The nature and organization of facies within incised-valley estuaries is controlled by the interplay between marine processes (waves and tides), which generally decrease in intensity up-estuary, and fluvial processes, which decrease in strength down-estuary. All estuaries ideally possess a three-fold (tripartite) structure: an outer, marine-dominated portion where the net bedload transport is headward; a relatively low-energy central zone where there is net bedload convergence; and an inner, river-dominated (but marine-influenced) part where the net transport is seaward. These three zones are not equally developed in all estuaries because of such factors as sediment availability, coastal zone gradient and the stage of estuary evolution. Two distinct but intergradational types of estuaries (wave- and tide-dominated) are recognized on the basis of the dominant marine process. Wave-dominated estuaries typically possess a well-defined tripartite zonation: a marine sand body comprised of barrier, washover, tidal inlet and tidal delta deposits; a fine-grained (generally muddy) central basin; and a bay-head delta that experiences tidal and/or salt-water influence. The marine sand body in tide-dominated estuaries consists of elongate sand bars and broad sand flats that pass headward into a low-sinuosity ("straight") single channel; net sand transport is headward in these areas. The equivalent of the central basin consists of a zone of tight meanders where bedload transport by flood-tidal and river currents is equal in the long term, while the inner, river-dominated zone has a single, low-sinuosity ("straight") channel. These facies models and their conceptual basis provide a practical means of highlighting the differences and similarities between estuaries. They also allow the predication of the stratigraphy of estuarine deposits within a sequence-stratigraphic context.

Estuarine facies models; conceptual basis and stratigraphic implications

1. Introductory remarks 2. Convolvulacaea 2. Scrophulariaceae, Gesneriaceae, Labiatae, etc. 4. Cruciferae, Papaveraceae, Resedaceae, etc. 5. Geraniaceae, Leguminosae, Onagraceae, etc. 6. Solanaceae, Primulaceae, Polygoneae, etc. 7. Summary of the heights and weights of the crossed and self-fertilised plants 8. Difference between crossed and self-fertilised plants in constitutional vigour and in other respects 9. The effects of cross-fertilisation and self-fertilisation on the production of seeds 10. Means of fertilisation 11. The habits of insects in relation to the fertilisation of flowers 12. General results Index.

The Effects of Cross and Self Fertilisation in the Vegetable Kingdom: CONVOLVULACEÆ

A new scheme for the description and analysis of bioturbation and the resultant ichnofabrics is proposed. This system can be used in core and field-based studies and consists of two parts. (1) A bioturbation index in which a descriptive grade is assigned to the degree of bioturbation. This integrates the sedimentology and ichnology, where the higher grades of bioturbation result from increased burrow overlap and the subsequent loss of the primary sedimentary fabric. (2) An ichnofabric constituent diagram which records the detail of the ichnofabric by graphically plotting the dimensional data of the ichnotaxa and their order of emplacement against their coverage. This scheme differs from previous attempts to characterize bioturbation using semi-quantatitive methods and visually portrays the ichnofabric so that comparative studies can be carried out. This is of particular use in facies analysis, the establishment of the ichnocoenoses and tier diagrams, and within sequence stratigraphic studies so that hiatal surfaces can be recognized.

Description and analysis of bioturbation and ichnofabric

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Morphologic and facies trends through the fluvial–marine transition in tide-dominated depositional systems: A schematic framework for environmental and sequence-stratigraphic interpretation

A review of coastal palaeoclimate and relative sea-level reconstructions using δ13C and C/N ratios in organic material

Because of fundamental differences between trace fossils and body fossils, ichnologic nomenclature is beset with difficulties. Foremost is inconsistent treatment by the International Commission on Zoological Nomenclature (lack of sanction for post-1930 names, confusion over the "rule of priority") and inadequate curation of type specimens. However, ichnologists have contributed their own problems via inadequate diagnoses and descriptions, misconceptions of ichnologic and taxonomic principles, proliferation of names and failure to engage in true monographic revisions. All these difficulties are illustrated in a thorough reevaluation of the ichnogenera Planolites Nicholson and Palaeophycus Hall. Contrary to a popular but ill-founded scheme in which these ichnogenera are differentiated simply on the presence or absence of branches, Planolites is an unlined burrow infilled with sediments having textural and fabricational characters unlike those of the host rock, whereas Palaeophycus is a lined burrow filled with sediments typically identical to those of the surrounding matrix. Planolites represents active backfilling of sediment in an ephemeral burrow constructed by a mobile deposit feeder and Palaeophycus represents passive sedimentation within an open dwelling burrow constructed by a predaceous or suspension-feeding animal. In addition to ichnological nomenclature and ethology, the ramifications are important in paleoecology, sedimentology and diagenetic studies. Currently recognized ichnospecies of Planolites include P. montanus Richter, P. beverleyensis (Billings) and P. annularis Walcott. Those of Palaeophycus include P. heberti (Saporta), P. tubularis Hall, P. striatus Hall, P. sulcatus (Miller and Dyer) and P. alternatus n. ichnosp.

Trace fossil nomenclature and the Planolites-Palaeophycus dilemma

Ophiomorpha: Its morphologic, taxonomic, and environmental significance

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

Salt marshes, which represent the final stage in the leveling of marine delta plains or the filling of depressions, embayments, and other irregularities along coasts, are to some extent a measure of coastal stability or equilibrium. The overall sedimentary sequence is therefore a potential record of coastal history; it may reveal complete successions from original estuary, delta, lagoon, or bay floors to the highest intertidal flat, including lateral variations in contemporaneous facies or subfacies. Associated mineral suites are equally important indicators of both sources and possible recycling of coastal sediments. As habitable dwelling space for numerous organisms, some of which are uniquely adapted to stressful conditions, salt marsh substrates record many details of significance in paleoecology, ichnology, and environmental reconstruction.

Coastal Salt Marshes

The monospecific ichnogenus Scoyenia White is characterized by longitudinally striat- ed wall linings surrounding meniscate burrow fills. Ancorichnus Heinberg is similar but has an unornamented exterior. Ichnospecies of Ancorichnus are based upon fabricational differences in menisci; those of A. coronus (n. ichnosp.) are continuous with the wall lining, whereas those of A. ancorichnus Heinberg are not. Scoyenia and Ancorichnus are interpreted as feeding structures, although certain details of the feeding-burrowing mechanism remain conjectural. The Scoyenia organism is thought to be an arthropod (other than insects or decapods); Ancorichnus ancorichnus may have been produced by priapulids, sipunculids, or ethologically equivalent worms, whereas A. coronus seems to have been made by arthropods somewhat akin to the Scoyenia animal. These last two forms also may have more or less similar environmental significance. By definition, Scoyenia gracilis is diagnostic of the Scoyenia ichnofacies. However, various different interpretations or applications of this ichnofacies concept have rendered it virtually mean- ingless beyond a general nonmarine connotation. Recent work suggests that 1) nonmarine ichno- facies are equally as numerous and different as marine ichnofacies, 2) the Scoyenia ichnofacies is only one among many nonmarine assemblages, and yet 3) even the Scoyenia ichnofacies remains largely undefined and poorly understood. As a test of the distinctiveness and validity of the concept, we suggest that future designations of this ichnofacies be restricted to trace fossil assemblages in which Scoyenia gracilis, Ancorichnus coronus, or ethologically and ecologically equivalent burrows predominate. Known occurrences of such trace fossils indicate that the tracemakers preferred moist or wet nonmarine substrates, whether shallow aquatic deposits periodically exposed to air or low- lying subaerial deposits periodically inundated by water.

Robert W. Frey

Papers

Trace fossil nomenclature and the Planolites-Palaeophycus dilemma

Ophiomorpha: Its morphologic, taxonomic, and environmental significance

Uniformity in marine invertebrate ichnology

Coastal Salt Marshes

Morphological, ethological, and environmental significance of the ichnogenera Scoyenia and Ancorichnus