Indigirka-Oloy sedimentary-volcanic-plutonic assemblage 

(Middle Jurassic to Early Cretaceous (Neocomian)) 

(Southeastern to northwestern Russian Northeast, units Ks, KJs, Js, lJs, KJvs, KJv, KJvi, KJvf, 
lJvf, lJvi, lJvm, lJpf)

Occurs in a broad northwest-striking region. Consists chiefly of shallow-marine and nonmarine late Middle 
Jurassic to Neocomian formations overlying Precambrian, Paleozoic, and early Mesozoic rocks of the 
Kolyma-Omolon superterrane. Mainly sandstone, siltstone, shale, conglomerate, and volcanic rocks of 
varying composition. Abundant and various macrofossils. Weak deformation of belt with formation of 
large doubly-plunging anticlines and synclines. The Indigirka-Oloy assemblage includes coeval plutonic 
rocks and the following distinct volcanic belts and sedimentary basins:

1. The Uyandina-Yasachnaya volcanic belt is located in the southeastern part of the Indigirka-Oloy 
assemblage (Chersky Range). It consists of calc-alkalic basalt, andesite, and rhyolite interlayered with 
shallow-marine and nonmarine sandstone, siltstone, shale, and conglomerate, and is interpreted as an arc 
that formed along the margin of the Kolyma-Omolon superterrane. The belt contains Oxfordian, 
Kimmeridgian and Early Volgian macrofossils. The basal part includes thick Bathonian and Bathonian to 
Callovian conglomerate and sandstone. The belt also includes a Bathonian to Callovian olistostrome that 
contains Paleozoic limestone, greenschist, and ophiolite fragments. The Uyandina-Yasachnaya volcanic 
belt overlies the Prykolyma, Omulevka, and Rassokha terranes of the Kolyma-Omolon superterrane. To the 
west, volcanic rocks of the Uyandina-Yasachnaya volcanic belt grade into thick Middle-Late Jurassic 
turbidite deposits with rare macrofossils that are located in the Polousny and In'yaly-Debin synclines. The 
turbidite deposits overlie the Kular-Nera terrane and occur in tight northwest- and southwest-verging folds 
which are cut by granitic rocks with Ar-Ar and K-Ar ages of 120 to 144 Ma. Back-arc deposits are present 
to the northeast in the Ilin-Tas anticline.

2. The Zyryanka sedimentary basin is located in a 60-km-wide and 550-km-long basin that extends toward 
the northwest in the southwestern and central part of the Indigirka-Oloy assemblage. The basin contains 
Upper Jurassic marine black shale, siltstone, and sandstone (1,000 to 2,000 m thick), Lower Cretaceous 
lagoonal, deltaic, and lacustrine-alluvial sandstone, siltstone, shale, and coal (4,000 m thick), Upper 
Cretaceous sandstone, siltstone, clay, conglomerate, and brown coal (500 m thick), and Paleogene and 
Neogene nonmarine fluvial sedimentary rocks with thin brown coal beds (1,500 m thick). The Zyryanka 
basin formed in the back-arc region of the Uyandina-Yasachnaya arc.

3. The Late Jurassic-Neocomian Oloy-Svyatoy Nos volcanic belt occurs along the northeastern margin of 
the Kolyma-Omolon superterrane and adjacent to the South Anyui terrane. The belt consists of mainly 
shallow-marine, rarely nonmarine basalt, andesite, rhyolite, and tuff with interlayered sandstone, 
conglomerate, siltstone, and shale. The belt also contains small bodies of granite, granodiorite, and 
monzogranite.

4. Along the southeastern margin of the Kolyma-Omolon superterrane are the small Ainakhkurgen, 
Umkuveem, and Upper Penzhina basins which are filled with Volgian and early Neocomian graywacke 
and shale up to 3000 m thick. Eastward, these basins are overlapped by Albian to Late Cretaceous volcanic 
rocks of the Okhotsk-Chukotka belt. 

5. The North Omolon basin occurs along the boundaries of the Omolon, Oloy, and Berezovka terranes, and 
consists of shallow marine and nonmarine Late Jurassic and Neocomian sandstone, shale, conglomerate, 
and alkalic basalt that range up to 3,000 m thick. REFERENCES: Paraketsov and Paraketsova, 1973; 
Filatova, 1979; Koporulin, 1979; Sosunov and others, 1982; Parfenov, 1984; Stavsky, 1984; Terekhov and 
others, 1984; Natapov and Surmilova, 1986; Archegov and others, 1987; Gaiduk, 1988; Gaiduk and others, 
1989, 1993; Danilov and Dylevsky, 1990; Shul'gina and others, 1990.