered by
unconsolidated carbonate sand, macro-algae and
seagrass, underlain in wide areas by hardgrounds
consisting of early diagenetically cemented calcar-
enites (Shinn, 1969; Evans
et al
., 1973). Six coral
assemblages of variable live cover were known
from within this area.
(a)
m
˚
'
˚
'
'
˚
(A)
Large, widely spaced
Porites lutea
and other
Porites
mixed with several other massive
species; widely distributed on hardgrounds.
Coherent patches of tabular colonies of
(b)
(B)
Acropora clathrata
and
A. downingi
cover-
ing 40-90% of the substratum.
Edges of (B) with less space cover (<25%)
(B1)
'
˚
but still
Acropora
dominated.
Clusters of faviids (most notably
(C)
Platygyra
lamellina
,
P. daedalea
,
Cyphastrea serailia
,
Favia
spp.) either widely spaced or densely
packed.
Widely spaced
(c)
(D)
Siderastrea savignyana
col-
onies on sandy hardgrounds.
Patches of densely spaced (80% coral cover)
(E)
columnar
Porites harrisoni
intermingled
with faviids (
Favia
spp.,
Platygyra
spp.).
'
As a second study area, a major island/shoal
complex associated with the Great Pearl Bank
(Purser, 1973) was investigated using Landsat
imagery at the Murrawah and Al Gharbi shoals
complex, which includes shoals around the
islands of Murrawah, Al Heel, Fiyya and Al Gharbi.
The shoals are roughly circular or oblong, with
a fringe of reefal sediments, followed by grain-
stones and a largely muddy interior (Purser, 1973;
Schlager, 2005).
A system comparable to the present-day
Arabian Gulf existed in the Miocene Paratethys
and is partly represented by the Austrian Leitha
Limestone. This unit, of the Miocene Badenian
central Paratethys stage (= Langhian to Lower
Serravalian Mediterranean stage = Foraminifera
Biozones M5 to M7 of Berggren
et al.,
1985),
represents a shallow subtidal ramp sloping into
a peripheral basin of the subtropical Paratethys
(Fig. 1) (Piller & Vavra, 1991; Piller
et al.
, 1996).
The term “Leitha Limestone” is used here in a
purely descriptive manner since a redefi nition
in Papp
et al.
(1978) was not in accordance with
the stratigraphic codes (Steininger & Piller, 1999).
m
Fig. 1.
(a) Study area in the Arabian Gulf. The landscape
evaluated was a mixture of sandy and hardground facies
with biostromal coral frameworks in a typical carbonate
ramp setting. (b) Landsat Image showing location of study
areas. (c) Palaeogeographical setting of the Leitha Limestone
in the Vienna basin. An island arc on Triassic basement
spanned the Alpine and Carpathian piedmont that formed
the coastline around the fl ooded Vienna basin, which was
a peripheral basin of the Paratethys epicontinental sea. On
this arc of islands and shoals, Leitha Limestone was depos-
ited. Around islands, corals and shallow-water carbonate
facies are found. Contour lines at 20 m depth interval.
Two systems were studied in detail.
A fi ne-scale study covered only a few square-
kilometres that were investigated with Ikonos sat-
ellite imagery. The details of the imagery and of
image processing are given in Purkis
et al.
(2005)
and Purkis (2005). This system is near Ras Hasyan,
in the UAE (Fig. 1) and extended shore-parallel
