Two episodic changes of trace fossils through the Permian-Triassic transition in the Meishan cores, Zhejiang Province

Abstract

Six ichnogenera, Chondrites, Palaeophycus, Planolites, Rhizocorallium, Skolithos, and Thalassinoides, were identified from the drilling cores near the Global Stratotype Section and Point (GSSP) of Permian-Triassic boundary at Meishan, Zhejiang Province. The ichnological indices, including abundance, bioturbation index, and disturbed depth of trace fossils, show two episodes of intense changes near the Permian-Triassic Boundary (PTB). Episode I occurred in Beds 25-27b when the ecologically complicate forms such as Chondrites, Skolithos, Rhizocorallium, and Thalassinoides disappeared hereafter, the bioturbation index reduced from 1-5 to 1-3, and the disturbed depth declined from 5-66 to 2-5 cm. Episode II took place at the base of Bed 33 with the disappearance of Palaeophycus and Planolites, and subsequent absence of trace fossils and bioturbation till the middle-upper part of Bed 41 when the disturbed structures reoccurred, but they are only tiny Planolites and the bioturbation index was never higher than 3 and the disturbed depth less than 4 mm. Episode I shows an intense change, corresponding to the main stage of the end-Permian mass extinction, whereas Episode II is relatively weak, corresponding to the epilogue of the mass extinction of trace makers in the Early Triassic. Subsequently, ichnofossils were dominated by surface tracks in simple ecological habit and structures. This phenomenon indicates that the Early Triassic benthonic fauna is changed from sessile benthic system to mobile benthic system after the end-Permian mass extinction. In other words, the evolution of the trace fossils across the Permian-Triassic transition had an episodic process similar to the body fossils. In addition, the change of ichnofabrics is well coincided with the negative excursion of carbon isotopes and the expansion of cyanobacteria. As the results of physical and biogenic processes, trace fossils provided unique materials for the study of the biotic and environmental events, as well as their coupling evolution through the great Permian-Triassic transition.trace fossils, bioturbation index, disturbed depth, the Permian-Triassic transition, two episodic evolution, Meishan cores Citation:Zhao X M, Tong J N. Two episodic changes of trace fossils through the Permian-

Thermal and Nutrient Stress Drove Permian-Triassic Marine Extinctions

“…This 45 suggests that the nature of the mass extinction event at Meishan, except for ostracods, is best characterized as an extinction interval (51 cm), from beds 25 to 29a ( C. meishanensis – I. isarcia conodont zones). Such interpretation is also relatively consistent with a stark reduction in bioturbation and tiering depth at the base of bed 25 ( 10 ). Whereas ostracods record an earlier major extinction interval from beds 22-23a and a subsequent minor pulse at bed 24d ( 11 ), suggesting that this group of organisms were more sensitive to initial environmental changes or 5 responded to different environmental changes prior to the main extinction interval.…”

Framboidal pyrite evidence for persistent low oxygen levels in shallow-marine facies of the Nanpanjiang Basin during the Permian-Triassic transition

“…compositions (e.g. Grice et al, 2005;Cao et al, 2009;Zhao and Tong, 2010;Chen et al, 2015;Li et al, 2016). Similar results, based on framboidal pyrites, were also noted from deeper facies sections, including Shangsi, Tianqiao, Changtanhe, Xiakou, Chaohu and Xiaojiaba ( Fig.…”

Thermal and nutrient stress drove Permian-Triassic shallow marine extinctions

“…This suggests that the nature of the mass extinction event at Meishan, except for ostracods, is best characterized as an extinction interval (51 cm), from beds 25 to 29a (C. meishanensis -I. isarcica conodont zones). Such an interpretation is also relatively consistent with a stark reduction in bioturbation and tiering depth at the base of bed 25 (Zhao and Tong 2010).…”