Ichnofabrics and Their Environmental Interpretation from the Fluvial Deposits of the Middle Triassic Youfangzhuang Formation in Western Henan, Central China

Fluvial deposits from the Middle Triassic Youfangzhuang Formation in Henan Province, China contain a low-diversity trace fossils. Vertical dwelling burrows of opportunists dominate in active channel, whereas horizontal deposit-feeding, grazing, and vertical dwelling burrows occur in overbank deposits. Seven recurrent ichnofabrics were distingushed. The Palaeophycus tubularis ichnofabric pre- serves below scour interface between two fluvial cycles. The Skolithos linearis ichnofabric forms in middle to high-energy, soft substrates in the middle and upper parts of active channel deposits under semi-arid climate. The Skolithos linearis-Planolites montanus ichnofabric occurs in the sediments just a little above the Skolithos linearis ichnofabric and is formed in middle-energy, soft substrates in the up- per part of active channel deposits. The Planolites montanus ichnofabric is mostly preserved in associa- tion with medium- to thick-bedded brown-red silty mudstones or siltstones in low-energy, perennial muddy bottom ponds in overbank settings. The Taenidium barretti ichnofabric is interpreted as peri- odically exposed ephemeral ponds or low-energy distal floodplain. The Skolithos isp. ichnofabric com- monly occurs in middle to high-energy firm ground of proximal foodplain or crevasse-splay deposits. The root trace iehnofabric occurs in the crevasse splay deposits. The presence of thin palaeosols and the abundance of calcretization in mudstones indicate a seasonal climate ranging from humid to semi-arid, with high temperature, rainfall, and well-defined dry and wet seasons.

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.

Ichnofabric analysis of bathyal chalks:the Miocene Inglis Formation of the Andaman and Nicobar Islands,India

In the Bay of Bengal,the Andaman and Nicobar Islands represent part of the Burma-Sunda-Java subduction complex.The Islands are composed of sediments ranging in age from Jurassic to Recent,represented by ophiolites,flysch sediments,along with deep marine sediments scraped off from the subducting plate.The stratigraphic succession that overlies meta-sedimentary and ophiolite suites consists of turbidite and non-turbidite sequences,along with thick-bedded nannofossil chalks.The present study describes ichnofabrics of chalks from the Inglis Formation(Early to Middle Miocene).These chalks are highly to moderately bioturbated and comprise several levels of ferruginised layers as weak discontinuity surfaces.The studied section shows the recurring occurrence of ichnotaxa belonging to Asterosoma,Chondrites,Cladichnus,Ophiomorpha,Palaeophycus,Planolites,Taenidium,Thalassinoides,and Zoophycus.Sediments are represented by Bioturbation indices varying between BI-2 to BI-5,represented by(a)light coloured trace fossils in dark sediment(LID ichnofabric)and(b)dark coloured trace fossils in light sediment(DIL ichnofabric).Ichnofabric analysis suggests multiple colonization,complex tiering,and multilayer tiering.The LID ichnofabric exposed at Kalapathar reveals three tiers,a diverse shallow tier and a moderately low diverse middle and deep tiers.At the Lacam Point Section,in contrast,the LID ichnofabric is represented by condensation of the tiers and the absence of shallow tiers.The DIL ichnofabric at the Kalapathar Section seems to be more expanded and is represented by four tiers with extensive bioturbation.Ichnofabric analysis supports deposition of the chalk sediments in a lower bathyal paleoenvironment and suggests that organic matter,pore water,and bottom-water oxygenation were the main controlling factors.Thus,the ichnofabric analysis of the EarlyMiddle Miocene Inglis Formation gives first-hand information regarding the poorly known chalk facies of the Andaman and Nicobar Islands pre-Bengal fan stage of the Indian plate.

Recent progress and focuses of ichnology:Outline of the 14^(th) International Ichnofabric Workshop

The 14^（th） International Ichnofabric Workshop was held successfully in Taipei, China from April 29 thto May 2^（nd）. From the oral presentations, posters, intra-and post-workshop field trips, and workshop discussions, a few promising aspects of ichnological study can be outlined：（1） Ichnotaxonomy is, and will be the major endeavour of ichnologists, supplying important behavioural information for palaeontological studies, and also providing reasonable, objective, and convenient taxonomical framework for further sedimentological and palaeoecological studies;（2） Ichnofabric analysis is widely applied to in-depth sedimentological, palaeoclimatical, and petroleum exploration studies, offering a wealth of biological information that cannot be properly obtained from traditional sedimentological and geochemical analyses;（3） Study of trace fossils in the context of evolutionary palaeoecology sheds light on some intriguing issues of the biological responses during certain critical periods in Earth＇s history;（4）Work on combining geomicrobiology and ichnology is under way;（5） Quantitative morphological characterization has become increasingly useful in grasping the finer ingredients of functional morphology.