Robert W. Dalrymple

Classification of clastic coastal depositional environments

Abstract This paper proposes a new classification for clastic coastal environments which includes the full range of major depositional settings including deltas, strand plains, tidal flats, estuaries and lagoons. This classification includes both morphologic and evolutionary components and is based on dominant coastal processes. It has the potential to predict responses in geomorphology, facies and stratigraphy. The significance of this classification is its evolutionary capability, and its inclusion of all major clastic coastal depositional environments, making it more comprehensive than previous classifications. We employ a ternary process classification with two axes. The first (horizontal axis) is defined as the relative power of wave versus tidal processes. The second (vertical) axis represents relative fluvial power (increasing upward). A ternary diagram defined by these axes can be used to illustrate the genetic process-response relationships between major coastal environments. The evolutionary classification combines the concept of two sediment sources (river and marine) with a relative sea-level parameter to classify embayed as well as linear and elongate/lobate shorelines. This approach identifies the evolutionary relationships between coastal sedimentary environments. The new ternary approach to process classification can be applied to estuaries and lagoons to define wave and tide end-member facies models, each consisting of a tripartite facies zonation. The evolutionary classification is compatible with sequence stratigraphy because sediment supply and relative sea level are included, and serves as a starting point for more refined coastal stratigraphic analyses.

Incised-Valley Systems

Incised-Valley Systems: Origin and Sedimentary Sequences - Incised valleys were not widely recognized prior to the 1980?s. Most early workers forced the isolated, incised-valley deposits along an uncomformity into a single continuous unit, ignored them by including them within larger stratigraphic units, or interpreted them as deltaic distributaries or non-incised fluvial channels. In the last decade, intense interest in the influence that changes in accommodation space have on stratigraphic organization has focused attention on incised-valley systems, because they are one of the most visible records of major decreases in accommodation. In practical terms, they are also a significant key to the identification of sequence-bounding uncomformities. As a result, many successions have been re-examined and incised-valley fills are being found in rapidly growing numbers. This volume is an outgrowth of this widespread interest in incised-valley sedimentation. Many of the papers were initially presented at the Special Session on ?Recognition and Facies of Incised Valley Fills? held at the AAPG-SEPM Annual Meeting (Calgary) in June, 1992.

First steps on land: Arthropod trackways in Cambrian-Ordovician eolian sandstone, southeastern Ontario, Canada

Basal terrestrial deposits in the Cambrian-Ordovician Nepean Formation (Potsdam Group) near Kingston, Ontario, contain arthropod-produced trackways that extend the record of the first arthropod landfall back by as much as 40 m.y. The presence of large, simple cross-beds and of wind-produced structures, including adhesion ripples and wind-ripple lamination, indicates that the host strata were deposited in an eolian dune field, probably in a marginal-marine setting. The trackways were preserved mainly as undertracks and record the activities of large, amphibious arthropods, possibly euthycarcinoids.

Tide- and wave-generated fluid mud deposits in the Tilje Formation (Jurassic), offshore Norway

The Tilje Formation (Early Jurassic; 120–300 m thick) consists predominantly of heterolithic deposits and is thought to have accumulated in tide-dominated estuarine and deltaic environments in an active rift setting. Anomalously thick (>0.5 cm) and internally structureless mudstone layers, which are interpreted to represent fluid-mud deposits, are widespread and occur in three different environmental settings: (1) in the basal part of upward-fining tidalfluvial channels where they generate upward-sanding successions: (2) in the deposits of mouth bars and terminal distributary channels where they are associated with the coarsest sands and the least-bioturbated sediments, suggesting deposition during tidally modulated river floods; and (3) in delta-front successions where they immediately overlie thick, wave-generated storm beds, suggesting that these fluid-mud deposits result from wave resuspension of previously deposited mud. These observations provide criteria for the recognition of ancient fluid-muds and for interpreting their origin. The tectonic setting may be responsible for their abundance.

Sedimentology of Modern, Inclined Heterolithic Stratification (IHS) in the Macrotidal Han River Delta, Korea

ABSTRACT An occurrence of inclined heterolithic stratification (IHS) is described from a tidal point bar in a 40-m-deep distributary of the macrotidal (tidal range 3.6-7.8 m), Han River delta, Korea. The channel bank demonstrates a convex-upward profile with intermittent presence of wave-formed scarps and terraces near the low-water level. The vertical succession of IHS is approximately 25 m thick and dips into the channel with angles reaching 14°. The IHS overlies 15 m of trough cross-bedded sand deposited in the channel thalweg and lower point bar. Even though the channel as a whole is ebb dominated, the preserved cross bedding is predominantly flood directed because the mutually evasive nature of the ebb and flood currents causes the point-bar surface to be flood dominated. This pattern may be a common feature of tidal point bars. The IHS itself consists of interstratified fine sand, sandy silt, and silt with an upward-fining textural trend. Tidal rhythmites are well developed in the middle and upper intertidal zone, and may also be present in the subtidal zone, but are poorly developed near the low-water level because of wave action. Seasonal discharge variations of the Han River are not obvious in the deposits, because the large size, distal location, and energetic tidal environment of the studied channel reduces the impact of river-stage fluctuations. Despite the moderate salinity levels, bioturbation is rare, except in the upper intertidal zone, because of the rapid sedimentation and energetic conditions.

Eolian action and the distribution of Cambrian shales in North America

Prolonged eolian action on the barren (prevegetation) craton provides a better explanation for the absence of shale in the Cambrian and Lower Ordovician orthoquartzite-carbonate suite of east-central and Arctic North America than does marine bypassing. It is hypothesized that paleo-trade winds transported much of the missing silt and clay to the southern and western United States and southwestern Canada, while the remainder diffused radially off the craton under the influence of variably directed storm winds. The distribution of shale in the Sauk sequence supports this and indicates that the orthoquartzite-carbonate suite of upwind regions is replaced by a shale-carbonate suite in downwind areas.

Principles of Tidal Sedimentology

Preface 1.Tidal Constituents of Modern and Ancient Tidal Rhythmites: Criteria for Recognition and Analysis 2. Principles of Sediment Transport Applicable in Tidal Environments 3. Tidal Signatures and Their Preservation Potential in Stratigraphic Sequences 4. Tidal Ichnology 5. Processes, Morphodynamics and Faces of Tide-Dominated Estuaries 6.Stratigraphy of Tide-Dominated Estuaries 7. Tide-Dominated Deltas 8. Salt Marsh Sedimentation 9. Open Coast Tidal Flats 10. Siliclastic Back-Barrier Tidal Flats 11. Tidal Channels on Tidal Flats and Marshes 12. Morphology and Facies Architecture of Tidal Inlets and Tidal Deltas 13. Shallow-Marine Tidal Deposits 14. Deep-Water Tidal Sedimentology 15. Precambrian Tidal Facies 16. Hypertidal Facies from the Pennsylvanian Period: East and West Interior Coal Basins, USA 17. Tidal Deposits of the Campanian Western Interior Seaway (WIS), Wyoming, Utah and Colorado, USA 18. Contrasting Styles of Siliciclastic Tidal Deposits in Developing Thrust Sheet-Top-Basins - the Lower Eocene of the Central Pyrenees (Spain) 19. Holocene Tidal Flats 20. Tidal Sands of the Bahamas Archipelago 21. Ancient Carbonate Tidalites Index.

Processes, Morphodynamics, and Facies of Tide-Dominated Estuaries

As defined in this chapter, an estuary forms during a shoreline transgression and then fills during a progradational phase that is transitional to a delta. The spatial distribution of processes, grain sizes and facies within tide-dominated estuaries is predictable in general terms. Tidal currents dominate sedimentation along the axis, with wave-dominated sedimentation occurring along the flanks of the estuary in its outer part. Tidal energy increases into the estuary but then decreases toward the tidal limit, with a gradual transition to river-dominated sedimentation at its head. The interaction of the tidal wave with the morphology of the estuary, and with river currents, causes the outer estuary to be flood-dominant, with a net landward movement of sand. By contrast, the inner estuary is ebb-dominant, creating a bedload convergence within the estuary. The axial sandy deposits are typically finest at this location. In transgressive-phase estuaries, the main channel shows a low—high—low pattern of sinuosity, with the tightest bends (sinuosity ≥ 2.5) occurring at the bedload convergence. These bends experience neck cutoff in the transition to the progradational phase of estuary filling. The estuary-mouth region is characterized by cross-bedded sands deposited on elongate sand bars, although wave-generated structures can be important in some cases. Estuaries that are down-drift of major rivers have anomalously muddy outer estuarine deposits. Further landward, upper-flow-regime parallel lamination can be widespread. The margins of the inner estuary are flanked by muddy salt-marsh and tidal-flat deposits that can contain well-developed tidal rhythmites and evidence of seasonal variations in river discharge.

Glendonites in Neoproterozoic low-latitude, interglacial, sedimentary rocks, northwest Canada: Insights into the Cryogenian ocean and Precambrian cold-water carbonates

Stellate crystals of ferroan dolomite in neritic siliciclastic and carbonate sedimentary rocks between Sturtian and Marinoan glaciations in the Mackenzie Mountains are interpreted as replaced glendonites. These pseudomorphs after ikaite indicate that shallow seawater at that time was near freezing. Stromatolites verify that paleoenvironments were in the photic zone and physical sedimentary structures such as hummocky cross-bedding confirm that the seafloor was repeatedly disturbed by storms. Glendonites within these low-latitude, continental shelf to coastal sedimentary deposits imply that global ocean water during much of Cryogenian time was likely very cold. Such an ocean would easily have cooled to yield widespread sea ice and, through positive feedback, growth of low-latitude continental glaciers. In this situation gas hydrates could have formed in shallow-water, cold shelf sediment, but would have been particularly sensitive to destabilization as a result of sea-level change. Co-occurrence of pisolites and glendonites in these rocks additionally implies that some ooids and pisoids might have been, unlike Phanerozoic equivalents, characteristic of cold-water sediments.

Shallow-Marine Tidal Deposits

Shallow-marine tidal deposits form on open shelves, and more specifically in open-mouthed embayments and semi-enclosed epicontinental seas, where the oceanic tide is amplified by resonance. They are also present in straits and seaways where the tidal currents are accelerated by flow constriction. Complex interactions of the tide with the seafloor and coastal topography bring about tidal asymmetry, generating tidal-transport pathways with net, unidirectional transport of sediment over long distances. Tidal currents are commonly capable of resuspending mud in shallow-marine settings, but little is known about the role of tidal currents in the deposition of muddy deposits in the offshore domain. The best-known shelf tidal deposits are sandy and bioclastic transgressive ‘lags’ that mantle flooding surfaces. These lags are generally thin, but can reach thicknesses of 10–30 m in tidal-current ridges and sand sheets. These deposits are composed of dominantly well-sorted, cross-bedded sands with good reservoir properties. Careful architectural analysis allows the distinction between the deposits of compound dunes, tidal-current ridges and migrating sand sheets. The occurrence of shallow-marine tidal deposits is sensitive to changes in sea level; paleotidal modeling has great potential to help understanding their occurrence in space and time.