Abstract The facies characteristics of the shallow marine environment are largely determined by the complex interplay and relative importance of wave energy, tidal flux, storm magnitudes and frequencies, and river-sediment input. Ichnology is a valuable tool in constraining these processes when integrated with sedimentological and stratigraphic analysis. Trace fossils are biogenic sedimentary structures, strongly facies controlled, and generally temporally long ranging, making them ideal for facies analysis. Ichnofossils are also readily observable at outcrop and core scales, making their identification and interpretation as routine as that of primary physical sedimentary structures. The ichnofacies paradigm is exceptionally well poised to offer critical information about the conditions operating during deposition (e.g., softground ichnofacies) or during development of stratigraphic discontinuities (e.g., substrate-controlled ichnofacies and palimpsest softground suites). The ichnofacies concept stands as one of the most elegant but also most widely misunderstood and misused concepts in ichnology. Softground ichnofacies have been refined to include proximal, archetypal, and distal expressions, permitting high-resolution subdivision of depositional environments such as strandline shoreface complexes. Models addressing brackish-water-induced stresses, substrate consistency changes, reduced oxygen levels, and energy variations on bioturbation have enhanced the identification and subdivision of estuarine incised-valley, embayment, and interdistributary-bay deposits. The ichnological characteristics of these brackish-water settings include: (1) suites characterized by reductions in the numbers and diversities of ichnogenera, corresponding to impoverished marine assemblages; (2) traces that are generally diminutive compared to their fully marine counterparts; (3) a predominance of simple opportunistic structures of inferred trophic generalists; (4) suites comprising elements that record variations in substrate consistency and depositional rates; and (5) successions showing locally high degrees of bioturbation, as well as monogeneric trace suites. Ongoing work concentrates on the effects of hypopycnal-induced water turbidity, hyperpycnal discharge, freshets, fluid-mud deposition, heightened depositional rates, and storm events on infaunal behavior, and helps to identify the deltaic ichnological signal, elucidating the relative importance of waves, tides, and fluvial discharge. Generally reduced and sporadically distributed bioturbation intensities, common unburrowed and mud-draped event beds, abrupt juxtaposition of fully marine suites with impoverished suites, predominance of facies-crossing deposit-feeding structures adapted to sandy substrates, and a paucity of dwelling structures attributable to suspension-feeding organisms constitute the recurring ichnological deltaic signal that has been elucidated to date.Ultimately, such models could be applied to along-strike variations in linked depositional systems, enhancing paleogeographicreconstructions.

Abstract The lithological characteristics of wave- and/or storm-dominated delta-front deposits are fundamentally similar to those of facies deposited on the wave-formed shorefaces of strandplain settings. Differentiating ancient shoreface deposits from those that record deposition in proximity to contemporaneous wave-dominated deltas, therefore, is challenging, especially where the facies represent deposits that are intermediate between end-member strandplains and delta fronts. To date, archetypal facies models are inadequate to describe and distinguish between such deposits. The challenge is further accentuated where studies are limited entirely to core and other subsurface data. Depositional processes typical of deltaic settings influence infaunal organisms in subtle but significant ways. The resulting ichnological signatures clearly reflect the innate differences in physicochemical conditions and paleoenvironmental stresses operating in these settings, such as variations in sedimentation rates, substrate consistencies, oxygenation, salinities, energy conditions, increased turbidity levels, and episodic deposition associated with river floods. Lower Permian successions of the Wasp Head, Pebbley Beach, and Snapper Point Formations of the southern Sydney Basin in southeastern Australia are spectacularly exposed in extensive coastal outcrops. The preserved lithologies and many of the primary sedimentary structures are virtually identical to those characteristic of offshore and strandplain shoreface deposits. Integration of the lithological, sedimentological, and subtle ichnological differences, however, demonstrate that these units were deposited under the influence of paleoenvironmental stresses. There is also considerable evidence of very cold climatic conditions and concomitant effects on the depositional environment from ice rafting, which imposed additional paleoenvironmental stresses. For the most part, fair-weather beds closely resemble strandplain shoreface deposits, with trace-fossil suites that are very diverse and contain a mixture of structures that reflect a variety of feeding strategies characteristic of the Cruziana and Skolithos Ichnofacies. Variations in the ichnological signatures, and departures from the archetypal ichnofacies expressions, in the form of sporadic bioturbation levels, reduced assemblage diversities, and reductions in ichnogenera sizes compared to their unstressed counterparts, suggest intermittent physicochemical stresses. Associated storm deposits display many of the sedimentological and ichnological characteristics associated with river influx and deltaic conditions, including: soft-sediment deformation structures and sediment-gravity-flow deposits, recording rapid sediment emplacement; mudstone drapes that are characteristic of hyperpycnally emplaced fluid muds and rapidly flocculated muds that are produced along the zone of mixing at the base of a hypopycnal (buoyant) mud plume; unbioturbated, carbonaceous mudstone interbeds with synaeresis cracks consistent with freshet-induced salinity fluctuations; an abundance of phytodetrital material, and allochthonous wood and large logs; and sandstone beds with “stressed” trace-fossil suites attributable to the Cruziana Ichnofacies, where ordinarily suites representative of the Skolithos Ichnofacies would be expected. These characteristics suggest that fair-weather beds reflect ambient wave shoaling, but during and immediately following storms, increased river discharge strongly influenced the depositional environment and thus the characteristics of the resultant event beds. Overall, the successions are therefore interpreted as wave- and storm-dominated prodelta to proximal delta-front deposits. Variations in storm signature throughout the successions reflect temporal and spatial variations in the preservation and, therefore, abundance of fair-weather beds. Such variations may represent changing storm climates, climatic seasonality, fluctuations in river discharge, increased amalgamation of beds by persistent storm activity, subtle changes in storm tracks with respect to delta-front orientation, and subtle shallowing or deepening along the delta front.