Thick Sedimentary Sequence Research Articles

Using Formation Processes to Explore Low-Density Sites and Settlement Patterns: A Case Study from the Swabian Jura

Paleolithic archaeologists often rely on cave and rockshelter sites with rich occupation levels to explore hominin behavior and settlement patterns. However, a closer look into regional occupation data may reveal an uneven distribution of sites and the presence of occupational hiatuses or low-density occupation horizons that often remain understudied. In contrast to this trend, this paper focuses on low-density occupation data to explore regional settlement patterns, using the rich and well-studied Paleolithic record of the Swabian Jura, Germany, as a case study. In this regard, we employ a geoarchaeological approach based on micromorphology to investigate the formation processes of two low-density occupation sites, Schafstall II and Fetzershaldenhöhle, and compare their formation history with the geogenic sequence from Lindenhöhle. We demonstrate that the investigated sites have comparable formation processes, despite their differences in chronology and context. We argue that humans used Schafstall II and Fetzershaldenhöhle for short-term activities, while the sites mostly served as carnivore activity areas, emphasizing the importance of fauna in the accumulation of thick sedimentary sequences. In addition, our findings corroborate the regional climatic record and provide novel insights into the geomorphological history of the less studied Lauchert Valley, where Schafstall II is located. By comparing our results with data from intensively occupied caves in the Swabian Jura, we provide broader implications for the settlement patterns of Upper Paleolithic hunter-gatherers. We conclude with methodological suggestions for investigating sites in hunter-gatherer contexts combining a distributional and a site-specific approach.

Contrasting thermal histories for the Indian passive margins during syn‐ and post‐Gondwana break‐up: Insights from apatite fission‐track thermochronology

AbstractNew and published apatite fission‐track data provides evidence for differential exhumation between the eastern and western passive margins of southern India. The eastern margin records significant Late Jurassic to Early Cretaceous rifting‐triggered exhumation in response to Gondwana break‐up and minor Cenozoic cooling. In contrast, Meso–Cenozoic rifting and posterior tectonic events did not deeply exhume the basement of the western margin. The anomalous thick crust of the Western Dharwar Craton might explain why Mesozoic deformation in this area was subdued. In addition, the Cenozoic eastward tilting of the Indian plate and the onset of Bengal Fan sedimentation ca. 23 Ma allowed the accumulation of thick sedimentary sequences in the eastern coastal basins, probably inducing a flexural response of fault reactivation on the eastern margin. More generally, we demonstrate the influence of lithospheric strength and post‐rifting sedimentation to the exhumation history of passive margins.

Dynamic processes of upper plate deformation at the New Guinea Trench

The interactions between arc-continent collision and subduction zones are still poorly understood. Here, we use 2D seismic data to document upper plate deformational features and identify different structural styles along the New Guinea Trench, western Pacific, and discuss their broader significance. In the western section, normal faults and negative flower structures occur within the strata of the upper plate. An unconformity represents the signal of tectonically driven subsidence. In the eastern section, both thick-skinned and thin-skinned thrusting are found within the frontal upper plate. In the central section, rare extensional or shortening deformation is identified within the forearc basement and overlying strata. Horizontal, thick sedimentary sequences within the Caroline subbasin have been subducted beneath the upper plate. This suggests that Miocene subduction in the eastern section led to the formation of a thrust-deformed ophiolitic basement in the upper plate. Since the Miocene, strike-slip tectonic processes dominated in the upper plate, causing compressional deformation in the strata in the eastern section and extensional to transtensional deformation in the strata in the western section. The strike-slip tectonic processes might have been weakened in the upper plate in central section due to the incoming Eauripik Rise. Over geologic time, arc-continent collision processes and related changing of regional tectonic forces can have a long-lived influence on shaping and deforming subduction systems.

Late Pleistocene history of aggradation and incision within a bedrock gorge, Narmada River, central India: implications for resurgent tectonic activity and changing climate

Bedrock gorges occurring on the Indian Peninsula are sites of intense erosive activity where thick sequences of fluvial sediments are conspicuously absent. We identified unusually thick and coarse fluvial sequences within the Dhadgaon (DG) gorge in the lower reaches of the Narmada River in central India. Stratigraphic interpretations, sediment character and optically stimulated luminescence (OSL) ages revealed episodic aggradation at ~70 ka and ~28 ka in response to tectonically induced steepening of the upstream channel gradient. Incision of the DG gorge and sedimentation of the alluvial fan downstream was facilitated by a climatically induced decrease in the sediment supply/discharge ratio in addition to the tectonic slope. The final evacuation of sediments from the DG gorge and incision of the Banganga channel occurred during the early Holocene. Collectively, the results show a major influence of tectonics, hillslope processes and lithology on aggradation–incision patterns supported by climatic conditions during the late Quaternary.

The Sierra Nevada de Santa Marta (Colombia) and Nevado de Famatina (Argentina): The effects of tectonic syntaxis on the topography of the Andes

The Sierra Nevada de Santa Marta (Santa Marta) in Colombia and Nevado del Famatina (Famatina) in Argentina are two isolated peaks within the Andes of South America, having elevations of about 5,500 and 6,000 m, respectively. Both massifs are bounded by major wrench faults of opposite kinematics but comparable magnitude in their lateral displacement. Despite the volumes of research available, little has been said in the literature about the tectonics surrounding these particular systems. In this context, digital terrain elevation (DEM), regional geology, satellite imagery and geophysical data were analysed to illustrate how a network of transcurrent faults uplifted the peaks. We propose a model to account for topography by the opposed movement of faults operating in two compartments: internal (acute) and external (obtuse). Fault motion caused uplift of the internal compartments: a) the Santa Marta tectonic syntaxis is generated by the sinistral Santa Marta-Bucaramanga Fault on the west and the dextral Oca-Pilar Fault to the north whilst, b) the Famatina tectonic syntaxis is caused by the Valle Fértil sinistral fault on the western side and the dextral Tucumán lineament to the north. Elevation maps documenting the lateral displacement of modern alluvial fans provide evidence of the existence and kinematics of these faults. Active since the Neogene, the transcurrent faults resulted in displacements in the order of 25–60 km, with velocities of approximately 1–2 cm/year. Seismic records suggest that the syntaxis occurred after reactivation of oblique discontinuities in the basement due to the convergence of the Nazca, Caribbean, and South American plates. This tectonic framework led to the formation of a remarkable positive relief and the development of internal positive compartments subject to constrictive forces. Simultaneously, external distensive and negative compartments controlled the syntectonic deposition of thick sedimentary sequences. The significant topographic difference between the internal positive compartments and their external negative counterparts triggered high rates of erosion, transport, and ultimately sedimentation. Regional subsurface surveys indicate strong anomalies of the underlying bedrock influenced by tectonic syntaxis.

Evolution of Paleogene weathering intensity in the Qaidam Basin, northeastern Tibetan Plateau: Insights from clay geochemistry

An integrated multiproxy dataset involving both mineralogical and geochemical investigations of the northern Tibetan Plateau helps in assessing regional weathering processes linked to topographic evolution and environmental change. However, changes in landscape and drainage reorganizations caused by active tectonics and remarkable climate change during the Cenozoic characterize the basins in and around the Tibetan Plateau by frequent facies changes and coarse lithologies, which largely limit the reliability of bulk geochemical indicators for revealing the regional weathering history. Here, we present detailed geochemical investigations of clay-sized sediments collected from the Hongliugou section (54–26 Ma) in the northern Qaidam Basin to reconstruct high-resolution chemical weathering records of the northern Tibetan Plateau. To prevent chlorite bias when calculating the chemical index of alteration (CIA) in the clay-sized sediments, we propose a modified CIA formula (CIAMg+), in which Mg is added as a soluble cation that can be removed during weathering, similar to Na, K and Ca; thus, CIAMg+ = Al2O3/(Al2O3 + Na2O + K2O + CaO* + MgO) × 100. The CIAMg+ and illite chemistry indices are generally the highest values in the early Eocene Climate Optimum (∼52–49.5 Ma) and a long-term decreasing trend is present from ∼ 49.5–26 Ma; the Mg/Al ratios of the clay-sized sediments and hydrochloric acid leachates are the lowest during the EECO and present a long-term increasing trend in the following 49.5–26 Ma, thus collectively indicating a continuous decrease in the regional chemical weathering intensity. The weakening weathering process during the Paleogene is mainly attributed to the decreasing global temperature and decline in precipitation caused by global cooling. Our study suggests that the proposed geochemical index based on clay-sized sediments can serve as an efficient proxy for regional chemical weathering reconstruction, even in thick sedimentary sequences with frequently changing facies and lithology.

Using mineralogy and Sr-Nd isotopes of gypsum to constrain the provenance of sediments in the western Qaidam Basin, northern Tibetan Plateau: Implications for neo-tectonic activities

The extremely thick sedimentary sequence in the Qaidam Basin, northeastern Tibetan Plateau (TP) is closely related to the uplift of the TP. Due to the scarcity of minerals that can be dated continuously, little is known about the isotopic responses of the minerals in this area to the changes in the weathering and sources over a long time period. A 938.5-m long core (magnetostratigraphic age of ∼ 2.8–0.1 Ma) was drilled in the western Qaidam Basin in 2008. The mineralogy and isotopic compositions of gypsum in this core were investigated. The gypsum recorded the primary information about the brine that formed during ∼ 2.8–0.1 Ma. The variations in the Sr isotopes (0.709817–0.714473, average of 0.711249) and Nd (0.512114–0.512614, average of 0.512184) of the gypsum samples suggest that the weathering products of the rocks in the Kunlun and Altyn mountains (Mts) likely exerted a strong control on the Sr-Nd isotopes of the lakes. The climate and the Sr content/isotopic compositions of the gypsum samples were affected by the regional tectonic activities throughout the evolution of the paleolake since 2.8 Ma. The results of this study demonstrate that Sr-Nd isotopes are useful tools for investigating the origins of evaporite deposits and the interactions between tectonic activities and climate change.

The Provenance and Tectonic Settings of the Greywacke Member of the Late Neoproterozoic Hazara Formation Lesser Himalayas, Northern Pakistan: Evidence from Geochemistry and Petrography

The petrographic and geochemical analysis of the greywacke horizon of the late Neoproterozoic Hazara Formation from the Hazara Mountains has been investigated to determine the provenance, tectonic settings and weathering history of the sediments. The Late Neoproterozoic Hazara Formation is a thick sedimentary sequence comprising of greywacke, shale, argillites, siltstone, and limestone. The greywackes are characterized by fine to medium-grained, moderately sorted and sub-angular to sub-rounded framework grains. They are rich in quartz, lithic fragments and clay minerals. The petrographic investigation of the greywackes categorized them as feldspathic greywacke in the QFR diagram. The quartz content is higher in sandstone and may reach to 70%, which indicates a weathered felsic source. Chemical Index of Alteration values of greywacke suggests that the source region has experienced highly weathering conditions with a warm and moist climate. Various geochemical interpretations, elemental ratios like Th/Sc, La/Sc,Th/Cr, and positive Eu anomalies indicate that the greywackes of the Hazara formation derived from a felsic source and were deposited within an active continental margin tectonic settings. The main source area of the sediments of the greywackes was located to south to southeast, which may possibly be the Aravali orogeny, central Indian craton and Bundelkhand craton. Finally, the geochemical data of the major elements point to a felsic igneous provenance for the greywacke.

CO2 Storage Potential Reconnaissance of the Newly Identified Red Beds of Hazlehurst in the Southeastern United States

The states of Georgia and South Carolina emitted ∼100 million tons (Mt) of CO2 in 2019 from point sources. Integration and interpretation of subsurface data enabled identification of a previously unrecognized, regionally extensive, and thick (up to 450 m) sedimentary sequence—the Red beds of Hazlehurst (RbH)—as a potential saline reservoir for CO2 storage in the southeastern United States. Based on the renewed stratigraphic framework and structural interpretation of the RbH interval, we analyzed detailed well logs and the depositional environments to provide reconnaissance-level regional scale estimations of the storage resource. The volumetric results suggest the effective storage area (∼85,000 km2) has a maximum resource potential for 390 gigatons (Gt) of anthropogenic CO2. Petrophysical measurements suggest the permeability of RbH ranges from 0.001 to 48 mD, and the porosity ranges from 11.1 to 18.4%. Residual/capillary trapping and solubility trapping act as the main trapping mechanisms for long term storage and prevent vertical migration of CO2 into the shallow freshwater aquifers. Due to the heterogeneity observed in geophysical logs and the scarcity of well penetrations, future data collection is needed to characterize the storage aquifer and confining aquitards of a site-specific system at this stage.

Geological permeability controls streamflow generation in a remote, ungauged, semi-arid drainage system

Study regionA semi-arid drainage system overlying a thick (12 km) sedimentary sequence on the Dampier Peninsula in northwestern Australia. Study focusIn this study we combine aerial geophysics, geological mapping, hydrometry and hydrochemistry with aerial image analysis and stream mass balance modeling to delineate the key hydrogeological structures and processes that control streamflow generation within a remote ungauged semi-arid watershed. New hydrological insights for the regionFour distinct processes of streamflow generation were identified, each dependent on the spatial distribution of lithological permeability; (1) ephemeral rainfall runoff over low-permeability surface lithologies, (2) intermittent flow generated by seasonal groundwater discharge from the unconfined aquifer above a newly mapped clay layer, (3) persistent flow from contact springs via interbedded high- and low-permeability layers, and (4) perennial flow associated with regional groundwater discharge at headwater springs. This study highlights the importance of geological permeability and the resultant hydrogeological processes as controls on streamflow generation, particularly in low-relief and arid regions where topography is less likely to determine the distribution of streamflow.

Pedosedimentary and microbial investigation of a karst sequence record

A 3-m thick sediment sequence, found in a limestone mine located in the south of Italy at a depth of ca. 25–30 m from the current ground level, was investigated. Samples from 5 layers were analysed by X-ray diffraction, elemental analysis, Inductively Coupled Plasma Mass Spectrometry and micromorphology. Microbial DNA was analysed by 16S rRNA gene metabarcoding. The main mineral compounds found in the 5 layers were calcite (70–80%) and clay minerals in layers #1 and #5, goethite (75%) and hematite in layer #2, manganese (66%) and iron oxides in layer #3, and almost exclusively goethite in layer #4. Micromorphology data allowed to shed light in understanding whether these sediments formed by subsequent weathering of carbonates and silicates or by migration of soil sediments from the surface, or also by the accumulation of shallow marine sediments occurring between the middle Pliocene and the lower Pleistocene, when the extreme western sector of this area underwent strong subsidence. From the microbiological point of view, upon the 16S rRNA gene analysis, these 5 layers appear to cluster in three groups. Overall, such a distribution suggests that, both in the top (#1) and in bottom layers (#4 and #5), different communities would have undergone in situ reproduction and colonization exploiting metabolically the substrate, whereas the two mid layers would have received bacterial convection by passive transport of percolating waters. At the same time, micromorphological data show that each layer preserved its distinct features to be related to the environmental condition at the time of deposition. The chemical, mineralogical and micromorphological features of the layers and the known physiology of the microbial taxa thereby encountered highlight the possible role of the latter in elucidating the occurrence of certain mineral species as well as the biogeochemistry of elements like Mn and Fe in sediment layers.

Controls on distributions of sulphate, fluoride, and salinity in aquitard porewater from the North China Plain: Long-term implications for groundwater quality

Groundwater interacts with porewater within clay-rich sequences. However, the effects of aquitard porewater on groundwater quality are generally poorly understood. This study explores potential links between porewater chemistry in a thick clay-rich sequence of Quaternary sediments, and groundwater quality in the North China Plain (NCP), one of China’s most important water supply aquifers. Previous studies have hypothesised the release of salinity, fluoride, and sulphate from aquitards in response to intensive pumping, without explicitly analysing the chemistry of aquitard porewaters. This study further investigated this hypothesis through targeted analysis of porewater chemistry profiles through the NCP sedimentary sequence. Two cores were analysed – one in the central plain (Hengshui, HS) and the other in the coastal plain (Cangzhou, CZ). Both areas have experienced significant groundwater extraction over recent decades from confined aquifers inter-layered with clays. Aqueous extraction (AE) and squeezing (SE) methods were both used to assess porewater chemistry. The hydrochemical characteristics of groundwater are closer to those of the squeezed porewater, which can be regarded as more closely corresponding to in-situ porewater compositions than AE profiles. Chloride was generally consistent between the two methods, while sulphate and fluoride concentrations were greater using AE, ranging from 340 to 48,700 mg/L and 8.8 to 144 mg/L, compared to 350 to 8860 mg/L and 0.2 to 4.3 mg/L using SE, respectively. The much greater concentrations of fluoride derived from the AE method indicates a high susceptibility to release during changes to the ambient geochemical environment. While the primary fluoride sources in groundwater and porewater are likely minerals from weathering of volcanic rocks in the sedimentary sequence, release into groundwater appears linked to common geochemical influences such as high Na/Ca ratio (increased during cation exchange) and the presence of iron and aluminium oxides (providing sorption sites). The primary source of solutes is interpreted to be different in each profile, with evapotranspiration important in the central plain and marine solutes important in the coastal profile, indicating significant storage of salinity, fluoride, and sulphate within low permeability sediments. Our data supports the hypothesis that release of these ions is driving degradation of groundwater quality, in response to decades of intensive groundwater extraction, which is an ongoing threat to the quality of groundwater in the NCP.

Post-rift magmatism and hydrothermal activity in the central offshore Otway Basin and implications for igneous plumbing systems

Spatially and volumetrically extensive igneous rocks are exposed onshore in southeastern Australia and provide important information about the Cenozoic evolution of the region. However, the morphology and distribution of igneous rocks are still not well constrained in the ~70 km wide continental shelf of the central Otway Basin. Within this region, we present seismo-geomorphological characteristics of 30 volcanoes and 27 hydrothermal vents, as well as several lava flows and magmatic sills, based on 2D and 3D seismic reflection data. Hydrothermal vents formed mainly during the mid-Eocene, while igneous complexes developed between the mid-Eocene to late Miocene, both post-dating continental break-up in the basin. The distribution and morphology of igneous rocks and hydrothermal vents is influenced by rift-related faults, as most of these features are linked to the underlying faults by near-vertical zones of disruption and are elongated in an NW-SE direction that parallels the primary fault trend. Magma for volcanoes and heat sources for hydrothermal vents within the study area are likely supplied by deep-sourced dykes, as magmatic sills only have a scattered distribution in this region. This implies a dyke-dominated plumbing system for magmatism in the Otway Basin. In comparison, the nearby Bight Basin, which has a thin basement but a relatively thick sedimentary sequence, displays magma propogation more prone to forming igneous sills. There are significant lithological and tectonic similarities between the Otway and Bight basins; thus, we propose that a relatively thin sedimentary sequence over a thick basement in the Otway Basin produced sufficient magma pressure for a predominantly dyke-dictated igneous plumbing system. This work highlights the critical role of basin structures, such as the thickness of basement and overlying strata, in the control of igneous plumbing styles and the distribution of post-rift igneous complexes along magma-poor continental margins. Our work, therefore, aids the estimation of different magmatic components within the sedimentary basins and facilitates the understanding of their diverse impacts on the exploration of frontier basins. This result also provides some constraints on the prediction of possible future eruption centres within active volcanic fields.

Combined On-Fault and Off-Fault Paleoseismic Evidence in the Postglacial Infill of the Inner-Alpine Lake Achensee (Austria, Eastern Alps)

The Eastern European Alps are characterized by slow active deformation with low- to moderate seismicity. Recurrence rates of severe earthquakes exceed the time span of historical documentation. Therefore, historical and instrumental earthquake records might be insufficient for seismic hazard assessment and high-quality paleoseismic data is required. However, primary geological observations of postglacial fault activity are scarcely found, because major faults are buried below thick sedimentary sequences in glacially overdeepened valleys. Moreover, high erosion rates, gravitational slope processes and penetrative anthropogenic landscape modification often obscure geomorphic features related to surface ruptures. Here we present one of the rare paleoseismic data sets showing both on-fault evidence as subaqueous surface ruptures and off-fault evidence as multiple coeval mass-transport deposits (MTDs) and megaturbidites within a single high-resolution seismic-stratigraphic framework of the inner-alpine lake Achensee. Co-occurrence of on-fault and off-fault paleoseismic evidence on three stratigraphic levels indicates seismic activity with inferred moment magnitudes MW ∼6–6.5 of the local, lake-crossing Sulzgraben-Eben thrust at ∼8.3 ka BP and twice in Late Glacial times. Additional eight stratigraphic levels with only off-fault paleoseismic evidence document severe seismic shaking related to the historical MW ∼5.7 earthquake in Hall (CE 1670) and seven Holocene earthquakes, which have exceeded a local seismic intensity of ∼VI (EMS-98) at Achensee. Furthermore, we discuss natural and methodological influencing factors and potential pitfalls for the elaboration of a subaqueous paleoseismic record based on surface ruptures and multiple, coeval MTDs.

Sedimentary processes and palaeoenvironments from La Combette sequence (southeastern France): climatic insights on the Last Interglacial/Glacial transition

During the Last Interglacial-Early Glacial transition (MIS5-MIS4; ~73 ka), substantial hydroclimatic changes affected morphogenetic processes, landform dynamics, and ecosystem variability over the Mediterranean sub-alpine valleys. This transition is mainly preserved in the northern Mediterranean region in continuous marine, lacustrine, and peat bog archives. To understand better local-to-regional hydro-sedimentary processes, their climatic significance, and their direct impact on prehistoric settlements, this manuscript reinvestigates a known continental sedimentary record with revised methods. The Middle Palaeolithic site of La Combette in the western Provence region (southeastern France) presents a thick sedimentary key sequence for studying environmental changes from the MIS5 to the MIS3. A review of previous studies with the integration of new micromorphological, sedimentological, physicochemical, malacological, and luminescence ages allows us to characterize the sedimentary processes and environmental patterns during this major climatic transition. Alternating warm and cold conditions and shifting vegetation patterns reflect the strong environmental instability of the end of the Last Interglacial Period. The emergence of a steppe-like ecology dominated by cryo-turbated loess deposition marks the beginning of the Early Würmian Glacial period (MIS4-MIS3; ~73 ka to ~50 ka), contemporaneous with the last Neanderthal occupation at La Combette rock shelter. Comparisons with regional palaeoclimatic data allow us to detail local climatic settings and provide evidence of divergences with larger-scale quantitative reconstructions during a period of significant environmental and socio-cultural shifts.

Glacial, fluvial and contour-current-derived sedimentation along the northern North Sea margin through the Quaternary

The thick sequence of Quaternary sediments preserved within the northern North Sea contains important information about the glacial history, palaeo-oceanographic conditions and slope stability of this region during the last 2.6 million years. The interplay between glacial, fluvial and contouritic processes can be determined from seismic stratigraphic studies. Here, seismic horizon, attribute and geomorphological interpretations of an extensive 2D seismic dataset (∼100,000 km2) and two 3D seismic cubes (∼18,400 km2) are integrated with lithological data from eight exploration wells to map sandy sedimentary units. Mapping of seismic horizons and facies reveals that, in addition to prograding glacial sediments derived from the Norwegian mainland, the Quaternary succession includes wedge-shaped units with prograding internal clinoforms building out from the East Shetland Platform, relatively flat-lying units of acoustically stratified sediments within the central northern North Sea, and aggrading to prograding units with low-amplitude internal reflections on the continental slope. The lowermost unit of Quaternary sediment is interpreted as an ∼800 km3 earliest Pleistocene (∼2.6 Ma) turbidite-contourite deposit, in which turbidites derived from a fluvial delta building out from the East Shetland Platform transition seaward into aggrading to prograding sediments of the Shetland Drift. The wedge-shaped units are intercalated with glacigenic sediments in the central northern North Sea, showing that the East Shetland Platform was a major source area for the delivery of coarse-grained sediments during the Early Pleistocene (∼2.6–0.8 Ma). The distribution of units of aggrading to prograding geometries suggests that contourites continued to develop on the continental slope, including on the North Sea trough-mouth fan, throughout the Quaternary. These interpretations constrain a new model for the Quaternary evolution of the northern North Sea that reconciles the development of the eastern and western sides of this margin, and shows the importance of fluvial-deltaic and contouritic sedimentation during periods of reduced glacigenic sediment input. Our model also provides a high-resolution analogue for the sedimentary architectures and seismic facies that can be produced by the interplay of down-slope and along-slope processes on other continental margins.

Multi-Proxy Records of Late Holocene Flood Events From the Lower Reaches of the Narmada River, Western India

Analyses of a fluvial sedimentary sequence from the lower reaches of the Narmada River establish a record of rhythmic cycles of sediment facies that represent floods during the late Holocene. The south-west Indian monsoon strongly influences the study area, and heavy rainfall or cyclones which originate from either the Bay of Bengal or the Arabian Sea, also affect the region. Optically stimulated luminescence dating places the 8 m thick sediment sequence in the climate transition phase which ranges from the Medieval Warm Period to the Little Ice Age. Multi-proxy analyses including high-resolution granulometry, magnetic susceptibility, ferromagnetic mineral concentration, facies major oxide geochemistry, and micro-fossil records (from two sedimentary units) are used to study these late Holocene flood events. The latter are characterised by multiple sediment facies, depositional events, changes in channel morphology, and distinctive flood signatures. Integration of these records enables to identify two distinct aggradations viz. phase I and phase II, as well as a relative change in channel morphology. The study describes 11 flooding events and their imprints over multi-proxy records. Historic documents and instrumental records from the town of Bharuch referring to floods, movement of channel sand, channel shallowing, and the dysfunction of the ancient port of Bharuch further validate the inferences drawn from the sedimentary sequence. The study exemplifies the need to use high resolution and multi-proxy studies to interpret paleoflood records and climate signatures in order to build archives of monsoonal rivers.

Angular Unconformity of the Late Quaternary Strata in the Hetao Basin, North of the Ordos Block (West China): Timing and Its Tectonic Implications

Following the uplift of the Tibet Plateau and the continuous subduction of the Pacific Plate, graben faulting began to appear around the Ordos Block in the Cenozoic. The Hetao Basin is a Cenozoic rift basin between the Ordos Block and the Yinshan Mountains, and Late Quaternary sedimentary strata, which have lacustrine facies, are widely distributed inside this basin. However, the evolution of the Hetao Basin and its related fault systems has been debated for a long time due to the lack of tectonic evidence. In this study, four sections named Haolaigou, Bianqianghao, Huhesala, and Hazigai are selected along the north margin of the Hetao Basin. With the lithology and structural analysis of the Upper Pleistocene series in these sections, two new angular unconformities are found within the 10 m thick sedimentary sequence of the lacustrine sediments. Based on the dating results, we speculate that these two upper and lower angular unconformities are formed between 33 ka BP and 40 ka BP, and 60 ka BP and 80 ka BP, respectively. The angular unconformities also provide tectonic constraints for the latest and ongoing tectonic activity in the Quaternary. This tectonic movement begins at around 80 ka BP and causes two different unconformities of the lower strata with varying degrees of deformation (tilt) but also leads to the final death of the ancient lake.

Evidence for a grounding line fan at the onset of a basal channel under the ice shelf of Support Force Glacier, Antarctica, revealed by reflection seismics

Abstract. Curvilinear channels on the surface of an ice shelf indicate the presence of large channels at the base. Modelling studies have shown that where these surface expressions intersect the grounding line, they coincide with the likely outflow of subglacial water. An understanding of the initiation and the ice–ocean evolution of the basal channels is required to understand the present behaviour and future dynamics of ice sheets and ice shelves. Here, we present focused active seismic and radar surveys of a basal channel, ∼950 m wide and ∼200 m high, and its upstream continuation beneath Support Force Glacier, which feeds into the Filchner Ice Shelf, West Antarctica. Immediately seaward from the grounding line, below the basal channel, the seismic profiles show an ∼6.75 km long, 3.2 km wide and 200 m thick sedimentary sequence with chaotic to weakly stratified reflections we interpret as a grounding line fan deposited by a subglacial drainage channel directly upstream of the basal channel. Further downstream the seabed has a different character; it consists of harder, stratified consolidated sediments, deposited under different glaciological circumstances, or possibly bedrock. In contrast to the standard perception of a rapid change in ice shelf thickness just downstream of the grounding line, we find a flat topography of the ice shelf base with an almost constant ice thickness gradient along-flow, indicating only little basal melting, but an initial widening of the basal channel, which we ascribe to melting along its flanks. Our findings provide a detailed view of a more complex interaction between the ocean and subglacial hydrology to form basal channels in ice shelves.

A PHOTOGRAPHIC ATLAS OF THE ARCHITECTURE, FLOW GEOMETRY AND MORPHOLOGY, AND FACIES OF SERRA GERAL GROUP (PARANÁ IGNEOUS PROVINCE) IN THE STATE OF PARANÁ, BRAZIL

The rocks that make up the Serra Geral Group spread over approximately 100,000 km2 of the State of Parana, which represent about 10% of the Parana Igneous Province. The geologic mapping of the Serra Geral Group in the State of Parana was carried on from 2003 to 2018, and revealed a great diversity of features and facies of basic and acidic lava lows, as well as the presence of interbedded volcaniclastic deposits. This paper presents an inventory of this geodiversity along with brief descriptions, a wealth of photographic documentation, and the georeferenced location of each outcrop, making it easy to access the documented sites, in order to assist the development of scientiic research in this geologic compartment, which occupies nearly half of the Parana territory. The processes responsible for the lithologic features are interpreted in compliance to the knowledge accumulated on the various continental basaltic provinces by many researchers, including the authors of this paper, so to build up a genetic system for the Serra Geral Group more complete and coherent with the paleogeography of Gondwana in its initial breakup stage. In the early Cretaceous, during ca. 1.2 Ma with the paroxysm at 134.7 Ma, a huge magma amount, which is estimated at least in 600,000 km3, lowed over the thick sedimentary Paleozoic sequence of the Parana Basin, stacking up a volcanic sequence. The interaction between the rising magma with the sedimentary sequence up to 7,000 m thick, gave rise also to thousands of intrusive bodies, such as sills and dikes, almost all of a basic nature. Furthermore, the ascending magma interacting with aquifer systems gave rise to explosive volcanism – hydrovolcanism – which produced many maic volcaniclastic deposits MVDs, interbedded to the basic lows. Thus, in South America, during this relatively short lapse of time, basic and acidic lows covered the Parana Basin, being reported in Brazil, Argentina, Paraguay, and Uruguay under diverse names. In the present article, it will be simply referred as Serra Geral Group (SGG). The lithological inventory represented by the present photographic atlas comprises diagnostic features of basalt, andesi-basalt, rhyolite and dacite lava lows, maic volcaniclastic deposits MVDs, and dykes of basic composition.