Gerilyn S. Soreghan

Dust covers a significant portion of Mars' surface, with dust storms periodically engulfing the planet. Despite this, the origins of Martian dust are poorly understood, especially for ancient dust deposits. To address this deficit, we conducted experiments to replicate the mechanical abrasion of saltating sand grains in a Martian desert dune field under storm wind conditions, measured rates and particle‐size distributions of produced dust, and scaled results to determine potential planetary‐wide significance. Two basalt sand samples were collected to act as Martian dune sand analogs (from Hawaii and Iceland). Samples were processed to remove any pre‐existing dust‐sized sediment and then abraded inside a novel device designed to replicate the grain‐on‐grain collisions experienced by saltating sand in a desert aeolian system. These experiments demonstrate the significance of dust production by aeolian saltation of basalt sand at the planetary scale. Results show that basaltic sand from Iceland produced 4 times more dust and 2.5 times more fine sand than Hawaiian samples, suggesting that differences in composition, shape, and size of the sand grains influence the amount of dust produced. If our experiments are valid replications of natural dust production, then aeolian saltation over 1 million to 1 billion years on Mars could produce a geologically significant amount of dust capable of influencing the planetary climate. These results have implications for the deep time climate of Mars when the atmosphere was denser, and aeolian saltation was more frequent.

The Songliao Basin preserves a complete Cretaceous continental sedimentary succession. Previous researchers have conducted extensive cyclostratigraphic studies on the Upper Cretaceous Nenjiang Formation, but paleoclimatic research has primarily focused on the lower part of the formation. The relationship between climatic changes and astronomical parameters in the middle and upper sections of the Nenjiang Formation has not yet been fully investigated. This study conducted cyclostratigraphic analysis of the second to third members of Nenjiang Formation Late Cretaceous (K₂n^2-3) in the Songliao Basin using high-resolution gamma-ray logging (GR) data, while also performing paleoclimatic analysis in conjunction with palynological data. The fossil spores and pollen from the K₂n³ indicate a geological age of the Late Cretaceous Campanian. Based on the ecological data of the parent plants of the spores and pollen, the vegetation types, climatic zones, and humidity types of the lower part of the K₂n³ were analyzed, confirming its semi-warm and semi-humid paleoclimatic characteristics. Time-series analysis reveals persistent 405-kyr (long eccentricity), 95-kyr (short eccentricity), 38.3-kyr (obliquity), and 22.8-kyr (precession) sedimentary cycles, further validated by an optimal sedimentation rate model. We established a 3.24-Myr floating astronomical time scale for K₂n^2-3 by tuning the GR series to orbital targets. This timescale is anchored by a volcanic ash age (83.269 ± 0.044 Ma) at the K₂n² base, generating an absolute age framework spanning 83.33–80.00 Ma. Vertical transitions in palynofloral assemblages correspond to the 38.3-kyr obliquity cycle, indicating significant obliquity forcing on regional paleoclimate dynamics.

The Permian witnessed some of the most profound climatic, biotic, and tectonic events in Earth’s history. Global orogeny leading to the assembly of Pangea culminated by middle Permian time, and included multiple orogenic belts in the equatorial Central Pangean Mountains, from the Variscan-Hercynian system in the East to the Ancestral Rocky Mountains in the West. Earth’s penultimate global icehouse peaked in early Permian time, transitioning to full greenhouse conditions by late Permian time, constituting the only example of icehouse collapse on a fully vegetated Earth. The Late Paleozoic Ice Age was the longest and most intense glaciation of the Phanerozoic. Reconstructions of atmospheric composition in the Permian record the lowest CO2 and highest O2 levels of the Phanerozoic, with average CO2 levels comparable to the Quaternary, rapidly warming climate. Fundamental shifts occurred in atmospheric circulation: a global megamonsoon developed, and the tropics became anomalously arid with time. Extreme environments are well documented in the form of voluminous dust deposits, acid-saline lakes and groundwaters, extreme continental temperatures and aridity, and major shifts in biodiversity, ultimately culminating in the largest extinction of Earth history at the Permian-Triassic boundary.The Deep Dust project seeks to elucidate paleoclimatic conditions and forcings through the Permian at temporal scales ranging from millennia to Milankovitch cycles and beyond by acquiring continuous core in continental lowlands known to harbor stratigraphically complete records dominated by loess and lacustrine strata. Our initial site is in the midcontinental U.S.— the Anadarko Basin (Oklahoma), which harbors a complete continental Permian section from western equatorial Pangaea. We will also address the nature and character of the modern and fossil microbial biosphere, the chemistry of saline lake waters and groundwaters, Mars-analog conditions, and exhumation histories of source regions. Importantly, data from Deep Dust will be integrated with Earth-system modelling. This is crucial for putting the (necessarily local) drill core data into the broader global context and for understanding relevant mechanisms and feedbacks of the Permian Earth system.

Sedimentary rocks can provide information about the Earth paleoenvironment and are studied extensively to understand the causes and consequences of global climate changes in deep time. They facilitate long-time perspectives that constrain climate models and provide analogues for how Earth systems may respond to, and recover from, intervals of profound environmental change, including projected anthropogenic change. The Norwegian Svalbard archipelago offers an extensive Phanerozoic stratigraphic record that reflects the geological evolution of the northern flanks of continental assemblages that include Laurentia, Eurasia, and Pangea. Svalbard’s Phanerozoic sedimentary and paleoclimatic archive is controlled largely by Svalbard’s overall northward plate-tectonic motion from equatorial to high latitudes, but also by regional to local formation of topography and basins in response to long-term plate reorganization, as well as the near- and far-field influence of large igneous province activity on the tectono-stratigraphic and paleoclimatic development. Various sedimentary and geochemical proxies, such as bentonite beds and carbon isotope excursions associated with the far-reaching environmental effects of the Siberian Traps, the High Arctic Large Igneous Province, and the North Atlantic Igneous Province are present in Svalbard’s near complete geological record. As such, Svalbard is unique in that these and numerous other global environmental perturbations are recorded within a relatively restricted study area, with most of the key events preserved and recorded in easily accessible drill cores and well-exposed outcrop sections. Here we review deep-time paleoenvironmental and paleoclimate research in Svalbard by summarizing 148 peer-reviewed scientific articles. The review builds on the well-established tectono-stratigraphic and lithostratigraphic framework, as well as state-of-the art environmental reconstructions to provide insights into the Earth system during the Phanerozoic northward drift of Svalbard and the many major biotic crises in the geological past. We focus on globally significant events including i) the expansion of Devonian vegetation, ii) the Carboniferous-Permian response to icehouse conditions during the Late Paleozoic Ice Age (LPIA), iii) the End-Permian Mass Extinction (EPME) and the subsequent Triassic recovery, the iv) Carnian Pluvial Episode, v) Jurassic-Early Cretaceous climate perturbations including the Volgian Isotopic Carbon Excursion (VOICE) and the Aptian Ocean Anoxic Event 1a (OAE1a), and vi) the Paleocene-Eocene Thermal Maximum (PETM). We present and synthesize existing core and outcrop data that preserve biological and geochemical proxies and climate sensitive sedimentary facies that reflect environmental change in terrestrial and marine settings. Finally, we discuss the Phanerozoic climate recorded in Svalbard and its role in providing high latitude calibration points for several global paleoclimate events to provide a higher latitude perspective to complement the dominance of mid- and low-latitude locations and datasets in the literature.

If you could time travel to the central U.S. 300 million years ago, you would find yourself at the equator of the supercontinent Pangea. At first you might enjoy a warm climate, surrounded by seas filled with life. But, after some millions of years, the seas would vanish as the climate turned increasingly hot, dry, and hostile. Billowing dust would engulf you, and nearly all life on Earth would vanish in an event called the Great Dying. How do we know? Geoscientists reconstruct past landscapes and climates by drilling into ancient sediments—tiny grains of sand and silt. These tiny particles tell us how fast the mountains rose and which way the wind blew. Microscopic fossils reveal water and air temperatures. And miniature bubbles trapped in salt preserve actual fossil water, from nearly 300 million years ago. Travel back in time with us to explore the Great Dying.

Permo-Carboniferous strata in the Lodève Basin (France) documented as paleo-loess deposits share characteristics analogous to correlative units in continental basins of eastern equatorial Pangaea (Western Europe). Thick successions of massive red mudstone typically interpreted as playa lake or floodplain deposits document what may have been widespread semi-arid conditions in these low-latitude systems, as well as abundant atmospheric dust, perhaps generated in part in the glaciated alpine terranes of the low-latitude Variscan Belt. Volcanic dust (ash) sourced from contemporaneous explosive and abundant volcanism in Western Europe supplemented this dust flux and could have enhanced the nutrient reactivity of mineral dusts via acidic atmospheric processing. Dust loading was important in the late Paleozoic as continental environments aridified, but the impact of nutrient feedbacks on (marine) organic carbon burial and the reduction of pCO2 is not well constrained. Using quantitative data from the Upper Paleozoic geological record (ie., eruptive recurrence interval, documented volcanic centers) and observed data from modern analogues (gas flux, nutrient load), preliminary results of sensitivity tests using an Earth system model (cGENIE) show that perhaps the impact of volcanic dust flux on biogeochemical cycling during this time was not as important as the fertilization effect caused by non-volcanic mineral dust and/or the elevated iron solubility of atmospheric aerosols (in a volcanically-influenced acidic atmosphere).

Response: commentary: detecting upland glaciation in Earth’s pre-Pleistocene record