Zagunao Fm

Synonym: Zagennei Fm, Zagenaenao Fm

Lithology and Thickness:

It is mainly composed of thick gray massive fine-grained feldspar quartz sandstone or fine-grained calcareous quartz sandstone. Its thickness is 391 m

Lithology-pattern: Fine-grained sandstone

Relationships and Distribution:

Lower contact:

The bottom is marked by the first and last occurrence of the thick sandstone. It is in pseudo-conformational contact with the underlying Zhagashan Fm.

Upper contact:

The top is marked by the first and last occurrence of the thick sandstone. It is in pseudo-conformational contact with the overlying Zhuowu Fm.

Regional extent:

GeoJSON:

Fossils:

Age:

In view of the existence of Late Triassic Carnian bivalves in the Zhuwo Formation, the overbearing strata of the Zagennei Fm, there are three possible time periods of the Zagennei Formation: (1) Carnian; (2) the late Ladinian period; (3) Late Ladinian -- early Carnian period. In this Lexicon, the layer of the heterogluteneae modified by Rao Rongbiao (1987) is temporarily placed at the uppermost part of the Ladinian order.

Age span:

Beginning stage: Ladinian

Fraction up in beginning stage: 0.5

Beginning date (Ma):

Ending stage: Ladinian

Fraction up in ending stage: 1.0

Ending date (Ma):

Depositional setting:

Depositional-pattern:

Additional Information

It is named as "Zaguenao Strata", which refers to the lower part of the original Xikang Gr, including a set of metamorphic sand slate above the Permian system and limestone strata at the bottom. In 1961, the survey team of the second area of Sichuan Geological Bureau renamed it Zagenao Fm, and the strata containing Claraia in the lower part was named Potzigou Fm. The modified Zagunao Fm is a set of metamorphic sandstone and splintstone strata, which overlays the lower Triassic Bozigou Fm (Rilagou Fm in this Lexicon usage) and underlies the upper Triassic Zhuwo Fm, and is roughly equivalent to the Middle Triassic Anisian-Ladinian. In 1975, the stratigraphy corresponding to the lower member of Zagnao Formation was named Zagashan Fm by the delegation from the Second District of Sichuan Geological Bureau in Zagat Mountain, southwest of Songpan County, Sichuan Province. In 1982, Zhao Jinke et al. applied the name of the glutenic (gravel-rich) brain group and limited its time limit to the Early Triassic Olenekian to the Middle Triassic Ani. In 1987, Rao Rongbiao et al. found a standard Middle Triassic Ladinian fossil, Daonella lommeli, in the lower part of the HGT, so the HGT was separated with the upper part was still called the HGT, which was dated to the early Late Triassic. The lower member was now called the Zagashan Fm, which is from the Middle Triassic Anisian to Ladinian stages.