Journal
PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY
Volume 524, Issue -, Pages 212-229Publisher
ELSEVIER
DOI: 10.1016/j.palaeo.2019.03.034
Keywords
Conodont; Natural assemblage; Pelagic Panthalassa; Triassic; Soft tissue impressions
Funding
- Japan Society for the Promotion of Science [23840012, 24740340]
- Fujiwara Natural History Foundation
- Fukada Geological Institute
- Grants-in-Aid for Scientific Research [23840012, 24740340] Funding Source: KAKEN
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We report the first discovery of Lower Triassic Clarkina assemblages: four natural conodont assemblages from Lower Triassic pelagic black claystones of the North Kitakami Belt in northeastern Japan (Akkamori section). The fossils were obtained from the 2.5-m horizon level above the black claystone base, which is assigned to the end-Permian mass-extinction event. This horizon has been dated to the earliest Triassic (Griesbachian) by the occurrence of Hindeodus parvus, which is the index species for the base of the Triassic, in the same and subjacent horizons. These four fossil assemblages include a paired segminiplanate-formed P-1 element, which was identified as the genus Clarkina, and have fully or partially preserved the original components of conodont elements. The most complete assemblage among them includes 15 distinctive elements, namely S-0 and pairs of M, S-1,S-2, S-3, S-4, P-1, and P-2. It is noteworthy that these fossil assemblages preserve probable impressions of 'eyes,' which were replaced by aggregations of silicate, phosphate, and sulphide minerals. The occurrence of several sets of fossils that retain the original positioning of the conodonts' elemental apparatuses, as well as the original presence of soft tissue, may be attributed to the process by which the conodonts' bodies were transported to the deep seafloor, and by which the activity of agents of decomposition was inhibited in near-abiotic sediments under anoxic conditions in the pelagic deep sea during the earliest Triassic.
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