Stratigraphic Research Articles

LARGE WOODY DEBRIS ACCUMULATIONS IN THE LATE PENNSYLVANIAN TROPICS—EVOLUTIONARY SIGNAL OR TECTONO-CLIMATIC ARCHIVE?

ABSTRACTBy colonizing drylands, plants fundamentally changed continental deposition and, thus, intensified the interaction between life and sediments. Fossil large woody debris in epiclastic strata is a key archive of this environmental turnover, although its interpretation remains challenging due to taphonomic biases. We review voluminous fluvial red-bed successions with sizeable silicified trunks that characterize Middle Pennsylvanian–lower Permian strata of east-central Europe. The stratigraphic occurrence, petrography, architecture of the deposits, and the preservation and nature of the fossil wood are discussed in the context of the tectono-climatic and vegetational evolution of the central-Pangean low latitudes. The log-bearing successions are assigned to five distinct, regionally traceable stratigraphic levels between the middle Moscovian and early Asselian. Up to 20 m long, mostly decorticated trunk fragments occur isolated in more or less feldspathic channel deposits, the architectures and dimensions of which point to large-scale river systems with highly variable discharge. Wood anatomy and floodplain adpression-fossils show that the trunks were derived from cordaitaleans, conifers, and arborescent sphenopsids in more diverse, gymnosperm-dominated dryland floras. The fossil record is biased towards successions formed in large-catchment river systems and, thus, does not accurately document the genuine nature of plant-distribution patterns. Rather, the strata show that large woody debris preservation depended on fluvial style and hydrological regime, hence turning the woody deposits into climate archives. The strata elucidate the climate development in equatorial Pangea, paralleling the acme of the Late Paleozoic Ice Age.

Marine mammals fossil remains and synthesis of the sedimentary and paleontological record of the Furninha Cave Pleistocene (Peniche, Portugal)

The Gruta da Furninha is a cave-site in Lower Jurassic limestones, of mainly marine genesis located at ~850 m SE of the Carvoeiro Cape, on the southern coast of the Peniche peninsula (central western mainland Portugal). The entrance gallery, situated in the middle of the cliff, is at ~15 m of altitude. This cave contained a rich and diverse fossiliferous set of Late Pleistocene vertebrates, distributed in several stratigraphic levels, currently housed at the Geological Museum of LNEG (Lisbon). The cave had a record of primitive human occupations documented by 106 Middle to Late Paleolithic artefacts, found in the lower lithostratigraphic unit (Pleistocene). It had also another human occupation in an upper unit (Neolithic, Holocene), where were found human skeleton elements and artefacts. This study focuses on two teeth previously identified as crocodile, housed in collections of the Geological Museum in the assemblages of the Furninha Cave and on a set of five bones, housed at Centro Português de Geo-História e Pré-História (CPGP) collected in a marine terrace in the Furninha cliff. The occurrence of crocodile remains in the Upper Pleistocene of Portugal is not consistent with the fossil record of this period or with the environmental conditions associated with the fully marine paleoenvironments around Furninha Cave. A more detailed analysis of these teeth and their stratigraphic location, now supports that they are cetacean teeth with ~80 ka, which is consistent with the fossil association, depositional environments and climate conditions of the Late Pleistocene in mainland Portugal. To add to these two teeth, in 2017 in sedimentary field work in the marine terraces on the cliffs of the Gruta da Furninha, at the level of 4 to 7 m, found five bones remains, which could be carpal bones of marine mammals.

New remains of Eleutherocercus (Xenarthra, Cingulata, Glyptodontidae) from the Pampean and Northwestern regions of Argentina: morphology and phylogeny of late Neogene Doedicurinae

ABSTRACT The subfamily Doedicurinae is a monophyletic group of glyptodonts with their own anatomical features and is mostly known on the basis of the Pleistocene genus Doedicurus, one of the largest recorded taxa. The most distinctive character of the subfamily, unique within Cingulata, include the absence of ornamentation with large foramina, on the exposed surface of the carapace osteoderms. In terminal forms of the late Pleistocene, osteoderms have large foramina which tend to cross the entire thickness. The knowledge of the late Neogene diversity of the clade, as well as its evolutionary and geographical history, has increased in recent years, with important records in Argentina, where two late Miocene-Pliocene species are recognised: Eleutherocercus solidus from Catamarca and Tucumán provinces, and Eleutherocercus antiquus from Buenos Aires province. The most complete skull of E. antiquus from the early Pliocene Monte Hermoso Formation (ca. 5–4.2 Ma) is reported here. The specimen studied shows a conspicuous pathology on the parietal bones, first reported for fossil cingulates. In addition, the carapace of E. solidus is first described, on the basis of a partially complete specimen from the late Miocene-Pliocene (unknown stratigraphic level) from Tucumán province. Previous phylogenetic hypotheses of the relationships within the Doedicurinae, as well as their relationship with the remaining clades of Glyptodontidae, is tested in this study, adding new synapomorphies to the subfamily. The comparative study suggests that a third species previously proposed (E. paranaensis) from the ‘Mesopotamiense’ (late Miocene, Northeastern region of Argentina), must be considered as Eleutherocercus sp. Since their oldest record in the late Miocene, the latitudinal distribution of the Doedicurinae seems to have expanded rapidly reaching middle latitudes, particularly during the Pliocene, but during the Pleistocene (particularly the final lapse of this period), they began to retract latitudinally.

Planktonic foraminifera and stable isotopes of the upper Cenomanian–middle Turonian in central Tunisia: Implications for bioevents synchronicity and paleoenvironmental turnover

The upper Cenomanian–middle Turonian planktonic foraminifers and stable isotopes analyses of the Oued Ettalla section (central Tunisia) were incorporated to establish the temporal framework and unveil the paleoenvironmental signal of the Oceanic Anoxic Event 2 (OAE2). Some bioevents were reported at a lower stratigraphic level compared to their worldwide records; such as the synchronous extinction of Rotalipora cushmani and Globigerinelloides bentonensis at the onset of the δ13C peak A, besides the Heterohelix shift between δ13C peaks A and B. Thus, an intensified surface-water eutrophism complemented by a local acceleration in the thermal stratification collapse of the upper water column had occurred by the OAE2 onset. The results assign the pre-OAE2 interval to stable, reasonably ventilated meso-oligotrophic surface-water conditions. The paleoenvironment had shifted toward stressed, highly eutrophic, less stratified circumstances by the OAE2 onset, as evidenced by eliminating the taxa that occupied deep and intermediate habitats. The planktonic foraminifers alongside oxygen isotopes data denote an extreme warm condition during the OAE2 with a brief cooling episode, slightly after the δ13C peak A, equivalent to the so-called Plenus Cold Event. The presence of whiteinellids and prevalence of dwarfism excluded each other among the planktonic foraminifers assemblage within the OAE2 interval, indicating minor shifts in the eutrophication. The environmental wakeup from the OAE2 was stepwise and initiated well within the topmost part of the Whiteinella archaeocretacea Zone, as reflected from the permanent existence of the whiteinellids and the associated reoccurrence of the keeled taxa.

Combined ERT and GPR Data for Subsurface Characterization of Weathered Hilly Slope: A Case Study in Zhejiang Province, Southeast China

Rain-triggered landslides frequently threaten public safety, infrastructure, and the economy during typhoon seasons in Zhejiang Province. Landslides are complex structural systems, and the subsurface features play a significant role in their stability. Their early identification and the evaluation of potential danger in terms of the rupture surface and unstable body are essential for geohazard prevention and protection. However, the information about the subsurface acquired by conventional exploration approaches is generally limited to sparse data. This paper describes a joint application of ground-penetrating radar (GPR) with a 100 MHz antenna and the electrical resistivity tomography (ERT) method with the Wenner configuration to identify the stratum structure and delineate the potentially unstable body of a clay-rich slope, the results of which were further verified using borehole data and field observation. The acquired results from the GPR and ERT surveys, consistent with each other, indicate two stratigraphic layers comprising silty clay and silty mudstone. Moreover, the potential rupture zone very likely exists in the highly weathered mudstone in the depth range of 3–7 m, and the average depth is 5 m. In addition, the thickness of the unstable mass is greater on the east and crest parts of the slope. Conclusively, the optimum combination of ERT and GPR is reliable for conducting rapid and effective delineation of subsurface characteristics of clayey slopes for risk assessment and mitigation during the typhoon season.

Evolution of an aggradational wave-dominated delta: Sediment balance and animal-substrate dynamics (Upper Cretaceous La Anita Formation, Southern Patagonia)

Aggradational deltaic successions are uncommon in the stratigraphic record since deltas are progradational by nature. However, deltaic coastlines fed by multiple small distributaries rather than by a well-defined trunk fluvial distributary system might result in aggradational successions if the sediment is effectively redistributed from river mouths by active basinal processes (e.g., tides, fairweather waves, and/or storm waves). The wave-dominated deltaic succession in the lower part of the La Anita Formation accumulated during the foreland stage of the Austral-Magallanes Basin (Argentina). Through a sedimentological and ichnological study of the interval, we evaluate and discuss the potential controls on the evolution of aggradational wave-dominated deltaic successions.The studied stratigraphic interval is up to 150 m thick and includes facies deposited in wave-dominated prodelta, wave-dominated distal delta-front, wave-influenced mouth bar, terminal channel, and distributary channel settings. These facies associations stack vertically, forming clear thick aggradational sets. Fairweather wave processes largely dominate the delta-front and prodelta deposits, although discrete beds point to the periodic importance of linked storm-wave and river-flood processes. Owing to the alternation of beds generated during fairweather shoaling waves with those of coupled storm-wave and river-flood cycles, it is proposed that the overall aggradational stacking pattern of the delta is the response to the sediment balance. Clastic material supplied by the distributary channels of the delta was easily transported alongshore during fairweather conditions by longshore currents and basinward via storm-generated waves, and/or hyperpycnal currents and hypopycnal plumes generated by river floods.The alternation of these depositional processes strongly affected the benthic faunal communities, which is well expressed by the resulting ichnological suites. Storm-wave and river-flood events led to the widespread defaunation of tracemaking organisms, leading to generation of unburrowed beds. Between these events, short-lived colonization windows appeared locally, allowing sparse, facies-crossing dwelling and detritus-feeding burrows to be constructed by the recovering benthic communities. By contrast, during prolonged periods of fairweather shoaling, river-induced physico-chemical stresses were greatly reduced, and the resulting beds display elevated bioturbation intensities with greater numbers of burrows that record a wide range of behaviors.

Climatic reconstruction at the early Miocene La Rinconada mine (Ribesalbes-Alcora Basin, eastern Spain) based on Coexistence Approach, CLAMP and LMA analysis

The early Miocene La Rinconada mine from eastern Iberian Peninsula contains a rich megafloral assemblage with abundant leaf fossils from a single stratigraphic level of the sedimentary succession. This has provided a good opportunity to undertake detailed comparative quantitative palaeoclimate reconstruction using different approaches, namely the Coexistence Approach (CA), Climate Leaf Analysis Multivariate Programme (CLAMP) and Leaf Margin Analysis (LMA). Considering the results of all techniques used, the palaeoclimate estimates are the following: mean annual temperature (MAT) CA = 10–16.5 °C/CLAMP = 11.48 °C, warmest month mean temperature (WMMT) CA = 25–26.4 °C/CLAMP = 23.31 °C, coldest month mean temperature (CMMT) CA = 4.3–4.8 °C/CLAMP = 0.84 °C, mean annual precipitation (MAP) CA = 1217–1297 mm, mean precipitation of the wettest month (MPWet) CA = 116–164 mm and mean precipitation of the warmest month (MPWarm) CA = 118–131 mm. Temperature and precipitation values obtained through CLAMP, LMA and CA indicate the occurrence of a wet and warm climate the whole year around with marked seasonality for rainfall and temperature but without a summer-dry regime. The climatic values obtained in the La Rinconada mine are in well accordance with other Burdigalian and late Burdigalian–early Langhian sites from the Iberian Peninsula (e.g. S 141 Borehole) and Central-Southern Europe (e.g. Holedeč, Čermníky, Přívlaky, Bílina Delta, Manisa-Soma, Spanokhorion and the Evia Island), suggesting the absence of a clear latitudinal gradient in temperature and precipitation for this period in Europe. This climate is consistent with the plant communities described in the area from taxonomic studies and IPR analysis.

Evidence of Seismic-Related Liquefaction Processes within the Volcanic Record of the Campi Flegrei Caldera (Italy)

We report the occurrence of several sand liquefaction structures, such as sand dikes, in the stratigraphic record of the Campi Flegrei volcano, located both inside and outside the caldera. Five sites were analyzed within the caldera and two outside. The grain size analysis of the sand fillings indicates that these deposits are very fine-to-coarse sands generally poorly sorted. All of the granulometry curves fall within the field of the liquefiable, loose sediments. Frequently, dikes are characterized by two fillings: a rim showing poorly sorted finer sands and a core with extremely poorly sorted coarser sediments. We suggest that seismic-related liquefaction processes triggered the injection of these sand dikes during unrest episodes in the last 15 kyr. In particular, the sand dikes located outside the caldera, characterized by larger thicknesses and lengths, mark an important extensional episode, probably associated with the caldera formation during the Neapolitan Yellow Tuff eruption at 15 ka. Furthermore, liquefaction structures within the caldera are related to the seismic activity, probably occurring during the Agnano–Monte Spina caldera formation and the volcano-tectonic ground deformation, predating Epoch 3b (4.3 ka) and the Monte Nuovo (1538 CE) eruptions. This study highlights that these seismic-related liquefaction structures are common within the volcanic record of the Campi Flegrei, suggesting that the sand source can be both the widespread marine succession underlying the Epoch 3 deposits in the caldera central sector and the primary ash layers extensively present in the volcanic record.

Characteristics of a Benchmark Loess–Paleosol Profile in Northeast China

The Chaoyang profile represents a rare multi-period, continuous and complete sequence of aeolian paleo-deposits with a stable sedimentary origin and multi-stage paleoclimatic cycles. Benchmark profiles including soil types at different pedogenic stages can be used for the recognition and classification of paleosols and paleoclimate reconstruction. The loess–paleosol sequence benchmark profile (LBP) is also helpful in comparing the results of paleoenvironment reconstruction from different ecological regions. In this study, a loess–paleosol profile derived from thick loess in Chaoyang city of Liaoning province, Northeast China, was investigated as a well-preserved LBP that included various paleosol types. To determine the nature and origin of the Chaoyang profile, the geographic, stratigraphic and morphological characteristics were described in the field. Bulk samples from 42 horizons were collected for chemical and physical analysis, and sub-sampling of 946 samples at 2 cm intervals from the surface to the bottom were taken to measure grain size distributions and magnetic susceptibility. Results showed that the 19.85 m thick loess–paleosol profile had been continuously deposited since 423 ka BP. The upper part (0–195 cm), or UPP, was predominantly of aeolian loess deposition origin but was mixed with water-reworked materials from a nearby secondary loess source. The middle part (195–228 cm), or MIP, was also indirectly affected by the water-reworking process through the leaching of materials from the overlying UPP. The lower part (228–1985 cm), or LOP, was characterized by four reddish stratigraphic layers interbedded with five yellowish ones, indicating several types of paleosols developed under different ecological environments. The multi-stage paleoclimatic cycles as evidenced by morphological and physical characteristics as well as age dating and magnetic susceptibility correlated well with the Lingtai section and LR04 benthic δ18O. Because of these attributes, the Chaoyang profile can be deemed as a benchmark loess–paleosol profile for the recognition and classification of paleosols and paleoclimate reconstruction in Northeast China. The differences in morphological and physical properties between paleosols and loess suggest different soil fertility and agronomic properties and need further studies to assess their functionality with climate fluctuation.

Investigations of polygonal patterned ground in continuous Antarctic permafrost by means of ground penetrating radar and electrical resistivity tomography: Some unexpected correlations

AbstractThe results of a combined geophysical and geomorphological investigation of thermal‐contraction‐crack polygons near Gondwana station (Germany) in northern Victoria Land (Antarctica) are reported. An area of about 20,000 m2 characterized by random orthogonal polygons was investigated using integrated ground penetrating radar, electrical resistivity tomography, geomorphological surveys, and two trench excavations. The polygons are well developed only at elevations higher than 6–7 m above current sea level on Holocene‐age raised beaches. It is concluded that the polygons are composite in nature because the shallow linear depressions that outline the polygons are underlain by fissures that can contain both sandy gravel and foliated ice (i.e., ice wedges) even in the same polygon network and at distances of just a few meters. Unexpectedly, most of the polygons follow the border of the raised beaches and develop in correspondence with stratigraphic layers dipping toward the sea, imaged by ground penetrating radar (GPR) profiles and interpreted as prograding layers toward the present‐day shoreline.

Exploring the Shallow Subsurface of Mars with the Ma_MISS Spectrometer on the ExoMars Rover Rosalind Franklin

An essential part of the Exomars 2022 payload is the Mars Multispectral Imager for Subsurface Studies (Ma_MISS) experiment hosted by the drill system. Ma_MISS is a visible and near-infrared (0.4–2.3 μm) miniaturized spectrometer with an optical head inside the drill tip capable of observing the drill borehole with a spatial resolution of 120 μm. Here we report on how the Ma_MISS hyperspectral information provides in situ investigation of the subsurface at very fine resolution, prior to the collection of the samples that will be manipulated and crushed for further analysis by the analytical laboratory on the rover. Ma_MISS is the instrument that will closely investigate the subsurface mineralogical characteristics in its original geologic context at depths never reached before in Mars exploration. Ma_MISS recognizes all the major spectral features of the clays, basaltic, and minor phases expected at the ExoMars landing site, Oxia Planum. The high spatial resolution on the borehole wall is such that single grains of about 100 μm can be distinguishable in the assemblage of minerals observed by Ma_MISS. The spatial distribution of the mineralogies within the borehole walls is associated with the rocks and the processes that put these materials in place and possibly altered them with time, characterizing the habitats found in the stratigraphic record, indicating which ones are the most suitable to have held or to be holding nowadays traces of life.

Quaternary and Neogene Reservoirs of the Norwegian Continental Shelf and the Faroe-Shetland Basin

Glaciogenic reservoirs host important hydrocarbon resources across the globe. Examples such as the Peon and Aviat discoveries in the North Sea show that Quaternary and Neogene reservoirs can be prospective in the region. In this study, we interpret 2D and 3D reflection seismic data combined with borehole information to document unconventional play models from the shallow subsurface of the Norwegian Continental Shelf and the Faroe-Shetland Basin. These plays include (i) glacial sands in ice-marginal outwash fans, sealed by stiff subglacial tills (the Peon discovery), (ii) meltwater turbidites, (iii) contouritic fine-grained glacimarine sands sealed by gas hydrates, (iv) remobilized oozes above large evacuation craters which are sealed by megaslides and glacial muds, and (v) Neogene sand injectites. The hydrocarbon reservoirs are characterized by negative-polarity reflections with anomalously high amplitudes in the reflection seismic data as well as density and velocity decreases in the borehole data. Extensive new 3D reflection seismic data are crucial to correctly interpret glacial processes and distinguish shallow reservoirs from shallow seals. These data document a variety of play models with the potential for gas in large quantities and enable the identification of optimal drilling targets at stratigraphic levels which have so far been overlooked.

Imperfection of stratigraphic record

Imperfection of stratigraphic record

Sulfur isotopes link atmospheric sulfate aerosols from the Siberian Traps outgassing to the end-Permian extinction on land

Throughout Earth history, large volcanic eruptions that inject sulfur-bearing gases are believed to have imparted strong forcings on global climates and ecosystems. Sulfur outgassing by the Siberian Traps Large Igneous Province (STLIP) is hypothesized to have catalyzed environmental catastrophe associated with the end-Permian extinction (EPE). However, there is as yet only sparse evidence for dispersal of atmospheric sulfate aerosols that precisely coincided with the EPE on land. Here we report S-isotopic compositions of pyrite (δ34S) from the Sydney Basin in SE Australia, where we find a sharp δ34S decrease from 0.04‰ to −21.52‰ coinciding with the stratigraphic level of the terrestrial extinction. The negative δ34S values in the extinction interval provide new evidence for a significant increase in atmospheric sulfate concentrations linked to fallout of sulfate aerosols originating from the Siberian Traps eruptions. We suggest that climatic perturbations of short-term cooling caused by the sulfate aerosols, along with longer-term global warming, and their interactions, may have contributed to the EPE on land. Our data suggest that sulfuric acid rain and ozone depletion may have greatly deteriorated global environments, leading to the terrestrial EPE.

A quantitative depositional model of a large distributive fluvial system (Megafan) with terminal aeolian interaction: The Upper Jurassic Guará DFS in southwestern Gondwana

ABSTRACT Recent studies have shown that distributive fluvial systems are the dominant fluvial forms in modern continental sedimentary basins, thus composing a large part of the stratigraphic record. This study provides a basin-scale architectural analysis of the Guará Formation, from the Upper Jurassic record of southwestern Gondwana, and attempts to compare the formation's depositional model to those developed for distributive fluvial system (DFS) successions. This time interval is significant because it was a period of intense tectonic activity related to the Paraná–Etendeka plume and the Gondwana breakup. Quantitative analyses were performed on stratigraphic sections at 17 locations (exposing a total of 720 m of stratigraphy) located in southern Brazil and northern Uruguay, from a larger dataset of 64 locations (comprising a total of 1070 m of stratigraphy). Four facies associations were identified: perennial fluvial channel fills, ephemeral fluvial channel fills, floodplain deposits, and aeolian deposits, indicating a dryland climate. Spatial trends were analyzed along a downstream-oriented transect (NNE–SSW) across the system. Grain size, channel-body thickness, number of stories, and bar thickness decrease downstream, indicating a reduction in channel depth, flow capacity, and channelization of the fluvial system, interpreted to be associated with downstream-increasing bifurcation, infiltration, and evapotranspiration. Based on spatial trends and distribution of facies associations, the deposits are interpreted to have been accumulated from a large DFS which can be divided into four zones, from proximal to distal: Zone 1, dominated by perennial fluvial channels; Zone 2, a mixture of perennial and ephemeral channels; Zones 3 and 4, deposits situated externally of the fluvial channel belts dominated by aeolian and floodplain deposits prevailing in each zone, respectively. The Guará Formation likely records the stratigraphic signature of the largest distributive fluvial systems reconstructed from both modern and ancient datasets, and one of the first where fluvio–aeolian interaction is quantified. The Guará Formation DFS model presented herein is key to understanding paleoenvironmental, paleoclimatic, and geotectonic changes related to Gondwanan fragmentation.

Contourite systems around the northern exit from the Vema Channel

Several drifts of different types and sizes are identified near the northern exit of the Vema Channel, within the projects Neogene-Quaternary contourites of the Central and South Atlantic and Lateral sedimentation in the deep ocean (on the examples from the Central and South-Western Atlantic). Herein, we discuss new results of a multidisciplinary study of sixteen sediment cores and high-resolution sub-bottom (seismoacoustic) profiles, to address the impact of Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW) passing through the Vema gateway on contourite accumulation and erosion. To the west of the northern exit from the Vema Channel, an anticyclonic gyre of LCDW is instrumental in the development of contourite drifts and sediment waves. The contourite origin of generally silty terrigenous sediments in the Santa Catarina Plateau – São Paulo Plateau area is ascertained by both morpho-seismic and sedimentary characteristics. Sedimentary features include: a lack of primary sedimentary structures and pervasive bioturbation; sharp erosional contacts, local hiatuses and stiff mud horizons; some sandy/silty layers and indistinct bedding; mostly fine grain-size, very poor sorting and distinctive bi-gradational sequences; a high degree of correlation between the content of sortable silt (SS) in the total < 63 μm size fraction and SS mean sizes in all eight cores studied. Biostratigraphy, oxygen isotope records and ten new accelerator mass-spectrometry (AMS) 14C dates reveal the mid to late Quaternary age of this mainly terrigenous contourite depositional system (CDS).By contrast, the dominantly calcareous Ioffe Drift, overlying the Florianopolis Fracture Zone (FFZ) ridge to the northeast of the Vema Channel, is far from any source of terrigenous material, and accumulated in an area of low biological productivity. The overall asymmetric geometry, mainly lenticular, upward-convex seismic units separated by erosional unconformities, reflection truncation, small-scale moats dissecting the drift surface collectively indicate its contourite origin. The interpretation of the drift as the CDS is supported by sediment characteristics including common hiatuses corresponding in some cases to erosional contacts, pervasive bioturbation, generally poor sediment sorting, and more or less well-developed bi-gradational sequences. The erosion and deposition in the drift area are mostly controlled by the main LCDW branch following northeastward along the FFZ. Extensive erosion by bottom currents has created numerous hiatuses and markedly reduced the thickness of drift's sediments. The stratigraphic record from the Ioffe Drift sediment cores reveals an Upper Pliocene – Quaternary succession. The results of detailed analyses of six cores from the Ioffe Drift area, compared with two cores and the upper part of DSDP Site 516 from the Rio Grande Rise, notably the use of a SS analogue, provide new information on calcareous biogenic contourites deposited in the pelagic realm of the South Atlantic.

Contrasting Along-Slope vs. Downslope Sedimentation Style on the High-Latitude Eastern Canadian Continental Margin During the Last 40 ka

Late Pleistocene Labrador Sea depositional systems developed in front of ice streams and glacier outlets from the Laurentide Ice Sheet (LIS) are documented by Huntec and 3.5 kHz seismic profiles and piston cores. Due to efficient grinding by the LIS, massive amounts of fine-grained sediments and meltwater in addition to the icebergs linked to the Heinrich events (H events) of the last glaciation were delivered to the neighboring Labrador Sea. The position of the Hudson Strait ice stream during the periodic expansion and contraction on the Labrador margin allowed fine-grained sediments and meltwater direct delivery on the lower shelf and upper slope. These discharges were then transported southward by the Labrador Current and western boundary current. In contrast to the lower shelf and upper slope, sediments delivered on the mid to the lower Labrador Slope were transported by the Northwest Atlantic Mid-Ocean Channel to distal sites. The nepheloid flow layer at or near the sea bottom or at mid-water depths developed from meltwater loaded with an excessive charge of fine-grained sediments. Contrastingly, the non-discriminatory ice rafting process delivered detritus of all sizes, but its total contribution to the sediment column was only minor, notwithstanding its paleoclimatic significance during H events. Heinrich H1, H2, and H4 layers were identified by their characteristic nepheloid flow layer deposits, that is, alternating coarse silt and clay-sized laminae with thin ice-rafted debris interspersed by coarse- to fine-grained dropstone. Furthermore, the progressive thinning and eventual disappearance of the fine-laminae (i.e., coarse and fine silt/clay) in H layers at the distal sites suggest the exhaustion and raining out of fines due to long-distance transport. However, the H3 layer was identified by a combination of nepheloid flow layer deposits (upper slope) and finely laminated mud turbidites (lower slope and deep basin) at proximal sites. In the lower Labrador Slope and Basin, the H3 stratigraphic equivalent layer was identified by exorbitantly thick finely laminated carbonate-rich mud turbidites. The divergent sedimentation style (i.e., reflected by the sediment facies) and the thickness of the H3 layer compared to other H events suggest that the Hudson Strait ice stream position was different from other H events. Therefore, our data imply that the divergence in the H3 layer between the eastern and western North Atlantic might lie with the position of the Hudson Strait ice stream on the Labrador continental margin.

Scanning X-ray Fluorescence Data Analysis for the Identification of Byzantine Icons' Materials, Techniques, and State of Preservation: A Case Study.

X-ray fluorescence (XRF) spectrometry has proven to be a core, non-destructive, analytical technique in cultural heritage studies mainly because of its non-invasive character and ability to rapidly reveal the elemental composition of the analyzed artifacts. Being able to penetrate deeper into matter than the visible light, X-rays allow further analysis that may eventually lead to the extraction of information that pertains to the substrate(s) of an artifact. The recently developed scanning macroscopic X-ray fluorescence method (MA-XRF) allows for the extraction of elemental distribution images. The present work aimed at comparing two different analysis methods for interpreting the large number of XRF spectra collected in the framework of MA-XRF analysis. The measured spectra were analyzed in two ways: a merely spectroscopic approach and an exploratory data analysis approach. The potentialities of the applied methods are showcased on a notable 18th-century Greek religious panel painting. The spectroscopic approach separately analyses each one of the measured spectra and leads to the construction of single-element spatial distribution images (element maps). The statistical data analysis approach leads to the grouping of all spectra into distinct clusters with common features, while afterward dimensionality reduction algorithms help reduce thousands of channels of XRF spectra in an easily perceived dataset of two-dimensional images. The two analytical approaches allow extracting detailed information about the pigments used and paint layer stratigraphy (i.e., painting technique) as well as restoration interventions/state of preservation.

The role of organic matter diversity on the Re-Os systematics of organic-rich sedimentary units: Insights into the controls of isochron age determinations from the lacustrine Green River Formation

The range of 187Re/188Os values measured from samples of five organic-rich lacustrine mudstones units in the Eocene Green River Formation in the easternmost Uinta Basin covaries with organic matter diversity driven by changing water column conditions. A set of samples from the Douglas Creek Member has the highest pristane/phytane ratio and lowest β-carotane/n-C30 ratio compared to overlying units, indicating deposition in an oxic-anoxic environment with low salinity that would have allowed for the accumulation of a diverse assemblage of aquatic organisms. These samples define the broadest 187Re/188Os range of 1504. In contrast, samples from the R6 and Mahogany zones possess lower pristane/phytane ratios and higher β-carotane/n-C30 ratios indicating deposition in a more restricted lacustrine environment with elevated salinities and alkalinities that would have limited aquatic organic matter diversity. The R6 and Mahogany zones have the narrowest range of 187Re/188Os values measured in this study of 254.9 and 154.6, respectively. As noted by previous workers, these results suggest that organic matter diversity plays a primary role in determining the range of 187Re/188Os ratios in a sample set, and in turn the uncertainty of Re-Os age determinations from organic-rich sedimentary rocks.The Re-Os data from the R3 zone and R6 zone yield ages of 49.7 ± 3.4 Ma and 42.0 ± 18 Ma, respectively, which are statistically indistinguishable based on 2σ uncertainty from three previously reported Re-Os age determinations and those provided by 40Ar/39Ar geochronology of interbedded volcanic ash beds. Although the age uncertainty is high, these findings further highlight the importance of Re-Os geochronology in lacustrine basins, particularly those with thick mudstone successions that lack volcanic ash layers, reliable biostratigraphy, or magnetostratigraphic control. In these cases, even ages with large uncertainties can be useful to constrain burial history and thermal history models.Together, the initial 187Os/188Os ratios of five sets of samples analyzed from the Uinta Basin define the largest Os isotope stratigraphic record from any lacustrine basin compiled to date and record a shift from a value of 1.40 to 1.48 between the R3 and R4 zones in the lower part of the Parachute Creek Member. This small shift may signify a change in the chemical weathering products that entered the lake preserved 20 to 50 m above the contact between the Douglas Creek and the lower Parachute Creek members during a period when the basin transitioned from a shallow lake with mostly open hydrology to an alkaline lake with more frequent basin restrictions.

Controls on near-surface and burial diagenesis of a syn-rift siliciclastic rock succession: A study from Permian Barren Measures Formation, Southern India

Distinct processes during the syn-depositional sedimentation and the post-depositional diagenesis determine the fabric of a clastic sedimentary rock. Temporal and spatial variations in any of these processes cause development of specialized characters in the sedimentary rocks. The Permian Barren Measures Formation in the Pranhita-Godavari Valley in southern peninsular India, is characterized by signatures of early to late diagenetic cementations within coarse-grained sandstones and mudstones. An integrated petrographic-geochemical study is carried out to understand the post-depositional near-surface and burial processes. Facies architecture manifests sedimentation in fluvial (channel, bar and overbank) to tide-influenced fluvio-tidal mixed depositional condition. Post-depositional near-surface early diagenesis changes include – (i) partial dissolution of detrital grains, (ii) biotite kaolinization, (iii) localized extensive ferruginous cementation, (iii) calcite cementation, and (iv) development of rhizocretions observed at different stratigraphic levels. These point to the role of meteoric water during the pre-burial stage that changed the pore water chemistry within the fluvial channel and bar sediments, along with onset of pedogenic (calcretization) processes in the vadose zone within the fine-grained overbank deposits. Marine (tidal) water influx in fluvial regime under a semi-arid climate modified the pore water chemistry. Shallow burial diagenetic changes, under elevated temperature and pressure include – (i) extensive calcite cementation in intergranular pore spaces and fractures, and (ii) late phase partial dissolution producing secondary porosity. A predictive model is derived to decipher the role of post-depositional changes in developing potential reservoir heterogeneity in a fluvio-tidal mixed depositional system.