Zoophycos is one of the most complex and enigmatic trace fossils recorded in marine strata from Cambrian to Quaternary worldwide, which is invaluable for the study of Phanerozoic development of organism–environment interactions. Here we address and demonstrate the macroevolution of Phanerozoic Zoophycos by assembling 448 points in constructing the Phanerozoic Zoophycos database based on 291 papers from 1821 to 2015 and 180 specimens from Cambrian to Palaeogene. The comprehensive dataset reveals, for the first time, five peaks and six depressions in Phanerozoic Zoophycos occurrence frequency. Secondly, the palaeogeographical distribution of Zoophycos is closely associated with the supercontinent Pangaea shifting, independent of the latitude. Our data also attest that the bathymetrical shift of Zoophycos from the littoral–neritic to bathyal environments is synchronized with the tiering shift from shallow to deep. By detailed comparison with body fossils, geochemical and palaeogeographical records, we conclude that the macroevolution of Phanerozoic Zoophycos is multi-affected by the global biodiversity expansion, benthic nutrient enhancement, and the biotic macroevolution of the Zoophycos-producers. The macroevolution of development evidenced by the morphological changes of Zoophycos and other trace fossils, may have great implications on the behavioural and physiological adaptation of ancient animals to the environments.
Bioturbation plays a substantial role in sediment oxygen concentration, chemical cycling, regeneration of nutrients, microbial activity, and the rate of organic matter decomposition in modern oceans. In addition, bioturbators are ecosystem engineers which promote the presence of some organisms, while precluding others. However, the impact of bioturbation in deep time remains controversial and limited sediment mixing has been indicated for early Paleozoic seas. Our understanding of the actual impact of bioturbation early in the Phanerozoic has been hampered by the lack of detailed analysis of the functional significance of specific burrow architectures. Integration of ichnologic and sedimentologic evidence from North China shows that deep-tier Thalassinoides mazes occur in lower Cambrian nearshore carbonate sediments, leading to intense disruption of the primary fabric. Comparison with modern studies suggest that some of the effects of this style of Cambrian bioturbation may have included promotion of nitrogen and ammonium fluxes across the sediment-water interface, average deepening of the redox discontinuity surface, expansion of aerobic bacteria, and increase in the rate of organic matter decomposition and the regeneration of nutrients. Our study suggests that early Cambrian sediment mixing in carbonate settings may have been more significant than assumed in previous models.
A Lower Devonian (Emsian) tempestite in the western Yangtze plate, China, was studied based on ichnological and stratigraphical features. The results indicated that the local tempestite can be grouped into clastic constituent types, which include bottom erosion structures, graded beds, swaley cross‐stratification (SCS), parallel lamination, bioturbation and the new composition Zoophycos ichnofabrics. Five storm sequences and three Zoophycos ichnofabrics (Zoophycos–Chondrites ichnofabric, Zoophycos–Chondrites–Thalassinoides ichnofabric and Zoophycos–Thalassinoides–Palaeophycus ichnofabric) were discerned. It is demonstrated that the Zoophycos‐producers from the complex types of Zoophycos in storm sequences were opportunistic organisms (r‐strategists). This study reveals storm‐generated physical and biogenic structures and textures and provides a good ichnological method to identify storm deposits. Copyright © 2013 John Wiley & Sons, Ltd.
Trace fossils are known to be good indicators of sedimentary environments (Knaust and Bromley, 2012). The type, morphology, and diversity of trace fossils are now known to be a proxy to paleoenvironmental factors, including energy level, substrate stability, salinity variations, and oxygenation levels (Curran, 1985;Ekdale, 1988;Knaust and Bromley, 2012). The most significant advantage of trace fossils is that they are autochthonous indicators of paleoecological conditions (Bromley, 1996). In most cases, trace fossil data contribute to a better understanding of the sediments from the perspective of organism-substrate interactions (Uchman et al., 2004).The Lower Devonian sediments of the western Yangtze Plate are divided into the Pingyipu, Ganxi, Ertaizi, and Yangmaba formations, known for their well-exposed and complete stratigraphic record and long history of investigations (Hou et al., 1988). Several aspects of the sedimentology, paleontology, sequence stratigraphy, and isotope geochemistry of the mentioned formations in the Ganxi section (Figures 1a and 1b) were studied over the last fifty years (e.g., Xian et al., 1995;Zheng and Liu, 1997;Liao and Ma, 2007). Lower Devonian trace fossils of the region are poorly known. Lin et al. (1986) mentioned the presence of Diplocraterion and Thalassinoides in the Pingyipu Formation. Yang et al. (1988) listed some trace fossils from the studied units, including Arenicolites, Chondrites, Cruziana, Dimorphichnus, Helminthopsis, Phycodes, Planolites, Skolithos, Thalassinoides, and Zoophycos. Moreover, in recent years, a variety of wellpreserved trace fossils have been found and recorded in the Lower Devonian of the Ganxi section. The aim of the present paper is to provide a detailed ichnological and sedimentological analysis of the Ganxi section. Geological settingThe studied area is located in the northwestern part of the Upper Yangtze Plate and belongs to the Lower Paleozoic Longmenshan Basin (Figures 1c and 1d). The Devonian strata in this region were deposited on a continental margin Abstract: Abundant and diverse trace fossils occur in the littoral-neritic sediments recording an Early Devonian transgression in South China. The well-exposed Ganxi section is located in the Longmen Mountain 100 km northwest of Chendu, Sichuan. The Lower Devonian strata are dominated by sandstones, siltstones, muddy shales, limestones, bioclastic limestones, and muddy limestones. About thirteen ichnogenera were systematically described, including Arenicolites, ?Balanoglossites, Chondrites, Cylindrichnus, Diplocraterion, Planolites, Palaeophycus, Phycodes, Rhizocorallium, Rusophycus, Skolithos, Thalassinoides, and Zoophycos. Six trace fossil associations under different sedimentary environments have been recognized as follows: the Skolithos and Diplocraterion-Skolithos associations mainly consist of domichnia derived from a high-energy zone of the foreshore to upper shoreface; the Rusophycus-Phycodes association is characterized by fodinichnia and cubichnia generated in a lower-energy zone of...
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