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Most sequence stratigraphic models are based on the premise that relative changes in sea level (RSL) control stacking patterns in continental-margin settings. An alternative hypothesis, however, is that upstream factors, notably variations in relative water discharge (RQW) or the ratio of water to sediment discharge can influence or control stratal stacking patterns in fluvial systems. Sequence boundaries of RQW-driven systems differ from those driven by base-level fluctuations in that: 1) the depth of incision increases updip, and 2) rates of erosion are spatially uniform, leading to the formation of widespread, planar sequence boundaries. This paper presents an architectural and stratigraphic analysis of the well-exposed Masuk Formation of the Henry Mountains Syncline in southern Utah, an Upper Cretaceous coastal-plain fluvial succession that is interpreted to have been influenced significantly by RQW. Six lithofacies are recognized, three (Facies 1–3) recording floodbasin, mire, and (in one short interval) estuarine environments, and three (Facies 4–6) record different kinds of channel fills on a coastal alluvial plain. Seven major composite channel bodies (Facies 4–6), separated by intervals of non-channel deposits (Facies 1–3), are recognized in the stratigraphic interval. Composite channel bodies display planar, sheet-like geometry and are laterally continuous to a significantly greater extent (> 10 km) than would be expected from purely autogenic channel-belt construction. Together, these intervals record a series of high-frequency sequences, formed along the western margin of the Western Interior Seaway. In each individual sequence is a repetitive facies succession from a basal chaotic sandstone with admixed mudrock and sandstone transitioning upward to a more organized cross-bedded and stratified sandstone. This is interpreted to record cyclical changes from a peaked (flashy) discharge regime to a more normal runoff regime. Paleoflow data indicate a dominance of transverse (eastward-directed) dispersal early in the accumulation of the Masuk Formation, shifting to a pattern of greater axial (northward) dispersal over time. The RQW signal is strong in the lower part of the formation, decreasing upward. This suggests that the relatively short-headed streams draining from the rising Sevier fold–thrust belt were strongly influenced by climatic cyclicity, whereas more distally sourced systems were not. This study provides new insights into the architecture and stacking patterns of coastal-plain fluvial successions, emphasizing the plausible role that climate can play in shaping alluvial architecture in the rock record.

Uncertainty persists over whether repetitive stratal rhythms in the Pennsylvanian of Euramerica (so-called “cyclothems”) were externally forced, in all likelihood by waxing and waning of glacial ice centers on Gondwana, or were controlled by autogenic processes. A key to resolving this dispute is the lateral extent of the individual cyclothems, with broad regional extent (beyond the plausible breadth and length of individual depositional systems such as deltas) arguing in favor of an external forcing control. This study provides a sedimentological and sequence stratigraphic analysis of the middle Pennsylvanian (Desmoinesian to early Missourian in North American stratigraphic terminology, Moscovian to early Kasimovian in the terms of the global stratigraphic nomenclature) succession of the southern Illinois Basin in Illinois, Indiana, and Kentucky, eastern USA. An array of eleven lithofacies is recognized, recording deposition of clastic, humic organic, and bioclastic carbonate sediments on a broad, low-gradient, low-paleolatitude shelf and coastal plain that were undersupplied by sediment. These facies are arranged into thirteen repetitive vertical cycles (sequences), each of which can be traced across the entire basin west to east (perpendicular to the paleoslope direction) across a distance of 250 km. Sequences are bounded by erosion surfaces that define 1–4 km-wide, deeply incised valley-fills (IVFs) that are mostly elongate towards the south-southwest, the dominant direction of paleoflow. In the west–east direction, valley erosion surfaces pass laterally into well-developed paleosols, incised locally by smaller channels. Each of these surfaces is laterally persistent across the basin. IVFs comprise multi-story bodies of conglomerate–breccia and sandstone, passing upward into heterolithic sandstone–mudrock associations, recording fluvial and later estuarine environments. Coal bodies typically occur at the tops of IVFs and are interbedded with heterolithic facies recording tidal influence, indicative of initial flooding by the sea. They are in turn overlain by estuarine and marine mudrocks and bioclastic carbonates, recording the maximum extent of marine flooding in a cycle. Each sequence is completed by heterolithic to sandstone-dominated facies of deltaic aspect that are typically truncated by the next erosion surface (sequence boundary). Plausible modern analogs suggest that sea-level excursions were of the order of 20–40 m. The great lateral persistence of not only the thirteen sequences, but also many of their component beds, argues strongly for an external control on sediment accumulation. Eccentricity-paced glacial cycles in Gondwana are invoked as the most likely cause of the cyclicity. The low-accommodation context of the Illinois Basin (average accumulation rate 6 cm/ky) contributed to the incomplete, condensed, and strongly top-truncated nature of preserved sequences.

In the Big Snowy Mountains of central Montana, USA, late Visean to Bashkirian strata preserve a nearly complete, but poorly documented, paleotropical stratigraphic succession that straddles the range of current estimates of the onset of the Late Paleozoic Ice Age (LPIA). Sedimentologic and stratigraphic investigation of the Otter (late Visean to Serpukhovian) and Heath (Serpukhovian) formations, with secondary focus on the overlying Tyler (late Serpukhovian to Bashkirian) and Alaska Bench (Bashkirian) formations, facilitated an appraisal of paleotropical environmental change preserved in this succession. Three facies associations reminiscent of environments currently forming in Shark Bay, Australia, were identified in the Otter Formation: shallow semi-restricted littoral platform, intertidal platform, and supratidal plain. Five facies associations broadly comparable to modern environments present in the Sunda Shelf and southern coast of the Persian Gulf were identified in the Heath Formation: offshore outer ramp, mid- to outer ramp, inner ramp, coastal plain, and sabkha. Facies associations preserved in the Heath Formation are here explained in the context of a protected, homoclinal carbonate ramp situated in a partially silled epicontinental embayment. A shift from low-magnitude relative sea-level oscillations preserved in the Otter Formation to a cyclothemic stratigraphic pattern entailing ≥ 6 fourth-order, high-frequency and high-magnitude relative sea-level fluctuations in the Heath Formation is here interpreted to record the main eustatic signal of the LPIA in central Montana. Current published biostratigraphic constraints for the observed stratigraphy estimate the main eustatic signal of the LPIA to have occurred approximately between 331 (base Serpukhovian) and 327 Ma in central Montana. A distinct upward transition from coal and paleosol-bearing depositional sequences in the lower Heath to evaporite and limestone-bearing depositional sequences in the upper Heath preserves a broad humid to arid paleoclimate shift during deposition of this unit, which influenced hydrographic circulation patterns and the resultant distribution of anoxic environments in the Big Snowy Trough during this time interval. Improved depositional and sequence stratigraphic models of the Heath Formation proposed in this study permit new insight into the theoretical distribution of, and water depth necessary to preserve, black, organic-rich claystone and shale in partially silled intracratonic basins, in addition to new temporal constraints on LPIA onset in paleotropical western Laurentia.

Pervasive 18O-depleted carbonate cements in sediment cores acquired by the Cape Roberts Project (CRP) in McMurdo Sound, Antarctica, were previously attributed to mixing of glacial meltwater and seawater in the subsurface. However, a more recent discovery of 18O-depleted, connate brine formed by seawater freezing in a nearby sediment core (AND-2A core) called this interpretation into question. This core contains widespread carbonate cements in the glaciomarine sediments, which have been demonstrated to precipitate from the brine by conventional (δ18O) and clumped (Δ47) isotopic data. Building on findings from the AND-2A core, this study investigates the geochemical nature, origin, and distribution of diagenetic fluids, and re-evaluates their impact on diagenetic patterns in glaciomarine deposits of the composite Oligocene to lower Miocene succession from the CRP cores. Sandstones were characterized in the context of a well-established chronostratigraphic and sequence stratigraphic framework by systematic point counting and modal analysis using optical microscopy. Diagenetic carbonate phases and mineralogies were assessed by cathodoluminescence microscopy and energy-dispersive X-ray spectrometry. Low-Mg calcite cement is the most widespread diagenetic phase and was selected for analyses of stable carbon and oxygen isotopes. Similar to the AND-2A core, the cement increases in crystal size and decreases in δ18O value (–4.8 to –19.5‰ VPDB) with increasing depth to ∼ 700–800 m. These patterns indicate calcite precipitation from interstitial brine along local geothermal gradients. When considered in the context of Neogene climate, tectonic, and burial history, timing of calcite cementation is linked to a period of extensive formation of cryogenic brine during c. 13 to 10 Ma when the region transitioned into a cold, polar climate regime and McMurdo Sound was periodically glaciated by expanded, cold-based Antarctic ice sheets. Beyond McMurdo Sound, the propensity for formation of cryogenic brine exists in most glaciomarine settings. As such, the potential for diagenetic alteration by such fluids should be considered in studies of the deposits of ancient glaciated continental margins.

Depositional-dip-oriented transects through coastal-plain to nearshore marine domains are essential elements of generic sequence stratigraphic models for continental-margin successions. Many questions remain about the validity of these models, however, because well-constrained outcrop examples are sparse. Presented herein is the first detailed study of a 30-km-long, almost continuously exposed, depositional-dip transect through nonmarine and marine facies of the fluvio-deltaic Ferron Sandstone. This transect is connected to the southern end of a previously documented, 67-km-long, depositional-strike-oriented section. Excellent exposure reveals relationships among facies, stacking patterns, and bounding surfaces across three orders of sequences and various shoreline trajectories. Deposits of sequences are dominated by falling-stage systems tracts, suggesting a regime dominated by long, gradual relative falls in sea level punctuated by shorter relative rises. Widespread fluvial downcutting is generally absent. Distributary-channel sandstones pass down dip into broadly contemporaneous shoreface and delta-front sandstones. A composite sequence boundary divides the study interval into two composite sequence sets. Sequence sets I–III comprise eastward-dipping, offlapping clinoform sets defining a descending, regressive shoreline trajectory (falling-stage deltas). Sequence sets IV–VI overlie a thin transgressive deposit and consist of progradational to aggradational clinoform sets (highstand deltas). Key bounding surfaces are similar at all scales of the hierarchy: they are diachronous, cryptic, and pass down depositional dip into conformable surfaces where they are almost impossible to recognize as key surfaces. Differentiation between units and surfaces that develop at different hierarchical levels is possible only by integrating detailed outcrop observations with regional stratigraphic architecture.

Shallow marine sandstone bodies isolated within marine mudrock successions are still incompletely understood. A robust understanding of such bodies is of interest not only scientifically, but also in order to facilitate successful exploration for and production of petroleum and other natural resources. Such bodies are preserved in the Turonian Frontier Formation of the northern Uinta Basin in Utah and Colorado, U.S.A., where they have been previously interpreted as the products of “offshore bars.” A reappraisal of these bodies in the uppermost Frontier Formation (herein defined as the Turonian Ashley Valley Member) reveals three northeast–southwest elongate, incised highstand, forced regressive, and lowstand offshore sandstone bodies partially to fully encased in offshore marine mudrock. These bodies are herein named the Buckskin Hills, Kane Hollow, and Raven Ridge sandstones (from oldest to youngest). Five lithofacies were identified from 47 measured outcrop sections located along the western and southern margins of Dinosaur National Monument. They are 1) marine shelf claystones and siltstones, 2) lower–upper offshore marine admixed siltstone and sandstone, 3) lower–upper offshore thin-bedded sandstones and siltstones, 4) distal lower shoreface heavily bioturbated very fine-grained sandstone, and 5) transgressive lag conglomerate. Wireline logs from 112 drillhole locations throughout the Uinta Basin were calibrated with nearby outcrop locations to construct cross sections and net-sandstone isochore maps. From these, regionally traceable horizons (flooding surfaces and internal erosion surfaces) facilitated an analysis of stacking patterns, development of a stratigraphic framework, and a depositional-environment interpretation. Overall, the Ashley Valley Member preserves a basinward-offlapping stacking pattern, indicative of shoreline progradation in response to the late Turonian Greenhorn global eustatic regression that was interrupted by two, high-frequency transgression–regression cycles. This nested cyclicity cannot be explained by global eustasy alone, and instead is suggestive of a secondary allogenic control, likely related to Western Cordilleran Foreland Basin (WCFB) geodynamic driving mechanisms. As a result, the Ashley Valley Member provides an example of tectonic forcing on stratal stacking patterns, highlighting the importance of intrabasinal tectonic processes on dispersal patterns and high-frequency relative base-level fluctuations within the WCFB stratigraphic record.

A facies model for the deposits of tidal bores (upstream-propagating hydraulic jumps associated with the flood tide in estuarine rivers) has not yet been developed, despite the publication of data from laboratory experiments and some modern estuaries. Moreover, only one example of tidal-bore deposits has hitherto been identified in the rock record. Herein, we document evidence for tidal bores in an Upper Pennsylvanian (Virgilian, Gzhelian) incised-valley fill in northeastern Kansas, USA. Across the flanks and crest of a bank-attached bar remnant in this fill are thin (< 10 cm) lenses of muddy, massive sandstone and massive, plant-debris-rich sandstone bounded by erosion surfaces exhibiting symmetrical wave ripples and irregular scouring. This interval is enclosed by sandstones with bidirectional cross-stratification, rhythmites, mud drapes, flaser bedding, and related sedimentary structures that together record appreciable tidal influence. The erosion surfaces bounding the massive sandstone lenses, and the massive sandstone lenses themselves, are evidence for scour and sediment suspension by upstream-propagating bores followed by deposition from suspension after their passage. Not only are these deposits the first sedimentary record of tidal bores to be documented in the Pennsylvanian of the USA, they are only the second example of such deposits to be documented in the global rock record. On the basis of our observations, we propose a provisional facies model for tidal-bore deposits that can be refined by future work.

Incorporation of ichnological (trace fossil) data into facies models for deltaic systems and their deposits has yielded useful new criteria for discriminating between alternative interpretations. Nevertheless, despite the recognition that trace-fossil suites may vary spatially across an individual delta system, few spatially resolved datasets are currently available to inform these interpretations. We present a new sedimentological and ichnological analysis of the Upper Cretaceous (Cenomanian) Peay Sandstone Member of the Frontier Formation in the northern Bighorn Basin, Wyoming, U.S.A., based on three-dimensional mapping of surface exposures and subsurface drilling data. Both down-depositional-dip and across-depositional-strike trends can be determined and quantified prima facie from this dataset. The Peay Sandstone Member is a crudely coarsening-upward sandstone body that has an elongate planform shape, projecting southeastward into the basin. Based on a facies analysis, the vertical facies succession in the core of the body represents, from base to top, deposits of prodelta (stratified siltstone), distal delta front (thinly interbedded siltstone and sandstone), through medial–proximal delta front (thickly interbedded siltstone and sandstone to bioturbated fine-grained sandstone), to mouth bar (amalgamated, largely unbioturbated, fine- to medium-grained sandstone) environments. This complete progradational succession persists for at least 40 km in the depositional dip direction, thinning and fining abruptly over a few kilometers south of the town of Greybull, Wyoming. Transects from the delta axial core to the peripheral flanks reveal changes in facies reflecting a transition from a high-energy, river-dominated mouth-bar environment to a tide- and wave-influenced medial–proximal delta flank, and ultimately, to a low-energy, storm- and wave-influenced distal delta flank setting on the peripheries of the delta lobe. The trace assemblage in the axial core is interpreted as a highly stressed expression of the Skolithos Ichnofacies. This passes gradationally down depositional dip into stressed expressions of the Cruziana Ichnofacies, and along depositional strike into an archetypal (unstressed) expression of the Cruziana Ichnofacies on the delta flanks. This spatial variation in bioturbation intensities and trace-fossil assemblages is interpreted to reflect dissipation of physico-chemical stresses from the axial core to peripheral flanks. The outcomes of this study emphasize the point that data acquired on an ancient deltaic deposit in isolation of their paleogeographic context may give rise to a misleading impression of that system, and potentially a less than parsimonious interpretation of its process balance and planform geometry.

The internal architecture and external form of fluvial channel bodies is governed by both intrinsic and extrinsic controls. Extrinsic controls such as climate, eustasy, and tectonism are believed to have modest effects on channel-body types and geometries in high-subsidence settings. The effects of climate are particularly cryptic in high-accommodation settings and have proven extremely difficult to separate from other extrinsic controls such as tectonics and eustasy. The thick successions preserved in such basins have the potential to be relatively stratigraphically complete and are, therefore, valuable for interpreting basin evolution. This study documents the external geometry and internal architectural styles of fluvial channel bodies in a spectacularly exposed, 7-km-thick, Mississippian–Permian section from the Cumberland Basin, Atlantic Canada. Four fluvial styles are recognized: perennial, strongly seasonal, ephemeral, and fixed. Fluvial styles are not randomly distributed throughout the stratigraphic succession; instead discrete stratigraphic intervals consist of predominantly one type of fluvial style. Four stratigraphic intervals (E1–E4) in which strongly seasonal fluvial styles are predominant are recognized and alternate with intervals that are characterized by either perennial or ephemeral deposits. This suggests that a coherent record of climate change as manifested by changes in precipitation and runoff regime is recorded in the internal architecture of sandbodies.

Exposures of Upper Cretaceous strata in the Book Cliffs have played a key role in the formulation of modern sequence stratigraphic concepts, and yet correlations with time-equivalent strata in nearby regions remain uncertain, resulting in an incomplete understanding of regional paleogeography. This study presents detailed high-resolution correlations of the Upper Cretaceous stratigraphy between the Book Cliffs, the Wasatch Plateau, and the western Henry Mountains Syncline in Utah with emphasis on the Campanian interval. Two newly acquired measured vertical sections at Coal Canyon near Green River, in the Book Cliffs, and Blind Trail, in the Henry Mountains, inform the correlations, which also incorporate the substantial body of previous research. Correlations are further constrained by vertical and lateral facies stacking patterns, and changes in sediment dispersal directions at discrete stratigraphic horizons derived from paleocurrent measurements. Much of the Campanian succession can be characterized as a single, low-frequency (third order) depositional sequence, within which are nested numerous high-frequency sequences. While it is not possible to correlate every high-frequency sequence recognized in individual outcrop areas, we define four intervals (numbered 1–4, in ascending stratigraphic order) that we correlate across the entire region. Interval 1 (basal Campanian) is represented by initially deltaic and later wave-dominated shoreface strata of the Star Point Sandstone and equivalent basal Muley Canyon Sandstone. Interval 2 (lower Campanian) comprises coastal-plain facies passing eastward into shallow marine strata of the lower Blackhawk Formation and equivalent Muley Canyon Sandstone. Interval 3 (lower to mid middle Campanian) comprises a thick aggradational stack of coastal-plain fluvial strata that pass eastward into coastal and shallow marine facies (Blackhawk Formation and equivalent Masuk Formation). Interval 4, overlying a major facies dislocation (third-order sequence boundary), comprises amalgamated sheet fluvial deposits of the lower Castlegate Sandstone and equivalent Tarantula Mesa Sandstone. During the early to middle Campanian, the northern Wasatch Plateau and western Henry Mountains regions were along depositional strike with respect to one another. The Book Cliffs near Green River were located obliquely down depositional dip from the western Henry Mountains region during the Campanian. These new correlations, and the improved understanding of paleogeography that derive from them, have the potential to inform basin-scale stratigraphic interpretations to a greater extent than has been hitherto possible.

The Platte River of Nebraska, central USA, has been used by sedimentologists as a type example of a sandy, braided river system for some forty years. Despite this designation, however, the details of the river’s subsurface stratigraphy have never been evaluated, and so the extant facies model for the Platte River remains unvalidated. This paper analyzes the Holocene stratigraphy of the central and lower Platte River. It utilizes newly acquired data from wireline logs, sediment cores, aerial photography, and ground-penetrating radar (GPR) traverses to characterize subsurface geology, in addition to surface sediment and geomorphic mapping, sampling, and analysis of serial aerial imagery. Cores and GPR profiles show that the lithosome of the active Platte is 6–8 m in thickness and consists predominantly of medium sand. Although macroform features are common on the surface of the modern (active) central and lower Platte River in Nebraska, the shallow subsurface stratigraphy is dominated by mesoform cross-bedding and planar stratification overlying channel scour fills. This differs markedly from the vertical succession predicted by the Platte River facies model of Miall (1977). Data from inactive portions of the central and lower Platte River, however, show macroform cross-bedding indicative of the downstream and cross-stream migration of linguoid and transverse bars, which would be predicted by the published model. The typical architecture of the Holocene channel-belt sand body in the areas studied thus comprises a lower unit dominated by macroform-scale cross-bedding, overlain by an upper unit dominated by mesoform-scale cross-bedding and scour fills. Furthermore, time-series analysis of aerial photography of the river in the vicinity of Grand Island, Nebraska, shows that: (1) the river has become dominated by aggressively vegetated subaerially exposed channel-bed domains (termed “vegetated channel islands”) that superficially resemble bars; and (2) that this stretch is no longer dominated by downstream-accreting macroform bars, which were abundant in the 1960s and 1970s. Contraction of the active channel in this region has accompanied these changes, somewhat independently of discharge variation. New vertical sequence facies models are presented to account for these differences. Our data show the futility of seeking to characterize a fluvial system by means of a single vertical sequence model, and furthermore indicate that the Holocene facies architecture of the sandy, braided Platte River varies both in space and in time. The dominance of mesoform-scale structure in the shallow subsurface of the central and lower Platte River likely reflects the ongoing process of gradual abandonment of the system. It further highlights the need for caution in interpreting subsurface structure from surface geomorphology in fluvial systems.

The internal architecture and genetic-stratigraphic analysis of coastal-plain fluvial successions has applications to both academic understanding of continental-margin stratigraphy and to the economic evaluation of subsurface hydrocarbon and water reservoirs. Despite the abundance of exposed ancient examples of such coastal-plain to shallow marine transitions, however, the lateral facies changes and stratigraphic stacking patterns of such transitions remain largely unresolved in detail. This study presents a sedimentological and stratigraphic analysis of the Campanian Masuk Formation in the Henry Mountains syncline of Utah, western USA, and proposes a sequence-stratigraphic model to explain the geometries of fluvial-channel lithosomes found in the unit. At its type section, the Masuk Formation is an ~ 220-m-thick succession of interbedded sandstone, mudstone, and coal with minor intraformational breccias. Six facies are defined: Facies 1, coal and carbonaceous shale, records accumulation of organic sediments in coastal-plain mires; Facies 2, mudrock, records coastal-plain floodbasin settings; Facies 3, thinly interbedded sandstone and siltstone, represents estuarine-basin deposits with one interval of marine flooding; Facies 4, admixed siltstone-sandstone with intraformational breccia, represents chaotically filled coastal plain channels; Facies 5, interbedded sandstone-siltstone with inclined heterolithic stratification (IHS), records deposits of coastal-plain channels with variable sediment supply; and Facies 6, trough-cross-bedded sandstone, records sand-dominated coastal-plain channel deposits. Facies 4, 5, and 6 all show evidence of coastal and tidal influence on sediment accumulation (IHS, low-diversity trace-fossil assemblages, bimodal to bipolar paleocurrent distributions, mud drapes on small-scale sedimentary structures) to varying degrees. Facies analysis and tracing of key surfaces such as regionally extensive erosion surfaces (sequence boundaries) and flooding surfaces suggest that the entire Masuk Formation (and the uppermost part of the underlying Muley Canyon Sandstone) is a single depositional sequence. The typically multilateral channel bodies are traceable in a depositional strike direction over distances much greater than empirically calculated estimates of channel-belt width. This pattern suggests an allogenic control on stacking patterns. Multistory and multilateral channel bodies typically have a Facies 4 unit at the base, overlain by one or more stories of Facies 5, and in turn capped by Facies 6. This stacking pattern could reflect cycles of incision, initial lowstand channel filling, and subsequent backfilling of estuarine channels during transgressions. This pattern further hints at the possibility of preservation of high-frequency sequences nested within the longer-term sequence. This study provides new insights into the stacking patterns of coastal-plain fluvial successions and their interpretation.

Accumulations of logs and flood sediment frequently block modern channels and may trigger avulsion, but these effects are difficult to demonstrate for the ancient record. Braided-fluvial channels in the Pennsylvanian South Bar Formation of Atlantic Canada contain sandstone successions up to 6 m thick of sigmoidal cross-beds, plane beds, and antidunes, deposited rapidly at high-flow-stage. These strata are commonly capped by accumulations up to 2.5 m thick of flattened, coalified logs and coal intraclasts (originally peat fragments), many of which are overlain by mudstone laid down in abandoned channels. The logs include lycopsids, calamiteans, tree ferns, pteridosperms and cordaitaleans, inferred to have grown on inactive braided tracts near the channels. A compaction estimate suggests that one log accumulation was originally more than four times its present thickness. Most accumulations are interpreted as stable “transport log jams” formed during floods, although some may have been “unstable jams” stranded on bars during peak-flow recession. Associated with the logs are extrabasinal gravel and intraclasts of mudstone and coal, which suggest that floods in sediment-choked channels undercut banks of gravelly sand capped by mud and forested peat, widened the channels, and toppled riparian vegetation. An estimated blockage ratio of 8% for one accumulation (ratio of the cross-sectional areas of the log jam and host channel) is close to the 10% value considered to cause substantial blockage in some modern rivers. In two instances, a radical change in paleoflow between pre- and post-abandonment channels is consistent with an interpretation that log jams and flood sediment buildup promoted channel-belt avulsion. Although large trees had evolved by Middle to Late Devonian times, it is unlikely that riparian plants occurred in stands that were sufficiently dense to exert a major influence on river dynamics until the Pennsylvanian. Thus, we report some of the earliest evidence for the effects of woody debris on ancient fluvial systems.

High-latitude carbonate rocks that formed in subpolar Paleozoic oceans contain critical information about past climate, but they are neither well documented nor fully understood. Lower and middle Permian limestones that were deposited in such paleoenvironments at 45°S to 55°S along the southeastern margin of Gondwana are now exposed in eastern Australia. Such carbonates constitute a small but important and well-preserved part of the siliciclastic glacigene succession in the Bowen Basin from southern and central Queensland. Cleanest limestones accumulated on topographic highs in the eastern (seaward) parts of the basin that were isolated from siliciclastic sediment input from the western craton. Shallow-water deposits are composed of large eurydesmid bivalves, spiriferid and productid brachiopods, bryozoans, infaunal and epifaunal benthic foraminifers, calcareous sponge spicules, and abundant crinoids in the form of locally cross-bedded rudstones and grainstones. Deeper-water, muddy carbonates are dominated by bryozoans, crinoids, and productids (shells and spines). Deepest-water sediments are argillaceous floatstones or shales containing fenestrate bryozoans, thin-walled productids, and siliceous sponge spicules. When integrated with recent studies of coeval sedimentary rocks along the 2000-km-long paleocontinental margin, a clear pattern of sedimentation emerges wherein deposition took place in similar settings during three discrete periods of deglaciation: late Sakmarian, late Artinskian, and Wordian. All of the carbonates are distinguished by a low-diversity, high-abundance heterozoan biota with no phototrophs and express a recurring deepening-upward stratigraphic motif that is interpreted to reflect rising sea level accompanying glacial meltdown. They also record a strong poleward gradient of increasing ice-rafted debris, increasing skeleton size, decreasing invertebrate diversity, decreasing epifaunal calcareous benthic foraminifers, and reduction in crinoids; glendonites are confined to siliciclastic sediments deposited during glacial periods. Comparison with coeval northern hemisphere carbonates indicates a strong parallelism of facies and depositional systems. This study helps to establish these deposits as a template for a global Paleozoic high-latitude carbonate facies model.

Models of late Paleozoic ice-age climate dynamics have remained enigmatic, in part because preservation of mid- to Late Carboniferous, ice-proximal, Gondwanan glacial deposits is limited to very few Gondwanan regions. As such, detailed sedimentologic and stratigraphic analysis of six formations comprising the well-preserved, mid-Carboniferous to Lower Permian (Namurian or Serpukhovian to late Sakmarian), terrestrial, glacially influenced record from the Tamworth Belt, New South Wales, Australia, provides a unique opportunity to test existing models of late Paleozoic climate, characterize regional glaciation, and resolve the internal pacing of climate during the late Paleozoic ice age. Facies analysis based on twelve logged vertical sections and lateral facies relationships suggests that sediment accumulated in an eastward-draining, volcaniclastically influenced alluvial fan (facies association FA1), fluvial (FA2), and lacustrine (FA3) landsystem. Evidence for proglacial outwash fan (sandar), glaciofluvial, and glaciolacustrine deposition is preserved in the form of texturally diverse diamictite, outsized clasts in fine-grained facies, and rhythmically laminated sandstone and siltstone. The association of these facies, which is termed herein as “distinctly glacial facies” and is taken as direct evidence of glaciation, does not occur through the stratigraphic extent of formations, suggesting that the Tamworth Belt of New South Wales, Australia, was subject to episodic, mountain/valley-type or outlet-type, temperate to subpolar glaciation during the Carboniferous and Early Permian. Climatic shifts and trends occurred on multiple timescales, termed herein “nested cyclicity.” Alternations between distinctly glacial facies and facies that lack evidence of glacial influence, interpreted to record alternating glacial and nonglacial conditions, occurred on timescales on the order of ~ 106 years. The cited age estimates are based on published estimates of glacial interval durations from the region, which in turn reconcile all available radiogenic isotopic data and biostratigraphic zonations. Facies trends within successions recording glacial intervals are interpreted in terms of glacial advance and retreat, which can be estimated to have occurred on timescales shorter than the duration of glacial intervals (shorter-term, sub-106-yr-order timescales) and may include Milankovitch-band cyclicity. These conclusions support the emerging view that the late Paleozoic was characterized by rapid and dynamic climatic shifts on multiple timescales, rather than as one, long protracted event as portrayed by earlier models of Gondwanan glaciation. Furthermore, this study provides an improved understanding of high-latitude climate dynamics and pacing, which may prove useful in constructing improved global models of late Paleozoic climate.

Glendonites, calcite pseudomorphs after ikaite (CaCO3 • 6H2O), feature prominently in fine-grained, glacially influenced Permian marine strata of eastern Australia, which accumulated in a series of extensional basins that occupied polar to temperate latitudes along the southeastern margin of Gondwana. Because ikaite formation in the marine environment requires near-freezing temperatures, high alkalinity, and elevated concentrations of orthophosphate, the presence of glendonites in ancient strata implies a particular array of paleoenvironmental conditions. A petrographic and geochemical study was carried out to assess the veracity of isotopic data from glendonites as proxy indicators of ancient ocean chemistry, sea-floor temperature, and diagenesis. In thin section, glendonites consist of inclusion-zoned, equant to bladed calcite crystals, interpreted as the ikaite replacement phase, enclosed in a matrix of calcite and minor chalcedony and pyrite cements. Carbon and oxygen isotope data show a negative covariance, with δ18O values ranging from −22.5 to +0.3‰ and δ13C values from −27.7 to −4.5‰ V-PDB. Of the calcite phases examined, the ikaite replacement phase is the most enriched in 18O and most depleted in 13C; enclosing cements possess lower δ18O and higher δ13C values and are interpreted to have formed during later stages of burial diagenesis. The δ18O values of the ikaite replacement phase do not correspond to formation with Permian seawater at near-freezing temperatures unless isotopic disequilibrium is assumed. The δ13C values are similar to the carbon isotope composition of bulk organic matter in the host sediment, and suggest that the alkalinity and orthophosphate necessary for ikaite stability were generated in the zone of suboxic to anoxic diagenesis. Results indicate that although δ18O and δ13C values from glendonites are useful for understanding early to late diagenetic processes, they are not ideal proxies for seawater chemistry and temperature.

A comprehensive literature review shows that the magnitude of eustatic fluctuations varied throughout the Carboniferous and Permian and that at least eight distinct phases can be recognized. Facies juxtapositions in carbonate successions and erosional relief in clastic successions indicate that glacioeustatic fluctuations of 20–25 m, and occasionally as much as 60 m, took place throughout the early Mississippian (Tournaisian)—a widely recognized glacial period. Middle Mississippian (mid-Chadian through Holkerian) shallow marine carbonate and clastic successions indicate that eustatic fluctuations were 10–25 m, a decrease that matches well with the paucity of coeval glacial deposits. Late Visean (Asbian through mid-Brigantian) glacioeustatic fluctuations of 10–50 m record the initial phases of ice accumulation in advance of the widespread mid-Carboniferous glacial event. The latest Mississippian–earliest Pennsylvanian (mid-Brigantian through Langsettian) was a time of widespread glaciation, and strata of this age commonly exhibit evidence of glacioeustatic fluctuations of as much as 40–100 m. Although middle Pennsylvanian (Duckmantian through Asturian) glacial deposits are present in eastern Australia, paleovalley depths suggest that coeval glacioeustatic fluctuations were less than 40 m. Glacioeustatic fluctuations of as much as 100–120 m have been widely reported from late Pennsylvanian–earliest Permian (Stephanian through mid-Sakmarian) successions in North America, an increase that corresponds to the growth of large ice sheets across much of Gondwana and the accumulation of ice in the northern hemisphere. Incision and facies juxtaposition in Early–middle Permian (mid-Sakmarian through Kungurian) successions in eastern Australia indicate that glacioeustatic fluctuations of 30–70 m occurred during the waning stages of major glaciation. Erosional relief in paleoequatorial carbonates and the presence of coeval glacial deposits in Australia suggests that eustatic fluctuations of 10–60 m occurred during the final stages of glaciation in the middle to Late Permian (Roadian through Capitanian), but the modest size of most of these fluctuations makes it difficult to isolate the glacioeustatic signature. This review demonstrates that far-field cyclic successions record changing glacial conditions in Gondwana, that the magnitude of glacioeustatic fluctuations was directly related to the volume of glacial ice, that Carboniferous–Permian glacioeustasy was more variable than previously recognized, and that generalizations from short temporal intervals are probably not representative of the late Paleozoic ice age as a whole. Although any attempt to quantify the magnitude of ancient eustatic changes is based on caveats and assumptions, this review incorporates the results of over 100 published papers on the topic in an attempt to minimize the errors inherent in any one study.

Floodplain deposits in semiarid and subhumid settings with erratic rainfall may contain relatively high proportions of sand because of climatically controlled patterns of discharge and vegetation cover. Ancient formations with abundant floodplain sands may record fluvial systems with extreme discharge variability of this type but are difficult to interpret because of the paucity of published modern analogues. The Lower Burdekin and Haughton river alluvial and delta plains of north Queensland, Australia, are used here to illustrate this type of fluvial architecture. The modern Burdekin and Haughton channels have gravelly sand beds and transport a mixed load in the wet season. The channels have low-relief levees that decrease in amplitude downstream across the low-gradient floodplains. Tropical-cyclone activity results in high-magnitude, short-duration, sediment-charged floods that inundate large areas of the coastal lowland. Bankfull discharge is infrequently exceeded (return interval > 25 years) because the channels are enlarged by major cyclone-induced runoff events and between these events flows are too small to modify the channel form significantly. Suspended-sediment loads and the proportions of these that are sand are particularly high when intense rainfall occurs after prolonged drought, when vegetation cover is reduced. As a consequence of these factors, most of the deposition on the levees and floodbasins occurs in very large discharge events with significant suspended sand load. These floods carry a lot of sand out of the channel and efficiently in suspension over the floodplains because of deep inundation. Boreholes drilled in these floodplains encountered sharply bounded and gradationally bounded sand beds that fine upward or show no vertical grain-size trend. These are interbedded with thin silt, clay, and minor gravel beds. Holocene paleochannels make up about 30% of the floodplain area and consist predominantly of coarse sand that is similar to modern channel-bed deposits. The overbank sand, in contrast, is predominantly fine–medium-grained, and beds have distinctly different granulometry from each other and from channel-floor deposits. Efficient sediment partitioning in the runoff and extreme variation in flood magnitude explain variations in sand-bed granulometry. In the alluvial valley and upper delta plain individual sand beds are difficult to correlate between adjacent boreholes even over very short distances (tens of meters). In contrast, on the lower delta plain overbank sands have a more sheet-like geometry. This is explained by the lower-lying landscape, negligible levee development, greater inundation depths, and reduced surface roughness. In addition the channel bodies are thinner and wider and may be connected to overbank sand "wings."

The Burdekin River of northeastern Australia has constructed a substantial delta during the Holocene (delta plain area 1260 km2). The vertical succession through this delta comprises (1) a basal, coarse-grained transgressive lag overlying a continental omission surface, overlain by (2) a mud interval deposited as the coastal region was inundated by the postglacially rising sea, in turn overlain by (3) a generally sharp-based sand unit deposited principally in channel and mouth-bar environments with lesser volumes of floodplain and coastal facies. The Holocene Burdekin Delta was constructed as a series of at least thirteen discrete delta lobes, formed as the river avulsed. Each lobe consists of a composite sand body typically 5–8 m thick. The oldest lobes, formed during the latter stages of the postglacial sea-level rise (10–5.5 kyr BP), are larger than those formed during the highstand (5.5–3 kyr BP), which are in turn larger than those formed during the most recent slight sea-level lowering and stillstand (3–0 kyr BP). Radiocarbon ages and other stratigraphic data indicate that inter-avulsion period has decreased through time coincident with the decrease in delta lobe area. The primary control on Holocene delta architecture appears to have been a change from a pluvial climate known to characterize the region 12–4 kyr BP to the present drier, ENSO-dominated climate. In addition to decreasing the sediment supply via lower rates of chemical weathering, this change may have contributed to the shorter avulsion period by facilitating extreme variability of discharge. More frequent avulsion may also have been facilitated by the lengthening of the delta-plain channels as the system prograded seaward.

Distinguishing the deposits of mouth bars from delta distributary channels in the rock record may not be as straightforward as often portrayed, because mouth-bar deposits can be more variable than usually presumed. Mouth bars with triangular plan-view subaerial geometry are well developed at the mouth of the modern Burdekin River of northeastern Australia. This planform is intermediate between the elongate, lozenge-shaped mouth bars typical of river-dominated deltas and the beach-ridge geometries characteristic of wave-dominated deltas. Surface and shallow-subsurface bar deposits are predominantly moderately sorted, coarse-grained sand, similar to that of adjacent, lower-delta-plain-channel floor. Sedimentary textures are modified at seaward sides of mouth bars by waves into a foreshore of well-sorted fine to medium-grained sand, and mouth bar sands pass distally and laterally into more mud-dominated lithologies. The Holocene section beneath the lower delta plain is dominated by 5–8 m thick, sharp-based bodies of coarse-grained sand, texturally indistinguishable from the modern mouth bar with no vertical grain-size trend, a slight upward-fining trend, or in a few cases a coarsening-upward trend. These sand bodies have low-angle seaward-dipping internal bedding surfaces and are bounded by surfaces of similar attitude. The Holocene Burdekin Delta was and is flood-dominated (rather than strongly wave-influenced, as proposed previously) and prograded by rapid deposition of mouth bars during river floods (most of which last for only a few days). Mouth-bar construction takes place over tens of years. The variable vertical grain-size profiles of mouth-bar deposits suggests formation by both aggradation and progradation, and this is supported by the cross-sectional geometry of mouth-bar clinoform sets imaged geophysically. Once a mouth bar has become emergent and is stabilized by vegetation, a new bar is initiated seaward. In this way, delta "lobes" are constructed over 100s to 1000s of years before being abandoned following an avulsion of the trunk river channel to another part of the delta. Caution is needed in the interpretation of ancient shallow-water deltaic successions, where sharp-based, fining-upward mouth bar deposits may be confused with distributary-channel facies.

The Carnian-Rhaetian Callide Coal Measures are preserved in a small (22.5 km by 8 km), partially fault-bounded basin remnant in east-central Queensland, Australia. The

The Bowen Basin is a Permo-Triassic, back-arc extensional to foreland basin that developed landward of an intermittently active continental volcanic arc associated with the eastern Australian convergent plate margin. The basin has a complex, polyphase tectonic history that began with limited back-arc crustal extension daring the Early Permian. This created a series of north-trending grabens and half grabens which, in the west, accommodated quartz-rich sediment derived locally from surrounding uplifted continental basement. In the east, coeval calc-alkaline, volcanolithic-rich, and volcaniclastic sediment was derived from the active volcanic arc. This early extensional episode was followed by a phase of passive thermal subsidence accompanied by episodic compression during the late Early Permian to early Late Permian, with little contemporaneous volcanism. In the west, quartzose sediment was shed from stable, polymictic, continental basement immediately to the west and south of the basin, whereas volcanolithic-rich sediment that entered the eastern side of the basin during this time was presumably derived from the inactive, and possibly partly submerged, volcanic arc. During the late Late Permian, flexural loading and increased compression occurred along the eastern margin of the Bowen Basin, and renewed volcanism took place in the arc system to the east. Reactivation of this arc led to westward and southward spread of volcanolithic-rich sediment over the entire basin. Accordingly, areas in the west that were earlier receiving quartzose, craton-derived sediment from the west and south were overwhelmed by volcanolithic-rich, arc-derived sediment from the east and north. This transition from quartz-rich, craton-derived sediments to volcanolithic-rich, arc-derived sediments is consistent with the interpreted back-arc extensional to foreland basin origin for the Bowen Basin.