Geology of Tunceli - Bingöl Region of Eastern Turkey
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GEOLOGY OF TUNCELİ - BİNGÖL REGION OF EASTERN TURKEY F. A. AFSHAR Middle East Technical University, Ankara ABSTRACT. — This region is located in the Taurus orogenic belt of the highland district of Eastern Turkey. Lower Permian metasediments and Upper Permian suberystalline limestone are the oldest exposed formations of this region. Lower Cretaceous flysch overlies partly eroded Upper Permian limestone discordantly. The enormous thickness of flysch, tuffs, basaltic - andesitic flows, and limestones constitute deposits of Lower Cretaceous, Upper Cretaceous, and Lower Eocene; the deposits of each of these periods are separated from the others by an unconformity. Middle Eocene limestone is overlain discordantly by Lower Miocene marine limestone which grades upward into lignite-bearing marls of Middle Miocene and red beds of Upper Miocene. After Upper Miocene time, this region has been subjected to erosion and widespread extrusive igneous activities. During Permian this region was part of Tethys geosyncline; in Triassic-Jurassic times it was subjected to orogenesis, uplift and erosion, and from Lower Cretaceous until Middle Eocene it was part of an eugeosyncline. It was affected by Variscan, pre-Gosauan, Laramide, Pyrenean, and Attian orogenies. The entire sedimentary section above the basement complex is intensely folded, faulted, subjected to igneous intrusion, and during five orogenic episodes has been exposed and eroded. INTRODUCTION In the August of 1964 the Mineral Research and Exploration Institute of Turkey assigned the writer to undertake geologic study of the region which is the subject of discussion in this report. This region is located in the highland district of Eastern Turkey, extending from Karasu River in the north to Murat River in the south. It comprises the districts of Pülümür, Tunceli, Hozat, Mazgirt, Bingöl, and Kiği (Fig. 1). With the exception of the area to the south of Mazgirt, this region has very rugged topography with numerous high peaks and deep valleys (Photo 1). The highest peak of this region, located 18 km east of Pülümür, is Bağırbaba Dağı with an elevation of 3287 m above sea level, and the lowest point is located south of Göktepe village in Mazgirt district, where Munzur River leaves the region at an elevation of 900 m above sea level. In most of this region, except Bingöl area, the beds are dipping at high angle and differential erosion has produced prominent escarpments. Bingöl area is a basaltic plateau with enormous thickness of almost horizontal flows of extrusive rocks. Numerous streams of the area have cut deep and narrow valleys in this plateau (Plate I). STRATIGRAPHY PALEOZOIC Permian The oldest exposed rocks in this region consist of a series of sericitic schist interbedded with thin beds of quartzite. These metasediments of clastic origin grade upward into Upper Permian subcrystalline limestone of enormous thickness. One of 34 F. A. AFSHAR the localities where this schist-quartzite series is exposed is situated 20 km northwest of Tunceli. Here a section of 15 m thickness, consisting of 50 cm to 2 m of gray- colored schist alternating with thin beds of quartzite, is exposed on the south bank of Munzur River. Another area where the schists with quartzite beds are exposed is located within the immediate vicinity of Dolan village, about 7 km west of Karakoçan. They are exposed also in a small area about one kilometer west of Hoyer village and 2 km south of Dolan. Base of this schist and quartzite series is not exposed in any part of this region and there is no break in sedimentation between them and overlying subcrystalline Upper Permian limestone. From their lithology and stratigraphic position they are probably correlative of upper Lower Permian Grödner Sandstein of Karnic Alps which belong to Kungurian stage. The schist beds are overlain concordantly by a very thick subcrystalline limestone which contains Neoschwagerina carticulifera in its upper part. This fossil is typical of Upper Permian of Tethys geosynclinal area. Lower part of this limestone formation consists of thin beds of limestone of 5 to 8 m thick, interbedded with thin beds of schist. Toward the upper part of the section intercalations of terrigenous sediments disappear and it becomes a massive limestone. The limestone has typically dark-brown color with considerable amount of organic matter disseminated in it. High organic content has given it the dark color and when the rock is subjected to friction it gives off hydrocarbon odor. Due to tectonic disturbances it is intricately folded (Photo 2), extensively fractured and the fractures are filled with numerous calcite veins. In some places it is subjected to granitic intrusion (Plate II, a). It is metamorphosed to a sub- crystalline limestone, however, the degree of metamorphism varies from place to place, GEOLOGY OF TUNCELİ - BİNGÖL REGION OF EASTERN TURKEY 35 in general, stratigraphically lower parts of the formation and areas of granitic intrusion show higher degree of metamorphism. The distribution of Upper Permian limestone in the regions occupied by Tethys geosyncline during Upper Paleozoic is widespread. This limestone is known as Bellero- phon Limestone in the Alps, Zechstein in Germany, Sosio Limestone in Sicily and it occurs in Djulfa district of Azerbaijan and in Zagros Mountains of Iran. In this region, it is exposed rather extensively in two localities, and there are several small outcrops scattered through. The largest area of exposure starts from about 2 km north of town of Tunceli and extends for a distance of 34 km toward north, and in NE-SW direction it is exposed for a distance of 45 km. This area of exposure is crossed on the east by Harçik River and on the west by Munzur River. Removal of post-Paleozoic forma- tions in this area is partly due to erosional action of these two rivers and mainly due to orogenic uplift. About 20 km northeast of Tunceli on Erzincan highway, Harçik River has cut a narrow gorge of about 200 m of depth in a localicy 2 km west of Harik village. From here to the vicinity of Hodik village, a distance of about 40 km along Harçik River, the outcrops consist entirely of this suberystalline limestone. Due to intricate folding, this formation shows enormous thickness in this locality. About 30 km northeast of Tunceli, in the vicinity of Zel Dağı it attains a thickness of about 1250m measured from the banks of Harçik River; whereas, an unknown thickness of it lies below the river bed. This enormous thickness is due to complex folding and the actual thick- ness of the formation is considerably less than this amount, being approximately 800 m thick. The northern limit of this Permian limestone is defined by a major fault beyond which Mesozoic and Cenozoic formations are exposed. In this locality of Permian limestone exposure, there are several isolated patches of Eocene flysch resting directly on the limestone without any Mesozoic rocks in between, indicating that at the end of Mesozoic this fault block was uplifted and subjected to erosion, as a result of which Mesozoic rocks on it were removed before deposition of Eocene flysch. In Munzur valley, at a distance of about 9 km northwest of Tunceli, this limestone is intruded by granite. Another area where this crystalline limestone is extensively exposed is located about 19 km north of county seat Çemişkezek. Here, its width in NW-SE direction is about 14 km and its length in NE-SW direction is more than 30 km, extending to Euphrates River in Kemaliye district. Here, measured from bottom of Tagar Deresi to the top of Yılan Dağı it shows an apparent thickness of about 1700 m. In this locality its degree of metamorphism is less than in Tunceli district and Neoschwagerina carti- culifera fossils are found in the outcrops near Euphrates River. The actual thickness of this formation is about 800 m. Several small and isolated outcrops of this Permian crystalline limestone occur in the immediate vicinity of Kılcan village and adjacent areas about 20 km southeast of Pülümür. They crop out from underneath Eocene flysch. About 26 km east of county seat Mazgirt, on the banks of Büyüksu River in the environs of Bağın village, several small outcrops of the crystalline limestone occur. Here a hot spring comes out of a fracture in this limestone. In the Bingöl area, about 7 km west of Karakoçan, in the vicinity of Dolan and Hoyer villages small outcrops of highly metamorphosed facies of this limestone are exposed. 36 F. A. AFSHAR. On the eroded surface of this Permian, formation in some places Mesozoic beds and in other places Cenozoic beds are lying discordantly. MESOZOIC The Mesozoic formations in this region are typical of eugeosynclinal mobile belt. They consist of enormous thickness of flysch deposits intercalated with pyroclastics, andesitic-basaltic flows and marine limestones of Lower and Upper Cretaceous period. These are deposited on the intensely folded and eroded surface of Permian suberystalline limestone. In this region I could not find any beds of Triassic or Jurassic period; it is probable that in the early Mesozoic times this area was emergent above sea level, during which folding and extensive erosion of Permian deposits were accomplished. During Lower Cretaceous this area was undergoing intense crustal disturbance and the sediments were deposited in deep geosynclinal trough accompanied by paroxysmal vol- canic eruption and igneous extrusion. The Permian formation in this area as a result of intense folding has assumed enormous thickness, and is a regional uplift in the form of a tectonic axis trending in NW-SE direction. To the north of this axis Mesozoic and Cenozoic formations are subjected to intense folding and faulting, due to pressures origiriating farther north. As a result of these severe orogenic movements, they are uplifted and subjected to erosion in such a way that most of the Cenozoic deposits are removed and great majority of outcrops consist of Mesozoic rocks.