Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
2,267
result(s) for
"Mason, Paul"
Sort by:
Climate control on banded iron formations linked to orbital eccentricity
Astronomical forcing associated with Earth’s orbital and inclination parameters (Milankovitch forcing) exerts a major control on climate as recorded in the sedimentary rock record, but its influence in deep time is largely unknown. Banded iron formations, iron-rich marine sediments older than 1.8 billion years, offer unique insight into the early Earth’s environment. Their origin and distinctive layering have been explained by various mechanisms, including hydrothermal plume activity, the redox evolution of the oceans, microbial and diagenetic processes, sea-level fluctuations, and seasonal or tidal forcing. However, their potential link to past climate oscillations remains unexplored. Here we use cyclostratigraphic analysis combined with high-precision uranium–lead dating to investigate the potential influence of Milankovitch forcing on their deposition. Field exposures of the 2.48-billion-year-old Kuruman Banded Iron Formation reveal a well-defined hierarchical cycle pattern in the weathering profile that is laterally continuous over at least 250 km. The isotopic ages constrain the sedimentation rate at 10 m Myr−1 and link the observed cycles to known eccentricity oscillations with periods of 405 thousand and about 1.4 to 1.6 million years. We conclude that long-period, Milankovitch-forced climate cycles exerted a primary control on large-scale compositional variations in banded iron formations.Long-period Milankovitch eccentricity oscillations controlled compositional variations in the 2.48-billion-year-old Kuruman Banded Iron Formation, according to cyclostratigraphic analysis and high-precision dating.
Journal Article
Surfing
Explains what surfing is, its origins, and safety tips designed to protect the rider and those around him/her.
Book
A window into transition metal availability in early palaeoproterozoic seawater
Metals are required by all life to build metalloproteins, but the metal preferences of the dominant microbes have evolved over geological time. Consistent with this, experiments and models predict that metal availability in anoxic seawater during the Archean and Proterozoic eons (4.0–0.541 billion years ago) would have been radically different to today. Corroborating this in the geological record is challenging because bulk rock geochemistry reflects complex histories. Here we take a novel approach, determining the transition metal content of micron-scale laths of greenalite, a primary Fe(II)-silicate mineral, from the Kuruman Formation of the Transvaal Supergroup, South Africa. Our data provide a high-resolution snapshot of seawater chemistry ~ 2.46 Ga, and reveal striking compositional differences compared to today: Zn and V were relatively scarce, Ni was similar, Co was enriched, and Mn was highly-enriched. Our data are largely consistent with chemical predictions and overlap with constraints from a range of different geological archives. Ancient seawater was therefore dominated by Fe and Mn, consistent with evidence that early life preferentially utilised these transition metals. Extremely high Mn concentrations could have interfered with cellular homeostasis, as well as disrupting DNA synthesis, potentially driving faster rates of evolution.
Journal Article
Amphibole perspective to unravel pre-eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes: a case study from Ciomadul volcano (SE Carpathians)
Ciomadul is the youngest volcano in the Carpathian–Pannonian region produced crystal-rich high-K dacites that contain abundant amphibole phenocrysts. The amphiboles in the studied dacites are characterized by large variety of zoning patterns, textures, and a wide range of compositions (e.g., 6.4–15 wt% Al
2
O
3
, 79–821 ppm Sr) often in thin-section scale and even in single crystals. Two amphibole populations were observed in the dacite: low-Al hornblendes represent a cold (<800 °C) silicic crystal mush, whereas the high-Al pargasites crystallized in a hot (>900 °C) mafic magma. Amphibole thermobarometry suggests that the silicic crystal mush was stored in an upper crustal storage (~8–12 km). This was also the place where the erupted dacitic magma was formed during the remobilization of upper crustal silicic crystal mush body by hot mafic magma indicated by simple-zoned and composite amphiboles. This includes reheating (by ~200 °C) and partial remelting of different parts of the crystal mush followed by intensive crystallization of the second mineral population (including pargasites). Breakdown textures of amphiboles imply that they were formed by reheating in case of hornblendes, suggesting that pre-eruptive heating and mixing could take place within days or weeks before the eruption. The decompression rim of pargasites suggests around 12 days of magma ascent in the conduit. Several arc volcanoes produce mixed intermediate magmas with similar bimodal amphibole cargo as the Ciomadul, but in our dacite the two amphibole population can be found even in a single crystal (composite amphiboles). Our study indicates that high-Al pargasites form as a second generation in these magmas after the mafic replenishment into a silicic capture zone; thus, they cannot unambiguously indicate a deeper mafic storage zone beneath these volcanoes. The simple-zoned and composite amphiboles provide direct evidence that significant compositional variations of amphiboles do not necessarily mean variation in the pressure of crystallization even if the Al-tschermak substitution can be recognized, suggesting that amphibole barometers that consider only amphibole composition may often yield unrealistic pressure variation.
Journal Article
Formula 1
\"Explains the history of Formula 1 racing and the how-to of the sport\"--Provided by publisher.
Book
Emergence of felsic crust and subaerial weathering recorded in Palaeoarchaean barite
Reconstructing the emergence and weathering of continental crust in the Archaean eon is crucial for our understanding of early ocean chemistry, biosphere evolution and the onset of plate tectonics. However, considerable disagreement exists between elemental and isotopic proxies that have been used to trace crustal input into marine sediments, and data are scarce before 3 Ga. Here we show that chemical weathering modified the Sr isotopic composition of seawater as recorded in 3.52–3.20 Ga stratiform barite deposits from three different cratons. Using a combination of Sr, S and O isotope data, barite petrography and a hydrothermal mixing model, we calculate a Sr isotope evolution trend of Palaeoarchaean seawater that is much more radiogenic than the curve previously determined from carbonate rocks. Our findings suggest that evolved crust containing high Rb/Sr was subaerial and weathering into the oceans from approximately 3.7 ± 0.15 Ga onwards with impacts on ocean chemistry and the nutrient supply to the marine biosphere.
Chemical weathering of subaerial felsic crust modified the composition of Palaeoarchaean seawater, suggesting possible Eoarchaean crustal emergence, according to the radiogenic strontium isotope composition of 3.5–3.2 Ga barite deposits.
Journal Article
Indy cars
\"Explains the history of Indy Car racing and the how-to of the sport\"--Provided by publisher.
Book
Early Oldowan technology thrived during Pliocene environmental change in the Turkana Basin, Kenya
Approximately 2.75 million years ago, the Turkana Basin in Kenya experienced environmental changes, including increased aridity and environmental variability. Namorotukunan is a newly discovered archaeological site which provides a window into hominin behavioral adaptations. This site lies within the upper Tulu Bor and lower Burgi members of the Koobi Fora Formation (Marsabit District, Kenya), presently a poorly understood time interval due to large-scale erosional events. Moreover, this locale represents the earliest known evidence of Oldowan technology within the Koobi Fora Formation. Oldowan sites, older than 2.6 million years ago, are rare, and these typically represent insights from narrow windows of time. In contrast, Namorotukunan provides evidence of tool-making behaviors spanning hundreds of thousands of years, offering a unique temporal perspective on technological stability. The site comprises three distinct archaeological horizons spanning approximately 300,000 years (2.75 − 2.44 Ma). Our findings suggest continuity in tool-making practices over time, with evidence of systematic selection of rock types. Geological descriptions and chronological data, provide robust age control and contextualize the archaeological finds. We employ multiple paleoenvironmental proxies, to reconstruct past ecological conditions. Our study highlights the interplay between environmental shifts and technological innovations, shedding light on pivotal factors in the trajectory of human evolution.
Here, the authors present archaeology of the Namorotukunan site in Kenya’s Turkana Basin that demonstrates adaptive shifts in hominin tool-making behaviour spanning 300,000 years and increasing environmental variability. They contextualize these findings with paleoenvironmental proxies, dating, and geological descriptions.
Journal Article