Duguan Fm
Type Locality and Naming
Western Henan. The Duguan Fm was named by the Qinling Party of Regional Geological Survey, Ministry of Geology in 1959. The type section is in Bugou, Duguan Township, Lushi County, Henan Province. It is within the upper portion of the Guandaokou Gr.
Synonym: （杜关组）
Lithology and Thickness
The Duguan Fm is dominated by variegated thin-bedded dolomitic carbonate rocks. The base is composed of grey-green sandy-pebbly shale, sandy-pebbly dolomite sandwiched with feldspar quartz sandstone, while the middle and upper parts, grey-white medium-thick-bedded dolomite and slaty muddy dolomite. The dolomite contains chert bands and basin-clastic conglomerate. The Duguan Fm is regarded as a key bed for regional lithostratigraphic correlation, its stable stratigraphic position, slightly changeable thickness and remarkable lithological character. The formation is 197 m thick.
Relationships and Distribution
Lower contact
It disconformably overlies on Xunjiansi Fm.
Upper contact
It is overlain by the Fengjiawan Fm (the uppermost formation of the Guandaokou Gr).
Regional extent
The formation is distributed mainly in Luonan and Longxian counties, Shaanxi Province, and Lushi, Luanchuan counties, Henan Province.
GeoJSON
Fossils
In north of Tielugougully, Chen'er, Luonan County, the slate and dolomite, occurring in middle and lower parts of the formation yield microplants: Trematosphaeridium sp., Taeniatum crassum, Tielingella tielingensis. Trachysphaeridium rude, Asperatopsophosphaera cf. partialis, Pseudozonosphaera verrucosa. The stromatolites in the formation are: Scopulimorpha irregularis, Chihsienella chihsiensis; Pseudotielingella chihsienensis, Baicalia baicalica, Chihsienella chihsienensis, Inzeria f., Paracolonnella laohudingensis, P. shimenensis.
Age
Depositional setting
Additional Information
In 1962, the Henan Geological Institute attributed the Duguan Fm to the Nantianmen Gr which is now abolished. The Shaanxi Party of Regional Geological Survey, Bureau of Geology named the Duguan Fm as the Xiangziping Gr in the area south of Shimen-Panhe-Machaoying fault, which is now abolished too.