Tidal Sedimentary Structures Research Articles

Revisions to the chronostratigraphic framework of the Upper Jurassic Walloon Coal Measures of the Surat Basin, Australia

The Upper Jurassic Walloon Coal Measures (WCM) in the Surat Basin host the largest coal seam gas (CSG) resource in Australia. Despite this, a poorly defined lithostratigraphic framework hinders the development of reservoir models and groundwater flow simulations. Correlations in the WCM are challenging, owing to the complex arrangement of facies over short distances and the absence of a reliable regional stratigraphic datum. To better correlate the strata, 26 tuff beds were dated using the U–Pb chemical abrasion thermal ionisation mass spectrometry methodology across the Surat Basin CSG fairway. This initially suggested that coal-bearing strata in the basin were diachronous. However, the acquisition of a new date from the Surat Basin has identified a five million year time gap between dated tuffs ~20 m apart. This suggests the presence of an unconformity and that there were two independent episodes of coal accumulation in the basin. Above the unconformity, there are incised valleys with a sedimentary infill that transitions from fluvial- to tidal-influenced facies, as indicated by dinoflagellate cysts and tidal sedimentary structures, including double mud drapes. The cause of the unconformity is likely to be tectonic, as eustatic sea-level was rising during the Kimmeridigian. The marine incursion into the basin is the consequence of a highstand of sea-level during the early Tithonian. The application of the new chronostratigraphic framework should elucidate the evolution of fluviolacustrine systems in the basin and aid in resource prediction. Further dating of tuffs in the basin could refine the stratigraphic framework.

Evolution of the depositional environments of the Jurassic Walloon Coal Measures, Surat Basin, Queensland, Australia

AbstractThe Jurassic Walloon Coal Measures of the Surat Basin in eastern Australia host the continent's most significant coal bed methane resources. Previous studies have interpreted the Walloon Coal Measures within a single depositional facies model encompassing a wholly terrestrial setting. Using a multidisciplinary approach (facies analysis, palynology and wireline logs), the evolution of the Walloon Coal Measures is described within a new chronostratigraphic framework defined by accurate and precise U–Pb tuff dates. Analysis of sedimentary facies indicates that the majority of the Walloon Coal Measures was deposited by relatively small (<300 m wide), low gradient rivers on a poorly‐drained floodplain with numerous small lakes and mires. However, this study also identified some marine‐influenced facies with brackish palynomorphs (notably dinoflagellate cysts) and tidal sedimentary structures. These facies appear to have been deposited in estuaries during times of transgression. The evidence for base level shifts suggests that the coals may not have coevally accumulated with at least some of the thicker sandstones. Palaeogeographic maps for eleven time intervals suggest that rivers drained towards to the south/south‐west and south‐east, as indicated by sandstone percentage and gross unit isopach maps, presumably into proximal estuarine complexes. Marine incursions into the continent probably came from the north and east during times of high eustatic sea level and as precursors to those of the more persistent and extensive transgressions of the Early Cretaceous. A similar multidisciplinary approach should help to elucidate the evolution of other fluviolacustrine systems in other basins and aid in resource prediction.

Facies and architecture of river-dominated to tide-influenced mouth bars in the lower Lajas Formation (Jurassic), Argentina

The Middle Jurassic Lajas Formation in the Neuquen Basin of Argentina has been considered an ideal analog for tide-dominated deposits because of the widespread presence of tidal sedimentary structures and its heterolithic nature. Outcrops of the Lajas in the Los Molles area provide excellent exposures allowing both sedimentary structures and large-scale architectural information to be documented in detail. The extensive event bed stratification that characterizes the delta front and interdistributary bay deposits is interpreted to be the result of river floods because of the sharp base, fining-upward grain size trend, and seaward-directed paleocurrent indicators within each bed. The absence of wave-generated structures precludes a storm wave origin for these beds. Interflood deposits have two forms. The first is fine-grained sandstone and siltstone that is highly bioturbated with no tidal structures and is indicative of an overall river-dominated system. The second is also finer grained than the river flood beds but shows distinctive tidal features, indicative of a tide-influenced system during times when river influence was least. Mouth bars can be classified as purely river-dominated or river-dominated with tidal influence, depending on the type of interflood beds present. Tide-influenced mouth bars tend to be muddier, with more internal flow baffles or barriers and a lower-angle dip than their river-dominated counterparts. This study suggests that heterolithic successions containing pervasive tidal structures need not be tide-dominated because not all tidal structures are of equal importance in environmental interpretations. Their location (in river flood layers versus interflood layers) can be used as a methodology for determining the dominant and subordinate processes responsible for shaping the delta.

Tidal rhythmites in the southern Bouse Formation as evidence for post-Miocene uplift of the lower Colorado River corridor

Abstract Uncertainty over depositional paleoenvironments of the upper Miocene to lower Pliocene Bouse Formation obscures our understanding of the timing and magnitude of regional uplift as well as the conditions and processes that were active during integration and early evolution of the Colorado River (western United States). This paper presents new sedimentologic and quantitative evidence for a strong tidal influence on deposition of the basal carbonate member of the southern Bouse Formation. Lithofacies with tidal sedimentary structures include lime mudstone with reed and grass imprints; heterolithic facies with horizontal, flaser, wavy, and lenticular bedding; and cross-bedded grainstone with sigmoidal bundles, reactivation surfaces, and complex bedding. Systematic alternation of relatively thick and thin layers records a predominantly semidiurnal mixed-tidal depositional environment, and Fourier analysis highlights the cyclic, non-random nature of layer-thickness trends. These observations provide evidence that the southern Bouse Formation accumulated in a pre–Colorado River tide-dominated marine setting at the north end of the Gulf of California. Deposition at sea level requires ∼330 m of uplift in the lower Colorado River and western Colorado Plateau region during the past ∼5.0 m.y.

Sedimentology and ichnology of the fluvial reach to inner estuary of the Ogeechee River estuary, Georgia, USA

Through the integration of sedimentological and ichnological observations, this paper explores the character of sediments deposited across the fluvio-tidal transition zone of the upper microtidal, mixed-energy, sand-dominated Ogeechee River estuary, Georgia, USA. A transect of tidally influenced to fluvial channel-bars and their facies variability is reported. Field and laboratory methods were employed, including observation of physical and biogenic sedimentary structures on the point-bar surfaces and in trenches, collection of grab samples, suction and box coring, grain size and total organic carbon analyses, optical microscopy, core logging, and daylight photography. The data presented in the paper can help in predicting facies changes across the fluvio-tidal transition of sand-dominated fluvio-tidal deposits in the rock record.The lower inner estuary is characterized by medium-fine and fine-medium sand with planar and trough cross-bedding, small-scale ripple lamination, tidal sedimentary structures (flaser and wavy bedding, herringbone cross-stratification), abundant organic debris, and mud rip-up clasts. Bioturbation of the intertidal point bars is low, but cryptobioturbation is locally observed. Upper inner estuary deposits comprise coarse-medium- and medium-coarse-grained sand, and are characterized by faint high-angle planar and trough cross-bedding. Organic debris, mud rip-up clasts, herringbone and current-ripple lamination are rarely observed. Bioturbation is absent to sparse. The fluvio-tidal transition is represented by very-coarse- to coarse-grained sand and granules. Physical sedimentary structures constitute massive, graded planar and trough cross-bedding with abundant plant detritus. Except for rare Siphonichnus- and Lockeia-like traces, bioturbation is absent. The fluvial setting is characterized by coarse-medium sand with unidirectional cross-bedding, current-ripple lamination, and rare organic-rich mud clasts. Bioturbation is absent. Inner estuary and fluvio-tidal transition zones are bounded by supratidal marsh deposits, and may develop a substrate-controlled Glossifungites ichnofacies, comprising Psilonichnus-like burrows. The fluvial reach is surrounded by forested floodplain with crayfish domes and chimneys, forming Camborygma-like traces.

North Atlantic climatic events recorded in Aptian Naskapi Member cores, Scotian Basin

Early Aptian black laminated organic mudstones, including the Selli Level, are recognized over large areas of Tethys and western European basins. This interval was investigated in a 75 m-thick continuously cored section of varicoloured shale in the lower Naskapi Member from the Panuke B-90 well in the Scotian Basin, offshore eastern Canada. This study complements the palaeogeographic range of correlatable Selli black shales and provides information on their relationship to sea-level change and palaeoclimate. Total organic carbon (TOC) was measured on 127 discrete samples, chemical environmental proxies (Th/K, Mn/Ti, K/Ti, Th/Ti, V/Ti) were measured with a portable X-ray fluorescence (pXRF) spectrometer, and colour parameters L*a*b* were measured by spectrophotometer. Several black shale levels are recognized and correlated with similar shales in Europe between the Barremian–Aptian boundary and the Selli Level. The Th/K ratio proxy for hinterland humid or arid climate conditions shows no systematic variation with black shale levels. Several sea-level lowstands are inferred from condensed sandy intervals with some brackish water biota and tidal sedimentary structures. Black shale intervals are found in highstand intervals, with no systematic relationship to inferred transgressions. The formation of black shales is related to palaeoceanographic changes that may be driven by conditions remote from the Scotian Basin.

The potential of trace fossils as tidal indicators in bays and estuaries

Ichnological datasets have been used to infer the presence of tidal processes primarily through the identification of trace-fossil assemblages characteristic of brackish-water settings. However, this limited means of (ichnologically) identifying tidal settings is unsatisfying and the establishment of ichnological–tidal relationships for the purpose of discerning tidal depositional processes is desirable. We suggest that several types of ichnological data can be used to identify tidal influence: (1) ichnological response to rhythmic sedimentation; (2) the presence of tubular tidalites (i.e. biogenic structures infilled by tidally derived sediments); (3) the identification of anisotropic resource exploitation associated with food-rich slack-tide laminations; (4) the identification of tidal-flat deposits through bioturbation intensity and ichnological composition; (5) the recognition of brackish-water trace fossils; and potentially (6) system-scale ichnological distributions (which are presently poorly understood). As with tidal sedimentary structures, the inference of tidal processes from biogenic sedimentary structures should depend on identifying as many of the above characteristics as possible.

Estuarine deposition of a mid-Viséan tetrapod unit, Ducabrook Formation, central Queensland: implications for tetrapod dispersal

At Ducabrook property, central Queensland, the mid-Viséan Ducabrook Formation has yielded a diverse vertebrate fauna (fish and one tetrapod taxon) from a thin unit among siltstone interbedded with sandstone, minor oolitic limestone and conglomerate. Five lithofacies can be distinguished: the Oolitic Facies, distinguished by oolitic limestone and straight parallel ripple crests; the Sandy Facies, composed of plane-laminated and current-rippled sandstones; the Conglomeratic Facies, represented by pebble conglomerate displaying planar cross-bedded megaripples; the Silty Facies of siltstone with abundant calcrete nodules or sand/silt/clay interlaminations; and the Lime-Flake Facies, characterised by abundant locally derived lime flakes. The last includes the fossiliferous tetrapod unit. The Oolitic Facies was deposited in the inner (proximal) and outer (distal) zones of an estuary, based on identification of tidal sedimentary structures (e.g. mud drapes) and estuarine oolitic fabrics; the Lime-Flake Facies and Silty Facies were deposited in the estuary and lower reaches of a river and its surrounds; and the Sandy and Conglomeratic Facies represent braid-river deposits. Overall, the sequence represents intermittent deposition throughout an estuary, both within the tidal channel and the surrounding tidal flats, with additional deposition from the feeder river. The tetrapod unit, from the Lime-Flake Facies, represents a twin-peaked storm-induced flood event onto the tidal channel floor. The vertebrate bones have a shared taphonomic history and have undergone only local transport. The tetrapod and fish were spatially and temporally concurrent, probably in a shallow tidally influenced proximal estuarine habitat experiencing monsoonal conditions. Estuarine adaptations of these vertebrate taxa can explain migration along shallow-water continental shelves between the supercontinents during the Late Devonian and Early Carboniferous.

Late Quaternary incised-valley fill of the Yangtze delta (China): its stratigraphic framework and evolution

A Late Quaternary stratigraphic framework of the Yangtze delta, China, has been established based on the analysis and correlation of over 600 cores. Thirty cores were drilled and analyzed during this study, and the rest were collected from numerous publications. The Late Quaternary stratigraphic framework of the Yangtze delta consists of incised-valley fill and two interfluvial sequences. The incised valley roughly coincides with the modern Yangtze delta. From bottom to top, the incised-valley fill sequence is typically composed of channel, floodplain–estuary, estuary–shallow marine, and modern deltaic facies. The interfluvial sequences occur along the two flanks of the incised-valley fill. On the southern flank, seaward of the maximum-transgression line, the interfluvial sequence is typically composed of marsh–nearshore, shallow marine, and tidal flat facies with predominantly muddy deposits. On the northern flank, the interfluvial sequence is typically composed of barrier–lagoon, tidal sand ridge, and littoral–tidal flat facies with predominantly sandy deposits. The interfluvial sequence landward of the maximum-transgression line on both flanks is composed mainly of lacustrine muddy deposits. The post-glacial fining-upward incised-valley fill sequence was formed by retrogressive aggradation in the lower reach of the Yangtze River, induced by sea-level rise. The upstream extent of the retrogressive aggradation exceeds the reach of flood tidal currents, which explains the lack of marine fossil and tidal sedimentary structures in the channel sand deposits. A huge estuary was formed in the present Yangtze delta area when the post-glacial transgression reached maximum at about 7500 years BP. The shallow marine mud was deposited broadly in the estuary and the maximum flooding surface, which separates the underlying transgressive sequence from overlying regressive sequence, located within the muddy stratum. An erosional surface between the channel sand unit and deltaic sand unit exists at the apical area of the Yangtze delta. The modern Yangtze delta developed after the post-glacial transgression maximum was reached. The delta development was dominated by the abundant fluvial sediment supply. Six sub-deltas with a southward migrating trend have developed.

Tidal sedimentary structures from upper precambrian rocks of the Ming Tombs District, Beijing (Peking), China

The Ming Tombs District is a famous historic and scenic site in the vicinity of Beijing. The Proterozoic strata of this region contain many types of tidal sedimentary structures. This paper deals mainly with tidal or shallow water sedimentary structures from carbonates but some examples are also described from silicilclastic rocks. The structures include burrow-like tube fillings (from the nearly 2 Ga old Changzhougou Formation), herringbone cross stratification, double-crested interference ripple marks, and lenticular and flaser bedding from carbonate rocks of the Gaoyuzhuang Formation. Well developed sedimentary structures in these upper Precambrian rocks indicate that tidal conditions prevailed throughout deposition of most of a 4500 m thick succession. Supratidal, intertidal and subtidal environments have all been recognised. Widespread occurrence of tidal sedimentary structures in carbonate rocks suggests that they were mainly deposited under the influence of physical processes.