Paleosols formed in direct contact with the Earth's atmosphere, so they can record the composition of the atmosphere through weathering processes and products. Herein we critically review a variety of different approaches for reconstructing atmospheric O2 and CO2 over the past three billion years. Paleosols indicate relatively low CO2 over that time, requiring additional greenhouse forcing to overcome the 'faint young Sun' paradox in the Archean and Mesoproterozoic, as well as low O2 levels until the Neoproterozoic. Emerging techniques will revise the history of Earth's atmosphere further and may provide a window into atmospheric evolution on other planets.
Authoritative, accessible, and updated introduction to sedimentary rocks for undergraduate students Sedimentary Petrology provides readers with a concise account of sedimentary rock composition, mineralogy, texture, structure, diagenesis, and depositional environments. The new edition of this classic text incorporates the many technological and analytical advances of the last decade, revealing exciting details of processes such as microbial precipitation, how microporosity is created within mudrocks, and the chemical composition of foraminifera deposits, which can be a key indicator for changing seawater temperature. This fourth edition offers a comprehensive update and expansion of the previous editions with a new set of illustrations, new references, and further reading. The new co-author Stuart Jones has brought his considerable expertise in clastic sedimentology to the rewritten chapters on sandstones and mudrocks. The addition of color images throughout the text will aid students immensely in their studies and petrographic fieldwork. Sample topics covered in Sedimentary Petrology include: Advances in modeling and programming to simulate depositional-diagenetic conditions and controls which support field-lab descriptions and interpretations Ocean acidification and the demise of coral reefs, and the role of the oceans in carbon capture and storage Sedimentary ironstones and iron-formations, sedimentary phosphate deposits, coal, oil shale and petroleum, and cherts and siliceous sediments Limestones, evaporites, volcaniclastic sediments, sandstones, conglomerates, breccias, and the effects of microplastics on marine organisms Aimed at undergraduates in geology and earth science, Sedimentary Petrology is an excellent teaching and learning resource for introductory courses in sedimentary rocks.
Diverse and abundant lipid biomarker assemblages have been reported from a variety of Proterozoic marine environments from the careful analysis of well-preserved rocks and oils. These molecular biosignatures have provided unique insights into the communities and the environmental conditions which characterized the Proterozoic marine biosphere. We summarize some of the major temporal patterns evident in Proterozoic lipid biomarkers found to date, whilst emphasizing the scale of local heterogeneity found within Neoproterozoic oceans from region to region, and their relationship with the evolving ecological, climatic and ocean/atmospheric redox conditions. Short commentaries on a selection of papers published from the last 15 years of biomarker literature are given. The focus here is on key studies, highlighted for further reading, which have helped to better constrain the timing of the ecological expansion of eukaryotes in Proterozoic oceans or which have impacted on our knowledge of the biological sources of Proterozoic biomarkers.
Ancient iron formations - iron and silica-rich chemical sedimentary rocks that formed throughout the Precambrian eons - provide a significant part of the evidence for the modern scientific understanding of palaeoenvironmental conditions in Archaean (4.0–2.5 billion years ago) and Proterozoic (2.5–0.539 billion years ago) times. Despite controversies regarding their formation mechanisms, iron formations are a testament to the influence of the Precambrian biosphere on early ocean chemistry. As many iron formations are pure chemical sediments that reflect the composition of the waters from which they precipitated, they can also serve as nuanced geochemical archives for the study of ancient marine temperatures, redox states, and elemental cycling, if proper care is taken to understand their sedimentological context.
Studies of Sr isotopic composition of thousands of samples of marine sediments and fossils have yielded a curve of 87Sr/86Sr versus age for seawater Sr that extends back to 1 billion years. The ratio has fluctuated with large amplitude during this time period, and because the ratio is always uniform in the oceans globally at any one time, it is useful as a stratigraphic correlation and age-dating tool. The ratio also appears to reflect major tectonic and climatic events in Earth history and hence provides clues as to the causes, timing, and consequences of those events. The seawater 87Sr/86Sr ratio is generally high during periods marked by continent-continent collisions, and lower when continental topography is subdued, and seafloor generation rates are high. There is evidence that major shifts in the seawater ratio can be ascribed to specific orogenic events and correlate with large shifts in global climate.
Magnesium is a major constituent in silicate and carbonate minerals, the hydrosphere and the biosphere. Magnesium is constantly cycled between these reservoirs. Since each of the major planetary reservoirs of magnesium have different magnesium isotope ratios, there is scope to use magnesium isotope ratios to trace 1) the processes that cycle Magnesium at a spatial scales from the entire planet to microscopic and 2) the relative fluxes between these reservoirs. This review summarises some of the key motivations, successes and challenges facing the use of magnesium isotopes to construct a budget of seawater magnesium, present and past.
Explores soil as a nexus for water, chemicals, and biologically coupled nutrient cycling Soil is a narrow but critically important zone on Earth's surface. It is the interface for water and carbon recycling from above and part of the cycling of sediment and rock from below. Hydrogeology, Chemical Weathering, and Soil Formation places chemical weathering and soil formation in its geological, climatological, biological and hydrological perspective. Volume highlights include: The evolution of soils over 3.25 billion years Basic processes contributing to soil formation How chemical weathering and soil formation relate to water and energy fluxes The role of pedogenesis in geomorphology Relationships between climate soils and biota Soils, aeolian deposits, and crusts as geologic dating tools Impacts of land-use change on soils The American Geophysical Union promotes discovery in Earth and space science for the benefit of humanity. Its publications disseminate scientific knowledge and provide resources for researchers, students, and professionals. Find out more about this book from this Q&A with the Editors
Vanadium isotope ratios (51V/50V) have potential to provide information about changes in past ocean oxygen contents. In particular, V isotopes may find utility in tracing variations at non-zero oxygen concentrations because the redox couple that controls V elemental and isotopic abundances in seawater (vanadate-vanadyl) appears to operate around 10M O2. This characteristic sets V isotopes apart from many other metal isotope redox proxies that require more reducing conditions to register significant changes in their isotope budgets. The oxygen abundance sensitivity range of V isotopes suggests that this paleoproxy could be particularly useful in tracing marine oxygenation changes throughout the Phanerozoic and potentially beyond.
Molybdenum (Mo) is a widely used trace metal for investigating redox conditions. However, unanswered questions remain that concentration and bulk isotopic analysis cannot specially answer. Improvements can be made by combining new geochemical techniques to traditional methods of Mo analysis. In this Element, we propose a refinement of Mo geochemistry within aquatic systems, ancient rocks, and modern sediments through molecular geochemistry (systematically combining concentration, isotope ratio, elemental mapping, and speciation analyses). Specifically, to intermediate sulfide concentrations governing Mo behavior below the 'switch-point' and dominant sequestration pathways in low oxygen conditions. The aim of this work is to 1) aid and improve the breadth of Mo paleoproxy interpretations by considering Mo speciation and 2) address outstanding research gaps concerning Mo systematics (cycling, partitioning, sequestration, etc.). The Mo paleoproxy has potential to solve ever complex research questions. By using molecular geochemical recommendations, improved Mo paleoproxy interpretations and reconstruction can be achieved.
Written expressly for undergraduate and graduate geologists, this book focuses on how geochemical principles can be used to solve practical problems. The attention to problem-solving reflects the authors'belief that showing how theory is useful in solving real-life problems is vital for learning. The book gives students a thorough grasp of the basic principles of the subject, balancing the traditional equilibrium perspective and the kinetic viewpoint. The first half of the book considers processes in which temperature and pressure are nearly constant. After introductions to the laws of thermodynamics, to fundamental equations for flow and diffusion, and to solution chemistry, these principles are used to investigate diagenesis, weathering, and natural waters. The second half of the book applies thermodynamics and kinetics to systems undergoing changes in temperature and pressure during magmatism and metamorphism. This revised edition incorporates new geochemical discoveries as examples of processes and pathways, with new chapters on mineral structure and bonding and on organic matter and biomarkers. Each chapter has worked problems, and the authors assume that the student has had a year of college-level chemistry and a year of calculus. Praise for the first edition "A truly modern geochemistry book.... Very well written and quite enjoyable to read.... An excellent basic text for graduate level instruction in geochemistry." --Journal of Geological Education "An up-to-date, broadly conceived introduction to geochemistry.... Given the recent flowering of geochemistry as an interdisciplinary science, and given the extent to which it now draws upon the fundamentals of thermodynamics and kinetics to understand earth and planetary processes, this timely and rigorous [book] is welcome indeed." --Geochimica et Cosmochimica Acta
