4. Paleogeographic Evolution of the Hydrographic Basin and the Lacustrine Basin

The central-longitudinal area of the Eastern Carpathians belongs to the Crystalline-Mesozoic unit. This area, known as the Carpathians, belongs to the Crystalline-Mesozoic unit, whose sector is known as the Moldavian Compartment (the Tisa-Ciuc Compartment) (Grasu C, Miclăuş C, Brânzilă M, Baciu DS (2010) Munţii Hăşmaşului. Monografie geologic şi fizico-geografică. “Al.I.Cuza University” Publishing House, Iaşi; Mutihac V (1990) Structura geologică a teritoriului României. Technical Publishing House, Bucharest). To the east, the Mesozoic sedimentary is known as the External Marginal Syncline. It is separated into two compartments: the Hăghimaş syncline in the south and Rarău in the north. The Hăghimaş Mountains, which also comprise the Red Lake lacustrine basin, correspond to the Mesozoic syncline, located between Frumoasa-Ciuc in the south and Bistricioara in the north (Grasu C, Miclăuş C, Brânzilă M, Baciu DS (2010) Munţii Hăşmaşului. Monografie geologic şi fizico-geografică. “Al.I.Cuza University” Publishing House, Iaşi). The Red Lake was formed in the summer of 1837, when, after heavy rainfalls, a landslide diluvium fell from the Ghilcoş (Ucigaşu) Mountains and blocked the stream of the Bicaz brook. The Ghilcoş-Hăghimaş-Mezinul Crest is located in the northern compartment of the central unit within the Eastern Carpathians. The most frequent rocks within the Red Lake hydrographic basin are the following: limestones and dolomites (Triassic), limy sandstones (Lias-Dogger), sandstones and conglomerates (Barremian-Albian) and crystalline schists (Maastrichtian). There are five sedimentation cycles: the first comprises sequences of conglomerates, sandstones, loam and limestones; the second is associated with Lias limestones; the third is represented by conglomerates, calcareous sandstones and Dogger-Portlandian grey limestones; the fourth mostly comprises Neocomian whitish grey limestones; and the last one comprises conglomerates (along the Bicăjel valley, at the contact with the slopes) with loam and sandstone intercalations (the bottom of the Bicăjel valley).