Yanan Formation

{{Short description|Geological formation in China}}

{{Infobox rockunit

| name = Yanan Formation

| age = {{fossilrange|Toarcian|Bajocian}}

| period = Middle Jurassic

| image =

| imagesize =

| caption =

| type = Geological formation

| prilithology = Sandstone, siltstone, mudstone, shale

| otherlithology = Coal

| unitof =

| subunits = Y1, Y2, Y3, Y4, Y5

| underlies = Zhiluo Formation

| overlies = Fuxian Formation

| thickness = up to {{Convert|220|m|ft|-1}}

| area =

| map = {{Location map+ | China#Ningxia

| relief = 1

| width = 250

| float = center

| places =

{{Location map~ | China#Ningxia

| lat_deg = 38.1

| lon_deg = 106.7

| mark = Blue pog.svg

| marksize = 12

}}

}}

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| coordinates = {{coord|38.1|N|106.7|E|display=inline,title}}

| paleocoordinates = {{coord|42.1|N|111.7|E|display=inline}}

| region = Ningxia, Shaanxi, Inner Mongolia

| country = China

| extent = Ordos Basin

| namedfor = Yan'an

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}}

The Yanan Formation, alternatively spelled the Yan'an Formation ({{zh|s=延安组}}), is a geological formation in China, it is also alternatively considered a group. The age of the formation is uncertain, with estimates ranging from Toarcian to Bajocian. It is divided up into 5 members, with the designation of Y1 through Y5. Y2, Y3 and Y4 are predominantly dark shales, while Y1 and Y5 are composed of sandstones, coal beds{{Cite journal|last1=Ao|first1=Weihua|last2=Huang|first2=Wenhui|last3=Weng|first3=Chengmin|last4=Xiao|first4=Xiuling|last5=Liu|first5=Dameng|last6=Tang|first6=Xiuyi|last7=Chen|first7=Ping|last8=Zhao|first8=Zhigen|last9=Wan|first9=Huan|date=January 2012|title=Coal petrology and genesis of Jurassic coal in the Ordos Basin, China|journal=Geoscience Frontiers|volume=3|issue=1|pages=85–95|doi=10.1016/j.gsf.2011.09.004|bibcode=2012GeoFr...3...85A |issn=1674-9871|doi-access=free}} and interbedded mudstones. The depositional environment at the time was when the Ordos Basin formed a large inland lake, surrounded by floodplains. The dark shales have been explored for the potential of producing shale gas.{{Cite journal|last1=Wang|first1=Dong-dong|last2=Shao|first2=Long-yi|last3=LI|first3=Zhi-xue|last4=LI|first4=Ming-pei|last5=Lv|first5=Dawei|last6=Liu|first6=Haiyan|date=September 2016|title=Hydrocarbon generation characteristics, reserving performance and preservation conditions of continental coal measure shale gas: A case study of Mid-Jurassic shale gas in the Yan'an Formation, Ordos Basin|journal=Journal of Petroleum Science and Engineering|volume=145|pages=609–628|doi=10.1016/j.petrol.2016.06.031|bibcode=2016JPSE..145..609W |issn=0920-4105}} The coal has also been explored for the production of coalbed methane.{{Cite journal|last1=Xu|first1=H.|last2=Tang|first2=D.Z.|last3=Liu|first3=D.M.|last4=Tang|first4=S.H.|last5=Yang|first5=F.|last6=Chen|first6=X.Z.|last7=He|first7=W.|last8=Deng|first8=C.M.|date=June 2012|title=Study on coalbed methane accumulation characteristics and favorable areas in the Binchang area, southwestern Ordos Basin, China|journal=International Journal of Coal Geology|volume=95|pages=1–11|doi=10.1016/j.coal.2012.02.001|bibcode=2012IJCG...95....1X |issn=0166-5162}} The formation is also notable for its fossil content, with dinosaur footprints having been found in the formation.{{Cite journal|last1=Xing|first1=Lida|last2=Lockley|first2=Martin G.|last3=Tang|first3=Yonggang|last4=Klein|first4=Hendrik|last5=Zhang|first5=Jianping|last6=Persons|first6=W. Scott|last7=Dai|first7=Hui|last8=Ye|first8=Yong|date=2015-01-02|title=Theropod and Ornithischian Footprints from the Middle Jurassic Yanan Formation of Zizhou County, Shaanxi, China|journal=Ichnos|volume=22|issue=1|pages=1–11|doi=10.1080/10420940.2014.985670|bibcode=2015Ichno..22....1X |s2cid=129509962|issn=1042-0940}} The dinosaur Lingwulong was formerly thought to have been found in this formation,{{Cite journal|last1=Xu|first1=Xing|last2=Upchurch|first2=Paul|last3=Mannion|first3=Philip D.|last4=Barrett|first4=Paul M.|last5=Regalado-Fernandez|first5=Omar R.|last6=Mo|first6=Jinyou|last7=Ma|first7=Jinfu|last8=Liu|first8=Hongan|date=2018-07-24|title=A new Middle Jurassic diplodocoid suggests an earlier dispersal and diversification of sauropod dinosaurs|journal=Nature Communications|volume=9|issue=1|pages=2700|doi=10.1038/s41467-018-05128-1|issn=2041-1723|pmc=6057878|pmid=30042444|bibcode=2018NatCo...9.2700X}} but the strata was later attributed to the overlying Zhiluo Formation.{{Cite journal |last1=Dai |first1=Hui |last2=Tan |first2=Chao |last3=Xiong |first3=Can |last4=Ma |first4=Qingyu |last5=Li |first5=Ning |last6=Yu |first6=Haidong |last7=Wei |first7=Zhaoying |last8=Wang |first8=Ping |last9=Yi |first9=Jian |last10=Wei |first10=Guangbiao |last11=You |first11=Hailu |last12=Ren |first12=Xinxin |year=2022 |title=New macronarian from the Middle Jurassic of Chongqing, China: phylogenetic and biogeographic implications for neosauropod dinosaur evolution |journal=Royal Society Open Science |volume=9 |issue=11 |pages=220794 |bibcode=2022RSOS....920794D |doi=10.1098/rsos.220794 |pmc=9627447 |pmid=36340515 |quote=However, valid Middle Jurassic neosauropods are rarely reported before the discovery of dicraeosaurid Lingwulong from middle/late Middle Jurassic (late Bathonian–early Callovian) (The horizon was revised from Yan'an Formation (Aalenian–Bajocian) to Zhiluo Formation (Bathonian–early Oxfordian)}}