Lava Formation

The Lava Formation is a Mesozoic geologic formation in Lithuania. Fish remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specific genus. The Jotvingiai Group Toarcian deposits were deposited likely in a shallow lacustrine basin or a near-sea freshwater lagoon, with the other environment of the formation consisting of shallow marine conditions, seashore barriers, and dunes, on a hot and humid climate. Due to the abundant presence of deltaic sediments (Including Plant fragments of Protophyllocladoxylon? sp.) on the upper part, it is considered to be related to the retry of the sea level, as in the Polish equivalent formation, the Ciechocinek Formation. The climate at the time of deposition was strongly seasonal, probably with monsoonal periods. 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.
Paleogeography.
While most of Europe was occupied by sea, Lithuania has a dominated continental regime, which lasted about 32 million years. The low elevation lands were flooded along with the Toarcian rise and fall of the sea level, measured also on the Ciechocinek Formation, where the decomposition products were taken to separate depressions where they accumulated lagoon sediments, along with marine deposition of the sea basin lying on the southwest of Lithuania. The southwest was composed mostly by a series of deltaic successions, along with several unidentified water bodies.
The deposition of the formation shows a transition from deltaic to basinal facies at the west, where the sea shallow bays flooded the region, while in the northeast the land remained. The Lava Formation shelf had a depth of 200–250 m. The climate was humid, slightly warmer than in average latitudes, with drier climate periods. In this climate, lush vegetation grew on the edges of the basins, leading to
the formation of brown coal interlayers. Aalenian-Oxfordian marine activity led to changes, with the rise of the sea level, until it retreated on the southwest near the Cretaceous strata.