Tidal Bundles Research Articles

Quantifying a tide-dominated, wave-, and river-influenced delta in Miocene facies of the Niger Delta basin

ABSTRACT The modern Niger Delta has long been classified as a mixed tide-, wave-, and river-influenced delta. Still, no detailed studies have quantified the relative proportions of formative processes and facies. This work presents the first quantitative estimate of the relative influence of formative processes in Miocene deposits based on core data from the Greater Ughelli, Central Swamp, and Coastal Swamp depositional belts of the Niger Delta basin. Facies analysis of 288.2 m of core from four wells shows approximately 53% tidal facies, 33% fluvial facies, and 14% wave-formed facies, indicating deposition in a prograding tide-dominated, wave-, and river-influenced delta. Cores from the Greater Ughelli and Central Swamp depobelts exhibit coarsening-upwards, prograding deltaic facies successions overlain by fluvial mudstone. Tidal deposits in the Coastal Swamp depobelt show coarsening-upwards prograding deltaic facies successions with well-developed tidal bundles indicating seasonal deposition. The basal part of these facies successions also reveals repeated floods characterized by slump and load structures and dewatering features. Delta-plain and delta-front–prodeltaic facies associations are identified based on physical sedimentary and biological structures. The delta-plain facies association consists of weakly bioturbated mudstone, fissile mudstone, and coarse-pebbly stratified sandstone facies with sparse trace fossils. The delta-front–prodeltaic facies association contains muddy and sandy heteroliths, stratified, medium and coarse-grained, cross-bedded sandstone, and convoluted mudstone facies. The facies vary but characteristically contain trace-fossil assemblages of the recently proposed Rosselia and Phycosiphon Ichnofacies, indicating delta-front and prodeltaic settings, respectively. Variability in the facies is determined by the relative influence of hydrodynamic processes (tide, wave, and river), variations in physicochemical stress, and the episodic character of deposition. In addition, based on the relative influence of each hydrodynamic processes, the facies differ through the successions, sometimes subtly.

Significance of a Mesoproterozoic tide-reworked fan delta – tidal flat transition: A transgressive-regressive model

Records of tide-reworked fan delta facies models are rare in literature, attributed to their lower abundances due to complex sediment distribution pattern by two exclusive end-member flows, viz., a seaward directed subaerial to subaqueous debris flow, and dominant tidal current system interfering with and reworking the debris flow. Lack of appropriate analogues of tide-reworked fan deltas makes the ancient examples more significant. The analysis of such rare tide-reworked fan deltas from deep-time, e.g., Mesoproterozoic, turns out to be unique due to the gap in clear understanding of the alluvial-fluvial vs marine processes in non-vegetated land parts. The lower part of the Mesoproterozoic Rajgarh Formation, Lalsot Basin, North Delhi Fold Belt, Aravalli Craton in NW India, provides a rare record of a tide-reworked fan delta depositional system. Sedimentary facies analysis reveals eleven lithofacies grouped under three major facies associations, viz., (i) gravel-rich conglomerate facies association, characterized by stacked debris flow deposits forming a subaerial alluvial fan, representing the delta topset component, followed downslope by (ii) pebbly, cross-stratifed sandstone facies association, characterized by reworking of the subaqueously emplaced debris flows by ebb-tidal currents, to produce the mouth bar and the delta front depositional systems, and finally, (iii) sandstone-mudstone heterolithic facies association, characterized by abundant tidal signatures in pebble-free thin-bedded sandstone-mudstone heteroliths with tidal bundles, herringbone cross-strata and wave ripples, characterizing a stable platformal subtidal-intertidal flat depositional system. The lower-middle part of the succession records an aggradational stratal stacking pattern of the subaerial alluvial fan changing to progradational stratal stacking of the laterally accreted debris-rich tide-led clinoforms producing the delta topset – mouth bar – delta front transiton of a tide-reworked fan-delta under successive regressive conditions, representing syn-rift deposition near the basin margin. A retrogradational stratal stacking pattern overlies the fan-delta succession, and signifies a transgression by landward encroaching tidal flat system over the fan-delta system during post-rift phase in a stable platformal setup, where debris supply is ceased. A regressive-transgressive model characterizing the transition from a fan-delta to tidal flat depositional systems portrays fluctuations in the accommodation conditons in response to complex interplay of basin tectonics and relative sea level changes in the Mesoproterozoic riftogenic Lalsot Basin.

New stratigraphic and paleoenvironmental constraints on the Paleogene paleogeography of Western Amazonia

The rise of the Andes and the associated propagation of the retroarc foreland basin during the Mesozoic Cenozoic in western South America shaped the paleogeography and paleoenvironmental settings of Western Amazonia. Much attention has been paid to the Neogene evolution of the Amazonian Basin, but few studies have investigated in detail the paleoenvironments of Western Amazonia during the Paleogene. We present a multi-proxy study that includes new biostratigraphic and paleontologic data, the interpretation of depositional environments and zircon U–Pb data from the Upper Cretaceous-Paleogene sedimentary sequence exposed in the Huallaga Basin (northern Peru). The biostratigraphic dating suggests that the lower part of the sequence is Maastrichtian in age. The maximum depositional age and maximum likelihood age according to the U–Pb zircon dating of Paleogene sedimentary rocks indicate Lutetian to Bartonian ages (from 43.5 ± 0.64 Ma to 37.6 ± 0.85 Ma). These results reveal a hiatus in the depositional record during Paleocene time. Two depositional systems can be distinguished: a lacustrine system composed of red mudrocks interbedded with thick sandstone layers and carbonate beds, and a siliciclastic tide-dominated system composed of fine-to medium-grained sandstones associated with tidal bundles, reactivation surfaces and heterolithic stratifications. However, the carbon and oxygen stable isotope values in carbonates tend to characterize a freshwater system, with a transition to brackish conditions toward the upper part of the section (Bartonian), thereby suggesting the presence of an estuary system. Finally, we suggest that the Bartonian shallow marine incursion recorded in the Huallaga Basin occurred from the north through the Caribbean Sea, and that it might have played a role in regional biodiversity patterns in the Paleogene.

Constraints on Moon's Orbit 3.2 Billion Years Ago From Tidal Bundle Data

AbstractThe angular momentum of the Earth‐Moon system was initially dominated by Earth's rotation with a short solar day of around 5 hr duration. Since then, Earth gradually transferred angular momentum through tidal friction to the orbit of the Moon, resulting in an increasing orbital radius and a deceleration of Earth's rotation. Geologic observations of tidal deposits can be used to verify and constrain models of lunar orbital evolution. In this work we reexamine the oldest tidal record suitable for analysis from the Moodies Group, South Africa, with an age of 3.22 billion years. Time frequency analysis of the series of thicknesses of the sandstone‐shale layers yields a periodicity of 15.0 layers, taking into account the possibility of missing laminae. Assuming a mixed tidal system, the duration of two neap‐spring‐neap cycles was 30.0 lunar days for dominant semidiurnal or 30.0 sidereal days for dominant diurnal tides. We derive the relationship between this observation and the past Earth‐Moon distance and re‐visit related published work. We find that the Earth‐Moon distance 3.2 billion years ago was about 70% of today's value. The Archean solar day was around 13 hr long. The ratio of solar to lunar tide‐raising torque controls the leakage of angular momentum from the Earth‐Moon system, but deviation from the assumed ratio of 0.211 results in only moderate changes. A duration of a postulated 21‐hr atmospheric resonance shorter than 200 million years would be consistent with our observation; it would significantly alter the Earth‐Moon distance.

Reassessing evidence of Moon–Earth dynamics from tidal bundles at 3.2 Ga (Moodies Group, Barberton Greenstone Belt, South Africa)

AbstractPast orbital parameters of the Moon are difficult to reconstruct from geological records because relevant data sets of tidal strata are scarce or incomplete. The sole Archean data point is from the Moodies Group (ca 3.22 Ga) of the Barberton Greenstone Belt, South Africa. From the time‐series analysis of tidal bundles from a well‐exposed subaqueous sand wave of this unit, Eriksson and Simpson (Geology, 28, 831) suggested that the Moon’s anomalistic month at 3.2 Ga was closer to 20 days than the present 27.5 days. This is in apparent accordance with models of orbital mechanics which place the Archean Moon in a closer orbit with a shorter period, resulting in stronger tidal action. Although this study’s detailed geological mapping and section measuring of the site confirmed that the sandstone bed in question is likely a migrating dune, the presence of angular mud clasts, channel‐margin slumps, laterally aggrading channel fills and bidirectional paleocurrents in overlying and underlying beds suggests that this bedform was likely located in a nearshore channel near lower‐intertidal flats and subtidal estuarine bars; it thus carries risk of incomplete preservation. Repeated measurements of foreset thicknesses along the published traverse, measured perpendicular to bedding, failed to show consistent spectral peaks. Larger data sets acquired along traverses measured parallel to bedding along the 20.5 m wide exposure are affected by minor faulting, uneven outcrop weathering, changing illumination, weather, observer bias and show a low reproducibility. The most robust measurements herein confirm the periodicity peak of approximately 14 in the original data of Eriksson and Simpson (Geology, 28, 831). Because laminae may have been eroded, the measurements may represent a lower bound of about 28 lunar days per synodic month. This estimate agrees well with Earth–Moon dynamic models which consider the conservation of angular momentum and place the Archaean Moon in a lower orbit around a faster‐spinning Earth.

Unravelling depositional setting, age and provenance of the Simlipal volcano-sedimentary complex, Singhbhum craton: Evidence for Hadean crust and Mesoarchean marginal marine sedimentation

The Singhbhum craton of eastern India preserves an extensive record of basin formation spanning the Paleoarchean to Neoarchean. Although spatially extensive and well exposed, the absolute age, depositional environment, and regional correlations of many of the purportedly Archean basins of this craton remain poorly resolved. We present a detailed lithostratigraphic analysis of siliciclastic strata in the (lower) Simlipal volcano-sedimentary succession and report the first detrital zircon U-Pb ages from this succession. The studied section is dominated by fine- to medium-grained, quartz-rich sandstones, which preserve herringbone stratification, tidal bundles, soft sediment deformation structures along with ubiquitous trough cross-stratification. Petrographic study confirms these sandstones as quartz arenites and reveal their high textural and mineralogical maturity. These features are consistent with deposition of the lower siliciclastic succession of the Simlipal volcano-sedimentary complex within a tidally-influenced marginal marine setting. The new detrital zircon data support a ~3.08 Ga maximum depositional age for the succession and reveal a provenance with age peaks at ca. 3.55–3.45 Ga, 3.38–3.24 Ga, and 3.10–3.08 Ga. These ages likely correspond to local basement sources including the Older Metamorphic Tonalite Gneisses, the Singhbhum Granitoid Complex, and the Mayurbhanj Granite Suite. Two detrital zircons from our dataset have concordant ages of ~4.02 Ga and ~4.03 Ga. They represent the first Hadean detrital zircons recovered from any Archean strata in the Singhbhum craton, documenting the involvement of Hadean crust in the early development of the craton. The detrital zircons show prominent Pb-loss at ~1.2–1.0 Ga that exemplifies the tectonothermal imprint of a late Mesoproterozoic to early Neoproterozoic orogeny (likely related to the assembly of Rodinia) on the Singhbhum craton. Our findings further support the interpretation that the lower siliciclastic strata in the Simlipal succession are the lateral facies equivalents of alluvial fan deposits at the base of the Dhanjori Formation, exposed to the north.

Recognizing tide- and wave-dominated compound deltaic clinothems in the rock record

Abstract Many modern deltas exhibit a compound geometry that consists of a shoreline clinoform and a larger subaqueous clinoform connected through a subaqueous platform. Despite the ubiquity of compound clinoforms in modern deltas, very few examples have been documented from the ancient sedimentary record. We present recognition criteria for shelf compound-clinoform systems in both tide- and wave-dominated deltas by integration of ancient and modern examples from multiple types of data. The compound clinothem can be identified by using a combination of: (1) the three-dimensional (3-D) configuration identified in bathymetric or seismic data, (2) bipartite stacked regressive units, consisting of a lower muddy coarsening-to-fining-upward (CUFU) or coarsening-upward (CU) unit (30–100 m thick) and an overlying sandier CU unit (5–30 m thick) (together they represent the subaqueous and shoreline clinoform pair), and (3) distinct facies described herein, though both types of delta have highly bioturbated mudstone and siltstone bottomsets. Tide-dominated deltas have muddy foresets with tidal scours containing tidal rhythmites or inclined heterolithic strata in the subaqueous clinothem overlain by river and tidal deposits of the shoreline clinothem. Wave-dominated deltas show mainly wave-enhanced sediment-gravity-flow (WSGF) beds and some thin hummocky/swaley cross-stratified (HCS/SCS) sandstones toward the top in the subaqueous muddy foreset, and upward-thickening HCS/SCS and trough/planar cross-bedded sandstones interbedded with siltstones in the shoreline clinothem. The subaqueous platform, which links the clinoform couplet, shows evidence of frequent tidal or wave reworking and redeposition. The platform in tide-dominated deltas is characterized by tide-generated heterolithic strata (e.g., bidirectional current-rippled and cross-stratified sandstones, spring and neap tidal bundles, tidal rhythmites) with occasional storm-wave–influenced strata. In contrast, the wave-dominated platform comprises small-scale swales with scours and mud clasts and some WSGF deposits. The proposed criteria can aid in the recognition of compound deltaic clinothems in other basins, particularly those with limited amounts and/or types of data.

Pterosaur track assemblages from the Upper Jurassic (lower Kimmeridgian) intertidal deposits of Poland: Linking ichnites to potential trackmakers

Two distinct tetrapod track assemblages, dominated by pterosaur traces, are reported from Upper Jurassic (lower Kimmeridgian, Hypselocyclum Zone) tidal flat carbonate deposits exposed in Wierzbica Quarry, 20 km south of Radom, Poland. The pterosaur tracks, tentatively assigned to Pteraichnus isp. are well preserved as a positive hyporelief in intertidal facies. Some are preserved with anatomical details (e.g., skin, claw or digital pad impressions) and quality sufficient to make preliminary ichnotaxonomic assignment. Nearly all collected specimens are larger than most other pterosaurian ichnites of the Late Jurassic age, thus adding to the growing diversity of pterosaur traces known from this time period. Morphometrical and anatomical analyses show that ctenochasmatoids or possibly non-pterydactyloid monofenestratans or rhamphorhynchids were most likely the trackmakers. Anatomical comparisons give new insights into the morphology of the pes of pterydactyloids and the most closely related non-pterodactyloids which may be correlated with a niche expansion into marginal marine and lacustrine environments by Middle and Late Jurassic pterosaurs. The palaeoenvironmental interpretation as tidal flat is confirmed by presence of vertically accreted tidal bundles, each representing deposition in one tidal cycle. Most likely then, this was one of the environments frequented by these pterosaurs and other small tetrapods. The wider palaeoecological significance of the tracks is evaluated in the context of other similar reports from the Late Jurassic of Europe, Africa and North America.

Tidal bar cyclicity record in the Lower Permian: The Rio Bonito Formation, Paraná Basin, southern Brazil

Tidal bars register gravitational interactions between the Earth, Moon, and Sun and allow inferences about astronomical positioning through the cyclic variation of sandstone layer thickness throughout depositional events. Measurements of sandstone layers thickness in a tidal bar of the Rio Bonito Formation (Paraná Basin, southern Brazil) and further spectral analysis allowed the definition of the tide patterns imprinted on rock layers. The study was based on a remarkable tidal bar outcrop located in the Candiota paleovalley in the southern basin, Candiota town, Brazil, with sedimentary characteristics that suggest to a tidally dominated estuary depositional environment. The tidal bar shows a medium- to large-scale cross-stratification, reactivation surfaces, bidirectional structures, and tidal bundles. The spectral analysis resulted in a significant frequency peak (0.0329) which corresponds to a period of 30.45 layers per cycle. Six of these cycles are recognizable in the tidal bar by its cyclic thickening-thinning of layers, that range from 1.5 to 11 cm. This cyclic pattern is interpreted as being produced by the neap-spring tide cycle. Our study also allows us to infer that the south Paraná Basin Permian tide had a semi-diurnal pattern, with a neap-spring tide period of 14.9 days. Comparison with previous studies points to small changes in the duration of the neap-spring tide cycle in the last 900 Ma (15.2 days in the Cambrian, 14.9 days in the early Permian and 14.7 days today), explained by the distance and acceleration of the movement of the Moon's revolution and decrease in the speed of rotation of the Earth.

Cambrian wave‐dominated tidal‐flat deposits, central Wisconsin, USA

AbstractIn central Wisconsin, Cambrian strata of the Elk Mound Group record deposition on open‐coast, wave‐dominated tidal flats. Mature, medium‐grained quartz arenite is dominated by parallel‐bedding with upper‐flow regime parallel‐lamination, deposited during high‐energy storms that also produced three‐dimensional bedforms on the flats. Abundant wave ripples were produced as storms waned or during fair weather, in water depths ≤2 m. Indicators of variably shallow water (washout structures and stranded cnidarian medusae) and subaerial exposure (adhesion marks, rain‐drop impressions and desiccation cracks, including cracked medusae) are abundant. Parallel‐bedded facies preserve a Cruziana ichnofacies, similar to other Cambrian tidal‐flat deposits. Flats were dissected by small, mainly straight channels, the floors of which were grazed intensely by molluscs. Most channels were ephemeral but some developed low levées, point bars and cut‐banks, probably reflecting stabilization by abundant microbial mats and biofilms. Channels were filled with trough cross‐bedding that is interpreted to have been produced mainly during storm runoff. The strata resemble deposits of open‐coast, wave‐dominated tidal flats on the east coast of India and west coast of Korea. Ancient wave‐dominated and open‐coast tidal flats documented to date appear to have been limited to mud‐rich strata with ‘classic’ tidal indicators such as flaser bedding and tidal bundles. The Cambrian (Miaolingian to early Furongian) Elk Mound Group demonstrates that sandy, wave‐dominated tidal flats also can be recognized in the stratigraphic record.

Characterization of middle Eocene tide-influenced delta: A study from core samples of Hazad Member, Ankleshwar Formation, South Cambay Basin, India

The Hazad Member (Middle Eocene) of the Ankleswar Formation in Cambay Basin, India, is traditionally reported as deltaic system. Present work documents three major facies associations, namely, (i) sandstone-rich upper delta plain (FA-1) deposits, (ii) sandstone-mudstone heterolithic lower delta plain–delta front (FA-2) deposits, and (iii) shale-dominated prodelta (FA-3) deposits, in an overall coarsening-up to fining-up succession. Tidalites are well preserved in FA-2 and are represented by laterally accreted tidal bundles, tidal beddings and vertically accreted tidal rhythmites, described from drill core samples in this communication. Laterally accreted tidal bundles with reactivation surfaces in sand-dominated heterolithic units indicate time-velocity asymmetry in subtidal condition. Tidal beddings and tidal rhythmites in mud-dominated heterolithic units, associated with asymmetric/symmetric ripple forms and desiccation cracks, indicate periodic subaerial emergence in intertidal flat depositional setting. Systematic analysis of the architecture of the tidalites in different parts of the basin signifies rapid shift in sedimentation from subtidal to intertidal flat within the lower delta plain. Transitions from prodeltaic to tidally (subtidal-intertidal) affected delta front to lower delta plain and fluvial-dominated upper delta plain depositional systems attest to high frequency transgressive-regressive cycles in response to changing accommodation, as a result of sea level fluctuations and basinal tectonisms in the Cambay Basin.

Multiscale Gilbert-type delta lobe architecture and heterogeneities: The case of the Roda Sandstone Member

ABSTRACT The Roda Sandstone Member (Lower Eocene, Tremp-Graus Basin, Spanish Pyrenees) is interpreted as a well-exposed multiscale Gilbert-type delta. It is formed by multiple prograding lobate-shaped sandstone bodies up to 5 km (3 mi) long and 2–3 km (1–2 mi) wide, each constructed by a number of smaller scale (hunderds of meters) lobes that stack in a compensational mode responding to relative base level changes. In general, the proximal part of each lobe is dominated by trough cross stratification, the medial part by impressive clinoforms, and the distal part by more tabular cross stratification. Well-developed tidal bundles occur abundantly in delta lobe-front attached and detached tidal bars; the latter are up to 5 km (3 mi) long and 2 km (1 mi) wide. Cemented layers cover both the individual lobes as well as the lobate-shaped sandstone bodies. The three-dimensional (3-D) architecture of small-scale (decimeter to meter) heterogeneities at lithofacies scale formed by millimeter- to centimeter-thick mud layers in the tidal bars have been studied to better understand hydrocarbon flow through heterolithic tide-dominated successions. The Roda Sandstone has been used as an analog to many oil and gas fields with a particular focus on 3-D lobe geometry, compartmentalization, stacking patterns, and associated correlation concepts.

Shoreface to estuarine sedimentation in the late Paleocene Matanomadh Formation, Kachchh, western India

Late Paleocene sedimentation in the pericratonic Kachchh Basin marks the initial marine transgression during the Cenozoic era. A 17m thick sandstone-dominated succession, known as the clastic member (CM) of the Matanomadh Formation (MF), is exposed sporadically in the basin. Three facies associations are reconstructed in the succession in three different sections. Facies association-1 contains matrix-supported pebbly conglomerate facies, horizontally-laminated sandstone-mudstone alternation facies, hummocky- and swaley cross-bedded sandstone facies, wave-rippled sandstone facies and climbing ripple cross-laminated sandstone facies. This facies association developed between shoreface and foreshore zone under the influence of storms on a barrier ridge. Facies association-2 contains sigmoidal cross-bedded sandstone facies, sandstone-mudstone alternation facies, flaser-bedded sandstone facies, herringbone cross-bedded sandstone facies and tangential cross-bedded sandstone facies. This facies association possessing tidal bundles and herringbone cross-beds developed on a tidal flat with strong tidal influence. Facies association-3 comprises pebbly sandstone facies, horizontally-bedded sandstone facies, tangential cross-bedded sandstone facies exhibiting reactivation surfaces and tabular cross-bedded sandstone facies. This facies association represents sedimentation in a river-dominated estuary and reactivation surfaces and herringbone cross-beds indicating tidal influence. The bipolar paleocurrent pattern changes to unipolar up-section because of the change in the depositional currents from tidal to fluvial. The sedimentation took place in an open coast similar to the Korean coast. The presence of neap-spring tidal rhythmites further suggests that a semidiurnal system similar to the modern day Indian Ocean was responsible for the sedimentation. Here, the overall sequence developed during the transgressive phase where barrier ridge succession is succeeded by the tidal flat succession and the latter, in turn, is succeeded by the estuarine succession. This study resolves the most debated issue of initial marine transgression in the Kachchh Basin during the Cenozoic.

The discovery and significance of a sedimentary hiatus within the Carboniferous Taiyuan Formation, northeastern Ordos Basin, China: Discussion

The paper by Jiang et al. (2012) documented a hiatus and overlying incised-valley fill between the Lower Pennsylvanian Taiyuan Formation (Ct1) and the Upper Pennsylvanian Taiyuan Formation (Ct2). Herein, we provide credible evidence suggesting that the incised-valley fill mentioned by Jiang et al. (2012) is a barrier island. Our work also indicates that the contact between Ct1 and Ct2 is continuous and without hiatus. The Paleozoic Ordos Basin has two stages of sedimentary environments: the early Paleozoic marine carbonate deposition and the Late Paleozoic (Carboniferous to Permian) transformation from paralic to terrestrial. Most scholars believe that the Carboniferous Taiyuan Formation is a barrier–lagoon–tidal flat system (Zhao and Liu, 1990; Hao et al., 2007; Luo et al., 2011) that formed during the relatively large-scale transgression at the North China block. The predominant sedimentary environment of the Taiyuan Formation is the barrier shoreline and has been documented as a barrier island, lagoon, and swamp (Chen et al., 2001; Yang et al., 2005; Hao et al., 2007; Luo et al., 2011). In particular, Jiang et al. (2012) confirmed the facies of Ct1 as a barrier–tidal system and interpreted the interval of Ct2 as a northeast–southwest-trending incised-valley fill and further claimed a hiatus between the Ct1 and Ct2 units. Well D23 locates in the incised-valley fill, as mentioned in figure 14 of Jiang et al. (2012). Its core of the lower Ct2 (above the bottom coal of D23; Figure 1) suggests that it is tidal in origin based on the following sedimentary structures: lens (starved ripples), ripples, and flaser beddings; herringbone bedding; and tidal bundles (couplet) (Figure 1). The fining-upward succession with erosive-based structures of tidal origin is a tidal inlet (Figure 1C, H). The coarsening-upward succession with parallel …

Process-Driven Architectural Variability In Mouth-Bar Deposits: A Case Study From A Mixed-Process Mouth-Bar Complex, Drumheller, Alberta, Canada

Abstract Mouth bars can develop in locations where fluvial distributary channels deliver coarse sediment to the shoreline. As a consequence, they are typically considered, by default, to be fluvially dominated. However, depending upon the relative balance of fluvial, wave, and tidal energies at any given shoreline location, the preserved sedimentary structures, geometry, and internal architecture of the mouth bar will reflect the relative balance of these energies. Hence, mouth bars can be fluvial-, wave-, or tide-dominated and can also exhibit sedimentary structures formed by more than one of these processes. The ability to recognize, and to predict the architecture of these mixed-process systems is important for accurately interpreting the ancient record and has implications for hydrocarbon exploration and exploitation strategies. A detailed description and interpretation is given herein of a mixed-process mouth-bar complex which forms part of an asymmetrical delta system from the Campanian of Alberta, Canada. This mouth-bar complex is interpreted as a mixed-influence, wave-dominated system that transitions laterally into a mixed-influence, fluvially dominated system. The mouth-bar complex represents a single progradational phase of deposition, is up to 8 m thick, and can be traced over an area of approximately 60 km2 in both outcrop and the subsurface. It comprises multiple, kilometer-scale lobe geometries (elements, element sets, and element complexes) with internal dipping, mudstone- and carbonaceous-draped clinoform surfaces at two scales (intra-element and inter-element set). The lobe geometries are oriented subparallel to the coastline. The influence of tides on the system is illustrated by tidal bundle sequences in intra-element mouth-bar clinoform bedsets, networks of tidally overdeepened, mudstone-filled distributary channels, and the development of significant thicknesses (up to 3.5 m) of swash-zone deposits at the tops of the wave-dominated mouth-bar successions. Depositional architectural units of the mouth-bar complex are estimated to have been generated by autogenic events from daily (tidal couplets), through decadal (elements) to centennial (element sets) and millennial (element complex and element complex set) time frames. A Holocene partial analog for these types of depositional systems is suggested from the Gulf of Carpentaria, Australia. Geometries, aspect ratios, and facies relationships of these mixed-process mouth-bar complexes vary significantly from the archetypal fluvial-dominated mouth bars described in the published literature.

Morphologic and hydrodynamic controls on the occurrence of tidal bundles in an open-coast macrotidal environment, northern Gyeonggi Bay, west coast of Korea

Tidal dunes with well-defined rhythmic tidal bundles are documented from the lower intertidal zone of an open-coast macrotidal environment in Gyeonggi Bay, Korea. Based on combined morphologic, sedimentologic and hydrodynamic datasets, this study aims to characterize the factors that govern the temporal and spatial variability of tidal bundles in a non-barred, unconfined macrotidal environment. The tidal dunes are flood-asymmetric and of longer wavelength (10–20m) with small ebb caps on the upper bank, and symmetric to slightly ebb-asymmetric and of shorter wavelength (5–10m) with larger ebb caps on the lower bank. The upper-bank dunes are characterized by more steeply dipping flood-directed planar cross-beds and thinner mud drapes than the lower-bank dunes. Each tidal bundle consists of a single mud drape that is stratified to cross-stratified, rich in silt and very fine sand. It overlies ebb-directed ripples and represents dynamic mud deposition during the ebb tidal phase. The presence of strong rotary currents (up to 0.25m/s) and low suspended-sediment concentration of flood currents prevent deposition of mud drapes during the high-tide slack-water period. The distinct asymmetry in the water elevation at which the velocity peaks during the ebb and flood phases results in the preferential preservation of flood-directed cross-beds in the lower intertidal zone, where the ebb current – although stronger than the flood currents – is of shorter duration and hence unable to reverse the dune profile. The pronounced time–velocity asymmetry at the higher elevation combined with the distinct velocity peak asymmetry leads to a better preservation of hierarchical tidal cycles in the upper-bank dunes. The present study suggests that the persistent occurrence of single, stratified to cross-stratified mud drapes, which reflect dynamic mud deposition during the ebb phase, and the dominance of flood-directed cross-beds are diagnostic features of tidal bundles in the intertidal zone of unbarred, open-coast macrotidal environments. A proposed model for mud drape deposition provides a new perspective on the origin of tidal bundles together with useful criteria for reconstructing the paleo-depositional setting.

Deposition of the Upper Rewa Sandstone Formation of Proterozoic Rewa Group of the Vindhyan Basin, M.P., India: A Reappraisal

Abstract The Upper Rewa Sandstone Formation of the Rewa Group in the Vindhyan basin is composed mainly of medium to very fine grained, iron pigmented arenaceous rocks variously interpreted as fluvial, marine or continental deposits. The Upper Rewa Sandstone Formation consists of channelized, laterally shifting sand bodies comprising 1-2 m thick fining upward (FU) sharply/erosionally based cycles. Each shoaling bar cycle is characterized by presence of large scale planar and trough cross-bedding, horizontal bedding showing primary parting lineation, wave and current ripples, herringbone cross-bedding and tidal bundles with double mud-drapes and indicates marine environment of deposition and rule out the possibility of continental sedimentation. However, channelized nature of sand bodies composed of shoaling bar cycles with signatures of wave modification and exposure in the lower part of the succession and well developed horizontally bedded lithofacies showing primary parting lineation and well sorted character of sandstones in the upper part of the succession may imply deposition under subtidal to intertidal setting in estuarine to bordering beach environments. The palaeocurrent study shows polymodal to bimodal and unimodal palaeocurrent patterns. The dominant polymodal palaeocurrent patterns with temporal trends directed towards NW, N and SW also corroborate marine origin and sediment dispersal under combined action of wave and currents. Petrographically, sandstone is quartzarenite and consists of mostly monocrystalline quartz, feldspar, mica, rock-fragments and heavy minerals such as hypersthene, zircon, hornblende, tourmaline, rutile, augite, kyanite and andalusite indicating sediment contribution from mixed sedimentary/metamorphic and igneous source terrain. Qm-F-Lt and Qt- F-Lt plots reveal that the Upper Rewa Sandstone Formation shows continental block province with stable craton (C) and in uplifted basement (B) where C>B.

Record of Permian Tethyan transgression in eastern India: A reappraisal of the Barren Measures Formation, West Bokaro Coalfield

The Barren Measures Formation (middle Permian, ∼271–260 Ma), the non-coaliferous lithounit sandwitched between two major coal-bearing formations in the Indian Lower Gondwana succession, was earlier interpreted as continental fluvio-lacustrine deposits. The present contribution documents sedimentary attributes of marginal marine tide–wave interference from the Barren Measures Formation of eastern peninsular India, exposed along the Bokaro River section, West Bokaro Coalfield, Jharkhand. Tidalites, including various tidal bundle sequences with frequent reactivation surfaces (velocity asymmetry) and single/double mud drapes (pause planes), systematic arrangement of tidal beddings (flaser, wavy, lenticular) and tidal rhythmites with alternate sand-dominated and mud-dominated plane-laminated units, manifest sedimentation by open marine spring–neap–spring tidal cycles under diurnal inequalities in a semi-diurnal tidal system. The architecture of tidalites attests to sedimentation in shallow subtidal to intertidal flat facies, affected by intermittent strong to week reworking by open marine waves/storms. Wave reworking is manifested by wave ripples, combined-flow ripples and wave-generated tidal bundles. Their coexistence and gradation with tidalites indicate low-energy wave/storm interference with tidal currents in a sheltered, tide-dominated estuary, especially on tidal flats along estuary channel banks. Overall fining-up facies sequence, upward increase of prodeltaic mud over tide–wave led sediments, signify a sustained transgressive phase onlaping the estuary system in eastern peninsular India during middle Permian (Guadalupian).

Stratigraphic architecture of a tide‐influenced shelf‐edge delta, Upper Cretaceous Dorotea Formation, Magallanes‐Austral Basin, Patagonia

ABSTRACTThe Magallanes‐Austral Basin of Patagonian Chile and Argentina is a retroforeland basin associated with Late Cretaceous–Neogene uplift of the southern Andes. The Upper Cretaceous Dorotea Formation records the final phase of deposition in the Late Cretaceous foredeep, marked by southward progradation of a shelf‐edge delta and slope. In the Ultima Esperanza district of Chile, laterally extensive, depositional dip‐oriented exposures of the Dorotea Formation contain upper slope, delta‐front and delta plain facies. Marginal and shallow marine deposits include abundant indicators of tidal activity including inclined heterolithic stratification, heterolithic to sandy tidal bundles, bidirectional palaeocurrent indicators, flaser/wavy/lenticular bedding, heterolithic tidal flat deposits and a relatively low‐diversity Skolithos ichnofacies assemblage in delta plain facies. This work documents the stratigraphic architecture and evolution of the shelf‐edge delta that was significantly influenced by strong tidal activity. Sediment was delivered to a large slump scar on the shelf‐edge by a basin‐axial fluvial system, where it was significantly reworked and redistributed by tides. A network of tidally modified mouth bars and tidal channels comprised the outermost reaches of the delta complex, which constituted the staging area and initiation point for gravity flows that dominated the slope and deeper basin. The extent of tidal influence on the Dorotea delta also has important implications for Magallanes‐Austral Basin palaeogeography. Prior studies establish axial foreland palaeodrainage, long‐term southward palaeotransport directions and large‐scale topographic confinement within the foredeep throughout Late Cretaceous time. Abundant tidal features in Dorotea Formation strata further suggest that the Magallanes‐Austral Basin was significantly embayed. This ‘Magallanes embayment’ was formed by an impinging fold–thrust belt to the west and a broad forebulge region to the east.

Ichnology and Depositional Environment of the Cambrian Nagaur Sandstone (Nagaur Group) Along the Dulmera Section, Bikaner-Nagaur Basin, Rajasthan

The Lower Cambrian Nagaur Sandstone (Marwar Supergroup) has yielded trace fossils Treptichnus, Cruziana, serially repeated Rusophycus, Diplichnites, Monomorphichnus, Bergaueria, arthropod swimming traces and leap frogging marks of Cruziana ichnofacies. This ichnofossils assemblage is dominantly preserved in fine to medium grained red sandstone beds of the Mohra Member (Nagaur Sandstone). The presence of graded rip-up clasts, current ripples, dune cross-stratification with mud drapes and tidal bundles indicates a subtidal paleoenvironment for the deposition of Nagaur Sandstone Formation, which is corroborated by the Cruziana ichnofacies trace fossil assemblage.