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STRUCTURE OF THE CHENAREH ANTICLINE
IN LURESTAN, ZAGROS:
ROLE OF GRAVITY IN FOLDING STYLE
Master en Geología Experimental, Universitat de BarcelonaGroup of Dynamics of the Lithosphere (GDL), Institut de Ciències de la Terra “Jaume Almera”, CSIC
Barcelona, 2007
Mohammad Hasem Hasan Goodarzi
Universidad de Barcelona Facultat de Geología (UB)
Consejo Superior de Investigaciones Científicas (CSIC)
Institut de Ciències de la Terra “Jaume Almera” Departament d’ Estructura i Dinàmica de la Terra
Master en Geología Experimental de la Universitat de Barcelona
STRUCTURE OF THE CHENAREH ANTICLINE IN LURESTAN, ZAGROS:
ROLE OF GRAVITY IN FOLDING STYLE
Mohammad Hasem Hasan Goodarzi
Master's degree (M. Sc.)
Director: Tutor:
Jaume Vergés Masip Francesc Sàbat
Barcelona, March, 2007
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The research reported in this Master is a contribution of the Group of Dynamics of the Lithosphere (GDL) Department of Structure and Dynamics of the Earth Institute of Earth Sciences “Jaume Almera”, CSIC
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ACKNOWLEDGMENTS
This study has been financed by a collaborative project between the NIOC
(NATIONAL IRANIAN OIL COMPANY), the Institute of Earth Sciences “Jaume
Almera”, CSIC of Barcelona (Spain) and NORSK HYDRO (HYDRO ZAGROS)
Tehran Iran. I would like acknowledgment the talents and efforts the numerous
individual who have contributed in this study. I am especially indebted to the
Exploration Directorate of National Iranian Oil Company (NIOC) for providing the data
set and field trip facilities. Especial thanks are due to: M. Mohaddes, M.
Zadehmohammadi and A. Ahmadnia for their support of this project over many years. ).
. I am also indebted to the people in the Group of Dynamics of Lithosphere and
especially to Jaume Vergés for his guidance on many and varied aspects in this study…
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ABSTRACT
This structural study explores the geometry of three anticlines in the Pusht-e Kuh Arc
in Zagros, Iran. These are the Chenareh, Kush-Ab and Rit anticlines near the SE
boundary of the tectonic arc. However, this work will mostly concentrate along the
Chenareh anticline. This study presents a combination of field work, seismic
interpretation of old seismic lines and geological corss-section construction to better
define the structure of these anticlines at depth that could represent new targets for HC
exploration.
The nice whale back Chenareh anticline is a NW-SE oriented anticline with 65 km of
length and 8 km of width at the level of Asmari Formation. The anticline is doubly
plunging below the evaporites of the Gachsaran Formation. The anticline can be divided
in three longitudinal segments depending on their different structure: a) the NW
segment very well preserved with little normal faulting; b) the central part defined by
the gravitational collapse of the SW flank of the anticline; and c) the SE segment
showing the oldest rocks at the level of Bangestan Group that seems to be rotated to the
SW.
Using depth projection methods and constant thickness the Chenareh anticline shows
the main detachment level at a depth corresponding to the evaporites of the Dashtak
Formation of Triassic age. This level also corresponds to the main intermediate
detachment in the Kabir Kuh anticline (the next to the SW). Shortening in these cross-
sections give and amount of 7.2% in compression and extension of the SW flank in the
central segment gives 1.06%.
The position of the Chenareh anticline and of its SE termination is favourable for HC
exploration since it plunges beneath the Dezful Embayment from where most of the HC
generate and migrate upwards. This is demonstrated by the occurrence of abundant oil
seeps along the contact between Asmari and Gachsaran Formations along the Bala Rud
Fault near the SE termination of the Chenareh anticline.
In NIOC we benefited from this work because we better understand the need for
good constrained geological cross-sections, as well as combined with other
complementary disciplines of geosciences, to better define and constrain the potential
for HC of other areas outside the Dezful Embayment.
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TABLE OF CONTENTS
ACKNOWLEDGMENTS.............................................................................................. 5
TABLE OF CONTENTS ............................................................................................... 9
FOREWORDS / OBJECTIVE OF RESEARCH...................................................... 11
Flow work and methodology...................................................................................... 12
1. INTRODUCTION .................................................................................................... 15
1.1. Southern Iran and Zagros fold-thrust belt ........................................................... 15 1.2. Timing of tectonic events .................................................................................... 16 1.3. Mechanical stratigraphy of Lurestan Province.................................................... 17
II. SHORT REVIEW OF PREVIOUS WORK ON DETACHMENT FOLDING 23
2.1. Detachments / rounded hinges and axial surfaces ............................................... 25 2.2. Kinematics of detachment folding....................................................................... 25 2.3. The structure of the Competent Group (Lower Structure): folding by multiple stratigraphic units in Lurestan Province with special view on Chenareh anticline .... 28
III. THE CHENAREH ANTICLINE ......................................................................... 29
3.1. Location of Chenareh anticline in Zagros fold-thrust belt .................................. 29 Previous work on the Chenareh anticline ................................................................... 30 3.3. Geometry of Chenareh anticline.......................................................................... 31 3.4. Chenareh cross-section I...................................................................................... 35
3.4.1. First version of cross-section I ..................................................................... 35 3.4.2. Second version of cross-section I ................................................................. 38 3.4.3. Shortening along cross-section I .................................................................. 40
3.5. Chenareh cross-section II .................................................................................... 41 3.6. Chenareh cross-section III ................................................................................... 45
IV. ROLE OF GRAVITY IN PRESENT GEOMETRY OF CHENAREH
ANTICLINE ................................................................................................................. 50
V. CONCLUSIONS...................................................................................................... 58
REFERENCES ............................................................................................................. 60
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FOREWORDS / OBJECTIVE OF RESEARCH
The Zagros Mountains of Southwest of Iran are one of the most prolific fold-and
thrust belts in the World. They contain 8.6% of oil and 15% of gas proven World
reserves.
The occurrences of sediments and traps that generated and preserved hydrocarbons
are linked to the history of the Arabian plate margin evolution. The thick sedimentary
cover of the Zagros orogenic belt records all the stages of evolution of the basin,
evolving from a rift and passive continental shelf to a foreland basin associated to
several stages of deformation related with ophiolitic obduction and continental collision.
The change in hydrocarbon exploration towards deeper targets associated to higher
economical costs requires a better understanding of the structure of the traps at depth.
Seismic and well data acquired during the last decade have shown that the structural
configuration of the deeper objectives often do not match with shallower ones. Some of
the wells located on or near the crest of apparently undisturbed anticlines at surficial
levels went out of the target at depth.
One way to better understand the varying geometry of these anticlines at depth is to
construct accurate sections using available data by means of an integration of different
data bases (field data, geological maps, seismic lines, and oil wells).
The Chenareh anticline is a nicely outcropping fold, which is located in the
Southeastern border of Pusht-e Kuh Arc in the Zagros Mountains in Iran. This anticline
is more than 65 Km long and displays a mean width of about 8 Km. The northwestern
termination changes its name to Kialoo anticline. Its geometry is very regular in
geological map whereas it changes the geometry along the fold strike. The anticline is
double plunging in both extremities below the evaporites of the Gachsaran.
The Chenareh anticline shows a nicely preserved geometry in its NW half and a
rather disturbed geometry in its SE half. This segment of the anticline is disturbed by a
set of normal faults in the proximity of the Mountain Frontal Flexure along the Bala
Rud Fault.
The Khush Ab and Rit anticlines are located to the north of the Chenareh anticline
and these will be included in this work as they show a continuous folded structure.
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The main objectives of this work are:
1) to determine the geometry of the Chenareh anticline as well as of its northern
Khush-Ab and Rit anticlines
2) to determine the relationships between these anticlines and the Mountain
Frontal Flexure, especially along the Bala Rud Fault
3) to understand the role of the gravity in the SE termination of the Chenareh
anticline
Flow work and methodology
Different methods of study and data bases have been used to accomplish the
objectives of this work:
1) available previous studies, topographic maps, geologic maps, satellite images,
geological cross-sections, oil and gas exploration wells included in an ArcGis project;
2) 2 weeks of field work to better understand key points of the structure of the
anticlines;
3) 4 structural cross-sections were constructed across the Chenareh and Rit anticlines
using about 100 km of old 2D seismic lines and 10 wells by means of drawing programs
like Canvas and cross-section construction programs like 2D Move.
The cross-sections are located perpendicular to the fold axis and close or following
existing seismic lines. In addition, unpublished well data were also used to interpret the
structures at depth. Seismic quality was frequently poor in study area. The oldest rocks
cropping out in the core of the anticline are Upper Cretaceous.
The study of few seismic lines across both the Chenareh anticline and Khush-Ab
anticline to the N shows the implication of two main geological factors that control the
geometry and structure of these anticlines: a) the deep structure of the Mountain Frontal
Flexure (MFF); and b) the rapid pinch-out of the Amiran, Taleh Zang and Kash Kan
Formations along the axis of the Chenareh anticline.
The coupled Chenareh and Khush-Ab anticlines show large outcrops of gently folded
Asmari limestones. The Chenareh anticline to the S displays limestones from the Ilam
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Fm., whereas the larger and shallower Khush-Ab anticline shows only to the level of the
Amiran Fm. To the N, the core of the Sultan anticline constituted again by Ilam Fm. is
transported above a SW-directed thrust fault.
In order to construct the cross-sections we followed the listed procedures: 1) we
import the JPG files with seismic lines into the Canvas drawing program (similar to
Corel, Illustrator and Freehand) and then we interpret them using the dip domain
technique to select both the position of axial surfaces delimiting the dip domains as well
as to detect potential changes in thickness of selected units; 2) the JPG files are
converted to depth using a uniform velocity of about 2.3 Km/sec, which is probably
correct for shallow levels but slow for the deeper levels of the section; 3) we combine
this interpretation with surficial dips from both geological maps (NIOC geological maps
at scale 1/100,000) and field data.
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1. INTRODUCTION
1.1. Southern Iran and Zagros fold-thrust belt
The NW-SE trending Zagros fold and thrust belt (Fig. 1) extends for about 1,800
kilometer from a location in Taurus Mountain some 300 km SE of the east Anatolian
fault in NE Turkey, through northern Iraq and SW Iran, to the Strait of Hormuz where
the north-south trending Oman Line separates the Zagros belt from the Makran
accretionary prism (Falcon, 1974; Haynes and McQuillan, 1974).
The North –East limit of Zagros belt is marked by the Main Zagros Thrust, which is
rotated about a horizontal axis to form a steeply NE-dipping to sub-vertical reveres
fault with a right lateral component of movement of unknown magnitude (Berberian
and Berberian, 1981; Stöcklin, 1981). However, some of published results (Falcon,
1974; Haynes and McQuillan, 1974; Alavi, 1994) considered the metamorphic rocks,
located to the NE of the Main Zagros Thrust known as Sanandaj. Sirjan Zone to be a
segment of the Zagros Belt
Southern Iran is the area located in Southwest of Neo-Tethys Suture zone and
consist high Zagros and Zagros and all of the Lurestan, Khuzestan and Fars and also
base on geographical data Zagros divides to Lurestan, Khuzestan and Fars area.
Based on Hormuz salt deposit distribution the Zagros is divided in two segments. SE
Zagros or Hormuz Basin and NE Zagros. The boundary between these two parts is the
Ghatar-Kazerun Fault.
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Fig. 1 Location Map of the Zagros Mountain in SW Iran. The Main Recent fault Zagros Main Thrust is considered as the suture zone between two colliding plate (central Iran and Arabian plate). Imbricated zone correspond to narrow belt between the Zagros fault Zone and Main Recent fault Zagros Main Thrust. It consists of the highest mountain and deepest exposures across the belt. Zagros fold belt with a major topographical step located south of Zagros fault Zone. It shows less deformation and wide variety of folded structures with respect to their size, shape and tectonic complexity. N-S strike-slip faults, like as Kazerun fault, are assumed to be continuation of Arabic trends in to the Zagros basement.
1.2. Timing of tectonic events
Late Cretaceous ophiolites abduction was followed by the closure of Neotethys and
collision between Arabian plate and Central Iran during the early Miocene (e.g., Alavi,
1994, 2004). A major regional angular unconformity between the Agha Jari and
Bakhtyari Formations is generally considered to have marked the late Pliocene climax
of orogeny in the Zagros fold Thrust belt (Haynes and McQuillan, 1974; James and
Wynd, 1965; Kashfi, 1976). Growth strata within the upper Agha Jari Formation show
older movement before this major unconformity.
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The new seismic data in the inner part of Zagros show also the pinch outs of the
Miocene evaporites (upper Gachsaran Fm.). The seismic reflectors pinch out against
some of the anticlines, which could be related to the beginning of folding process in
Middle Miocene time in the North of Dezful Embayment (Sherkati and Letouzey, 2004;
Sherkati et al., 2005).
Although the upper part of the Agha Jari deposits have been considered as
syntectonic since the very early publications on the Zagros folds and it is only recently
that several workers pointed out its importance for dating the folding development in
different regions of the Zagros fold belt. The magnetostratigraphic study carried out on
2800 m thick Agha Jari deposits filling the Changuleh growth syncline in the Pusht-e
Kuh Arc resolved the timing of folding initiation and its duration (Homke et al., 2004).
Initial folding took place about 8.1-7.2 Ma and had duration of about 6 Myr until the
Pliocene-Pleistocene boundary. This age of initial fold growth is older than the usually
accepted Pliocene times. The duration of deformation includes both folding growth and
uplift related to the development of the Mountain Frontal Flexure, which are difficult to
differentiate.
1.3. Mechanical stratigraphy of Lurestan Province
The stratigraphy of Lurestan Province consists of a 10-12 km thick succession that
encompasses the Paleozoic and Mesozoic Arabian passive margin deposits followed by
the sediments corresponding to the long–lived Cenozoic Zagros orogenic phase. This
tremendous pile of sediments was probably deposited on top of the Proterozoic-early
Cambrian Hormuz evaporates. Most of this stratigraphy of this section is based on
James and Wynd (1965) and Colman-Sadd (1978), (Fig. 2 and Fig. 3).
The Paleozoic sequence is the best documented in the Izeh Zone where it forms the
hangingwall of the High Zagros fault (O'B Perry and Setudenia, 1967). The base of the
hangingwall section is formed by 1160 m of Cambrian rocks followed by 925 m of
Carboniferous and Permian deposits. These thicknesses agree with result from deep
exploration wells in the study area. The Kabir Kuh and the Samand wells penetrated
783 m and 1057 m of Permian rocks, respectively. These Permian corresponds to a new
widespread deposition characterized by little or non deposition. The Permian is
constituted by shallow water carbonates cyclically interbedded with evaporates
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(Beydoun et al., 1992). Older rocks were only intersected in the Kabir Kuh well where
about 200 m of Ordovician rocks were drilled. The interpretation of deep folded
horizons in the seismic lines across the north-west frontal regions of the Dezful
Embayment strongly suggests that lower Paleozoic siliciclastic deposits with thin
carbonatic units are present beneath the external parts of the Lurestan Province. The
broad extent of the lower Paleozoic is interpreted to have formed within the wide, stable
and long–lived northern passive margin along the paleo-Tethyan border of Gondwana
(e.g., Beydoun et al., 1992). The Mesozoic sequence of the north-eastern Arabian
platform was very stable centre the Late Cretaceous when oceanic obduction took place
along this margin. The succession is about 3 km thick in the Lurestan province and
encompasses the Triassic, the Khami Group (Jurassic-Aptian) and the Bangestan Group
(Albian to middle Campanian) (James and Wynd, 1965). During the Triassic, Jurassic
and Early Cretaceous, the region was dominated by a large carbonate platform (Khami
Group) with associated marls, shales, and argillaceous carbonates interbedded with
episodic plugs of evaporites (e.g., upper Jurassic Gotnia Fm.). These anoxic basins
provided several large areas of potential source rocks through this long sedimentary
sequence (e.g., Murris, 1980; Stoneley, 1981). Shallow marine sedimentation continued
from mid Campanian to Paleocene Gurpi Fm. including two extensive fossiliferous
carbonate members (Emam Hasan and Lofa Members), (Fig. 2 and Fig. 3).
The sedimentary conditions, intensity of folding, variation of thickness and variation
of facies make the geology of the Lurestan (Pusht-e Kuh Arc) very complex. In
Lurestan the Jurassic strata, which consists of dolomite and anhydrite in Fars area,
(Surmeh and Hith formations) change to limestone, shale and anhydrite? (Alan, Mos,
Adayeh, Najmeh, Sargalo and Gotnia Formations).
The Lower Cretaceous sediments are totally different from the Fars Province. The
Fahlian, Gadvan and Darian Formations, which are constituted by carbonates and
shales, change to shales in the Garau Formation. The sediments of middle Cretaceous
are mostly pelagic and consist of Ilam, Surgah, and Sarvak Formations. Upper
Cretaceous and lower Paleogene rocks of Pabdeh and Gurpi Formations contain more
carbonatic members and a thinner limestone horizon in Pabdeh Formation. Eocene
sediments include reefal limestones, which correspond to the Taleh Zang Formation and
some clastic deposit (Kash Kan Formation), which is the result of erosion of radiolarites
in the NE of the Lurestan Province across Main Zagros Reveres Fault (Fig. 3).
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At the base of Oligocene-Miocene deposits there is an anhydrite unit in Lurestan
area, which disappears towards the NE, and changes to sandstone toward to S (Kalhur
Member and Ahwaz sandstones). In younger sediments such as Gachsaran evaporites,
Agha Jari sandstones and Bakhtyari conglomerates there are also some variation (Fig.
4).
In the North of Lurestan the Pabdeh Formation laterally changes to Amiran
Formation with turbidites, sandstones, marls, shales and clastic limestones. This
stratigraphy unit is the result of compressive deformation, which started after
Coniacian-late Santonian ophiolitic obduction along the strike of Zagros Main reveres
fault (Berberian, 1995; Homke et al., in press). The age of the Amiran Formation in the
centre of the basin is Paleocene (Homke et al., in press). The Amiran Formation pinches
out in the Southern flank of the Chenareh anticline. The Amiran Formation has different
thickness and age along the northern flank of the Khorramabad anticline where 1950 m
of conglomerates showing growth strata patterns are dated as Maastrichtian (Fakhari
and Soleimany, 2003), (Fig. 4).
Fig. 2 Stratigraphy for the pre-Fars Group. The panel crosses from the Kuh-e Kalak to the Kuh-e Sefid anticlines. Datum = Base of Gachsaran Formation
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Fig. 3 Paleozoic and Mesozoic stratigraphy of the Zagros Fold Belt in the Lurestan Province showing sedimentary facies and dominant structural style.
Fig. 4 Tertiary stratigraphy of the Zagros Fold Belt in the Lurestan Province showing sedimentary facies and dominant structural style.
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The mechanical behavior of the thick sedimentary pile in response to folding was
firstly discussed by O'Brien (1950) and by Dunnington (1968), and has been the locus
of several recent papers (e.g., Sattarzadeh et al., 2000; Molinaro et al., 2004) and
Sherkati et al., 2005 among others). O'Brien (1950) and Dunnington (1968) used
regional stratigraphy and divided the succession of the Zagros Fold Belt in 5 structural
units with relatively uniform characteristics (Fig. 3 and Fig. 4): 1) Basement
(Precambrian crystalline basement), 2) Lower Mobile Group (Late Proterozoic-early
Cambrian Hormuz evaporites), 3) Competent Group (Palaeozoic and Mesozoic to mid
Tertiary passive margin and early foreland carbonates), 4) Upper Mobile Group (mid-
late Miocene Gachsaran evaporites), and 5) Passive Group (late Miocene-Pliocene
foreland clastics). These groups of strata do not exactly correspond with the large scale
geodynamic cycles that molded the NE margin of the Arabian Plate, especially the
Competent Group (Fig. 3 Fig. 4). This group constitutes the full passive margin period
as well as the early foreland basin period up to the Asmari Formation. Although the
sedimentary pile is grouped in two stiff units and two weak detachments their position
and upper and lower limits are also important for defining the differences in style of
deformation in the different layers. The Competent Group deforms between the Lower
Mobile Group as a basal detachment and the Upper Mobile Group as a roof detachment.
The Upper Mobile Group flows between two rigid and disharmonic units. Finally, the
Passive Group is folded and thrusted disharmonically above the upper detachment
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II. SHORT REVIEW OF PREVIOUS WORK ON DETACHMENT FOLDING
Among the three main classes of folds which are generally recognized, fault-bend
folds, fault-propagation folds and detachment folds, these last ones, though commonly
observed, are the least understood in terms of kinematic evolution. This is due to the
fact that there is no univocal relationship between a given geometry and a kinematic
scenario. The concept of detachment folding was implicitly acknowledged at a very
early stage under concepts such as the “break thrust fold” of Willis (1893) (Fig. 5) or
the “stretch thrust” of Heim (1921), in which the development of a thrust fault was
considered to be the final stage in the fold evolution.
a b
Fig. 5 Break-thrust fold of Willis (1893). Note that in stage (a) preceding the development of the fault, the fold is implicitly depicted as a detachment fold.
The first explicit recognition of detachment folding can probably be attributed to
Buxtorf (1916), with his cross-sections through the Jura Mountains (Fig. 6).
Detachment folds have been documented from numerous other mountain belts around
the world, notably the Parry Islands fold belt (Harrison, 1995), the Pyrenees (Vergés et
al., 1992) and the Zagros fold belt (Colman-Sadd, 1978).
Detachment folds are characterized by a rounded and often symmetrical geometry at
surface and usually display large wavelengths, even at low shortening ratios. De Sitter
(1956) was the first to recognize that in concentric regimes of folding, implicit to
detachment folds, the size of the structure is directly a function of the thickness of the
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folded panel. Mechanical analyses have demonstrated that the physical properties of the
stronger dominant member in the stratigraphic succession will have a determining effect
on the final size of the structures (Biot, 1961). Dahlstrom (1969a) pointed out that in
concentric regimes of folding, implicit to detachment folds, a fold train is necessarily
bounded by an upper and a lower detachment (Fig. 7).
Fig. 6 Example of detachment anticlines in the Jura Mountains, Switzerland. Redrawn by Epard and Groshong (1993) from Buxtorf (1916). No vertical exaggeration.
Fig. 7 Dahlstrom (1969b) conceptual model explaining why a concentrically folded panel is necessarily bound by an upper (UD) and a lower (LD) detachment zone.
While the lower detachment always exists, sometimes the upper detachment may not
and can correspond to the interface between rock and air/water (Dahlstrom, 1969b). From
(Fig. 7) one can remark that depending of the level of erosion, very different fold
geometries will be observed at surface. Close to the lower detachment one will observe
tight anticlines, with potential internal disharmonic folding, separated by broad gentle
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synclines, while towards the upper detachment one will have the impression of tight
synclines and broad anticlines.
According to most authors, a prerequisite condition for the generation of detachment
folds is the existence of a high competency contrast between the sedimentary units
involved in the folding process. The simplest model therefore consists of a basal
incompetent layer acting as a detachment zone, such as salt, overlain by a thick
competent unit such as carbonates or sandstones. The basal unit responds in a ductile
manner to fold growth, with migration of ductile material towards the core of the
anticlines causing down warp of the adjacent synclines. The structure will develop more
or less symmetrically depending on the viscosity of the basal detachment: in areas such
as Zagros characterized by ductile detachment horizons (Davis, 1985).
2.1. Detachments / rounded hinges and axial surfaces
The well-exposed anticlines in the Zagros Fold have been used as examples of folds
since long time ago in many articles and books. However, the geometry of these
anticlines at depth remains still unclear.
In the Pusht-e Kuh Arc there is a large number of different anticlines with different
lengths and width mostly formed of the two thick competent limestone units, which in
turn are the two main reservoirs for hydrocarbons in the surrounding oil rich region. The
Kabir Kuh anticline is the largest fold of the Pusht-e Kuh Arc. One third of the total
width the Pusht-e Kuh Arc extends towards the foreland side of the Kabir Kuh anticline
(to the SW). On the hinterland side of the Kabir Kuh anticline (to the NE) there is a
relatively large number of small anticlines whereas to its foreland side (SW) there is a
smaller number of anticlines but larger (Samand and Anaran anticlines among others).
The Kabir Kuh anticline is a 200-km and long anticline is up to 2700 m high and
constitutes the present drainage divide of the Pusht-e Kuh Arc (Vergés, in press 2007)..
2.2. Kinematics of detachment folding
The first author to explicitly discuss the geometric evolution of buckle folds was De
Sitter (1956), who proposed a model where the anticlines grow by increase in limb dip
as the synclinal axes slide toward one another on the underlying detachment (Fig. 8).
However, this model was later shown by Dahlstrom (1990) to violate the law of
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conservation of volume of Goguel (1952) since it implied a drastic variation in the
location of the detachment horizon with the amount of shortening. With his paper,
Dahlstrom (1990) set the foundations of the modern ideas on the kinematics of
detachment folds by proposing, based upon balancing criteria, an evolution model
“wherein the anticlinal fold limbs are short at the inception of folding and grow longer
as dips increase and the fold grows”
There are two main mechanisms which are now generally thought to contribute to the
growth of a detachment fold: (1) limb lengthening by migration of beds through hinges
and (2) limb rotation. A whole series of papers were published during the last decade
dealing with the kinematics of detachment folds (Homza and Wallace, 1997; Mitra,
2002; Poblet and McClay, 1996; Rowan, 1997). The main debate on these papers
consists of which of these two competing mechanisms is the most important during
different stages of fold development (Fig. 9).
Fig. 8 (De Sitter, 1956) model of geometric evolution of a concentric buckle fold, with illustration of particle trajectories on the flanks of the anticline.
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Fig. 9 Three possible models of growth of a detachment anticline after Poblet and McClay (1996): Model 1 shows growth by hinge migration; model 2 shows growth by limb rotation; and model 3 displays growth by a combination of hinge migration and limb rotation.
The progression of the detachment fold evolution is generally considered to involve a
thrusting through the forelimb with increasing shortening (i.e. a faulted detachment
fold; Mitra, 2003) (Fig. 10). This is basically the concept that was already implicitly
suggested by Willis (1893).
a
c
b
d
Fig. 10 Typical evolution sequence of a faulted detachment fold, after Mitra (2002). Note that the fold is initiated as a quasi-symmetric structure (a & b) and that the development of the asymmetry coincides with the propagation of a fault (c & d).
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In the light of our observations and the considerations exposed above, we believe
that these models could be viewed as mere steps in a same continuous process of
folding and ductile flow of the detachment level. The relative importance of each of
these stages will primarily depend on the characteristics of the basal detachment. For a
fold developed over a thin and relatively competent detachment horizon, the stage of
buckling will probably be short lived and will be rapidly replaced by the propagation of
a fault (e.g., Sans and Vergés, 1995). On the other hand, a fold developed over a thick
ductile detachment will likely develop over a longer time by simple buckling. It is only
when all the ductile material available to fill in the core of the anticline has been
completely evacuated from the adjacent synclines that the fault will start propagating
through the forelimb.
2.3. The structure of the Competent Group (Lower Structure): folding by multiple stratigraphic units in Lurestan Province with special view on Chenareh anticline
The Pusht-e Kuh Arc exposes the later passive margin and early foreland basin
folded stratigraphy in the core of the anticlines. The younger foreland basin succession
is only exposed in rare deep synclines in the Pusht-e Kuh Arc and in the entire Dezful
Embayment. Along the folded arc there are main domains distinguished by folding of
different amplitudes. In the north-east, the Khorramabad anticline is cored by the
Bangestan Group and shows high amplitude and wavelength. In the central part of the
Lurestan the outcropping cores of anticlines are mostly constituted by Amiran to
Asmari Formations. The amplitude and wavelength are normally smaller than in the
previous domain. To the south-west, the Kabir Kuh, Chenareh, Samand and Anaran
anticlines show again strata of the Bangestan Group cropping out in their cores. The
different characteristic of these domains are directly related to variation in the
mechanical stratigraphy across the Pusht-e Kuh Arc as previously discussed (e.g.,
Vergés et al:, submitted).
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III. THE CHENAREH ANTICLINE
3.1. Location of Chenareh anticline in Zagros fold-thrust belt
Previous workers (Berberian and King, 1981; Falcon, 1974; Stöcklin, 1968) divided
the Zagros fold- thrust belt into different sub-divisions, mostly parallel to the strike of
the belt. The division is essentially base on amount of shortening or intensity of
deformation. (Fig. 11) The folded zone forms the most southwesterly deformation zone
of the Zagros orogen. Elevation of the Zagros fold rise gradually to wards northeast the
boundary between folded zone and Imbricated zone is generally abrupt. It corresponds
to high angle thrust fault running parallel to the Zagros range and was named High
Zagros fault. (Berberian 1981). Imbricated zone is a narrow belt, which contains the
highest mountains in the entire range and also exposures of Lower Paleozoic rocks. The
northeastern limit of Imbricated Zone is the Main Zagros reverse fault that was
attributed to the suture zone between Arabian and central Iran by Stöcklin (1968).
The complex evolution of the Zagros basin caused lateral and vertical facies and
thickness variations of sedimentary units. These sediment logical variations, which
caused structural differences during deformation, are the principal reasons to divide the
Zagros folded zone belt into different tectonic sedimentary units, namely Lurestan,
Kohistan and Fars Provinces. (Motiei, 1995).
The Chenareh anticline is located in the Lurestan Province. It is in north of Dezful
and south of Khorramabad cities. The anticline is limited to the south west by the Bala-
Rud Fault that corresponds to the oblique segment of the Mountain Frontal Flexure that
separates the arc from the Dezful Embayment, which contains the major hydrocarbon
reserves of the Iranian Zagros. The Chenareh anticline as well as the Rit and Sultan
anticlines is known for oil and gas exploration in mid Cretaceous and Permian
carbonates. In the west of the Chenareh anticline, the Maleh Kuh anticline is one of the
few discovered oil fields in the Pusht-e Kuh Arc. .
30
Fig. 11 Location Map, Zagros Mountain, SW Iran and study area.
Previous work on the Chenareh anticline
Most of efforts in oil exploration were focused in the Dezful Embayment and Fars
Arc but after first oil discovery in Cretaceous carbonate in the Pusht-e Kuh Arc,
geological exploration started in this tectonic arc. Geological maps at different scale
1.250000 and 1.100000 were produced after field work during several decades by O'B
Perry and Setudenia (1967) and Takin et al. (1970). On the Chenareh anticline there is
only one structural geology report, which was written by (Fakhari et al, 1995). In this
report, the main objective of research was to determine the potential of hydrocarbon for
the group of linked anticlines in this region: the Rit, the Kush-Ab, the Chenareh and the
Marab anticlines. Fig. 12 shows one of the cross-sections, which was constructed in this
report (Fig. 13).
31
Fig. 12 Cross-section from an Internal Report from NIOC (NIOC internal report).
Fig. 13 Geological map showing the location of cross-section and seismic lines.
3.3. Geometry of Chenareh anticline
The Chenareh anticline is a nicely outcropping anticline located in the SE border of
the Pusht-e Kuh Arc (Fig. 14). The anticline has more than 65 kilometer long and
displays a mean width of 8 kilometers at the level of Asmari limestones. Its shape is
quite regular in map view. The anticline plunges in both ends below Gachsaran
evaporites. The. Kush-Ab anticline with wider amplitude together with the Marab
smaller anticlines is located to the north of the Chenareh anticline. The oldest outcrop in
the Chenareh anticline corresponds to the Sarvak Formation (Upper Cretaceous).
32
The Chenareh anticline shows a nicely preserved geometry in its NW segment and
shows a rather disturbed geometry in its SE segment by a set of normal faults. On the
other hand based on field observation in the Kush-Ab anticline there is a local uplift and
likely in this structure the thickness of Amiran formation is not too thick. So, the
geometry of Kush-Ab and Chenareh anticlines at the level of Asmari Formation is
completely different (Fig. 15 and Fig. 16).
The presented geological cross-sections show the variations in fold geometry from
east to west along the Chenareh anticline as observed in . The western segment shows a
very well preserved box folding geometry that is modified by normal faulting that
collapse the southwestern flank of the anticline nearby the Mountain Frontal Flexure
along the Bala Rud Fault (Fig. 17).
Fig. 14 Geological map to show the position of the Chenareh, Kush-Ab and Rit anticlines nearby the Bala Rud Fault. This image is composed with NIOC geological maps and DEM from Google Earth.
33
Fig. 15 Geological map to show the position of the Chenareh, Kush-Ab and Rit anticlines nearby the Bala Rud Fault. This image is composed with NIOC geological maps and DEM from Google Earth.
Fig. 16 Five cross-sections at the level of Asmari limestones to show the strong variation in the style of the folding along the Chenareh anticline. Aerial view towards the SE along the eastern segment of the Chenareh anticline showing the normal faulting that collapses the SW flank of the anticline above the Mountain Frontal Flexure (Bala Rud Fault).
34
Fig. 17 Five cross-sections at the level of Asmari limestones to show the strong variation in the style of the folding along the Chenareh anticline.
35
3.4. Chenareh cross-section I
3.4.1. First version of cross-section I
Cross-section 1 has a length of 28.6 Km and is located 23 Km away from its north-
east plunge (Fig. 18 and Fig. 19). The cross-section crosses the Khush-Ab anticline,
located between the Rit and the Chenareh anticlines. The youngest rocks cropping out
along this section are evaporites of the Gachsaran Formation and the oldest rocks are
Taleh Zang deposits. This cross-section shows the geometry of the eastern segment of
the Chenareh anticline with the normal faults that produce the collapse of the SW flank.
Fig. 18 Map showing location of cross-section I.
36
Fig. 19 Aerial view towards the north-east of the Chenareh anticline with the position of the geological cross-section I
These faults expand the wide of anticline in surface at the level of the Asmari
Formation. So, based on field observations and photos of this area there is no good and
reliable data such as dip and strike. The dip of the Gachsaran Formation in the north of
the Khush-Ab anticline is 5º towards the south-west and there is no surface evidence
showing the other flank of the anticline. For this reason, the Khush-Ab anticline is a
monocline. At the level of the Asmari limestones in the southern flank of the monocline
there are two dip domains: the first one is 5º and the second is 10º. In Chenareh
anticline on the north flank as you see in picture there are 5º dip domain, which put in
contact the Gachsaran and Asmari Formation. The second domain dips 25º, the third is
35º and the fourth is 25º that changes to 13º finally. In the southern flank the Asmari
limestones have been effected by a set of normal fault, However, the anticline shows an
increasing dip downwards reaching 70º-75º dip at the contact with Gachsaran
evaporites. All cross-sections constructed by kink method are based on constant
thickness preservation (Fig. 20).
37
Fig. 20 Geological cross-section I version 1.
38
3.4.2. Second version of cross-section I
In this cross-section I assumed that the topography almost corresponds to the near
top of the Asmari limestones. As well as for the former version of the cross-section I
applied constant thickness for the Amiran, Taleh Zang and Kash Kan Formations that
totalize about 1500 meters along the northern flank of the anticline. Along the crest of
the anticline there is a clear graben with antithetic normal faults that do not propagate
too deep in the culmination. The displacement of the northern fault is about 100 meters
dying about the Asmari-Gurpi contact not affecting the Bangestan Group strata. Also
this cross-section shows a complex geometry in the southern flank of the Chenareh
anticline because the dips between Asmari and Gachsaran are more than 70º and rapidly
change towards the crest of the anticline where are only 10º and 25º.
The wide of anticline in this area expands approximately 600 meters, which seems to
be unreasonable. Otherwise the dip between Gachsaran and Asmari Formations based
on west and east of this section on Asmari is about 45º. The dip on Asmari along the
section is 70º and change to overturned and then change to normal to 45º.
The Bangestan Group crops out in the centre of the anticline showing a disturbed
zone of 980 meter elevation above sea level according longitudinal cross-section. Based
on 2º-dip towards the west of the Asmari formation in cross-section 1 the top of the
Bangestan Group should be located at 300-320 meters of elevation above sea level. So,
in this cross-section the top of the Bangestan Group is located at 320 above sea level
and the thickness of Kash Kan, Taleh Zang, Amiran and Gurpi Formations changed to
1000 meters. This thickness applied for Chenareh anticline increases to the north. In this
version of the cross-section the geometry of the top of the Bangestan Group is
symmetric (Fig. 21)
39
Fig. 21 Geological cross-section I version 2.
40
3.4.3. Shortening along cross-section I
The displacement of the Asmari Formation in the segment of the anticline affected
by the normal faulting, measured along the normal fault, is more than 600 meter
towards the southwest. Shortening is 7.2% only across the Chenareh anticline and
extension is about 1.06%..
41
3.5. Chenareh cross-section II
Cross-section II is 38.5 kilometer long and is located in the middle side of the
Chenareh anticline. The oldest outcrop in the core of the anticline corresponds to the
Sarvak Formation whereas the youngest one corresponds to recent deposits. Cross-
section II is located in a disturbed part of the anticline, which was affected by a set of
normal faults.
I started to draw this section from surface information by using data from the
geological map. Because the level of outcrop in the core of the anticline is at the Sarvak
Formation I complemented this study with a longitudinal section to determine the
structural positions of both the top and bottom of the Asmari Formation on cross-section
II. The top of the Asmari Formation is approximately located at 2500 meters above sea
level (Fig. 22). To complete the cross-section in the anticlines I measured the minimum
thicknesses of outcropping Gachsaran evaporites that turned to be of about 300 meters.
I used all these data together with field observations to construct the geological
cross-section II (Fig. 23 and Fig. 24).
42
Fig. 22 Longitudinal cross-section along the Chenareh anticline.
43
Fig. 23 Aerial picture of the southern part of geological cross-section II.
44
Fig. 24 Geological cross-section II.
45
3.6. Chenareh cross-section III
The geological cross-section III is located across the eastern segment of the anticline
about 7.5 kilometer before its plunge towards the east on top of the Bala Rud Fault (Fig.
25 Fig. 26Fig. 27). This section also crosses an area where the Asmari limestones
change laterally to the Pabdeh Formation. The oldest outcrops correspond to the Gurpi
Formation in the core of the Chenareh anticline and the youngest rocks correspond to
the Labhari Member (Agha Jari Formation) Based on the geological maps and field
observations, the variation in thickness for the Amiran Formation has been taken in
account to build the section. The section also shows that the geometry depicted by the
Asmari Formation is not matched by the rocks of the Bangestan Group at depth.
The geometry of the folds is more difficult to prove along the syncline existing
between the Kabir Kuh and Chenareh anticlines because there are no data in geological
maps nor good observation in the field. Our analysis is based on well data from the
Qaleh Nar oil field where the thickness of the Gachsaran Formation is about 1200
meters (Fig. 27).
According to the well data Qaleh Nar 3, the top of the Asmari Formation should be
located at 2750 m below sea level and the thickness for Pabdeh and Gurpi Formations
should be about 550 m. The Kash Kan Formation is only represented by a thin tong or
rocks. In addition, I assumed 550 m of thickness for the Pabdeh and Gurpi Formations.
The most common variations in the geometry and evolution of detachment fold from
the model in Fig. 28 are: 1) an asymmetric geometry, 2) faulting of limbs to form
faulted detachment fold, 3) complex fold and faulted geometries resulting from multiple
detachment horizons.
In Chenareh anticline you can see all common variation in geometry, also you can
see the evolution of detachment fold (Fig. 28).
46
Fig. 25 Location map to show the situation of the geological cross-section III.
Fig. 26 View to the north-west that shows the central part of cross-section III across the Chenareh anticline.
47
Fig. 27 Geological cross-section III.
48
A
B
C
D
Fig. 28 Cartoon to scale to see the evolution of the Chenareh anticline proposed detachment folding.
49
50
IV. ROLE OF GRAVITY IN PRESENT GEOMETRY OF CHENAREH ANTICLINE
Gravity is one of the important phenomena in modifying the folding structure
especially in those displaying a stratigraphy formed by multilayer sequence with
contrasting mechanical behavior. Among the many authors, who explained complex
structural features in Zagros Mountains, it is worth to mention [Harrison, 1934 #7879] .
These authors recognized the importance of gravity in folds in which a succession of
limestones and marls was exposed creating structural complexity in places where the
underlying structure is simpler. A “flap structure” is one of these spectacular structures,
which were explained by these authors. It is a part of an isoclinally folded limestone
sheet (Fig. 29). For Harrison and Falcon (1934) flaps are purely gravitational structures
resulting from the collapse of over steepened flanks into the eroded valleys synclines).
Fig. 29 Evolution of a flap structure (after Harrison and Falcon, 1934).
Following Saint Bezar et al. (1998), I consider that “flap structures” are recumbent
synclines developed by collapse along the limb of anticlines that maybe enhanced
during the migration of synclinal hinges.
51
In the following I will explain how these gravitational structures observed along the
Chenareh anticline have been included in the geological cross-sections. The Chenareh
anticline displays a strong set of fractures developed in both flanks of the anticline (Fig.
30A). Where dips of the flank are high, thick competent limestones may slide down
above marls using the fractures to detach in the upper part of the slide (Fig. 30B). The
formation of the slide strongly depends on the dip of the anticline flank and on the
correct juxtaposition of limestones and marls that act as detachment levels (Fig. 30C).
In the Lurestan Province, the Amiran, the Gurpi, the Garau and the Dashtak
Formations are potential detachment levels to produce or enhance folds. But in the
study area the larger wavelength of the Chenareh and Rit anticlines seems to suggest
that the fold detachment is located deeper in the section and that the evaporites of the
Dashtak Formation or a deeper units in the Lower Paleozoic are the potential
detachments.
In all these structures in the Zagros Fold Belt a striking characteristic is the absence
or scarcity of thrust faults controlling the geometry and kinematics of the folds: This
scarcity is also observed at the level of subsidiary faults (the so-called “fold-
accommodation faults”, (Mitra, 2002)). Thus the folds presented in this study seem to
correspond also to detachment anticlines. As in the Dezful Embayment, continuing
deformation resulted with the activation of secondary detachment levels. In particular,
there are numerous field examples testifying the role of the Pabdeh-Gurpi marls as a
secondary detachment, which controls the development of minor structures. Different
cases can be separated: Here in the Chenareh anticline the Amiran Formation is the first
detachment level below the Asmari Formation and as you can see the geometry of
structure in Bangestan Group is wider than the one in the Asmari level. The activation
of the Amiran and Gurpi Formations secondary detachment can also trigger the
development of gravity collapse structures as firstly recognised by Harrison and Falcon
(1934). Following these authors, a flap is “a part of a limestone sheet, which has bent
over and backward without breaking” until a completely overturned position has been
attained. We have observed such flaps in the Asmari limestones situated in front of the
Chenareh anticline (Fig. 31). For Harrison and Falcon (1934) flaps are purely
gravitational structures resulting from the collapse of over steepened flanks into eroded
valleys. Following De Sitter (1956), we think that they rather originated during folding.
More precisely and following Saint Bezar et al. (1998), I consider that flap structures
52
along the southern flank of the Chenareh anticline is a recumbent anticline born by the
collapse along the limbs of the anticlines and accentuated during the migration of the
anticline hinges. In any case, the development of a flap structure requires the disruption
by erosion of the Asmari layers involved in the structure (Fig. 32, Fig. 33 and Fig. 34).
This photograph was /taken from the north-west flank of the Chenareh anticline. And
also some times we can see some auxiliary fold which was generated by thrust and
backthrust as you see in photograph in Fig. 32.
53
A
B
C
Fig. 30 A) Oblique fracture system with respect to the anticline axis; B) Opening fractures near the top of a potential new sliding segment of the flank of the anticline; C) Initial movements on the upper part of a gravitational collapse of the flank of the anticline.
54
Fig. 31 Photograph shows sliding of limestone sheet from Asmari on underling marl.
Fig. 32 Photograph shows an auxiliary fold which was generated by back thrust.
55
Fig. 33 A) Photograph and interpretation of a kind of flap structure showing a recumbent fold of Asmari limestones above Gachsaran evaporites. This structure differs from the real flap structures in which the isoclinal syncline faces in the same direction than the anticline flank (Harrison and Falcon, 1934]; B) Line drawing showing recumbent anticline in Oligo-Miocene carbonate (Asmari formation). It has been already described as gravity collapse structure and was named as "flaps" by previous workers (Harrison and Falcon, 1934). I consider that flaps are recumbent anticlines born by collapse along the steep limb of anticlines and accentuated during the migration of the anticlines hinges. So its development requires disruption by erosion of the Asmari carbonate at top structure.
56
Fig. 34 Different helicopter pictures showing the gravitational collapse of the southern flank of the Chenareh anticline.
57
58
V. CONCLUSIONS
The Chenareh anticline outlined at the level of the limestones of the Asmari
Formation is one of the most outstanding whale back anticlines of the Pusht-e Kuh Arc
with a regional NW-SE direction. It is located at the SE border of the Pusht-e Kuh Arc
in Zagros Iran. The anticline has more than 65 km of length and displays at the level of
Asmari Formation a width of 8 km. The Khush-Ab anticline with wider wavelength is
located to the NE of the Chenareh anticline together with an auxiliary fold, which is
called Marab anticline in its south-western flank.
The oldest outcrop in the core of the Chenareh anticline is the Sarvak Formation
(Upper Cretaceous) and the youngest one is Bakhtyari Formation (Pliocene).
The Chenareh anticline exhibits three different segments: a) the NW segment very
well preserved with little normal faulting; b) the central part defined by the gravitational
collapse of the SW flank of the anticline; and c) the SE segment showing the oldest
rocks at the level of Bangestan Group that seems to be rotated to the SW.
In its NW segment, the Chenareh anticline shows a rounded geometry with defined
relatively sharp and rounded hinges bounding steep flanks and flat crestal domains. The
relatively steep flanks and flat crustal domain as well as the rapid decrease in dip at the
base of both NE and SW flanks configure a symmetric box folding geometry, that is
typical of detachment mechanisms.
In the central segment of the anticline, normal faults detach as in many other folds at
the base of the Asmari limestones using marls as detachment horizons. In the lower
parts of the anticline, compressional structures as flaps exist.
The SE segment of the Chenareh anticline is located above the Mountain Front
Flexure along the Bala Rud Fault. The extensive normal faulting affecting the central
segment of the anticline as well as the slight rotation of the SE segment are probably
linked to the Bala Rud Fault. Normal faults and rotation of the anticline can be used to
better define the deep structure of the oblique segment of the Push-e Kuh Arc along the
Bala Rud Fault.
59
Using depth projection methods and constant thickness the Chenareh anticline shows
the main detachment level at a depth corresponding to the evaporites of the Dashtak
Formation of Triassic age. This level also corresponds to the main intermediate
detachment in the Kabir Kuh anticline (the next to the SW).
Shortening in these cross-sections give and amount of 7.2% in compression and
extension of the SW flank in the central segment gives 1.06%.
The Chenareh anticline finally plunges towards the SE beneath the Dezful
Embayment where most of the hydrocarbons are concentrated. These hydrocarbons
migrate upwards and could charge the Pusht-e Kuh Arc anticlines as demonstrated by
the occurrence of abundant oil seeps along the contact between Asmari and Gachsaran
Formations along the Bala Rud Fault near the SE termination of the Chenareh anticline.
In this work I became conscious about the complexities of cross-section construction
using combined data sets. The possibility to constrain the geometry at depth is
important because the Pusht-e Kuh Arc lacks of good seismic data. This is a new area
for exploration that was abandoned long time ago because the repeated dry exploration
wells drilled in the region. Now, with new techniques in exploration from both geology
and geophysics it is worth to start again to explore for smaller oil and gas fields in this
area.
The understanding of the deep structure of the anticlines is needed taking in account
that gas has also a good economical potential nowadays due to the high prices in the
world market. This gas could be used locally in relatively large cities in the Lurestan
Province.
In NIOC we benefited from this work because we better understand the need for good
constrained geological cross-sections, as well as combined with other complementary
disciplines of geosciences, to better define and constrain the potential for HC of other
areas outside the Dezful Embayment.
60
REFERENCES Alavi, M., 1994, Tectonics of the Zagros orogenic belt of Iran: new data and interpretations:
Tectonophysics, v. 229, p. 211-238.
Alavi, M., 2004, Regional stratigraphy of the Zagros fold-thrust belt of Iran and its proforeland evolution: American Journal of Science, v. 304, p. 1-20.
Berberian, M., 1981, Active faulting and tectonics of Iran, in H. K. Gupta, and F. M. Delany, eds., Zagros-Hindu Kush-Himalaya-Geodynamic evolution: Geodynamics Series, v. 3: Washington D.C., American Geophysical Union, GSA and Ed. Board, p. 33-69.
Berberian, F., and M. Berberian, 1981, Tectono-plutonic episodes in Iran, in H. K. Gupta, and F. M. Delany, eds., Zagros-Hindu Kush-Himalaya-Geodynamic evolution: Geodynamics Series, v. 3: Washington D.C., American Geophysical Union, GSA and Ed. Board, p. 5-32.
Berberian, M., 1995, Master "blind" thrust faults hidden under the Zagros folds: active basement tectonics and surface morphotectonics: Tectonophysics, v. 241, p. 193-224.
Berberian, M., and G. C. P. King, 1981, Towards a paleogeography and tectonic evolution of Iran: Canadian Journal of Earth Sciences, v. 18, p. 210-265.
Beydoun, Z. R., M. W. Hughes Clarke, and R. Stoneley, 1992, Petroleum in the Zagros Basin: A Late Tertiary Foreland Basin Overprinted onto the Outer Edge of a Vast Hydrocarbon-Rich Paleozoic-Mesozoic Passive-Margin Shelf, in R. W. Maequeen, and D. H. Lackie, eds., Foreland Basins and Fold Belts, American Association of Petroleum Geologists Memoir 55, p. 309-339.
Biot, M. A., 1961, Theory of folding of stratified viscoelastic media and its implication in tectonics and orogenesis. : Geological Society of America Bulletin, 72, 1595-1620.
Buxtorf, A., 1916, Prognosen und Befundc beim Hanensteinbasis und Grenchenberg
tunnel unde die Bedeutung der Letzeren fur die Geologie de Juragebirges,: Verhand. Naturf. Gesell., Bask, Band XXVII, pp. 185-254.
Colman-Sadd, S. P., 1978, Fold development in Zagros simply folded belt, southwest Iran: The American Association of Petroleum Geologists Bulletin, v. 62, p. 984-1003.
Dahlstrom, C. D. A., 1969a, Balanced cross sections: Canadian Journal of Earth Sciences, v. 6, p. 743-757.
Dahlstrom, C. D. A., 1969b, The upper detachment in concentric folding: Bull. of Can. Pet. Geo., v. 17, p. 326-346.
Dahlstrom, C. D. A., 1990, Geometric constraints derived from the law of conservation of volume and applied to evolutionary models for detachment folding: American Association of Petroleum Geologists Bulletin, v. 74, p. 336-344.
Davis, D. M., and Engelder, T., 1985, The role of salt in fold-and-thrust belts: Tectonoph., v. 119, p. 67-89.
De Sitter, L. U., 1956, Structural Geology. McGraw-Hill, , 551 pp.
Dunnington, H. V., 1968, Salt-tectonic features of northern Iraq: Geological Society of America Special Paper, v. 88, p. 183-227.
Epard, J.-L., and R. H. Groshong, Jr., 1993, Excess area and depth to detachment: Am. Asso. Pet. Geol. Bull., v. 77, p. 1291-1302.
Fakhari, M., and B. Soleimany, 2003, Early anticlines of the Zagros Fold Belt, South West Iran: 2003 GSA Seattle Annual Meeting (November 2–5, 2003), Paper No. 156-23.
61
Falcon, N. L., 1974, Southern Iran: Zagros Mountains, in A. M. Spencer, ed., Mesozoic-Cenozoic Orogenic Belts. Data for Orogenic Studies, v. 4, Geological Society of London, Special Publication, p. 9-22.
Goguel, J., 1952, Traité de tectonique. 1 vol. 8, 384 p., 203 fig., Masson, Paris.
Harrison, J. C., 1995, Tectonics and Kinematics of a Foreland Folded Belt Influenced by Salt, Arctic Canada, in M. P. A. Jackson, D. G. Roberts, and S. Snelson, eds., AAPG Memoir 65 on Salt Tectonics: a global perspective, v. Chapter 19, p. 379-412.
Harrison, J. V., and N. Falcon, 1934, Collapse structures: Geological Magazine, v. 71, p. 529-539.
Haynes, S. J., and H. McQuillan, 1974, Evolution of the Zagros Suture Zone, Southern Iran: Geological Society of America Bulletin, v. 85, p. 739-744.
Heim, A., 1921, Geologie der Schweiz. Band I Molasseland und Juragebirge. Tauchniz, Leipzig.
Homke, S., J. Vergés, M. Garcés, H. Emami, and R. Karpuz, 2004, Magnetostratigraphy of Miocene–Pliocene Zagros foreland deposits in the front of the Push-e Kush Arc (Lurestan Province, Iran): Earth and Planetary Science Letters, v. 225, p. 397– 410.
Homke, S., J. Vergés, J. Serra-Kiel, G. Bernaola, M. Garcés, R. Karpuz, I. Sharp, M. H. Goodarzi, and I. M. Verdú, in press, Late Cretaceous-Paleocene formation of the early Zagros foreland basin: biostratigraphy and magnetostratigraphy of the Amiran, Taleh Zang and Kashkan sequence in Lurestan Province, SW Iran: Geological Society of America Bulletin, v. xx, p. xx.
Homza, T. X., and W. K. Wallace, 1997, Detachment folds with fixed hinges and variable detachment depth, northeastern Brooks Range, Alaska: Journal of Structural Geology, Special Issue on Fault-Related Folding, v. 19, p. 337-354.
James, G. A., and J. G. Wynd, 1965, Stratigraphic Nomenclature of Iranian Oil Consortium Agreement Area: Bulletin of the American Association of Petroleum Geologists, v. 49, p. 2182-2245.
Kashfi, M. S., 1976, Plate tectonics and structural evolution of the Zagros geosyncline, southwestern Iran: Geological Society of America Bulletin, v. 87, p. 1486-1490.
Mitra, S., 2002, Fold-accommodation faults: American Assiociaton of Petroleum Geologists Bulletin, v. 86, p. 671-693.
Mitra, S., 2003, A unified kinematic model for the evolution of detachment folds: Journal of Structural Geology, v. 25, p. 1659–1673.
Molinaro, M., J. C. Guezou, P. Leturmy, S. A. Eshraghi, and D. Frizon de Lamotte, 2004, The origin of changes in structural style across the Bandar Abbas syntaxis, SE Zagros (Iran): Marine and Petroleum Geology, v. 21, p. 735–752.
Motiei, H., 1995, Petroleum Geology of Zagros. Publ. Geol. Surv. Iran (in Farsi), 589 p.
Murris, R. J., 1980, Middle East: Stratigraphic Evolution and Oil Habitat: Bulletin of the American Association of Petroleum Geologists, v. 64, p. 597-618.
O'B Perry, J. T., and A. Setudenia, 1967, Küh-e Kamestãn Geological Compilation Map 1:100,000 (Sheet 20821E), National Iranian Oil Company (NIOC).
O'Brien, C. A. E., 1950, Tectonic problems of the oil field belt of southwest Iran: Proceedings of 18th International of Geological Congress, Great Britain, part 6, p. 45-58.
Poblet, J., and K. McClay, 1996, Geometry and Kinematics of Single-Layer Detachment Folds: American Association of Petroleum Geologists Bulletin, v. 80, p. 1085-1109.
62
Rowan, M., 1997, Three-dimensional geometry and evolution of a segmented detachment fold, Mississippi Fan foldbelt, Gulf of Mexico: Journal of Structural Geology, Special Issue on Fault-Related Folding, v. 19, p. 463-480.
Sans, M., and J. Vergés, 1995, Fold development related to contractional salt tectonics: southeastern Pyrenean thrust front, Spain, in M. P. A. Jackson, D. G. Roberts, and S. Snelson, eds., AAPG Memoir 65 on Salt Tectonics: a global perspective, v. Chapter 18, p. 369-378.
Saint Bezar, B., D. Frizon de Lamotte, J. L. Morel, and E. Mercier, 1998, Kinematics of large scale tip line folds from the High Atlas thrust belt, Morocco: Journal of Structural Geology, v. 20, p. 999-1011.
Sattarzadeh, Y., J. W. Cosgrove, and C. Vita-Finzi, 2000, The interplay of faulting and folding during the evolution of the Zagros deformation belt, in J. W. Cosgrove, and M. S. Ameen, eds., Forced folds and fractures: Geological Society, London, Special Publications, v. 169: London, Geological Society of London, p. 187-196.
Sherkati, S., and J. Letouzey, 2004, Variation of structural style and basin evolution in the central Zagros (Izeh zone and Dezful Embayment), Iran: Marine and Petroleum Geology, v. 21, p. 535-554.
Sherkati, S., M. Molinaro, D. Frizon de Lamotte, and J. Letouzey, 2005, Detachment folding in the Central and Eastern Zagros fold-belt (Iran): salt mobility, multiple detachments and late basement control: Journal of Structural Geology, v. 27, p. 1680-1696, doi:10.1016/j.jsg.2005.05.010.
Stöcklin, J., 1968, Structural history and tectonics of Iran: a review: American Association of Petroleum Geologists Bulletin, v. 52, p. 1229-1258.
Stöcklin, J., 1968, Structural history and tectonics of Iran: a review: American Association of Petroleum Geologists Bulletin, v. 52, p. 1229-1258.
Stöcklin, J., 1981, A brief report on geodynamics in Iran, in H. K. Gupta, and F. M. Delany, eds., Zagros-Hindu Kush-Himalaya-Geodynamic evolution: Geodynamics Series, v. 3: Washington D.C., American Geophysical Union, GSA and Ed. Board, p. 70-74.
Stoneley, R., 1981, The geology of the Kuh-e Dalneshim area of southern Iran, and its bearing on the evolution of southernTethys: Journal Geological Society of London, v. 138, p. 509-526.
Takin, M., Y. Akbari, and J. H. Macleod, 1970, Pul-e Dukhtar Geological Compilation Map 1:100,000 (Sheet 20812 E), National Iranian Oil Company (NIOC).
Vergés, J., J. A. Muñoz, and A. Martínez, 1992, South Pyrenean fold-and-thrust belt: Role of foreland evaporitic levels in thrust geometry, in K. R. McClay, ed., Thrust Tectonics: London, Chapman and Hall, p. 255-264.
Vergés, J., in press 2007, Drainage responses to oblique and lateral thrust ramps: a review, in G. Nichols, C. Paola, and E. Williams, eds., Sedimentary processes, environments and basins: a tribute to Peter Friend, v. Special Publication of the International Association of Sedimentologists.
Vergés, J., R. Karpuz, J. Efstatiou, M. H. Goodarzi, H. Emami, and P. Gillespie, submitted 2007, Multiple Detachment Folding in Pusht-e Kuh Arc, Zagros. Role of Mechanical Stratigraphy, in K. McClay, J. Shaw, and J. Suppe, eds., AAPG Memoir on "Thrust Fault Related Folding".
Willis, B., 1893, Mechanics of Appalachian Structure, U.S.G.S. Annual Report 13 (1891-1892), part 2, 217-281, in G. Mitra, and G. Fisher, eds., Structural Geology of Fold and Thrust Belts, v. 5, Johns Hopkins Studies in Earth and Space Sciences, p. 191-206.
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