Stratified formations

A.V. Mikolaichuk

Late Proterozoic (Late Riphean) sediments

Karakorum Formation (R3 kr). The formation was defined by A.B. Bakirov in 1967. The stratotype section (apparent thickness > 400 m) is located at the Karakorum Pass, Kungey Range, to the east of the Kyrgyz Range. The section is composed of rhyolite-dacite tuffs containing rare dacite flows. The Late Riphean age of 733 ± 8 Ma is based on U/Pb dating on zircons (Mikolaichuk, 1998).
In the investigated area, the Karakorum Formation are dacites transformed into thin-banded mylonites and epidote-chlorite-quartz schists occurring as a >3 km thick level on the northern slope of the Kyrgyz Range. Chemical analyses reveal the dacite composition of the original rock (catalogue of geochemical data). This formation is intruded by Early and Late Ordovician granites.

Z.I. Cherniavskaya, A.V. Mikolaichuk

Paleozoic sediments

Toraygyr Formation (Ɛ-O₁ tr). The formation was defined by Yu.V. Zhukov in 1964. The stratotype area is the Toraygyr Brook on the northern slope of the Kungey Range (Mikolaichuk, 1998), where carbonate strata with basal conglomerates overlap Karakorum Formation tuffs. At this site, the 1025 m thick formation consists of 3 parts. The lower part is composed of white, massive marbles and gray, thin-bedded dolomites containing interbeds of quartz sandstones or sandy limestones. The middle part is comprised of carbon-bearing limestones and siltstones. The upper part contains fine-grained and thin-bedded marbles. An assemblage of acritarchs – Sphaeromorphitae (Leispharidia sp., Lophoshaeridium sp.), Acantomorphitae (Micrhystridium div. sp.), Tasmanites sp. and spiculs of sponges – Hexactinellida, defines the Cambrian–Ordovician age (Ogurtsova et al., 1993).
Within the investigated area, the Toraygyr Formation occurs as large xenoliths in Late Ordovician and Silurian granites on the southern slope of the Kyrgyz Range (the Boirek – Chaartash interfluve). On the northern slope of the range, Toraygyr limestones were reached under Quaternary sediments in Borehole B5s. 

Karakatty Formation (Ɛ kr). The stratotype section is located to the south of the investigated area, in the Karakatty Range (Mambetov, Apayarov, 1990). The formation does not exceed 1125 m in thickness and consists of 2 parts. The lower part is composed of pillow lavas and basalt tuffs and breccias. Basalts are chemically related to oceanic basalts of marginal basins (Lomize et al., 1997).The upper part is dominated by tuff-sandstones and breccias, tuff-siltstones with discontinuous interbeds of limestones and cherts (Mambetov, Apayarov, 1990). 
These sediments outcrop in the western Djumgal-Too Range, in the upper streams of the Karator and Uchtor rivers, where they belong to allochthonous thrust sheets. The top is represented by tuff-breccias and cherts. Along the Karator River, Late Cambrian conodonts were sampled in cherts: Muellorcdus sp., Westergaardodina sp. (fauna catalogue). Early, Middle and Late Cambrian fossils characterize the stratotype section (Mambetov, Apayarov, 1990; Mikolaichuk et al., 1997). 

Kentor Formation (Ɛ-O₁? kt). It is defined along the northern slope of the Karamoynok Range, in the Kentor – Koshtor interfluve (Klishevich, 1988). The lower part of the formation (about 300 m) is predominantly composed of lithoclastic tuffs alternating with flows of porphyric and amygdoidal basalts and siliceous siltstones with small lenses of cherts and limestones. The upper part (650-700 m) is represented by alternation of trachybasalts, large-porphyric subalkaline olivine basalts, leucocratic basalts and chert lenses. The relationships with underlying and overlying formations are unknown because the section is overturned and enclosed in a tectonic block. Radiolarians define the Cambrian-Ordovician age: Inanigutta sp. ind. and Porifera spiculas (fauna catalogue; Klishevich, 1988). The Kentor Formation is lithologically similar to the Karakatty Formation but volcanites have larger alkali content (Na2O / K2O = 0,4–0,87) (Zakharov, 1992).

Shyrgyi Formation (Ɛ-O₁ šr). The stratotype section is situated in the Shyrgyi River valley, on the southern slope of the Kungey Range, and was first described by V.P. Turchinskyi in 1962 (Rubtsov, 1999). The thickness of homogenous beds reaches 200-250 m in the 2200-2570 m thick formation. The lower part consists of light-gray and greenish-gray lavas, clastic lava and dacite tuffs. The middle part is comprised of andesite-dacite lava flows alternating with psephitic and psammitic lithoclastic tuffs. Greenish-gray lavas and andesitic tuffs complete the section. A. Mambetov determined Early Ordovician conodonts from sediments of the uppermost part of the formation: Acodus cf. firmus Viira, Cordulodus ex qr. proavus Muller, C. cf prion Lindsdstrom, Drepanodus sp. (Khristov, 1997; Rubtsov, 1999).
The Shyrgyi Formation sediments were found only along the eastern border of the mapped area as small xenoliths in Late Ordovician granites.

Karadjorgo Formation (Ɛ₃-O₁ kd). The stratotype section was described in the western part of the Karadjorgo Range, to the southwest of the investigated area (Zima, Maksumova, 1990). This Formation is 1250 m thick and is composed of tephroids, tuff-siltstones, tuff silicites, cherts and andesite tuffs which are distinguished by their variegated, red, bright cherry and green colors.
On the investigated map, I.L. Zakharov (1992) described similar sediments throughout the southern slope of the Djumgal-Too Range, in the Uchtor River basin. Dominantly red, vinous, cherry tuff-siltstones and tuff silicites alternate with green tuff-siltstones overlain by dark-green greywacke sandstones and tuff-sandstones alternating with variegated tuff-siltstones. Sandstones are typically graded. Psephitic and psammitic tuffs of andesites and dacites alternating with cherts, tuff silicites and siltstones complete the section. Along the right bank of the Uchtor River, Early Ordovician conodonts were sampled: Drepanodus (?) costatus Aboimova, Scolopodus (?) rex Lindstrom (fauna catalogue). The Karadjorgo Formation represents island-arc slopes of Late Cambrian to Tremadocian age (Mikolaichuk et al., 1997)

Djelamysh Formation (O₁ dj). I.L. Zakharov (1982) described this formation on the northern slope of the Kyrgyz Range. The bottom and the top of the > 3000 m thick, unfossiliferous formation are unknown; the most complete section outcrops in the Sokuluk – Djelamysh interfluve where thin-bedded greenish-gray and vinous-gray inequigranular greywacke sandstones containing gritstone lenses form the base. 1300 m of massive gray-green and green conglomerates and gritstones containing interbeds of up to 5 m thick greywacke sandstones overlap these sediments. Sandstone interbeds increase upward whereas interbeds of gray-green and brown siltstones and shales occur. Pebbles of conglomerates and gritstones are well-rounded and derived from volcanites, jaspers, cherts, siliceous shales, quartzites and crystalline schists. 700-800 m of gray-green greywacke sandstones with a typical bluish tint follow up section. Some levels contain scattered gravel debris of variegated siliceous rocks. Greywacke sandstones (500–550 m) with lenses and streams of conglomerates and <1.5 m thick gritstones cap the section. 
The formation has been intruded by Early Ordovician granites of the Alamedin Formation (Ala-Archa River) and is unconformably overlapped by Late Ordovician conglomerates of the Karamoynok Formation (Alamedin River). Based on the sandstone composition, the Djelamysh Formation is correlated with the Cholponata Formation in the Kungey Range, which contains Tremadocian graptolites (Grischenko et al., 1987). 

Dolon Formation (O₁ dl). This formation was defined as an olistostrome in the Dolon Pass area, Karadjorgo Range (Ges`, 1980). In the stratotype section, the olistostrome rests unconformably on Cambrian–Ordovician sediments of the Karadjorgo Formation. The sequence begins with large sheet fragments of gray crystalline limestones, which are replaced along strike by smaller blocks enclosed in a matrix of green and cherry siltstones. Few meters blocks of gray and pink limestones occur up-section. The matrix is made of green and tobacco-colored, vaguely bedded micaceous siltstones and fine-grained sandstones. Bottoms and tops of individual olistoliths were observed in some well-exposed areas. The bottoms show a sharp, sheared contact with the matrix rocks; gradual disintegration with a decreasing size of fragments was observed in the tops and along the strikes of the blocks. A fine-grained matrix and lack of clastic polymictic rocks are typical of this olistostrome. The olistostrome sequence is less than 300 m thick (Mikolaichuk et al., 1997).
On the map, the Dolon olistostrome outcrops in the western end of the Karamoynok and Djumgal-Too ranges (basins of the Kentor, Karator, Aktash, and Archalytor rivers). The 615 m thick "Aktoy" section (stratigraphical sections) is the most complete (Khristov, 1997). The lower part displays alternating siliceous breccias and conglomerates with red-brown and green inequigranular sandstones and gravel greywacke sandstones. The clastic material is made of chert, limestone, andesite, dacite, tuff, tuff-sandstone, rarely basalt, quartz diorite, monzodiorite and crystalline schist. The middle part of the section contains numerous limestone and lava olistoliths, which are laterally replaced by ungraded polymictic conglomerates and black and variegated siltstones. Siltstones and cherts alternating with carbonate and siliceous breccias dominate the upper part.
The limestone olistoliths contain a rich fauna of Middle Cambrian–Tremadocian trilobites, brachiopods and algae, (fauna catalogue). Poorly preserved Ordovician graptolites were found in matrix siltstones (Mikolaichuk et al., 1997). These data, together with the location of the olistostrome beneath the Late Arenigian–Early Llanvirnian flysch and terrigenous-siliceous sequence, allow assigning the Dolon Formation to the Middle Arenigian. 

Westsuek Formation (O₁₋₂ ws). The stratotype "Suek" section is located in the West Suek River valley (Khristov, Chernyshuk, 1987), where sediments conformably lay on the Dolon olistostrome. The 1200 m thick Westsuek Formation is composed of rhythmically alternating sandstones and siltstones containing subordinate andesite-dacite tuffs. In the up to 160 m thick lower part, graded beds of greywacke sandstones, tuff-sandstones and acid ash tuffs alternate with siltstones and siliceous shales. Siltstones and shales increase up-section, continuing with turbidite sandstones (up to 270 m) overlain by siltstones and siliceous shales (300-330 m) containing separate horizons of dacite, tuffs and volcaniclastic conglomerates. Black and dark-gray shales prevail in the 380 m thick upper part. Late Arenigian and Early Llandeilian graptolites (fauna catalogue, site 9) indicate deposition in a thick basin that was adjacent to, and to the north of the Stepnyak–North Tien-Shan Volcanic Belt (Degtyarev, 2003; Mikolaichuk et al., 1997).

Aktoy Formation (O₁₋₂ ak). The stratotype "Aktoy" section is located in the Aktoy River valley (Khristov, Chernyshuk, 1987). Absence of coarse sediments defines the bottom boundary with the underlying Dolon olistostrome. The formation thickness varies from 250 to 480 m. The lowermost part is composed of thin-bedded vinous-red siliceous siltstones containing interbeds (0.2-1.5 m) of green, light-green, dark-gray and black, thinly bedded (from 1-5 mm to 2-3 cm) cherts containing one 95 m thick bed of andesite tuffs. The middle part is characterized by alternation of green and red siliceous siltstones with thin (1-2 mm) beds of brown contourites, and by beds of graded chert, jasper, psammitic and pelitic andesite tuffs and dark-green tuff-sandstones. The upper part of the formation is composed of alternating variegated siliceous and ferruginous siltstones (from 2-3 to 15-20 cm), red-brown, green and black jaspers and cherts. Thin (1-7 mm) and fine-grained sandstones interbedded with the siltstones impart the banded aspect of the rock. The sediments are distal facies of turbidite fans. Early and Middle Ordovician conodonts were found in the "Aktoy" section, (fauna catalogue, site 7).

Melange, (m O₃). This 300 to 800 m thick and 10 km long formation is located in the western part of the Djumgal-Too Range. To the east and west the melange zone is intruded by Late Ordovician granites. This polymictic melange contains blocks and lenses of serpentinite and serpentinite schists, gabbro, pyroxenite, rocks of the Karakatty, Karadjorgo and Dolon formations, Proterozoic metamorphic schists and marbles. Blocks vary in size from few meters to 1300 m in length and up to 400 m in thickness. The quantity of serpentinite matrix varies from 10 to 60 % (Khristov, Chernyshuk, 1987). The Late Ordovician age of the melange was assigned on the basis that tectonic blocks contain fragments of Dolon Formation and Late Ordovician sediments.

Karamoynok Formation (O₃ kr). This formation unconformably resting on Middle Ordovician sediments was identified by K.D. Pomazkov in 1958 (Osmonbetov, 1982) in the Karamoynok Range, where it is 1760 m thick; it is 2780 m thick in the Kyrgyz Range (Zakharov, 1992) where it unconformably lays on the Karakorum and Djelamysh formations; to the west of the map, a conglomerate covers an Early Ordovician granite (Baktybai section, Zakharov, 1992).
In the Karamoynok Range, 450-500 m thick brown, gray-brown, greenish-brown and green-gray conglomerates and gritstones with rare interbeds of inequigranular polymictic sandstones (up to 10-20 m) represent the base of the formation. Pebbles in conglomerates and gritstones are well-rounded green, gray, black and red cherts, siliceous siltstone, shale, quartzite, jasper, sandstone, siltstone, quartz, rarely acid volcanite, quartz diorite and granite. Up-section, a unit of brown polymictic coarse to gravel sandstone (300-560 m) contains interbeds of fine-grained sandstone, gritstone and conglomerate. Above, brown medium-pebbled conglomerates (150-250 m) have rare interlayers of medium-grained quartz-feldspathic sandstones and gritstones. These rocks are overlain by a monotonous alternation (200-250 m) of green and brown coarse lithoclastic sandstones, gritstones and small-pebbled conglomerates and 200 m thick brown medium-pebbled conglomerates. The upper 450 m of the section are inequigranular brown and brown-green quartz-feldspathic and polymictic sandstones interlayered with violet and brown shales and siltstones. The age of the formation is undetermined but Late Ordovician fossils were found in overlaying sediments.

Karabalta Formation, (O₃ kb). The stratotype section, located 25 km to the west of the described map, on the northern slope of the Kyrgyz Range, in the middle stream of the Chon-Kaindy River (Burtman, 1960), is made of monotonous green-gray polymictic sandstones, siltstones and shales. In the Baktybai–Chulama interfluve (Zakharov, 1992) and in the middle stream of the Alamedin River, the sandstones lay over the Karamoynok Formation conglomerates.
In the lower part of the formation (500-700 m) thin-bedded gray and gray-green siltstones and shales contain interbeds of fine-grained massive polymictic sandstone. The rock color changes upward to yellowish-green and snuff-green; the amount of sandstone sharply decreases and bedding becomes ill defined. The middle part comprises dark-green sandstones alternating with siltstones and siliceous-sericite shales (1-15 cm). Dark-gray and black siltstones and shales alternating with fine- to medium-grained polymictic sandstones (up to 0.7 m) and limestones represent the uppermost part of the section. The formation is 3200 – 4200 m thick (Zakharov, 1992).
Early Caradocian graptolites were found in the map area (fauna catalogue, site 11). To the west, in the Turuk–Karabalta watershed, trilobites Triarthus turkestanensis Web. (V.I. Goncharova's determinations) are Llandeilian–Lower Caradocian (Grischenko, 1967). On the left bank of the Chon-Kaindy River, 20 m above the top of the Karabalta Formation, brachiopods Pseudolingula sculptata Cooper indicate, according to V.A. Goryanskyi's, the Llandeilian age of the rocks (Burtman, 1960). This age determination requires revision. In the Almaly Formation, an analogue of Karabalta Formation at the western end of the Kyrgyz Range, Goryanskyi had determined Middle Ordovician inarticulate brachiopods (Osmonbetov, 1982), later established to be Caradocian from their assemblage with conodonts in the Almaly Formation (Bekzanov, 2000).

Chonkaindy Formation (O₃ čk). I.I. Bessonov defined this formation in 1949 along the Chon-Kaindy River, where it lays over the Karabalta Formation (Osmonbetov, 1982). The base comprises polymictic conglomerates whose thickness decreases from 250 m to the west (Cholok-Kaindy River) to few meters in the map. Pebbles include sandstone, siltstone, gabbro, leucogranite, amphibolite and gneiss. The conglomerates are gradually replaced up-section by light-gray polymictic and quartz-feldspathic gravel sandstones with interbeds of red-brown hematite siltstones. The conglomerate horizon is identified as an alluvial debris cone (Khristov, Shilov, 1998) replaced by a monotonous red-brown strata (475-850 m) of rhythmically alternating polymictic and feldspathic-quartz inequigranular sandstones and siltstones (0.5-0.6 m), in turn overlain by red-brown, vinous-red thin-bedded siltstones and calcareous shales (100-450 m). The upper part is represented by contrasting alternation of dark-colored, gray-green and red-colored sandy-siltstone beds. Interbeds of dark-gray to black siltstones and claystones containing rare lensoid interbeds of algal limestone (1100–1750 m) are typical for the formation, as well as bedding and cross bedding, ripple marks, roiling and slumping structures, intraclastic breccias, and bioturbated paleosoils. These features indicate upper shelf and delta environments (Khristov, Shilov, 1998; Zakharov, 1992). In the Chon-Kaindy River valley V.P. Chernyshuk discovered and determined Ashgillian conodonts: Zigognathus pyramidalis Br.et M. (Zakharov, 1992).

Djartash Formation (O₃ dž). The stratotype section was described in the Djartash River valley, in the Kyrgyz Range (Zakharov, 1992). This 1200-2000 m thick formation conformably rests on the Chonkaindy Formation. Gray-green and black calcareous siltstones containing interbeds of limestone (5-10 m) and fine-grained, typically cross bedded and ripple-marks-bearing quartz sandstones (1.5-10 cm) form the 265 m thick base of this formation. In headstreams of the Sokuluk and Karator rivers, 10-20 m thick conglomerates occur at the base of the section.
Up-section, black and gray coal-bearing limestones, shales and siltstones (155-500 m) lay below 260-300 m thick calcareous, coal-bearing–calcareous and siliceous shales. Above, massive and banded gray-green siltstones occur (350-650 m). Ribbon-banded, thin-undulated and lens-like bedding is typical. 300-500 m thick rhythmical alternation (1-2 cm – 1-1.5 m) of coal-bearing shales and pelitomorphic coal-bearing limestone complete the section.
To the east, in headstreams of the Ala-Archa and Alamedin rivers, quartz sandstones with lenses of gritstones and conglomerates predominate. On the right bank of the Alamedin River, nearly 600 m thick conglomerates and gritstones represent the upper part of the formation. Pebbles are ill-rounded quartzites and two-mica schists. The monotonously thin-bedded, ribbon-banded and lens-bedded siltstones and sandstones indicate lacustrine or lacustrine-deltaic sedimentation (Khristov, Shilov, 1998; Zakharov, 1992).
Unspecific Early Cambrian to Carboniferous algae were found in the limestones (fauna catalogue, site 10). The Late Ordovician age of the Djartash Formation is not disputed, as it follows Ashgillian sediments and is intruded by 450-418 Ma old Issykata Formation granites (isotope age catalogue).

Kolbashy Formation (D₁? kb). This up to 800 m thick formation occurs only on the southern slope of the Kyrgyz Range, within the Kolbashy Trough (tectonic scheme). N.E. Goretskaya (1939) described the stratotype section in the Karabalta River headstream, 12 km to the west from the investigated map (Osmonbetov, 1982). The Kolbashy formation, mainly composed of subalkaline and alkaline intermediate volcanites, comes in sharp angular unconformity onto Upper Ordovician sediments of the Chonkaindy Formation. The bottom, 90-100 m thick horizon of agglomeratic tuffs contains blocks of trachytes and sandstones of the Chonkaindy Formation and 1-2 m thick interbeds of psammitic intermediate tuffs. Above, 1-5 m thick lava flows and clastic lavas of trachytes and plagiotrachytes alternate over 250 to 300 m in thickness. The section changes eastward with 100 m of trachyandesites and trachyandesite-basalts monotonously alternating up-section with tuff-gritstones and tuff-conglomerates containing clasts of trachytes and leucogranites (300-350 m). The upper part is composed of leucite trachytes with amygdoidal structure (120 m), which are replaced up-section by agglomerates of alkaline trachytes (1-4 m) with spheroidal jointing (180 m). Rocks are brown, greenish-brown and brownish-gray. Clastic lavas are laterally replaced by lavas, rarely by tuff-conglomerates; within a single lava flow, leucitophyres transform to leucite trachytes and alkaline trachytes.
Dikes of monzonite-porphyries and quartz syenite-porphyries are associated with the alkaline volcanics. A NW-SE-striking dike swarm along the banks of the Boirek Brook, (tributary of the Aksu River) has intruded Late Ordovician sediments.
The formation has been assigned to the Early Devonian because it occurs at the bottom of a Devonian volcanic trough. A Rb-Sr isochrone has yielded 360 ± 5 Ma (Solomovich, 1997; isotope age catalogue), i.e. Late Devonian. This age cannot be rejected since alkaline lavas are unknown in the volcanic troughs of the North Tien Shan but are reported in association with Late Devonian sediments of the Chu-Ili Mountains in Kazakhstan (Abdulin, 1980). If this age is correct, then the whole section of the Kolbashy Trough is Late Devonian.

Sugandy Formation (D₁ sn). The stratotype section is located in the Chu-Ili Mountains of Kazakhstan (Dvortsova, 1965). Within the investigated area it conformably lays on the Kolbashy Formation in the southern slope of the Kyrgyz Range and rests with a sharp angular unconformity on Early Paleozoic volcanic formations of the northern slope of the Kyrgyz Range. The Aksu Trough provides the most complete, 1150-1250 m thick section. The 150 m thick lower part mainly contains brown-violet and brown-green volcaniclastic conglomerates containing lens-shaped interbeds of tuff-gritstones and tuff-sandstones. The clastic material derives from rhyolites, rhyodacites, sandstones, siltstones and shales, rarely intrusive rocks. Above, 550-650 m thick flows and clastic andesites and andesite-basalts display horizons and beds of agglomeratic andesite tuffs. The 450 m thick upper part is composed of gray-green and violet-green psammitic andesitic tuffs, in which thin lava flows are intercalated. 
Up to 3 km long and 10-20 m thick dikes of diorite-porphyrites represent intrusive facies of the Sugandy Formation.
The base of the formation does not outcrop in the Kashkasu Trough. Green-gray and dark-gray andesite-basalts and andesites overlain by their tuffs and clastic lavas are <400 m thick. In the Kolbashy Trough, the Sugandy Formation is no more than 315 m thick (Grischenko, 1965, 1967; Zakharov, 1992). The Early Devonian age of the formation is based on floristic finds in the stratotype section (Dvortsova, 1965).

Aksu Formation (D₁₋₂ as). The 675-800 m thick type section was described along the Aksu River valley, in the western part of the map (Grischenko, 1967). On the northern slope of the Kyrgyz Range the formation conformably lays on the Sugandy Formation; in the Kolbashy Trough, it lays unconformably on volcanics of the Kolbashy and Sugandy formations. 
In the Aksu Trough, 10 m thick spherulitic rhyolites mark the base of the formation. They are followed up-section by 100-125 m of rhyolite, rhyodacite and dacite lava flows, clastic lavas and gray and gray-green tuffs. The 350 m thick middle formation begins with tuff-conglomerates (20 m, pebbles of andesite, andesite-basalt and rhyolite) replaced upward by rhyolite, rhyodacite and dacite (5-12 m) clastic lavas with 3-5 m thick horizons of acid tuffs, tuff-sandstones and tuff-gritstones. Variegated lavas, clastic lavas and rhyolite, rarely dacite tuffs make the formation top (325 m).
In the Kashkasu Trough the 50-70 m thick basal part is comprised of dacitic and rhyolitic gravel tuffs containing horizons of rhyodacitic clastic lava. They are overlain by 380-400 m of red-brown dacites, rhyodacites and rhyolites containing horizons of dacitic breccias. The section is capped by ignimbrites, agglomerate tuffs and clastic rhyolites, rhyodacites and dacites (500 m). The formation thickness is 930-970 m.
In the Kolbashy Trough the lower part (100-400 m) is composed of volcaniclastic conglomerates and gritstones containing rhyolitic lavas and clastic lavas (2-4 m) with interbeds of acid and psammitic tuffs.  Above, 700 to 1400 m of rhyolite and dacite lava flows alternate with clastic lavas, tuffs and tuffites. The formation is 1800 m thick (Grischenko, 1965, 1967; Zakharov, 1992).
The Early-Middle Devonian age is assessed from similarity with rocks in the Kastek Range that yielded Lower-Middle Devonian flora (Dvortsova, 1965; Osmonbetov, 1982). In the Aral Trough, in the western part of the Kyrgyz Range, A.V. Djenchuraeva discovered and determined Middle and Upper Devonian foraminifers in them: Irregularina cf. angulata Pojark., Umbella cf. bella Buk. in calcareous sandstones of the Aksu section. (Bashkirov, 1998).
Small (<2.5 km2) bodies and dikes of granite-porphyries, quartz porphyries and granodiorite-porphyries represent intrusive facies. The largest body (near 4 km2) is located in the Alamedin River headstream. The granite-porphyries are often spatially related to Devonian volcanites but may occur away from them. The subvolcanic bodies are most abundant in the Aksu River Basin.

Aral Formation (D₂₋₃ ar). T.A. Dodonova described in 1964 the stratotype section within the Aral Trough (Osmonbetov, 1982), in the western Kyrgyz Range, 120 km to the west of the map where this 550-600 m thick formation stratigraphically covers the volcanites of the Aksu Formation. In the Aksu Trough, 3-4m thick conglomerates with pebbles of andesites, rhyolites and rhyolite tuffs mark the base. They are overlain by 300-400 m of basalts and andesite-basalts containing horizons of volcanic breccias and tuffs, and rare andesites followed by 100-200 m of brown and grayish-brown andesite-basalts. Ash tuffs of andesite-basalts alternating with tuff-sandstones form the top of the section (80-100 m).
In the eastern Kyrgyz Range (Boordu region) a Middle Devonian flora was found in terrigenous sediments (Osmonbetov, 1982); within the Aral Trough (western Kyrgyz Range) A.V. Djenchuraeva found and determined Frasnian foraminifers: Sycidium sp., Uraninella sp., Parathurammina sp., Septaglomospiranella sp., and algae: Incertae sedis from calcareous sandstones of the formation (Bashkirov, 1998).

Djardysu Formation (D₃ ds). The stratotype section is located in the Djardysu River valley, on the northern slope of the Kyrgyz Range, where this 600 m thick formation lays unconformably on Devonian volcanites and Ordovician terrigenous sediments (Zakharov, 1992). At the base, a 20 m thick breccia contains angular debris of the underlying Chonkaindy Formation siltstones and shales. The 270 m thick lower part of the formation is composed of alternating beds of red-brown and brown, medium- and thin-bedded polymictic sandstones and cherry siltstones with lenses of up to 1 m thick brown-gray gritstones. Massive (bed thickness = 3-5 m) conglomerates and gritstones represent the upper part of the formation.
In the Ala-Archa River Basin the formation is up to 700m thick. The lower part (50–350 m) is composed of green-gray and brown-gray thin-bedded and massive sandstones alternating with brown cross-bedded and lens-bedded siltstones. The upper part is comprised of red-brown, brown-gray polymictic sandstones containing lenses of gritstones and small-pebbled conglomerates. In some places, sandstones have interbeds of pelitomorphic, clayey and sandy limestones. Famennian foraminifers and algae were collected along the right bank of the Ala-Archa River (fauna catalogue, site12, 19).

Torsu Formation (D₃-C₁ tr). The stratotype section was described in the southern slope of the Kyrgyz Range, in the Torsu-Aksu interfluve (Burtman, 1962), 2 km from the western boundary of the map. This formation lays conformably on the Djardysu Formation and, where the latter is absent, unconformably on various Lower Paleozoic rocks. Sedimentary facies and layer thickness typically change rapidly. Over the mapped region, 2 subformations can be distinguished.
Gray to brown-gray polymictic conglomerates associated with gritstones, gravel and sandy-siltstone interlayers dominate the 300 to 3500 m thick lower subformation. The pebbles derive from the underlying Devonian lavas and Ordovician sandstones and magmatic rocks. On the northern slope of the Kyrgyz Range the conglomerates are laterally replaced by brown-red sandy-siltstone beds, whereas on the southern slope and further towards the south, within the Karamoynok Range, the conglomerates are replaced by gray and green-gray sandstones and siltstones. Widespread cross bedding in the sandstones and siltstones indicate alluvial (fluvial and flood-plain) facies.
The 500–2500 m thick upper subformation is more monotonous. It is composed of red-colored fine-grained sandstones, siltstones, claystones and carbonate lens-like interbeds. Cross bedding, ripple marks and intraclastic breccias indicate upper shelf and delta environments. The stratotype section yielded Late Devonian flora: Leptophloeum cf. rhombicum Dawson (Burtman, 1962). On the map, Late Devonian and Early Carboniferous foraminifers, conodonts and prints of armored fishes were found (fauna catalogue, site 13-17, 21).

Minteke Formation (C₁ mn). The stratotype section is on the right bank of the Kegaty River, 35 km to the east of the map (Djenchuraeva et al., 1997). The 320 to 1160 m thick, volcaniclastic-dominated formation conformably covers the Torsu Formation. At the base, brownish-cherry and green polymictic and volcaniclastic sandstones alternate with siltstones. They are replaced upward by cherry-brown siltstones and ash tuffs of rhyolitic composition with thin (1-2 m) interlayers of tuff-sandstones and lenses of gritstones and conglomerates. The middle section is characterized by a 5-10 m thick layer of gray-green, fine-pebbled conglomerates laterally replaced by gritstones and tuff-gritstones; up-section a bed of red and green siltstone alternates with similarly colored tuff-sandstones and acid, intermediate tuffs containing rare rhyolitic flows and associated clastites; this sequence is overlain by a bed of clayey limestones. Tuff-sandstones alternating with intermediate tuffs make the top of the formation. 
S.B. Guschin discovered and determined Tournaisian–Lower Visean foraminifers Tournayella sp. in limestones of the stratotype section (Djenchuraeva et al., 1997). To the west of the map there are Tournaisian–Lower Visean foraminifers: Glomospiranella sp. (Grischenko, 1967).

Kegaty Formation (C₁₋₂ kg). The stratotype section is located 25 km to the east of the map, on the left bank of the Kegaty River (Schukina, 1961). This formation conformably lays over the Minteke Formation.
The 360-705 m thick Kegaty Formation outcrops in the western part of the map. At its base, variegated polymictic and volcaniclastic sandstones, tuff- sandstones and tuffs of andesite-dacites contain abundant and up to 15 m thick beds of sandy, organo-detrital limestones and red-brown siltstones with calcareous nodular concretions. The upper part is composed of tuffs and tuffites of andesite-dacites, cherry-brown siliceous siltstones, tuff-siltstones and tuff-conglomerates; brick-red tuff-siltstones containing single interbeds of tuff-sandstones, rhyolite lavas and tuffs become predominant towards the top. 
Numerous Bashkirian foraminifers, corals and brachiopods of Plectostaffella bogdanovkensis zone and Plectostaffella seslavica – Semistaffella inconstans zone were collected in the stratotype section (Djenchuraeva et al., 1997). A rich Late Visean – Early Serpukhovian benthic fauna is reported in the mapped area (fauna catalogue, site 18). 

Djanbulak Formation (C₂ bd). On the left bank of the Kegaty River, this 430-450 m thick formation rests conformably on the Kegaty Formation (Schukina, 1961). It cores a syncline in the western part of the map, in gradual transition on the Kegaty Formation. The lower part of the Djanbulak formation (130-150 m) is characterized by coarse, green and gray volcaniclastic sandstones containing interbeds of conglomerates and gritstones (1-3 m), rhyolite flows (1-4 m) and rhyolitic clastites, tuffs, tuffites and rare tuff-gritstones (2-3 m). About 100 m of gray-green, dark-gray, brown, brownish-gray and bluish-gray large-, medium-grained volcaniclastic sandstones and tuff-sandstones with typical rounded calcareous concretions (1-6 m) represent the middle part. The upper part (nearly 200 m) displays thin (0.5-1.5 m) bedded, vinous-red volcaniclastic sandstones, tuff-sandstones, tuff-siltstones, siliceous siltstones and cherts with separate levels (1.2-3.5 m) of clastic lavas and rhyolitic tuffs. The amount of effusive and pyroclastic rocks increases eastward. 
No fossils are reported. The Middle Carboniferous age is assigned from its stratigraphic position on the Kegaty Formation.

A.V. Mikolaichuk, M.V. Gubrenko

Cenozoic sediments

Continental sediments composing the Suusamyr and Chu basins and the Kyrgyz Range foothills represent the Cenozoic Formations of the mapped area.

Suluterek Formation (E1-2 st). The stratotype section is described near the Suluterek River mouth – left confluent of the Chu River (Chediya et al., 1973), 180 km to the east of the map. Similar sediments are called Kokturpak Formation in the Issyk-Kul and Naryn Basins. Inequigranular, ungraded calcareous sandstones, gritstones, red - brown plastered clays or carbonate rocks (marls, dolomites, limestones and syngenetic carbonate breccias) unconformably cover the Paleozoic basement. Locally, well-rounded fine to medium-pebbled alluvial conglomerates contain cherts and quartzites. The rocks listed above alternate irregularly. Rare basalt flows belong to the sequence. The stratotype section is 150 m thick though the formation is usually not thicker than a few tens of meters. Conversely, it is 635 m thick in Borehole S6 (Chediya et al., 1973).
Pollens and chemogenic dolomites, gypsums, syngenetic carbonate breccias indicate arid conditions and ephemeral desert lakes (Chediya et al., 1973; Fortuna et al., 1994).
The Paleocene-Eocene age of the Suluterek Formation and its equivalents is based on finds of tapiridians from Deperetella genus and of rhinoceros-like animals from Hyracodontidae family in the northern Issyk-Kul Basin (Turbin et al., 1972) and on K/Ar and Ar/Ar ages of basalts in the Central Tien Shan (63–48 Ma; Sobel and Arnaud, 2000). Basalt flows in the Suluterek Stream are 57.4  ±  0.9 Ma (Ar/Ar;  M.M.Buslov,  personal communication).

Shamsi Formation (E3–N1šm). This formation conformably lays over the Suluterek Formation. The stratotype section is described along the Tuyuk Stream – left confluent of the Shamsi River (Chediya et al., 1973), 35 km to the east of the map border. Vinous-red, brown or brick-red sediments represent proluvial cones, rarely alluvial sediments for which coarse, cross bedding is typical. Sandstones and loams dominate the lower part of the formation and grade upward into gritstones and conglomerates. Stratified, proluvial sediments with gravel filler and up to 20 cm thick horizons with large pebbles of andesite-dacite and Devonian brown sandstones occur locally. The formation thickness varies from 300 to 1285 m in Borehole S6 (Chediya et al., 1973). The top layers of the Shamsi Formation are replaced in the Issyk-Ata and Alamedin rivers interfluve by lacustrine sediments.
The Oligocene-Miocene age is defined by finds of tortoise Stylemus karakotensis Riab., teeth of giraffe Samotherium sp. and Antilope sp. in the Issyk-Kul Basin (Turbin et al., 1972), and ostracodes: Lineacypris? genus; Ilyocypris errabundis Mandelst found in test cores of Borehole S6 (fauna catalogue, site 25.1).

Kyrgyz Redstone Formation (E1–N1kg). Early studies of the Central Tien Shan sediments described the two lower formations of the Cenozoic section with this name (Schulz, 1946). We use it when gathering the Suluterek and Shamsi formations for the western part of the sheet, where they are together no more than a few tens of meters thick.

Djel'dysu Formation (N1dj). The "Nooruz" section (Ibragimov and Turdukulov, 1965) is stratotype (see layer of sections). A horizon (so called Serafimovka Formation) of variegated clays with salts (mirabilite, glauberite, halite) and layers and lenses of gypsum marks the base of the formation, which is mostly composed of alternating clays, claystones, mudstones, silts and fine-grained sandstones with grey, green or red-brown color. Uniformly colored terrigenous rocks compose 4-12 meters thick layers with interbeds and lenses of gypsum, clays and silts gradually replaced upward by marls. 50-60 m of green-gray marls including interbeds of clayey limestone and massive medium-grained sandstones represent the upper part of the formation. Our field observations testify that the 2100 m thick saliferous sediments cored in Borehole S6 result from pinching of ductile rocks into the core of an anticline.
In the Nooruz-Djel'dysu rivers interfluve alternating salts and clays are crumpled in complicated disharmonic folds, which have lost their stratigraphic position. In Borehole S7, 2.5 km away from S6, salt-bearing sediments are tectonically absent. The original thickness of the formation is not less than 450 m. It is interpreted as evaporites from a playa-margin (Bullen et al., 2001).
Miocene ostracodes were found in the lower saliferous horizon in Borehole S6 and hyparion was found in the upper layers of the formation (fauna catalogue, sites 25.2; 27). Magnetostratigraphic data yield an age of 9-8 Ma. (Bullen et al., 2001).

Saryagach Formation (N1sg). The "Nooruz" section is stratotype (layer of sections) for this 400-440 m thick formation of alluvial fan and a playa-lake margin (Bullen et al., 2001) that conformably lays on the Djel'dysu Formation but differs from it by red – brown and brick-red color of rocks (Ibragimov, Turdukulov, 1965). Badly sorted sandstones and gravel sandstones (0.5-2 m) alternating with thin-bedded variegated (white, gray, green and rick-red) siltstones dominate the composition of the formation. The last rocks compose beds with thickness of from 5-10 cm up to 40 cm. Upward increase in coarse-grained material is related to reduction of siltstone interlayers and to appearance of conglomerate horizons. Channel scours, cross-beds, and pebble imbrication, document northwestward paleoflow. 
Turtle fossils of Stylemus genus (fauna catalogue, site 26) allow a wide age range specified by magnetostratigraphic dates as Upper Miocene (Bullen et al., 2001).

Chu Formation (N2 ču). The "Nooruz" section is stratotype (layer of sections) of this 1250-1700 m thick formation (Chediya et al., 1973), whose pale-yellow, pale-grey color makes discrimination with the underlying Saryagach Formation by (Ibragimov and Turdukulov, 1965).
The lower part of the formation is composed of claystone-siltstone beds (up to 20 m) alternating with medium to fine-grained thin sandstone beds or rhythmically laminated sandy-gritstone (5-10 m). Conglomerates are subordinate. The claystone-siltstone interbeds are often pink or grey, locally with tan tint. Some calcareous siltstones are light coloured. Sandstones and conglomerates dominate the upper part of the section. Dense, gray conglomerates beds of the middle part increase upward in abundance and thickness. The clastic component is well-rounded, moderate to well sorted, up to 15 cm in diameter, and commonly imbricated. This strata is interpreted as braided-river and alluvial-fan deposits (Bullen et al., 2001).
Vertebrates, gastropods and flora imprints are Late Miocene–Pliocene in age (layer and fauna catalogue, locations 22; 23). Magnetostratigraphic correlations correspond to the Lower Pliocene (Bullen et al., 2001).

Sharpyldak Formation (N2-Q1šr). The stratotype section was documented on the southern boundary of the Issyk-Kul Basin (Schulz 1948), where Upper Pliocene–Lower Pliocene conglomerates lay with a gradational contact on the Chu Formation. In the central part of the Chu Basin, this 950 m thick formation truncates Paleogene and Neogene sediments and may directly rest on Paleozoic rocks. We have traced this unconformity from the Djelamysh River in the western part of the map up to the Aksu River in the eastern part. Along the left bank of the Aksu River, the basal conglomerates lay with angular (10º) unconformity on loams and gritstones of Shamsi Formation and on calcareous breccias of Suluterek Formation. The Sharpyldak Formation is composed of 6 rhythmic, 65 up to 230 m thick beds. At the base of each of them conglomerates are replaced upward by gravel-sandy beds including lenses of conglomerates. The amount of conglomerates and the size of their fragments increase upward to boulder conglomerates in the upper rhythmic units. Pebbles derive from Early–Middle Devonian to Late Devonian–Early Carboniferous rocks.
In the central part of the Chu Basin, the 1300 m thick (Bullen et al., 2001) Sharpyldak Formation (Ibragimov, Turdukulov, 1965) is composed of coarse conglomerates becoming upward fanglomerates with granite boulders up to 1-2 m in diameter. North-directed paleocurrents document continued progradation of transverse alluvial and debris-flow fans into the Chu Basin (Bullen et al., 2001). This piedmont apron tapers northward and does not exceed a few tens meters in foothills of the Kendyktas Range.
The Djel’dysu River section delivered fossils of Stenon horse, (fauna catalogue, site 24), which define the age as 2.6 Ma. (Bullen et al., 2001). Magnetostratigraphic data specify 3.0-1.5 Ma. (Bullen et al., 2001).

M.V. Gubrenko

Quaternary sediments

Quaternary sediments are linked to the river network of the area. In the Сentral Tien Shan where crystalline ranges trend approximately east-west, the river network comprises first-order east-west flowing rivers draining the intermontane basins and second-order north- and south-flowing rivers draining the ranges. 
P.G. Grigorienko (1960) and A.K. Trofimov (Trofimov et al., 1976) developed the Quaternary stratigraphy of the Tien Shan region with reference to the global glacial and interglacial periods. Trofimov et al. (1976) and K.E. Abdrakhmatov (1988) more specially studied the Quarternary stratigraphy of the mapped area. Recent work and radiocarbon dating (Chediya et al., 2000; Thompson, 2001) confirmed their stratigraphic scheme.
Fluvioglacial and alluvial sediments replace downstream sediments of the four main glacial events. The height of the alluvial terraces with respect to the river flood-plains is a steady parameter used to correlate terraces of various river systems. Coeval glacial, alluvial and proluvial sediments compose complexes attributable to the Early Pleistocene (QI), Middle Pleistocene (QII), Late Pleistocene (QIII) and Holocene (QIV) glaciation and the interglaciation stages (Trofimov et al., 1976; Abdrakhmatov, 1988).

Alluvial sediments

The stratigraphic record of fluvial erosion and sedimentation on a terrace integrates past spatial and temporal variations in river sediment supply, river transport capacity, and vertical movement of the underlying bedrock. The stratigraphic elements of the terraces that lie within the Tien Shan Cenozoic basins consist of an eroded bedrock surface (typically carved in weakly cemented Cenozoic sandstone or siltstone) a few to tens of meters of cobble to boulder gravel, and a few centimeters to several meters of silt, sand, and minor gravel. The thickness and composition of the silt and sand deposits capping the terraces differ depending on the distance from adjacent terrace risers or valley walls (colluvial deposition), and local history of overbank flood and loess deposition (Trofimov et al., 1976; Abdrakhmatov, 1988; Thompson, 2001).
In the investigated area, the Early Quaternary Complex (QI) demands special investigations. 140-160 m (QII1) and 50-70 m (QII2) high QII terraces are composed of boulder-pebble sediments with interbeds of sands and gravels (10-12 m), which are covered by loess-like loams (12-15 m). The basement is usually made of dislocated Cenozoic sediments.
The Middle Pleistocene age is documented from numerous finds of bone fossils and primitive tools in slopes of the Chu River valley (Trofimov et al., 1976). In the documented map, bone fossils of this age were found in the Djelamysh River valley. Mammal teeth Equus moshachensis, Cervus elapus fossilis and also phalanx Saiga imberbis fossilis estimated as Early–Middle Pleistocene fossils are mentioned without exact site indication (Trofimov et al., 1976). Based on Thompson’s data (2001) an IRSL (infrared-stimulated luminescence) age of 170 ± 25 ka is the minimum age of the QII2 terrace along the Alamedin River (catalogue CLum_age, site 14).
QIII terraces contain the broad, often extensive deposits that can stand 10 to 50 m above the active stream. These terraces are composed of pebbles, gravels and sands (4-12 m) in a zone of foothills and loams with numerous horizons of buried soils (up to 20 m) within the flat part of the Chu Basin. Koulan fossils (fauna catalogue, site 28) were found in the loams of the Djelamysh terrace. An IRSL and radiocarbon age of the QIII2 terrace along the Sokuluk and Alamedin Rivers ranges from 8.430 ± 0.06 to 26.1 ± 0.9 ka (catalogue CLum_age, sites 10, 13 and 15). Based on these results, river incision and terrace formation are believed to have occurred during the global glacial-interglacial transition (Thompson, 2001).
The Holocene sediments represent channels, flood-lands and a 2 to 7 m high flood-land terrace. The latter is represented by well-rounded gravel-pebbled sediments covered by <0,5 m thick loams (Trofimov et al., 1976). Modern rivers flowing in valleys with broadly preserved terraces have braided into meandering channels with a cobble and boulder bed. The upper reaches of most major tributary rivers lie in recently glaciated catchments or contain small glacier cirque.
Detrital charcoal samples and land snail shells collected from above flood-land terraces of the major Tien Shan intramontane basins indicate terrace formation during the Early to Middle Holocene. Radiocarbon ages of these samples vary from 4690± 50 up to 9840 ± 50 years (Thompson, 2001).

Glacial sediments

Valley glaciers and rarely bottom glaciers generated 10 to 350 meters thick QII moraines composed of non-rounded, unsorted rubbly-clumpy deposits. The ends of the moraines are at 1600 to 1800 m a.s.l.

Valley glaciers QIII moraines occur at bottoms of Middle Quaternary trough valleys. The moraine surfaces are turf-covered but their morphology is clearly definable. Because glaciers were rather small, Late Quaternary moraines are usually located in the upper parts of Middle Quaternary troughs. The 40 to 300 m thick moraines are usually composed of loamy rubbly-clumpy unsorted heaps. Frontal moraines are at an altitude of 1500-2200 m in the northern slope of the Kyrgyz Range and up to 2600-2800 m in its southern slope.
QIV moraines are characterized by fresh shapes, are not turf-covered and have pronounced final embankments and lateral ridges. The moraines are composed of 50-70 m thick rubbly-clumpy material that fills up kars and upper parts of trough valleys. Outwash plains of boulder pebbles and sands occur at the ends of glaciers and recent moraines higher than 3000-3500 m. Narrow belts of Holocene fluvioglacial sediments of mountain rivers in headstreams of valleys evolve to terraces (Trofimov et al., 1976).

Proluvial sediments

Proluvial sediments do not differ in composition through time and are represented by loess-like loams, loess-like pattum loams and sandy loams. Surfaces of QII and QIII terraces are mostly covered by thick cone-debris composing the submontane tail area of the Kyrghyz Range.
Trofimov A.K. and his co-authors (Trofimov et al., 1976) note that active processes of sliding and gravitational displacement of material partly related to seismic events are typical for the Holocene (layer of seismodislocations). Trenches made across the Issyk-Ata Fault zone yielded fossils and paleosoils dated at 5250±60; 5130±50; 3530±40; 3180±40; 2830±50; 2410±50 and 1850±40 years, which were buried during thrusting and collapse of Pleistocene sediments (Chediнa et al., 2000; Thompson, 2001).

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Edited by J-P. Burg 
SNF, Project No 7KSPJ065518; http://www.kyrgyzstan.ethz.ch