Fair-weather Wave Research Articles

Keratose sponge–microbial consortia in stromatolite-like columns and thrombolite-like mounds of the Lower Ordovician (Tremadocian) Mungok Formation, Yeongwol, Korea

Lower Ordovician stromatolite-like columns and thrombolite-like mounds, composed of fossilised keratose sponges (keratolites) and microbial carbonates, are reported from the Tremadocian Mungok Formation, Yeongwol, Korea. The stromatolite-like columns, which are up to 10 cm wide and high, consist of an inner core with low-angled (10–45°) layers that are covered by high-angled (>45°) layers. The inner core is made up of millimetric layers of alternating keratolite and microbial carbonate, and microbial carbonate dominantly comprises the outer cover. The entire columns are surrounded by bioclastic packstone to grainstone. The thrombolite-like mounds are domes a maximum of 100 cm high and 40–60 cm wide embedded within lime mud and shale. These mounds consist of keratolite–microbial carbonate clots and minor lithistid sponge–microbial carbonate clots. The stromatolite-like columns were formed in a high-energy subtidal setting, in which laminoid keratolite and microbial carbonate formed the tight laminar frame columns. Continued growth of the column narrowed the intercolumnar space, resulting in higher-energy hydrodynamic conditions that limited the growth of sponges but promoted growth of microbial organisms. In contrast, thrombolite-like mounds developed in a low-energy environment below fair-weather wave base, where irregular to bulbose keratose sponges with minor lithistid sponge–microstromatolite associations formed cluster reefs. There appear to have been ecological and/or environmental factors that affected the distribution of these sponges; keratose and lithistid sponges rarely occur together in the Mungok reefs, whereas lithistids are pervasive within coeval intermediate-energy microbial reefs elsewhere. These results demonstrate the importance of hydrodynamic controls on overall reef morphology and configurations during the Early Ordovician, and suggest that keratosan–microbial consortia may have been an integral component of the Great Ordovician Biodiversification Event, together with the lithistid sponge–microbial consortium.

Fossil molluscs from borehole Hollum (Ameland, the Netherlands) constrain three successive Quaternary interglacial marine intervals in the southern North Sea Basin

Abstract When dealing with stratigraphic successions in marginal basin settings, the geological record is often fragmented due to erosion and reworking processes. The North Sea Basin is an example: it has a fragmented Quaternary record; in particular, Middle Pleistocene intervals are poorly known. As a result, we have little insight into climate, marine environmental conditions and biodiversity in this period. Here we describe and discuss a succession of three interglacial marine mollusc-bearing intervals in a borehole from Ameland in the northern Netherlands (borehole B01H0189 near Hollum). These intervals are attributed to marine isotope stages MIS7, MIS5e and MIS1. The Holocene Celtic type of faunas (interval 0–26.24 m below surface (b.s.)) and Eemian Lusitanian type of faunas (26.24–30.40 m b.s.) are well-known from previous research. The newly reported MIS7 Oostermeer fauna (32.80–39.00 m b.s.) represents mostly full marine settings between storm wave base and fair-weather wave base. In composition and diversity, the MIS7 and MIS1 faunas strongly resemble and differ from the MIS5e fauna. This is the first well-documented record of three stacked marine interglacial assemblages from the southern North Sea Basin at one location. This new record enables us to make complete marine faunal characterisations of successive interglacial periods. Key implications for southern North Sea stratigraphy and palaeogeography are the resemblance of marine faunas and conditions in MIS7 and MIS1, the presence of a relatively warm latest MIS6 freshwater interval and confirmation and characterisation of the warm Eemian interval north of the classical type area.

Shales of Palaeo-Mesoproterozoic Vindhyan Basin, central India: insight into sedimentation dynamics of Proterozoic shelf

AbstractThe Vindhyan Supergroup represents the largest Proterozoic sedimentary basin fill in the Indian shield. In addition to some significant palaeobiological discoveries, the sedimentary sequence of the Vindhyan, particularly its argillaceous intervals, holds crucial information for our understanding of sedimentation dynamics in Proterozoic clastic shelves. Here we attempt an extensive, although not exhaustive, review of the physical characteristics of six argillaceous (shale) intervals (Arangi, Koldaha, Rampur, Bijaygarh, Rewa and Sirbu shale) from the Son valley sector, Vindhyan Basin, augmented with new observations to unravel the status of current understanding in terms of palaeo-flow dynamics, shelf sedimentation processes and dispersal pattern, depositional cyclicity and basinal tectonics. The sedimentary attributes of Vindhyan shales reveal their deposition largely in relative bathymetry fluctuating from distal shoreface or inner shelf (near to fair-weather wave base) to distal shelf below storm wave base. More often than not, the Vindhyan shelf was storm-infested and the operation of both storm-generated return flow and Coriolis-force-guided geostrophic currents are documented from different stratigraphic intervals of argillaceous successions. The thick arenaceous intervals interrupting the deposits of the Koldaha, Rewa and Sirbu shales at multiple stratigraphic levels indicate the presence of a fan delta and braided fluvial system during intermittent regressive stands of sea level or event deposition during a sea-level highstand, respectively. Based on facies pattern and flow vectors, a rift-related half-graben model is inferred for Arangi and Koldaha shale and a low-gradient stable-shelf model with well-defined energy gradient is proposed for successions from Rampur shale onwards.

Complex depositional environments on a siliciclastic-carbonate platform with shallow-water turbidites: The Natividade Group, central Brazil

The Natividade Group is a Paleo-Mesoproterozoic metasedimentary sequence outcropping in the external zone of the Northern Brasília Belt, western margin of the São Francisco Craton, Brazil. The present study delimited eleven sedimentary rock types grouped into four rock assemblages: i) Sand-Silt-Carbonate; ii) Sand-Conglomerate; iii) Sand, iv) Silt-Clay. A geological map for the region was produced, and six stratigraphic columns were composed. Based on the descriptions of rock types and on lateral variation of rock assemblages, it was possible to establish four depositional environments for the Natividade Group, including mixed platform (siliciclastic-carbonate deposition), internal siliciclastic platform, open-marine siliciclastic platform, and a shallow water turbidite (mass flow slope deposition). The mixed platform was controlled by the basement paleogeography, which allowed the deposition of carbonates in warm, agitated, and clean, shallow water conditions in parallel to deposition in deeper water setting, where thin siliciclastic sediments were deposited. The siliciclastic internal platform consists mostly of quartzite, originating from sandy sediments, probably indicating deposition dominated by bedload currents under shallow water shoreface conditions. The open-marine siliciclastic platform is dominated by fine-grained sediments, indicating deepening water conditions under lower shoreface conditions below the fair-weather wave base. Shallow water turbidite occurs in the southern parts of the study area. The elevated paleorelief in the southeast of the Natividade basin is considered as the provenance area providing suitable slope environments for density flow initiation. The basin was shallower in the southern portion with a predominance of carbonate and gravitational flux deposits and deeper to the north, evidenced by the northward predominance of fine-grained sediments. Finally, the study shows that the Natividade Group was deposited in a basin controlled by thermo-flexural subsidence.

Regressive Shoreface Depositional System of the Cretaceous Yolde Formation of the Gongola Sub-Basin Northern Benue trough N. E. Nigeria

The characterization of lithofacies of the Yolde Formation at Briyel town in the Gongola Sub-basin of the Northern Benue Trough indicated coarsening upwards cycles composed transitional succession of six lithofacies that comprises of trough cross-beds, planar cross-beds, massive beds, ripple laminations, parallel laminations and mudstone. This coarsening and thickening upward symmetry is defined by a densely bioturbated mud dominated lower part transitionally grading into heterolithic interval composed thinly bedded sandstone and mudstones both of which developed below fair-weather wave base. This is capped by a succession of moderately bioturbated trough-planar crossbedded sandstone with poly-directional paleocurrent system. These assemblages reflect shoreface deposits and devoid of hummocky cross-stratification therein may account for a moderate wave oceanographic system. Evolution of this setting in the Gongola Sub-basin is indicative of a scenario of a broaden coastline in the coastal palaeogeography of the Yolde Formation typically suppressing due to frictional damping.

Upper Triassic (Carnian) sponge reef mounds from South Canyon, central Nevada

An important interval for reef evolution occurs in the Triassic Period. However, Late Triassic reefs along the edge of the Panthalassa Ocean receive much less attention than their Tethys region counterpart. To improve our understanding of reef evolution along the Panthalassa, we present a quantitative microfacies analysis to characterize reef facies types from a central Nevada locality. We point counted thin sections to quantitatively assess the relative abundance of reef and interstitial components from six Carnian reef mounds. Reef mound formation occurs at three different stratigraphic intervals. Each interval records a different reef mound size and shape. The oldest stratigraphic interval consists of four separate reef mounds; each mound is approximately 3–12 m wide and 2–4 m high. The second youngest stratigraphic interval consists of one large ~ 10-m wide and 15.5-m high domal reef mound. The third, and youngest, reef mound is smaller in comparison (i.e., 1-m wide and 1.5-m high). We recognize two reef facies types within these reef mounds. Different calcareous sponges, bound together by microproblematica and clotted micrite, form the overall reef framework. We suspect that changes in relative sea level affect the initial colonization, different growth capacities, and overall preservation of the South Canyon reef mounds. When South Canyon reefs are compared to other Panthalassa reefs, it seems that “Wetterstein-type” reef–sponge bindstone facies containing biogenic crusts dominate and corals are less abundant and persist generally in both shallow and deeper water environments. However, significant differences in primary and secondary framebuilder abundances exist due to differences in where the reefs grew in relation to fair-weather wave base (FWWB). Thus, changes in relative sea level may affect the initial colonization, different growth capacities, and overall preservation of reef but water depth may also control the primary and secondary reef builders. Consequently, quantitative assessment of reef ecosystems within a sequence stratigraphic framework undoubtedly facilitates fewer problematic comparisons between reefs but it also enhances our understanding of reef development.

Ichnologic note first occurrence of the microcoprolite Palaxius salataensis in the Aptian (Lower Cretaceous) of northeast Mexico and its paleoecological implications

Microcoprolites of Palaxius salataensis are non-skeletal carbonate grains produced by callianassid shrimps. This ichnospecies is recognized by four longitudinal canals arranged around a bilateral plane of symmetry, with crescent outline in cross-section. Palaxius salataensis has been previously reported from other countries and in strata from the late Paleozoic to the Mesozoic. In this study, we describe the first Aptian record of the ichnospecies, the first Cretaceous occurrence in North America, and the fifth occurrence worldwide. Palaxius salataensis was found in a packstone-grainstone with abundant pellets and common gastropod shell fragments and subangular, poorly sorted intraclasts. The paleoenvironment was characterized by shallow-waters with high energy conditions, occurring between fair-weather wave base and storm wave base, close to the platform margin, where well-oxygenated and nutrient-rich conditions predominated. The microcoprolite-rich bed of the La Huasteca Canyon occurs on top of an oolitic grainstone interval in the upper levels of the Cupido Formation, interpreted as the termination of the early Aptian Oceanic Anoxic Event 1a (OAE 1a). The presence of P. salataensis in the upper levels of the Cupido Formation is directly related to the availability of organic matter rather than to oxygen recovery.

Characteristics and context of high-energy, tidally modulated, barred shoreface deposits: Kimmeridgian–Tithonian sandstones, Weald Basin, southern U.K. and northern France

ABSTRACTThe influence of tides on the sedimentology of wave-dominated shorefaces has been emphasized in recent studies of modern shorelines and related facies models, but few ancient examples have been reported to date. Herein, we use a case study from the stratigraphic record to develop a revised facies model and predictive spatio-temporal framework for high-energy, tidally modulated, wave-dominated, barred shorefaces.Kimmeridgian–Tithonian shallow-marine sandstones in the Weald Basin (southern England and northern France) occur as a series of laterally extensive tongues that are 5–24 m thick. Each tongue coarsens upward in its lower part and fines upward in its upper part. The lower part of each upward-coarsening succession consists of variably stacked, hummocky cross-stratified, very fine- to fine-grained sandstone beds and mudstone interbeds that are moderately to intensely bioturbated by a mixed Skolithos and Cruziana Ichnofacies. This lower part of the succession is interpreted to record deposition on the subtidal lower shoreface, between effective storm wave base and fairweather wave base. The upper part of each upward-coarsening succession comprises cross-bedded, medium- to coarse-grained sandstones that are pervasively intercalated with mudstone-draped, wave-rippled surfaces (including interference ripples) which mantle the erosional bases of trough cross-sets. Bioturbation is patchy, and constitutes a low-diversity Skolithos Ichnofacies. Cross-bedded sandstones are arranged into cosets superimposed on steeply dipping (up to 10°) clinoforms that dip offshore and alongshore, and extend through the succession. These deposits are interpreted to record shallow subtidal and intertidal bars on the upper shoreface, which likely contained laterally migrating rip channels or formed part of a spit. The lower, upward-coarsening part of each sandstone tongue represents an upward-shallowing, regressive shoreface succession in which the internal bedding of upper-shoreface sandstones was modulated by tidal changes in water depth. The upper, upward-fining part of each sandstone tongue typically comprises an erosionally based bioclastic lag overlain by subtidal lower-shoreface deposits, and constitutes an upward-deepening succession developed during transgression.Regressive–transgressive sandstone tongues fringe the northeastern margin of the basin, which was exposed to an energetic wave climate driven by westerly and southwesterly winds with a fetch of 200–600 km. The high tidal range interpreted from the shoreface sandstone tongues is attributed to resonant amplification in a broad (150–200 km), shallow (18–33 m) embayment as the tidal wave propagated from the Tethys Ocean into the adjacent intracratonic Laurasian Seaway, of which the Weald Basin was a part.

Early to Middle Devonian ironstone and phosphorite in the northwestern Gondwana Parnaíba Basin, Brazil: A record of an epeiric margin paleoceanographic changes

Pragian to Givetian successions in the Canindé group, Parnaíba Basin (Brazil), present phosphorites, ironstone and organic rich sediments that globally coincide with greenhouse conditions and an increase in continental weathering, ocean oxygen levels and black shale deposition events. These facies are associated with the evolution of the northern Gondwana epeiric sea margin of the Rheic Ocean and can tell us how ocean chemistry changed and the paleoceanographic factors involved in this particular transition of the ocean record. We conducted an integrated study based on sedimentology, sequence stratigraphy, petrography, scanning electron microscopy and X-ray diffraction to understand the paleoenvironmental, stratigraphic and diagenetic controls. Lithofacies stacking patterns indicate that deposition occurred during marine transgressions resulting in four depositional sequences. Late Eifelian and Givetian maximum flooding surfaces are represented by phosphogenesis and francolite precipitation associated with condensed zones. Pragian-Emsian to Givetian ironstones were represented by authigenic coated phosphatic iron silicate (odinite, chamosite/clinochlore, francolite) and siderite precipitation. These are related to normal regressions under lowstand and highstand systems tract. Oxic waters prevailed and episodic upwelling is interpreted as the source of nutrients that maintained Fe, Si and P supply on a storm-influenced to storm-dominated shelf with an additional source of iron also associated with river discharges. Phosphorite was formed in a stratified ocean, near storm wave base, under anoxic (sulfide reducing bacteria microbial communities) and suboxic conditions (productivity fueled by recycled P). Shallower anoxic conditions (near the fair weather wave base) existed, possible related to a shift in the locus of upwelling, and then resumption to oxic conditions indicate that water column stratification was not a stable feature due to variations in base level, ventilation, terrigenous or marine contribution and progressive microbial degradation. At the beginning of late Eifelian transgression, an event of increased delivery of continental flux and eutrophication can also be proposed. The link between organic-rich intervals and third order black shale events (Daleje, Chotěc and Kačak) suggests that extinction events can be tracked by analyzing sections in South America. Global correlation with ironstone precipitation and organic rich sediments shows that stepped periods of C sink conditions probably contributed to the ocean oxygenation.

Depositional model for mixed carbonate-clastic sediments in the Middle Cambrian Lower Zhangxia Formation, Xiaweidian, North China

In order to make accurate decisions in interpreting depositional environments of sedimentary rocks, a multi-proxy approach is best employed. In the Middle Cambrian Lower Zhangxia Formation exposed at Xiaweidian in the Northern China, lack of this form of approach puts doubts on the various models (e.g. carbonate ramp and isolated platform) proposed by previous workers. In this study, we integrated field outcrop investigation with laboratory examinations of thin sections with light and electron microscopies to further understand sedimentary environments of the Lower Zhangxia Formation. Dominant rock types of this formation include oolitic limestone, muddy limestone, flat-pebble limestone and calcareous mudstone. Evidence from ooid features and lime-mud content of oolitic limestones suggests their deposition in an environment with intermittent high energy level. The muddy limestones were formed on a restricted platform with lower wave energy, which is supported by the existence of pyrites in a reducing environment and the input of terrestrial clays from neighboring clastic environments. The flat-pebble limestones were formed by storm reworking of early deposits on restricted platform below a fair-weather wave base, due to their composition and clast features. Mudstones with occurrences of terrestrial silts could be associated with clastic shallow marine adjacent to the restricted platform. A mixed carbonate-clastic depositional model is suggested for this formation and can be used as model for other researchers working in the North China. Cited as : Zhang, X., Pang, X., Jin, Z., Hu, T., Toyin, A., Wang, K. Depositional model for mixed carbonate-clastic sediments in the Middle Cambrian Lower Zhangxia Formation, Xiaweidian, North China. Advances in Geo-Energy Research, 2020, 4(1): 29-42, doi: 10.26804/ager.2020.01.04

Ichnological signatures from wave- and fluvial-dominated deltas: The La Anita Formation, Upper Cretaceous, Austral-Magallanes Basin, Patagonia

Depositional processes operating in deltaic shorelines create a variety of physico-chemical stressful conditions that impact directly on benthic fauna. The ichnological signatures of deltaic successions reflect these physico-chemical stresses, such as rapid sediment influx, elevated water turbidity, periodically reduced oxygenation, salinity fluctuations, and wave- and tidal-energy. In the Campanian La Anita Formation of the Austral-Magallanes Basin, two examples of deltaic successions, each showing different relative dominance of wave and fluvial processes, are described in detail, allowing the recognition of contrasting stresses that acted differentially in a wave-dominated, fluvial-influenced delta and a fluvial-dominated delta. Variations in the burrowing intensity and ichnodiversity allowed us to discriminate the different physico-chemical stresses. In the wave-dominated, fluvial-influenced deltaic deposits, the alternation between fair-weather waves and storm events acted as the main controlling factor on benthic fauna in the facies of the prodelta and distal delta front, displaying facies-crossing and horizontal elements attributable to the Skolithos and Cruziana Ichnofacies, such as Arenicolites isp., Chondrites isp., Cylindrichnus isp., Diplocraterion isp., Gyrochorte isp., Ophiomorpha isp., Palaeophycus isp., Planolites isp., Rhizocorallium isp., Rossellia isp., Schaubcylindrichnus isp. and Skolithos isp. Water turbidity and periodically reduced bottom water oxygenation conditions also played an important but subordinate role. The proximal delta front, and distributary and terminal distributary channel deposits show low burrowing intensities and ichnodiversities with structures attributable to the depauperate Skolithos Ichnofacies with few Diplocraterion isp., Gordia isp., Lockeia isp., Macaronichnus isp., Ophiomorpha isp., Schaubcylindrichnus coronus and Siphonichnus isp., showing stress conditions associated with rapid sediment influx, high energy and reduced salinity conditions related to fluvial discharges as the most important controlling factors. Periodically, fluctuations in salinity conditions due to river discharges and channel avulsion may have also played important roles. The fluvial-dominated deltaic deposits show that the controlling factors were associated with fluvial discharge and river-sediment influx with no clear influence of wave or tidal action. The facies of the distal delta front were controlled by episodic sedimentation, elevated water turbidity, periodically reduced oxygenation and salinity fluctuations, the associated trace fossil suite consists of a monospecific assemblage of Ophiomorpha isp. and sparse Palaeophycus isp. The proximal delta front and the distributary channel deposits are mostly unburrowed, locally displaying a few Arenicolites isp., Lockeia isp., Ophiomorpha isp., Psilonichnus isp. and Teredolites isp. The development of these suites was controlled mainly by heightened sedimentation rates influx triggered by high fluvial discharges, elevated water turbidity due to heightened suspended load and buoyant plumes, periodic fluctuations in salinity conditions caused by river discharges and channel avulsion. Interdistributary areas are characterized by facies preserving evidence that reduced oxygenation was the most important controlling factor in this subenvironment. Fluvial processes generate the most extreme stressful conditions for benthic colonization by tracemakers. Wave processes tend to buffer the stresses produced by river discharge. The effect of waves on fluvial stress is reflected in the higher bioturbation intensities and ichnodiversities that the wave-dominated deltaic deposits of the La Anita Formation delta show in relation to the fluvial-dominated ones.

Upper Devonian (Frasnian) stromatactis-bearing mud mounds, western Alberta, Canada: reef framework dominated by peloidal microcrystalline calcite

ABSTRACT Two well-preserved mud mounds, approximately 50 m thick, in the Mount Hawk Formation (Upper Devonian, Frasnian) in western Alberta provide an unparalleled opportunity to study the microstructure of this reef type in detail for this time interval. This reveals that they are composed dominantly of peloidal sediments—more than a quarter of mud mound volume—along with dense micrite, particulate micrite, bioclasts, and stromatactis cavities. Five types of peloids are differentiated: bacterial, cyanobacterial, bioclastic, intraclastic, and pseudo-peloids. Bacterial peloids were generated by bacterial metabolic activities with possibly some contribution from organomineralization in areas within spicular networks. Three subtypes of cyanobacterial peloids are distinguished based on whether they are physically reworked calcified filaments, aggregates of calcified coccoids, or precipitated within stromatolite-forming cyanobacterial mats or biofilms. Bioclastic peloids are fully micritized fragments of skeletons and shells. Intraclastic peloids are eroded fragments of early-lithified matrix. Pseudo-peloids represent artifacts of poorly preserved sponge spicular networks reflecting the interplay between dissolution of spicules and organomineralization. The distribution of the various peloid types shows specificity in different microfacies. They prove to be valuable paleoecological indicators, and taken together suggest that the mud mounds accreted within the photic zone above storm wave base but below the fair-weather wave base, during deposition of a transgressive and perhaps highstand systems tracts. They are the products reflecting a dynamic balance between constructional versus destructive processes. Bacterial peloids combined with dense micrite constitute the framework, which in turn makes up close to 40% of the mud mounds. This indicates that microbial activities are responsible for the early-indurated framework. The onset of bacterial peloid formation in the bedded sediment immediately underlying the mud mounds further demonstrates that it may have been a necessary precursor to mud-mound initiation. Bacterial peloids appear to characterize most Paleozoic and Mesozoic reefal mud mounds as an essential framework element.

Depositional model of early Cretaceous lacustrine carbonate reservoirs of the Coqueiros formation - Northern Campos Basin, southeastern Brazil

Abstract Recent discoveries of giant hydrocarbon accumulations in coquinas and other lacustrine carbonate rocks of Rift and Post-rift (pre-salt) super-sequences of the Campos and Santos Basins have motivated a series of studies focused on understanding the genesis of these unique reservoirs. An integrated petrologic-sedimentologic-stratigraphic-seismic study of the Coqueiros Formation delineated the depositional model and evolution of reworked bioclastic rocks and other associated rocks deposited on the external high in the northern Campos Basin during the transition between late-rift and sag stages. Bioclastic rudstones and grainstones with moderate to high shell reworking represent 65% of the samples described. The following pieces of evidence point to a predominantly shallow lacustrine depositional environment, dominated by storm currents: (i) presence of high-angle (>14°) longshore cross-bedded rudstones; (ii) limited occurrence of muddy sediments interbedded with thick packages of amalgamated bioclastic rudstones; (iii) great lateral continuity of rudstone deposits devoid of matrix on the structural high, consistent with processes of storm action on large expanses of shallow lakes; (iv) deposits of massive rudstones, with disorganized shells, similar to the modern coastal bioclastic deposits of California and Shark Bay. Three sets of facies association are proposed: (i) high-energy facies, composed of bioclastic rudstones and grainstones devoid of matrix deposited above the fair weather wave base (FWB); (ii) low energy facies, composed of hybrid rocks with muddy or peloidal matrix and other fine grained rocks deposited below the FWB or in protected shallow environments; (iii) an alkaline set, composed of mainly magnesian clay ooids deposited in a more alkaline composition of lake water. The evolution of the facies associations over time demonstrates an overall fall of the relative lake level. High proportion of low energy facies associated with a deeper lacustrine environment occurs at the Coqueiros Fm. base, while at the top predominate high energy facies associated with a shallow lacustrine environment, in addition to magnesian clay-rich facies associated to restricted and alkaline water bodies. Paleocurrents suggest the activity of two main wind direction (northwest and southeast) over the external high that result in clean bioclastic facies with good reservoir potential on both flanks. The knowledge of wind directions during the late Barremian and early Aptian in the northern Campos Basin is extremely important for targeting the best depositional facies for hydrocarbon accumulation in the Coqueiros Formation.

Famennian carbonate microfacies from the Preslavtsi-2 well (Moesian Platform, north-eastern Bulgaria)

The most representative subsurface section of the Famennian carbonate succession from the Moesian Platform in Bulgaria occurs in the R-2 Preslavtsi well. Nine microfacies types (MFTs 1–9) have been distinguished and described in the intraclastic and peloidal limestone unit and the organogenic limestone unit. They are grouped in four microfacies associations: 1) protected shallow subtidal (lagoon) (MFT 1, bioclastic-peloidal packstone/grainstone; and MFT 2, oncoidal wackestone); 2) wave-dominated shallow subtidal (MFT 3, intraclastic-peloidal grainstone and rudstone; MFT 4, oncoidal rudstone; MFT 5, peloidal-bioclastic packstone and grainstone); 3) reef (MFT 6, solenoporacean-calcimicrobial-stromatoporoid boundstone; MFT 7, crinoid-stromatoporoid floatstone); and 4) open-marine (MFT 8, bioclastic wackestone/packstone with intraclasts and peloids; and MFT 9, bioclastic wackestone and packstone). The carbonate deposits are interpreted as formed in various shallow- to open-marine environments at or above the fair-weather wave base (MFTs 1–7) and below it (MFTs 8 and 9). Most of the described microfacies are comparable with Wilson’s (1975) Standard Microfacies Types.

Microbialite fields developed in a protected rocky coastline: The shallow carbonate ramp of the Aptian Romualdo Formation (Araripe Basin, NE Brazil)

The Aptian Romualdo Formation is a siliciclastic-dominated sedimentary unit recording the last marine ingression within the Cretaceous interior basins of northeastern Brazil. At the western margin of the Araripe Basin, rocks of the Romualdo Formation are mainly represented by carbonates resting abruptly over the Proterozoic crystalline basement. Detailed mapping and stratigraphic analysis revealed two stromatolite fields that were described and discussed for the first time. Several bioherms, biostromes and isolated stromatolites characterized by distinct microbialite morphologies associated with echinoid-rich strata have been identified, suggesting that hypersalinity, water depth and hydraulic conditions were the main factors controlling stromatolite morphogenesis. A cm-thick amalgamated bivalve rudstone, resting directly on the basement and representing a shell concentration formed above the fair-weather wave base was also recorded. Based on the regional distribution of the stromatolite types and associated sedimentary facies, we interpret the depositional environment as a local low-gradient carbonate ramp deepening to the east. Our data robustly indicated that the western rocky shorelines of the Araripe Basin during the Aptian were populated by microbial mats and stromatolites in a condition analogous to the modern world-famous Hamelin Pool, Shark Bay, Western Australia. Finally, the development of stromatolites and echinoid-bearing microbialites at the western margin of the basin may be correlated with the formation of bakevelliid- and cassiopid-rich shell beds in the upper part of the Romualdo Formation at the eastern margin.

Overwash‐dominated stratigraphy of barriers with intermittent inlets

AbstractThe morphodynamics and structure of barriers with persistent tidal inlets have been well studied. In contrast the stratigraphy and functioning of barrier systems with ephemeral inlets is poorly understood. This article examines the barrier‐inlet systems of two intermittently closed open lagoons or temporarily open closed estuaries on the east coast of South Africa. Multiple geophysical surveys using ground‐penetrating radar (GPR) were correlated with exposed sections of the barrier where inlet formation revealed the internal stratigraphy. Stratigraphic observations were placed in the context of the contemporary wave dynamics and mesoscale geomorphic evolution. The integrated databases reveal an absence of migrating channel features. Instead the stratigraphy is dominated by landward dipping sheets of alternating high‐ and low‐amplitude reflectors. These correlate with gravel, shell debris and heavy mineral‐lined beds formed by overwash processes. Where ephemeral inlet structures are preserved in the stratigraphy, their fills comprise aggrading, high‐amplitude reflectors, linked to washover infilling of the inlet mouth. Multiple small channels in the more distal portions of the barrier in georadar stratigraphy are related to channelized washover flow.These barriers often breach during high swell and are subsequently sealed during fairweather wave conditions. Time series analysis of waves and satellite imagery shows a link between storms from the south and breach events. This is consistent with the truncations in subsurface images and inferred barrier lowering by overwash channelling. These barriers experience quasi‐stable oscillations in their landward and seaward shore position, punctuated by periods of barrier rollover associated with the most intense storms. As overwash is responsible in part for both the constructive and destructive phases of the barrier, these barriers have low preservation potential. Persistent rollover driven by overwashing will terminate once accommodation space is eliminated and the barriers are eroded by storm activity. © 2019 John Wiley & Sons, Ltd.

Morphometric characterization of foredunes along the coast of northern Spain

Foredunes are defined as the first shore-parallel dune ridges adjacent to stable and prograding beaches, formed on the backshore by aeolian sand deposition influenced by vegetation. Foredunes have the important functions for mitigating impacts caused by extreme events, providing sediment to the beaches during storm and accumulating sediment again under fair weather wave conditions. Mainly for this reason, there is currently great interest in preserving, building or recovering foredunes. On a long-term timescale (decades), foredunes are recognized as exhibiting possible equilibrium conditions. The identification of this condition is of interest to projects involving the recovery and creation of foredune/beach systems. Therefore, the main objective of this work is to identify the morphometric characteristics of equilibrium foredunes and the interrelations between the morphometric parameters of height, width, volume and maximum slope (allometric relationships). To reach this objective, 193 foredune/subaerial beach profiles from along the northern coast of Spain that have characteristics close to equilibrium conditions were evaluated. The results indicate that foredune size can vary significantly; however, strong correlations between morphometric parameters have been verified and allometric relationships between foredune volume, height, width and maximum slope are proposed.

High-frequency depositional cycles in the Muschelkalk (Middle Triassic) of southern Poland: Origin and implications for Germanic Basin astrochronological scales

High-frequency depositional cycles are often used for long-distance correlations within sedimentary basins and constructing high-resolution chronostratigraphic scales calibrated to the orbital clock. Such an approach has been used for the tropical, epicontinental Muschelkalk Sea covering most of Europe in the Middle Triassic. This paper aims at establishing the spatial extent and internal architecture of shallow-marine Muschelkalk cycles within a small (120 by 50 km) area of the Germanic Basin, to identify their local vs. regional distribution and cycle-forming mechanisms. Three groups of cycles are distinguished: 1) peritidal cycles representing a tidal flat-lagoon system which experienced longer periods of emersion; 2) shallow subtidal cycles formed around the fair-weather wave base; and 3) deep subtidal cycles developed around the storm wave base. The three cycle types differ markedly in the composition, facies homogeneity, sedimentary trends, hierarchical organization, continuity, and degree of lateral changeability and complexity, which collectively translates into the ease of cycle recognition. Despite the differences, the defined cycles do not extend laterally beyond the studied area and have laterally variable facies heterogeneities, sedimentary trends, and thicknesses. This variability resulted from more or less mosaic infilling of accommodation space, reflecting local bathymetry, physicochemical conditions, and carbonate production and accumulation rates on the platform. Accommodation space evolved by the interplay of eustatic sea-level fluctuations regional subsidence, and synsedimentary tectonic-block movements, but the contribution of these factors changed over time and was to varying degrees masked for each of the three cycle types by intrinsic sedimentary processes. The study shows that Middle Triassic cycles of the Germanic Basin have a local to sub-regional distribution and thereby are inappropriate for basin-wide correlations and chronostratigraphic inferences. It also strengthens the opinion of several workers that correlation of idealized cycles is unrealistic without checking the horizontal continuity of facies and key surfaces directly in the field.

Facies analysis and depositional environment of the Campano – Maastrichtian coal-bearing Mamu Formation in the Anambra Basin, Nigeria

Detailed sedimentological logging was carried out within the exposed rock sections of the late Campanian to early Maastrichtian successions of the coal-bearing Mamu Formation, southeastern province of Nigeria. Lithofacies analytical approach was employed in describing the outcropping rock units. The focus was to understand the distribution of these facies and their depositional environments. Eleven lithofacies recognized were found occurring within fining/thinning upward successions typical of retrogradational stacking patterns formed during transgressive episodes and coarsening/thickening succession typical of progradational stacking patterns formed during regressive episodes. These lithofacies were further classified into five facies associations, namely: lagoonal or swamp deposits (FA1); barrier island deposits (FA2); shoreface deposits (FA3); offshore-transition zone deposits (FA4) and; open shelf deposits (FA5). FA1 is dominantly coal and carbonaceous shale deposited in a swamp or lagoonal setting. FA2 is dominantly parallel laminated and cross-bedded fine to medium grained sandstones formed by wave and longshore currents within barrier island complexes. FA3 is dominantly bioturbated sandstone, planar and rippled laminated sandstones, and planar and trough cross-bedded sandstones facies deposited in a shoreface environment, by migrating dunes formed under unidirectional flows above fair-weather wave base. FA4 is mainly wave ripple laminated, hummocky and swaley cross-bedded sandstones deposited by waning oscillatory and combined flows within a storm wave-dominated shelf region, below fair-weather wave base. FA5 is fissile shales and mudstones deposited in an open shelf setting below fair-weather and storm wave base. This study indicates that outcropping units represent lithofacies, which record depositional elements of high frequency transgressive and regressive events in a coastal swamp through shelfal depositional environment. In addition, the coal seams and carbonaceous shale facies (source/seal rocks), and the sandstones, siltstone and heterolithic facies (reservoir rocks) indicate the possible presence of key elements of petroleum system in the Mamu Formation of the Anambra Basin.

Gyrophyllites cristinae isp. nov. from Lower Ordovician Shallow-Marine Deposits of Northwest Argentina

The lower Paleozoic marine siliciclastic succession of the Central Andean Basin, northwestern Argentina, provides a valuable record of the onset of the Great Ordovician Biodiversification Event in western Gondwana. A new ichnospecies of rosette trace fossil, Gyrophyllites cristinae, is documented from lower and upper Tremadocian (Tr1 and Tr2) deposits of this basin. It is characterized by five to six non-overlapping petaloid lobes and can be easily differentiated from the other four formally defined ichnospecies. Gyrophyllites cristinae occurs at the top of hummocky cross-stratified sandstone regularly interbedded with mudstone. These deposits are interpreted as reflecting the alternation of high-energy storm events and low-energy fair-weather conditions immediately below the fair-weather wave base, representing deposition in offshore transition environments. Gyrophyllites has been traditionally interpreted as the product of worms of uncertain taxonomic affinity that mined the sediment in search for food (fodinichnia). The occurrence of Gyrophyllites cristinae in these Ordovician deposits records post-storm colonization. Storms may have increased oxygenation and supplied fresh organic detritus that were exploited by worm-like, surface detritus- or shallow deposit-feeders exploring the uppermost silt-rich fine-grained sediments.