{{Short description|Geological formation in Latvia}}
{{Infobox rockunit | name = Gauja Formation | image = Ergeljuklintis424aug037qg.jpg | caption = The Ergelu Cliffs along Gauja River, Latvia belong to the Gauja Formation | type = Geological formation | age = Givetian<br>~{{fossil range|388|384}} | period = Givetian | prilithology = Sandstone | otherlithology = Siltstone | namedfor = Gauja River | namedby = | region = | country = Estonia, Latvia | coordinates = {{Coord|57.30|N|25.12|E|display=inline,title}} | paleocoordinates = {{Coord|10.9|S|10.7|E|display=inline}} | unitof = | subunits = Sietin & Lode Members | underlies = Amata Formation | overlies = Plavinas Formation | thickness = {{convert|80|m|ft|abbr=on}} | extent = | area = | map = {{Location map+ | Latvia | relief = 1 | width = 250 | float = center | places = {{Location map~ | Latvia | lat_deg = 57.3 | lon_deg = 25.12 | mark = Gold pog.svg | marksize = 10 }} }} | map_caption = }} The '''Gauja Formation''' is a Middle Devonian fossil locality in Estonia and Latvia.<ref name="estonia">{{cite web|url=http://geokogud.info/tug/stratigraphy.php?id=185|title=Gauja Stage|publisher=Geological collections of Estonia, Institute of Geology at TUT, University of Tartu, Estonian Museum of Natural History}}</ref> It is named after the Gauja River, where it is exposed along the banks.<ref name="gnp">{{cite web|url=http://www.gnp.lv/node/434|title=Gauja River|publisher=Tūrisma informācija īpaši aizsargājamā dabas teritorijā – Gaujas nacionālajā parkā|url-status=dead|archive-url=https://web.archive.org/web/20120326172951/http://www.gnp.lv/node/434|archive-date=2012-03-26}}</ref>
== Description == The Gauja Formation has a maximum thickness of {{convert|80|m|ft|abbr=on}}. It is composed of weakly to moderately cemented layers of fine-grained to very fine-grained sandstone. The layer is predominantly light to yellowish-gray in color, but can be pinkish brown or variegated. It is mostly composed of quartzose arenites. It is overlain by the {{convert|30|m|ft|abbr=on}} thick Amata Formation and the Plavinas Formation.<ref name="kleesment">{{cite journal|author1=Anne Kleesment |author2=Väino Puura |author3=Toivo Kallaste |year=2002|title=Clastic dikes in Middle Devonian sandstones of the Gauja Formation, southeastern Estonia|journal=Proceedings of the Estonian Academy of Sciences, Geology|volume=52|issue=3|pages=155–177|publisher=Estonian Academy Publishers|url=https://books.google.com/books?id=QT_j22wsdzcC&pg=PA155}}</ref>
The Gauja Formation contains two cyclic members. The lower layers are known as the Sietiņi Member and are composed mostly of sandstone with a thin layer of siltstone at the top. <ref name="kleesment" />
The upper layers are thicker, and the lower part of it is known as the Lode Member. The Lode Member dates from the Middle Devonian and is composed of light colored sandstone. The area is indicative of a near-shore environment of retreating sea.<ref name="kleesment" />
== Paleontology == The Sietiņi and Lode members have yielded numerous fossils of fishes. Among them are ''Asterolepis'', Bothriolepis, Psammolepis, Cheirolepis, ''Glyptolepis baltica'', ''Laccognathus panderi'', ''Livoniana multidentata'', Strunius, Panderichthys and ''Megadonichthys kurikae''<ref name="estonia" /><ref name=":0">{{Cite journal |last=Upeniece |first=I. |date=2001-01-01 |title=The unique fossil assemblage from the Lode Quarry (Upper Devonian, Latvia) |url=https://www.researchgate.net/publication/307735390 |journal=Fossil Record |volume=4 |issue=1 |pages=101–119 |doi=10.5194/fr-4-101-2001 |doi-access=free |bibcode=2001FossR...4..101U |issn=2193-0074}}</ref><ref name="Ahlberg2000">Ahlberg et al., 2000</ref><ref>{{Cite journal |last=Upeniece |first=Ieva |title=A new species of Strunius(Sarcopterygii; Onychodontida) from Latvia; Lode quarry (Upper Devonian) |url=https://www.researchgate.net/publication/213775369 |journal= Geobios|date=1995 |volume=28 |pages=281–284 |doi=10.1016/S0016-6995(95)80127-8|bibcode=1995Geobi..28..281U }}</ref> The first fossils of young placoderms ever discovered were found in the Gauja formation. Ranging in size from as small as 10.4 mm to as big as 38 mm (0.4 to 1.4 in) long, these fossils are important for our understanding of ontogeny in extinct fish.<ref name=":0" />
thumb|Asterolepis ornata
Only large plant remains and miospores are known from this member. Examples of which include ''Hostinella'', ''Archaeopteris'', ''Retusotriletes rugulatus'', and ''Ancyrospora''. Palynological studies indicate that the Middle to Upper Devonian boundary may exist in this member.<ref name="kurik">{{cite journal|author1=Elga Mark-Kurik |author2=Alain Blieck |author3=Stanislas Loboziak |author4=Anne-Marie Candlier |year=1999|title=Miospore Assemblage from the Lode Member (Gauja Formation) in Estonia and the Middle-Upper Devonian Boundary Problem|journal=Proceedings of the Estonian Academy of Sciences, Geology|volume=48|issue=2|pages=86–97|publisher=Estonian Academy Publishers|doi=10.3176/geol.1999.2.02 |url=https://books.google.com/books?id=OhH-gqPrkmcC&q=gauja+formation&pg=PA86 |url-access=subscription}}</ref>
thumb|Archaeopteris sp.
== See also == * List of fossiliferous stratigraphic units in Latvia * List of fossil sites * Gauja National Park * Gauja valley * Gauja River
== References == {{Reflist|2}}
=== Bibliography === * {{cite journal |first1=P.E. |last1=Ahlberg |first2=E. |last2=Lukševis |first3=E. |last3=Mark-Kurik |year=2000 |title=A near-tetrapod from the Baltic Middle Devonian |journal=Palaeontology |volume=43 |issue=3 |pages=533–548|doi=10.1111/j.0031-0239.2000.00138.x |bibcode=2000Palgy..43..533A |s2cid=129654491 }}
Category:Geologic formations of Europe Category:Geology of Estonia Category:Geology of Latvia Category:Devonian System of Europe Category:Givetian Stage Category:Sandstone formations Category:Shallow marine deposits Category:Devonian southern paleotropical deposits Category:Fossiliferous stratigraphic units of Europe Category:Paleontology in Estonia Category:Paleontology in Latvia