Sedimentological Characteristics Research Articles

Facies analysis, petrography and textural characteristics of the onshore Paleogene-Neogene Lawin Basin, Perak, Peninsular Malaysia: Insights into palaeodepositional environment and provenance

Sedimentological features of the onshore Paleogene-Neogene Lawin Basin are of importance in better understanding the basin evolution and geodynamics. The N-S trending Lawin Basin, which is situated within the Western Belt of Peninsular Malaysia, is an extensional basin that formed during the sinistral movement of the Bok Bak Fault zone. This study evaluates the palaeodepositional environment, reveals the provenance, and interprets the transport dynamics of the mini-basin by integrating facies, petrographic, and grain size analyses. The basin lithologies can be broadly divided into conglomerate and sandy facies, with the former consisting of clast-supported conglomerate, matrix-supported conglomerate, cross-stratified pebble conglomerate, and bedded pebbly conglomerate, whereas the latter comprises massive pebbly sandstone, horizontally bedded sandstone, planar cross-bedded sandstone, and ripple laminated sandstone. The lithologies can be grouped into three main facies associations, including massive conglomerate, stratified conglomerate, and fluvial sandstone deposits, which reflect alluvial fan (debris/gravity flow deposits), braided gravel bar, and channel bar elements, respectively. Petrographic data indicate that the conglomerates are clast- and matrix-supported and were derived from a proximal source. The QFL range of detrital framework grains reveals that sandstones are composed of quartz (43–80 vol%), feldspar (9–54 vol%), and lithic fragments (2–16 vol%). The sandstones are coarse-grained, poorly-sorted, and sub-rounded to sub-angular in texture. They are arkose, sublitharenite, and lithic arkose in composition. QtFL/QmFLt ternary diagrams show that the sandstones are primarily derived from a provenance area comprising continental block material, including uplifted basement rocks and transitional continental deposits. This study proposes that the sandstones had a nearby granitic source (Bintang) and a debris source derived from recycled sedimentary rocks (the Baling Group sediments). Grain size parameters ranges (mean, −2.37 to 0.74 Φ; sorting, 1.22 to 2.07 Φ; skewness −0.21 to 0.91 Φ, kurtosis, 0.66 to 1.98 Φ, and average mean-sorting index of −0.24) are consistent with immature to sub-mature sedimentation deposited within a high-energy fluvial environment.

Foraminiferal sandy contourite of the Limpopo Corridor (Mozambique margin): Facies characterization and paleoceanographic record

Contourites encompass a wide variety of sedimentary facies. Some of them show common facies with others deep-water deposits, such as turbidites and hemipelagites. Sedimentological characterization at macro- and microscales is valuable to discriminate those close facies but the distinction is not always clear. Contourites are increasingly used in paleoceanographic and paleoclimatic reconstructions. Improving their characterization is therefore essential to their interpretations.This study aims at characterizing a foraminiferal sandy contourite facies from a sediment core collected on top of a contourite drift under the influence of the Antarctic Intermediate Water/North Atlantic Deep-Water interface located in the Limpopo Corridor (Mozambique margin, Indian Ocean) at 2000 m depth. This work is based on a detailed analysis of the sedimentary record using physical properties (gamma density and magnetic susceptibility) as well as laser grain size and X-Ray Fluorescence core scanning data.Our results show that: (1) the foraminiferal sand is vertically continuous and homogenous over 633 kyr with an average sedimentation rate of 0.26 cm.kyr−1; (2) this contourite facies results from sedimentation with low terrigenous inputs under stable hydrodynamic conditions over time, with relatively strong bottom currents for this water depth (∼16 cm.s−1); (3) during glacial stages, sedimentation rates are lower and bottom current speed is higher than during interglacial stages. We also propose the concept of “Contourite Graphical Chart” which summaries the theoretical distribution of contourite endmembers from cross-plot of “sorting versus grain-size median D50” and their related sedimentary processes.This study highlights the relevance of condensed foraminiferal sandy contourites as long time-scale paleoceanographic archives and provides new insights for studies related to paleoclimatology and paleoecology.

PALYNOFACIES AND SEDIMENTOLOGY OF HB-001 WELL

The palynofacies and sedimentological analyses of the sedimentary succession of the HB-001 well were carried out to establish biozones and the palaeodepositional environment. Ninety-six samples of ditch cutting within intervals of depth of 1250 -4011 m were analyzed. Most of the previous researchers established biozones with alpha-numeric method. The use of palynomorphs and palynofacies analyses to delineate paleoenvironment of deposition has been applied to a limited extent in the Niger Delta Basin in Nigeria. The analysis produced fairly diverse and moderately abundant pollen and spores with high recoveries of palynomaceral 1 and 2 and minimal retrievals of palynomaceral 3 and 4. The textural, lithologic, as well as wireline log data point out that the whole studied interval in the HB-001 well fit in to the Agbada Formation. Late Miocene age was assigned on the bases of the analysis of stratigraphic age range of indicative palynological markers for example Zonocostites ramonae, Verrucatosporites sp., Laevigatosporites sp., Monoporites annulatus, Pachydermites diederixi and Psila,tricolporites crassus. Two assemblage zones were established in the well with the use of the International Stratigraphic Guide for the biozones establishment. The two recognized palynostratigraphic zones are Cyperaceaepollis sp. – Nympheaepollis clarus, and Stereisporites sp Zones. Lower delta plain, pro-delta and delta front depositional environments have been deciphered for well with the use of the palynofacies association, palyno-ecological groupings, and sedimentological features. Bodies of sand that signify sub-environments inside these settings are deposited in sequences. Every sequence begins with a transgressive stage, after that considerable regression. The palyno-ecological groupings of the retrieved palynomorph taxa revealed that the well intervals studied were deposited under alternating wet and dry paleoclimatic settings. The zones of dry climate presented high account of montane and savannah taxa and low incidence of rainforest, mangrove and freshwater taxa. The zones of wet climate signified increased account of rainforest, freshwater and mangrove taxa and lower incidences of montane and savannah taxa.

Ancient Siliciclastic-Evaporites as Seen by Remote Sensing Instrumentation with Implications for the Rover-Scale Exploration of Sedimentary Environments on Mars.

Accurate interpretation of the martian sedimentary rock record-and by extension that planet's paleoenvironmental history and potential habitability-relies heavily on rover-based acquisition of textural and compositional data and researchers to properly interpret those data. However, the degree to which this type of remotely sensed information can be unambiguously resolved and accurately linked to geological processes in ancient sedimentary systems warrants further study. In this study, we characterize Mars-relevant siliciclastic-evaporite samples by traditional laboratory-based geological methods (thin section petrography, X-ray diffraction [XRD], backscattered electron imaging, microprobe chemical analyses) and remote sensing methods relevant to martian rover payloads (visible-near-mid infrared reflectance spectroscopy, X-ray fluorescence mapping, XRD). We assess each method's ability to resolve primary and secondary sedimentologic features necessary for the accurate interpretation of paleoenvironmental processes. While the most dominant textures and associated compositions (i.e., bedded gypsum evaporite) of the sample suite are readily identified by a combination of remote sensing techniques, equally important, although more subtle, components (i.e., interbedded windblown silt, meniscus cements) are not resolved unambiguously in bulk samples. However, rover-based techniques capable of coordinating spatially resolved compositional measurements with textural imaging reveal important features not readily detected using traditional assessments (i.e., subtle clay-organic associations, microscale diagenetic nodules). Our findings demonstrate the improved generational capacity of rovers to explore ancient sedimentary environments on Mars while also highlighting the complexities in extracting comprehensive paleoenvironmental information when limited to currently available rover-based techniques. Complete and accurate interpretation of ancient martian sedimentary environments, and by extension the habitability of those environments, likely requires sample return or in situ human exploration.

Late Quaternary marine transgressions inferred from the pyrite sulfur content and isotopes within core sediments from the southeast coast of China

Paleoenvironmental reconstructions of coastal areas during geological history are critical for understanding past responses to marine transgression. Identifying transgressive layers in sedimentary strata is therefore of great importance. To this end, we examined the content and isotopic composition of pyrite sulfur, in combination with classical organic geochemical indicators (e.g., C/N ratio and the δ13C of organic carbon), to trace the marine transgressions along the southeast coast of China since Marine Isotope Stage (MIS) 5. Our results suggest that the mass ratio of total organic carbon and pyrite sulfur (C/S ratio) is sensitive to seawater intrusion. Three transgressive layers were identified by low C/S ratios in core NDGK2, which correspond to sea level rise during MIS5, MIS3, and MIS1. Sediments deposited during MIS1 are represented by low C/S ratios with an average of 2.31, while those deposited during MIS5 and MIS3 have slightly higher C/S ratios, indicating a less extensive influence of seawater. Pyrite production in sediments deposited during MIS5 and MIS3 may have been limited by sulfate supply, as reflected by more positive values of δ34Spyr, whereas pyrites deposited during MIS1 were likely formed without sulfate limitation, as reflected by more negative values of δ34Spyr. The isotopic signals of pyrite sulfur thus further confirm the inference based on the C/S ratio. The magnitude of the transgression increased from MIS5 to MIS1, which is in agreement with the findings from classical organic geochemical indicators examined in this study, as well as geochemical and micropaleontological salinity indicators from previous studies. Our findings provide a promising method for identifying marine transgressions and their magnitude from the depositional record, especially when sedimentary strata lack diagnostic micropaleontological and sedimentological characteristics.

Hydrological, thermal and chemical influence of an intact rock glacier discharge on mountain stream water

Rock glaciers are the most prominent permafrost-related mountain landforms. This study investigates the effects of the discharge from an intact rock glacier on the hydrological, thermal and chemical dynamics of a high-elevation stream in the NW Italian Alps. Despite draining only 39 % of the watershed area, the rock glacier sourced a disproportionately large amount of discharge to the stream, with the highest relative contribution to the catchment streamflow occurring in late summer - early autumn (up to 63 %). However, ice melt was estimated to be only a minor component to the discharge of the rock glacier, due to its insulating coarse debris mantle. The sedimentological characteristics and internal hydrological system of the rock glacier played a major role in its capability to store and transmit relevant amounts of groundwater, especially during the baseflow periods. Besides the hydrological influence, the cold and solute-enriched discharge from the rock glacier significantly lowered the stream water temperature (especially during warm atmospheric periods) as well as increased the concentrations of most solutes in the stream. Furthermore, in the two lobes forming the rock glacier, different internal hydrological systems and flowpaths, likely driven by different permafrost and ice content, caused contrasting hydrological and chemical behaviours. Indeed, higher hydrological contributions and significant seasonal trends in solute concentrations were found in the lobe with higher permafrost and ice content. Our results highlight the relevance of rock glaciers as water resources, despite the minor ice melt contribution, also suggesting their potential, increasing hydrological importance in the light of climate warming.

Turbidite channel-levée transitions: insights from the Tachrift system (Complex 6, Taza-Guercif Basin, NE Morocco)

This contribution reports on the outcrop of one (Complex 6, hereafter) of multiple turbidite channel-levée complexes making the Tachrift system (Late Tortonian- early Messinian), beautifully exposed in NE Morocco as part of the clastic fill of the Taza-Guercif Basin. Geological mapping was integrated with facies analysis on 46 logs and physical stratigraphic correlations. Complex 6 consists of three sandstone-rich units labelled A, B, and C that progressively increase in grain-size and are laterally stacked in a SE-ward shifting fashion. Particularly, channel- fills and correlative levées of Units B and C have contrasting architectural styles which likely reflect changes in flow parameters (e.g., grain size, volume, density stratification etc.), channel sinuosity, and morphodynamics. Owing to magnificent 3D exposures, the ongoing study of Complex 6 outcrops will provide sedimentological characterization of channel-fills and correlative levée deposits, insights into evolution of their parent channel from inception trough abandonment, and sub-seismic lithological calibration of subsurface analogues.

Sedimentological characteristics and their relationship with landsliding in the Bhilangana Basin, Garhwal Himalaya, India

Every year during the Indian Summer Monsoon, large landslides occur in the Lesser and the Greater Himalayan rock formations, triggered by intense rainfall episodes coupled with physiography and anthropogenic activities. The present study investigates the slope failure mechanism's relationship with slope material compositions. Hence, sediment samples of 25 landslides were collected along the road corridors. These samples were collected from the Lesser and Greater Himalayan ranges and rock formations. The sediment was collected from the active landslides to understand particle size, clay content, moisture content, mineral composition, crystallographic structures, and the influence of geomorphic processes on the landslide failure processes. The samples were analyzed using a sieve, X-ray Diffractometry (XRD), and Scanning electron microscopy (SEM) to accomplish the study's objectives. The analysis indicates that the Lesser Himalayan meta-sedimentary rock formations have a high composition of fine and medium-size particles, lesser quartz mineral compositions with calcite, and a highly crushed and fractured presence, conchoidal fractures types of morphological features. Micrographs obtained from the schist and phyllite rock of the Lesser Himalayan origin shows highly sheared and crushing, crystal overgrowth; and, in turn, have a higher susceptibility to landslides. The relationship between slope materials and instability has shown a definite pattern in the study area. The debris flow and slump have a comparatively higher percentage of clay and silt compared to debris fall, debris slide, and rockfall. The particle size composition of sediment collected from the slip zone is significantly related to the types of landslides. The present study is helpful in understanding the sediment composition and slope failure mechanism.

Landsystem analysis of a tropical moraine‐dammed supraglacial lake, Llaca Lake, Cordillera Blanca, Perú

Tropical glaciers of the Cordillera Blanca, Perú are rapidly thinning and retreating as a result of climate warming. The retreat of these glaciers along narrow linear bedrock valleys has increased the number and size of moraine‐dammed glacial lakes formed in the valleys. This study aims to identify the geomorphological and sedimentological characteristics of an enlarging moraine‐dammed supraglacial lake (Llaca Lake) in the Cordillera Blanca. Field‐based sedimentological observations and geomorphological mapping were combined with remotely sensed data and a photogrammetric model derived from aerial surveys by an uncrewed aerial vehicle to identify landform‐sediment assemblages. The geomorphological and sedimentological characteristics of Llaca Lake are synthesized into three landsystem zones: Zone 1: distal portions of Llaca Lake and the latero‐frontal moraine; Zone 2: the central zone of ice‐cored hummocks; and Zone 3: the active glacier margin. These zones are differentiated based on the spatial distribution of landforms, sediments, and active geomorphological processes. This is the first study to describe the landform‐sediment assemblages in a tropical moraine‐dammed supraglacial lake system and provides a framework for further landsystem element analysis of these growing supraglacial lakes in rapidly deglaciating high‐altitude environments.

Oxygen isotopic composition of Paleoproterozoic seawater revealed by clumped isotope analysis of dolomite, Vempalle Formation, Cuddapah, India

The Paleoproterozoic (∼2.0–1.9 Ga) Vempalle Formation, in the south-western part of the Cuddapah Basin, is a well-studied Paleoproterozoic succession. Detailed descriptions of sedimentological features, micro-textures, and isotopic compositions of dolomite in the stromatolites and associated lithologies suggest that the succession was deposited on a carbonate ramp. Early burial diagenesis of the dolomite modified the original isotopic signatures. Nonetheless, here we discern evidence for two distinct depositional events based on clumped isotopic signatures preserved within dolomitic stromatolite and the underlying dolomite mud. Dolomitic muds within cherty precipitate record original thermometry signatures from these rocks. Clumped isotope analyses suggest that the lowest temperature of the Paleoproterozoic seawater was 21.8 ± 2 °C, and that its isotopic composition (δ18OVSMOW) during dolomite precipitation at equilibrium was −9.6 ± 0.1‰, which is lighter than that of present-day ocean water. The overlying stromatolitic dolomite exhibits a temperature range of 70.7–109.8 °C, reflecting late-stage diagenetic processes and hydrothermal activity. Hydrothermal fluids were isotopically enriched (up to 4.9‰) suggesting their mantle origin and interaction with evaporative seawater. We evaluated the degree of water-rock interaction with water of heavier isotopic composition that was responsible for the precipitation of late phase dolomite found in the strata overlying carbonate mud.

Sedimentological features of asbestos cement fragments in coastal environments (Taranto, southern Italy)

Asbestos cement materials (ACMs) are widespread in coastal environments as result of illegal dumping activities. This study focuses on the Taranto area (Italy) in the Mar Grande basin within the northern sector of the Ionian Sea. The complex history of dumping building materials containing high amounts of ACM into the coastal zone, and the erosion, transport and deposition in Marechiaro Bay is a serious environmental hazard. An interdisciplinary research methodology defines the temporal dumping succession, and the erosional processes and phases, the diffusion of ACM, the mineralogical characteristics, and existing physical status of the ACM. A multiscale investigation was conducted. Results show that from 1992 to 2000 a significant increment of dumping operations have occurred. The current cliff has been subject to erosion and redeposition phases, developing a new beach composed of these polluted man-made sediments. The findings persuade the local authorities to close the beach requiring remediation interventions.

Analysis of the Sabellaria spinulosa Bioconstruction Growth in a Laboratory

Sabellaria spinulosa (Leukhart, 1849) is a suspension feeding polychaeta that lives in tubes consisting of terrigenous particles captured by the worm itself. They form impressive reefs containing millions of worm tubes. In temperate marine areas, under optimal environmental conditions, these structures can become natural breakwaters and can play an active role in sandy beaches’ defense. In this work, we report procedures aimed to analyze the growth of S. spinulosa bioconstructions in laboratory. By collecting biological replicas from a wild reef, this study aimed to identify sedimentological characteristics of sands that induce faster tube growth. During the tank experiments, the grain size and mineralogy of the sand were modified. By employing thin sections and X-ray microtomography analyses, the structures observed and measured during and after the tests were analogous to those naturally formed. The fastest growth was recorded in the presence of bioclastic sands with a grain size between 125 and 350 μm. Defining the physical conditions that induce faster growth is fundamental for the defense of these vulnerable habitats but also the surrounding marine environment. This study also lays the foundations for coastal protection interventions in which bioconstructions grown in the tank could be directly implanted on submerged natural and artificial substrates that are already present in situ.

Late Paleoarchean to Neoarchean sedimentation on the Singhbhum Craton, eastern India: a synthesis

Subaerial rise of Earth's first continents took place 3.3–3.2 Ga years ago. This had significant influence on the ocean, atmosphere, and biosphere. Two important sedimentological consequences of continental emersion were (1) development of terrestrial (alluvial fan–fluvial–aeolian) depositional systems and (2) formation of shallow-marine sedimentary basins near the continental margin. Late Paleoarchean–Neoarchean terrestrial deposits, including development of an extensive paleosol around 3.2 Ga, and Meso–Neoarchean shallow-marine deposits have been reported from the Singhbhum Craton, eastern India from several localities. However, lateral and vertical changes in sedimentary facies associations and stratigraphic correlation between these terrestrial to shallow-marine sedimentary deposits have not yet been investigated. In this paper, we have reviewed the sedimentological characteristics of Late Paleoarchean to Neoarchean (3.2–2.8 Ga) stratigraphic successions of the Singhbhum Craton and have discussed sea level change and mode of stratigraphic sequence building. Our analysis shows that Singhbhum granitoid complex was emplaced around 3.3 Ga in an intracontinental setting, resulting in high continental freeboard conditions that triggered terrestrial (alluvial fan–braided fluvial) sedimentation (Dhosrapahar Formation). Continental sedimentation continued until ca. 3.0 Ga. In the eastern (Simlipal Group), western (Birtola Formation), and southwestern (the Mankarchua, Mahagiri, and Keonjhar formations) parts, shallow-marine sedimentation occurred after 3.0 Ga as a result of transgression. However, in the northern part (Dhanjori Formation), continental sedimentation prevailed throughout the Archean. These Late Paleoarchean to Neoarchean terrestrial and near-coastal successions of Singhbhum Craton should be the prime targets for intense geobiological research.

Late Cretaceous–Paleogene terrestrial sequence in the northern Kitakami Mountains, Northeast Japan: Depositional ages, clay mineral contents, and vitrinite reflectance

AbstractForearc basin deposits on continental margins contain important information that can be used to reconstruct the tectonic setting, volcanism, and climate at the time of their deposition. Coal‐bearing terrestrial to shallow marine strata in Northeast Japan were deposited in a forearc basin along the Eurasian continental margin during the Cretaceous–Paleogene. The rocks exposed in the Kado district, Iwate Prefecture, in the northern Kitakami Mountains include the Upper Cretaceous Yokomichi Formation and the Paleogene Kogawa Group; the latter is known for high‐quality refractory clay (kaolin clay). However, their stratigraphy and sedimentological characteristics are not yet fully understood. To reconstruct the formation and filling of the basin, we investigated field observations, U–Pb dating of tuff samples, XRD analysis of tuff and mudstone samples, and vitrinite reflectance of coal samples in this sequence. The U–Pb ages of the Yokomichi Formation and the Kogawa Group are ∼86 Ma and 58–52 Ma, respectively. The U–Pb age of the kaolin‐dominated tuffaceous rock (“red rocks”) is 56.1 ± 0.2 Ma. The mean random vitrinite reflectance (VRr) ranges from 0.37% to 0.53% through the sequence. We propose the following sequence for the formation and filling of the basin. (1) The basin initially formed during the Coniacian–Santonian (Late Cretaceous) and was filled by fluvial–lacustrine sediment. (2) These sediments kept the shallow burial depths during a ∼28 Myr and made a hiatus (86–58 Ma). (3) The basin was reactivated and covered by tuffs during the Thanetian, and the tuffs were altered to kaolin clay during the Paleocene–Eocene Thermal Maximum. (4) The basin was filled rapidly by alluvial fan deposits and subsided <2300 m (assuming a geothermal gradient of >30 K/km). (5) The basin was uplifted and exhumed at a rate of >50 m/Myr faster than the mean exhumation rate of the Kitakami Mountains since the Paleogene.

REVISED LITHOFACIES AND FRACTURE ANALYSIS OF MIOCENE MURREE FORMATION, ISLAMABAD

A thorough understanding of a rock formation’s structure and sedimentology is crucial before engaging in hydrological exploration or any development project. Islamabad is going through rapid development, so it’s crucial to update the subsurface studies for the benefit of the citizens. This research aims to study the Sedimentological characteristics of the Murree Formation through lithofacies analysis and to know the hydrological characteristics through Fracture analysis. Fracture analysis was conducted using the circle inventory method to calculate fractured porosity and permeability within the Murree Formation in the Islamabad region, and the lithofacies analysis was performed by observing the Sedimentological characteristics of each rock bed. Fracture analysis indicates that the rock formation in the Shah Alla Ditta region is not suitable enough to be classified as an aquifer. At the same time, the lithofacies study shows that the Murree Formation was deposited in a fluvial environment.

Evidence of upwelling on the Brazilian continental shelf of Rio Grande do Norte

This study evaluates Foraminiferal assemblages and their relation with grain size, calcium carbonate content, organic matter, and mineralogy of sediment samples collected at the sediment-water interface along a transect on the northern continental shelf of Rio Grande do Norte State, Brazil, adjacent to the city of Areia Branca. The sedimentary sequence of this shelf is represented by lithostratigraphic units of a marine regressive sequence dominated by four facies: Siliciclastic sand, Silicibioclastic Sand, carbonate mud, and Biosiliciclastic sand. The carbonate content ranged from 5.83% to 85% and the organic matter content from 1.16% to 27.05%. Mineralogical characters separated the predominant siliciclastic content (37% to 92%) from the bioclastic content (8% to 63%). We have identified 14 species out of 50 species of Foraminifera, associated to particular depths and sediment types as follows: (1)deeper-water sediments in the middle shelf contain Bolivina striatula, Bulimina marginata, Triloculina trigonula, Pyrgo ringens, Textularia gramen (2)the shallowest sediments in the inner shelf contain Ammonia tepida, Buccella peruviana, Miliolinella subrotunda, and Quinqueloculina patagonica, (3)the central parts of the transect, also in the inner shelf, provide habitats for Quinqueloculina lamarckiana, Textularia earlandi, Buliminella elegantissima, Discorbis peruvianus, and Pyrgo nasuta. The distribution of Uvigerina striata and Buccella peruviana is probably related to colder water temperatures and possibly the occurrence of an upwelling phenomenon for the deepest parts of the area rather than the sedimentological features discussed here.

Sedimentary records and implications for the evolution of sedimentary environments inferred from BH1302 during the late Quaternary in the Bohai Sea, China

Under the influence of glacial-interglacial climate change and regional tectonic activities in the Quaternary, the sedimentary environments of the Bohai Sea changed greatly, providing significant information on transgression-regression events, East Asian monsoon changes and regional tectonic activities. This study analyzed the sedimentological characteristics of the BH1302 core (water depth of 12.3 m, length of 70.2 m) in the southern Bohai Sea based on grain size, foraminiferal assemblages, carbon and oxygen isotopes in foraminiferal shells and element geochemistry, and established a chronological framework based on AMS 14C, optically stimulated luminescence dating and Oxcal age-depth model using Bayesian modeling. The results showed that three interglacial transgressions and one interstadial transgression were revealed in BH1302 since the late Quaternary, corresponding to marine isotope stages (MIS) 7, 5, 3 and 1, and three subinterglacial transgressions were further identified during MIS 7. The sedimentary environments of Laizhou Bay transitioned from an estuary environment dominated by rivers to a neritic environment dominated by marine conditions because of subsidence of the Miaodao uplift in late MIS 7.1. Three subinterglacial transgressions occurred in MIS5 and two subinterstadial transgressions in MIS 3, and the highstand sea level of MIS 3 reached approximately −18 ∼ −21 m. Under the influence of sea level fluctuations and the East Asian monsoon, the sedimentary environments of MIS 1 can be divided into a low salinity tidal-flat environment (12.0–7.0 kyr BP), a low salinity neritic environment (7.0–4.5 kyr BP) and a modern neritic environment (∼4.5 kyr BP).

GEO-TOURIST SITES AND ROUTES IN THE TERRITORY OF SAMBIR-KHYRIV TERRACE FOOTHILLS

The geological and geomorphological objects of Sambir-Khyriv terrace foothills have been characterized as natural monuments and potentially popular geo-touristic sites. The foothills cover the pre-Carpathian sections of the Stryvihor and Dniester valleys, the entire Bolozivka valley and the uplands of the interfluves. The main geomorphological elements of the study area are river valleys with a complex of river terraces of different ages. Outside the valleys, in the uplands of the interfluves, the most ancient foothill terraces and different-aged denudation leveling surfaces are spread. Relief-forming deposits of the foothills are mainly represented by Neogene and Anthropogenic accumulations. The anthropogenic depositsoverlapping the older accumulations are extremely heterogeneous in terms of genesis, age, and lithological structure. Within the foothills, the most valuable natural monuments are the following objects: sections of anthropogenic accumulations Slokhyni, Torhanovychi 1 and 2 and Kruzhyky, as well as landforms, i.e. a fragment of Krasna surfacedeveloped on the eastern macro-slope of RadychMountain and the western part of the Bolozivka valley. We identify the listed objects as stratigraphic and geochronological (sections of Slokhyni, Torhanovychi 1 and 2 and Kruzhyky), paleontological (section of Kruzhyky), geomorphological (surface of Krasna, Bolozivka valley),and scenic natural monuments (surface of Krasna). Foothill natural monuments are important in terms of research and geo-educational functions, in particular to study and illustrate stratification of sedimentary accumulations of anthropogenic age; lithological and sedimentological features of continental deposits; variability of paleogeographic conditions of anthropogenic age; cyclicityof continental morpholithogenetic processes; formation of exogenic forms of relief due to denudation shearing of uneven surface of the Earth, erosion and accretion activity of fluvial flows; soil-forming processes; and geological age of human material culture. The described natural monuments are important for the organization of events intended to popularize geological and geographical science, as well as environmental education among people, and teach the skills of careful attitude to the environment. It would befeasible to integrate them into the existing network of tourist routes inLviv region. Key words: Sambir-Khyriv terrace foothills; natural monuments; sections of anthropogenic deposits; surface of Krasna; Bolozivka valley.

Lithology of the Upper Triassic Sedimentary Rocks of Chukotka and Wrangel Island and Their Relationship with Coeval Rocks of the Eastern Arctic

Abstract—The correlation between the sedimentologic characteristics of the Upper Triassic deposits of Wrangel Island and the Chukchi Peninsula (Chukotka) is discussed. These deposits are similar in isotopic, petrographic, and geochemical features. It has been established that the Upper Triassic sand strata accumulated at different sites of a single sedimentary basin, in shallow-water prodeltas of Wrangel Island and in deeper-water environments of Chukotka. In the latest Triassic, the portion of the sand component in the sections increased. At the same time, the average size of the sand grains decreased, which indicates weakening of the tectonic factor in some zones of the provenance and its general peneplanation with the formation of a weathering crust. The eroded complexes are composed of granitoid, metamorphic, and metavolcanic rocks. They stayed on land for a long time, being subjected to chemical weathering. The depth intervals with the large amount of sandy material in the section of Wrangel Island and Chukotka are correlated with those in the sections of the Sverdrup Basin and the northern slope of Alaska.

The influence of hybrid sediment gravity flows on distribution and composition of trace‐fossil assemblages: Ordovician succession of the north‐eastern Alborz Range of Iran

ABSTRACTThe distribution of conventional subichnofacies in deep‐water fan systems (i.e. Ophiomorpha rudis–Paleodictyon–Nereites‐subichnofacies) depends on the presence of fully turbulent non‐cohesive flows such as low‐density turbidites and high‐density turbidites. However, changes in flow state between laminar and turbulent conditions can affect the distribution style of conventional subichnofacies. This study deals with the effects of environmental or ecological stressors as a result of hybrid sediment gravity flows (hybrid event beds) on distribution and composition of trace fossils in the deep‐marine depositional system of the Ordovician Ghelli Formation in the north‐eastern Alborz Range. The spatial distribution and sedimentological character of hybrid sediment gravity flows, in particular their abundance in the down‐dip parts of lobe‐related facies associations, are interpreted as products of longitudinal and lateral transformation from turbidity currents to debris flows promoted by incorporation of significant claystone and mudstone clasts into the flow by seafloor erosion and flow bulking. Seven trace‐fossil assemblages were recognized in the channel and lobe‐related facies associations. The observed spatial distribution of trace‐fossil assemblages in the interpreted frontal and lateral lobe fringes, somewhat contrasts with conventional subichnofacies distribution models. The development of cohesive flows and rapid emplacement of turbidite, banded and debrite beds could be accompanied by fluctuations in physico‐chemical conditions and, hence, the time available for colonization and the lifestyle of producers. This study suggests that, compared to the archetypal models of the subichnofacies in down‐dip parts of lobe‐related facies associations, ichnodiversity and density of bioturbation are drastically reduced, and trace fossils are limited to simple, shallow‐tier feeding strategies. Commonly, the presence of cohesive flows may have forced the producers in the Paleodictyon and Nereites‐subichnofacies to migrate into lateral lobe fringe with more participation of low‐density turbidites. This study shows that, in addition to sedimentological and architectural criteria, ichnological criteria can also be used to distinguish between frontal and lateral lobe‐fringe deposits in unconfined systems.