Changes In Sedimentary Facies Research Articles

Spatial variations of sills and implications for magma dispersal across the Karoo basin

Abstract Dolerite sill complexes of the Karoo Large Igneous Province (ca. 183 Ma) show systematic variations in emplacement style and size throughout the Karoo basin. These variations are explained in terms of three main, interrelated factors, namely the overburden thickness or emplacement depth, variations in host rock rigidities as a result of sedimentary facies changes in the Karoo basin, and proximity to magma feeders. In the northern parts of the thinner (<500 m) and more coarse-clastic Karoo stratigraphy, sills intrude preferentially below more rigid sandstone horizons that acted as stress barriers causing the arrest of magma ascent and lateral spreading below sandstone beds. The low overburden promotes roof uplift above sills and associated brittle faulting can initiate the formation of inclined sheets that limits the lateral propagation path of inner sills. Roof uplift is further promoted by the proximity to magma feeders in the basement and resulting variations in magma pressure that control the spreading rate and inflation of sills. Localised dyke networks spaced at regular intervals and rooted in underlying sills reflect the stretching of roof rocks above inflating sills. The combination of these effects results in relatively small (<10 km) diameters of sills in the northern parts of the basin. Sills emplaced at intermediate depths (ca. 700 m) in the central Karoo basin are marked by larger diameters (>30 km) and thicknesses of up to 100 m. This reflects the higher overburden pressures and the delay of roof failure and subsequent formation of inclined sheets. Dyke networks in the roof of these sills become more irregular and non-systematic at these greater depths. At even greater depths of up to 2 km in the southern parts of the Karoo basin, mega-sills reach diameters of 50 to 80 km, but thicknesses of only up to 35 m. Thick shale-rich sequences in the southern Karoo basin facilitate sill emplacement through internal host-rock deformation and ductile flow. The thicker overburden and different host rock rigidity delay or suppress roof failure and formation of inclined sheet, thus allowing for the lateral propagation of sills. The deeper-seated sills are typically not associated with local dyke networks.

Quaternary sediment dispersal in the Zambezi turbidite system (SW Indian Ocean)

This study investigates the Late Quaternary sediment distribution of the Zambezi turbidite system (Mozambique Channel, Western Indian Ocean) from a set of piston cores that characterizes the sedimentation in the Intermediate Basin and in the proximal and distal parts of the Zambezi Fan. Sedimentological and geochemical analyses permit to define variations in sediment composition, sediment accumulation rates and timing of turbiditic deposits over the past 720 kyr. Our study reveals low sediment inputs and rare turbiditic deposits in the Zambezi turbidite system, and the deep (>2,500 m) Mozambique Channel in general, over the studied time interval. The reconstruction of the terrigenous flux in the upper part of the system suggests monsoon-related precipitation changes as the main forcing for riverine inputs variability in the Zambezi system. However, the occurrence of turbiditic deposits in the cores suggests that there is no genetic link between their triggering and evolving climate and sea-level conditions, thus emphasizing transformation of failed (slide-generated) sediment from the continental slope as the main initiation process for turbidity currents in the Zambezi system. Finally, our data highlight regional-scale changes in sedimentary facies through time, interpreted as successive ‘on-off’ switches in the activity of the distal Zambezi Fan, and by extension, regional-scale depocenter shifts. The last one likely occurred at 350 ± 42 kyr, and is concomitant with a significant increase in terrigenous inputs into the proximal Intermediate Basin. It is speculated that this depocenter shift is related to a major southward migration of the Zambezi delta.

Rapid Change in Sedimentary Facies from Wave- to Tide-dominated Macrotidal Flat in the Sinduri Bay, West Coast of Korea

Yoon, H.H.; Chun, S.S., and Hong, S.H., 2020. Rapid change in sedimentary facies from wave- to tide-dominated macrotidal flat in the Sinduri Bay, west coast of Korea. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 728-732. Coconut Creek (Florida), ISSN 0749-0208.Macrotidal wave-dominated coastal environments are widely distributed on the western open coasts of Korea, although various muddy intertidal flats occur also in the inner part of embayed areas influenced strongly by geomorphological factor. The surface sediment of wave-dominated sandflat and tidal beach, which are developed on the northern Sinduri Bay coast, consists mostly of very well sorted medium to fine sand. Swash bars, which are parallel to the coastline and continuously migrating landward, play the important role in the formation of this macrotidal sandflat. The surface sedimentary facies in this southern embayed area consists mostly of mud. The mud flat is very gentle in slope with slight concave-up profile, and dominantly shows a highly bioturbated mud facies. The distribution of surface sedimentary facies, slope profile, hydrodynamic analysis and the transport pattern of coarse-grained sediment show a rapid change in sedimentary facies with very narrow transition zone from wave-dominated sandflat facies to tide-dominated mudflat facies. Both wave- and tide-dominated coasts have been formed together within a small single geomorphological unit. The co-occurrence of different types of coasts and the rapid shift of sedimentary facies can be indicative of one of characteristics in the macrotidal open-coast depositional environment in which geomorphology, sediment supply and hydrodynamic factors have been closely associated within a relatively small bay area. Sedimentary processes in the two coastal sytems are separated and independent each other. The development of separated depositional systems are also evident even in cored sediments, indicating that the recent depositional setting has been continued much longer time.

KARAKTERISTIK ENDAPAN DANAU RAWA PENING DI MUARA INLET SUNGAI GALEH, KECAMATAN AMBARAWA, KABUPATEN SEMARANG

The Galeh River inlet estuary on Lake Rawa Pening is located in Ambarawa District, Semarang Regency. Sampling of Rawa Pening sediment at two points using modern coring methods. The coring results were observed and granulometric analysis was done using lazer scanning method with Master Sizer 2000. Core RWP-01 samples in the form of fine clastic sediments (Sand-Silt), reflecting the inlet river estuary environment in the hydrological lake system which is influenced by the fluvio-lacustrin process and showing characterizer of shallow lake facies. RWP-02 core samples in the form of fine-textured sediments (mud) rich in organic material, reflecting a relatively calm and stable depositional environment, formed by the density current mechanism that characterize the deep lake facies. The development of these sedimentary characters shows changes in sedimentary facies, namely shallow lake facies developing into clastical lake lacustrine into deep lake lacustrine facies.

Quartenary Sediment Facies Distribution in Meandering River Environment: Study Case at The Kampar River, Rumbio Area and Surroundings, Riau Province

Study area is located on the Kampar river in the district Rumbio and surrounding areas, located on the upstream side which is about 100 kilometres from the source of the sediment that Bukit Barisan mountain, Kampar river has a length of 413.5 km, the average width of 143 m and a depth average 7.7 m. This river is a river with meanders type carrying supplies suspended sediment and bed - load (mixed load) together with a low energy. This study aims to investigate the characteristics of sedimentary facies sediment quarter and deployment. The method used is a field survey to obtain core data rocks (1-3 meters) by 8 points wells, and cross sections measured(trenching) which is a layer of sediment that have been exposed (1-8 meters), then performed the sieve analysis to determine the grain size and sedimentary facies analysis and continued with sedimentary facies distribution map-making quarters in the study area. The facies sediment formed that Channel with the characteristic blocky to fining up succession have dominant deployment is the southernmost area of research with a thickness of 200 – 320 cm. Deployment sediment sand bar with characteristic coarsening up succession is in the northeast and southeast regions of study area with a thickness of 125 - 145 cm Next oblique accretion with upward fining characteristics that are in the north-eastern part of the area of research with a thickness of 40 cm. As well as having overbank sediment that contains a lot of organic material such as roots, stems, and foliage, with its spread is in the west and southwest area of research with a thickness of 100-160 cm. meandering river system leads to changes in sedimentary facies laterally intensive.

Mechanical controls on horizontal stresses and fracture behaviour in layered rocks: A numerical sensitivity analysis

In layered materials, the deformation style, orientation, confinement, and 3D connectivity of natural fractures is generally impacted by changes in sedimentary facies and alternations in mechanical properties. In this study we address this effect and perform a numerical sensitivity analysis. Mechanical properties, confining pressures, and interfacial frictions are varied for a three-layered model, to investigate and quantify the relation between contrasting material properties, the principal horizontal stresses and fracture behaviour (i.e. deformation style and orientation). Firstly, the results show that tensile stresses develop in the stiffer layers due to the contrasting elastic parameters. The magnitude of these stresses is dependent on the ratio between the elastic parameters of stiffer and softer layers (i.e. Estiff/Esoft and νstiff/νsoft). There are no horizontal tensile stresses, when applying a compressive horizontal confining pressure (approx. 1/5 of the applied vertical stress). Implementing an interfacial friction lower than 0.2 will result in decoupling of the layers, resulting in slip on the layer boundaries and no tensile stresses within the stiffer layers. Further, the acquired numerical results are in good agreement with previously conducted laboratory work. Finally, we discuss whether the presented results can be used for better relating contrasting mechanical properties to potential fracture deformation styles and orientations in layered outcrops or subsurface reservoirs.

Discovery of a 400 km2 honeycomb structure mimicking a regional unconformity on three-dimensional seismic data

AbstractRecognition of seismic unconformities is crucial for interpreting basin history from seismic reflection data sets in both siliciclastic and carbonate settings. While it is well established that non-erosional changes in sedimentary facies can create seismic reflections that mimic seismic unconformities (i.e., pseudo-unconformities), these features are generally considered to be localized and uncommon, and, therefore, are largely overlooked during interpretation. Diagenetic alteration of strata can also affect the morphology of seismic reflectors and mislead seismic interpreters. This study is based on a three-dimensional (3-D) seismic data set and documents a 400 km2 honeycomb structure (HS) masquerading as a regional erosional unconformity in the Oligocene–Miocene carbonate strata of Australia’s North West Shelf. This HS is located at the transition between the topsets and the foresets of clinoforms of carbonate to marly composition. The HS expression in 3-D seismic data cross sections is irregular, giving the HS the appearance of a truncated surface that could erroneously be interpreted as a regional seismic unconformity. Closer examination reveals that the HS crosscuts chronostratigraphic clinoform reflectors, and frequency extraction processing shows that the HS dominantly falls within a lower-frequency band than the clinoform reflectors. The morphology of the HS (i.e., continuous with densely packed cells) and its time-transgressive nature suggest that it has a burial diagenetic origin. This suggests that creation of pseudo-unconformities at basin scale by burial diagenesis may lead to surface misidentification, with negative consequences for paleoenvironmental studies and petroleum exploration activities.

Sedimentary environments and lithofacies distribution of zeit formation, red sea- Sudan

The Sudanese red sea coastal plain is geologically characterized by Cenozoic siliciclastic and shallow marine rift related sedimentary se-quences. Pliocene-Pleistocene is represented by the thick older gravel unit and the emergent linear reef terraces. In this study, wire line logs besides the investigations of cutting samples were used to investigate the un cored facies successions, to detect changes in grain size distribution, lithology and sedimentary facies and hence to interpret depositional environment. Confirmation of the log behavior using the cores and the cutting samples was undertaken. Furthermore, core to gamma-ray and spontaneous potential log correlations were set up. The lithofacies association and the depositional patterns of Zeit Formation were controlled by allocyclic and autocyclic processes, which include tectonic, palaeo climatic as well as depositional mechanisms. The lithofacies Distribution of Lower Zeit Member shows the southwestern part of the area is dominated by terrestrial to marginal marine partly supra tidal domain where some channel feeders can support the sand distribution from south to north. The central part of the area is dominated by shallow marginal marine to partly supra-tidal domains. The Middle Zeit Member was dominated by marginal marine to supratidal domain. The Upper Zeit Member repeated pattern of facies distribution being similar to that of Middle Zeit, however the sandy facies influxes increased towards the S. Suakin, Digna- area, towards Bashayer area and Durwara area from south to north.

Geological setting of the Moorowie Formation, lower Cambrian Hawker Group, Mt Chambers Gorge, eastern Flinders Ranges, South Australia

Geological mapping in 1970 of lower Cambrian outcrop in the eastern Flinders Ranges of South Australia included the description and naming of the Moorowie Formation, representing the uppermost Hawker Group. The mapping is supported by 885 m of measured sections. An early Cambrian regressive-marine shelf-margin succession is described, from the massive Wilkawillina Limestone (base), the grey laminated limestones, syndepositional slump-induced intraformational folds and breccias, collapse talus, and graded sediment gravity flow deposits of the Mernmerna Formation, terrace-edge attrition megabreccias and reefs of the Moorowie Formation, passing up to the red beds of the Billy Creek Formation (top). Rapid changes in sedimentary facies are attributed to basement block movements and diapiric influence on sedimentation with abrupt vertical relief and paleoslope indicated by syndepositional slumping and platform margin collapse. Tuffs in the Mernmerna Formation record contemporaneous volcanism. Massive archaeocyathan limestones, ooid grainstones, peloid limestones, reef-sourced megabreccias and red shales define five members in the overlying Moorowie Formation, signalling shallow-marine regressive conditions and the development of a biologically diverse carbonate platform seaward of evaporitic lagoons and supratidal sabkhas. The megabreccias of the Moorowie Formation formed as thin semi-autochthonous debris aprons or shallow tidal-channel infills resulting from gradual and persistent wave attrition and repeated collapse of a carbonate terrace that was vigorously reworked by tidal currents. Shale interbeds within the Moorowie Formation represent lightly channelised shallow-marine ramp deposits, with adjacent mud flats, as easterly equivalents of the Oraparinna Shale, the earliest of which formed the substrate to the attrition megabreccias. Emergent evaporite diapirs near Mt John and Mt Frome are the probable sources of coarse siliciclastics within the carbonates. Some of the siliciclastics were likely transported onto the carbonate platform by sandstorms or migrating dunes. Late in the Cambro-Ordovician Delamerian Orogeny, earlier salt diapirs at depth were compressed and reactivated as highly mobile evaporite-rubble breccias and intruded as small plugs and dykes into fissures in a lithified and folded cover.The intrusive breccias include metasediment and metabasic xenoclasts attributable to the Callanna Group, while diapir-related faults also host minor copper, lead and barite mineralisation. Documentation of this unique record contributes to wider investigations of the Ediacaran-to-early-Cambrian succession of the Flinders Ranges sector of the Arrowie Basin, adding to its global heritage values, effective management and appreciation by the wider community.

Cretaceous termination of subduction at the Zealandia margin of Gondwana: The view from the paleo-trench

During the Permian to Cretaceous, Zealandia occupied a position on the proto-Pacific-facing, convergent margin of Gondwana. Subduction on this margin ceased somewhere between ~105 Ma and perhaps 70 Ma, but the timing of this tectonic transition remains controversial. Resolution of this uncertainty is important for tectonic reconstructions of the southwest Pacific and for global plate-tectonic models. Here, we revisit the problem by reference to new stratigraphic and geochemical data from the East Coast Basin of New Zealand, which occupied a position adjacent to and possibly superimposed on the relict Cretaceous subduction trench at the time subduction ceased; this basin is expected to preserve direct structural and stratigraphic evidence for or against Late Cretaceous subduction.In western parts of the East Coast Basin – the “Western Sub-belt” – a conspicuous unconformity separates undoubted accretionary prism rocks of the Torlesse Composite Terrane from younger Cretaceous “cover” units. Strata beneath and overlying this unconformity vary in age from place to place, but abundant paleontological data and published ages of detrital zircons (some reinterpreted herein), indicate that exposed Torlesse rocks are nowhere younger than ~100 Ma. Overlying Zealandia Megasequence “cover” strata are mostly younger than ~110 Ma. Between ~110 and ~85 Ma, the entire length of the Western Sub-belt reveals complex stratigraphic architecture of relatively small-scale depocentres subjected to alternating episodes of subsidence and local uplift and erosion. There is widespread evidence for compression on the Western Sub-belt over this period, although the overall amount of shortening is likely to be relatively modest. In contrast, the Eastern Sub-belt preserves a record of near-continuous and apparently simple deposition over the same interval of time. We see little and somewhat equivocal evidence for extension in either sub-belt through the Late Cretaceous. Superimposed on this general pattern, we observe discrete, widespread or basin-wide, tectonic events at 95 Ma, and within the intervals ~86–83 Ma and ~83–81 Ma, indicated by the presence of unconformities and sedimentary facies changes. Importantly, all these events can be correlated with coeval events recorded elsewhere in Zealandia, suggesting that the East Coast Basin was subject to the same tectonic regime as the rest of Zealandia and shared a common history during the mid- to Late Cretaceous.Integrating these findings with data from elsewhere in Zealandia, we argue that there is diverse evidence to indicate that subduction finished along the New Zealand segment of the Gondwana margin by 100 Ma. That said, the causes of on-going, Late Cretaceous compression in the East Coast Basin and in other parts of Zealandia are not well constrained, although several possible explanations are plausible. There are few analogue, abandoned subduction margins described in the literature; however, the situation in the South Shetland Trench shows strong similarities with patterns and complexities observed in the East Coast Basin.

Along-strike variations in thin-skinned thrusting style controlled by pre-existing basement structure in the easternmost Jura Mountains (Northern Switzerland)

Abstract A detailed analysis of the Late Miocene Mandach Thrust, a key tectonic structure of the easternmost Jura Mountains (northern Alpine foreland), is presented providing insights into the modes of along-strike structural cover–basement interactions in a classical foreland setting. Our study builds on the construction, restoration and forward modelling of eight closely spaced cross-sections constrained by depth-migrated 2D seismics and geological maps. The results indicate predominantly thin-skinned thrust tectonics without significant inversion of underlying basement structures. However, inherited pre-thrusting normal faults exerted a strong control on the observed thrusting style, changing along-strike from a comparatively simple geometry to a complex, partly overthrust, partly reactivated normal fault. The observed variations relate to changes in the relief of the mechanical basement and the characteristics of pre-thrusting normal faults. The thrust's complexity is further increased by the local activation of secondary detachment horizons and possibly along-strike sedimentary facies changes within the thrust-faulted sedimentary sequence. The variations in thrusting style go along with subtle changes in shortening that may point towards as yet undetected transfer structures. As such, our structural analysis of the Mandach Thrust provides an improved understanding of the fault's kinematics and serves to highlight existing exploration uncertainties.

Holocene history of a lake filling and vegetation dynamics of the Serra Sul dos Carajás, southeast Amazonia.

Down-core changes in sedimentary facies, elemental geochemistry, pollen, spore, δ13C, δ15N and radiocarbon records from a filled lake, named R4, of the Serra Sul dos Carajás were used to study the relationship between the paleomorphological and paleoecological processes and their significance for Holocene paleoclimatology of the southeast Amazonia. The sediment deposition of the R4 lake started around 9500 cal yr BP. Increase of detrital components from 9500 to 7000 cal yr BP suggests high weathering of surrounding catchment rocks and soils, and deposition into the lake basin under mudflows. At that time, montane savanna and forest formation were already established suggesting predominance of wet climate. However, from 7000 to 3000 cal yr BP, a decline of detrital input occurred. Also, forest formation and pteridophytes were declined, while palms and macrophytes were remained relatively stable, indicating that water levels of the lake is likely dropped allowing the development of plants adapted to subaerial condition under drier climate conditions. After 3000 cal yr BP, eutrophication and low accommodation space lead to high lake productivity and the final stage of the lake filling respectively, and forest formation may has acquired its current structure, which suggests return of wetter climate conditions.

Reorganization of sediment dispersal in the Jiuxi Basin at ~17 Ma and its implications for uplift of the NE Tibetan Plateau

The Tibetan Plateau offers an example for understanding the processes of continental collision and subsequent intracontinental deformation. The Jiuxi Basin, located at the northeastern margin of the plateau, bears crucial information on the growth processes of the NE Tibetan Plateau. Combined with published magnetostratigraphic constraints, integration of stratigraphic investigation and detrital zircon geochronological analysis on the sediments of the Cenozoic Hongliuxia section in western Jiuxi Basin suggests a major reorganization of the basin infill process at the period between depositions of the Baiyanghe and Shulehe formations at ~17 Ma. This finding is documented by (1) a generally upward-thinning sequence followed by an upward-coarsening sequence with corresponding changes in sedimentary facies, (2) shifting of the paleocurrent from the south to the north, and (3) shifting of the provenance from the Bei Shan-Kuantan Shan-Hei Shan in the north to the North Qilian Shan in the south. These results suggest that tectonic deformation arrived in the North Qilian Shan by ~17 Ma and lend support to the outward-growth model for the Tibetan Plateau.

Palaeoenvironmental implication of grain-size compositions of terrace deposits on the western Chinese Loess Plateau

Sedimentary sequences that developed on river terraces have been widely investigated to reconstruct high-resolution palaeoclimatic changes since the last deglaciation. However, frequent changes in sedimentary facies make palaeoenvironmental interpretation of grain-size variations relatively complicated. In this paper, we employed multiple grain-size parameters to discriminate the sedimentary characteristics of aeolian and fluvial facies in the Dadiwan (DDW) section on the western Chinese Loess Plateau. We found that wind and fluvial dynamics have quite different impacts on the grain-size compositions, with distinctive imprints on the distribution pattern. By using a lognormal distribution fitting approach, two major grain-size components sensitive to aeolian and fluvial processes, respectively, were distinguished from the grain-size compositions of the DDW terrace deposits. The fine grain-size component (GSC2) represents mixing of long-distance aeolian and short-distance fluvial inputs, whilst the coarse grain-size component (GSC3) is mainly transported by wind from short-distance sources. Thus GSC3 can be used to infer the wind intensity. Grain-size variations reveal that the wind intensity experienced a stepwise shift from large-amplitude variations during the last deglaciation to small-amplitude oscillations in the Holocene, corresponding well to climate changes from regional to global context.

Evolution of sedimentary facies and fossil communities in the Middle Permian Maokou Formation in Zigui County, Hubei Province, South China

A geological event that happened at the end of the Middle Permian resulted in different levels of erosion in a shallow-water platform of South China, which led to diverse geological records in different sections. The Lianziya section in western Hubei Province of South China has a well-exposed stratigraphic sequence of the late Middle Permian rocks with abundant fossils and sedimentary facies types, providing new evidences for understanding the evolution of marine biota and environment in the late Middle Permian. Our study shows that four fossil communities can be recognized with the change of sedimentary facies in the late Middle Permian: Foraminiferal–algal community, phylloid algal community, bryozoan community and Ungdarella community. The foraminiferal–algal community is dominated by fusulinids and calcareous algae, but was soon replaced by the phylloid algal community. With an increase of terrestrial input, the phylloid algal community was again replaced by the bryozoan community. Near the end of the Middle Permian, with a decrease of terrestrial input, the bryozoan fossil community disappeared while the Ungdarella community became dominant. A 10 cm-thick weathered crust occurred at the top of the Middle Permian limestone, marking a large amplitude fall in sea-level and the beginning of a terrestrial erosion stage. The sedimentary facies and fossil community changes in the Lianziya section indicates that the Middle Permian crisis was a gradual process while the sea-level fall mainly occurred in the latest Middle Permian.

Xenoconformities and the stratigraphic record of paleoenvironmental change

Most interpretations of the stratigraphic record are founded on the premise that the depositional environments that produced it either have not changed appreciably through time, or else have changed very slowly. Paradoxically, some of the most important transitions in the sedimentary archive are those interpreted to reflect relatively rapid, comprehensive paleoenvironmental change. Recognition of the anomalous nature of such transitions is vital to accurately understanding their significance but is not systematically incorporated in current stratigraphic models. The new term “xenoconformity” is therefore proposed, and defined as a stratigraphic surface or gradational interval that records a fundamental, abrupt, and persistent change in sedimentary facies across basinal to global scales. Xenoconformities may mark major paleoenvironmental tipping points and signal transformations in how paleoenvironmental signals were transferred into the stratigraphic record.

Human-induced changes in sedimentary facies and depositional environments, Sarum area, Red Sea coast, Saudi Arabia

This paper aims to study the environmental impact of the human inference on the coastal zone of Sarum area, Red Sea coast, Saudi Arabia. In the past, the study area was occupied by coastal lagoons that were connected with the sea with several inlets. Change detection technique based on multi-date satellite images in the last 44 years indicated the occurrence of environmental changes accompanied the construction of the main asphaltic road of the Red Sea that separated some coastal lagoons at the studied area from the Red Sea. Field investigation and litho- and bio-facies distribution indicated the existence of six lateral facies types: gypsum, microbial mats, halite, Quaternary coral reef terrace, bioclasts, and siliciclastic sand sheets. The lateral distribution of these facies is related to the following changes: (1) disconnection between the coastal lagoons and the sea, (2) extensive contraction of the coastal lagoons and formation of saline ponds, (3) exposure of the submerged Quaternary coral reef terrace, (4) increasing of the salinity of the ponds up to 270‰, and (5) deposition of the evaporitic facies types (gypsum and halite) over intertidal and subtidal marine carbonates. Based on the above-mentioned criteria, the human activity leads to environmental changes in the Sarum area from coastal lagoons dominated with carbonate deposits into hypersaline ponds dominated with evaporitic deposits.

Sedimentary environment and paleosols of middle Miocene fluvial and lacustrine sediments in central Japan: Implications for paleoclimate interpretations

Sedimentary facies analysis and description of paleosols were carried out for the middle Miocene Tokiguchi Porcelain Clay Formation (PCF) in central Japan in order to interpret the soil-forming environments during a long hiatus in the Japanese Islands. The sedimentary facies suggests that deposition occurred mainly in a lacustrine environment, with minor channel-fill and debris-flow deposits associated with alluvial fan environments. The coarse-grained sediments, which are inferred to have been deposited in channel-bar and debris-flow deposits, are present only in the marginal area of the sedimentary basin. Mature paleosols are identified in the Tokiguchi PCF, characterized by illuviated clay, identifiable soil horizons including Bt horizons and many in situ plant fossils, and are then similar to Ultisols. Most tree trunk fossils, however, were preserved by burial beneath debris-flow deposits. Most of paleosols formed on lacustrine deposits and were covered by lacustrine clay and silt deposits, without intervening coarse-grained deposits, such as flood-flow deposits. This change of sedimentary facies indicates a dramatic change of hydrologic environment, from stagnant water to entirely desiccated conditions, promoting weathering and soil formation. The relationship between sedimentary facies and Pedotypes, consequently, implies the repetition of specific events, i.e., submergence and emergence of lake bottom, most likely due to formation and drainage of a dammed lake. These isolated events and development of mature paleosols might suggest specific characteristics of middle Miocene weathering conditions, such as seasonally heavy rainfall and/or warm climatic conditions in the Japanese Islands.

The sediments of Dagh-e-Sorkh playa, Ardestan, central Iran

The Dagh-e-Sorkh playa is a closed basin in central Iran. The sediments of this playa were studied for sedimentologic and geomorphologic characteristics, the interaction of sedimentation mode of a terminal ephemeral fluvial-fan system and adjacent lacustrine/aeolian sediments in the area. Evaporite minerals including calcite, gypsum and halite were the most dominant minerals. The two main types (pediment and playa type) and few sub-types facies were identified. Based on the surface and subsurface study, the area was zoned and sedimentary–stratigraphic column for each zone was interpreted and six zones were characterized. These data clearly show that different conditions are dominant for the deposition of sediment and vertical changes in sedimentary facies around the area.

Temporal evolution of a carbonate coastal system, Abu Dhabi, United Arab Emirates

The southern shore of the Persian/Arabian Gulf comprises a low-angle carbonate–evaporite ramp system that provides a rare Recent analogue for ancient epeiric settings, including many carbonate petroleum reservoirs. During the 1960s several studies documented the distribution of naturally occurring shallow-marine facies in the shallow marine environments proximal to Abu Dhabi Island. Subsequent coastal engineering projects have significantly modified the coastline and sublittoral zone – many sedimentary environments have been lost, with marine sites now sited beneath buildings, parks or roads. The data from the earlier studies are used as a pre-anthropogenic base-line in order to document and assess the temporal changes in the characteristics and distribution of carbonate sedimentary facies as observed today. The locations of earlier sample sites were revisited in order to represent the complete range of shallow-marine sedimentary environments. The shallow subtidal environments adjacent to Abu Dhabi Island continue to be areas of active carbonate sedimentation. Temporal changes in facies belt geometries and occurrence are assessed. Changes are recorded for most of the investigated sedimentary settings, both in terms of sedimentary environment distribution and sediment composition. Offshore reefs and their associated back-reef lagoons are no longer present. Ooid shoal and delta complexes are much-reduced in their aerial extent, now being replaced with shoreface facies or dredged channels. Significant dredging activity has increased tidal flow to lagoon environments thereby increasing connectivity to open-marine conditions. However, land reclamation has substantially reduced the volume of the area of the lagoon environments. Despite these changes, many facies display surprising resilience to anthropogenic activities with no discernible change in sedimentary facies or biotic distributions. Understanding these modifications, and their associated driving mechanisms, allows discrimination between anthropogenic and naturally-occurring environmental perturbations. This, in turn, develops our understanding of the temporal evolution of shallow-marine carbonate facies under natural and anthropogenic influences.