The effects of linear coarse-grained slope channel bodies on the orientations of fold developments: a case study from the Middle Eocene-Lower Oligocene Kırkgeçit Formation, Elazığ, eastern Turkey Hasan ÇELİK* Department of Geological Engineering, Engineering and Architecture Faculty, Bozok University, Yozgat, Turkey Received: 06.02.2012
Published Online: 27.02.2013
Abstract: A significant magnitude of tectonic feature deflection away from the principal stress direction was investigated. This was caused by oblique spatial orientation of coarse-grained sediment bodies, principally large conglomerate and sand-filled deep-water slope channels, in an otherwise mud-rich sedimentary section. After detailed mapping and field work to find the cause of this localised fold axis deflection, superbly exposed conglomerate and sand filled deep-water slope channel bodies were found both in and/or next to the core of the folds with the same spatial orientation as the folds. It was concluded that the channel bodies are effectively dictating the orientations of the tectonic structures such as bedding attitude, fold axis orientation, and both trend and location of shearing fractures are related to the folds. It was interpreted that fold growth and propagation have been controlled by the channel orientation within the stratigraphy in this study. The implications of this study urge inclusion of sedimentary body mapping as part of all structural geology work. Conversely, mapping of fold orientation in detail in three-dimensions on seismic data, from subsurface deep-water slopes with hydrocarbon potential, may reveal a direct association between fold axes and the location of coarse-grained reservoir bodies within otherwise low net:gross (muddy) deep water sections. This is a case study in this subject which may also possibly lead to examination of other currently unpublished outcrops and subsurface examples such as the Alikayası Canyon Member of the Tekir Formation in Maraş, eastern Turkey and the Rehy Hill Channel in the Ross Sandstone Formation, Loop Head Peninsula (County Clare), western Ireland, given in the discussion section. Key Words: Linear channels, deep-water, muddy slope, fold deflection, Elazığ, Eastern Turkey
1. Introduction Submarine channels have been a focus of significant research efforts since their discovery in the 1940s on the continental margins of North America (Menard 1995). More recently they have been recognised as important hydrocarbon reservoirs (McGee et al. 1994). Now they are key architectural elements of submarine fans associated with many of the world’s major river systems (Bouma et al. 1985; Damuth et al. 1988; Schwenk et al. 2005). Many of these settings are affected by thin-skinned gravitational collapse, and are characterised by coeval sedimentation and deformation (Clark & Cartwright 2009). Channel-fill elements, together with terminal and intraslope fans and crevasse splays, are exploration targets in buried turbidite systems. Many of the reservoirs in recent discoveries off West Africa consist of sinuous shoe-string, ribbon- and pod-shaped sand bodies deposited within canyons and valleys (Prather 2003; Gee & Gawthorpe 2006). Many of the other systems are commonly described from such *Correspondence: firstname.lastname@example.org
settings, including the Niger Delta (Adeogba et al. 2005; Heinio & Davies 2007; Clark & Cartwright 2009), the Gulf of Mexico (Weimer & Link 1991; Posamentier 2003) and the Nile Delta (Samuel et al. 2003; Clark & Cartwright 2009), Brunei (Demyttenaere et al. 2000). Outcrop analysis, seismic data, borehole and hydrocarbon production data all show that many deepwater channels have complex internal fills, with multiple phases of erosion, bypass and fill (Mutti & Normark 1987; Cronin 1994, Schwab et al. 2007). This complexity could be the result of external factors, such as changes in sediment supply from the shelf, climate and relative sea level (Cronin et al. 2000a, 2000b; Posamentier & Kolla 2003; Cronin et al. 2005). It could also be due to the dynamic nature of slopes, which are complicated by active, growing structures such as faults, folds, salt or mud diapirs and withdrawal basins, and also knickpoint formation along a present-day channel thalweg are due to fold growth (Cronin 1995; Heinio & Davies 2007).
ÇELİK / Turkish J Earth Sci The aim of this study is to show that fold development and resultant orientation in the Middle Eocene–Lower Oligocene Kırkgeçit Formation has been controlled by the previous orientation of coarse-grained linear channelised sedimentary bodies in an otherwise low net:gross (muddy) deep-water slope sequence. The channel body orientations, and thus the fold axis orientations, are oblique to the known regional directions of principal compressive stress. This means that fold axis orientations alone may be misleading to structural geologists who aim to unravel these relationships. Also this will be a good case study to open a new window for geoscientists to work on similar outcrops like the Alikayası Canyon Member of Tekir Formation, Maraş, eastern Turkey and the Rehy Hill Channel in the Ross Sandstone Formation, Loop Head Peninsula (County Clare), western Ireland, and other subsurface relationships between channels and folds. In previous studies, the interactions or relationships between channel and folds show the effect of folds on channel development. This is the first study in the literature explaining the effect of the deep water channels on fold development. 2. Geological setting Turkey is characterised by a very complex geology, and consists of several continental fragments which were combined into a single landmass in the late Cenozoic, whose main features are still poorly understood despite the increasing amount of geological data that have become available in the last 25 years. The complex geology has
resulted in widely different views on the geological evolution of Turkey. Every geological picture of Turkey will therefore be a personal one and subject to future modifications and corrections (Okay et al. 2006; Okay 2008). The study area is a good example of this complexity. The study area (Figure 1) is situated in the eastern part of the Tauride Orogenic Belt, one of the four major tectonic subdivisions of Turkey, in the East Anatolian Compressional Province (Ketin 1977). The stratigraphy of the study area, shown in Figure 2 and Figure 3, ranges from latest Palaeozoic to Pliocene and is described below. Around Elazığ (Figure 1 and Figure 2) units ranging from Permo-Triassic to Pliocene age crop out. In the southern part of Figure 2, Jurassic–Lower Cretaceous Guleman Ophiolites, the Upper Maastrichtian–Middle Eocene Hazar Group and the Middle Eocene Maden Group have no contact with the Middle Eocene–Lower Oligocene Kırkgeçit Formation, which contains the channel deposits influencing the fold developments. The Permo-Triassic Keban Metamorphites (Figure 2 and Figure 3), forms one of the basement units to the Cenozoic sediments. This unit, consisting of marbles, calc-phyllites, calc-schists and metaconglomerates, which have undergone amphibolitegreenschist facies metamorphism and been thrust over younger formations (Turan & Bingöl 1991), is the oldest unit in the Elazığ area. The Senonian Elazığ Magmatic Complex (Turan et al. 1993) consists of very varied lithological components in the Hakkari area (Figure 1), but has an orderly vertical
Study area ELAZIĞ
ch ren o T ab r t S
Dead Sea Fault
SYRIA North Anatolian Fault Zone East Anatolian Fault Zone Bitlis Suture Zone Normal Fault
Figure 3. Stratigraphy of the study area (modified from Özkul 1988).
sequence from gabbroic–dioritic plutonic rocks at the base, through basaltic–andesitic volcanics, volcaniclastics and granodioritic-tonalitic rocks at the top in the Elazığ area. In the study area, the Elazığ Magmatic Complex (Figure 4) consists of basaltic lava flows, pillow lavas, pyroclastic and volcanoclastic rocks cut by dykes and thrust over the Kırkgeçit Formations around Elazığ (Figure 2). It is unconformably overlain by the Upper Maastrichtian Harami Formation, which crops out north-west of the study area, starting with reddish conglomerate and coarse pebbly
sandstones at the base, passing upwards into recrystallised massive limestones, particularly immediately north-east of Elazığ (Naz 1979; Tuna 1979; Perinçek 1980a; Özkul 1982, 1988; Turan 1984, 1993; İnceöz 1994) shown in Figure 4. The formation has been clearly affected by various tectonic events since the Laramide between Maastrichtian and Early Palaeocene, clearly manifest as shearing fractures in the limestones (Figure 4). The Kırkgeçit Formation (Middle Eocene-Lower Oligocene), contains the channels, and is the one of the
ÇELİK / Turkish J Earth Sci
1600 m 1405 m
Dip and strike
+ __ + _
te era glom Basal con
Harami Formation, Kh (U. Maastrichtian)
Kemb Basalt, andesite
Elazig Magmatics (Senonian)
Kirkgeçit Formation (M.Eocene -Lower Oligocene)
A' Karabakir Formation (U. Miocene-Lower Pliocene)
Cross section line in Figure 7b
_ + + _
+ _ +
Location of Figure7a
Hasret Mnt. _
Channel location number
Vertical bedding 30
Kemd Dioritic rocks 0
Figure 4. Geological map of Hasret Mountain and nearby areas (expanded and modified from Cronin et al. 2000a, 2000b). The geology from the northern part of Oymaağaç in the map is from İnceöz (1994). A-A’ cross section is in Figure 7b.
most widespread units in the Eastern Taurus region. The type locality for the formation is around Kırkgeçit village near Van (a city in the far east of Turkey, Figure 1), and was first named by Perinçek (1979a). In the Elazığ region
the unit covers an E–W oriented area about 40 km wide and 100 km long (Figure 4, grey outcrops) and has been the subject of many studies (Perinçek 1979a, 1980a; Tuna 1979; Naz 1979; Özkul 1982, 1988; Turan 1984,
ÇELİK / Turkish J Earth Sci 1993; İnceöz 1994; Cronin et al. 2000a, 2000b; Cronin et al. 2007a, 2007b). The Kırkgeçit Basin around Elazığ is confined by approximately E–W oriented block faults, so the basin extends in an E–W direction, as shown in Figure 8a. The Kırkgeçit Formation overlies the Elazığ Magmatic Complex and the Harami Formation with angular unconformity (Figure 3) in the Elazığ region. The Kırkgeçit Formation was overthrust by the Elazığ Magmatic Complex to the north of the study area. It is interpreted as having been deposited in a back-arc setting, behind the Permo-Triassic Bitlis Massif (Aksoy & Tatar 1990). Block-faulting on the northern and southern margins of the Kırkgeçit Basin is thought to have occurred within an extensional regime, caused by subduction of the Arabian plate under the Anatolian plate (Özkul 1988). Subduction is thought to have occurred in several phases, as indicated by vertical and lateral facies changes east of Elazığ (Turan 1984). The Kırkgeçit Formation in the Elazığ region consists of a basal conglomerate, overlain by a deep-water facies which has been interpreted as a slope apron in the east and a distally-steepening, mud-prone submarine ramp 70 km to the west, both propagating from an E–W orientated, south facing, steep, backarc basin margin (Cronin et al. 2000a, 2000b). These facies are overlain, locally disconformably, by shelf facies.
In the study area the slope and shelf sequence of the back arc basin are exposed east of the city of Elazığ, in badlands on the western slope of Hasret Mountain (Figure 2 and Figure 4). The badlands sink area is 3 km wide and 6 km long, dissected by one trunk wadi and further dissected by a dense network of smaller wadis that drain the mountain. The badlands are surrounded on three sides by younger Kırkgeçit Formation shelf facies (Figure 4), which prograded over the deep-water slope sequence from the north and east. The formation is in unconformable contact with the Elazığ Magmatic Complex basement rocks (Cronin et al. 2000a, 2000b). A geological map of Hasret Mountain area is shown in Figure 4. In the southern half of the figure, in the main area of this study, five channel localities are seen. Northern channel localities are not subject of this study since they were highly affected by the thrust and lost their initial relationships with the folds. These are nested in a background of shale and capped by muddy debris flow and slump deposits (mass transport complexes, or MTCs), shales and shelf facies. Palaeocurrents within the channel bodies are towards the south–south-west. These palaeocurrents change to west–south-west near the contact with the Elazığ Magmatic Complex at Channel 4 (Figure 4 and Figure 5). The MTCs form packages up to 30 m thick, composed of massive mudstones with scattered cobbles, boulders and olistoliths of intra- and extra-basinal material
Elazığ Magmatics (Senonian)
Kırkgeçit Formation (M.Eocene - Lower Oligocene)
Channel location number
500 m Elazığ Magmatics (Senonian)
Figure 5. Interpretation of planform geometry of the Kirkgeçit Formation deep water slope channels related to the folds. The channels form a tributary system (modified from Cronin et al. 2000a, 2000b).
ÇELİK / Turkish J Earth Sci (Figure 7b), and extend laterally for several kilometres, making them useful lithostratigraphic markers. Deepwater sandstone sheet facies are correlatable as packages of tabular sandstones (Figure 7b) with lateral extents of up to several hundreds of metres over all of the channels: all channels and sheets are found within the same narrow stratigraphic interval (Cronin et al. 2000a, 2000b). The coarse-grained channel bodies were highly affected by synsedimentary tectonism and the effects are seen as shearing fractures and gravity faults, particularly wellexposed at the Channel 1 locality (Figure 4). Also folds are seen in the study area and are associated with the channel orientations. Correlation of the channel bodies by tracing fill packages laterally, GPS mapping and aerial photographs have resolved three separate channel complexes. These channel complexes are interpreted to have been active at the same time, from their stratigraphic relationships, and the similarities between their multistorey fills (Figure 4 and Figure 5). Previously, four channels were identified from four exposures in this area, and called Channels 1-3 and Channel 4, or the Main Channel (Özkul 1988). However, more extensive mapping resolved three complexes (Cronin et al. 2000a, 2000b). These complexes formed an approximately syn-depositional tributary network on a steep, deep-water slope (Figure 5). These deep-water channels are very well exposed through the labyrinthine modern wadis that dissect the western and eastern slopes of Hasret Mountain, as are their related levees and overbank complexes (including crevasse splays and channel levee breach plugs). These have been described in detail elsewhere (Cronin et al. 2000a, 2000b). The youngest formation of the study area is the Upper Miocene–Lower Pliocene Karabakır Formation which was first described by Naz (1979) and the Çaybağı Formation (Upper Miocene–Pliocene?, Türkmen 1991), subsequently studied by various authors (Sungurlu et al. 1985) elsewhere in the Elazığ area, and they rest with angular disconformity on the older formations (Figure 3 and Figure 4). 3. Tectonic features of the study area The eastern part of Turkey is a continuation of the Alpine–Mediterranean Belt (Ketin 1977), and the presentday tectonic setting (Figure 1) is the result of continued continental collision between the Arabian and Anatolian plates, which began in the Middle Miocene. The Middle Miocene is widely regarded as the start of Neotectonic time in south-eastern Turkey (Şengör 1980; Şengör & Yılmaz 1983; Şengör et al. 1985). The exact movement direction of the Arabian plate towards the Anatolian plate is controversial and it is debated whether or not its movement is simply towards the north (Şengör 1980; Şengör & Yılmaz 1983; Tatar 1987;
Aksoy & Tatar 1990). Şaroğlu and Yılmaz (1987) pointed out that the Eastern Anatolian Fault has a dominantly dip slip movement along the area between Maraş and Hatay (Figure 1) and therefore the plate movement cannot be towards the north but towards the north-east. Tatar (1987) emphasised that there is a NNW direction of convergence around Erzincan and Sivas (Figure 1) and a NNE direction of convergence in the Elazığ area. The convergence direction between the two plates was determined as N–S by Aksoy and Tatar (1990) around the city of Van, further to the east (Figure 1). Closing of the Tethys Ocean by subduction in that direction under the Anatolian Plate resulted in a final continental collision between the Arabian and Anatolian plates in the Middle Miocene (Arpat & Şaroğlu 1975; Şengör 1980; Şengör & Yılmaz 1983; Yalçın 1985; Şaroğlu & Yılmaz 1987; Aksoy & Tatar 1990; Turan 1993). An approximately N–S directed compressional regime was formed by continental collision in the Middle Miocene in eastern Turkey. This N–S compressional regime is indicated by crustal thickening by thrusting, E–W directed fold axes, thrust faults (Figure 2 and Figure 6) and intramontane basins, N–S directed tension fractures, and by both NE–SW directed left-lateral and NW–SE directed right lateral strike slip faults in the Eastern Anatolian area (Şengör 1980; Şengör & Yılmaz 1983; Şaroğlu & Yılmaz 1987). The controversial exact movement direction of the Arabian plate towards the Anatolian plate discussed above is derived from kinematic analysis of the tectonic structures, such as shearing fractures, fold axes and bedding attitudes (e.g. Tatar 1987; Aksoy & Tatar 1990; Turan 1993; Turan et al. 1993). Since some of these structures are related to the competent channel bodies in muddy slope sequences as in the following sections, the structural works show different movement directions. As seen above, the direction of plate convergence is controversial in this area, and that this paper attempts to improve understanding of why the interpretation of the direction of movement of the Arabian Plate relative to the Anatolian Plate in the area has been so problematic, since the principal compressive stress directions are frequently measured for tectonically important areas, such as around eastern Anatolia, by using obvious folds and other structures such as those accessible outcrops around Elazığ, Eastern Turkey. Conclusions from this important local series of interrelationships between deep-water sedimentary architecture and subsequent fold growth and propagation may be drawn which have potentially significant impact on studies of analogous areas at outcrop and in the subsurface. The orientation of the tectonic features in the study area differ significantly from the general E–W trend of folds
Figure 6. Simplified structural map showing relationship between general orientation of folds in Elazığ area and the study area. Main arrows (P) represent the direction of the compression caused by convergence between Arabian and Anatolian plates. a)
Figure 7. (a) A photo showing Channel 1, Channel 5 and related folds and attitudes; (b) A-A’ cross section (location of this section is shown in Figure 2).
ÇELİK / Turkish J Earth Sci
Kırkgeçit Formation S Harami Formation (M. Eocene-Lower Oligocene) (U. Maastr.)
Keban Metamorphics (Permo-Carb.) Sea level 1
Elazığ Magmatics (Senonian)
Slope Channel Fills Elazığ Basin Main thrusts: Late Cretaceous - Early Paleocene (foreland basin setting) Gravity faults: Eocene (back-arc basin setting) A
atics agm ) M ğ ı n Elaz enonia (S
atic Magm Elazığ onian) ( Sen
+_ e) n cen atio Oligo m r or it F owe geç ne-L k r Kı Eoce . (M
Hasret Mnt. 1621
l) ne an h c
s tic ma g ) Ma ian zığ non a l E ( Se
Keban Metamorphics (Permo-Carb.)
Folded area related to the channels
Harami Formation (U. Maastr.)
Shelfal calcarenites Slope Channel Fills
Elazığ Magmatics (Senonian) 1 2
Late Miocene thrust faults. Reactivated old thrust fault in the Middle Miocene (see a- 1 )
Kırkgeçit Formation (M. Eocene-Lower Oligocene) Elazığ Magmatics (Senonian)
Figure 8. (a) Block diagram showing the palaeogeography of the Elazığ Basin during the late Middle Eocene. The dashed box represents the studied section of the basin (modified from Cronin et al. 2005); (b) Simplified geological map of the study area; (c) An oblique cross section of the channels and fold orientation along the A–B line in Figure 8b (Left part of the section represents the northern continuation of the photo in b).
ÇELİK / Turkish J Earth Sci N
N P1 (305°)
S b. Vertical shearing fracture orientation in Channel-1 (n=40)
S a. Bedding planes and fold orientations of the study area (n=56) P1 (340°)
c. Vertical shearing fracture orientation in slope channel overbank (rib) (n=28)
d. Vertical shearing fractures in shelfal calcarenite (n=28)
Figure 9. Interpretation of fold axis orientation, based on bedding attitudes (a) and principal stresses based on vertical shear fracture orientations of various lithologies (b-d) of the Hasret Mountain area in stereonet and rose diagrams.
and general fractures in Eastern Anatolia described in section 2. In Figure 6, the folds numbered 1 to 5 developed in the Kırkgeçit Formation clearly have an approximate E–W orientation. All the folds in the formation, including in study area, developed at the same time during postOligocene compressional tectonism (Turan et al. 1993). The folds in Figure 11 and Figure 12 deform the Upper
Miocene–Pliocene Çaybağı Formation (Türkmen 1991). The orientation of the fold axes in the study area deviate about 45° from the E–W directed fold axes found elsewhere in an east–west section from Baskil–Elazığ–Palu, north of Lake Hazar, which is located on the Eastern Anatolian Fault (Figure 6).
ÇELİK / Turkish J Earth Sci
Figure 10. Simplified model for relationship between maximum principal stress (P) and the channels and fractures located in the studied area (P1 and P2 are components of P).
3.1. Relationship between the channels and the folds Two folds and one monocline are documented in this study to illustrate the phenomenon of sediment bodycontrolled fold axis deflection (Figure 4 and Figure 7a,b). The importance of these undocumented structures is that the location and orientation of the fold axes mirror the sedimentological orientation of the coarse-grained deep water channels. The palaeogeography of the northern basin slope is shown in Figure 8a. The folds in the Kırkgeçit Formation, with axes shown in Figure 8b, have been controlled by the channels. Detailed mapping and measurement of the attitudes of structural components in the study area showed that
channels and fold axes have a NE–SW trend (Figure 4, Figure 5 and Figure 8 a,b,c). Palaeocurrents within Channel 1 (Figure 4) are from NE to SW. The Channel 1 location is exactly on the core of the anticline (Figure 7a,b). Channel 1 and the anticline (Figure 4 and Figure 8 a, b, c) have a plunge of 12° towards the SW (Figure 9a). The attitudes of the beds in Figure 4 and Figure 9a show that this fold is an asymmetric anticline. Channel 1 is also cut by several minor normal faults (Figure 4). The second fold is an asymmetric syncline and its axis is parallel to both the axes of Channel 1 and the anticline (Figure 4 and Figure 7a,b). In Figure 4 it is seen that the syncline is located between Channel 1 and Channel 5. This
N (Plio-Quaternary fluvial sediments)
S (Plio-Quaternary fluvial sediments)
Çaybağı Formation (U. Miocene-Pliocene?)
500 m A
Figure 11. A Google Earth image showing overturned folds and an A–B cross section in the Upper Miocene-Pliocene Çaybağı Formation west of Çaybağı town (the location is in Figure 6).
ÇELİK / Turkish J Earth Sci N
Çaybağı Formation (U. Miocene-Pliocene?)
(Plio-Quaternary fluvial sediments)
mud ston e, si ltsto ne sand ston e
920 880 Hacısam Stream
Figure 12. Overturned fold in the Çaybağı Formation east of Çaybağı town (the location is in Figure 6).
indicates that the two channels controlled the orientation of the syncline here (Figure 8 b,c). The monocline is situated on Channel 5 and its axis is also parallel to the orientation of the channels (Figure 5 and Figure 8 b,c). 35°E
Other evidence for a relationship between the channel body orientations and fold orientation and location is in the attitudes of the beds on the northern side of Channel 4 (Main Channel). As mentioned in section 2, since the
T U R K E Y Z
37° 30' N
d S ea
UN MO OS
KE İS Y BA
T. FL Golbaşı
F l t.
ARABIAN PLATFORM 36° 30' N
Figure 13. Location map of the Miocene Maraş Basin (boxed area), eastern Turkey (mainly after Kang and Kozlu 1990). AKM: Alikayası Canyon Member.
Alikayası canyon fill w
ÇELİK / Turkish J Earth Sci
Figure 14. View of the western margin of the Alikayası Canyon (indicated in Figure 13 NW of Maraş). The dips in the centre of the canyon are shallow and steepen towards the western margin of the canyon, where the Aslantaş Thrust Fault is present.
compressional regime is N–S the strikes of the beds should have been in an E–W orientation. But they are parallel to the axis of the Main Channel at this locality, and so the cause of the present attitudes of the beds is because of the location of the channel here (Figure 4 and Figure 8 a,b,c). 3.2. Interpretation of the structural data using stereonet and rose diagrams The measurements from bedding, vertical fractures and fissures in the study area were evaluated in stereonet and rose diagrams (Figure 9) and the relationship between orientation of main stress (P) and fold axes were analysed for the study area. General strata dip orientation (Figure 9a). This figure shows the general attitudes and the poles of the beds in the study area on stereonet. Most of these measurements were taken from south-westerly plunging fold limbs. This figure shows that the axes of the folds trend NE–SW and plunge SW with an angle of 12°. The strike of the main stress (P) has to be NW–SE. The number of measurements, n, was 56.
Shearing fractures of Channel 1 (Figure 9b). Since all the shearing fractures are vertical in the study area, rose diagrams were used. From plotting measurements from vertical shearing fractures and fissures in Channel 1 (Figure 7a), which has a large number of fractures, it was observed that the bisector of the acute angle is N 55° W. This angle suggests that the maximum principal stress (P) strikes NW–SE. The number of measurements, n = 40. Shearing fractures in overbank sediments (Figure 9-C). Twenty-eight vertical shearing fracture measurements (n) from slope channel overbank (Figure 4) sediments and sandstone sheets overlying the channel-fill bodies (sandstone ribs) were plotted in this rose diagram and the result is that the bisector (P) is oriented N 20° W. Shearing fractures in shelf calcarenites (Figure 9-D). Shearing measurements were taken from shelf calcarenites at the top of the sequence (Figure 4), 28 and the bisector (P) orientation is N 30° W. The average direction of the mean stress (P) obtained from the rose diagrams is N
Figure 15. Close-up view of right bottom part of Figure 14. Note the truncated surfaces between the phases because of the canyon-fold development interaction. Canyon axis is moving eastwards, in the right hand side of the picture. Scale is a man, 168 cm tall.
ÇELİK / Turkish J Earth Sci 20 N
30 10 25
24 10 16 20 15
30 35 30 16 50 50
32 30 25
10 Kilbaha Bay
30 20 10 Rehy Hill Kilcloher 10 Bay
Mouth of the Shannon 3 km
Figure 16. Simplified structural map of the Loop Head Peninsula. The map illustrates strike and dip measurements and the all fold axis orientations in the area. Modified from Pyles (2008).
35° W. This is approximately perpendicular to axes of the channels and the folds. This orientation of mean stress is different from the mean N–S stress orientation accepted by previous workers (see references in section 2) for this part of eastern Turkey. The reason for this observed difference is discussed below. 3.3. Comparison of the structural features in the study area with the general tectonic features of the Elazığ Area Around the study area, the general orientations of fold axes are approximately E-W (Figure 6). But in the study area the fold axial orientations and the strike of general bedding planes are NE–SW. The reason for this difference is thought to be the NE–SW oriented deep-marine coarsegrained channels located in the study area (Figure 4, Figure 5 and Figure 8). The margins of the Elazığ Kırkgeçit Basin (Figure 2) and the normal faults forming the basement structure are aligned E–W (Figure 8a); for this reason the E–W oriented basement structures are unlikely to control the NE–SW oriented channels and folds formed by N–S directed main compression (Figure 6 and Figure 10). Outside the map area, no other channels are observed since the Senonian Elazığ Magmatics were subsequently thrust over the Middle Eocene–Lower Oligocene Kırkgeçit Formation from North to South and covered all the channels and folds. 3.4. Interpretation of the relationship between main Stress and the structural features In Figures 6 and 10 the main compressional N–S directed stress affecting the Eastern Taurides is represented by the largest arrows (P). As clearly seen in these figures, the orientations of the structural features in the study area are not perpendicular to the direction of the main stress (P), as they should be. Since the channels are present in the cores or are next to the folds, the components of main stress (P1 and P2) are effectively controlling occurrence of
the folds. Thus, the coarse-grained deep water channels play a determinative role on the location and orientation of these folds (Figures 9 and 10). The average bedding dips on the fold limbs is 20° in the study area, as the components P1 and P2 of the main stress P cause the development of the folds (Figure 10). In contrast, the folds east of the study area near Çaybağı town (Figures 6 and 11) within the Upper Miocene–Pliocene Çaybağı Formation (Türkmen 1991), younger than the Middle Eocene–Lower Oligocene Kırkgeçit Formation, are overturned because the main stress P is directly affecting the beds in the Çaybağı Formation (Figure 6, Figure 11 and Figure 12). Their axes are perpendicular to the main stress P (Figure 6), since there are no channel bodies in the Çaybağı Formation, and much less enveloping shale around the folds. 4. Discussion Fold geometry controlled by competent linear channel bodies within less competent mudstone dominated rocks is a new subject. In this study it was presented that coarse grained channels in muddy deposits can control fold orientations during subsequent deformations. Previous studies about the channel–fold relationship only presented how folds affect channel orientations. As this is a case study in this subject, there is no other work to show as an analogue. The number of studies which address the interactions between submarine channel development and deformation is relatively low and they tend to focus only on a particular aspect of channel evolution, such as the channel axis. These studies have shown, for example, that increases in slope gradient caused by structural highs result in increased submarine channel incision, with channel down-cutting being localised where the gradient increase is highest. These studies have also shown that submarine channel
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Figure 17. View and line drawing of the channel elements in the lower part of the Ross Sandstone Formation exposed at Rehy Hill cliff. Note that the fold axis to the right of the figures, as well as the other fold axes in the Figure 16, is not parallel to the cliff.
sinuosity is a key factor in the development of potentially sand-rich lateral accretion packages (Abreu et al. 2005). In structurally complex slope settings, submarine channel sinuosity can vary according to changes in gradient. Higher sinuosity channel reaches tend to be localised where the underlying slope gradient decreases (Clark & Cartwright 2009). Some recent studies (Clark & Cartwright 2009; Hubbart et al. 2009; Clark & Cartwright 2011) aimed to document the interactions between submarine channel systems and deformation within deep-water compressional provinces. In deep-water fold belt settings, where submarine channel systems develop on a structurally deformed seafloor, four end member channel–structure interactions (confinement, diversion, deflection and blocking) were defined by Clark and Cartwright (2009), who have observed that these four types of interaction are common wherever submarine channels occur in structurally active deep water settings such as the deep water Gulf of Mexico and deep water Nigeria. Clark and Cartwright (2011) stated that where deformation is coeval with channel development an increase in the relative rate of uplift versus deposition and erosion causes a transition from channel deflection to blocking. Diversion and confinement are linked by the number, scale and orientation of structures relative to the channel flow path. Other analogues that can support this study may be found in other formations subsurface or at outcrops elsewhere. Here, two examples found in our ongoing studies, which have not yet been published, were summarised in the following sections 4.1 and 4.2.
4.1. Alikayası Canyon Member of the Tekir Formation, Maraş, eastern Turkey The Alikayası Canyon Member of the Tekir Formation occurs in a thick sequence of deep-water slope deposits on the northern margin and centre of the lower–middle Miocene Maraş foreland basin in eastern Turkey (Figure 13). The canyon was one of at least four major sedimentbypass systems that were sourced from a narrow shelf otherwise occupied by thick, coeval carbonate reefs (Figure 13 and Figure 14). What remains of the source hinterland indicates that thick fan deltas propagated directly into the heads of the deep-water canyons that characterise these bypass systems (Cronin et al. 2007c). The Alikayası Canyon is exposed as an almost completely exhumed sediment body in an area of sparse vegetation, where the contemporaneous shelf margin is still largely intact, and it represents the youngest of these four systems. It forms a 10-km long, up to 300-m thick, and up to 1-km wide sediment body, dissected once by a river, which is now drowned by an artificial lake behind the Menzelet Dam (Figure 14). The exposure is complete apart from a 1.5 km section through its most proximal reaches, and a 2 km section in its most distal reaches where it feeds into a series of sandy lobes. The canyon fill is characterised by stratified conglomerates and pebbly sandstones in its lower part, stratified conglomerates and braid-plain-style conglomerates and pebbly sandstones in its middle part (Figure 14), and steeply dipping fan-delta conglomerate clinoforms in its upper part. The axial area of the canyon is dominated by these coarse-grained deposits, although
ÇELİK / Turkish J Earth Sci locally remnants of intracanyon shales, in the form of floating rafts, shale blocks, and clasts, or less common in situ shale horizons, are also seen (Cronin et al. 2007c). The canyon fill is situated in a transition area between the two main thrust fault zones, namely the Aslantaş Fault Zone to the western side of the Maraş Basin (Figure 13) and the Engizek Fault Zone marking the northern side of the basin. The arrow represents the palaeocurrent direction and the axis of the Alikayası Member canyon fill shown by pebbly sandstone pattern in the location map NW of Maraş (AKM in Figure 13). The dip orientation of the beds on both sides of the canyon defines a syncline in which the canyon fill is situated with its axis parallel to the syncline axis. Figure 14 shows the western margin of the canyon fill and the western limb of the syncline dipping east. Dips change rapidly towards the Aslantaş Thrust Fault (Figure 13) on the western margin of the canyon and become horizontal at the top of the canyon fill stages. The basin underwent synsedimentary compressional tectonism (Kang & Kozlu 1990), and it is thought that the Alikayası canyon fill dictated the formation of the syncline in its present position. Also, a synsedimentary interaction can be seen as truncated surfaces in the lower part of the canyon (Figure 15). Reactivation of the Aslantaş Thrust fault from west to east caused the eastward shift of the canyon axis during the earlier stages of the canyon fill, and Miocene destabilisation and movement of the sediment via deep sea systems, particularly slope collapse and development of mass-transport complexes. When the canyon fill became a huge structure in its later stages, it dictated the formation of the syncline parallel to its lineation by preventing the eastward movement of the channel axis caused by the Aslantaş Thrust Fault. 4.2. Rehy Hill Channel in the Ross Sandstone Formation, Loop Head Peninsula (County Clare), western Ireland The Ross Formation of the Western Irısh Namurian Basin (WINB) (Strachan 2002) was deposited in the Carboniferous Shannon Basin, one of many Namurian basins located in northwest Europe and crops out on the Loop Head Peninsula (Figure 16) and Ballybunnion areas of western Ireland (Pyles 2008). The intracratonic basin was formed on a continental crust with active extension during the Late Devonian–Early Carboniferous and is structurally controlled (Collinson et al. 1991). The Ross Formation is an example of an ancient submarine fan that was deposited in a transtensional basin (Collinson et al. 1991; Strachan 2002). The formation consists of four main divisions, namely basal, lower, middle and upper parts (Pyles 2008). Around Kilbaha Bay and Rehy Hill (Figure 16 and Figure 17) the lower part of the formation is layered, with most of the amalgamation of the broad channels occurring where erosional axes (Figure 17) cut into underlying
sand bodies at the sea-cliff exposures dominated by compensationally stacked, broad channel complexes up to several hundred metres wide and about 8-15 m thick (from one of our field trips in 2008). The exposures of the formation commonly contain well-exposed, laterally continuous strata that are deformed by postdepositional Variscan folds (Pyles 2008). The fold axis orientations in the Ross Formation (Figure 16) on the Loop Head Peninsula are aligned ENE–WSW. At Rehy Hill, a channel about 200 m wide and 15 m crops out at the cliff section. On the eastern side of the channel an anticline with an axis trending NNW–SSE is seen in Figure 17. It is thought that the same channel-fold relationship, the subject of this study, is seen here between the fold development and the Rehy Hill channel. This example also needs to be worked on in detail in this manner, as well as the Maraş Alikayası Canyon. 5. Conclusions The close relationship between sedimentology and tectonism is clearly illustrated, with specific sedimentary bodies in the sediment architecture deflecting major tectonic features, such as fold development and propagation away from the directions of the main compressional stress. The coarse-grained deep-water channels are the sedimentary bodies that appear to have controlled the fold development. Their linear geometry within the stratigraphy in the study area deviates the fold axes from an E–W to a NE–SW direction. The spatial orientation of the channels also has an effective control on the attitudes of bedding, axes of folds and their locations, and the orientation of shearing fractures. If the main stress is not perpendicular to the strike of channels, as explained in the text, the angles of dips of the fold limbs related to the channels become much lower as they are older. The tectonic interpretation of the direction of regional compressional stress in areas which include coarsegrained channel bodies in a muddy envelope requires further attention. Some investigators describe the main stress resulting from the convergence of Arabian and Anatolian plates (P) as NW–SE in the Elazığ area, although the trends of the fold axes, however, prove that the principal compressive stress (P) was N–S. This study has implications for the solution of such problems in these kinds of complicated and tectonically active areas. We cannot rely on data collected purely from fold axes without an awareness of formation architecture, a knowledge of which can only be garnered from detailed sedimentological mapping. In the interpretation of subsurface data, such as three dimensional seismic data, close attention should be paid to the development of fold structures in muddy deep water sedimentary successions. Local obliquity of fold axis
ÇELİK / Turkish J Earth Sci orientation may well be caused by the location of coarser sedimentary bodies (potential hydrocarbon reservoirs). This is particularly important in both compressional settings such as offshore Brunei, and in passive margin settings with large scale compressional structures caused by gravitational collapse of slope or delta fronts, such as the ultra deep-water Gulf of Mexico, or West Africa. The result of this study can be applied to many other outcrops affected by post-sedimentary compressional stresses such as the Alikayası Canyon Member of the Tekir Formation, Maraş, eastern Turkey and the Rehy Hill Channel in the Ross Sandstone Formation, Loop Head Peninsula (County Clare), western Ireland. The channel-fold relationship gives useful information about the relative timing of channel fills and fold development. In this study fold diversion because of a channel fill resulted from compressional stress which postdated the channel development.
Acknowledgements The author wishes to thank Dr. Bryan T. Cronin (Deep Marine, Aberdeen, U.K.) for 14 years of annual field work in the area, for his input from his knowledge of deep-water sedimentology and basin development in extensional and compressional settings, and for his reviews of versions of this paper. The author is also grateful to Professor Dr. Erdal Kerey, who, with Professor Gilbert Kelling (Keele University, UK) and Professor Andrew Hurst (University of Aberdeen, UK), introduced the author to the exposures in the Elazığ area. Staff at Fırat University, Elazığ, Turkey, Professor Dr. Ercan Aksoy and Professor Dr. İbrahim Türkmen; are warmly thanked for their hospitality and assistance in the field. The sponsors of the Turkey II Project in the University of Aberdeen (Scotland, UK) are thanked for their support through this project: B. P. Angola Business Unit (Ed Jones and Mike Mayall); Conoco Phillips (Dave McGee, Geoff Haddad, Julia Eriksson); and UNOCAL (Kevin Doyle).
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