Guanling Formation | |
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Stratigraphic range: early-mid Anisian (Pelsonian) ~ | |
Type | Geological formation |
Underlies | Yangliujing Formation |
Overlies | Jialingjiang Formation |
Lithology | |
Primary | Mudstone, limestone |
Other | Dolomite |
Location | |
Coordinates | 25°30′N104°54′E / 25.5°N 104.9°E |
Approximate paleocoordinates | 11°42′N94°12′E / 11.7°N 94.2°E |
Region | Guizhou & Yunnan Provinces |
Country | ![]() |
Extent | Yunnan–Guizhou Plateau |
The Guanling Formation is a Middle Triassic (Anisian or Pelsonian in the regional chronostratigraphy) geologic formation in southwestern China.
The formation encompasses two members. The first member is primarily calcareous mudstone and dolomite, indicative of a coastal environment. The second member is a thicker marine sequence of dark micritic limestone with some dolomite. Two distinct fossil assemblages are found in the second member. The older Luoping biota preserves abundant arthropods (including isopods, [1] decapods, [2] mysidaceans and thylacocephalans [3] ) along with fossils from other invertebrates and vertebrates, which are rare but well-preserved. The slightly younger Panxian fauna has a more diverse and common assortment of marine reptiles such as sauropterygians. [4]
A tuff bed in the Luoping biota has been dated to 244.5 ± 2.2 Ma via U-Pb SHRIMP dating. The Luoping biota as a whole was deposited over a period of 340 ± 71 kyr. This estimate is justified by cyclostratigraphic evidence, as indicated by fluctuations of terrestrial proxy metals. [5]
Among others, the following fossils were reported from the formation:
Genus | Species | Member | Notes | Image |
---|---|---|---|---|
Barracudasauroides [6] | B. panxianensis | Upper Member [6] [4] | A small mixosaurid ichthyosaur, either a member of its own genus [7] or a species of Mixosaurus . [4] | |
Phalarodon [8] [9] | P. cf. fraasi [8] | Upper Member [4] | Known from a skull of a small mixosaurid ichthyosaur with durophagous dentition. | |
P. atavus [9] | Upper Member [4] | A small mixosaurid ichthyosaur known from a complete skeleton. Might represent a member of its own genus, Contectopalatus . | ||
Xinminosaurus [10] | X. catactes | Upper Member [4] | A medium-sized early ichthyosaur with durophagous dentition, possibly a member of Cymbospondylidae. |
Genus | Species | Member | Notes | Image |
---|---|---|---|---|
Atopodentatus [11] | A. unicus | Upper Member [11] | A bizarre, likely herbivorous [12] sauropterygian with possible placodontiform affinities, [13] known from several well-preserved specimens. | |
Placodus [14] | P. inexpectatus | Upper Member [14] [4] | A medium-sized placodontid placodont, known from a complete specimen. [14] |
Genus | Species | Member | Notes | Image |
---|---|---|---|---|
Largocephalosaurus | L. polycarpon [15] | Upper Member [15] [4] | A mid-sized basal saurosphargid sauropterygian. | |
L. qianensis [16] | Upper Member [16] [4] | A mid-sized basal saurosphargid sauropterygian. | ||
Sinosaurosphargis [17] | S. yunguinensis | Upper Member [17] [4] | A small armoured saurosphargid sauropterygian. |