around 7,000 BC. Geologically, the Lake Ladoga depression is a
graben and
syncline structure of
Proterozoic age (
Precambrian). This "Ladoga–Pasha structure", as it is known, hosts
Jotnian sediments. During the
Pleistocene glaciations the depression was partially stripped of its
sedimentary rock fill by glacial
overdeepening. During the
Last Interglacial (Eemian), around 130-115,000 years ago, the lake formed part of marine channel between the Baltic and White Seas. During the
Last Glacial Maximum, about 17,000 years
BP, the lake served likely as a channel that concentrated ice of the
Fennoscandian Ice Sheet into an
ice stream that fed glacier lobes further east. Deglaciation following the
Weichselian glaciation took place in the Lake Ladoga basin between 12,500 and 11,500
radiocarbon years BP. Lake Ladoga was initially part of the
Baltic Ice Lake (70–80 m. above present
sea level), a historical
freshwater stage of
Baltic Sea. It is possible, though not certain, that Ladoga was isolated from it during
regression of the subsequent
Yoldia Sea brackish stage (10,200–9,500 BP). The isolation threshold should be at
Heinjoki to the east of
Vyborg, where the
Baltic Sea and Ladoga were connected by a strait or a river outlet at least until the formation of the River Neva, and possibly even much later, until the 12th century AD or so. At 9,500 BP,
Lake Onega, previously draining into the
White Sea, started emptying into Ladoga via the
River Svir. Between 9,500 and 9,100 BP, during the transgression of
Ancylus Lake, the next freshwater stage of the Baltic, Ladoga certainly became part of it, even if they hadn't been connected immediately before. During the Ancylus Lake subsequent regression, around 8,800 BP Ladoga became isolated. Ladoga slowly
transgressed in its southern part due to uplift of the
Baltic Shield in the north. It has been hypothesized, but not proven, that waters of the
Litorina Sea, the next brackish-water stage of the Baltic, occasionally invaded Ladoga between 7,000 and 5,000 BP. Around 5,000 BP the waters of the
Saimaa Lake penetrated
Salpausselkä and formed a new outlet,
River Vuoksi, entering Lake Ladoga in the northwestern corner and raising its level by 1–2 m. The
River Neva originated when the Ladoga waters at last broke through the threshold at Porogi into the lower portions of
Izhora River, then a tributary of the
Gulf of Finland, between 4,000 and 2,000 BP. Dating of some sediments in the northwestern part of Lake Ladoga suggests it happened at 3,100
radiocarbon years BP (3,410–3,250 calendar years BP). File:Eemian Baltic sea level.jpg|Map of the Baltic-White Sea region during the
Last Interglacial (115-130,000 years ago), showing Lake Ladoga as part of a marine passageway between the Baltic and White Seas File:Lake Ladoga as part of Baltic Ice Lake.jpg|Lake Ladoga as part of the
Baltic Ice Lake (between 11200 and 10500 yr BP). The light blue line marks the margin of the ice sheet by 13300 cal yr BP. File:Lake Ladoga as part of Ancylus Lake.jpg|Lake Ladoga as part of the
Ancylus Lake (between 9300 and 9200 yr BP). The dark green line marks the southern shoreline of Lake Ladoga during the
Yoldia stage of the Baltic basin. ==Wildlife==