Maychat Fm

Period:

Permian

Age Interval:

middle Permian

Province:
Zaisan (Zaysan) Basin - East, Zaisan (Zaysan) Basin - Central

Type Locality and Naming

Synonym: Michat Fm, Maichat Fm, Michatskaya

Lithology and Thickness

In borehole Sarybulak C-1, it is described as ca. 750 m with a prevalence of conglomerates, gritstones, sandstones and diabases. Aleurolite (siltstone) and claystone are present in subordinate volumes. Polymictic, weakly carbonized sandstone and aleurite. Diabase is jointy as a role. It is typical for the sandstone and diabase because of joints that a heightened porosite that provides intensive saturation with bitumen and points to prevalence of jointy rocks. Within the whole log, the Maychat Fm (Maichat Fm) suite rocks have the highest extent of bitumen and heavy oil saturation. Pyrite is disseminated in various horizons throughout.

In Well X-II, Primanrack Depression, it is " 750 m-thick, composed of interbedded sandstones siltstones, mudstones, and oil shales. Diabase lavas, tuff, and tuffaceous rocks predominate near the top of the formation. Oil was recovered from depths of 2385–2412 m and 2960–3036 m. Sandstones are impregnated with considerable amounts of degraded oil." And in Kenderlyk Trough (southern margin), it consists of " 150–300 m-thick, mudstones alternating with coal make up the lower (thinner) part of the formation, while the upper part is mainly composed of upward coarsening siltstones, sandstones and conglomerates. The formation is intruded by a 20 m-thick, 12 km-long diabase dike." (Nurbekova et al., 2023)

Lithology Pattern:

Clayey sandstone

Relationships and Distribution

Lower contact

Unconformable onto the Taranchi Fm

Upper contact

Underlies the Akkolka Fm (Akkola Fm)

Regional extent

Originally throughout the entire basin; but later tectonics and erosion during uplifts implies that the main surface exposures of the Late Carboniferous-Permian succession is a 2-km-thick succession in the Kenderlyk Trough in the southern part of the Zaisan (Zaysan) basin (Nurbekova et al., 2023).

GeoJSON

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Fossils

Age

middle Permian (Roadian-Capitanian?)

Age Span:

Beginning stage:

Roadian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

274.37

Ending stage:

Capitanian

Fraction up in the ending stage:

1.0

Ending date (Ma):

259.55

Depositional setting

"The Maychat Fm, based on a single sample, has been interpreted as brackish-saline lacustrine" (Nurbekova et al., 2023)

Depositional pattern:

Additional Information

Compiler:

Information provided by Nariman Jamikeshev from Kazakh-language sources and from other publications (e.g., Nurbekova et al., 2023. High-quality source rocks in an unexplored basin: The upper Carboniferous-Permian succession in the Zaysan Basin (Kazakhstan). Internat. Jour. Coal Geology, 272, article 104264.