The Yalvaç Basin is a

sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock They form when long-term subsidence ...

in Turkey, around

Lake Beyşehir Lake Beyşehir (; anciently, Carallis or Karallis (), or Caralis or Karalis (Κάραλις)) is a large freshwater lake in Isparta and Konya provinces in southwestern Turkey. It is located at around and is the largest freshwater lake in Turkey. ...

and the present-day town of

Yalvaç Yalvaç is a town of Isparta Province in the Mediterranean Region of Turkey. It is the seat of Yalvaç District.

. It lies within the geological region known as the Isparta Angle. It has existed since

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

times.

General description

The Yalvaç Basin is a

located in the northern tip of the Isparta Angle. It generally runs from northwest to southeast and is about 55 km long and 15 km wide.

occupies its southern part, while at its northwestern end is the village of Yarıkkaya. To the north, east, and west, the Yalvaç Basin is bounded by mountains, such as the Sultandağları mountains. The Yalvaç Basin's shape and size have been mostly the same since its formation, either during or shortly before the Middle

, and sedimentary deposition has been occurring here since then.

Stratigraphy

The Yalvaç Basin consists of four main geological formations, from oldest to youngest: the Bağkonak Formation, the Yarıkkaya Formation, the Göksöğüt Formation, and the Kırkbaş Formation. Their total thickness is about 800 m. Below these are

basement A basement is any Storey, floor of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the Furnace (house heating), furnace, water heating, ...

rocks of diverse origin including

ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle (Earth), upper mantle that has been uplifted and exposed, and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is ...

metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, caus ...

s from the Afyon zone, and non-metamorphic rocks that originally came from the Tauride fold and thrust belt and were thrust here in

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

through

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

times. *The Bağkonak Formation, the oldest formation in the basin,

unconformably 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 o ...

overlies pre-

Neogene The Neogene ( ,) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period million years ago. It is the second period of th ...

basement rocks. It is especially well exposed south of Yalvaç, near Özbayat and Bağkonak. It is about 250 m thick and mostly consists of "continental red

clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks by ...

s with dominantly conglomerates at the bottom and intercalating

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

and sandy-

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

towards the upper levels". It was probably formed by sedimentary deposits in

river delta A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creat ...

s and

alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to Semi-arid climate, semiar ...

s along the border between the Yalvaç Basin and the Sultandağları mountains. No fossils have been found in the Bağkonak Formation. *The Yarıkkaya Formation unconformably overlies the pre-Neogene basement rocks in the north and conformably overlies the Bağkonak Formation in the south. Its composition ranges from "coarse, sub-rounded, poorly sorted, grain-supported conglomerate" at the bottom to sandstone in the middle to coarser conglomerate at the top. The lower parts were likely formed as river deposits; towards the central part of the basin, "fine mud/clay,

marl Marl is an earthy material rich in carbonate minerals, Clay minerals, clays, and silt. When Lithification, hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. M ...

y limestone, and

tufa Tufa is a variety of limestone formed when carbonate minerals precipitation (chemistry), precipitate out of water in ambient temperature, unheated rivers or lakes. hot spring, Geothermally heated hot springs sometimes produce similar (but less ...

deposits" represent shallow lake deposits.

Lignite Lignite (derived from Latin ''lignum'' meaning 'wood'), often referred to as brown coal, is a soft, brown, combustible sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35% and is considered the lowest ...

seams represent deposition from swamp environments. Fossils include freshwater

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

species like ''

Planorbis ''Planorbis'' is a genus of air-breathing freshwater snails, aquatic animal, aquatic pulmonate gastropod molluscs in the family (biology), family Planorbidae, the sheep, ram's horn snails, or planorbids. All species in this genus have sinistral o ...

'' and '' Limnea'' found in mudstone and claystone deposits, and

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

s like

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

s and

hamster Hamsters are rodents (order Rodentia) belonging to the subfamily Cricetinae, which contains 19 species classified in seven genera. They have become established as popular small pets. The best-known species of hamster is the golden or Syrian ...

s found in upper levels deposited from lake environments. Various ages have been estimated for this formation; Yağmurlu suggested a Middle Miocene date based on the gastropod fossils, while Saraç proposed an Early-Middle Miocene date based on the vertebrate fossils. *The Göksöğüt Formation overlies the Yarıkkaya Formation, unconformably in the north and conformably in the south. At the bottom, it consists of "banded, highly porous brownish limestone", and further upward it coarsens into conglomerate. The overall formation is at least 150 m thick. It is especially exposed around Ayvalı and north of Körküler. The coarsening of deposits from bottom to top is interpreted by Koç et al. as sedimentary infilling of a lake basin by "high-energy" river systems. Fossils of the gastropods ''Planorbis'' and ''Limnea'' have been found in the marl and

claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone and shale. Most of the particles of which the stone is composed are less than and are too small to ...

levels of the Göksöğüt Formation, although Yağmurlu said these were "

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

" and cautioned against using them to date the formation. *The Kırkbaş Formation unconformably overlies the Göksöğüt Formation and mainly consists of "reddish, poorly consolidated conglomerate, sandstone, and mudstone alternations". It is itself overlain by

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

alluvial deposits. It is especially visible around Kırkbaş and east of Terziler. Around Tokmacık, ''

Hipparion ''Hipparion'' is an extinct genus of three-toed, medium-sized equine belonging to the extinct tribe Hipparionini, which lived about 10-5 million years ago. While the genus formerly included most hipparionines, the genus is now more narrowly defi ...

'' and ''

Mastodon A mastodon, from Ancient Greek μαστός (''mastós''), meaning "breast", and ὀδούς (''odoús'') "tooth", is a member of the genus ''Mammut'' (German for 'mammoth'), which was endemic to North America and lived from the late Miocene to ...

'' fossils have been found, indicating that the Kırkbaş Formation dates to the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58

Faults

The edges of the Yalvaç Basin are marked by various large-scale

normal fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

s. Within the basin, there are many medium-sized faults with displacements of a few centimeters to a few meters. The primary fault directions are northwest–southeast and northeast–southwest, indicating that the local tectonics are controlled by two main "zones of weakness". The most prominent

fault zone In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic f ...

in the area is the Yarıkkaya Fault Zone. It runs west toward the Karacaören Fault and east toward the Sultandağları mountains, where it dies out. Another zone is the Çakırçal Fault Zone, which goes northwest–southeast for over 15 km and is itself interrupted by the eastern part of the Yarıkkaya Fault Zone. Then there is the Sağır Fault Zone, which forms an 18 km-long valley running northwest–southeast west of Sağır. It is also cut up by the Yarıkkaya Fault Zone, as well as by the northeast–southwest-trending Kumdanlı Fault Zone. The Kumdanlı Fault Zone itself runs for about 20 km, from Mısırlı in the northeast to south of Aşağıtırtar in the southwest before disappearing into Lake Hoyran. Its northeastern end disappears into the Yalvaç Basin's sedimentary infill. Another fault zone is the northeast-southwest Yaka Fault zone, which is about 6 km wide and over 20 km long. It runs from south of Gelendost at its southwestern end to near Madenli in the northeast. The Yaka Fault Zone controls the southern margin of the Yalvaç Basin and separates the Yarıkkaya Formation from the underlying basement rocks.

References

{{coord missing, Turkey Sedimentary basins of Asia Geology of Turkey Landforms of Isparta Province Valleys of Turkey