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Sidazhai Formation
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Sidazhai Fm base reconstruction

Sidazhai Fm

Period: 
Permian

Age Interval: 
P2 (79), Kungurian Stage (late-Cisuralian Epoch; late-Early Permian) through the Guadalupian Epoch (Middle Permian)


Province: 
Guizhou

Type Locality and Naming

The type section is located in the Sidazhai Country to the northwest of the Houchang Region, Ziyun County, Guizhou Province. It was named by Xiao Weimin et al., in 1986.


Lithology and Thickness

Limestone (redeposited downslope). Representing psammitic (sandy) calcirudite, which is composed of lithoclastics and bioclastics all transported from the carbonate platform. The basal part of the formation consisting commonly of calcirudite or micrite-calcisiltite. Starting from these basal micro-conglomeratic clastics, the lithoclastics are grading upwards gradually into sandy clastics, silty clastics, and micritic clastics, showing a repeated occurrence of rhythmic layering, belonging to carbonate-sand turbidities. The carbonate-rich conglomerates are composed mainly of the lithoclasts, lithic fragments and bioclasts coming from the light-colored bioclastic limestones and reef-limestones occurring on the platform-margins, as well as of a small amount of lithoclasts and lithic fragments coming from the dark-colored on-the-spot micrites or those of them occurring on the platform-slope, with sharply angular and sub-rounded rubbles being randomly accumulated in an equal-axial, platy and prismatic form. This kind of carbonate-rich conglomerate of rubble is commonly found to occur in the upper part of the section, but laterally it is distributed in a mat-like or a fan-like form to constitute a fringe for the front collapsing part of the platform escarpment and gravity-flow- induced deep-water carbonate clastics; the composition of lime-conglomerate is similar to that of the carbonate-rich conglomerate of rubble, with the rubble being in a semi-round oriented arrangement, and with a good sorting; it represents submarine watercourse deposits. Micrite and siliceous rocks are possessed of horizontal beddings and traces of Lophoctenium and vermiglyph, and the biological fossils are rare which comprise mainly the ammonoids, radiolaria and sponge-spicules, etc., representing basin-margin in-situ deposits. In the Ziyun and Luodian regions it is 346- to 648-m thick.


Lithology Pattern: 
Limestone


Relationships and Distribution

Lower contact

Conformable contact with the marl or claystone of the underlying Nashui Fm. In the northern belt of the facies change, the formation is directly overlapping the Houziguan Limestone.

Upper contact

Conformable contact of its uppermost calcirudite with the siliceous rock and claystone of the overlying Shaiwa Gr (Baxian Fm) in the northern belt of the facies change.

Regional extent

Distributed extensively in the Yunnan-Guizhou-Guangxi Basin.


GeoJSON

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Fossils

The fossils the northern part of the region comprise the Fusulinid fauna represented by the Misellina range zone to the Neoschwagerina range zone, Ammonoids represented by the Popanoceras-Metaperrinites assemblage zone, and deep-water conodonts zone.


Age 

The time-rock span of the formation is from the Qixia’an Stage to the end of the Maokou’an Stage of the Early Permian Epoch, but the time of its formation in the northern part of the region is a bit later, which is in most cases starting from the late stage of the Qixia’an Stage, or to the middle stage of the Maokou’an Stage. [Qixia'an through Maokou'an = Kungurian Stage (late-Cisuralian Epoch; late-Early Permian) through the Guadalupian Epoch (Middle Permian)

Age Span: 

    Beginning stage: 
Kungurian

    Fraction up in beginning stage: 
0.5

    Beginning date (Ma): 
278.84

    Ending stage: 
Kungurian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
274.37

Depositional setting

It is interpreted as a downslope debris from a carbonate platform.


Depositional pattern:  


Additional Information


Compiler:  

Xiao Weimin

GeoJSON estimate by Can Cai and Xinyi Zhang (Chengdu Univ. Tech. students)