COPYRIGHTED MATERIAL

Int. Assoc. Sedimentol. Spec. Publ. (2011) 43, 1–10
Introduction to Quaternary carbonate and evaporite sedimentary
facies and their ancient analogues
A B D U L R A H M A N S . A L S H A R H A N an d C H R I S T O P H E R G . S t . C . K e nd a l l †
Faculty of Science, United Arab Emirates University, PO Box 17551, Al Ain, UAE
(E-mail: [email protected])
†
Department of Geological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA
(E-mail: [email protected])
ABSTRACT
MA
TE
RI
AL
Douglas James Shearman (1918–2003) used his imagination to extend our understanding of the sabkha evaporites of the Arabian Gulf, and their use as analogues for evaporites
that are now associated worldwide with hydrocarbon exploration and exploitation. His
work on the Holocene carbonates and evaporites of the southern coast of the Arabian
Gulf has meant that these are now the most frequently cited examples of type-analogues
for assemblages of shallow-water carbonates, evaporites and siliciclastics found
throughout the geological record. Striking examples from the United Arab Emirates
(UAE) and nearby regions include those found in the Tertiary and Mesozoic sedimentary
rocks of the immediate subsurface. Other analogues of this setting include the Palaeozoic
carbonates of the western USA, Europe and Asia, and the Mesozoic carbonates of the
Gulf of Mexico and Europe.
Until the late 1950s there were no welldocumented modern evaporite analogues to
ancient evaporite settings. However, this changed
with research into the carbonates and evaporites of
the Arabian Gulf, and particularly Abu Dhabi, in
the late 1950s and early 1960s with the initial work
of Emery (1956) and Houbolt (1957). The pace of
this research was stepped up when the Imperial
College of London research team, led by Graham
Evans and Douglas Shearman, arrived in Abu
Dhabi. As a result of carrying out extensive research
along the Abu Dhabi coast through 1961–1970, this
group became a leader in the study of modern
carbonates and evaporites. Initiated by Evans and
Shearman, the research observations of the group
were published in a mix of many PhD dissertations, which included those of David Kinsman,
Christopher Kendall and Patrick Skipwith, and
articles in professional journals and books. These
all documented the Holocene carbonate (ooids,
grapestones, pellets, mud and cyanobacterial flats)
and evaporite (halite, anhydrite and gypsum) sediments and various other associated sedimentary
facies that had their counter points in the subsurface of ancient sedimentary sections.
Shell Research of the Netherlands followed the
Imperial College team and carried out regional
surveys along the coast of the Arabian Gulf, from
ED
IN TR ODUCTION
CO
PY
R
IG
HT
The Arabic word for salt flat, “sabkha”, was coined
by Shearman in the field in 1961 to differentiate the
facies he first saw exposed on the then Trucial
Coast (now the United Arab Emirates, UAE). Since
then, the word sabkha has been incorporated into
the evaporite literature to describe both continental and near-coastal evaporative sediments that
accumulate close to the sedimentary surface. The
subaerial boundary of this flat is a geomorphic
surface whose level is dictated by, and is in equilibrium with, the local water table. Sabkhas are
occasionally covered by ephemeral shallow water,
but for most of the time, they are subaerial mud and
sand flats. The term “marine sabkha” normally
denotes a near-coastal salt flat dominated by marine-derived brines and processes, though the character of the adjacent continental water-table often
influences it. A “continental sabkha”, in contrast,
is an inland salt flat dominated by continental
brines and processes. Both settings receive water
via either subsurface or overland (storm-induced)
flow, and may be associated with aeolian dune
fields and intermittently submerged interdunal
corridors. All these settings were observed and
described more than half century ago by Shearman
and his colleagues from the Arabian Gulf.
Ó 2011 International Association of Sedimentologists and published for them by Blackwell Publishing Ltd
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A. S. Alsharhan and C. G. St. C. Kendall
I R A Q
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Fig. 1. Location map of the Arabian Gulf and adjacent area showing principal bathymetric provinces and depth of water (in
metres) (modified from Kassler, 1973; Alsharhan & Kendall, 2003).
Qatar to the UAE. Bruce Purser directed this
research, working with many now famous geologists that included Gene Shinn, Leslie Illing and
J.C.M. Taylor. Later, Purser and his team carried
out fieldwork sponsored by the National Museum
of Natural History of Paris and the TOTAL Oil
Company. Ken Hsu and his graduate students (who
included Godfrey Butler and Judith Mckenzie)
arrived from Riverside California and then
switched to the Polytechnic Institute of Zurich,
where they made significant contributions to
our understanding of the recent carbonates and
evaporites of Abu Dhabi in the early 1970s. These
workers were followed by Stjepko Golubic and
colleagues from Boston, who studied the cyanobacteria of the protected tidal flats of the UAE
in the late 1970s, as well as R.J. Patterson, R.K.
Park and D.J. Kinsman who came from Princeton
in the late 1970s and 1980s. Also in the 1980s,
Gunatilaka worked with Shearman in Kuwait,
while G. Walkden, and A. Williams from Aberdeen
investigated the southern margin of the Gulf.
A direct consequence of all these studies of the
southern coast of the Arabian Gulf (Fig. 1) is
that this region is now one of the best, if not the
best, documented modern sea-margin of Holocene
carbonate-evaporites and dolomites.
The Holocene marine and coastal sediments of
the southern Arabian Gulf coast represent the arid
equivalent of the shelf sediments of the Yucatan,
British Honduras and Florida, and the isolated
platform of the Bahamas. The sediments of the
Holocene of the UAE exhibit a wide range of
sedimentary facies (Fig. 2; Table 1) that include:
(a) offshore bivalve sands mixed with lime and
argillaceous mud; (b) bivalve-rich sediment in the
deeper tidal channels between the barrier island
lagoons and deeper portions of the Khor al Bazam;
(c) coral reefs and coralgal sands of coastal margins
to the west; (d) oolite shoals that accumulate on
the tidal deltas of channels that debouch from
between barrier islands to the east; (e) grapestones
that occur on exposed coastal terraces of the western Khor al Bazam and to the lee of the reefs
and oolite shoals in eastern Abu Dhabi; (f) pelleted
lime muds that accumulate in the lagoons of
Introduction to Quaternary carbonate and evaporite sedimentary facies and their ancient analogues
53°00'
53°30'
54°00'
3
54°30'E
Organic reefs & coral algal sands
Sabkha
Skeletal sands
Cyanobacterial mat
6
G
Bathymetry in metres
Pellets & lime mud
Pellets, grapestones & skeletal sands
Ooids
A
6
R
A
B
U
L
F
N
20
Rock & sandy desert
N
IA
Ras
Ghanadah
6
Al Sadiyat
6
20
24°30'N
Hail
Sir
Bani
Yas
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Al Bazam
Al Gharbi
KHO
Dagallah
R
Jebel
Dhannah
Marawah
Fiyah
AL
BAZA
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Ras
Al
Aish
Al Ruwais
Al Qala
GR E
AT P
EARL
BA
Halat
Al Bahrani
Al Dhabaiya
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Musafah
Khor
Salali
Jananah
Salaha
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Abu Al Abyad
Al Marfa
6
Bu Sharah
Al Rufayq
Al Tarif
A
I
0
AB
Sabkhat
Matti
AR
Al Khusaifah
ABU
DHABI
km
N
GU
LF
50
200 km
Fig. 2. General sedimentary facies along the coastal areas of Abu Dhabi Emirate.
Table 1. Types and characteristics of tidal flats along the United Arab Emirates coast.
Types
Characteristics
Occurrence
Barrier island-lagoon
sabkha
Sabkhas prograde into barrier lagoons that form
behind a series of Pleistocene barrier islands.
These sabkhas have complexities such as buried
beach ridges, abundant siliciclastic matrices
and facies, mosaic distributions of anhydritegypsum-dolomite.
Lack low-energy lagoonal sediments. Evaporites
form in the mixing zone between marine and
continental influenced groundwaters. They
infill depressions behind extensive Holocene
mainland beach-dunes.
These interdunal sabkhas are filled with late
Pleistocene/Holocene evaporitic sediments.
The evaporites are displacive sulphates
(gypsum and anhydrite) mixed in with
displacive and bedded halite in a siliciclastic
matrix. There appears to be a much higher
proportion of halite preserved in these
continental sabkhas compared to the coastal
sabkha.
The alluvial fans are fed by ephemeral streams
from the mountains and pass directly into the
waters of the Gulf. On the distal portions of these
fan deltas, sabkhas have nodular and bedded
gypsum, and displacive halite grows in a matrix
of siliciclastic fan delta sediments.
Coast of Abu Dhabi
Mainland beach-dune
sabkha
Continental interdunal
sabkha
Fan delta sabkha
NE of Ras Ghanada in Abu Dhabi
all the way to Dubai
In many of the interdunal
corridors there are currently
elongate interdunal sabkhas.
Sabkhat Matti is the largest in
the area.
Northern part of Ras Al Khaimah
in Al Rams area
4
A. S. Alsharhan and C. G. St. C. Kendall
the eastern Abu Dhabi; (g) cyanobacterial mats
and mangrove swamps lining the inner shores
of the protected lagoons of Abu Dhabi and the
east Khor al Bazam; and (h) supratidal salt flats
(sabkhas) where evaporite minerals accumulate
along the inner shoreline. The coastal sediments
pass landward into continental aeolian facies
(Alsharhan & Kendall, 2003).
Plio–Pleistocene tectonic events have dominated
the evolving morphology of the Arabian Gulf
though Quaternary erosion and deposition, and
have modified the relief of the resulting structures
(Kassler, 1973). For example a sea-level fall
of around 120 m during the Pleistocene left the
Arabian Gulf entirely exposed, with rivers channeling into its flanks and moving down its axis. During
this maximum fall and during the subsequent rise, a
series of platforms were cut into the pre-existing
surface (Kassler, 1973; Weijermars, 1999). The Late
Pleistocene and Holocene sea-level changes were
also associated with dramatic climate change, and
there is a broad coincidence between the deduced
sea-level and temperature curves of this time period. Currently, the Arabian Gulf is situated in the
low latitudes of the tropics, and the distribution of
its sediment is controlled by many factors that
include an arid climate, a mix of the influence of
low and high wave energy, a coastal orientation that
is a response to northwesterly Shamal winds
and the presence or absence of offshore barriers
(Wagner & Van der Togt, 1973).
ANCIENT ANALOGUES AND THE
SIGNIFICANCE OF EVAPORITES
F O R P E T R O L E U M E X P LO R A T I O N
Similar associations of shallow-water carbonateevaporite facies to those of the coastal areas of the
southern Arabian Gulf occur in the subsurface and
form good reservoirs in many parts of the world
(Table 2). The Arabian Gulf examples include the
Permian Khuff Formation, the Upper Jurassic Arab
Formation and Hith Anhydrite, and the Tertiary
Umm Er Rhaduma Formation and Fars Group.
Other similar associations from other parts of the
world include the Ordovician Red River Formation
of the Williston Basin, and the Ordovician Bauman
Fjord Formation of Ellsmere Island, the Devonian
of Western Canada and Western Australia, the
Pennsylvanian of the Paradox Basin of Utah, the
Permian of West Texas and the Zechstein Sea in
the North Sea area, the Jurassic sedimentary rocks
Table 2. Ancient sabkha reservoirs.
I. Marine and continental sabkha
1. Ordovician Red River Formation, Williston Basin,
USA.
2. Lower Clear Fork Formation (Permian), Texas.
3. Upper Minnelusa Formation, Wyoming.
4. Jurassic Smackover and Lower Buckner Formations,
South Texas.
5. Rift Basins: Gulf of Suez and Red Sea.
II. Shallow-water evaporite
1. Ferry Lake Anhydrite, Fairway Field, East Texas.
2. Jurassic Todilto Formation, New Mexico and
Colorado.
3. San Andres Formation, NW Shelf of Permian Basin,
West Texas.
4. Upper Part of the Arab Formation, Upper Jurassic,
Arabian Gulf.
5. Khuff Formation, Upper Permian, Arabian Gulf.
6. Permian Guadalupian, West Texas and SE New
Mexico.
III. Deep-water evaporites
1. Permian Delware Basin, Texas.
2. Permian Zechstein of Europe.
3. Upper Silurian of the Michigan Basin.
of the Gulf of Mexico, and parts of the Lower
Cretaceous of south-eastern Texas.
Cycles of ancient sabkha facies were distinguished in the Upper Jurassic Arab Formation of
Abu Dhabi by Wood & Wolf (1969). In fact, the
present UAE coastline appears to match some
of the evaporite settings of the Upper Jurassic
Hith and is a recognizable analogue of the Hith
(Alsharhan & Kendall, 1994). The Upper Jurassic
evaporitic sulphates and minor chlorides of
Arabia accumulated within a complex of giant
playas and sabkhas (72 million km2) along the
southern margin of the Tethys Ocean. These evaporites now form excellent seals to some of the
world’s most prolific oil reservoirs (Murris, 1980;
Ayres et al., 1982; Alsharhan & Kendall, 1986).
Examples of this association include the grain
carbonates of the Arab Formation of the eastern
Arabian Peninsula and the Hith Anhydrite. The
Hith forms an excellent seal in Saudi Arabia,
Qatar, Bahrain, and western Abu Dhabi. It prevents the upward movement of oil generated in
the Jurassic source rocks (Alsharhan & Kendall,
1994). This seal is dominated by the playa facies
but eastward, where the Hith facies change to a
dominantly sabkha and peritidal carbonate, oil
escapes upward and is found in the Lower Cretaceous reservoirs of eastern Abu Dhabi. In contrast,
the series of Holocene algal flats associated
Introduction to Quaternary carbonate and evaporite sedimentary facies and their ancient analogues
5
Table 3. Some carbonate hydrocarbon reservoirs associated with tidal-flat evaporites and algal flats.
Field(s)
Formation
Age
Location
Reference(s)
Puckett
Cabin Creek and
Pennel
Cabin Creek
Rainbow
Northwest Lisbon
Ellenberger
Red River
Ordovician
Ordovician
Texas, USA
Montana, USA
Intertake
Keg River
Leadville
Silurian
Middle Devonian
Mississippian
and Pennsylvanian
Mississippian
Loucks and Anderson (1985)
Clement (1985); Ruzyla
& Friedman (1985)
Roehl (1985)
Schmidt et al. (1985)
Miller (1985)
Mission
Canyon
Zechstein
Early Permian
Montana, USA
Alberta, Canada
Paradox Basin,
USA
North Dakota,
USA
Poland
Arab
Arab
Arab
Arab/Qatar
Late
Late
Late
Late
Saudi Arabia
Saudi Arabia
Abu Dhabi
Qatar
Chatom
Smackover
Late Jurassic
Mt. Vernon
Smackover
Late Jurassic
Sunniland
Sunniland
Limestone
Asmari
Early Cretaceous
Little Knife
Tarchaly, Rybaki,
and Sulecin
Qatif
Ghawar
Umm Shaif
Dukhan
Gachsaran and
Bibi Hakimeh
Jurassic
Jurassic
Jurassic
Jurassic
Oligocene
and EarlyMiocene
with high concentrations of organic matter interbedded with carbonates and evaporites in the
region is not common to the Hith. However,
hydrocarbon traps related to evaporite and carbonate cycles are quite common in the geological
record and support these authors’ contention that
the association between evaporites and carbonates seen in Abu Dhabi is not unique to the
Holocene. In fact, such associations may represent potential source rocks for some ancient carbonate petroleum reservoirs (Table 3).
Thick repetitions of dolomite-anhydrite in the
geological column are interpreted in terms of arid
coastal-plain accretionary processes, forming not
only the seal but also the reservoir and the source
rocks. Shoaling-upward sequences of carbonates
associated with evaporites are extremely common
as hydrocarbon traps. In the United States, similar
carbonate traps are associated with major oil
fields of the Central Basin platform and on the
northwest shelf of the Permian basin of Texas
and New Mexico, where shelf carbonates interfinger with updip evaporites and clastics (Ward
et al., 1986). This association also occurs within
fields of the Williston Basin, where the Madison
Limestone/Charles evaporites (Lindsay & Kendall,
1985) and the Ordovician Red River Formation
carbonate/evaporite sequence trap and form
Southeast Arkansas,
USA
South Arkansas,
USA
South Florida,
USA
Southwest Iran
Lindsay and Kendall (1985)
Depowski & Peryt (1985)
Wilson (1985)
Mitchell et al. (1988)
Alsharhan (1989)
Qatar General Petroleum Corp.
& Amoco Petroleum Co. (1991)
Feazel (1985)
Druckman & Moore (1985)
Halley (1985)
McQillan (1985)
hydrocarbon reservoirs (Roehl, 1985). Similar rocks
can also be found in the Western Canadian Basin,
where the Devonian shoaling-upward carbonates
and evaporites (Schmidt et al., 1985) are associated
with sequences that are similar to those seen in Abu
Dhabi and in Lake MacLeod (Alsharhan & Kendall,
1994). Kenig et al. (1989) demonstrated from their
studies that this association has some bearing on
the occurrence of petroleum in similar sequences in
the Middle East and the western United States and
Canada (see also Table 3).
P A P ER S I N T H I S V O LU M E
The Abu Dhabi International Conference on
“Evaporite Stratigraphy, Structure and Geochemistry, and their Role in Hydrocarbon Exploration
and Exploitation” was first held in Abu Dhabi on
12–13 October 2004 and a second conference was
held in Abu Dhabi on 7–8 November 2006.
The first conference in 2004 honoured Professor
Douglas Shearman’s outstanding research contributions to unravelling the causes of the character of
the sabkha evaporites of the United Arab Emirates
and his recognition that these were probably the
analogues for many similar ancient evaporite
sequences. The second conference honoured
6
A. S. Alsharhan and C. G. St. C. Kendall
Professor Bruce Purser’s outstanding research contributions to our current understanding of the
geology of the Holocene evaporites and carbonates
of the Arabian Gulf.
on evaporites from the Holocene to the ancient.
Shearman was an enthusiastic scientist who
inspired many geologists to examine the natural
world around them and establish the origins of the
evaporites they observed.
TOPICS
OVERVIEW OF CONTRIBUTIONS
The topics reflecting the theme of the two conferences have been divided into six parts:
(1) “An Abu Dhabi retrospective on contributions
from the 1960s and 1970s, their impact on our
current thinking on evaporites and their association with hydrocarbon exploration and
exploitation.”
(2) “Evaporite stratigraphic signals of base-level
change in the geological record” with contributions relating these to hydrocarbon exploration and exploitation in the Infracambrian,
Permian, Jurassic and Tertiary of the Arabian
Plate, the North Sea Zechstein, the Mediterranean Messinian salinity crisis, the Western
Canadian Devonian, the Permian Basin of
West Texas and New Mexico, the Paradox
Basin of the Four Corners area, the Sverdrup
Basin, and the Mesozoic evaporites of the
early Atlantic break up.
(3) “Tectonic response of evaporites to burial and
lateral compression” with contributions
related to hydrocarbon exploration and exploitation in the Middle East, the Gulf of Suez,
offshore Gabon, Equatorial Guinea, Brazil, the
Gulf of Mexico, offshore Senegal through Morocco, and Pakistan.
(4) “Geochemical controls on evaporites and associated dolomitization of carbonates” as related
to their contribution to the prediction of porosity and its role in hydrocarbon exploration
and exploitation.
(5) “Effect of evaporites on reservoir quality and
fluid flow” with contributions related to oil
exploration and exploitation associated with
salt plug and diapir examples of the Arabian
Gulf, and world-wide.
(6) “Evaporite controversies: evolution of evaporites in time and space” as related to their
contribution to hydrocarbon exploration and
exploitation.
The papers presented in this volume are dedicated to our friend the late Professor Douglas
Shearman, who is best remembered for his work
The papers in this volume are from the first and
second evaporites conferences held in Abu Dhabi
in 2004 and 2006 respectively. Selected papers
from these two meetings were chosen to reflect the
themes of the two conferences. In the dedication,
Evans enthusiastically recalls the contribution of
Douglas Shearman to the field of evaporite geology.
Shearman’s life is described and much of his bibliography is listed, providing a valuable resource
for future evaporite geologists.
This volume is divided into three parts, with the
first focused on the Holocene carbonate-evaporite
sequences and associated sediments, the second
deals with geochemistry, and the third part examines their ancient analogues. The reader will note
that the individual papers are broadly categorized
based on the themes of the two conferences. A brief
summary of the highlights from individual papers
is as follows:
Kendall & Alsharhan review the geomorphology of
the sedimentary settings formed along the coast
of the UAE. These are traced from the highenergy seaward reefs that rim the Pearl Banks
to the ooid barrier island shoals, to inner shelf
coastal terraces with grapestones and cyanobacterial mats. It is described how these sediments
relate to the evaporite-rich protected coast. In
the second contribution, Evans tracks the evolution of the Quaternary geological record of the
Arabian Gulf region. Emphasis is placed on the
influence of sea-level variations on the occurrence of aeolian sediments in the area. Park ties
the updip sabkha cycle of Abu Dhabi to the
cyclic character of many shoaling upward tidal
flat cycles. This cyclicity is related to variations
in sea-level that cause the carbonate/evaporites
to onlap onto the updip portions of a ramp.
Gunatilaka describes how stable isotopes can be
used to track the evolution of the sabkha evaporites of the Arabian Gulf region, from Kuwait
to the UAE. It is shown how the sabkha sedimentary cycles are a relatively recent phenomenon, related to an increase in the aridity of the
Introduction to Quaternary carbonate and evaporite sedimentary facies and their ancient analogues
local climate in the last 5000 years and its close
association with the sea. Earlier sedimentary
cycles reflect a cooler wetter climate when fresher
waters flushed the marine brines seaward.
Shinn describes carbonate beaches, spits and channelized sabkhas nurtured by longshore currents
on the coast of Qatar that favour evaporite
and carbonate sedimentation. Coastal spits are
shown to have accreted at a remarkable rate
since the mid-1960s by periodic beach/sabkha
complex “jumps”. Rapid beachrock formation
is noted on the low-energy landward side of
exposed linear ridges, while the seaward side
of the cheniers mix accretion and erosion. It is
suggested that this sedimentary complex could
serve as a model for exploration, and guide production drilling where similar ancient sabkha
and evaporitic settings occur. Strohmenger et al.
provide a detailed description of the assemblages of shallow-water carbonates, evaporites
and siliciclastics from a traverse of the sabkha
near Al Rufayq Island in Abu Dhabi. Numerous
spectacular illustrations of trenches cut in this
coastal sabkha demonstrate the shoaling-upward
character of the stacking patterns.
Mettraux et al. describe the formation of the Bar Al
Hikman sabkhas on the east coast of Oman in an
extremely arid climate with high evaporation.
These sabkhas accumulate over a complex geological substrate in which recent sea-level falls
and structural movement have caused the emergence of marine to lagoonal carbonates in which
evaporites form. Here, the sabkhas are grouped
into “coastal sabkhas”, “continental sabkhas”
and older sabkha deposits preserved as terraces.
The movement of groundwater along faults and
fractures is linked by the authors to early lithification of Quaternary sediments. Kendall &
Alsharhan record the occurrence of cyanobacteria coating and infesting carbonate grains
along the coast of the UAE. It is argued that these
cyanobacteria are a major cause of micritization
of the carbonate grains.
Epps recognizes the current building trends on
Abu Dhabi Island and its vicinity, and describes
how engineers have been testing the physical
properties and strength of the sediments in these
coastal areas. The geotechnical properties summarised in this paper will serve as an important
reference for construction engineers working in
the region.
Wood reviews current models of dolomitization
and considers a new mechanism that is based
7
on regional groundwater models. These models
are used to explain the current high magnesium
content of the groundwaters of the Eastern
Arabia and how this impacts on the coastal
dolomitization. Qabazard et al. describe the
organic matter associated with the shallowwater carbonates that accumulate on the areas
behind the Al Khiran barrier island of Kuwait.
The preservation of this organic matter is
explained by its occurrence in a protected reducing environment.
Kirkham offers an unconventional explanation for
the occurrence of bands of carbonate and evaporite found on the sabkha surface of Abu Dhabi.
It is proposed that these are the products of
deposition from lagoonal waters that have
flooded over the sabkha surface of Abu Dhabi.
This in contrast to most previous authors who
have ascribed storm washover onto a supratidal
surface as the source of widespread halite precipitation, but it has not generally been regarded
as the source of anhydrite banding.
Kenig describes the occurrence of cyanobacterial
mats at the margin of the inner coast of the
United Arab Emirates. A series of man-made
excavations that form canals in Abu Dhabi have
been used to trace the mats from their formation
on the early Holocene transgressive surface, to
where they currently occur within the regressive
coastal sediments. The descriptions provided
will assist sedimentologists in their interpretation of similar sediments that occur in the geological record, while the associated data should
help establish the source rock potential of carbonate tidal-flat sediments.
Wright & Kirkham explain the occurrence of
enigmatic carbonate fabrics that exhibit a variety
of exotic forms. These patterned fabrics are
ascribed to the replacement of evaporites by carbonates. Warren considers how periodic influxes
of freshwater into brine water-bodies induce
blooms of cyanobacteria in the water column. It
is argued that, should this organic matter be preserved, it has a good chance of maturing to become
the source rock for some hydrocarbon fields.
Costa et al. describe the extension and compression associated with the salt tectonics of passive
margin basins. A series of physical models
are reviewed that explain these features. These
examples should serve to help geologists making interpretations of the fabrics formed by the
massive halite often associated with the initial
phases of continental pull apart. Hafid et al.
8
A. S. Alsharhan and C. G. St. C. Kendall
describe the tectonic features found in the disturbed and distorted salt of the Essaouira Basin
of western Morocco. These features show many
of the fabrics found in other salt basins, while
their character within the near-surface seismic
sections provides excellent analogues for the
interpretation of similar features found elsewhere in the world.
Al-Suwaidi et al. describe the Arab sabkha cycles
found in the offshore Jurassic petroleum reservoir
facies using seismic cross-sections and well logs.
It is shown how the sediments of these cycles
change their character from west to east and
seaward, and how the hydrocarbons are trapped
at the updip pinch-out of the grain carbonates
beneath sabkha evaporites. Orti describes gypsum
crystals that form in many settings. The occurrence and character of gypsum is reviewed, with
a particular focus on the selenite fabrics of
Sicily, Italy, Spain and Poland. The information
presented should help both the novitiate and
evaporite expert to better understand other selenite fabrics in the geological record.
A C K NOW L E D G E M E N TS
We would like to thank Abu Dhabi National Oil
Company (ADNOC), Abu Dhabi Marine Operating
Company (ADMA-OPCO), Abu Dhabi Company
for Onshore Oil Operations (ADCO) and Zakum
Development Company (ZADCO) for their support
and encouragement for the conferences of 2004
and 2006. We extend our sincere thanks to the
authors of the papers in this volume for their
interest and timely contributions to this special
publication. We would like to thank all reviewers,
whose critical revisions of the manuscripts assured
us of the high quality and comprehensive compilations expressed by this volume. We greatly
appreciate the effort of Mr M. Shahid, who processed the chapters for this volume from inception
to final completion, incorporated the authors’
changes and handled all correspondences with
authors and reviewers.
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