Platform Morphology Research Articles

Electropsun non-woven luminescent two-dye pH sensors: Effect of morphology on the sensing performance

Electrospun (ES) non-woven matrices are regarded as promising platforms for the development of miniaturized sensing systems with improved detection capacity. Their high specific surface area and void-to-volume ratio are expected to promote higher and faster interaction of the sensing molecular probes with the target stimuli increasing sensor sensitivity and response time. However, the poor light transparency of ES non-woven mats appears as the main limiting effect regarding their use as optical sensor platforms being important to determine to what extent it affects the sensor prediction accuracy. This work addresses this question providing a comparative analysis of the performance of flat cast and ES non-woven cellulose acetate luminescent platforms loaded with a pH sensitive dye-pair, i.e. fluorescein isothiocyanate (FITC) and rhodamine 6 G (R6G). This study follows a comprehensive approach aiming at clarifying the effect of the platform morphology on the sensitivity of their spectral properties to pH and to understand about the advantages of using dual dye systems for pH detection. The presence of R6G improved remarkably the sensitivity of these ES matrices extending the analytical capacity of the probes to the alkaline range. The emission of ES matrices showed stronger sensitivity to pH. However, pH prediction accuracy was found to depend crucially on a synergistic effect from the platform morphology and the signal analysis methodology. ES non-woven matrices allows for accurate pH prediction, characterized by determination errors < 10 % for pH < 10, by exponential analysis of the dye-pair emission at λExc of 450 nm and λEm of 519 nm. Furthermore, it shows a strong reduction of the determination errors, at extremely acidic conditions, resulting in values comparable to that obtained by analysis of the emission signal from flat cast platforms with more complex Förster Resonance Energy Transfer (FRET) methodologies.

Sediment dynamics and geomorphology of a submarine carbonate platform canyon system situated in an arid climate setting

ABSTRACTChanges in neritic carbonate production and sediment transport off platforms are related to climate variations, sea‐level fluctuations and tectonic processes. Canyon systems marking the platform slopes represent critical source‐to‐sink pathways transporting shallow‐water sediments basinward. However, these export systems and related processes are primarily studied on platform slopes in humid to tropical climate settings. A newly discovered canyon system on the leeward margin of the Al Wajh platform (north‐east Red Sea) represents the ideal laboratory to investigate source‐to‐sink pathway dynamics in an arid climate that prevailed since the Late Pleistocene. A high‐resolution bathymetry map was established to characterize the slope morphology. The system displays a U‐shaped, 10 km long main channel dominantly sourced by the north‐west/south‐east running outer channel and two smaller 2 to 3 km long canyons. The latter are positioned perpendicular to the main canyon. A 4 km wide head scarp at the reef edge and dozens of amphitheatre‐shaped scarps along the mid to lower slope suggest significant slope failures over time. The analysis of four sediment cores collected on a profile down the canyon revealed sedimentation rates of 26 cm/ka at the mid‐slope to 9.4 cm/ka in the basin. Three main sediment‐export processes were identified: (i) sandy and neritic component‐poor turbidites; (ii) winnowing of strontium‐rich carbonate fines through surface currents; and (iii) remobilized carbonate fines on the upper slope. As of the Last Glacial, turbidites are predominantly deposited during times of significant sea‐level instability, both rises and falls, whereas their flat‐topped‐tropical counterparts show a higher turbidite frequency during highstands. Strontium‐rich carbonate fines are exported similarly through time in both climate settings. Overall, sediment export is controlled by: (i) the platform morphology (flat‐topped versus rimmed lagoon); (ii) variations in sediment production; (iii) sea‐level variations (exposure or flooding of sediment production areas); and (iv) the interaction between the sedimentary system and atmospheric changes (sediment production and delivery).

Engaging Learners in Educational Robotics: Uncovering Students’ Expectations for an Ideal Robotic Platform

Extensive research has been conducted on educational robotics (ER) platforms to explore their usage across different educational levels and assess their effectiveness in achieving desired learning outcomes. However, the existing literature has a limitation in regard to addressing learners’ specific preferences and characteristics regarding these platforms. To address this gap, it is crucial to encourage learners’ active participation in the design process of robotic platforms. By incorporating their valuable feedback and preferences and providing them with platforms that align with their interests, we can create a motivating environment that leads to increased engagement in science, technology, engineering and mathematics (STEM) courses and improved learning outcomes. Furthermore, this approach fosters a sense of absorption and full engagement among peers as they collaborate on assigned activities. To bridge the existing research gap, our study aimed to investigate the current trends in the morphology of educational robotics platforms. We surveyed students from multiple schools in Greece who had no prior exposure to robotic platforms. Our study aimed to understand students’ expectations of an ideal robotic companion. We examined the desired characteristics, modes of interaction, and socialization that students anticipate from such a companion. By uncovering these attributes and standards, we aimed to inform the development of an optimal model that effectively fulfills students’ educational aspirations while keeping them motivated and engaged.

Anomalously large marine potholes on a submerged relict shore platform: The Eastern Cape shelf of SE Africa

Marine potholes are common features along rocky shore platforms from around the world. Their occurrence can be used as a palaeo-sea level indicator, however, little attention has been given to submerged marine potholes found on relict shore platforms below the depth limits of SCUBA (≤50 m). This paper examines (n = 238) anomalously large potholes found on a submerged aeolianite shore platform on the outer shelf of the Eastern Cape, South Africa. Using a combined ultra-high resolution seismic reflection, side scan sonar and multibeam bathymetry approach, together with remote observation vehicle dives, the pothole occurrences are mapped.Potholes are either individual or occasionally conjoined, form on sediment-free aeolianite platform and cluster mostly between water depths of 85–95 m. Their sizes are an order of magnitude larger than previously documented, and larger than their fluvial equivalents. Pothole strings are common, associated with the high points between NNW-SSE striking bedding planes of the aeolianite that crop out at the seabed. Potholes are often elongated and aligned with these bedding planes, or in a coast parallel fashion, associated with joints and micro-cliffs in the aeolianite.The potholes possibly formed during several slowstands or stillstands surrounding the Last Glacial Maximum (LGM, 25,000 to 20,000 yr BP) and the Bølling-Allerød interstadial (B-A, 14,500 yr BP). Given their sizes, we ascribe part of their development to chemical weathering of the platform, especially during the periods where sea spray could pond to form dissolution pans in the supratidal part of the aeolianite platform. A wet and warm B-A climate exacerbated chemical weathering, with karst processes initially dominant, followed by mechanical weathering with shoreline migration. Once submerged, only horizontal enlargement ensued. Geological contingencies (joints, bedding planes and platform lowpoints), modified by early weathering-dominant and later wave-dominant processes, were responsible for the evolution of the shore platform morphology.

Seismic-based paleoenvironmental analysis of the Paleocene carbonate shelf in Ajdabiya Trough, north-central of Libya

Abstract The results of the seismic and well logs interpretation, together with previous literature, were used to construct a generalized model of the development of the Paleocene reefs, and a depositional model for the Paleocene carbonate shelf in Ajdabiya Trough that focuses on the initiation, growth, and demise of the reefs in this basin. The Intisar reefs began as algal-foraminiferal banks. Growth of the reefs was halted by a short-lived transgression that drowned reefs and led to shale deposition of Kheir shales. The inversion of 3-D seismic data to acoustic impedance has allowed for a better determination of the main facies in Intisar reefs. These facies reflect different depositional conditions and different ages. They are: 1) algal-foraminiferal packstone/grainstone; 2) bioclastic grainstone/packstone; 3) coralline floatstone/bindstone; 4) reefal boundstone and; 5) bio-lithoclastic talus. The Upper Sabil consists of a prograding carbonate shelf with ramp platform morphology, and its differentiated deposits indicate four main depositional facies tracts: 1) inner shelf margin; 2) barrier reefs; 3) pinnacle reefs and; 4) outer shelf margin. The proposed model for the growth of the Paleocene reefs in the Ajdabiya Trough represents consecutive stages of development: 1) the Lower Sabil Carbonate was deposited during the very early Upper Paleocene time; 2) the influx of the Sheterat Shale during the major marine transgression; 3) the sea-level began a very slow fall due to variable subsidence of the underlying strata (a deposition of micrite over the Sheterat Shale, the lower part of the Upper Sabil Carbonate); 4) the rise in sea level is evident from an increase in foraminifera and algae constituents over the high areas of the lower part of the Upper Sabil Carbonate; 5) the isolated Intisar reefs were born under the proper local circumstances. The rate of subsidence was very slow, and the coral reef had significant upward growth and; 6) a major transgression happened at the end of the Paleocene, and the consequent deepening of the water in the area drowned and killed the Intisar reefs and capped it with Kheir Shale.

The battle for the future of SERS – TiN vs Au thin films with the same morphology

This work compares for the first time the SERS activity of TiN and Au nano/micro-structures having the same morphology. Si pyramids formed by alkaline etching were coated with Au and TiN layers of three different thicknesses (20, 57 and 80 nm). The morphology of both platforms was investigated using SEM microscopy. The optical properties were examined by spectroscopic ellipsometry and diffuse reflectance spectroscopy.The results prove that both the Si/TiN and Si/Au microstructures exhibit plasmonic properties in the visible range, and can be effectively applied as SERS platforms.Two dyes were chosen as the Raman reporter molecules. Data analysis showed the highest EF for the thickest layer of the deposited Au and TiN layers. It was found that, for the 80 nm layer on both Au and TiN, even as low as 10-9M concentrations of tartrazine could be detected. In both cases, the SERS platform could be cleaned by rinsing in distilled water, and then re-used. It was found that for the Si-Au pyramids the reversibility was equal to 13, while the Si-TiN could be washed even after 20 cycles.

The effects of planform morphology on two-dimensional wave transformation over near-horizontal shore platforms

Shore platforms fronting cliffs have highly irregular planform configurations that could modify the alongshore distribution of wave energy, thereby influencing cliff erosion. However, research aiming to understand the geomorphological control of platform morphology on two-dimensional wave transformation remains scarce. We conducted detailed wave measurements within the intertidal zone of three commonly observed mesoscale planform geometries (straight, concave and convex seaward edges). Waves were measured using a phased array of pressure transducers near the seaward edge of three near-horizontal shore platforms in New Zealand. Waves were analysed at infragravity (IG: 0.002–0.05 Hz) and swell frequencies (SW: 0.05–0.125 Hz), with wave energy derived from the zeroth moment wave height, directional wave spectra derived from the Extension of the Maximum Entropy Method and phase lag derived from the cross-spectrum characteristics. Results showed that wave translation occurred on the straight edge platform, divergence on the concave platform, and convergence on the convex platform. These patterns generated areas of wave ray convergence and divergence over the platforms. Wave energy convergence coincided with increased IG energy and reduced SW energy decay, whereas divergence had the opposite effects. Wave reflection generated cross-shore standing IG waves, for which nodal states varied alongshore with platform width. These phenomena resulted in alongshore variations in normalised wave energy Ê over the three platforms, which were more pronounced for IG than for SW. Compared to the straight platform, alongshore variations of IG were twice as large on the concave platform and three times larger on the convex platform. This study shows that planform morphology impacts along-platform wave energy distribution. These effects likely influence planform rock coast evolution and should be considered in future numerical modelling studies.

Backstepping patterns of an isolated carbonate platform in the northern South China Sea and its implication for paleoceanography and paleoclimate

Backstepping of carbonate platform margins is an important process for understanding how carbonate platform responds to paleoenvironment changes. The products of backstepping, such as backstepped margin, backstepping surface and backstepping succession have been widely documented on both modern and ancient platforms around the world. However, the causes of platform backstepping have not been understood fully yet. This study presents a detailed description of variations in backstepping pattern of Xuande platform in the northern South China Sea using 2D seismic and bathymetric data. The results show two episodes of backstepping events occurred during the late Middle Miocene and the latest Miocene to the Early Pliocene. The former backstepping event occurred on the eastern margin of the platform and likely resulted from upwelling and turbulence related to the onset of contour currents in the Xisha Archipelago. The latter backstepping event shows a change of backstepping distances at different platform margins with more pronounced backstepping along the winter-monsoon windward side compared to the corresponding leeward side. It is proposed that this event was largely the result of vigorous currents and waves impinging on the platform margins related to an intensification of the East Asian monsoon and a relative sea-level rise. A difference in hydrodynamic energy was responsible for the variations in backstepping distances at platform margins. Platform margins exposed to higher-energy environment backstepped further than margins exposed to lower-energy envrionment. Results from this work indicate the morphology and stratigraphic architecture of carbonate platforms are strongly controlled by the hydrodynamic energy, here related to currents and waves driven by East Asian monsoon winds.

Tectonics and shore platform development: Rates and patterns of erosion on recently uplifted mudstone and limestone rocks at Kaikōura Peninsula, New Zealand

On tectonically active coasts, there is a dearth of erosion data documenting how rock coasts adjust (either fast or slow) in response to marine and subaerial processes immediately after coseismic uplift. Here we report erosion rates and evidence of reshaping of shore platform morphology at Kaikōura Peninsula, South Island, New Zealand, following the November 2016 Kaikōura 7.8 (Mw) earthquake, that uplifted platforms by ~1 m and extended their widths. High-resolution topographic data obtained from quarterly surveys over four years using a micro-erosion meter (MEM) and Structure-from-Motion Multi-View Stereo (SfM-MVS) surveys have provided rates of erosion and visual representation of surface morphologies. MEM data revealed variations in erosion, weathering and deposition rates across lithology, tidal positions, and platform elevation after the uplift. After four years, surface downwearing rates for all platforms were on average 2.25 mm/yr, a 104% increase from the pre-uplift rate of 1.10 mm/yr. Average lowering rates on limestone, hard, and soft mudstone platforms were 1.19 mm/yr, 2.31 mm/yr, and 3.21 mm/yr, respectively. Results show a change in patterns of erosion rates and faster rates on mudstone than limestone lithologies, but both faster when compared to pre-uplift rates. Previously reported seasonal trends in erosion rates have disappeared because post-uplift erosion rates are similar during the summer and winter. In contrast, statistically significant differences in lowering rates now exist across rock lithology and elevation. On one MEM site on the harder mudstone platform, a large increase from a pre-uplift erosion rate of 0.43 mm/yr to 19.23 mm/yr (1-year after uplift) and subsequent decline to 1.54 mm/yr after four years demonstrates the role of block detachment not previously seen in the MEM data from Kaikōura. For the first time, we complement MEM data with SfM-MVS-derived orthomosaics to provide evidence of changing rock morphology and processes such as granular disintegration, flaking and algal growth. Results from this study demonstrate how tectonism can fundamentally alter the way in which rock shore erosion rates are influenced by waves, tides, and weathering processes.

Limestone Sea Stacks (Rauks) Record Past Sea Levels and Rocky Coast Evolution in the Baltic Sea (Gotland and Fårö Islands, Sweden)

In this article, we explore the potential for sea-level change and rocky coastal evolution reconstruction hidden in one of the most intriguing rocky coastal landforms in the Baltic Sea region—rauks. Those unique limestone sea stacks are preserved along the coasts of a number of Swedish islands, with Gotland and Fårö as primary locations. We contributed to the long-standing debate on their origin and attempted to investigate the modern geomorphological processes operating on rauks using novel approaches in rock coast studies, including Schmidt hammer rock tests (SHRT)—to characterize zonation in the degree of coastal landforms weathering; traversing micro-erosion meters (TMEM)—to calculate shore platform downwearing rates; and terrestrial laser scanning (TLS) to monitor coastal abrasion and detect sea-level markers (notches) and describe their size and shapes. Our study shows the dominance of mesoscale changes in the shore platform morphology (erosion scars, spalling, and block erosion) over the microscale downwearing carried out by abrasion. We argue that the preservation of rauks along the modern coast of Baltic islands is a result of a favorable sequence of events including the rapid land uplift and their lithological resistance, significantly higher than observed on surrounding platforms and cliffs formed in different types of limestone. Our findings prove that the microrelief of rauks in the form of well-preserved notches records the sea-level changes from at least the late Ancylus Lake period. Finally, we incorporate the results of our observations into the classic notions of rauk formation and highlight the effect of cutting off sea stacks from the operation of littoral processes as a consequence of land uplift and dominance of subaerial weathering over the wave action.

Perspectives on wave transformation over a near-horizontal shore platform: Comparison of a two-dimensional and transect approach

Understanding wave transformations over intertidal shore platforms is necessary for managing rock coasts. Previous studies have investigated the effects of intertidal shore platform morphologies on wave transformation using instruments aligned in cross-shore and longshore arrays. This approach has provided a fundamental understanding of the influence of platform profile characteristics on wave transformation properties. However, it precludes the consideration of shore platform planform morphologies on two-dimensional wave transformation, which has been overlooked or only of secondary concern. We developed a two-dimensional approach to measure the wave direction of both swell waves (SW: 0.05 Hz < frequency < 0.125 Hz) and infragravity waves (IG: frequency < 0.05 Hz) during transformation across a near-horizontal shore platform (NHSP). Waves were measured using a grid of 14 pressure transducers (PT) recording at 2 Hz. Directional wave spectra were derived using the Extension of the Maximum Entropy Principle (EMEP) method. Both SW and IG were subject to strong directional changes over the NHSP induced by refraction on the lateral edges of the platform and reflection at the cliff toe. As a result, a dominance of oblique and reflected wave trains was observed over the inner platform while onshore waves propagating along the transect represented only 36% of the SW energy and 22% of the IG energy. These directional changes affected the wave energy distribution over the shore platform surface, generating complex energy patterns. A 77% decrease of refracted SW energy was recorded from the intertidal platform edges to the platform centre. Two dominant IG energy patterns were identified. The first was a long-shore increase of energy toward the central axis of the platform and a cross-shore increase of energy from the platform centre to the seaward and landward extremities. This pattern was seen for 81% of the submersion period. The second pattern also reported in previous research was an increase in IG from intertidal platform edges to the shoreline, but this was only observed for 15% of the submersion period. The two-dimensional approach developed in this paper allowed to provide field-based observations of the combined effects of wave reflection and refraction on wave energy distribution over a NHSP.

The effects of storms and a transient sandy veneer on the interannual planform evolution of a low-relief coastal cliff and shore platform at Sargent Beach, Texas, USA

Abstract. Coastal cliff erosion is alongshore-variable and episodic, with retreat rates that depend upon sediment as either tools of abrasion or protective cover. However, the feedbacks between coastal cliff planform morphology, retreat rate, and sediment cover are poorly quantified. This study investigates Sargent Beach, Texas, USA, at the annual to interannual scale to explore (1) the relationship between temporal and spatial variability in cliff retreat rate, roughness, and sinuosity and (2) the response of retreat rate and roughness to changes in sand and shell hash cover of the underlying mud substrate as well as the impact of major storms using field measurements of sediment cover, erosion, and aerial images to measure shore platform morphology and retreat. A storm event in 2009 increased the planform roughness and sinuosity of the coastal cliff at Sargent Beach. Following the storm, aerial-image-derived shorelines with annual resolution show a decrease in average alongshore erosion rates from 12 to 4 m yr−1, coincident with a decrease in shoreline roughness and sinuosity (smoothing). Like the previous storm, a storm event in 2017 increased the planform roughness and sinuosity of the cliff. Over shorter timescales, monthly retreat of the sea cliff occurred only when the platform was sparsely covered with sediment cover on the shore platform, indicating that the tools and cover effects can significantly affect short-term erosion rates. The timescale to return to a smooth shoreline following a storm or roughening event, given a steady-state erosion rate, is approximately 24 years, with the long-term rate suggesting a maximum of ∼107 years until Sargent Beach breaches, compromising the Gulf Intracoastal Waterway (GIWW) under current conditions and assuming no future storms or intervention. The observed retreat rate varies, both spatially and temporally, with cliff face morphology, demonstrating the importance of multi-scale measurements and analysis for interpretation of coastal processes and patterns of cliff retreat.

Marine carbonate factories: Review and update

AbstractThe carbonate factories model, as defined at the beginning of the century, provides a subdivision of marine carbonate sediment production‐systems based on the style of carbonate precipitation. The main factors controlling marine carbonate precipitation are light, water temperature, nutrients, salinity, substrate and carbonate saturation. Site‐specific controls influencing the systems comprise ocean currents, upwelling and non‐upwelling systems, ocean‐atmosphere systems, atmospheric systems, shallow‐water dynamics, and terrestrial sediment and water input.Each factory has its own sediment‐production window linking optimal sediment production with selected environmental controls. Sediment production in the tropical factory (T‐factory) is light and temperature‐dependent and negatively impacted by nutrients. Sediment production and export depends on the size of the shallow‐water areas within the photic zone. The cold‐water‐coral factory (CWC‐factory) is nutrient‐dependent, but light‐independent. Sediment production relates to nutrient supply enabling the growth of the cold‐water corals. The cool‐water factory (C‐factory) displays a strong link to nutrients and water temperature, with parts that are light‐dependent, for example, sediment production in kelp dominated environments. The sediment mineralogy and sediment production area within the high‐energy hydrodynamic zone govern sediment distribution with sediment behaviour comparable to siliciclastics. The microbial/mud‐mound factory (M‐factory) is nutrient‐dependent and to some extent temperature and light‐independent. Sediment production and export is referred to here as slope shedding and links to the main sediment production on the upper slope. The planktic factory (P‐factory) depends on variations in light, temperature and nutrients resulting in fluctuating pelagic fall‐out.Platform morphologies and slope profiles are also factory specific: T‐factories show a rimmed flat‐topped platform with adjacent exponential slopes or a carbonate ramp morphology; CWC‐factories display mound morphologies with steep slopes; C‐factories are associated with open shelf systems and Gaussian shaped slope profiles; while M‐factories are characterized by individual steep‐sided mounds or flat‐topped platforms with deepened margins and a linear shaped slope profile. The P‐factory provides biotic grains to all environments and at times, like for the Cretaceous, may dominate sedimentation patterns in the basin realm.The sequence stratigraphic patterns substantially differ between factories. The T‐factory being light‐dependent is characterized by higher sediment production when the platform tops are flooded (highstand shedding). It displays decoupled sediment wedges with the partial infill of accommodation in the shallow‐water realm and major sediment export towards the slopes and surrounding basins. The CWC‐factory is marked by in situ production and deposition with limited sediment export forming single CWC spots or sediment accumulation ridges. The C‐factory has a siliciclastic equivalent style of sediment distribution with lowstand‐dominated, shelf edge wedges and a shaved‐off shelf during sea‐level highstands. Slope shedding marks the M‐factory in which sediment production occurs within the upper slope realm of the flat‐topped platforms both during highstands and lowstands in sea‐level. This allows for fairly continuous sediment production exhibiting minor impact of sea‐level changes, but with progradation, aggradation and retrogradation of the system being only limited by local environmental changes. P‐factory sediment production may vary in accordance with variations in sea‐level, providing time‐lines and systems tracts boundaries in the pelagic realm.In summary, each factory is branded by an individual set of features, for example, production window, sediment production and export, morphologies and slopes. It is this unique set of variables marking each factory that determines the factory‐dependent response to small‐scale and large‐scale environmental changes through space and time as shown in the sequence stratigraphic development.

High-resolution acoustic data revealing periplatform sedimentary characteristics in the Xisha Archipelago, South China Sea

Newly collected high-resolution acoustic data are used to describe the morphologies and sedimentary characteristics along the slopes of isolated carbonate platforms in the Xisha (Paracel) Archipelago. Based on multibeam bathymetric and seismic data, we have identified seven types of morphological and depositional features around the platforms, including erosive grooves, mass transport deposits, gullies, confined channels, canyons, mounded sediments, and marginal contourite depressions. The occurrence of erosive channelized features around the platforms indicates that gravity flow is a major sediment-export mechanism for the transportation of excess neritic carbonates towards the slope. Marginal contourite depressions and mounded sediments are interpreted as bottom-current reworking products, suggesting an important role of bottom current and deepwater circulation of the South China Sea in shaping the slope morphology of the carbonate platforms. Furthermore, the bottom-current products tend to develop along the slopes of the carbonate platforms at the Xisha Uplift margin; in particular, erosional features formed by bottom current frequently occur in the southern side of the carbonate platforms. By comprehensive analysis of morphological and depositional features, we establish a facies model around the carbonate platforms to interpret different sedimentary transport processes, such as off-platform and along-slope sediment transport processes. These findings highlight a notable and complex relay-style channelized transport system consisting of grooves/gullies-channels-canyons, which has implications for linking neritic carbonate platforms into deep-sea basins.

Middle Triassic carbonates of Eastern Iberia (Western Tethyan Realm): A shallow platform model

Much of the eastern sector of the Mesozoic Iberian basin belongs to the ‘Mediterranean type’ Triassic. This type is characterized by a Middle Triassic stratigraphic record comprised of two carbonate Muschelkalk units (lower and upper) separated by a detrital-evaporite middle Muschelkalk unit. In the present study areas, the two first marine flooding episodes of the Middle Triassic led to the deposition of extensive shallow-water carbonates on a block-controlled epicontinental platform in the lower and upper Muschelkalk units. These carbonates were part of third-order transgressive–regressive sequences. The two carbonate sequences display similar vertical facies and stratigraphic sub-unit arrangements. The base of the two sequences is marked by a (lower) carbonate-marl alternation, which was deposited in mixed tidal flat-to-lagoon settings. In the middle of the sequences, the carbonate character is predominant and facies associations mainly suggest shallow waters and high environmental variability. The change from a transgressive to regressive trend occurs in the middle of the sequences, although the position of the maximum flooding zone can vary from one to another stratigraphic section. The tops of the sequences show two different lithological assemblages, which are coeval and grade laterally to each other. One assemblage is a ‘carbonate terminal complex’ formed by tidal flat and sabkha deposits, which is predominant in the lower Muschelkalk unit. The other assemblage is a lagoon-peritidal (upper) carbonate-marl alternation, predominant in the upper unit. Together, the two sequences suggest a complex platform morphology with a mosaic facies distribution, which evolved from a not very high energy ramp-like profile (transgressive phases, TST) to a lower energy rimmed shelf, ending with tidal/lagoon environments (regressive phases, HST). Facies associations, however, suggest somewhat deeper depositional settings for the upper than lower Muschelkalk unit. Here we compare the two carbonate units in the study areas with those described in the literature from other Triassic basins of Eastern Iberia and the SW Germanic Basin, all forming part of the Peri-Tethys area of the Tethyan Realm.

High resolution mapping and analysis of shore platform morphology in Galicia, northwestern Spain

Most research on shore platforms has been at fairly large spatial scales over distances ranging from hundreds to thousands of metres. Other work at much smaller scales, ranging from one to several decimetres, often corresponds to the dimensions of micro-erosion meter stations. Few studies have been concerned with platform morphology in which the basic data are acquired at intermediate or meso-scales ranging up to a few metres. This is due, in part, to terrestrial surveying at meso-scales being time-consuming while aerial surveys using LiDAR are expensive. A meso-scale study was made on three shore platforms in western Galicia, northwestern Spain using data from an Unmanned Aerial Vehicle (UAV) to produce high resolution Digital Surface Models (DSMs) and to calculate local surface elevation, roughness, slope, and joint density at a 0.5 m pixel scale, and joint orientation and length. This was supplemented by Equotip field measurements of rock hardness. A granitic platform was higher and had rougher surfaces and steeper slopes than two platforms in schist. The relationship between platform morphology and rock hardness and joint density was complex, however, reflecting in part the role of schistosity in accounting for the formation of low, regular platforms in hard schists with low joint density. The study suggested that while tidal range, inheritance, and other environmental and evolutionary factors can be dominant in determining platform morphology at the macro- or regional scale, geological, and particularly structural, factors become increasingly important in Galicia as the scale diminishes, and they are generally dominant at the local or meso-scale.

Coastal chalk cliff retreat rates during the Holocene, inferred from submarine platform morphology and cosmogenic exposure along the Normandy coast (NW France)

Submerged marine terraces potentially provide crucial information on past sea-level variations and paleo-coastline locations that may be used to estimate long-term coastal erosion rates. The Normandy coastline has recently been surveyed using a shallow water high-resolution mapping system. We identified a new continuous submarine platform, called the inner platform, limited by a shore parallel edge located between -9 m and -10 m (NGF) along the Normandy chalk coastline. A lower rock platform, called the outer platform, ranging from about -14 m to -17 m (NGF) appears locally. This corresponds to inherited preserved submarine terraces created during a past sea level highstand. The high cosmogenic 10Be concentration measured at the end of Mesnil-Val inner shore platform (including intertidal and subtidal shore platforms) is attributed to the last glacial cliff location at 6.5 ky ± 1 ky. From the spatial edge location of the inner platform in Normandy, we estimated cliff retreat rates since 6.5 ky ± 1 ky ranging from 0.051 ± 0.008 m/y to 0.090 ± 0.014 m/y from place to place. Comparisons with the current coastal chalk cliffs indicate a mean retreat rate estimated over the contemporary period suggesting such long-term retreat rates are 33% to 57% lower than the contemporary ones (0.10 m/y to 0.18 m/y). This confirms a contemporary acceleration of chalk cliff system retreat rates.

Oncoid distribution in the shallow domains of a Kimmeridgian carbonate ramp (Late Jurassic, NE Spain)

The distribution and abundance of oncoids in the shallow domains of a latest Kimmeridgian carbonate ramp was accomplished on the basis of a detailed sedimentological and petrographic analysis of the lower part of the Higueruelas Formation (Iberian Basin, northeastern Spain). Six types of oncoids are recognized based on the internal structure of the cortex, and show a preferential distribution on the carbonate ramp, which record from intertidal, lagoon, backshoal, shoal-sand blanket, foreshoal to offshore domains. Spherical type I oncoids, composed of continuous micritic laminae, occur in all the subenvironments in low proportions. Sub-spherical type II oncoids, constituted by micritic laminae and discontinuous organism-bearing laminae of mostly Bacinella irregularis, dominate in the higher-energy shoal-sand blanket domain. Type III oncoids, with alternating micritic and organism-bearing laminae of mostly Bacinella irregularis-Lithocodium aggregatum association, include two varieties: type IIIa oncoids, with micritic and organism-bearing laminae of similar thickness, preferentially formed in the foreshoal domain; and type IIIb oncoids, with thinner micritic laminae, formed in a low-energy sheltered lagoon. Irregular type IV oncoids characterize the low-energy settings, and include two varieties: type IVa oncoids, mainly consisting of a Bacinella-Lithocodium meshwork, which occur abundantly in the lagoon; and less abundant type IVb oncoids, composed of a continuous organism-bearing laminae of Lithocodium, which are found in the offshore domain. Water energy and platform morphology played an important role in formation and distribution of the oncoids in these shallow domains, where normal-marine water and oligotrophic conditions are highlighted by the high-diversity of light-dependant micro-encrusters in type III and IV oncoids. Comparable oncoid distribution patterns of diverse Late Jurassic shallow carbonate platforms enhance their potential use as reliable palaeoenvironmental proxies.

Bedrock hardness values and morphological zonation of a shore platform in South Africa

Shore platforms found along rock coasts worldwide are often interpreted as wave abrasion acting on uniform bedrock surfaces. Whilst this viewpoint may apply at the macroscale, there are complex feedbacks among bedrock properties (rock type, mineralogy, rock structures), weathering and erosion processes and rates, and microtopography at the meso- to microscale. In turn, these influence wave runup, backwash processes, and the extent of wave-splash and physical, chemical, and biological weathering processes that result. This study investigates the relationships among bedrock hardness properties, microtopography, and shore platform denudation processes from a site on the Indian Ocean-facing coast of South Africa. Three shore-normal transects (45–57 m in length) were surveyed across the sandstone platform using a differential global positioning system (GPS). These data were integrated with rock surface hardness measurements along the transects taken using a Proceq Equotip instrument. Results show that platform morphology and hardness values vary considerably, corresponding to the most dominant denudation processes found at different positions in the tidal frame. The lowest hardness values (most extensive rock weathering) are found on the landward third of the platform but away from the land margin. The highest and greatest variability of hardness values are found on bedrock highs immediately above the highest astronomical tide level, in the lower third of the profile. This position suggests a dominant role of wave-splash and wetting/drying. Variations in hardness values and microtopography through the transects were used to develop an evolutionary model linking rock hardness values to specific weathering and erosion processes of the rocky shore platform.

Environmental controls on the development of Mississippian microbial carbonate mounds and platform limestones in southern Montagne Noire (France)

AbstractLate Mississippian carbonates in southern Montagne Noire are dominantly domical to laterally‐accreted microbial mounds in some formations, as well as stratiform microbial limestones occurring in hundreds of olistoliths within a flysch basin, constituting pieces of a giant puzzle that are used to help reconstruct a platform in a region that is no longer preserved. Petrographic data of limestone samples from 14 continuous long sections of olistoliths have been analyzed statistically, using multivariate clustering (Q‐mode) of the components/matrix/cement and canonical correspondence analysis that allow the reconstruction of the environmental parameters of carbonate microbial communities in space and time. Clustering analysis separated microbial and non‐microbial facies. The calculation of indices along the various axes from canonical correspondence analysis allows recognition of the controlling factors of the mounds and microbial growth as being turbidity, light penetration, bathymetry and storms. Turbidity and light penetration are the primary factors controlling the morphology of the microbial limestones. Representation of the light penetration and bathymetry indices on the stratigraphical sections defines two vertical environmental gradients. Light penetration can be subdivided into euphotic, euphotic–dysphotic and dysphotic‐aphotic conditions. The representation of the bathymetry allows the subdivision of samples into a deeper outer ramp, external mid‐ramp and internal mid‐ramp. The curve distance from the section base = f (index) suggests a cyclicity for the platform that cannot be compared with the onlap curve defined from other cratonic areas (Moscow Basin), and thus the cyclic succession of the Montagne Noire is interpreted to have been mostly tectonically‐controlled. Integration of the data allowed the reconstruction of the original Mississippian carbonate platform, where, up to the Mikhailovian, it appears to correspond to a platform morphology, with narrow shallow water facies and wide turbiditic systems, whereas the width of shallow‐water settings expanded during the Venevian to the Protvian, forming a ramp or distally‐steepened ramp with widespread microbial limestones.