Taenidium barretti ichnofabric and rainfall seasonality:Insights into dryland suites of Scoyenia ichnofacies

The present work analyzes the monotypic Taenidium barretti ichnofabric developed in abandoned channels and floodplains to understand its paleoecological significance in highly seasonal fluvial systems.The data come from the Cretaceous paleosols of the Marília Formation(Bauru Basin,SE Brazil),in which the T.barretti ichnofabric and rhizoliths represent the biotic record.Beetle larvae are considered to be the most likely T.barretti tracemakers in these paleosols.The intensity and recurrence of bioturbation suggest that the windows of opportunity for beetle population growth were very short and controlled by the progressive substrate desiccation after flood cessation.The characteristics of the trace fossil assemblage suggest soil colonization by r-strategic organisms triggered by flooding events that provided the resource inputs necessary for their living during rainy seasons.The results also show that in fluvial systems with high discharge variations,the boundaries between a“pre-desiccation suite”and a“desiccation suite”in the Scoyenia ichnofacies can be diffuse due to the short duration of colonization windows and progressive terrestrialization of floodplains and channels.Therefore,the frequency of flooding events,the lowered water table,and the rapidity of substrate desiccation constrained colonization by other burrowers and may be considered as firstorder factors controlling the generation of a monotypic T.barretti ichnofabric.Thus,the monotypic Taenidium ichnofabric in the Scoyenia ichnofacies context is an ichnomarker of brief windows for colonization in highly seasonal environments.

The ichnofacies and ichnoassemblages in terrestrial deposits of China

Over the last 30 years,terrestrial ichnofossil research was mostly focused on three ichnofacies:the Scoyenia ichnofacies,characterizing transitional fluvio-lacustrine environments,the Mermia ichnofacies,characterizing fully lacustrine settings,and the Termitichnus ichnofacies,characterizing terrestrial environments,especially,paleosol deposits.Specially in China,many terrestrial ichnofossils,including at least 24 ichnogenera from fluvial deposits and 59 ichnogenera from lacustrine deposits,have been found in Mesozoic and Cenozoic basins.Most of them belong to the common elements of the three ichnofacies and consist of feeding,grazing,crawling,dwelling,and resting traces and rhizoliths.Based on the composition,occurrence and distribution characteristics of trace fossils from terrestrial sedimentary basins of China,36 ichnoassemblages have been proposed.However,the most common 12 ichnoassemblages,in which six are found in fluvial sedimentary environments from the Upper Cretaceous of the Sichuan Basin in western China and Xixia Basin in western Henan Province,include:(1)Scoyenia-Rusophycus ichnoassemblage generated in the floodplain along channels and the shallow water swales or lakes(such as oxbow lakes);(2)Skolithos-Arenicolites ichnoassemblage produced in the high energy sandy bar(heart bar or point bar)of the channel environment;(3)Gastruichnus-Palaeophycus ichnoassemblage developed in the channel-levee environment;(4)Beaconites-Taenidium ichnoassemblage occurring in the embankment(crevasse splay)sedimentary environment;(5)Beaconites-Rhizolithos ichnoassemblage appearing in the floodplain sedimentary environment,and(6)Beaconites-Scoyenia ichnoassemblage distributed in the periodically exposed overbank lake(extremely shallow lacustrine)sedimentary environments.The other six ichnoassemblages are found in lacustrine sedimentary environments:(1)Scoyenia-Skolithos ichnoassemblage always developed in periodically exposed,extremely shallow lakeshore and interdistributary bay of the lake delta plain under drought or semiarid climate conditions;(2)Palaeophycus-Arenicolites ichnoassemblage formed in the lakeshore to the upper part of the shallow lake,corresponding to the lake delta plain to delta front;(3)Planolites-Teichichnus ichnoassemblage generated in the lower part of the shallow lake,restricted lake bay or distal front delta;(4)Vagorichnus-Helminthopsis ichnoassemblage developed in the deeper lacustrine(profundal)turbidite sedimentary environment;(5)Mermoides-Neonereites ichnoassemblage occurring in the quiet deep or deeper lacustrine sedimentary environment;and(6)Semirotundichnus-Chondrites ichnoassemblage formed in even deeper lacustrine sedimentary environments with lower oxygen content.

Ichnology and Depositional Environment of the Cambrian Nagaur Sandstone (Nagaur Group) Along the Dulmera Section, Bikaner-Nagaur Basin, Rajasthan

The Lower Cambrian Nagaur Sandstone（Marwar Supergroup） has yielded trace fossils Treptichnus, Cruziana, serially repeated Rusophycus, Diplichnites, Monomorphichnus, Bergaueria,arthropod swimming traces and leap frogging marks of Cruziana ichnofacies. This ichnofossils assemblage is dominantly preserved in fine to medium grained red sandstone beds of the Mohra Member（Nagaur Sandstone）. The presence of graded rip-up clasts, current ripples, dune crossstratification with mud drapes and tidal bundles indicates a subtidal paleoenvironment for the deposition of Nagaur Sandstone Formation, which is corroborated by the Cruziana ichnofacies trace fossil assemblage.

Cambrian Stratigraphy and Faunal Elements Along the Kurgiakh-Surichun La Section(Kurgiakh Valley),Zanskar-Spiti Basin of Northwest Himalaya

The Cambrian rocks are well exposed along the Kurgiakh-Surichun La section,situated 78 km SE of the Padam Village along a track route at 33°03′787″N and 77°013′647″E in between the Kurgiakh and Surichun La,in Kurgiakh Valley(southeastern Zanskar).Around 715 m thick Cambrian succession was measured along the right and left banks of

Depositional Controls on the Ichnology of Ordovician Wave-dominated Marine Facies：New Evidence from the Shirgesht Formation,Central Iran

The Lower Ordovician Shirgesht Formation in central Iran is composed of siliciclastic and carbonate rocks deposited in diverse coastal and marine shelfal environments（tidal flat,lagoon,shoreface,offshore-shelf and carbonate ramp）.Five facies associations contain diverse ichnofossil assemblages that show distinct proximal to distal trends formed in a wide range of physical-chemical conditions.The ethological groups of trace fossils in the Shirgesht Formation reflect a gradient of depositional stress conditions across a wave-influenced shoreline and shelf.Deposits of waveinfluenced environments make up a significant component of the geological record of shallow marine settings,and the ability to determine paleoenvironments in detail in such successions is critical for reconstruction of depositional histories and sequence-stratigraphic interpretation.The Cruziana ichnofacies of the study shows highly diverse suites that record the establishment of a benthic community under stable conditions and a long-term colonization window.The Skolithos ichnofacies recognized is a low diversity opportunistic ichnocommunity suite that resulted from colonization after tempestite deposition in a stressed environment.The strata record an onshore to offshore replacement of the Cruziana ichnofacies（with abundant feeding traces of deposit-feeders） by the Skolithos ichnofacies（dominated by suspension-feeders and predators）.A transitional zone between the two ichnofacies coincides with the offshore-transition/distal lower-surface deposits.The distribution of ichnofacies,the diversity and range of ethological characteristics reflected by the ichnogenera,and the wide range of wave-dominated coastal facies demonstrate the potential to use individual trace fossils and ichnofacies for significantly refined palaeoenvironmental analysis of wavedominated coastal settings,particularly in Ordovician successions.

Continental Trace Fossils in the Semnan Area (Northern Iran)

Continental ichnology has been taking an ever increasing importance in stratigraphy. In this paper, Continental Trace Fossils in Semnan area have been studied. Semnan Province is one of the 31 provinces which is located in the north of Iran. In the East of Semnan City, Quaternary deposits occupy about 93% of the surface area, of which the Alluvial represents one of the most important geomorphological features in the area. Nevertheless, the outspread ichnological studies in Semnan City have received lesser attention in Continental Trace Fossils. Based on the systematic ichnology, 6 trace fossils are distinguished, namely Celliforma isp, Coprinisphaera isp, Palaeophycus tubularis, planolithes isp, Tombownichnus plenus, and Skolithos isp. The existence of Rhizoliths along with the tetrapod footprints and the survey of lithofacies all indicate that the trace fossils are related to Coprinisphaera ichnofacies. Based on ichnological and sedimentary facies analysis, the Continental Trace Fossils, in the study area, are located in the flood plain, point bar, and playa environment.

Significance of ichnofossils to genetic stratigraphy——Examples from the Cretaceous of Alberta, Canada

Trace fossils represent both sedimentological and paleontological entities, representing a unique blending of potential environmental indicators in the rock record. Trace fossils and trace fossil suites can be employed effectively to aid in the recognition of various discontinuity types and to assist in their genetic interpretation. Ichnology may be employed to resolve surfaces of strati-graphic significance in two main ways: 1) through the identification of discontinuities using substrate-controlled ichnofacies, and 2) through careful analysis of vertical softground (penecontem-poraneous) ichnologic successions (analogous to facies successions). Ichnological analysis is a valuable tool in genetic stratigraphic studies. Integrating the data derived from substrate-controlled ichnofacies with paleoecological data from vertical ichnologic successions greatly enhances the recognition and interpretation of a wide variety of stratigraphic surfaces. When this is coupled with conventional facies analysis and

Devonian ichnofossils and their environmental significance of northern belt of Western Qinling Mountains

It is beheved that the Shujiaba Formation belongs to a series of thick turbidites. 20 ichnogenera have been found in the formation, of which 14 genera were found in the Devonian System of China for the first time The ichnogenera are mostly of typical deep-water ones and belong to the Nereites ichnofacies A detailed study of morphology and behaviour of the trace fossils indicates that the Shujiaba Formation was deposited in a bathyal-abyssal environment.