Lithostratigraphic Data Research Articles

Fossil spring records from central Sudan reveal paleoenvironmental and settlement dynamics in the Eastern Sahel during the last 30 ka

Knowledge of past environmental change and prehistoric settlement dynamics in the Sahel east of the Nile is limited due to the scarcity of suitable sedimentary archives and archaeological sites. Here we present tufa-based paleoenvironmental records from the area of NW Butana (central Sudan, ∼55 km southeast of the Nile River) which show that increased rainfall and spring activity occurred in several discrete intervals during the last ∼30,000 years. Lithostratigraphic data combined with phytolith, malacological, paleopedological, and stable carbon isotope records revealed humidity peaks during late MIS3 and the early and middle Holocene. Gaps in lithological records correlated with dry periods of the Last Glacial Maximum and Younger Dryas. Minor wet pulses coinciding with Late Glacial interstadials indicate an early intensification of the African monsoon, which implies that a sharp climatic boundary existed between the Sahel and the Sahara during this period.These new paleoenvironmental records, together with archaeological evidence from Butana, provide a unique opportunity for understanding human ecology in the eastern Sahel. The peoples who inhabited this dryland area 30+ km from the Nile Valley could not rely on its relatively predictable resources of riverine, floodplain and lake habitats. New models of subsistence and settlement, and strategies of adaptations to seasonal and interannual environmental variability are needed.

A hybrid knowledge graph for efficient exploration of lithostratigraphic information in open text data

Rocks formed during different geologic time record the diverse evolution of the geosphere and biosphere. In the past decades, substantial geoscience data have been made open access, providing invaluable resources for studying the stratigraphy in different regions and at different scales. However, many open datasets have information recorded in natural language with heterogeneous terminologies, short of efficient approaches to analyze them. In this research, we constructed a hybrid Stratigraphic Knowledge Graph (StraKG) to help address this challenge. StraKG has two layers, a simple schema layer and a rich instance layer. For the schemas, we used a short but functional list of classes and relationships, and then incorporated community-recognized terminologies from geological dictionaries. For the instances, we used natural language processing techniques to analyze open text data and obtained massive records, such as rocks and spatial locations. The nodes in the two layers were associated to establish a consistent structure of stratigraphic knowledge. To verify the functionality of StraKG, we applied it to the Baidu encyclopedia, the largest online Chinese encyclopedia. Three experiments were implemented on the topics of stratigraphic correlation, spatial distribution of ophiolite in China, and spatio-temporal distribution of open lithostratigraphic data. The results show that StraKG can provide strong knowledge reference for stratigraphic studies. Used together with data exploration and data mining methods, StraKG illustrates a new approach to analyze the open and big text data in geoscience.

Reconstrucción probabilística mediante aprendizaje automático del sistema acuífero de la cuenca del Po (Italia)

AbstractA machine-learning-based methodology is proposed to delineate the spatial distribution of geomaterials across a large-scale three-dimensional subsurface system. The study area spans the entire Po River Basin in northern Italy. As uncertainty quantification is critical for subsurface characterization, the methodology is specifically designed to provide a quantitative evaluation of prediction uncertainty at each location of the reconstructed domain. The analysis is grounded on a unique dataset that encompasses lithostratigraphic data obtained from diverse sources of information. A hyperparameter selection technique based on a stratified cross-validation procedure is employed to improve model prediction performance. The quality of the results is assessed through validation against pointwise information and available hydrogeological cross-sections. The large-scale patterns identified are in line with the main features highlighted by typical hydrogeological surveys. Reconstruction of prediction uncertainty is consistent with the spatial distribution of available data and model accuracy estimates. It enables one to identify regions where availability of new information could assist in the constraining of uncertainty. The comprehensive dataset provided in this study, complemented by the model-based reconstruction of the subsurface system and the assessment of the associated uncertainty, is relevant from a water resources management and protection perspective. As such, it can be readily employed in the context of groundwater availability and quality studies aimed at identifying the main dynamics and patterns associated with the action of climate drivers in large-scale aquifer systems of the kind here analyzed, while fully embedding model and parametric uncertainties that are tied to the scale of investigation.

3D geological model to assess the fate of contaminant transport in groundwater: the case study of Maruzzella Landfill (Caserta, Italy)

In order to assess the potential risk of aquifer pollution in an alluvial plain area used as a landfill, a detailed geological and hydraulic model of the subsoil was realised. The chosen area is represented by the transfer site for solid urban waste called “Maruzzella”, in the lower plain of the Volturno River. The analysis of lithostratigraphic data allowed a 3D reconstruction of the subsoil, which was subsequently implemented thanks to a hydrostratigraphic characterization. Through the use of GIS, the calculation grids necessary for the characterization of the flows have been built, elaborated through the use of ModFlow with three different 3D models of the subsoil with increasing degrees of geological simplification. The dispersion models created with ModFlow made possible to establish the dispersive dynamics that predominate or coexist in relation to permeability and temporal progression considering different stress periods, respectively equal to 3650 days and 7300 days. The comparison of the geological scenarios highlighted the real dispersive processes, thus underlining the importance of a detailed knowledge of the stratigraphic architecture of the subsoil.

The Lower - Middle Miocene transition (Karpatian – Badenian) in the Krems Embayment (Central Paratethys, Lower Austria): a multistrati-graphic approach and the role of the Diendorf-Boskovice Fault System.

Abstract The Krems Embayment contains the westernmost fully marine depositional environments of the Karpatian and Bade-nian transgressions in the Central Paratethys. Four drill cores were investigated to analyse the bio- and lithostratigraphic, and tectonic relations. The investigated core sections cover the Karpatian Laa Formation (bio-zones M4, NN4) and the Badenian Gaindorf Formation (M5b-M6, NN4-NN5). Important biostratigraphic indicators identified are Praeorbulina glomerosa glomerosa, Praeorbulina glomerosa circularis and Orbulina suturalis for the Gaindorf Formation. The Laa Formation is indicated by the absence of Praeorbulina, Orbulina and Globigerina falconensis, low numbers of Globorotalia bykovae, and a prominent peak in Helicosphaera ampliaperta abundance at the end of the Karpatian. Cibicidoides lopjanicus and Cassigerinella spp. occur with high percentages in Badenian samples and show much longer stratigraphic ranges than known from literature data. The depositional gap at the Karpatian-Badenian boundary has a minimum duration of 0.41 My in the Krems Embayment. The combination of bio- and lithostratigraphic data allows the correlation across major faults. The Diendorf-Boskovice Fault System played an important role during basin formation and was identified as very active during the early to middle Badenian Stage. The results of this study show the complex interaction of sedimentation, tectonic activity and paleobiological developments in this peripheral part of a marginal sea.

Rift-related paleogeography of the European margin in the Eastern Alps (Central Tauern Window)

Continent-derived tectonic units in the Tauern Window of the Alps exhibit stratigraphic and structural traces of extension of continental margins eventually leading to the opening of the Alpine Tethys. In this study, we reassess lithostratigraphic data from the central part of the Tauern Window to reconstruct the post-Variscan evolution of this area, particularly the rift-related geometry of the European continental margin. The lithostratigraphy of the Alpine nappes reflects systematic variations of the structure of the European margin. The lowest tectonic units (Venediger nappe system, Eclogite Zone and Trögereck Nappe) are characterized by a thick succession of arkose-rich Bündnerschiefer-type sediments of probably Early Cretaceous age that we interpret as syn-rift sequence and which stratigraphically overlies thinned continental basement and thin pre-rift sediments. In contrast, the highest tectonic unit derived from Europe (Rote Wand Nappe) preserves a thick pre-rift sedimentary sequence overlying thinned continental basement, as well as a thick syn- to post-rift succession characterized by turbiditic Bündnerschiefer-type sediments of probable Cretaceous age. These observations point towards a highly segmented structure of the European rifted margin. We propose that this involved the formation of an outer margin high, partly preserved in the Rote Wand Nappe, that was separated from the main part of the European margin by a rift basin overlying strongly-thinned continental crust. The along-strike discontinuity of the Rote Wand Nappe is proposed to reflect the lateral variation in thickness of the outer margin high that resulted from margin-parallel segmentation of the European continental crust during highly oblique rifting antecedent to the opening of Alpine Tethys.

Biostratigraphic evidence for incremental tectonic development of early Cambrian deep-water environments in the Misty Creek embayment (Selwyn basin, Northwest Territories, Canada)

The early evolution of the Misty Creek embayment (MCE), a prominent, northwest-trending sub-basin of the economically important Selwyn basin, is poorly understood. The abrupt contact between Cambrian Stage 4 (traditional lower Cambrian) carbonate ramp strata of the Sekwi Formation and overlying Miaolingian (traditional middle Cambrian) deep-water, calciturbiditic strata of the Hess River Formation has been regarded as diachronous. This important transition, which marks the onset of long-lived, deep-water conditions in the MCE, remains unexplained. This study uses biostratigraphic data from a previously undescribed location in the MCE, existing biostratigraphic and lithostratigraphic data from the 1970s, and regional thickness patterns to characterise the sharp yet diachronous transition from lithofacies typical of the Sekwi Formation to those typical of the Hess River Formation. The dramatic change in depositional environments was diachronous yet non-gradational, precluding a eustatic cause. The change was geologically abrupt, probably through two extension-related subsidence events, with different geographic extents, which heralded the MCE’s long life as a deep-water basin. The onset of deep-water conditions in the MCE occurred semi-contemporaneously with other extension-related events that are recorded in the northern Canadian Cordillera, demonstrating that Cambrian Series 2 – Miaolingian was a time of widespread extension and subsidence along the western margin of Laurentia.

Subducted fragments of the Liguro-Piemont ocean, Western Alps: Spatial correlations and offscraping mechanisms during subduction

Fragments of subducted slow-spreading oceanic lithosphere are exposed continuously in the Liguro-Piemont domain of the Western Alps. By combining new and literature petrological data, interpolated maps of maximum temperatures, maximum Si contents of phengite as a proxy for peak pressure and thermodynamic modelling, we provide a detailed framework of the peak metamorphic conditions experienced by the distinct subduction slices. High-resolution mapping confirms the marked eastward increase in metamorphic grade throughout the domain, as well as within some slices. The compilation of lithostratigraphic, structural and radiochronological data and the estimation of sediment/mafic-ultramafic ratio for each slice allow refining the origin of these tectonometamorphic units within the former oceanic domain. The refined structural sketchmap allows to restore the geometries of the Alpine subduction at peak burial conditions. Results point to a trimodal distribution of the units with an increase in metamorphic conditions from the Upper (LPU; 320-400°C- 1.2-1.9 GPa) to the Middle (LPM; 415-475°C- 1.7-2.2 GPa) and to the Lower units (LPL; 500-580°C- 2.2-2.8 GPa). The blueschist-facies LPU and LPM units are dominated by sediments (>90%), whereas the eclogitic LPL units are far richer in mafic-ultramafic rocks (>40%). These characteristics, along with lithostratigraphic differences, reflect major differences in their initial paleogeography and/or in the mechanisms responsible for material offscraping from the downgoing slab. The peak burial depths of the LPU, LPM and LPL units are similar to those inferred for slicing and underplating in both modern and fossil subduction zones. Petrological and lithostratigraphic data suggest that the offscraping of the LPU and LPM units was mostly controlled by lithological contrasts, within pelagic shales or along contacts within the uppermost serpentinized mantle. In contrast, major dehydration reactions (such as lawsonite breakdown in sediments) likely controlled the offscraping of the LPL units at eclogite-facies conditions, possibly through high fluid pressure conditions and rocks embrittlement.

Transition between Variscan and Alpine cycles in the Pyrenean-Cantabrian Mountains (N Spain): Geodynamic evolution of near-equator European Permian basins

In the northern Iberian Peninsula, the Pyrenean-Cantabrian orogenic belt extends E-W for ca. 1000 km between the Atlantic Ocean and Mediterranean Sea. This orogen developed from the collision between Iberia and Eurasia, mainly in Cenozoic times. Lower-middle Permian sediments crop out in small, elongated basins traditionally considered independent from each other due to misinterpretations on incomplete lithostratigraphic data and scarce radiometric ages. Here, we integrate detailed stratigraphic, sedimentary, tectonic, paleosol and magmatic data from well-dated lithostratigraphic units. Our data reveal a similar geodynamic evolution across the Pyrenean-Cantabrian Ranges at the end of the Variscan cycle. Lower-middle Permian basins started their development under an extensional regime related to the end of the Variscan Belt collapse, which stars in late Carboniferous times in the Variscan hinterland. This orogenic collapse transitioned to Pangea breakup at the middle Permian times in the study region. Sedimentation occurred as three main tectono-sedimentary extensional phases. A first phase (Asselian-Sakmarian), which may have even started at the end of the Carboniferous (Gzhelian) in some sections, is mainly represented by alluvial sedimentation associated with calc-alkaline magmatism. A second stage (late Artinskian–early Kungurian), represented by alluvial, lacustrine and palustrine sediments with intercalations of calc-alkaline volcanic beds, shows a clear upward aridification trend probably related to the late Paleozoic icehouse-greenhouse transition. The third and final stage (Wordian-Capitanian) comprised of alluvial deposits with intercalations of alkaline and mafic beds, rarely deposited in the Cantabrian Mountains, and underwent significant pre- and Early Mesozoic erosion in some segments of the Pyrenees. This third stage can be related to a transition towards the Pangea Supercontinent breakup, not generalized until the Early/Middle Triassic at this latitude because the extensional process stopped about 10 Myr (Pyrenees) to 30 Myr (Cantabrian Mountains). When compared to other well-dated basins near the paleoequator, the tectono-sedimentary and climate evolution of lower-middle Permian basins in Western and Central Europe shows common features. Specifically, we identify coeval periods with magmatic activity, extensional tectonics, high subsidence rates and thick sedimentary record, as well as prolonged periods without sedimentation. This comparison also identifies some evolutionary differences between Permian basins that could be related to distinct locations in the hinterland or foreland of the Variscan orogen. Our data provide a better understanding of the major crustal re-equilibration and reorganization that took place near the equator in Western-Central Europe during the post-Variscan period. • The beginning of the Iberian Variscan orogenic collapse is late Carboniferous in the hinterland and early Permian towards the foreland. • Variscan orogenic collapse is associated with calc-alkaline magmatism that shifts to alkaline magmatism in middle Permian times. • The beginning of the Alpine cycle of sedimentation in the whole Pyrenean ranges occurred as three main Permian tectono-sedimentary extensional phases. • The Permian tectono-sedimentary evolution of the Pyrenean ranges shows common features to the ones of Central and W Europe basins.

Lake Imandra depression in the Late Glacial and early Holocene (Kola Peninsula, north-western Russia)

The paper summarizes the evidence of litho-, biostratigraphy and 14C dating of sedimentary sequences studied in natural outcrops and bottom deposits in small lakes, as well as data on coastal morphology in the depressions of Ekostrovskaya and Babinskaya Imandra, the southern sub-basins of Lake Imandra. Lithological, 14C and diatom data suggest that the brackish-water reservoir followed by the fresh-water one existed in the Ekostrovskaya Imandra depression during the Younger Dryas chronozone prior to 11,400cal. yr BP. The Fennoscandian Ice Sheet margin is assumed to have been located in the Lake Imandra basin, covering western Babinskaya Imandra earlier than c. 10,250 cal. yr BP. The early Holocene c. 11,400–8,500 cal. yr BP was marked by a significant westward retreat of the ice margin in the western Lake Imandra depression and adjacent areas, and an extensive fresh-water pra-Imandra Lake basin was formed there. At the end of the Preboreal, earlier than c. 9,210–8,500 cal. yr BP, the pra-Imandra Lake coastline was at least 16–18 m higher than the modern one, as can be assumed according to coastal morphology and lithostratigraphical data. The coastline of that reservoir changed, water square slightly reduced, and isolated small lakes emerged on coasts during the early Holocene.

The integration of public domain lithostratigraphic data into a series of cross-border North Sea well-penetration maps

Abstract As geological information about the North Sea is increasingly made available to the public, there is great potential to build cross-border datasets to enable people to more rapidly filter relevant geological data and also to better understand and further study the subsurface. This paper discusses the construction of such a geological database and presents the associated map set. Public domain lithostratigraphic data from petroleum exploration and appraisal wells drilled in the Norwegian, Danish, German, Dutch and UK North Sea sectors were used to create a series of 13 well-penetration maps, ranging from Basement to Eocene age. In order to produce the maps, lithostratigraphic well tops had to be translated into a chronostratigraphic scheme, followed by building a database and subsequent mapping in a GIS. Three well categories were used for each of the maps: wells that (1) fully penetrate a chronostratigraphic interval, (2) prove it is absent or (3) reach total depth in the interval under consideration. The resulting maps, which will all be discussed and presented in this paper, form a starting point for multiple types of (petroleum) geological screening studies. The North Sea database is freely available in QGIS format and can be easily imported into any geospatial software platform.

Underthrusting and exhumation of continent-derived units within orogenic wedge: an example from the Northern Apennines (Italy)

ABSTRACT The Punta Bianca Unit (NW Italy) is a continent-derived metamorphic unit that experienced underthrusting and later exhumation in the hinterland sector of the Northern Apennines fold-and-thrust belt. We present a novel 1:5000 scale geological map that aims to illustrate the polyphase tectonic evolution of the Punta Bianca Unit and its relationships with non-metamorphic units. The geologic data presented in the map are coupled with the structural analysis of the main tectonic elements, lithostratigraphic, finite strain and microstructural data that allow to highlight the tectonic history of the study area. In particular, we recognized that the Punta Bianca Unit underwent an early phase of underplating (D1), followed by syn-orogenic exhumation to shallow crustal levels and coupling with the overlying Tuscan Nappe (D2), and nappe stacking/refolding (D3). Low-angle semibrittle (D4) and high-angle brittle (D5) faulting affected both the Punta Bianca Unit and the Tuscan Nappe during the latest stages of deformation.

DONNÉES NOUVELLES SUR LA STRATIGRAPHIE ET LA MICROPALÉONTOLOGIE DES SÉRIES CARBONATÉES DE TALUS ET DE BASSIN DU CRÉTACÉ INFÉRIEUR DU GARGANO (ITALIE MÉRIDIONALE)

The stratigraphic revislon of the Iower Cretaceous successions from the Gargano peninsula provides new lithostratigraphic data ; two formations could be distinguished: the Vico del Gargano Limestones and the Mattinata Limestones corresponding to basin and talus deposits respectively. New micropaleontological data are given concerning the definition and the boundaries of Berriasian p.p. Valanginian p.p. The Aptian is well characterized and the substages Bedoulian, Gargasian and ClansayeSian are clearly separated by mean of significant foraminiferal assemblages, especially in the talus sedimentary successions. Hauterivian—Barremian p.p. and Albian intervals are poorly defined. From a sedimentological point of view basin and talus successions are clearly differentiated. These data will be used for further paleogeographic reconstructions.

Tectono‐sedimentary evolution of transverse extensional faults in a foreland basin: Response to changes in tectonic plate processes

AbstractLate Paleocene to Middle Eocene strata in the easternmost part of the Southern Pyrenees, up to 4 km thick, provide information on tectono‐sedimentary evolution of faults transversal to the Pyrenean chain. To know how changes in tectonic plate processes control the structural evolution of transverse faults and the synchronous thickness and lithological distribution of sedimentary strata in a foreland basin, field observations, interpretation of 2D seismic lines tied to lithostratigraphic data of exploration wells and gravity modelling constrains were carried out. This resulted in the following two tectono‐sedimentary phases in a foreland basin: first phase, dominated by transverse extensional faulting, synchronous with deposition of marine carbonates (ca. 57 to 51 Ma); and second phase, characterized by transverse contractional faulting, coeval to accumulation of marine and transitional siliciclastics (51 to 44 Ma). During the first phase, Iberia and Adria were moving to the east and west respectively. Therefore, lithospheric flexure in the easternmost part of the Iberian plate was developed due to that Sardinia was over‐thrusting Iberia. Consequently, activation of E‐dipping normal faults was generated giving rise to thick‐deep and thin‐shallow carbonate platform deposits across the hanging walls and footwalls of the transverse structures. During the second phase, a shearing interaction between Iberia and Sardinia prevailed re‐activating the transverse faults as contractional structures generating thin‐shelf and thick‐submarine fan deposits across the hanging walls and footwalls of the transverse structures. In the transition between the first and second phases, evaporitic conditions dominated in the basin suggesting a tectonic control on basin marine restriction. The results of our study demonstrate how thickness and lithology distribution, controlled by transverse faulting in a compressional regimen, are influenced by phases related to processes affecting motions and interactions between tectonic plates and continental blocks.

Style and timing of tectonic deformation across the Bou Arada-El Fahs troughs system, Northeast Tunisia: integration in the structural evolution of Atlas fold and thrust belt

The Bou Arada-El Fahs troughs system is a particularly E-W trending collapsed structure with the manifestation of normal-to-strike-slip faults. A combined multi-source and multi-scalar structural and geophysical investigation provides important insights on the geometry and the kinematics evolution of trough systems in the Atlas of Tunisia. New data, as well as a reappraisal of available data show that the studied troughs system is established during three main successive events: the Oligocene-Miocene, the Tortonian, and the Plio-Quaternary events. The goal of this paper is to present the structural evolution of the study area, on a pre-structured substratum. The structural evolution progressed from an extensional event, manifested by the formation of grabens, passing by an episode of reactivation of faults related troughs in strike-slip motion during the Atlas compression accompanied by an en-echelon folding in foot wall and hanging wall. These results acquired and presented in the following order: We will initially present the geological context by integrating and correlating the lithostratigraphic data. We continue by examining the geometry and kinematics of structure-related troughs via the detailed geological mapping, the interpretation of available 2D seismic data, and the interpretation of processed fault slip data. This integrated geological and geophysical study allows a better understanding of the BETS, and makes it possible to propose a new geometrical and kinetic model of the establishment of trough structure in the Tunisian Atlas.

Seismo-stratigraphic model of "La Bandita" area in the Palermo Plain (Sicily, Italy) through HVSR inversion constrained by stratigraphic data

Ambient noise Horizontal-to-Vertical Spectral Ratio (HVSR) technique is commonly used approach to obtain 1D models of the shear-wave velocity in the shallow surface of an investigated area. However, obtained models can have a wide margin of uncertainty if inversions have not been appropriately constrained by detailed stratigraphic information. An application of HVSR inversion constrained by lithostratigraphic data is presented in order to verify the effectiveness of this technique for purposes of geological and geophysical reconstruction of a sedimentary basin in a densely urbanized area. This is often the case of seismic microzonation studies, in which almost all the information derives from near surface stratigraphic drillings, since other geophysical methods are logistically difficult to carry out. In our work, we used stratigraphic constraints derived from 93 superficial bore-holes whose depth rarely exceeds 30 m. In an area called La Bandita, located in Palermo Plain (Sicily, Italy), a geophysical survey was performed by means of 55 microtremor recordings. Part of these was distributed randomly, while others very close to the available stratigraphic perforations. The reconstruction of the stratigraphy in the studied area has been obtained by a review of the main stratigraphic sequences and by a consequent stratigraphic three-dimensional modelling. HVSR curves have been interpreted taking care the thicknesses of the near surface successions derived by the stratigraphic 3-D model. The results, in terms of vertical profiles of the shear-wave velocity, have been interpolated to obtain a 3D seismic model. This has been used to extract basic information to identify and reconstruct the seismic bedrock and the main geological boundaries that were not directly identifiable by means of only stratigraphic logs. It results that the bedrock is affected by a fault system that generated adjacent depressions where Quaternary successions deposited.

High-resolution chronology for deglaciation of the Patagonian Ice Sheet at Lago Buenos Aires (46.5°S) revealed through varve chronology and Bayesian age modelling

Glaciolacustrine varves offer the potential to construct continuous, annually-resolved chronologies for ice-sheet deglaciation, and improved understanding of glacier retreat dynamics. This paper investigates laminated glaciolacustrine sediments deposited around the waning margins of the Patagonian Ice Sheet, following the local Last Glacial Maximum (LGM). Detailed macro- and microfacies analyses confirm an annual (varve) structure within these sediments. The correlation of annual layers (varves) across five sites in eastern Lago Buenos Aires yields a 994 ± 36 varve-year (vyr) chronology and thickness record. The floating chronology has been anchored to the calendar-year timescale through identification of the Ho tephra (17,378 ± 118 cal a BP) in the varve sequences. Using a Bayesian age model to integrate the new varve chronology with published moraine ages, the onset of deglaciation at 46.5°S is dated to 18,086 ± 214 cal a BP. New age estimates for deglacial events are combined with high-resolution analysis of varve thickness trends, and new lithostratigraphic data on ice-margin position(s), to reconstruct ice-margin retreat rates for the earliest ca. 1000 years of ice-sheet demise. Glacier retreat rates were moderate (5.3–10.3 m yr−1) until 17,322 ± 115 cal a BP, but subsequently accelerated (15.4–18.0 m yr−1). Sustained influxes of ice-rafted debris (IRD) after 17,145 ± 122 cal a BP suggest retreat rates were enhanced by calving after ice contracted into deeper lake waters. Ice persisted in eastern Lago Buenos Aires until at least 16,934 ± 116 cal a BP, after which the glacier started to retreat towards the Patagonian mountains.

Holocene tephrochronology of the lower Río Cisnes valley, southern Chile

Sediment cores from lakes and bogs in the Río Cisnes valley contain tephra from explosive eruptions of volcanoes in the southern part of the Andean Southern Volcanic Zone (SSVZ). These tephra, which thicken and coarsen to the west, are attributed to eruptions from Melimoyu, Mentolat, Hudson, and potentially either Macá, Cay or one of the many minor eruptive centers (MEC) located both along the Liquiñe-Ofqui Fault Zone (LOFZ) and surrounding the major volcanoes. Correlation of the tephra between two new cores in the lower Río Cisnes valley, and amongst other cores previously described from the region, and source volcano identification for the tephra, has been done using lithostratigraphic data (tephra layer thickness and grain size), petrography (tephra glass color, vesicle morphology, and type and abundance of phenocryst phases), and by comparison of bulk tephra trace-element characteristics with previously published whole-rock and bulk tephra chemical analysis. Four tephras in these cores are attributed to eruptions of Mentolat, four to eruptions from Melimoyu, one possibly to Hudson, and six cannot be assigned to a specific source volcano. Some of these tephra correspond to pyroclastic tephra fall deposits previously observed in outcrop, including the MEL2 eruption of Melimoyu and the MEN1 eruption of Mentolat. However, others have not been previously observed and represent the products of newly identified small to medium sized eruptions from volcanoes of the SSVZ. These results provide new information concerning the frequency and magnitude of explosive eruption of SSVZ volcanoes and contribute to the evaluation of volcanic hazards in the region.

State‐of‐the‐art remote characterization of shallow marine sediments: the road to a fully integrated solution

ABSTRACTCurrent methods for characterizing near‐surface marine sediments rely on extensive coring/pene‐trometer testing and correlation to seismic facies. Little quantitative information is regularly derived from geophysical data beyond qualitative inferences of sediment characteristics based on seismic facies architecture. Even these fundamental seismostratigraphic interpretations can be difficult to correlate with lithostratigraphic data due to inaccuracies in the time‐to‐depth conversion of geophysical data and potential loss and/or compression of high‐porosity and under‐consolidated sea‐floor material during direct sampling. To complicate matters further, when quantitative information is derived from marine geophysical data, it often describes the sediments using terminology (e.g., acoustic impedance and seismic quality factor) that is impenetrable to geologists and engineers. In contrast, for hydrocarbon prospecting, reservoir characterization using quantitative inversion of geophysical data has developed enormously over the past 20 years or more. Impedance and amplitude‐versus‐angle inversion techniques are now commonplace, whereas computationally expensive waveform inversions are gaining traction, and there is a well‐developed interface between these geophysical and reservoir engineering fields via rock physics.In this paper, we collate and review the different published inversion methods for high‐resolution geophysical data. Using several case study examples spanning a broad range of depositional environments, we assess the current state of the art in remote characterization of shallow sediments from a multidisciplinary viewpoint, encompassing geophysical, geological, and geotechnical angles. By identifying the key parameters used to characterize the subsurface, a framework is developed whereby geological, geotechnical, and geophysical characterizations of the subsurface can be related in a less subjective manner. As part of this, we examine the sensitivity of commonly derived acoustic properties (e.g., acoustic impedance and seismic quality factor) to more fundamentally important soil properties (e.g., lithology, pore pressure, gas saturation, and undrained shear strength), thereby facilitating better integration between geological, geotechnical, and geophysical data for improved mapping of sediment properties. Ultimately, we present a number of ideas for future research activities in this field.

Tectonosedimentary framework of Upper Cretaceous –Neogene series in the Gulf of Tunis inferred from subsurface data: implications for petroleum exploration

Abstract The objective and the main contribution of this issue are dedicated to using subsurface data to delineate a basin beneath the Gulf of Tunis and its neighbouring areas, and to investigate the potential of this area in terms of hydrocarbon resources. Available well data provided information about the subsurface geology beneath the Gulf of Tunis. 2D seismic data allowed delineation of the basin shape, strata geometries, and some potential promising subsurface structures in terms of hydrocarbon accumulation. Together with lithostratigraphic data obtained from drilled wells, seismic data permitted the construction of isochron and isobath maps of Upper Cretaceous-Neogene strata. Structural and lithostratigraphic interpretations indicate that the area is tectonically complex, and they highlight the tectonic control of strata deposition during the Cretaceous and Neogene. Tectonic activity related to the geodynamic evolution of the northern African margin appears to have been responsible for several thickness and facies variations, and to have played a significant role in the establishment and evolution of petroleum systems in northeastern Tunisia. As for petroleum systems in the basin, the Cretaceous series of the Bahloul, Mouelha and Fahdene formations are acknowledged to be the main source rocks. In addition, potential reservoirs (Fractured Abiod and Bou Dabbous carbonated formations) sealed by shaly and marly formations (Haria and Souar formations respectively) show favourable geometries of trap structures (anticlines, tilted blocks, unconformities, etc.) which make this area adequate for hydrocarbon accumulations.