The Gnishik Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

Armenia Armenia, officially the Republic of Armenia, is a landlocked country in the Armenian Highlands of West Asia. It is a part of the Caucasus region and is bordered by Turkey to the west, Georgia (country), Georgia to the north and Azerbaijan to ...

Azerbaijan Azerbaijan, officially the Republic of Azerbaijan, is a Boundaries between the continents, transcontinental and landlocked country at the boundary of West Asia and Eastern Europe. It is a part of the South Caucasus region and is bounded by ...

and

Iran Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...

. It preserves

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

dated to the

Wordian In the geologic timescale, the Wordian is an age or stage of the Permian. It is the middle of three subdivisions of the Guadalupian Epoch or Series. The Wordian lasted between and million years ago (Ma). It was preceded by the Roadian and fo ...

age of the

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 251.902 Mya. It is the s ...

period.Gnishik Formation
in the

Paleobiology Database The Paleobiology Database (PBDB) is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database originated in the NCEAS-funded Phanerozoic Marine Pale ...

The thin-bedded

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

s of the formation reach a thickness of in the Julfa section of northwestern Iran and in the Arpa River valley of

. The sediments were deposited in an open marine setting at the northern edge of the

Paleo-Tethys Ocean The Paleo-Tethys or Palaeo-Tethys Ocean was an ocean located along the northern margin of the paleocontinent Gondwana that started to open during the Middle Cambrian, grew throughout the Paleozoic, and finally closed during the Late Triassic; ex ...

. The coral '' Wentzellophyllum gnishikense'' was named after the formation.

Description

The Gnishik Formation was first formally described by Arakelyan in 1964, based on a section in the Gnishik River valley, after which the formation was named. The formation is mostly represented by thin-bedded, occasionally shaly, dark grey and black

bituminous Bitumen ( , ) is an immensely viscous constituent of petroleum. Depending on its exact composition, it can be a sticky, black liquid or an apparently solid mass that behaves as a liquid over very large time scales. In American English, the m ...

foraminiferal-algal biodetrital

s. The occasional admixture of clayey and terrigenous material colors the limestones light grey and yellowish. The thin-bedded layers alternate with coarser-bedded compact varieties.Leven, 1998, p.302 The open marine

s of the formation reach a thickness of in the Julfa section of northwestern Iran. In Iran, the formation overlies the Dorud Formation and is overlain by the Khachik Formation, while in Armenia the formation rests on top of the Asni Formation and is overlain by the Arpa Formation.Leven, 1998, p.301 The Gnishik Formation represents an increase in

subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...

rate in the Permian.Saidi et al., 1997, p.198 The sediments were deposited at the northern edge of the

. The formation is dated to the late Murgabian,Leven, 1998, p.308 which belongs to the

stage of the

Middle Permian The Guadalupian is the second and middle series/epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± 0. ...

. The Gnishik Formation is correlated with the Ruteh and Nesen Formations,Leven, 1998, p.314 and the Kuffengian stage of Chinese chronostratigraphy.Leven, 1998, p.320

Fossil content

Among many others, the following fossils have been reported from the formation:

Invertebrates

;Trilobites * '' Pseudophillipsia armenica'' * '' Pseudophillipsia (Carniphillipsia) paffenholzi'' * '' Acropyge sp.'' ;Cephalopods * Orthocerida indet.Stepanov et al., 1969 ;Gastropods * '' Pharkidonotus khairliensis'' * '' Naticopsis cf. spectatus'' * '' Bellerophon sp.'' * '' Naticopsis sp.'' * '' Straparollus sp.'' * '' ?Euphemites sp.'' * '' ?Platyceras sp.'' * Bellerophontidae indet. ;Corals * '' Ipciphyllum araxense'' * '' I. flexuosum''Kotlyar et al., 1989 * '' I. originale'' * '' I. ex gr. restriseptatum'' * '' I. simplex'' * '' I. subtimoricum'' * '' I. subelegans'' * '' Lonsdaleia aff. gracilis'' * '' L. aff. jenningsi'' * '' Lophocarinophyllum lophophyllidum''Ezaki, 1991 * '' L. pulchrum'' * '' L. aff. zaphrentoideum'' * '' Michelinia vesiculosa'' * '' Paraipciphyllum transcaucasicum'' * '' Parawentzelella (Parawentzelella) canalifera'' * '' Pentaphyllum leptoconicum'' * '' Praetachylasma alternatum'' * '' Protomichelinia microstoma'' * '' Sinopora asiatica'' * '' Szechuanophyllum szechuanense'' * '' Ufimia elongata'' * '' Wentzelella armenica'' * '' Wentzelella (Wentzelella) densicolumnata'' * '' Wentzellophyllum gnishikense''Kropatcheva, 1999 * '' W. parvus'' * '' W. volzi'' * '' Yatsengia asiatica'' * '' Lophophyllidium sp.'' * '' Wentzelella sp.'' ;Crinoids * '' ?Poteriocrinites ardjichensis''Stukalina, 1999 ;Rhynchonellata * '' Cryptospirifer omeishanensis''Nakamura & Golshani, 1981 * '' Septospirigerella baissalensis'' * '' Terebratuloidea davidsoni''Ruzhentsev & Sarycheva * '' Crenispirifer sp.'' * '' Septospirigerella sp.'' ;Strophomenata * '' Chonostegoides baissalensis'' * '' C. ogbinensis'' * '' Edriosteges poyangensis'' * '' Leptodus sp.'' ;Stenolaemata * '' Mackinneyella dzhulfensis''Shishova, 1964Morozova, 1970 * '' Rhabdomeson floriferum'' * '' Septopora lineata'' ;Fusulinina * '' Sichotenella cf. sutschanica'' * '' Yangchienia cf. haydeni'' * '' Nankinella cf. ovata'' * '' N. orbicularia'' * '' Staffella sphaerica'' * '' S. suborientalis'' * '' Eoverbeekina cf. intermedia'' * '' Pisolina abichi'' * '' P. subsphaerica'' * '' Leella ex gr. bellula'' * '' Sphaerulina crassispira'' * '' S. ogbinensis'' * '' Verbeekina cf. heimi'' * '' V. verbeeki'' * '' Eopolydiexodina darwasica'' * '' E. persica'' * '' Polydiexodina chekiangensis'' * '' Chusenella abichi'' * '' C. doraschamensis'' * '' Dunbarula sp.'' ;Foraminifera * '' Globigaetania angulata''Gennari & Rettori, 2019

Flora

;Dasycladophyceae * '' Atractyliopsis fecundus'' * '' Diplopora americana'' * '' Endoina stellata'' * '' Epimastopora nipponica'' * '' Gyroporella tenuimarginata'' * '' Johnsonia spinosa'' * '' Macroporella spinosa'' * '' Mizzia velebitana'' * '' Pseudogyroporella grandis'' * '' Pseudovermiporella serbica'' * '' Stolleyella yabei'' ;Rhodophyceae * '' Succodium ambiguum'' * '' S. difficile'' * '' Gymnocodium bellerophonte'' * '' G. novum'' * '' Permocalculus forospinus'' * '' P. fragilis'' * '' P. piai'' * '' Ungdarella stellata''

References

Bibliography