Helongshan Fm

Synonym: Longshan Fm

Lithology and Thickness:

It is composed of light gray banded and thin-layered limestone with gravity flow gravel sandy limestone, and nodular limestone. At the standard point, it can be divided into two sections: the lower part of the first section is yellow-green shale with a small amount of thin plate-like limestone and inconspicuous band-like limestone, and the limestone gradually increases upwards, and the thickness is 80 m; the second section is made of blue-grey and light-gray band-like limestone Mainly, with yellow-green shale in between, 205 m thick.

Lithology-pattern: Clayey limestone

Relationships and Distribution:

Lower contact:

The yellow-green shale at the bottom is in integrated contact with the thick limestone at the top of the underlying Lower Triassic Yinkeng Fm

Upper contact:

Conformable with Nanlinghu Fm.

Regional extent:

Distributed in the Lower Yangtze area, the lithology changes horizontally. In the west of Jiujiang, it is mainly gray, light gray, medium-thin crystalline dolomite, thin limestone, and granular limestone, with a thickness of 50-160 m; in the Chaohu area, thin-layered Stucco limestone intercalated with tumor-like limestone is mainly 19 m thick; in Tongling and Nanjing areas, it is thin-thick stucco limestone intercalated with partial shale, 57-153 m thick; in Susong, Anqing and Guichi areas, it is a strip Thick and thin limestone intercalated with gravel and sandy limestone deposited by gravity flow, 110-285 m thick; Xiangdong to Yixing and Guangde area, mainly thin and thick marl interbedded with slab-shaped gravel limestone, thick 100-150 m; in Wuxi, Suzhou and other areas, it is dominated by dolomitic limestone, stucco limestone, and spiky oolitic sandy limestone, with a thickness of 100-200 m.

GeoJSON:

Fossils:

It is characterized by rich production of ammonoids, followed by bivalves and conodonts. From top to bottom, it can be divided into two ammonoid belts: 1. Owenites zone; 2. Anasbunes zone; a conodont Neospathodus waageni zone can also be established.

Age:

Schematic stratigraphic column indicates early Olenekian.

Age span:

Beginning stage: Olenekian

Fraction up in beginning stage: 0.15

Beginning date (Ma):

Ending stage: Olenekian

Fraction up in ending stage: 0.6

Ending date (Ma):

Depositional setting:

This formation is characterized by gravity flow deposition.

Depositional-pattern:

Additional Information

After the creation of the name, Wang Yichang et al. (1966) and Min Qingkui et al. (1982) successively named the strata with the same meaning as the Helongshan Formation in the Tongling and Nanjing areas as the Tashan Fm and the Hushan Fm. In 1970, the Jiangsu District Investigation Team classified this part of the formation into the upper part of the Lower Qinglong Fm. This article proposes to discard the Tashan Fm., Hushan Fm. and Xiaqinglong Fm.