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Changes in diversity of trace fossils through time provide information about evolutionary innovations in animal‐substrate interactions. Global ichnodiversity changes at ichnogeneric rank are useful to capture major trends, but may be insufficient to reveal minor behavioural innovations. A quantitative analysis of ichnodiversity trajectories at ichnospecies rank for bioturbation structures has been performed for the first time at a global scale to evaluate how innovations in animal‐substrate interactions may be reflected at this ichnotaxonomic hierarchy. The timing of diversification at ichnospecific rank is highly variable, but mostly linked to the Cambrian Explosion (CE) and the Mesozoic Marine Revolution (MMR). Nearly all top‐heavy ichnogenera diversified during the MMR and most bottom‐heavy ichnogenera illustrate innovations during the CE. Timing of diversification at ichnospecies rank refines characterization of the ichnological equivalents of the Cambrian, Palaeozoic and Modern evolutionary fauna. Evaluating the timing of ichnospecific diversification within ichnogenera is a valuable tool in evolutionary palaeoecology. [ABSTRACT FROM AUTHOR]

Bioturbation plays an important role in enhancing the reservoir capacity of tight reservoirs. This study aims to understand the alteration mechanism and effects of bioturbation on oil and gas reservoirs, to clarify the key control factors and constraints influencing the production of bioturbation. The petrophysical characteristics of bioturbation and host sediments in carbonate rocks, such as mineral composition, pore spaces, porosity and permeability, were studied based on the detailed observation and description of the Ordovician cores from the Tahe oilfield. The effect of bioturbation on petrophysical properties of carbonate rocks were carefully analyzed. The results show: (1) Two types of bioturbation, Thalassinoides -like burrows and Planolites -like burrows, mainly occur in the Ordovician cores of the Tahe oilfield, ranging from the Lower–Middle Ordovician Yingshan Formation to the Middle Ordovician Yijianfang Formation. The burrow-fills are mainly composed of dolomite with subhedral and euhedral crystals. The host sediments mainly consist of micrite. (2) The pores in the host sediments are poorly developed and are incapable of forming effective reservoir spaces. However, well-developed intercrystalline pores among dolomites and microfractures in bioturbated sediments with better connectivity can form effective pore spaces. The results of porosity and permeability show that the host sediments without bioturbation are characterized by poor porosity and permeability. However, with the increase of bioturbation intensity, the porosity of the bioturbated sediments firstly increases and then decreases, whereas the permeability increases all the time. (3) Multiple burrows overprinted in the Ordovician carbonate rocks, forming a large-scale bioturbated carbonate rocks with lateral continuity and vertical connectivity, due to the suitable sedimentary setting, ecological conditions, favorable spatiotemporal sediment matching, and abundant organism–substrate interaction. Subsequently, diagenesis (particularly dolomitization and dissolution) has played a positive role in altering the rock fabric and improving the petrophysical properties of bioturbated carbonates. [ABSTRACT FROM AUTHOR]

Trace fossils are important evidence of benthic activity and proxies of bottom and interstitial water oxygen content, making them a promising tool to understand the oceanic redox evolution and extinction patterns during the end-Permian mass extinction (EPME). Detailed bed-by-bed ichnologic studies were performed at a high-resolution scale from two uppermost Permian sections (Shangsi and Dongpan) in South China, documenting the presence of Chondrites targionii , Chondrites isp., Nereites isp., Planolites isp. A, Planolites isp. B, Palaeophycus isp., Phycosiphon incertum , Thalassinoides isp., and Zoophycos isp. The uppermost Permian strata at the Shangsi section mainly comprise siliceous limestone interbedded with illite-montmorillonite claystone and shale, recording a deep shelf setting. The uppermost Permian strata at the Dongpan section consist of mixed chert, mudstone and claystone, formed in a slope environment. Bioturbation index in uppermost Permian strata is mostly 1–2, but with thin intervals reaching 3–4. Fluctuating bioturbation intensities, ichnofaunal composition ( Thalassinoides , Planolites , Zoophycos ) and ethologies, as well as the ratio of highly reactive iron to total iron (Fe Hr/ Fe T ) and the proportion of the highly reactive iron pool in the form of pyrite (Fe py /Fe HR ) suggest that bottom and interstitial oxygen levels were not permanently anoxic/euxinic, but were interrupted by brief periods of aerobic conditions during the latest Permian. Three bioturbation phases in the EPME are identified. Phase I is characterized by the absence of typical pascichnia ichnotaxa (e.g. Nereites isp.) and relatively large fodinichnia burrow (e.g., Planolites isp. B; Zoophycos isp.). Phase II mainly consists of smaller Planolites isp. A, Thalassinoides isp. and Chondrites isp., recording a transition from softground to firmground. Only occasional smaller Planolites isp. A occur in Phase III without any associated vertical burrows. Ichnodiversity and bioturbation index from Phase I to Phase III show a step by step decline, corresponding to the two-stage extinction patterns. Long-term environmental stress (e.g., oceanic anoxia, volcanic winter, global warming, ocean acidification, hypercapnia) may have played major role in the collapse of the infaunal ecospace and only facies-crossing, highly tolerant, opportunistic organisms may have persisted in otherwise vacant ecological niches in the aftermath of the extinction. [ABSTRACT FROM AUTHOR]

Large numbers of densely distributed Rhizocorallium provide a window to understanding the behavioural and functional changes of the trace maker after extreme environmental events. This study focuses on the analysis of Rhizocorallium from the Middle Triassic (Anisian) limestones in the Boyun section, Yunnan Province, Southwest China to investigate the ecological strategies and ethological signatures of its producers before and after storm events. Based on its morphological features, the studied Rhizocorallium is attributed to two ichnospecies Rhizocorallium jenense and R. commune , the latter showing two varieties R. commune var. auriforme and R. commune var. irregulare. In addition to Rhizocorallium , the trace fossil assemblage consists of Arenicolites , Palaeophycus , Planolites and Thalassinoides , which allows assignation to the Cruziana ichnofacies associated with the shallow marine environment. The studied ichnofossil-bearing intervals in the Boyun section are usually high bioturbated, with BPBI (bedding plane bioturbation index) around 5. The ichnoassemblage has a relatively low ichnodiversity and shows high density of Rhizocorallium , which is interpreted as the result of the opportunist strategy when the Rhizocorallium trace makers exploited the quiet, nutrient-rich substrates after storm events. Crosscutting relationships between multiple levels of Rhizocorallium indicate that earlier burrows were reworked by later ones due to successive storm events and erosion of the shallow-tier burrows. Orientation of the marginal tubes of Rhizocorallium jenense shows a bidirectional pattern at 295°NW and 160°SE, which may record the changes of the main flow direction. Diameter measurements support the total recovery of the macrobenthic trace makers during the Middle Triassic (Anisian). • Abundant Rhizocorallium in Anisian carbonates was studied quantitatively. • Distribution and density of Rhizocorallium suggests a r-selected strategy. • This Rhizocorallium record is associated to storm events. • The behavioural pattern of Rhizocorallium trace makers is reconstructed. • The total recovery of the ecosystem occurred during the Middle Triassic. [ABSTRACT FROM AUTHOR]

The carbonate rocks of the Ordovician Majiagou Formation from the northwestern part of Henan Province and their diverse trace fossils provide an outcrop analogue for bioturbated, low porosity and low permeability carbonate reservoirs. Three ichnofabrics can be defined based on the ichnotaxonomy, ichnodiversities, individual abundances and overall bioturbation indices. The Balanoglossites ichnofabric represented medium to relatively high-energy sedimentary environments such as intertidal zone and subtidal shoals in the carbonate platform. The Planolites ichnofabric suggested relatively low-energy, protected sedimentary environments such as lagoons in a restricted carbonate platform, but also occurs in the deeper-water depressions in the open carbonate platform. The Chondrites ichnofabric characterized low-energy and reduced oxygen conditions, with burrows penetrating below a shallow redox interface in deeper-water settings that include the distal slope as well as local depressions in the open carbonate platform. Our analysis suggests that the modifications of petrophysical parameters are controlled or influenced by the ichnofabric characteristics (burrow architecture, burrow cross-cutting relationship, degree of bioturbation and burrow connectivity), the permeability contrast between burrow-fills and matrix, and the dolomitization of burrow-fills. The micritic host sediments have negligible porosity and permeability. The bioturbated sediments have significant differences in fabric, texture, porosity and permeability. The burrow-fills are very commonly dolomitised. Each of the burrow-types can enhance reservoir properties, but the greatest differences are associated with the Balanoglossites ichnofabric, in which porosity and permeability can reach over 2% and 70 mD. Preliminary stratigraphic studies indicate that reservoir potential in the subsurface will be linked to an understanding of the distribution of shoal and intertidal facies as well as their associated Balanoglossites ichnofabrics. [ABSTRACT FROM AUTHOR]