The Lava Formation is a

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

geologic formation in

Lithuania Lithuania, officially the Republic of Lithuania, is a country in the Baltic region of Europe. It is one of three Baltic states and lies on the eastern shore of the Baltic Sea, bordered by Latvia to the north, Belarus to the east and south, P ...

and

Kaliningrad Kaliningrad,. known as Königsberg; ; . until 1946, is the largest city and administrative centre of Kaliningrad Oblast, an Enclave and exclave, exclave of Russia between Lithuania and Poland ( west of the bulk of Russia), located on the Prego ...

, being either the sister or the same unit as the

Ciechocinek Formation The Ciechocinek Formation (also known as the Gryfice Formation at Suliszewo, Choszczno County, Suliszewo) is a Jurassic (lower Toarcian) geological formation extending across the Baltic coast, primarily in Poland, with minor occurrences in Lithua ...

. It represents the outcrop of Lower Toarcian layers in the Baltic Syncline and in the Lithuanian-Polish Syneclise (C8-borehole in

Gdańsk Bay Gdańsk Bay or the Gulf of Gdańsk is a southeastern bay of the Baltic Sea. It is named after the adjacent port city of Gdańsk in Poland. Geography The western part of Gulf of Gdańsk is formed by the shallow waters of the Bay of Puck. The so ...

). It is known by the presence of Miospores and Pollen, as well Plant remains. The formation contains grey, greenish, and dark grey silt and clay with interealatians and lenses of fine-grained sand, pyritic concretions and plant remains (carbonised wood fragments). The Jotvingiai Group

Toarcian The Toarcian is, in the International Commission on Stratigraphy, ICS' geologic timescale, an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic. It spans the time between 184.2 Megaannum, Ma (million ...

deposits represent deposits laid down in fresh water and brackish basins, possibly lagoons or coastal plain lakes. The

Bartoszyce Bartoszyce (pronounced ; , ) is a town on the Łyna River in northern Poland, with 22,597 inhabitants as of December 2021. It is the capital of Bartoszyce County within the Warmian-Masurian Voivodeship. Geographical location Bartoszyce lies on t ...

IG 1 of the Ciechocinek Formation shows how at the initial phase of the Toarcian there was a regional transgression in the Baltic Syncline, indicated by greenish-grey mudstones, heteroliths and fine-grained sandstones with abundant plant fossils and plant roots, what indicates a local delta progradation between the Lava and Ciechocinek Fms. Then a great accumulation of miospores (+2500 specimens) indicates a local concentration, likely due to a rapidly decelerating fluvial flow in a delta-fringing lagoon forming a “hydrodynamic trap”, with the wave and currents stopping the miospores to spread to the basin. Latter a marsh system developed with numerous palaeosol levels, being overlayed by brackish-marine embayment deposits that return to lagoon-marsh facies with numerous plant roots ('' Radicites sp'') and palaeosol levels in the uppermost section, ending the succession. Overall the facies show that the local Ciechocinek-Lava system was a sedimentary basin shallow and isolated, surrounded by a flat coastal/delta plain with marshes, delivering abundant spores and Phytoclasts, indicators of proximal landmasses with high availability of wood and other plant material. This climate at the time of deposition was strongly seasonal, probably with monsoonal periods. Due to the abundant presence of deltaic sediments on the upper part, it is considered to be related to the retry of the sea level. The Lava Formation was deposited on a mostly continental setting, with its upper part, dominated by argillaceous sediments, corresponding to the Ciechocinek Formation. There is a great amount of kaolinite content, being present laterally in the basin, decreasing and lifting space to increasing smectite to the south-west of the formation. On the other hand, there is a great amount of coarsest sediments, which consist mostly of sands. __TOC__

Palynology

Megaflora

See also

References

Further reading