Relationships between ichnology and uniformitarianism are perhaps less complicated than those of their sister subdisciplines, paleontology and paleoecology. Trace fossils are manifestations of benthic behavior; and these traits, although evolving in significant ways, have remained stable over longer spans of time than individual species of invertebrates. The fossil record of behavior in fact originated earlier than the fossil record of invertebrate body parts. Although macroinvertebrates and their traces exhibit tremendous diversity of form and function, these fit into a relatively small number of behavioral patterns. The patterns, in turn, may correlate with prevailing environmental conditions, resulting in gradients among trace fossil assemblages, or ichnofacies. Behavioral patterns and characteristic ichnofacies therefore constitute the main basis for uniformity in ichnology. Thus, the most fundamental questions are: What is the specific function represented by the trace? How will it change as the tracemaker is influenced by other genetic, physiologic, or ecologic stimuli? In which facies will it likely occur? and what preservational biases are apt to modify the fossil record of this behavior and its environmental distribution? Approached from this standpoint, the present is indeed a key to the ichnologic past, and vice versa. In practice, however, the present has been studied considerably less than its importance would dictate.

Uniformity in marine invertebrate ichnology

Analyses of deltaic facies successions highlight recurring ichnological patterns that reflect a variety of physicochemical stresses imposed upon infaunal organisms by the interaction of various delta-front processes. Analysis of numerous ancient deltaic deposits in Canada, the United States, Australia, and offshore Norway persistently show reductions in bioturbation intensity and impoverishment in ichnological diversity, compared to those of nondeltaic shorelines. Some facies locally demonstrate sporadic colonization and recolonization of substrates left denuded by episodic depositional conditions. Deltaic ichnological suites also locally display size reductions of ichnogenera and a paucity of suspension-feeding ethologies. Resulting trace-fossil suites are overwhelmingly dominated by depositfeeding behaviors, even in sandy facies. Such ichnological characteristics largely reflect increased sedimentation rates and heightened fluvial discharge, which serve to impede infaunal colonization. River-derived stresses are profound: salinity changes, hypopycnal-flow-induced water turbidity, distributary flood discharges with accompanying phytodetrital (comminuted plant debris) pulses, hyperpycnal-flow-induced sediment gravity flows, and fluid-mud deposition all conspire to produce the overall depauperate nature of the ichnological assemblage. Freshet-discharge events during river floods, accompanied by hyperpycnal conditions, may lead to the episodic introduction of reduced-salinity waters immediately above the sediment–water interface in delta-front and prodelta depositional settings. Such conditions may facilitate development of synaeresis cracks and promote reductions in infaunal populations. Wave energy generally buffers fluvial effects, by dispersing suspended sediment offshore and encouraging the thorough mixing of waters of contrasting salinity. High mud concentrations near the delta front damp wave energy, however, limiting its effectiveness in remediating the benthic ecosystem, particularly immediately following distributary flood discharges and storm events. In wavedominated settings, strong alongshore drift also operates to extend river-derived stresses considerable distances downdrift from distributary mouths. Where asymmetric deltas are formed, markedly different ichnological expressions are expressed on either side of distributary-channel mouths. Updrift settings typically retain classic shoreface assemblages, whereas downdrift environments commonly acquire markedly stressed suites. Storm energy may be effective in dispersing mud and mixing waters, but it also results in erosion and episodic sediment deposition. Concomitant precipitation induces river floods, returning river-derived stresses to the delta front. Tidal energy and its effects on the infaunal communities of deltas are poorly documented. Tidal flux may trap mud plumes against the delta front, elevating water turbidity. Pronounced mud flocculation coupled with increased settling velocity associated with tidal mixing also leads to rapid deposition of thick fluid muds, particularly in low-lying areas, hampering or precluding colonization. Tidal energy also leads to marked changes in energy and salinity near the sediment–water interface at several time scales. Deltaic ichnological suites are characterized by structures of opportunistic trophic generalists, though mainly those of facies-crossing deposit feeders. High water turbidity, particularly near the sea floor, precludes most suspension-feeding behavior, and suppresses the development of the Skolithos ichnofacies, even in many proximal delta-front deposits. Ichnological characteristics record the dynamic interplay and relative importance of these different processes, both temporally and spatially. on delta systems. River Deltas—Concepts, Models, and Examples SEPM Special Publication No. 83, Copyright © 2005 SEPM (Society for Sedimentary Geology), ISBN 1-56576-113-8, p. xxx–xxx. INTRODUCTION Although general concepts of deltaic sedimentation are generally well understood, the specific details of the accompanying ichnology are not. Many recent studies of modern deltaic systems, including many in this volume, emphasize the physical sedimentology. Measured sections through cores typically depict sedimentary structures, textures, grain size, body fossils, microfossils, geochemical analyses, and age dating. Although most descriptions note that burrows are present, detailed analysis of the ichnology, such as assessment of the Bioturbation Index (BI; Figure 1) and its distribution, identification of ichnospecies, ichnogenera, and general information on the diversity, abundance, and ethological groupings of the trace-fossil suite are almost totally lacking. Consequently, there is a paucity of work addressing the potentially unique characteristics of those ichnological suites, which may be critical in identifying various deltaic subenvironments. Some of the ichnological terms used in this paper are included in a glossary following the references. Many sedimentary processes (e.g., formation of ripples or dunes) are not especially sensitive to the environment of deposition. Dunes, for example, can be formed in deserts, rivers, JAMES A. MACEACHERN, KERRIE L. BANN, JANOK P. BHATTACHARYA, AND CHARLES D. HOWELL, JR. 2 shorefaces, and shelves, and observation of cross bedding is not diagnostic of any particular environment. Organisms, in contrast, are extremely sensitive to the environment (Pemberton et al., 1992a, 2001). Environmental factors such as energy conditions, substrate consistencies, depositional rates, oxygenation, salinity, and other physicochemical conditions all lead to discrete biological communities (Ekdale et al., 1984; Bromley, 1990; Pemberton et al., 1992a). These faunal communities yield recurring, strongly facies-controlled groupings of trace fossils that reflect specific combinations of organism behaviors (ethology). Such recurring groupings have been designated “ichnofacies”. The environmental factors that control organism distributions and their traces only tend to change in response to changes in water depth, and consequently, trace-fossil groupings typically display, at most, a passive relationship to paleobathymetry (Frey et al., 1990). This paradigm lies at the heart of ichnology and ichnofacies analysis. Various general models and approaches for using trace fossils in the identification and interpretation of specific sedimentary environments have been developed (e.g., Seilacher, 1967; Howard and Frey, 1984; Savrda and Bottjer, 1989; MacEachern and Pemberton, 1992; Pemberton et al., 1992a; Pemberton et al., 1992b; Pemberton and Wightman, 1992; Gingras et al., 1999; MacEachern et al., 1999a, Taylor et al., 2003; Bann et al., 2004, among others). Animal–sediment interactions are well documented from the more uniform conditions associated with strandplain shorefaces, and the shoreface ichnofacies model is robust (Fig. 2) (e.g., Howard and Reineck, 1981; Howard and Frey, 1984; Pemberton and Frey, 1984; Frey, 1990; Vossler and Pemberton, 1989; MacEachern and Pemberton, 1992; Pemberton and MacEachern, 1995; MacEachern et al., 1999b; Bann and Fielding, 2004). Likewise, ichnological models are well established for inshore tidal settings, on the basis of studies of modern environments (e.g., German and Dutch North Sea; Schäfer, 1956; 1962; Reineck, 1958; Reineck et al., 1967; et al., 1968; Dörjes, 1970; Hertweck, 1970; the Normandy coast of France; Larsonneur, 1975; the Georgia coast of the United States; Frey and Howard, 1972; Hertweck, 1972; Dörjes and Howard, 1975; Howard and Frey, 1973, 1975; Howard et al., 1975; and Majou and Howard, 1975; the tidal flats of Taiwan; Dörjes, 1978; Reineck and Cheng, 1978; and Willapa Bay, Washington; Gingras et al., 1999). This paper reviews and integrates what is known from the ichnological and biological literature with sedimentological studies of both modern and ancient delta deposits, in order to develop a more robust framework for understanding the ichnology of deltaic depositional systems. In deltaic settings, the effects of faunal responses and therefore of animal-sediment characteristics are typified by the dynamic interplay of fluvial influx, fluvial discharge types, tidal energy, wave action, and storms (see Tables 1 and 2). Such interactions, at least as they affect infaunal diversity, abundance, feeding strategy and overall behaviors, are poorly understood. Moslow and Pemberton (1988) presented a preliminary assessment of deltaic ichnology, based on a single core each of the Lower Cretaceous Cadotte Member and Bluesky Formation of the Western Interior Seaway of Alberta. Raychaudhuri and Pemberton (1992) and Raychaudhuri (1994) summarized the ichnological characteristics of the Lower Cretaceous Bow Island Formation of south-central Alberta. Gingras et al. (1998) conducted a preliminary ichnological study of the waveand riverinfluenced delta lobes in the Upper Cretaceous Dunvegan Formation in west-central Alberta, building on the detailed stratigraphic analysis and mapping of the depositional systems of Bhattacharya (1989) and Bhattacharya and Walker (1991a, 1991b). This preliminary ichnological work was expanded upon by Coates and MacEachern (1999, 2000), Coates (2001), and MacEachern and Coates (2002), who also included a comparison with the more mixed-influence (fluvial–wave) deltaic deposits of the Upper Cretaceous Basal Belly River Formation. Siggerud and Steel (1999) presented an integrated ichnofabric and sedimentological assessment of the coarse-grained Eocene Sant Llorenç del Munt fan-delta complex of SE Ebro Basin, Spain. The ichnology of ancient deltaic intervals has become increasingly studied in recent years. Howell et al. (2004) and Gani et al. (2004) have concentrated on ichnological signals in deltaic strata of the Upper Cretaceous Wall Creek Member, Powder River Basin, Wyoming. Soegaard and MacEachern (2003) carried out a det

Ichnology of Deltas: Organism Responses to the Dynamic Interplay of Rivers, Waves, Storms, and Tides

Cluster analysis of Cambrian-Ordovician marine benthic communities and community-trophic analysis of Late Cretaceous shelf faunas indicate that major ecological innovations appeared in nearshore environments and then expanded outward across the shelf at the expense of older community types. This onshoreinnovation, offshore-archaic evolutionary pattern is surprising in light of the generally, higher species turnover rates of offshore clades. This pattern probably results from differential extinction rates of onshore as compared to offshore clades, or from differential origination rates of new ecological associations or evolutionary novelties in nearshore environments.

https://science.sciencemag.org/content/sci/222/4628/1123.full.pdf

Onshore-offshore patterns in the evolution of phanerozoic shelf communities.

Ichnotaxonomy of 1,840 of flysch trace fossil specimens from the Ksiązkiewicz collection is revised. The specimens derive from diverse Tithonian-Miocene flysch deposits of the Polish Carpathians. Their ichnotaxonomy, based on morphology, was published by Ksiązkiewicz in 1997. In the revision presented in this publication, the ichnotaxonomic subdivisions are based on type of behaviour represented by the considered trace fossil. As a result, several diagnoses are changed and several ichnospecies ascribed to other ichnogenera. Ichnogenera Hormosiroidea, Saerichnites, IParahaentzschelinia, Halopoa, Nereites, Beaconites, Cladichnus, Protovirgularia, Ubinia and Oscillorhaphe are used the first time in the Polish Carpathians. The ichnogenera Pararusophycus, Rhabdoglyphus, Fucusopsis, Traucumichnis, Sabularia, Granularia, Bostricophyton, Halymenidium, Buthotrephis, Tubuliclmium, Tuberculichnus, Helminthoida, Muensteria, Keckia, and Taphrhelminthoida are not recommended for further use. The new ichnogenus Belocosmorhaphe n. igen. and the new ichnospecies name Cosmorhaphe carpathica nom. nov. are proposed. Ichnotaxa Trichichnus linearis Frey, Imponoglyphus torquendus Vialov, Palaeophycus tubularis Hall, Chondrites Irecurvus (Brongniart) and Arenituba isp. are distinguished for the first time in the Carpathian flysch on the base of Ksiązkiewicz material.

1840 okazow fliszowych skamienialości śladowych z kolekcji Ksiązkiewicza poddano ichnotaksonomicznej rewizji. Okazy te pochodzą z roznych tytonsko-miocenskich utworow fliszowych Karpat polskich. Ich ichnotaksonomia, oparta na morfologii, byla przedstawiona przez Ksiązkiewicza w 1977 roku. W rewizji przedstawionej w niniejszej publikacji, wydzielenia ichnotaksonomiczne oparto na typie behawioru reprezentowanego przez daną skamienialośc śladową. W rezultacie, zmieniono szereg diagnoz. Wiele ichnogatunkow zaliczono do innych niz dotąd ichnorodzajow. Ichnorodzaje Hormosiroidea, Saerichnites, IParahaentzschelinia, Halopoa, Nereites, Beaconites, Cladichnus, Protovirgularia, Ubinia i Oscillorhaphe uzyto po raz pierwszy w Karpatch polskich. Ichnorodzaje Pararusophycus, Rhabdoglyphus, Fucusopsis, Traucumichnis, Sabularia, Granularia, Bostricophyton, Halymenidium, Buthotrephis, Tubulichnium, Tuberculichnus, Helminthoida, Muensteria, Keckia i Taphrhelminthoida nie są rekomendowane do dalszego uzywania. Zaproponowano nowy ichnorodzaj Belocosmorhaphe n. igen. i nową nazwe ichnogatunkową Cosmorhaphe carpathica nom. nov. Ichnotaksony Trichichnus linearis Frey, Imponoglyphus torquendus Vialov, Palaeophycus tubularis Hall, Chondrites 1 recurvus (Brongniart), Arenituba isp. są wyroznione po raz pierwszy we fliszu karpackim, w oparciu o material z kolekcji Ksiązkiewicza.

Taxonomy and ethology of flysch trace fossils; revision of the Marian Ksiazkiewicz Collection and studies of complementary material

Trace fossils at discontinuity surfaces may be classified as three distinct ’ assemblages, according to their time relationship with the depositional hiatus. These assemblages may be called the “preomission,” “omission “and “postomission” suites. Discrimination of these suites is essential for the stratinomic interpretation of the discontinuity surface. The three suites may represent the same ichnocoenose in different modes of preservation, or the appearance of a new ichnocoenose may suggest the environmental conditions responsible for the omission of sediments and the resumption of deposition.

Trace Fossils at Omission Surfaces

The flysch of Paleocene to Eocene age outcropping in an almost unbroken cliff section at the Playa de San Telmo, Zumaya, North Spain, has been the subject of a quantitative sedimentological analysis. It is inferred that sedimentation commenced with deposition of a limestone-red shale sequence below wave base and continued with proximal and then distal turbidite sandstones deposited in what may have been a gradually deepening trough. The trough was probably oriented approximately east-west, parallel to the subsequent main tectonic trend. Sediment transport within the trough appears to have been essentially axial, with calcareous and siliceous sand derived from the east, but some siliceous sand was also laterally transported mainly from a land mass to the north.

The sediments contain an abundant and varied suite of trace fossils. Thus, with the depositional environment already defined sedimentologically, it was possible to critically examine the relationship between facies, trace fossil distribution and possible water depth. The facies variations were shown to be reflected in a changing ichnofauna. Spreite such as Zoophycos and Rhizocorallium were present in limestones apparently deposited not far below wave base. These traces are replaced by rosetted, winding and meandering forms in the more proximal turbidite facies. In the more distal facies spiral and patterned trace fossils appear, winding and meandering forms are common but Zoophycos, Rhizocorallium and rosetted traces are absent. It is inferred that these changes reflect faunal distribution on the sea floor rather than preservational factors.

T. P. Crimes

Papers

From limestones to distal turbidites: a facies and trace fossil analysis in the Zumaya flysch (Paleocene—Eocene), North Spain