Tide-dominated Estuarine Systems Research Articles

Ichnological indicators of physico-chemical stresses in wave- to tide-dominated Miocene shallow marine environments (Argentine Patagonia)

An integrated analysis of ichnological and sedimentological features in ancient successions provides a robust dataset of high-resolution interpretations of environmental parameters, encompassing both depositional and ecological aspects. By characterising discrete and recurring bioturbation patterns in the Puerto Madryn Formation (Late Miocene, Argentine Patagonia), we arrive at key knowledge about predominant environmental stresses within transgressive phase shallow marine and estuarine systems, shedding light on their palaeoenvironmental implications. Given the inherent complexities of coastal settings, including the challenges posed by omission/erosion surfaces, it becomes imperative to consider the intricate interplay of multiple depositional processes and environmental factors.Through a detailed integration of sedimentological and ichnological approaches, we discern the establishment of a wave-dominated system overlain by a tide-dominated estuarine system.The wave-dominated marine system involves tabular bodies extending laterally over tens of kilometres, with upward fining and coarsening successions from the mid- to lower-shoreface to offshore-shelf environments. The influence of waves and tides on these systems is discussed in the absence of physical sedimentary structures and the need to find elements that bring us closer to elucidating whether waves or tidal processes influence shoreface to offshore systems. The ichnological assemblages allow for the characterisation of Cruziana ichnofacies with proximal (Taenidium and Thalassinoides), archetypal (Asterosoma, Chondrites, Cylindrichnus, Ophiomorpha, ?Rhizocorallium, Rosselia, Scolicia, Sinusichnus, Siphonichnus, Teichichnus, and Thalassinoides), and distal expressions (Chondrites, Helicodromites, Phycodes, Thalassinoides, and ?Zoophycos) in the lower shoreface to lower offshore and transitional settings with the shelf. However, the transition from these deposits to Chondrites-dominated beds associated with lower offshore to shelf environments—determined by changes in oxygenation, nutrients, and energy conditions—impedes assignment of all the successions to a particular ichnofacies.The tide-dominated estuarine system features wide, channel-shaped bodies filled with sandy to heterolithic facies, interpreted as intertidal and subtidal deposits. To differentiate between estuary mouths and other settings, the analysis involved characterisation of transgressive and regressive surfaces, ichnological assemblages, and facies distribution, determining net sediment movement—whether landwards or seawards—and its influence on system classification. The ichnological assemblages could be assigned to the Skolithos (Arenicolites, Gyrolithes, Maiakarichnus, Ophiomorpha, Schaubcylindrichnus, Skolithos, and Thalassinoides) and Cruziana ichnofacies (Ophiomorpha, Rosselia, Scolicia, and Siphonichnus). Variations in diversity and abundance often help to determine certain stressful conditions, although the transition to more open areas is discussed, addressing how it could modify the typical models linked with a direct relationship between abundance/diversity and physico-chemical stress.

Sandstones and red beds in the Lower Cretaceous Sidi Aich Formation, Chotts Basin (Southern Tunisia): facies, architecture and depositional environments

Abstract The Lower Cretaceous deposits of North Africa represent a terrestrial to shallow-marine sandstone-dominated succession often referred to as the ‘Continental Intercalaire’ and Nubian Sandstone informal groups. The upper Barremian Sidi Aich Formation of the Continental Intercalaire is distinguished throughout the Chotts basin of southern Tunisia by sandstone-dominated sequences within conglomerate, calcareous siltstone and palaeosol red bed occurrences. This paper aims to highlight: (1) the facies distribution, internal architecture and depositional environment of the sandbodies; and (2) the origin, spatial distribution and architecture of the red beds that underlined and topped sandbodies. Strata in the Zimlet El Beida anticlinal structure, Chotts basin, offer a good opportunity for detailed field observations and bed-by-bed logging of three representative lithostratigraphic sections. Detailed sedimentological investigation allows the recognition of several lithofacies grouped into three facies associations indicating tidal flat, tidal channel and tidal bar depositional settings characterizing a transgressive tide-dominated estuarine system that developed during an episode of relative sea-level fluctuations in the Early Cretaceous. The high-resolution petrographic, mineralogical and geochemical analyses of the red beds allow the differentiation of three distinct lithofacies sets including: (1) intraformational conglomerates; (2) calcareous siltstones; and (3) palaeosol. Major red beds comprise detrital grains inherited from the host or parent sediment and authigenic minerals (dolomite, calcite and hematite) precipitated during the diagenetic processes. Grain components have been partially or completely cemented and/or replaced by terrestrial phreatic dolomite. The negative δ 13 C and δ 18 O signatures of the dolomite analyses indicate that the dolomitization processes have been influenced by fluctuations of the groundwater table or climate change from semi-arid to semi-humid conditions. This study, therefore, may provide useful data for the better understanding of the internal architecture of the red beds associated with sandbodies that represent the main and significant potential reservoir within the Lower Cretaceous Continental Intercalaire sandstone-dominated groundwater aquifers of the Chotts basin.

Fossil maerl beds as coastal indicators of late Holocene palaeo-environmental evolution in the Bay of Brest (Western France)

The Bay of Brest (BB) is a mixed, tide-dominated estuarine system. The shore terraces of this bay are occupied by modern free-living (calcareous) coralline algae locally termed “maerl”, organized in bed-like morphologies (rhodolith deposits). Cores retrieved from around the bay reveal fossilized primitive maerl beds of Holocene age, interbedded in sandy-silt sedimentation. The alternation between biogenic constructions and estuarine sedimentation may provide evidence of varying environmental conditions of the late-Holocene period. This paper mainly focuses on the results of chronostratigraphic and bio-sedimentological interpretations of coring data collected in less than 15 m of water depth in an attempt to decipher the main stages of maerl colonization in the bay. In particular, this study raises several significant points allowing to draw links between centennial to millennial-scale climatic changes in marine estuary sedimentation and episodes within the development of maerl biocenoses. The paleo-bathymetry of the coastal terraces has not changed significantly over the last 5000 years. Yet, the first maerl occurrence only appeared around 2000 cal yr B.P., likely showing that the environmental conditions were not favorable for their emergence prior to that time. Pioneer maerl beds developed on coarse shell deposits inherited from the paleostorms affecting the Atlantic coasts during the colder climatic period of the Iron Age (3100–1950 cal yr B.P.). The accumulations then aggraded at various and discontinuous rates, sometimes reaching up to 2.1 m/kyr. Maerl beds temporarily disappeared in the southern part of the Bay of Brest when sedimentation rates increased throughout the bay during the Dark-Age cold period (1375–1250 cal yr B.P.), suggesting that maerl formations could not keep up with sedimentation rate exceeded a certain threshold. Muddy sedimentation conditions also dramatically changed on two occasions, with the establishment of coarse storm levels, set at the intervals 825–600 cal yr B.P. (MWP) and 113–0 cal yr B.P. But maerl deposits reseed the environment as a result of each new cold period, demonstrating the persistence of such coralline algae against drastic palaeoenvironmental changes in coastal areas.

Tectonic and eustatic controls on the spatial distribution and stratigraphic architecture of late early Cambrian successions at the northern Gondwana margin: The siliciclastic-carbonate successions of the Lalun Formation in central Iran

Abstract The lower Cambrian Lalun Formation of the Tabas Block, Central Iran, allows to generate a sequence stratigraphic model which characterises the sedimentary evolution and improves palaeoenvironmental interpretation of sedimentary successions along the northern margin of the Prototethys. This formation provides a key for understanding processes that took place during the late early Cambrian in Iran and is the best representative for the complex mosaic of mixed siliciclastic-carbonate systems which illustrate the development and evolution of fluvial and tide-dominated estuarine systems adjacent to an open coast during this interval in the region. Detailed facies analysis allows to differentiate five vertically-stacked groups of facies associations (fluvial facies associations; estuarine facies association; open coast tidal flat facies association; carbonate ramp facies association; and delta facies association) in the uppermost interval of the Lalun Formation. The conceptual depositional models for the siliciclastic-carbonate successions of the Lalun Formation are summarised in a sequence stratigraphic framework, including three third-order depositional sequences (braided fluvial systems; incised-valley fill; and carbonate ramp and tide-influenced delta systems). The data suggest that the Central Iranian Microcontinent broke up during latest Neoproterozoic–early Cambrian times, resulting in the Proto-/Palaeotethys rifting, with considerable differential subsidence recognizable from the reactivation of faults in the early Cambrian which led to new syn-rift successions. The mosaic pattern of deposition observed among the studied sections suggests a compartmentalization of the depositional setting as a result of the interplay between tectonics, sediment supply, and eustasy. Abrupt lateral changes in facies and thickness within the sequences depositional sequences suggest that deposition was controlled by repeated tectonic downdrop and uplift as a consequence of local syndepositional, extensional fault movements. Tectonic activities in the studied region controlled sedimentation and accommodation as well as the position of depocentres within the basin, and the stratal geometries within the sequences. However, the stratigraphic architectural style of the depositional sequences and the asymmetrical trend of the transgressive and regressive second-order sequences imply that the deposition of the late early Cambrian successions is at least partly a result of eustatic sea level changes and cannot be linked exclusively to differential subsidence due to fault movements. Our study indicates that stratigraphic relationship between carbonate and siliciclastic facies in the depositional sequences was also controlled by subsidence/uplift in the hinterland and the areas of siliciclastic input rather than climatic changes. The late early Cambrian depositional environments evolved from braided rivers and an incised valley system (lowstand) to transgressive incised-valley-fill successions which are capped by transgressive open coast tidal flat and carbonate open marine facies. Depositional history of the formation terminated with a regression that ceased with progradation of tide-influenced delta systems. The stratigraphic evolution described in this study documents an eustatic sea-level fall interposed between the top of the Lalun Formation and the base of transgressive tidal bars of the overlying Fasham Formation reflecting the complex (sub-)globally recognizable regressive–transgressive event at the lower–middle Cambrian boundary interval, which led to the establishment of an extensive middle–late Cambrian carbonate platform in present-day northern and central Iran.

An insight into the Eocene tide-dominated estuarine system: implications for palaeoenvironmental and sequence stratigraphic interpretations

This article describes a complete sedimentary succession of an ancient macrotidal tide-dominated estuarine system based on the detailed outcrop study. The Eocene siliciclastic sedimentary facies of Ameki Group in the south-eastern Nigeria provides a record of the sedimentary response to an initial regression, followed by marine incursion (transgression) into the Niger Delta Basin. These sedimentary successions are analogues to the subsurface petrolific Niger Delta lithostratigraphic units. Seven facies associations (FA 1 to FA 7) are documented in the study area and the sediments are interpreted as fluvial channel, tidally influenced fluvial channel, tidal channel, tidal flats, supratidal, tidal sand bar and estuarine embayment (open estuarine) deposits. The occurrence of low diversity ichnofaunal assemblages and/or localised high-density monospecific ichnofossil assemblages indicates brackish-water condition typical of estuarine settings. The suites of assemblages include Scoyenia, Skolithos, Cruziana, mixed Skolithos-Cruziana, Glossifungites, Psilonichnus and Teredolites ichnofacies. A complete depositional sequence is encountered in the Eocene Ameki Group which consists of the lowstand, transgressive, highstand and falling stage systems tracts. This depositional succession was most probably controlled by relative sea level changes, sediment supply, accommodation and regional tectonics which affected the development of Niger Delta Basin.

Trace fossil assemblages in the tide-dominated estuarine system: Ameki Group, south-eastern Nigeria

A systematic ichnological analysis with sedimentological study of the Eocene Ameki Group in south-eastern Nigeria, was conducted to infer depositional and biogenic processes operating during basin fill, identify discontinuities using substrate controlled ichnofacies, and identify the paleocological conditions that affected the diversity of the trace fossils. The Ameki Group represents a tide-dominated estuarine system characterised by a range of trace fossils assemblages. Eighteen individual ichnogenera and nineteen ichnospecies observed in the study area, were grouped into six recurring ichnofacies namely Scoyenia, Psilonichnus, Skolithos, Cruziana, Glossifungites and Teredolites. Skolithos and Cruziana ichnofacies are predominant in the estuarine deposits indicating that the sedimentary successions of the Eocene are dominantly of moderate to high energy marginal marine environments. The estuarine deposits (senus stricto) were controlled by low to fluctuating salinity levels, high sedimentation rate and fluctuating hydrodynamic energy. These resulted in the occurrence of low diversity of Scoyenia and Teredolites ichnofacies and low to moderate ichnodiversity of mixed Skolithos and depauperate Cruziana ichnofacies. Low levels of dissolved oxygen in quiescent water-embayment (open estuarine) resulted in low diversity of impoverished Cruziana ichnofacies. Glossifungites ichnofacies marked an amalgamated sequence boundary/marine flooding and an initial flooding surface at the base of the tidally influenced fluvial deposits.

Sedimentary petrology and provenance interpretation of the sandstone lithofacies of the Paleogene strata, south-eastern Nigeria

The Paleogene strata in the south-eastern Nigeria include the Imo Formation, the Ameki Group and the Ogwashi Formation. Petrographic studies suggest quartz arenite to arkosic arenite and sub-arkose for sandstones of the Imo Formation. Sandstones of the tide-dominated estuarine system of Ameki Group are classified as quartz arenites, sub-arkoses, sub-litharenites and litharenites. Sandstones of the Ogwashi Formation are classified as quartz arenites and sub-litharenites. These Paleogene sandstones are derived from mixed provenances based on the petrographic interpretation. The provenances include cratonic interiors, transitional continental blocks as well as recycled orogenic and transitional continental, transitional recycled and quartzose recycled. Paleoclimatic condition for the Paleogene region is semi-humid to humid climate. The sandstone composition suggests detritus from igneous rocks, metamorphic rocks and recycled sedimentary rocks. Heavy mineral analysis confirms the possibility of mixed provenance for the Paleogene sediments. The source areas include the Oban Massif, the West African Massif and the recycled sedimentary rocks of the older sedimentary rocks of probably the Anambra Basin and Afikpo Syncline.

Further comment to “Reply to Comment on impact structures in Africa: A review (Short Note)” by Reimold and Koeberl [J. Afr. Earth Sci. 100 (2014) 757–758

A systematic ichnological analysis with sedimentological study of the Eocene Ameki Group in south-eastern Nigeria, was conducted to infer depositional and biogenic processes operating during basin fill, identify discontinuities using substrate controlled ichnofacies, and identify the paleocological conditions that affected the diversity of the trace fossils. The Ameki Group represents a tide-dominated estuarine system characterised by a range of trace fossils assemblages. Eighteen individual ichnogenera and nineteen ichnospecies observed in the study area, were grouped into six recurring ichnofacies namely Scoyenia, Psilonichnus, Skolithos, Cruziana, Glossifungites and Teredolites. Skolithos and Cruziana ichnofacies are predominant in the estuarine deposits indicating that the sedimentary successions of the Eocene are dominantly of moderate to high energy marginal marine environments. The estuarine deposits (senus stricto) were controlled by low to fluctuating salinity levels, high sedimentation rate and fluctuating hydrodynamic energy. These resulted in the occurrence of low diversity of Scoyenia and Teredolites ichnofacies and low to moderate ichnodiversity of mixed Skolithos and depauperate Cruziana ichnofacies. Low levels of dissolved oxygen in quiescent water-embayment (open estuarine) resulted in low diversity of impoverished Cruziana ichnofacies. Glossifungites ichnofacies marked an amalgamated sequence boundary/marine flooding and an initial flooding surface at the base of the tidally influenced fluvial deposits.

Unincised fluvial and tide-dominated estuarine systems from the Mesoproterozoic Lower Tombador Formation, Chapada Diamantina basin, Brazil

The Mesoproterozoic Lower Tombador Formation is formed of shallow braided fluvial, unconfined to poorly-channelized ephemeral sheetfloods, sand-rich floodplain, tide-dominated estuarine, and shallow marine sediments. Lowstand braided fluvial deposits are characterized by a high degree of channel amalgamation interbedded with ephemeral, intermediate sheetflood sandstones. Sand-rich floodplain sediments consist of intervals formed by distal sheetflood deposits interbedded with thin layers of eolian sandstones. Tide-dominated estuarine successions are formed of tide-influenced sand-bed braided fluvial, tidal channel, tidal sand flat and tidal bars. Shallow marine intervals are composed of heterolithic strata and tidal sand bars. Seismic scale cliffs photomosaics calibrated with vertical sections indicate high lateral continuity of sheet-like depositional geometry for fluvial–estuarine successions. These geometric characteristics associated with no evidence of incised-valley features nor significant fluvial scouring suggest that the Lower Tombador Formation registers deposition of unincised fluvial and tide-dominated systems. Such a scenario is a natural response of the interplay between sedimentation and fluctuations of relative sea level on the gentle margins of a sag basin. This case study indicates that fluvial–estuarine successions exhibit the same facies distributions, irrespective of being related to unincised or incised-valley systems. Moreover, this case study can serve as a starting point to better understand the patterns of sedimentation for Precambrian basins formed in similar tectonic settings.

Bedload sediment transport dynamics in a macrotidal embayment, and implications for export to the southern Great Barrier Reef shelf

Keppel Bay is a macrotidal embayment on a tectonically stable, tropical coast, which links the Fitzroy River with the Great Barrier Reef continental shelf. Estuaries and deltas act as conduits between catchments and inner shelf environments. Therefore, understanding sediment transport pathways in these complex systems is essential for the management of ecosystems such as coral-reefs that are potentially vulnerable to enhanced river sediment loads. Furthermore, the morphology and sediment dynamics of subtidal sand ridges and dunes are relatively poorly characterised in macrotidal estuaries, particularly in turbid, episodic systems such as the Fitzroy River and Keppel Bay. Our sedimentological analysis of seabed samples, shear-stress modelling and three-dimensional acoustic imaging reveals that Keppel Bay is a mixed wave- and tide-dominated estuarine system. Areas of sediment starvation and shoreward transport characterise the offshore zone, whereas a complex of both active and relict tidal sand ridges, and associated subaqueous dunes, dominate the relatively protected southern Keppel Bay. Transport within this region is highly dynamic and variable, with ebb-dominated sediment transport through tidal channels into the outer bay where there is a switch to wave-dominated shoreward transport. Ultimately, bedload sediments appear to be reworked back inshore and to the north, and are gradually infilling the bedrock-defined embayment. Our characterisation of the Keppel Bay system provides a detailed example of the physiography of the seaward portion of a tide-dominated system, and shows that sediment transport in these areas is influenced by a variable hydrodynamic regime as well as relict channels and bedrock topography.