The trace fossil Rhizocorallium commune is abundant in shallow-marine deposits of the Upper Devon... more The trace fossil Rhizocorallium commune is abundant in shallow-marine deposits of the Upper Devonian (Frasnian) Tuqiaozi Formation in Ganxi, Sichuan Province, South China. It consists of U-shaped spreite burrows developed more or less parallel or slightly inclined to the bedding of marly limestone. Four types of iron framboids (mostly oxygenated from pyrite framboids) were found within the Rhizocorallium burrow, including (1) smooth, sheathed spherical, (2) prismatic, (3) octahedral, and (4) pyritohedral submicron crystals. Chemically , the submicron crystals mainly consist of iron, sulphur, oxygen and carbon. The iron framboids represent the stage of evolution of their original pyrite framboids from irregular morphologies and spherical framboids to octahedral and pyritohedral habits due to the activity of sulphate-reducing bacteria. No similar framboids were observed outside Rhizocorallium. Therefore, it is likely that sulphate-reducing bacteria colonised the Rhizocorallium spreite and marginal tube within a dysoxic environment. With increasing degree of oxygenation of pore water, the pyrite framboids were partly oxygenated into iron framboids and by exceptional circumstances preserved the original morphology of the crystals. Furthermore, it is proposed that the investigated Rhizocorallium was constructed by its trace maker for gardening with multifunctional purpose, where different microbial colonies were planted and cultured in the marginal tube and spreite on the mutual basis of food supply and redox conditions. These features indicate that a combined deposit-feeding and gardening model may apply for the construction of Rhizocorallium commune from the Devonian of Ganxi. The responsible trace maker probably was a worm-like organism, such as a polychaete.
New ichnological data from the Lower Triassic (Induan) Dongchuan Formation (Longmendong, South Ch... more New ichnological data from the Lower Triassic (Induan) Dongchuan Formation (Longmendong, South China) record the recovery interval of marginal-marine communities following the end-Permian mass extinction. Here, we document six ichnogenera from the upper part of the Dongchuan Formation of Dienerian (Early Triassic) age in the Longmendong area, Sichuan Province, South China. These are Cylindrichnus, Diplocraterion, Palaeophycus, Planolites, Siphonichnus, and Teichichnus, illustrating a depauperate Cruziana Ichnofacies. Facies analysis suggests that the depauperate Cruziana Ichnofacies is present in deposits recording the transition from fluvial to tide-dominated estuarine settings. Compilation of worldwide brackish-water ichnofaunas from Perm-ian (average alpha ichnodiversity = 6.2) to Triassic (average alpha ichnodiversity = 5.5) suggests that no significant ichnodiversity decrease took place in these settings as a result of the mass extinction and further implies that the impact of the mass extinction may have been less severe in marginal-marine settings. Ichnofaunas in pre-and post-extinction marginal-marine environments are remarkably similar and tend to be dominated by fa-cies-crossing ichnotaxa (e.g., Diplocraterion, Palaeophycus, Planolites) produced by opportunistic faunas.
The middle Cambrian Mantou Formation of the Mianchi section of western Henan Province, North Chin... more The middle Cambrian Mantou Formation of the Mianchi section of western Henan Province, North China provides an opportunity to address infaunal colonization during the aftermath of the Cambrian explosion. The trace fossil Diplocraterion is common within intertidal very fine-grained sandstone of the Member II of the Mantou Formation (Stage 5). Diplocraterion consists of perpendicular to bedding plane, lined U-shaped burrows with well-developed marginal tubes, having distinctive, dark and light colored, laminae forming retrusive and protrusive spreiten reflecting the activity of a suspension feeder. No scratches are observed on the wall of the marginal tubes. SEM-EDS mapping detection shows that the dark laminae are dominated by Si, Al and Fe, whereas the light laminae are dominated by Ca and Si. Based on ichnological, stratigraphical and SEM-EDS features, it is suggested that the specimens of Diplocraterion studied here results from the equilibrium behavior and that the delayed appearance of this ichnotaxon in North China is due to lack of appropriate siliciclastic facies. RIASSUNTO-[Diplocraterion parallelum dal Cambriano medio della Cina Settentrionale: significato etologico e controllo di facies]-La Formazione di Mantou (Cambriano), affiorante nella sezione di Mianchi (Provincia occidentale di Henan, Cina Settentrionale), permette di discutere la colonizzazione infaunale durante l'esplosione del Cambriano. La traccia fossile Diplocraterion è comune nelle arenarie fini del Membro II della Formazione di Mantou (Stage 5). Diplocraterion consiste di tane ad U perpendicolari alla stratificazione; gli esemplari sono caratterizzati da rivestimento ed esibiscono tubi marginali ben sviluppati. Sono presenti lamine scure e chiare che formano spreiten retrusivi e protrusivi, riflettenti l'attività di un organismo sospensivoro. Non si osservano bioglifi sulle pareti dei tubi marginali. La mappatura SEM-EDS rivela che le lamine scure sono dominate da Si, Al e Fe, mentre le lamine chiare sono contraddistinte da Ca e Si. Sulla base delle caratteristiche icnologiche, stratigrafiche e dell'analisi SEM-EDS, si suggerisce che gli esemplari di Diplocraterion qui studiati riflettano un comportamento di equilibrio. La mancanza di appropriate facies siliciclastiche spiega la comparsa ritardata di questo icnotaxon nella Cina Settentrionale.
Bioturbation plays a substantial role in sediment oxygen concentration, chemical cycling, regener... more 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. Bioturbation, involving both particle and solute transport within burrows, into the surrounding sediment and across the sediment-water interface, is one of the most important factors in affecting oxygen concentration in the sediment, chemical cycling, regeneration of nutrients, microbial activity and the rate of organic matter decomposition in modern oceans 1–3. In addition, burrowing animals represent ecosystem engineers that impact on community structure by either having negative (e.g., influence of infaunal deposit feeders on sessile epifaunal and infaunal suspension feeders) or positive (e.g., influence of infaunal deposit feeders on meiofauna and microbes) effects on other organisms 4,5. There is considerable debate regarding the timing of infaunalization and the role that bioturbation may have played in nutrient cycling and sediment mixing during the Cambrian Explosion. Unfortunately, precise evaluation 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 preserved in the fossil record. Whereas most research have focused on measuring degree of bioturbation and estimating maximum burrowing depths, the actual role of specific type of burrows in sediment mixing and impact on other organisms has received much less attention. As a result, no attempts have been made in order to establish a link between the functional significance of discrete burrow architectures and their potential impact on sediment properties and the accompanying benthic faunas. Integration of ichnologic and sedimentologic evidence from North China shows that intense bioturbation, mainly revealed by the ichnogenus Thalassinoides, took place in nearshore carbonate sediments during the early Cambrian, providing evidence of significant infaunalization and sediment mixing. Comparison of these burrow architectures with modern counterparts allows evaluating the role of these deep-tier bioturbators in sediment
The trace fossil Rhizocorallium commune is abundant in shallow-marine deposits of the Upper Devon... more The trace fossil Rhizocorallium commune is abundant in shallow-marine deposits of the Upper Devonian (Frasnian) Tuqiaozi Formation in Ganxi, Sichuan Province, South China. It consists of U-shaped spreite burrows developed more or less parallel or slightly inclined to the bedding of marly limestone. Four types of iron framboids (mostly oxygenated from pyrite framboids) were found within the Rhizocorallium burrow, including (1) smooth, sheathed spherical, (2) prismatic, (3) octahedral, and (4) pyritohedral submicron crystals. Chemically , the submicron crystals mainly consist of iron, sulphur, oxygen and carbon. The iron framboids represent the stage of evolution of their original pyrite framboids from irregular morphologies and spherical framboids to octahedral and pyritohedral habits due to the activity of sulphate-reducing bacteria. No similar framboids were observed outside Rhizocorallium. Therefore, it is likely that sulphate-reducing bacteria colonised the Rhizocorallium spreite and marginal tube within a dysoxic environment. With increasing degree of oxygenation of pore water, the pyrite framboids were partly oxygenated into iron framboids and by exceptional circumstances preserved the original morphology of the crystals. Furthermore, it is proposed that the investigated Rhizocorallium was constructed by its trace maker for gardening with multifunctional purpose, where different microbial colonies were planted and cultured in the marginal tube and spreite on the mutual basis of food supply and redox conditions. These features indicate that a combined deposit-feeding and gardening model may apply for the construction of Rhizocorallium commune from the Devonian of Ganxi. The responsible trace maker probably was a worm-like organism, such as a polychaete.
New ichnological data from the Lower Triassic (Induan) Dongchuan Formation (Longmendong, South Ch... more New ichnological data from the Lower Triassic (Induan) Dongchuan Formation (Longmendong, South China) record the recovery interval of marginal-marine communities following the end-Permian mass extinction. Here, we document six ichnogenera from the upper part of the Dongchuan Formation of Dienerian (Early Triassic) age in the Longmendong area, Sichuan Province, South China. These are Cylindrichnus, Diplocraterion, Palaeophycus, Planolites, Siphonichnus, and Teichichnus, illustrating a depauperate Cruziana Ichnofacies. Facies analysis suggests that the depauperate Cruziana Ichnofacies is present in deposits recording the transition from fluvial to tide-dominated estuarine settings. Compilation of worldwide brackish-water ichnofaunas from Perm-ian (average alpha ichnodiversity = 6.2) to Triassic (average alpha ichnodiversity = 5.5) suggests that no significant ichnodiversity decrease took place in these settings as a result of the mass extinction and further implies that the impact of the mass extinction may have been less severe in marginal-marine settings. Ichnofaunas in pre-and post-extinction marginal-marine environments are remarkably similar and tend to be dominated by fa-cies-crossing ichnotaxa (e.g., Diplocraterion, Palaeophycus, Planolites) produced by opportunistic faunas.
The middle Cambrian Mantou Formation of the Mianchi section of western Henan Province, North Chin... more The middle Cambrian Mantou Formation of the Mianchi section of western Henan Province, North China provides an opportunity to address infaunal colonization during the aftermath of the Cambrian explosion. The trace fossil Diplocraterion is common within intertidal very fine-grained sandstone of the Member II of the Mantou Formation (Stage 5). Diplocraterion consists of perpendicular to bedding plane, lined U-shaped burrows with well-developed marginal tubes, having distinctive, dark and light colored, laminae forming retrusive and protrusive spreiten reflecting the activity of a suspension feeder. No scratches are observed on the wall of the marginal tubes. SEM-EDS mapping detection shows that the dark laminae are dominated by Si, Al and Fe, whereas the light laminae are dominated by Ca and Si. Based on ichnological, stratigraphical and SEM-EDS features, it is suggested that the specimens of Diplocraterion studied here results from the equilibrium behavior and that the delayed appearance of this ichnotaxon in North China is due to lack of appropriate siliciclastic facies. RIASSUNTO-[Diplocraterion parallelum dal Cambriano medio della Cina Settentrionale: significato etologico e controllo di facies]-La Formazione di Mantou (Cambriano), affiorante nella sezione di Mianchi (Provincia occidentale di Henan, Cina Settentrionale), permette di discutere la colonizzazione infaunale durante l'esplosione del Cambriano. La traccia fossile Diplocraterion è comune nelle arenarie fini del Membro II della Formazione di Mantou (Stage 5). Diplocraterion consiste di tane ad U perpendicolari alla stratificazione; gli esemplari sono caratterizzati da rivestimento ed esibiscono tubi marginali ben sviluppati. Sono presenti lamine scure e chiare che formano spreiten retrusivi e protrusivi, riflettenti l'attività di un organismo sospensivoro. Non si osservano bioglifi sulle pareti dei tubi marginali. La mappatura SEM-EDS rivela che le lamine scure sono dominate da Si, Al e Fe, mentre le lamine chiare sono contraddistinte da Ca e Si. Sulla base delle caratteristiche icnologiche, stratigrafiche e dell'analisi SEM-EDS, si suggerisce che gli esemplari di Diplocraterion qui studiati riflettano un comportamento di equilibrio. La mancanza di appropriate facies siliciclastiche spiega la comparsa ritardata di questo icnotaxon nella Cina Settentrionale.
Bioturbation plays a substantial role in sediment oxygen concentration, chemical cycling, regener... more 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. Bioturbation, involving both particle and solute transport within burrows, into the surrounding sediment and across the sediment-water interface, is one of the most important factors in affecting oxygen concentration in the sediment, chemical cycling, regeneration of nutrients, microbial activity and the rate of organic matter decomposition in modern oceans 1–3. In addition, burrowing animals represent ecosystem engineers that impact on community structure by either having negative (e.g., influence of infaunal deposit feeders on sessile epifaunal and infaunal suspension feeders) or positive (e.g., influence of infaunal deposit feeders on meiofauna and microbes) effects on other organisms 4,5. There is considerable debate regarding the timing of infaunalization and the role that bioturbation may have played in nutrient cycling and sediment mixing during the Cambrian Explosion. Unfortunately, precise evaluation 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 preserved in the fossil record. Whereas most research have focused on measuring degree of bioturbation and estimating maximum burrowing depths, the actual role of specific type of burrows in sediment mixing and impact on other organisms has received much less attention. As a result, no attempts have been made in order to establish a link between the functional significance of discrete burrow architectures and their potential impact on sediment properties and the accompanying benthic faunas. Integration of ichnologic and sedimentologic evidence from North China shows that intense bioturbation, mainly revealed by the ichnogenus Thalassinoides, took place in nearshore carbonate sediments during the early Cambrian, providing evidence of significant infaunalization and sediment mixing. Comparison of these burrow architectures with modern counterparts allows evaluating the role of these deep-tier bioturbators in sediment
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