Unweathered Sediments Research Articles

Stratigraphy of the Cretaceous/Paleogene (K/Pg) boundary at the Global Stratotype Section and Point (GSSP) in El Kef, Tunisia: New insights from the El Kef Coring Project

The Cretaceous/Paleogene (K/Pg) boundary is marked by one of the largest mass extinctions in Earth’s history, with geological evidence for this event being expressed in hundreds of locations worldwide. An extensively studied section located near El Kef, northwestern Tunisia, is characterized by the classic iridium-rich K/Pg boundary layer, abundant and well-preserved microfossils, and apparently continuous sedimentation throughout the early Danian with no previously described structural complication. These features led to its designation in 1991 as the Global Stratigraphic Section and Point (GSSP) for the base of the Danian (i.e., the K/Pg boundary). However, the outcrop section has become weathered, and the “golden spike” marking the GSSP is difficult to locate. Therefore, the El Kef Coring Project aimed to provide a continuous record of unweathered sediments across the K/Pg transition in cores recovered from five rotary-drilled holes located close to the El Kef GSSP. Here, we present new, high-resolution lithologic, biostratigraphic, and geochemical data from these cores. The recovered stratigraphic successions of each hole (all drilled within ∼75 m of one another) are unexpectedly different, and we identified a formerly unknown unconformity within planktic foraminiferal biozone P1b. Our results provide evidence that sedimentation at El Kef was not as continuous or free from structural complication as previously thought. Despite these challenges, we present a new composite section from the five El Kef holes and an age model correlated to the orbitally tuned record at Walvis Ridge, South Atlantic Ocean, which is critical in placing the paleoenvironmental and paleoecological records from El Kef in a global context.

Heavy Metal Concentration in the Water and Sediment of the Lake Greenwood Watershed

We report on the concentration of heavy metals (cadmium, chromium, cobalt, copper, iron, and lead) in the water and sediment of Lake Greenwood and the streams and creeks that flow into the lake. Our results show heavy metal concentrations well below levels that were reported in 2012. The heavy metal concentrations reported for Lake Greenwood were on the order of the established background levels; our measurements indicate that heavy metal concentrations are now well below the established background levels. The concentration of heavy metals in creeks sediment and lake sediment was not statistically different for most metals (copper was statistically different). This significant drop in concentration suggests that the major flooding which occurred in 2015 has drastically altered the heavy metal profile of Lake Greenwood and the creeks which flow into the lake. The effect of introducing large volumes of relatively unweathered sediment has an observed lowering of the concentration of heavy metals. For all metals at all sites, the measured concentration of heavy metals in water samples collected was below the screening level established by the US Environmental Protection Agency. Also, our results also call into question the continued use of previously established background concentration of heavy metals after a significant flooding event, as the addition of large volumes of fresh sediment from flooding events significantly changes the heavy metal concentration.

Constraints from Geochemistry and Field Relationships for the Origin of Kornerupine-Bearing Gneiss from the Grenvillian New Jersey Highlands and Implications for the Source of Boron

Kornerupine ± prismatine is present in granulite-facies paragneiss at two locations in the Grenvillian New Jersey Highlands, occurring in an assemblage composed of quartz + biotite + K-feldspar + plagioclase + garnet + Fe-Ti oxides ± sillimanite ± rutile ± graphite. Estimates of the metamorphic conditions of the host gneiss are ≥600 MPa and ~740 °C during the Ottawan phase of the Grenvillian Orogeny. Geochemical compositions of kornerupine-bearing gneiss are consistent with protoliths that were graywacke sandstone and pelite. Metagraywacke is characterized by (in wt. %) 62–76% SiO2, 0.3–0.8% TiO2, 13–16% Al2O3, 0.6–4.3% CaO, 2.2–6.4% Na2O, 1.7–7.4% K2O, and 90–260 ppm Zr; metapelite has lower SiO2 (53–66%) and CaO (0.5–2.0%), higher TiO2 (0.9–1.8%), Al2O3, (15–26%), and Zr (210–490 ppm), and comparable Na2O (2.5–4.9%) and K2O (2.5–7.4%). Indices of weathering and alteration yield low to intermediate values implying a relatively unweathered sediment source. Provenance discriminants suggest the protoliths formed from immature, first-cycle sediments derived mainly from a felsic arc-related source. The geological relationships of kornerupine-bearing gneiss are most compatible with boron sourced from B-rich sediments deposited in the protoliths between ca. 1299 and 1238 Ma. The breakdown of these sediments due to dehydration reactions during Ottawan prograde metamorphism led to mobilization of a B-rich fluid that migrated short distances to favorable structural sites in the host gneiss, resulting in precipitation of the borosilicates.

Radiocarbon and Stable Carbon Isotopes of Labile and Inert Organic Carbon in the Critical Zone Observatory in Illinois, USA

ABSTRACTWe applied the high temperature pyrolysis-combustion technique to partition the total soil organic carbon (SOC) into labile and inert carbon pools for accelerator mass spectrometry radiocarbon (AMS 14C) dating and stable carbon isotope (δ13C), SOC, and carbonate carbon (CC) content analyses to examine SOC variability at a Critical Zone Observatory site in Illinois, USA. The AMS 14C dates of labile and inert carbon in the top 1.55 m overlap except in the Bt horizon. Below 1.55 m the labile carbon is younger by 8000–14,800 years. The SOC content decreases from 3.61% to 0.12% and CC content increases from 0% to 19.16% at this depth. Results indicate that SOC production exceeds its loss in the weathering zone causing a continuous turnover of both SOC pools. A small amount of modern SOC infiltrates into deeper sediment below 1.55 m, making the labile carbon pool much younger. Their difference of AMS 14C contents, ΔF14C, reveals 3−5% more modern carbon in the labile SOC pools except in the Bt horizon, further quantifying that <3−5% modern carbon with potential pollutants is translocated into the unweathered sediments. The δ13C reveals the sources for SOC cycling dynamics in both carbon pools at this site.

Characterization of how contaminants arise in a dredged marine sediment and analysis of the effect of natural weathering

Millions of tons of contaminated sediments are dredged each year from the main harbors in France. When removed from water, these sediments are very reactive, therefore their geochemical behavior must be understood in order to avoid dispersion of contaminated lixiviates in the surrounding soils. In this objective, it is necessary to evaluate the principal physicochemical parameters, and also achieve advanced mineralogical characterization. These studied sediments are highly contaminated by metals, notably copper (1445 and 835mg/kg, in the unweathered and naturally-weathered sediments, respectively), lead (760 and 1260mg/kg, respectively), zinc (2085 and 2550mg/kg, respectively), as well as by organic contaminants (PAH, PCB) and organometallics (organotins). A high concentration of sulfide minerals was also observed both in the unweathered sediment preserved under water (3.4wt% of pyrite especially), and in the naturally weathered sediment (2wt% pyrite), and in particular framboïdal pyrite was observed in the two materials.The presence of reactive mineral species in the naturally-weathered sediment can be explained by the deposit of a protective layer, composed of sulfide and their oxidation products (sulfate and iron oxides), thus preventing oxygen from diffusing through to the sulfide minerals. Additionally, the presence of aluminosilicates aggregates coating the sulfide minerals could also explain their presence in the naturally-weathered sediment. As organic matter is one of the principal constituents of the sediments (5.8 and 6.3wt% total organic carbon in the unweathered and weathered sediment, respectively), the aggregates are probably partially constituted of refractory humic material. It therefore appears that the natural weathering has led to a significant decrease in PAHs and organotins, but not in PCBs. The evolution of the granulometric structure and the distribution of the metallic contaminants could therefore lead us to consider a treatment by size separation, and a possible valorization of the dredged sediments in civil engineering.

The top of the Olduvai Subchron in a high-resolution magnetostratigraphy from the West Turkana core WTK13, hominin sites and Paleolakes Drilling Project (HSPDP)

One of the major challenges in understanding the evolution of our own species is identifying the role climate change has played in the evolution of hominin species. To clarify the influence of climate, we need long and continuous high-resolution paleoclimate records, preferably obtained from hominin-bearing sediments, that are well-dated by tephro- and magnetostratigraphy and other methods. This is hindered, however, by the fact that fossil-bearing outcrop sediments are often discontinuous, and subject to weathering, which may lead to oxidation and remagnetization. To obtain fresh, unweathered sediments, the Hominin Sites and Paleolakes Drilling Project (HSPDP) collected a ∼216-meter core (WTK13) in 2013 from Early Pleistocene Paleolake Lorenyang deposits in the western Turkana Basin (Kenya). Here, we present the magnetostratigraphy of the WTK13 core, providing a first age model for upcoming HSPDP paleoclimate and paleoenvrionmental studies on the core sediments. Rock magnetic analyses reveal the presence of iron sulfides carrying the remanent magnetizations. To recover polarity orientation from the near-equatorial WTK13 core drilled at 5°N, we developed and successfully applied two independent drill-core reorientation methods taking advantage of (1) the sedimentary fabric as expressed in the Anisotropy of Magnetic Susceptibility (AMS) and (2) the occurrence of a viscous component oriented in the present day field. The reoriented directions reveal a normal to reversed polarity reversal identified as the top of the Olduvai Subchron. From this excellent record, we find no evidence for the ‘Vrica Subchron’ previously reported in the area. We suggest that outcrop-based interpretations supporting the presence of the Vrica Subchron have been affected by the oxidation of iron sulfides initially present in the sediments -as evident in the core record- and by subsequent remagnetization. We discuss the implications of the observed geomagnetic record for human evolution studies.

Clay mineralogy, organic carbon burial, and redox evolution in Proterozoic oceans

Clay minerals formed through chemical weathering have long been implicated in the burial of organic matter (OM), but because diagenesis and metamorphism commonly obscure the signature of weathering-derived clays in Precambrian rocks, clay mineralogy and its role in OM burial through much of geologic time remains incompletely understood. Here we have analyzed the mineralogy, geochemistry and total organic carbon (TOC) of organic rich shales deposited in late Archean to early Cambrian sedimentary basins. Across all samples we have quantified the contribution of 1 M and 1 M d illite polytypes, clay minerals formed by diagenetic transformation of smectite and/or kaolinite-rich weathering products. This mineralogical signal, together with corrected paleo-weathering indices, indicates that late Archean and Mesoproterozoic samples were moderately to intensely weathered. However, in late Neoproterozoic basins, 2 M 1 illite/mica dominates clay mineralogy and paleo-weathering indices sharply decrease, consistent with an influx of chemically immature and relatively unweathered sediment. A late Neoproterozoic switch to micaceous clays is inconsistent with hypotheses for oxygen history that require an increased flux of weathering-derived clays (i.e., smectite or kaolinite) across the Precambrian–Cambrian boundary. Compared to previous studies, our XRD data display the same variation in Schultz Ratio across the late Neoproterozoic, but we show the cause to be micaceous clay and not pedogenic clay; paleo-weathering signals cannot be recovered from bulk mineralogy without this distinction. We find little evidence to support a link between these mineralogical variations and organic carbon in our samples and conclude that modal clay mineralogy cannot by itself explain an Ediacaran increase in atmospheric oxygen driven by enhanced OM burial.

Attenuation of nitrate in aquitard sediments of southern Ontario

To examine nitrate persistence, detailed geochemical profiling, using core-squeezed water and piezometer samples, was carried out at five sites in southern Ontario where groundwater is moving downward in silt-rich aquitard sediments at rates of 16 to more than 20 cm year −1. Elevated levels of NO 3 −-N (5–50 mg 1 −1) that occur in the shallow groundwater as a result of agricultural activity, were found to be consistently attenuated, generally to very low levels (< 0.05 mg 1 −1-N), at the ‘redoxcline’, the horizon marking the boundary between the surficial weathered (brown) sediments and the underlying unweathered (grey) sediments. Tritium dating suggests that groundwater at the redoxcline depths (3–5 m) was recharged between 1970 and 1980, thus the N03 depletion appears to result from biodegradation reactions since no major landuse changes have occurred during this period. The close association of the nitrate depletion zones with the redoxcline, where, in particular, sediment sulphur contents increase abruptly, and where also porewater SO 4 2− levels increase, suggests that the dominant attenuation reaction is autotrophic denitrification using reduced sulphur compounds present in the unweathered sediment as the electron donor. Mass balance calculations suggest that the increase in the downward rate of migration of the redoxcline, owing to added sulphur consumption from NO 3 − contamination, is only about 1 mm year −1 at these sites. Review of the literature indicates that most silt- and clay-rich sediments have S contents in the same range, or higher, than those investigated here, thus, in most cases where aquifers are overlain by several metres or more of unweathered confining sediments, it is likely that a high degree of protection is afforded from surficial NO 3 − contamination.

A determinative soil development index for pedo-stratigraphic studies

Pedologists and Quaternary scientists working with stratigraphic columns which may include paleosols have need of a simple, quantitative procedure to distinguish paleosols from unweathered sediments and to represent the degree of soil development. Soil development indices which are most widely used have been derived for soil chronosequences on relatively stable landscapes and require that soil properties be compared to those of the parent material in order to quantitatively assess soil development. In studying stratigraphic columns, which may represent dramatically unstable landscapes, parent material may not always be readily determined, or there may be multiple soil parent materials which make a comparative approach untenable. This paper presents a determinative index based on morphological and micromorphological properties which are most effective in distinguishing “soil” from “non-soil”. This index successfully separated soils and paleosols from unweathered sediments in a stratigraphic sequence in northern New Hampshire. A Kruskal-Wallis test determined that means of index value groups which corresponded to sets of observed chemical and morphological soil properties were significantly different. This index was also successful in distinguishing independently-assessed morpho-genetic soil horizons and correlated well with Harden index values for a set of soil toposequences in southern Wyoming.

Counter-clockwise rotations in the southern Apennines during the Pleistocene: paleomagnetic evidence from the Matera area

Sediments from late Pliocene to early Pleistocene age have been sampled at six different localities/ sections (38 sites) in the Matera area which is in the southern part of peninsular Italy (Basilicata). Three of the localities are from the Apenninic belt, the other three from the Bradano Unit, both of them west of the earlier sampled Apulian Unit. Stepwise thermal demagnetisation revealed that usually two important components contribute to the natural remanent magnetisation (NRM) of these clay sediments: a low-temperature (LT) component removed between 100 and 300–320°C and a high-temperature (HT) component removed between 300–320 and 430–450°C. The HT component is a characteristic remanent magnetisation (ChRM) for the sediments and has a clear primary (= pre-folding) origin. In fresh, unweathered sediments the LT component is identical in direction to the HT component, but there is evidence that moderate weathering replaced a high-intensity primary LT component with a low-intensity secondary LT magnetisation. The HT magnetisation is affected by this weathering process in a decrease of its intensity. A counter-clockwise deflection in declination is observed for the sites sampled in the Apenninic belt. The HT directions reveal a 23° counter-clockwise rotation relative to the magnetic north: D m = 336.6° and I m = 57.2°. Sites in the Bradano Unit have no tectonic rotation: D m = 359.1° and I m = 56.3°. Earlier sampled sites from the Apulian Unit also showed no tectonic rotation: D m = 359.4° and I m = 57.0°. Paleomagnetic data support the hypothesis that the southern Apennines rotated in the middle-late Pleistocene, after the major phase of extension in the southern part of the Tyrrhenian basin and contemporaneous with a regional compressional phase.

Stratigraphy and geochemistry of the Jiuzhoutai loess succession, northwestern China

Unweathered sediments and paleosols in the Jiuzhoutai loess sequence of northwestern China were studied to determine the degree of parent material uniformity and to attempt to establish, from geochemical and mineralogical changes in the paleosols, the range and variability of paleoclimates that existed during Quaternary soil-forming intervals. The primary chemical variability in this sample suite comes from differences in salt (NaCl) content. Because of these salt differences, the Na content of each sediment and soil sample must be estimated by correcting the measured Na content, using the Cl content to establish the Na content ssociated with NaCl. Small excesses of Ca (probably as CaCO 3) have slightly diluted the concentrations of other elements in the affected paleosols. The close relationship between the composition of the loessic sediments and most of the identified paleosols shows that there may be only a few true weathering zones in the sequence. Indeed, on the basis of low Ca contents, only paleosols S1, S4, S10, S12, S13, S14, S16 and S19 are identified as moderately weathered pedogenic zones, some of which are Camborthids. Using percent clay increase and geochemical indices as evidence for stronger weathering profiles S1, S2, S3, S4, S5, S6, S9, S11, S13, S16 and S18 may also be considered paleosols (e.g. Haplargids). All other identified paleosols do not show any increase in Ca, which might be expected from dry soil-forming intervals which mainly produce Aridisols (e.g. Calciorthids). Parent material uniformity is demonstrated by a number of inter-element ratios, indicating a chemically consistent source for the loessic sediments and paleosols.

Sedimentology of Basal Potsdam Sandstone in Adirondack Border Region, New York, Southeastern Ontario, and Southwestern Quebec: ABSTRACT

Field evidence supports the relatively widespread presence of nonmarine facies within the basal Potsdam formation of the Adirondack border areas of northern New York, southeastern Ontario, and southwestern Quebec. Detailed observations of areal extent, analysis of sedimentary structures and paleocurrent directions, and petrographic studies have been combined with the paleomagnetic determination of the temporal relationships of these strata to establish depositional patterns and facies trends within basal Potsdam units. Four distinct nonmarine lithofacies have been identified: massive matrix-supported conglomerate, stratified framework-supported conglomerate, conglomerate-arkose, and pebble conglomerate-arkose fining-upward sequences, interpreted to represent debris flows, proximal gravelly braided-stream deposits, intermediate to distal gravelly braided-stream deposits, and proximal sandy braided-stream deposits, respectively. Facies of eolian or possibly tidal, and shallow marine origin have also been identified at the base of the Potsdam sequence. Most basal Potsdam sediments are compositionally and texturally immature, derived directly from the crystalline detritus of the extensively weathered Precambrian surface and regoliths that may have locally developed on the craton. The desert-like environment of the Precambrian surface allowed for rapid transport and deposition of relatively unweathered sediments and the subsequent construction of a braided alluvial plain system. Field relations and evidence derived from consideration of the paleomagnetic properties inmore » five localities of fine-grained alluvium suggest that terrestrial Potsdam deposition in the Early and Middle Cambrian largely preceded the marine transgression that deposited the thick, shallow marine units typifying most of the Potsdam sequence.« less

Estudo sedimentológico das "bandas onduladas" de solos da formação Bauru na área balisada pelas cidades de Osvaldo Cruz: Rancharia e Tupã Estado de São Paulo

The thin layers of higher clay content than the surrounding soil, known as "bandas onduladas", frequently reported in the Bauru Formation area of the State of São Paulo occidental plateau (Brazil), are here studied in a region bound by Osvaldo Cruz - Tupã and Rancharia cities. The genetic significance of their sedimentological characteristics (grain size and heavy mineral composition) and other properties (clay, calcium carbonate and iron oxyde content) is considered in comparison with that of Bauru Formation unweathered sediments.

Information on groundwater composition obtained from a laboratory study of sediment-water interaction

Summary The dissolution of some superficial sediments was studied experimentally to determine the sediment's influence on groundwater composition and also to check the previous findings based on analyses of the sediment and of the natural pore water from a site at Dunsforth, 21 km north-west of York. In the experiments Ca was dissolved from carbonates, Mg from dolomite and clay minerals, K and probably Na also from clay minerals and possibly feldspars. Higher concentrations of Ca, Mg and K were dissolved from unweathered sediments than from weathered, whereas the concentration of Na remained relatively constant. These conclusions are in agreement with those based on a study of the natural system and thus some of the reactions can be reproduced in the laboratory. Equilibrium was achieved relatively rapidly in the experiments. It is therefore claimed that relatively simple experimental work can provide meaningful information in studies of groundwater chemistry.

Natural dust and acid rain

Atmospheric dust originates from three sources: terrestrial airborne matter, volcanic, and cosmic. Terrestrial natural dust makes up the main bulk reflecting the soil composition to 150 mi away. Soil erosion from flood plains, plowed fields and construction sites is the main source. Quartz, feldspar, the carbonates calcite and dolomite, and clay minerals are the components in decreasing order of frequency. Natural dust in the atmosphere interacts with rainwater converting the carbonates to benign gypsum (CaSO4.2H20). Naturally leached soils produce less calcite than unweathered sediments on flood plains and construction sites, and in granitic and crystalline rocks less than in limestone areas.