The Gauja Formation is a Middle Devonian fossil locality in Estonia and

Latvia Latvia ( or ; lv, Latvija ; ltg, Latveja; liv, Leţmō), officially the Republic of Latvia ( lv, Latvijas Republika, links=no, ltg, Latvejas Republika, links=no, liv, Leţmō Vabāmō, links=no), is a country in the Baltic region of ...

. It is named after the

Gauja River The Gauja River ( et, Koiva jõgi, german: Livländische Aa) is a river in the Vidzeme region of Latvia. It is the only large river of Latvia that begins and ends its flow in Latvia. Its length is 460 km, of which 93.5 km (approxim ...

, where it is exposed along the banks.

Description

The Gauja Formation has a maximum thickness of . 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 Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

arenites. It is overlain by the thick

Amata Formation According to Roman mythology, Amata (also called Palanto) was the wife of Latinus, king of the Latins, and the mother of their only child, Lavinia. In the Aeneid of Virgil, she commits suicide during the conflict between Aeneas and Turnus o ...

and the Plavinas Formation. The Gauja Formation contains two cyclic members. The lower layers are known as the Sietin Member and are composed mostly of sandstone with a thin layer of

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

at the top. It has yielded numerous fossils of fishes. Among them are '' Asterolepis'', '' Bothriolepis'', '' Glyptolepis baltica'', ''

Laccognathus panderi ''Laccognathus panderi'' is an extinct lobe-finned fish from northern Europe. They existed from the Middle Devonian to the Late Devonian (around 397.5 to 360 mya). ''L. panderi'' has been recovered from the Middle Devonian Gauja Formation an ...

'', '' Livoniana multidentata'',Ahlberg et al., 2000 and ''

Megadonichthys kurikae ''Megadonichthys kurikae'' is an extinct species of fish belonging to the family Osteolepididae Osteolepididae is an family of primitive, fish-like tetrapodomorphs (the clade that contains modern tetrapods and their extinct relatives) that l ...

''. 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. Only large plant remains and

miospore Cryptospores are fossilised primitive plant spores that first appear in the fossil record during the middle of the Ordovician period. Evidence that cryptospores derive from land plants Occurrence Cryptospores are generally found in non-marine roc ...

s are known from this member. Examples of which include ''

Hostinella ''Hostinella'' is a form genus, used for bare dichotomously branching stems (axes) which have not been found in association with spore-forming organs or sporangia and so cannot be assigned to a more precise genus or species. Specimens assigned t ...

'', ''

Archaeopteris ''Archaeopteris'' is an extinct genus of progymnosperm tree with fern-like leaves. A useful index fossil, this tree is found in strata dating from the Upper Devonian to Lower Carboniferous (), the oldest fossils being 385 million years old, ...

'', '' Retusotriletes rugulatus'', and ''

Ancyrospora ''Ancyrospora'' is a fossil 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 animal ...

''. Palynological studies indicate that the Middle to Upper Devonian boundary may exist in this member.

References

Bibliography

* {{cite LSA , first=P.E. , last=Ahlberg , first2=E. , last2=Lukševis , first3=E. , last3=Mark-Kurik , year=2000 , title=A near-tetrapod from the Baltic Middle Devonian , journal=

Palaeontology Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

, volume=43 , pages=533–548 Geologic formations of Europe Geology of Estonia Geology of Latvia Devonian System of Europe Givetian Stage Sandstone formations Shallow marine deposits Devonian southern paleotropical deposits Fossiliferous stratigraphic units of Europe Paleontology in Estonia Paleontology in Latvia

Description

See also

References

Bibliography