Interpretation Of Depositional Environments Research Articles

New palaeocurrent analysis approach from two‐dimensional trough cross‐strata using photographs and anisotropy of magnetic susceptibility

AbstractPalaeocurrent analysis is vital for basin analysis and helps in the interpretation of depositional environments (along‐slope or downslope). For that, it is crucial to have multiple measuring methods at hand to apply palaeocurrent analysis with a wide range of different datasets (outcrops, cores and photographs). Here, two relatively underexploited palaeocurrent measurement techniques are assessed when applied to trough cross‐stratification observed in the Arenazzolo Formation at Eraclea Minoa (Sicily). The first technique is a novel design of a qualitative approach to infer palaeocurrent directions from photographs of two‐dimensional sedimentary structures. The second technique involves measurements of the anisotropy of magnetic susceptibility from drilled samples. A broad agreement, with overlapping uncertainty boundaries, is observed between results from both techniques. This agreement validates the use of trough cross‐strata to infer palaeocurrent directions. Moreover, the addition of photographs improves reproducibility and prevents a bias towards the best‐exposed troughs. The application of both techniques to outcrops and sedimentary cores provides new opportunities for palaeocurrent analysis in any type of sedimentary environment.

Machine learning of the chemical elements for enhanced interpretation of depositional environments: Upper Jurassic strata case study in central Saudi Arabia

To explore how machine learning (ML) techniques can enhance the interpretation of depositional environments using chemical elemental data, this study analyzes data from 156 shallow marine strata samples. Several advanced machine learning (ML) techniques were integrated to predict lithofacies and stratigraphic units of shallow marine carbonate strata, focusing on the Arab-D reservoir equivalent outcrops in Central Saudi Arabia. Utilizing a detailed geochemical dataset comprising major, trace, and rare earth elements, we aimed to determine the feasibility of using chemical elemental data in sedimentary geology for predictive modeling. The studied strata are categorized into two lithological units based on depositional settings: one unit comprises rocks that dominantly deposited below the storm wave base with a single lithofacies association, whereas the other includes rocks dominantly deposited above the storm wave base, and consists of two lithofacies associations. The study demonstrates the efficacy of ML algorithms in distinguishing these two lithological units, with a minimum prediction accuracy of 76%. Four ML techniques, including K-nearest neighbors (KNN); random forest classifier (RFC); gradient boosting classifier (GBC); and multi-layer perceptron neural network (MLP-NN) were used, two of them (RFC and GBC) achieved 89% and 92% prediction accuracy. However, a slightly poorer performance was observed in predicting fine-scale lithofacies associations of these lithological units, especially for the lithofacies association representing a transitional interval between the two lithofacies units. Expanding the scope of the study, we tested the ML models against geochemically similar strata from the Oligocene shallow marine reef carbonates. These strata are globally comparable and provide an external validation for the predictive models developed from the Saudi Arabian dataset. GBC and RFC maintained a higher accuracy level than KNN and MLP, demonstrating their robustness and transferability across diverse geological settings. Based on these results, the study underscores the significance of specific oxides and elements as distinctive geochemical markers, elucidating the environmental conditions of the depositional environments and their deposits. This research advances the application of ML in interpreting the depositional environments of shallow marine strata using elemental data, as the majority of the existing researches focus on employing unsupervised machine learning for cluster analysis.

Gypsum lakes, sandflats and soils revealed from the Triassic Red Peak Formation of the Chugwater Group, north‐central Wyoming

AbstractBedded gypsum is relatively common in bedded evaporites associated with red bed siliciclastics of Permo‐Triassic Pangea. However, little attention has been paid to the textures of ancient gypsum, which can be used to refine interpretations of depositional environment and diagenetic history. This project describes the textures of bedded gypsum from an outcrop of the Triassic Red Peak Formation (Chugwater Group) near Greybull, Wyoming. Fieldwork, petrography and X‐ray diffraction reveal three distinct lithologies of bedded gypsum: bottom‐growth gypsum, laminated gypsum and clastic gypsum. Bottom‐growth gypsum precipitated at the bottom of shallow saline surface water bodies. Laminated gypsum probably formed in shallow saline lakes and mudflats. Clastic gypsum units are composed of aeolian‐reworked bottom‐growth gypsum crystals deposited in sandflats. Red siliciclastic mudstones are characterised by their massive nature and abundant blocky peds. Detailed study of this outcrop of the Red Peak Formation shows that it formed in shallow saline lakes and associated mudflats, sandflats and desert soils.

Sedimentary Facies, Palynology, and Organic Geochemistry of Eocene Kalumpang Formation in Lariang and Karama Areas, West Sulawesi, Indonesia

The Kalumpang Formation was deposited in a delta plain setting. A Middle to Late Eocene age (Proxapertites operculatus zone) was inferred from palynological analysis, with a paleoenvironment in a coastal plain setting with a strong terrestrial influence. Samples from the Kalumpang Formation indicate a marginal to early mature stage for hydrocarbon generation. It is mostly composed of gas-prone to oil and gas-prone Type III kerogen facies. The biomarker character of both the rock and oil samples suggests a terrestrial origin, with a significant contribution of estuarine or bay organic material. The oil derives from a non-carbonate lithology, while the rock samples are from carbonate/calcareous shale origin. The abundance of oleanane compound and C30 resins suggests higher plant angiosperm input of Late Cretaceous or younger age for both the rock and the oil samples. The oil seep contains more abundant oleananes compared to the carbonaceous mudstone of the Kalumpang Formation. This suggests that the oil originated from more marine facies than the rock samples, which were deposited in a delta plain setting. This study demonstrated the agreement of depositional environment interpretation and age assessment between lithofacies, palynological, and organic geochemistry analysis.

Palynostratigraphy and depositional environment of Tura and Pre-Tura sedimentary successions in Dhansiri Valley of Upper Assam Shelf, Assam & Assam-Arakan Basin, Assam, India

Detailed palynological investigations have been carried out to reconstruct stratigraphy and interpretation of depositional environment of Tura and Pre-Tura sedimentary sections in Dhansiri Valley of Upper Assam Shelf, Assam & Assam-Arakan Basin. Sediments of the Tura Formation dated as Early Eocene and interpreted to be deposited under subtidal to inner shelf environment. Pre-Tura sediments, developed in studied wells, led to the identification of Dergaon, Bamangaon and Moabund formations with intervening unconformities, having different tectonic history and distinct palynofossil assemblages. Early Permian sediments of the Dergaon Formation (=Talchir Formation), the oldest in the basin are deposited under the intracratonic phase, overlie the metamorphic basement complex. The sediments of the Dergaon Formation are unconformably overlain by the Bamangaon Formation deposited during the Early Cretaceous, whereas, in well DR-A, the sediments of the Dergaon Formation are directly overlain by the Moabund Formation corresponding to the Late Maastrichtian age. The sediments of the Tura Formation overlie the Maobund Formation in well DR-A, and they overlie the Bamangaon Formation in the rest of the wells in Dhansiri Valley.

Depositional environment and source rock distribution of the Late Cretaceous Rakopi formation in the deepwater Taranaki Basin, New Zealand

The interpretation of depositional environments and evaluation of potential source rocks in deepwater frontier basins are challenging because of the limited data availability. The Deepwater Taranaki Basin, the northwest extensional area of the Taranaki Basin in New Zealand, hosts the Late Cretaceous Rakopi Formation, which is one of the most important source rocks and potential reservoirs in the Taranaki Basin. This study utilized seismic data and well ties from the Romney-1 well to interpret three seismic units in the study area, representing different depositional environments and evolutions. These units were correlated with the regional Megasequences B2–B4 in the Deepwater Taranaki Basin. Sediment transport and progradation mainly occurred from the northeast to the southwest direction. Fluctuations in relative sea levels influenced the shifting of the shelf and marginal environments, potentially creating coal-bearing strata in the study area. The key source rock strata were identified within units 2 and 3 characterized by kerogen type III, coaly source rocks in a marginal environment. A minor source rock interval was found in unit 2, characterized by kerogen type II, marine organic matter in a bathyal environment in the depocenter of the study area. Coal seams were identified using seismic and well log data. However, thin coal seams were challenging to distinguish clearly, sometimes showing a similar response to sandstone beds, because of the limited seismic resolution. Thus, within limited data areas, source rock predictions can be made in the context of depositional interpretation.

An operational classification system for the South Atlantic pre-salt rocks

Abstract The giant Aptian reservoirs and associated lacustrine rocks of the South Atlantic pre-salt section present a series of unique characteristics, which make the systems created for marine carbonate rocks quite inadequate for their classification. Based on our experience with the characterization of thousands of samples of the pre-salt reservoirs and associated deposits from the Brazilian basins, and on a wide literature evaluation, we propose an objective and operational system for the classification of the unusual yet extremely important pre-salt lacustrine rocks. The system allows the coherent record of structure, fabric, primary texture and composition, and main diagenetic modifications of the in situ and resedimented rock types. The in situ rocks are directly classified according to the original proportion among calcite spherulites, fascicular shrubs, and mud matrix. The resedimented rocks are classified according to the original volume of > 2 mm particles and the proportion between sand and mud, using calcirudite, calcarenite, and calcilutite as unbiased names. Such an approach can also be applied to the classification of other particulate carbonate rocks, avoiding the conceptual problems and dubious interpretation of depositional environment and reservoir quality of currently used classification systems. The direct, objective, and intuitive proposed classification system shall contribute to the understanding, exploration, and production of the extraordinary South Atlantic pre-salt petroleum province.

Late Pleistocene clastic tufa from Gafsa, southern Tunisia: Implications for paleo-landscape interpretation

The landscape reconstruction in the Jebel El Mida area during the Late Pleistocene was based on the continental carbonate record, particularly on the clastic tufa deposits. Four main lithofacies types of clastic tufa were recorgnized in the Jebel El Mida area, these are: (1) grain-supported macrodetrital phytoclast tufa, (2) grain-supported macrodetrital oncolith tufa, (3) grain-supported macrodetrital lithoclast tufa, and (4) matrix-supported microdetrital tufa. The interpretation of depositional environment reveals spring-fed streams and pools with highly CO2-enriched water helped in carbonate precipitation and incrustation on the vegetation cover. Dating of tufa deposits has been based on archeological content and radiometric (U/Th) age dating. A major lag exists between the age of the archeological content and the radiometric age for tufa (170 ky) indicating transport and re-sedimentation of older reworked tufa within the stone tool-rich sandsone and conglomeratic substrates. The major fault of Gafsa that cross-cuts the studied area is the main conduit for upwelling carbonated waters for tufa precipitation and also the re-organization of the landscape after the recurrent tectonic activity during the Late Pleistocene. The deposition of Jebel El Mida tufa indicates particular depostional settings characterized by (1) abundant rainfall on the recharge areas with high water table, (2) acidic water infiltrations through plant cover and soils, and (3) dissolution of aquiferous Cretaceous carbonates resulting in water mineralization of the groundwater during a time span that predates Late Pleistocene.

Cretaceous depositional environment interpretation of offshore Otway Basin cores and wireline logs; application to the generation of basin-scale gross depositional environment maps

Gas production from the Inner Otway Basin commenced in the early 2000s but the deep-water part of this basin remains an exploration frontier. Historically, the understanding of plays in this region were largely model driven and therefore the ground-truthing of depositional environments (DE) and gross depositional environments (GDE) are critical. This aspect has been investigated for the Sherbrook Supersequence (SS) by the integration of legacy wireline and core data, with regional 2D seismic facies mapping of new and reprocessed data from Geoscience Australia’s 2020 Otway Basin seismic program. Core observations were matched to wireline logs and seismic facies with resulting well-based DE interpretations calibrated to seismic resolution Regional GDE intervals. Integration of well and seismic observations led to the compilation of a basin-wide Regional GDE map for the Sherbrook SS. This GDE map indicates the distribution of Sherbrook SS play elements such as source rock, seal and reservoir, especially across the Deep-water Otway Basin where well data is sparse.

Depositional Environment and Lithofacies Analyses of Eocene Lacustrine Shale in the Bohai Bay Basin: Insights from Mineralogy and Elemental Geochemistry

AbstractThe effect of various depositional parameters including paleoclimate, paleosalinity and provenance, on the depositional mechanism of lacustrine shale is very important in reconstructing the depositional environment. The classification of shale lithofacies and the interpretation of shale depositional environment are key features used in shale oil and gas exploration and development activity. The lower 3rd member of the Eocene Shahejie Formation (Es3x shale) was selected for this study, as one of the main prospective intervals for shale oil exploration and development in the intracratonic Bohai Bay Basin. Mineralogically, it is composed of quartz (avg. 9.6%), calcite (avg. 58.5%), dolomite (avg. 7%), pyrite (avg. 3.3%) and clay minerals (avg. 20%). An advanced methodology (thin‐section petrography, total organic carbon and total organic sulfur contents analysis, X‐ray diffraction (XRD), X‐ray fluorescence (XRF), field‐emission scanning electron microscopy (FE‐SEM)) was adopted to establish shale lithofacies and to interpret the depositional environment in the lacustrine basin. Six different types of lithofacies were recognized, based on mineral composition, total organic carbon (TOC) content and sedimentary structures. Various inorganic geochemical proxies (Rb/Sr, Ca/(Ca + Fe), Ti/Al, Al/Ca, Al/Ti, Zr/Rb) have been used to interpret and screen variations in depositional environmental parameters during the deposition of the Es3x shale. The experimental results indicate that the environment during the deposition of the Es3x shale was warm and humid with heightened salinities, moderate to limited detrital input, higher paleohydrodynamic settings and strong oxygen deficient (reducing) conditions. A comprehensive depositional model of the lacustrine shale was developed. The interpretations deduced from this research work are expected to not only expand the knowledge of shale lithofacies classification for lacustrine fine‐grained rocks, but can also offer a theoretical foundation for lacustrine shale oil exploration and development.

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

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

Depositional processes of the mixed siliciclastic-carbonate system in the Lower Cambrian Xiannüdong Formation in the northern Sichuan Basin, South China

Mixed siliciclastic-carbonate systems contain significant heterogeneity of facies associations which complicates the interpretation of depositional environments and platform evolution. The Lower Cambrian Xiannüdong Formation in the northern Sichuan Basin was deposited in a mixed system which is characterized by the non-skeleton grain (ooids and microbialites) dominated carbonates mixed with siliciclastic sediments. Such a depositional system provides a template to decipher the facies variability of mixed depositional systems and the evolution of platform geometry. Based on the facies analysis in outcrops and drilling wells, seventeen lithofacies were identified and grouped into seven lithofacies associations which represents a shallow-marine environment dominated by wave and storm activities. The vertical stacking pattern of lithofacies in the Xiannüdong Formation archives a regressive cycle which can be subdivided into four sub-cycles (i.e., S1 to S4). All the four sub-cycles exhibit the characteristic of the shallowing-upward successions, which are overlain by a flooding unit. The spatial distribution of lithofacies suggests an eastward-inclined platform. The migrating ooid shoals together with the storm activities may prevent the platform from evolving into a rimmed shelf. The lateral and vetical distribution of the terrigenous materials indicates that the provenance of terrigenous sediments were mainly sourced from the Kangdian and Bikou massifs, which indicates that the mixed system and the provenance area were separated by the Mianyang-Changning trough. Therefore, the transport of siliciclastic materials was related to the available accommodation space on the shelf, and was controlled by the eustatic sea-level fluctuation, with increased input of siliciclastic material occurred during phases of relative sea-level rise. The input of siliciclastic sediments brings nutrition for the growth of algal–archaeocyathan mounds, and therefore the mounds were mainly developed in the lower part of Xiannüdong Formation. Moreover, high siliciclastic sediments influx would also influence the growth of ooids by serving nuclei and promoting abrasion, which resulted in smaller ooid size compared to those of the relatively pure oolite. This study provides clues to understanding the facies variability in mixed systems and servers as a valuable reference for studies of other similar platforms.

Depositional environment and sequence stratigraphy architecture of continuous Upper Permian and Lowermost Triassic deep marine deposits in NW and SW Iran

The end-Permian mass extinction, the greatest biotic crisis through the Phanerozoic, caused a severe loss of marine organisms in terms of abundance and diversity. Knowing sea level fluctuations, environmental conditions and the sequence stratigraphic architecture of the Upper Permian deposits will enable us to reconstruct events before the mass extinction and across the Permian/Triassic boundary in a regional and global context. The Upper Permian deposits are examined in well-known sections in Julfa, NW Iran and Abadeh in SW Iran using microfacies analyses, depositional environment interpretation and sequence stratigraphic framework. Detailed petrographic examination and microfacies analyses show third- and fourth-order cycles both in Wuchiapingian and Changhsingian deep-water distally deposited strata of Julfa and Abadeh sections. Considering Iranian tectonics during Permian through Triassic time, there was rifting accompanied by drift and subsequent subsidence. Tectonics was a main factor that influenced the depositional environment and sequence stratigraphic framework in the study areas. According to previous studies, since subsidence increased in a North to SW direction during Middle Permian through Triassic time, this effect is seen in lithologic characteristics of the Wuchiapingian with more mid-ramp settings in Julfa Beds in Julfa area, compared to the more outer-ramp settings of the Unit 6 of the Hambast Formation in Abadeh area. Tectonic subsidence influence was also responsible for creating the fourth-order cycles within third-order cycles despite the absence of common glacial events to create high-frequency cycles in Iran during the Lopingian. The Lopingian successive deepening in Iran caused the faunal changes which is evident in decreasing trend of body size and biodiversity in brachiopods and ammonoids and also marks the beginning of the transgressive system tracts during this time interval.

Tectonic controls on geomorphological dynamics and sediment dispersal in source-to-sink systems in the Qingdong Sag, Bohai Bay Basin

Well-log and three-dimensional (3D) seismic data are used to investigate the tectonic controls during the depositional periods of the Kongdian and Shahejie formations from Ek–Es 4 L to Es 4 U–Es 3 L–M on strata distribution, depositional systems and sediment dispersal in the Qingdong Sag, Bohai Bay Basin, East China, from a source-to-sink perspective. This tectonic transition is characterised by the Tanlu Fault switching from sinistral to dextral strike-slip as the fault system changed from a dominant NW–WNW trend during the Ek–Es 4 L period to a dominant WNW–EW trend during the Es 4 U and Es 3 L–M periods. These changes subsequently controlled the framework and areal extent of sediment dispersal in the inner-basin source-to-sink systems and resulted in a change in trend of inner-basin secondary structural belts, from primarily being NW-trending during the Ek–Es 4 L period to E–W-trending during the Es 4 U and Es 3 L–M periods. The tectonic transition also resulted in the western and southern source-to-sink systems expanding with time and controlled the flow path and sediment redistribution within each source-to-sink system with migration of the subsidence centre of the Qingdong Sag and even the region. The significant changes in the basin structure controlled the source area, flow path, sediment transport distance and direction, and have a significant impact on the interpretation of depositional environments and reservoirs in rift basins with a multi-phase evolution history. KEY POINTS The Qingdong Sag, Bohai Bay Basin, experienced a tectonic transition during sediment deposition in the Eocene. The tectonic transition resulted in changes to the fault system and basin geomorphology. Fault movement and changes in basin geomorphology affected source-to-sink systems.

PLEISTOCENE PALYNOLOGY OF EAST JAVA

This study is a part of geological investigation on Pleistocene sediment in East Java in order to evaluate hydrocarbon potential within this sediment of this area. The area of study is located in the on-shore East Java (Figure 1). It is financially supported by the oil company as this is commercial work done by LEMIGAS Exploration Department. Therefore, data used in this paper will be incompletely presented as they are confidential. The name of the studied wells and their precise locations are hided in this paper. Data used in this study derives from three wells namely R, S and T. Three different disciplines are applied in this study including palynology, micropaleontology and nannoplankton analyses which are useful for crosschecking purposes. Apparently, the integration of these analyses gains accurate interpretation of stratigraphy and depositional environment. The area of study is in East Java Basin which can be classified as a classical back-arc basin. During Pleistocene, the area of study was marked by regional uplift and the cessation of open marine sedimentation (LEMIGAS, 2005). Therefore Pleistocene age was dominated by non-marine deposition. Generally, this type of sediment is separated from the underlying layer by an unconformity (LEMIGAS, 2005). Most Pleistocene sediment consists of volcanoclastic as a result of volcanic activity which related to uplifting period. It is possible that volcanic activity was responsible for the burning of grass as indicated by the occurrence of charred Gramineae cuticles. The previous investigations on Pleistocene sediment showed the domination of grass pollen of Monoporites annulatus which suggested the expansion of dry climate during Pleistocene glacial maxima. The pollen diagram from Lombok Ridge produced by van der Kaas (1991a) proves the domination of Gramineae pollen during Pleistocene (Figure 2). The period of dry climate (glacial climate) is characterised by abundant Gramineae pollen, whilst the period of wetter climate (interglacial climate) is indicated by an increase of coastal and mangrove palynomorphs, but greatly reduced frequencies of Graminaae pollen (Morley, 2000). In addition, Rahardjo et al. (1994) referred to the high abundance of Monoporites annulatus to propose Pleistocene pollen zone of M. annulatus (Figure 3).

Pleistocene Palynology Of East Java

This study is a part of geological investigation on Pleistocene sediment in East Java in order to evaluate hydrocarbon potential within this sediment of this area. The area of study is located in the on-shore East Java (Figure 1). It is financially supported by the oil company as this is commercial work done by LEMIGAS Exploration Department. Therefore, data used in this paper will be incompletely presented as they are confidential. The name of the studied wells and their precise locations are hided in this paper. Data used in this study derives from three wells namely R, S and T. Three different disciplines are applied in this study including palynology, micropaleontology and nannoplankton analyses which are useful for crosschecking purposes. Apparently, the integration of these analyses gains accurate interpretation of stratigraphy and depositional environment. The area of study is in East Java Basin which can be classified as a classical back-arc basin. During Pleistocene, the area of study was marked by regional uplift and the cessation of open marine sedimentation (LEMIGAS, 2005). Therefore Pleistocene age was dominated by non-marine deposition. Generally, this type of sediment is separated from the underlying layer by an unconformity (LEMIGAS, 2005). Most Pleistocene sediment consists of volcanoclastic as a result of volcanic activity which related to uplifting period. It is possible that volcanic activity was responsible for the burning of grass as indicated by the occurrence of charred Gramineae cuticles.

The Upper Cretaceous-Lower Eocene carbonate platforms of the Mateur-Beja area (NW of Tunisia): A pattern of isolated platform

Paleogeographic reconstruction of ancient carbonate platforms contributes to better understanding carbonate facies distribution and their economic interests. Based on facies analyses, depositional environment interpretations and a comparison with modern platforms, the present study interprets the Upper Cretaceous and Lower Eocene carbonate deposits of the Mateur-Beja area, northwestern Tunisian domain, as deposited in an isolated platform. Facies belts of this platform are dominated by detrital and lithoclastic limestone mixed with pelagic carbonate and occasionally skeletal-rich and/or breccia deposits. Facies analysis shows that facies spectrum was deposited by diverse transport agents including storm currents, gravity-driven currents and bottom currents. Paleogeographic reconstruction of platform architecture shows that the platform is characterized by a flat-topped edge during the Late Cretaceous and a shoal-rimmed platform edge during the Early Eocene passing basinward through a depositional slope margin. Lateral arrangement of slope facies as well as the predominance of lime mud and sand led us to interpret slope deposits as wedge-shaped carbonate apron. Paleogeographic conclusions inferred from this study of suggest that the northwestern Tunisian isolated platform was developed in an offshore domain presumably detached from Maghrebian continental margin.

The Capiru Group: From passive margin to syn-orogenic units, implications for the evolution of the northern margin of the Curitiba microplate, Western Gondwana

The Capiru Group (Neoproterozoic) is a 4 km-thick succession deposited on the northern margin of the Curitiba microplate, Southern Ribeira Belt, Brazil. The Capiru Group successions are deformed within the Brasiliano - Pan African Ribeira Belt, which culminated in the amalgamation of Western Gondwana. Even though the rocks are metamorphosed and deformed, preserved sedimentary structures and outcrop exposures allowed the interpretation of depositional environments and stratigraphic analysis. The Capiru Group metasedimentary rocks were studied by field mapping, measured sections and bulk-rock chemical compositions. Six formations were identified, termed from oldest to youngest as: Santana (proximal to distal marine shelf), Juruqui (proximal to distal deltaic), Rio Branco (carbonate platform), Morro Azul (lagoonal to shallow marine), Morro Grande (proximal to distal deltaic/marine) and Bocaina formations (estuarine to shallow-marine). Two main basin stages were identified: a passive continental margin stage, with increasing tectonic quiescence followed by a marine regression, and a syn-orogenic stage at the Curitiba microplate margin.Chemical and mineralogical Fe- and Al-rich compositions suggest continental denudation during the passive continental margin stage, with low sediment input rates from a relatively low-gradient relief, highly weathered continental source, and stability since Mesoproterozoic time. Sedimentological and stratigraphic similarities were found among Capiru Group passive margin successions and units deposited on the Río de Plata and Southern Paranapanema margins.The paleoenvironmental interpretations, such as greenhouse conditions and high weathering rates alternated with depositional gaps, indicate climatic changes during the Capiru Group deposition, with far-field or Phantom Glacial influence related to the regional discordances. These features are important for the paleogeographic reconstructions that must consider a tropical or equatorial position ∼650 - 635 Ma for the Curitiba microplate.During deposition of the Bocaina Formation, the arkosic composition of sandstones and lithic conglomerate lags suggest source rejuvenation during the syn-orogenic stage, prior to the collisional thrusting that led to the Western Gondwana assembly.

Thermochronology in South America

The Capiru Group (Neoproterozoic) is a 4 km-thick succession deposited on the northern margin of the Curitiba microplate, Southern Ribeira Belt, Brazil. The Capiru Group successions are deformed within the Brasiliano - Pan African Ribeira Belt, which culminated in the amalgamation of Western Gondwana. Even though the rocks are metamorphosed and deformed, preserved sedimentary structures and outcrop exposures allowed the interpretation of depositional environments and stratigraphic analysis. The Capiru Group metasedimentary rocks were studied by field mapping, measured sections and bulk-rock chemical compositions. Six formations were identified, termed from oldest to youngest as: Santana (proximal to distal marine shelf), Juruqui (proximal to distal deltaic), Rio Branco (carbonate platform), Morro Azul (lagoonal to shallow marine), Morro Grande (proximal to distal deltaic/marine) and Bocaina formations (estuarine to shallow-marine). Two main basin stages were identified: a passive continental margin stage, with increasing tectonic quiescence followed by a marine regression, and a syn-orogenic stage at the Curitiba microplate margin.Chemical and mineralogical Fe- and Al-rich compositions suggest continental denudation during the passive continental margin stage, with low sediment input rates from a relatively low-gradient relief, highly weathered continental source, and stability since Mesoproterozoic time. Sedimentological and stratigraphic similarities were found among Capiru Group passive margin successions and units deposited on the Río de Plata and Southern Paranapanema margins.The paleoenvironmental interpretations, such as greenhouse conditions and high weathering rates alternated with depositional gaps, indicate climatic changes during the Capiru Group deposition, with far-field or Phantom Glacial influence related to the regional discordances. These features are important for the paleogeographic reconstructions that must consider a tropical or equatorial position ∼650 - 635 Ma for the Curitiba microplate.During deposition of the Bocaina Formation, the arkosic composition of sandstones and lithic conglomerate lags suggest source rejuvenation during the syn-orogenic stage, prior to the collisional thrusting that led to the Western Gondwana assembly.

Re-interpretation of ‘hummocky moraine’ in the Gaick, Scotland, as erosional remnants: Implications for palaeoglacier dynamics

Many glaciated valleys in Scotland contain distinctive, closely spaced ridges and mounds, which have been termed ‘hummocky moraine’. The ridges and mounds are widely interpreted as ice-marginal moraines, constructed during active retreat of mainly temperate glaciers. However, hummocky terrain can form by various processes in glacial environments, and it may relate to a range of contrasting glaciodynamic regimes. Thus, detailed geomorphological and sedimentological studies of hummocky surfaces in Scottish glaciated valleys are important for robust interpretations of former depositional environments and glacier dynamics. In this contribution, we examine irregularly shaped ridges and mounds that occur outside the limits of former Loch Lomond Readvance (≈Younger Dryas; ~12.9–11.7 ka) glaciers in the Gaick, Central Scotland. These ridges and mounds are intimately associated with series of sinuous channels, and their planform shape mimics the form of the adjacent channels. Available exposures through ridges in one valley reveal that those particular ridges contain lacustrine, subglacial, and glaciofluvial sediments. The internal sedimentary architecture is not related to the surface morphology; thus, we interpret the irregularly shaped ridges and mounds as erosional remnants (or interfluves). Based on the forms and spatial arrangement of the associated channels, we suggest that the ridges and mounds were generated by a combination of ice-marginal and proglacial glaciofluvial incision of glaciogenic sediments. The evidence for glaciofluvial incision, rather than ice-marginal moraine formation, at pre-Loch Lomond Readvance glacier margins in the Gaick may reflect differences in glaciodynamic regimes and/or efficient debris delivery from the glacier margins to the glaciofluvial systems.