Editing Gulf of Finland (section)

==Geological history==
{{see also|Eridanos (geology)}}
The modern depression can be traced to the [[river incision|incision]] of large rivers during the [[Cenozoic]] prior to the [[Quaternary glaciation]].<ref name=Estonica>{{cite encyclopedia |title=The Gulf of Finland |encyclopedia=[[Estonica]] |url=http://www.estonica.org/en/Nature/Gulf_of_Finland_and_the_North-Estonian_coastal_plain/The_Gulf_of_Finland/ |date=28 September 2012 |publisher=[[Eesti Instituut]] |access-date=20 February 2018 |archive-date=16 December 2021 |archive-url=https://web.archive.org/web/20211216214703/http://www.estonica.org/en/Nature/Gulf_of_Finland_and_the_North-Estonian_coastal_plain/The_Gulf_of_Finland/ |url-status=dead }}</ref> These rivers eroded the sedimentary strata above the [[Baltic Shield|Fennoscandian Shield]].<ref name=Estonica/> In particular the eroded material was made up of [[Ediacaran]] (Vendian) and [[Cambrian]]-aged claystone and sandstone.<ref name=Estonica/> As erosion progressed, the rivers encountered harder layers of [[Ordovician]]-aged [[limestone]], leading to the formation of the cliffs of [[Baltic Klint]] in northern [[Estonia]] and [[Ingria]].<ref name=Estonica/> Subsequently, the depression was somewhat reshaped by glacier activities. Its retreat formed the [[Littorina Sea]], whose water level was some 7–9 metres higher than the present level of the Baltic Sea. Some 4,000 years ago the sea receded and shoals in the gulf have become its islands.<ref>{{Cite book|url=https://books.google.com/books?id=LElrclnl0C8C&pg=PA217|pages=217–219|title=Climate development and history of the North Atlantic realm|author=Gerold Wefer|publisher=Springer|year=2002|isbn=3-540-43201-9}}</ref><ref name="Geografiya Leningrada">{{Cite book|author = Darinskii, A.V.|title = Geography of Leningrad|publisher = Lenizdat|year = 1982|pages = 12–18|url=https://books.google.com/books?id=KuRdPAAACAAJ}}</ref> Later uplifting of the [[Baltic Shield]] skewed the surface of the gulf; for this reason, its ancient northern shores are significantly higher than the southern ones.<ref name="SPb Entsiklopediya">Saint Petersburg: Encyclopedia. – Moscow: Russian Political Encyclopedia. 2006 {{ISBN|5-8110-0107-X}}</ref>