The Zonguldak basin of northwestern
Turkey
Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a transcontinental country located mainly on the Anatolian Peninsula in Western Asia, with a small portion on the Balkan Peninsula in ...
is the only
basin in Turkey with mineable
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when ...
deposits. It has been mined for coal since the late 1800s. The basin takes its name after
Zonguldak, Turkey, and lies at approximately 41° N. It is roughly elliptical in shape with its long axis oriented roughly southwest to northeast, and is adjacent to the
Black Sea
The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Rom ...
. Three main regions have been recognized in the Zonguldak basin: from west to east, Armutcuk, Zonguldak, and Amasra.
[Sinayuç, C., and Gümrah, F. (2009) Modeling of ECBM recovery from Amasra coalbed in Zonguldak Basin, Turkey, International Journal of Coal Geology, 77, 162-174]
Depositional history
The Zonguldak basin has undergone two major periods of deposition. The first period began in the
Paleozoic
The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon.
The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838
by combining the Greek words ''palaiós'' (, "old") and ' ...
, and the second began in the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
. Isolated areas of deposition in the basin occurred during the Late
Permian
The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...
through the
Triassic
The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...
as well as the Latest
Jurassic
The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
.
Paleozoic deposition
The Zonguldak basin first experienced deposition in the
Ordovician
The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya.
T ...
.
[Yalçin, M.N. and Yilmaz, I. (2010). Devonian in Turkey – A review. Geologica Carpathica, 61 (3), 235-253] Deposition begins with the lower Ordovician Soḡuksu Formation. The Soḡuksu Formation is 700–1100 meters thick. At its base it consists of green
shale and
sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates ...
and coarsens upwards to
arkosic
Arkose () or arkosic sandstone is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar.
Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose.
Quartz is ...
conglomerates. The lower Ordovician Aydos Formation conformably overlies the Soḡuksu. It is a conglomerate of
quartzitic
Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tect ...
sandstone and is 50–200 meters thick. The Findikli Formation was deposited during the upper Ordovician,
Silurian, and lowermost
Devonian in the Zonguldak basin. It is 300–450 meters thick. Its
facies are indicative of a mixed
siliciclastic
Siliciclastic (or ''siliclastic'') rocks are clastic noncarbonate sedimentary rocks that are composed primarily of silicate minerals, such as quartz or clay minerals. Siliciclasic rock types include mudrock, sandstone, and conglomerate
Conglomera ...
-carbonate shelf environment that is shallowing through time.
The red, cross-bedded sandstones of the Ferizli Formation overlie the marly deposits of the Fendikli Formation. The
oolitic sandstones contain iron and an iron ore.
The formation, like the Findikli Formation, shows a shift toward shallower depositional environments and a shift to higher energy areas of deposition. The younger sediments of the Ferizli Formation become progressively more enriched in
calcium carbonate and eventually give way to the Yilanli Formation.
The Yilanli Formation is
Visean in age and is the beginning of the coal-related sequences in the Zonguldak basin.
[Görür, N., Monod, O., Okay, A.I., Sengör, A.M.C., Tüysüz. O., Yiğitbaş, E., Sakinç M., and Akkök, R. (1997) Paleogeographic and tectonic position of the Carboniferous rocks of the western Pontides (Turkey) in the frame of the Variscan belt. Bull. Soc. Géol. France, 168 (2), 195-205][Hoşgörmez, H. (2007). Origin and secondary alteration of coal bed and adjacent rock gasses in the Zonguldak Basin, western Black Sea, Turkey. Geochemical Journal, 41, 201-211] The Yilanli is a
dolomitic
Dolomite () is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dolomiti ...
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
unit with
calcareous
Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.
In zoology
''Calcareous'' is used as an ad ...
black and gray shales. It was deposited in a shallow marine passive margin setting. It is conformably overlain by the Alacaagzi Formation, and has accumulated over 1000 m of sediment.
The Alacaagzi Formation contains economic deposits of coal. It is comprised predominantly of crossbedded black
shales and silts in the lower sections of the unit and progressively becomes composed of sands, shale bearing coals, and conglomerates towards the top of the formation.
Facies analysis in the Alacaagzi Formation is suggestive of coastal environments including lacustrine, fluviatial, and fan deposits.
Conformably overlaying the Alacaagzi Formation is the Kozlu Formation. The Kozlu contains 19 coal seams totalling 30–32 m.
The Kozlu is composed of successional conglomerate, sand, silt, mud, and coal deposits. The Karadon Formation conformably overlies the Kozlu. The Karadon is lithologically similar to the Kozlu Formation, but contains less coal seams. An angular unconformity spans the top of the Karadon formation and ranges from 46.5
Ma–194 Ma in duration.
[Yalçin, M.N., Schenk, H.J., and Schaefer, R.G. (1994). Modelling of gas generation in coals of the Zonguldak basin (northwestern Turkey). International Journal of Coal Geology, 25, 195-212]
Localized deposition
Deposition resumes in the western portion of the Zonguldak basin with the deposition of the Çakraz Formation. The Çakraz spans the upper Permian through the Lower Jurassic. Unconformably overlying the Çakraz is the Inalti Formation. The Inalti was deposited during the upper Jurassic and is truncated by an
unconformity
An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...
.
The carbonates of the Inalti are representative of a shallow passive margin setting.
[Channel, J.E.T., Tüysüz, O., Bektas, O., and Sengör, A.M.C. (1996). Jurassic-Cretaceous paleomagnetism and paleography of the Pontides (Turkey). Turkey, 15 (1), 201-212]
Cretaceous deposition
During the late Cretaceous, the Zonguldak basin was roughly 25° N,
and was experiencing subsidence due to the formation of a back arc, the Black Sea. As a result, the Zonguldak experienced deposition from the early Cretaceous through the
Eocene
The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...
. Different authors present differing stratigraphic columns of the Zonguldak basin and this analysis will preferentially report more current research. The lithologies deposited during this period of deposition include limestones, mudstones, siltstones, and
dolomite Dolomite may refer to:
*Dolomite (mineral), a carbonate mineral
*Dolomite (rock), also known as dolostone, a sedimentary carbonate rock
*Dolomite, Alabama, United States, an unincorporated community
*Dolomite, California, United States, an unincor ...
s.
The Albian, 105–100 Ma, Zonguldak Formation is predominantly limestone with areas of dolomitization.
[Hoşgörmez, H., Yalçin, M.N., Cramer, B., Gerling, P., Faber, E., Schaefer, R.G., and Mann, U. (2002). Isotopic and molecular composition of coal-bed gas in the Amasra region (Zonguldak basin—western Black Sea). Organic Geochemistry,33, 1429-1439] It is conformably overlain by the Albian, 105–112 Ma, Kilimli Formation. The Kilimli is composed of sandstone and carbonaceous sandstone.
The Kilimli is unconformably overlain by the sandy limestone of the Cemaller Formation.
The unconformity lasts at least 6.5 Ma and the Zonguldak basin experiences continuous deposition from the Turonian – Campanian. The Cemaller is overlain by the siltstone and limestone of the Baþköy Formation. The Dinlence Formation overlies the Cemaller and consists of
andesite
Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predo ...
s and andesitic tuffites. It is possible that the Dinlence is the Yemislicay Formation since it too contains andesites and andesitic tuffites.
The Dinlence is overlain by the marls, and limestones of the Alapý Formation.
Tectonic history
Paleozoic
During the middle Paleozoic, the Zonguldak basin was part of the south-facing passive margin of the
Laurasian plate.
[Goncuoglu, M.C. and Kozlu, H. (2000). Early Paleozoic evolution of the NW Gondwanaland: Data from southern Turkey and surrounding regions. Gondwana Research, 3, 315-324] During the Carboniferous, the temperature of the sediment water interface was near 25 °C and heat flow into the Zonguldak basin was about 1.3 heat flow units (HFU).
Backstripping analysis of the Alacaagzi Formation, the lowest coal-bearing formation, reaches a maximum temperature and depth of 100 °C and 2.4 km, respectively, in the Zonguldak area during the Carboniferous. Similarly, the base of the Kozlu Formation reaches maximum temperatures of 85, 85, and 100 °C in the Armutcuk, the Zonguldak, and the Amasra regions, respectively.
[Yalçin M.N., İnan, S., Gülbin, G., Mann, U., and Schaefer, R.G (2002). Carboniferous coals of the Zonguldak basin (northwest Turkey): Implications for coalbed methane potential. American Association of Petroleum Geologists bulletin, 86 (7), 1305-1328]
The Zonguldak basin was tectonically active during the late Paleozoic and this strongly influenced its structural and burial history due to the
Hercynian
The Variscan or Hercynian orogeny was a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea.
Nomenclature
The name ''Variscan'', come ...
orogeny. The Hercynian orogeny was the result of the continent–continent collision between Laurasia and
Gondwana. This collision created many E-NE/W-SW striking faults, folds, and tilted the Paleozoic sediments.
This uplift of the basin, near the end of the
Westphalian, halted deposition and created the angular unconformity at the top of the Karadon Formation.
Heat flow remained constant in the Zonguldak basin during the Hercynian Orogeny,
while the uplift decreased the temperatures the sediments experienced. For example, at the end of the Permian the top of the Alacaagzi was roughly 70 °C and 1.6 km below the sediment surface in the Zonguldak area.
Mesozoic
During the Cretaceous, the Zonguldak basin experienced general
subsidence,
rift
In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics.
Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...
ing, and
faulting.
This led to another period of deposition in the region and faulted the coal seams. This faulting provided a pathway for meteoric water to enter the coal seams.
During the
Aptian, the Intrapontide Ocean, the ocean separating the Western Pontides tectonic region of Turkey form the Sakarya Continent, underwent subduction.
This led to the formation of a back arc basin, the Black Sea. The start of this subduction is responsible for the unconformity between the Kilimi and Cemaller formations and marks the beginning of the
Alpide orogeny in the region.
The andesitic volcaniclastic sediments of the Yemislicay support the subduction of oceanic crust in the region during this time. The Zonguldak basin was able to sustain deposition after the start of the Alpide orogeny due to rifting in the Black Sea basin. The rifting in the Black Sea also increased heat flow into the Zonguldak basin during the Cretaceous. Heat flows were as high as 1.5–1.75 HFU, and the temperature of the sediment water interface was about 25 °C.
Cenozoic
The Intra-Pontide Ocean stopped subducting with the collision between the Western Pontides terrain and the Eastern Pontides terrain. The Aplide orogeny stopped deposition and uplifted the Zonguldak basin during the Eocene epoch beginning at 42 Ma.
The coal bearing formations experienced the highest temperatures at the onset of the Alpide orogeny. For example, the base of the Kozlu Fm experienced temperatures of 125, 175, and 140 °C in the Armutcuk, the Zonguldak, and the Amasra regions, respectively.
The Alpide tectonic provinces in
Anatolia
Anatolia, tr, Anadolu Yarımadası), and the Anatolian plateau, also known as Asia Minor, is a large peninsula in Western Asia and the westernmost protrusion of the Asian continent. It constitutes the major part of modern-day Turkey. The ...
, from north to south, are the Pontides, Anatolides, Tarides, and Border Folds. These provinces have roughly an east–west strike. The Zonguldak basin is currently being uplifted by the Alpide orogeny.
Progressively older sediments outcrop toward the north of the basin.
Source rock
Coals
The coals of the Alacaagzi, Kozlu, and Karadon formations are of bituminous rank.
[Yürüm, Y., Bozkurt, D., and Yalçin, M.N. (2001). Change of the structure of coals from the Kozlu K20 G borehole of Zonguldak Basin with Burial Depth: 1. chemical structure. Energy Sources, 23, 511-520] The Alacaagzi, Kozlu, and Karadon formations contain greater than 70%, 81%, and 81% total organic carbon (TOC), respectively.
Structure
The coals of the Zonguldak basin follow the mean evolution of type III
kerogen
Kerogen is solid, insoluble organic matter in sedimentary rocks. Comprising an estimated 1016 tons of carbon, it is the most abundant source of organic compounds on earth, exceeding the total organic content of living matter 10,000-fold. It ...
s.
The coals of the Zonguldak basin show
vitrinite
Vitrinite is one of the primary components of coals and most sedimentary kerogens. Vitrinite is a type of maceral, where "macerals" are organic components of coal analogous to the "minerals" of rocks. Vitrinite has a shiny appearance resembling gla ...
reflectances (Ro) of 0.45–1.70%.
Hoşgörmez et al. (2002) determined that the coals of the Kozlu formation exhibit Ro of 1.0–1.2%, which gives them a coal rank of high volatile A bituminous.
[Strąpoć, D., Mastalerz, M., Dawson, K., Macalady, J., Callaghan, A.V., Wawrik, B., Turich, C. and Ashby, M. (2011). Biogeochemistry of microbial coal-bed methane. Annual Review of Earth and Planetary Sciences, 39, 617-656] Additionally, coalification increased with depth, and the coals became more aromatic with depth.
[Karayigit, A.I., Gayer, R.A., and Demirel, I.H. (1998). Coal rank and petrography of Upper Carboniferous coal seams (Amasra, Turkey). International Journal of Coal Geology, 38, 277-294] The calorification of the coals also increased with depth.
Methane
The two broad scale pathways of
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
production, thermogenic and biogenic generation, account for the majority of methane generation in coals.
Thermogenic production of methane in coals begins at temperatures around 80 °C and peaks around 0.7–1.6% of vitrinite reflectance.
Biogenic generation of methane takes place through two chemically distinguishable pathways. These pathways are
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
reduction and
acetate fermentation and methanol/methyl utilization.
Typically, biogenic production takes place early in the maturation of a coal bed, since the temperatures observed during the coalification process are high enough for sterilization. A coal bed may produce methane later in its history if it is uplifted and fractured. The uplifting of the beds cools them enough for colonization by microbes and fractures and faults provide inoculation pathways by the infiltration of surface water.
The coals of the Zonguldak basin were subjected to a complex depositional and tectonic history, and this influenced the basins methane generation. The Alacaagzi formation did not pass the 80 °C isotherm until it had been buried for 25 Ma.
The Kozlu formation experienced two different conditions during its first 260 Ma. The bottom of the Kozlu was mostly below the 80 °C isotherm while the top of the formation was above it. With deposition in the Cretaceous, the Kozlu formation was buried beneath the 80 °C Isotherm. The Alacaagzi and Kozlu were uplifted past the 80 °C around 5 Ma. At this point the rocks had been fractured and meteoric water could inoculate the system with methanogenic microbes.
Isotopic data from wells in the Zonguldak basin suggest that the methane is primarily thermogenic in nature. There may have been some initial microbial methane generation in the coal beds or generation after the basin had been uplifted and meteoric water could enter the beds. Reinoculation is supported by the evidence of isotopically lighter gas occurring near cleats in the coal beds.
Shales
The organic rich shales of the Yilani contain up to 7.9% TOC, and the shales and siltstones of the coalbearing formations can contain 2–26% TOC.
The organic matter is found as type II kerogen. While the Yilani entered the gas window, isotopic data suggest that most of the gas in the basin was derived from the Kozlu coal deposits and the associated organic rich shales.
Summary of source rock
The predominant source rock in the Zonguldak basin is coal. The most prolific source rock is the Kozlu Formation, containing the greatest volume of coal and the greatest amount of methane. This is in corroboration with the Ro values that suggest thermogenic production of methane in the Zonguldak basin would have been high. Methane generated by shale may be contributing a small amount to the total amount of methane found in the basin, but the majority is coal derived. Coal-derived methane appears to be mostly thermogenic in origin with some biogenic production.
Reservoir
Coal
Coal is the primary reservoir lithology in the Zonguldak basin. Coal, since it is a solid hydrocarbon, cannot migrate. Coal is also an important reservoir lithology in the basin for methane. Methane in coal beds is primarily found in a sorbed state, while a very small fraction is found as a free gas.
The gas is in the microporous structure of the coal at near liquid densities.
Hoşgörmez et al. (2002) estimated that the coals of the Zongulak basin contain up to 12 cm
3 g
−1 of methane. Additionally, 90% of the methane in the Karadon Formation is adsorbed to the coal while 10% of it is found as free gas.
The total volume of coal bed methane in the Karadon Formation in the Amasra region has been estimated to be 862.5–2600
million cubic metre
The cubic metre (in Commonwealth English and international spelling as used by the International Bureau of Weights and Measures) or cubic meter (in American English) is the unit of volume in the International System of Units (SI). Its symbol is m ...
s.
Other units
The dolomites of the Yilani Formation are characterized as potential reservoir units.
The sandstone units in the Alacaagzi, Kozlu, and Karadon formations are also potential reservoirs.
Another formation with good reservoir qualities is the Yemislicay or Dinlence Formation.
The base of the Yemislicay is characterized by a red
pelagic
The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...
limestone interlain with volcaniclastic sediments.
Seals
Due to the microporous nature of coal, coal is a significant seal in the Zonguldak basin. Outside of the coal-bearing formations, the only other formation that can serve as a seal is the Kilimli Formation.
Coal mines
Coal mines include
Armutçuk coal mine
Armutçuk coal mine is a coal mine located in Turkey's Zonguldak basin.
References
External links
Armutçuk coal mineon Global Energy Monitor
Global Energy Monitor (GEM) is a San Francisco-based non-governmental organization which c ...
and
Karadon coal mine.
See also
*
Zonguldak mine disaster
References
{{coord missing, Turkey
Mining in Turkey
Coal mining regions in Turkey
Zonguldak Province
Sedimentary basins of Asia