The Gauja Formation is a Middle Devonian fossil locality in Estonia

Estonia

Estonia , officially the Republic of Estonia , is a state in the Baltic region of Northern Europe. It is bordered to the north by the Gulf of Finland, to the west by the Baltic Sea, to the south by Latvia , and to the east by Lake Peipsi and the Russian Federation . Across the Baltic Sea lies...

 and Latvia

Latvia

Latvia , officially the Republic of Latvia , is a country in the Baltic region of Northern Europe. It is bordered to the north by Estonia , to the south by Lithuania , to the east by the Russian Federation , to the southeast by Belarus and shares maritime borders to the west with Sweden...

. It is named after the Gauja River, where it is exposed along the banks.

The Gauja Formation has a maximum thickness of 80 m (262.5 ft). It is composed of weakly to moderately cemented layers of fine-grained to very fine-grained sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

. The layer is predominantly light to yellowish-gray in color, but can be pinkish brown or variegated. It is mostly composed of quartzose arenite

Arenite

Arenite is a sedimentary clastic rock with sand grain size between 0.0625 mm and 2 mm and contain less than 15% matrix. The related adjective is arenaceous...

s. It is overlain by the 30 m (98.4 ft) thick Amata Formation 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

Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...

 at the top. It has yielded numerous fossils of fishes. Among them are Asterolepis

Asterolepis (fish)

Asterolepis is an extinct genus of placoderms from the Devonian of North America and Europe. They were heavily armored benthic detritivores with distinctive jointed limb-like pectoral fins.-See also:*Bothriolepis*List of placoderms...

, Bothriolepis

Bothriolepis

Bothriolepis was the most successful genus of antiarch placoderms, if not the most successful genus of any placoderm, with over 100 species found on every continent.-Description and palaeobiology:...

, Glyptolepis baltica, Laccognathus panderi

Laccognathus panderi

Laccognathus panderi is an extinct lobe-finned fish from eastern Europe. They existed from the Middle Devonian to the Late Devonian .L...

, and Megadonichthys kurikae.

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 miospores are known from this member. Examples of which include Hostinella

Hostinella

Hostinella is a form genus, used for bare dichotomously branching stems 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...

, Archaeopteris

Archaeopteris

Archaeopteris is an extinct genus of tree-like plants with fern-like leaves. A useful index fossil, this tree is found in strata dating from the Upper Devonian to Lower Carboniferous , and has a global distribution....

, Retusotriletes rugulatus, and Ancyrospora. Palynological studies indicate that the Middle to Upper Devonian boundary may exist in this member.