John M. Hayes 1940-2017. Father of isotopes in modern and ancient biogeochemical processes, biosynthetic carbon and hydrogen isotope fractionation and compound specific isotope analytical techniques

John Michael Hayes, Professor of chemistry and geology for 26 years at Indiana University (Bloomington) until 1996, then director of the National Ocean Sciences Accelerator Mass Spectrometry facility at Woods Hole Oceanographic Institution and adjunct professor at Harvard University until 2007, died peacefully at his home in Berkeley, California, on February 3rd, 2017

Methane Clumped Isotopes: Progress and Potential for a New Isotopic Tracer

The isotopic composition of methane is of longstanding geochemical interest, with important implications for understanding petroleum systems, atmospheric greenhouse gas concentrations, the global carbon cycle, and life in extreme environments. Recent analytical developments focusing on multiply substituted isotopologues (‘clumped isotopes’) are opening a valuable new window into methane geochemistry. When methane forms in internal isotopic equilibrium, clumped isotopes can provide a direct record of formation temperature, making this property particularly valuable for identifying different methane origins. However, it has also become clear that in certain settings methane clumped isotope measurements record kinetic rather than equilibrium isotope effects. Here we present a substantially expanded dataset of methane clumped isotope analyses, and provide a synthesis of the current interpretive framework for this parameter. In general, clumped isotope measurements indicate plausible formation temperatures for abiotic, thermogenic, and microbial methane in many geological environments, which is encouraging for the further development of this measurement as a geothermometer, and as a tracer for the source of natural gas reservoirs and emissions. We also highlight, however, instances where clumped isotope derived temperatures are higher than expected, and discuss possible factors that could distort equilibrium formation temperature signals. In microbial methane from freshwater ecosystems, in particular, clumped isotope values appear to be controlled by kinetic effects, and may ultimately be useful to study methanogen metabolism

Novel basin modelling concept for simulating deformation from mechanical compaction using level sets

As sedimentation progresses in the formation and evolution of a depositional geologic basin, the rock strata are subject to various stresses. With increasing lithostatic pressure, compressional forces act to compact the porous rock matrix, leading to overpressure buildup, changes in the fluid pore pressure and fluid flow. In the context of petroleum systems modelling, the present study concerns the geometry changes that a compacting basin experiences subject to deposition. The purpose is to track the positions of the rock layer interfaces as compaction occurs. To handle the challenge of potentially large geometry deformations, a new modelling concept is proposed that couples the pore pressure equation with a level set method to determine the movement of lithostratigraphic interfaces. The level set method propagates an interface according to a prescribed speed. The coupling term for the pore pressure and level-set equations consists of this speed function, which is dependent on the compaction law. The two primary features of this approach are the simplicity of the grid and the flexibility of the speed function. A first evaluation of the model concept is presented based on an implementation for one spatial dimension accounting for vertical effective stress. Isothermal conditions with a constant fluid density and viscosity were assumed. The accuracy of the implemented numerical solution for the case of a single stratigraphic unit with a linear compaction law was compared to the available analytical solution [38]. The multi-layer setup and the nonlinear case were tested for plausibility

BENTHIC FORAMINIFERA AND GEOCHEMISTRY ACROSS THE PALEOCENE-EOCENE THERMAL MAXIMUM INTERVAL IN JORDAN

© 2018 Cushman Foundation. All rights reserved. This study presents benthic foraminiferal data from two sedimentary successions across the Paleocene-Eocene Thermal Maximum (PETM) from Jordan. Calcareous nannofossil biozones NP9a, NP9b, and NP10 of latest Paleocene and earliest Eocene age were encountered in proximal (core OS-01) and distal (core OS-28) sites. Lithologically, the investigated sequence consists of marls, shales, and limestones attributed to the Muwaqqar Chalk-Marl Formation and the Urn Rijam Chert Limestone Formation. The δ 13 C org curve records the typical carbon isotope excursion (CIE) and shows four distinctive intervals (pre-CIE, CIE-"core", CIE "recovery", post-CIE) over the entire PETM interval in both cores. In the pre-CIE interval, the more proximal site (OS-01) shows high abundances of Neoeponides duwi co-occurring with an outer neritic Midway-type fauna. The fauna indicates mesoto eutrophic conditions in a middle to outerneritic setting. The more distal site (OS-28) is characterized by outer-neritic to upper-bathyal taxa (e.g., Cibicides pseudoacutus, Gavelinella beccariiformis, Nuttallides truempyî) suggesting well-ventilated, oligo-to mesotrophic seafloor conditions. The earliest Eocene corresponds to the CIE-"core" interval and is marked by a negative δ 13 C org signal, high TOC, low CaCO 3 contents, and near absence of benthic foraminifera. Oxygen deficiency in bottom waters with increased organic flux is the most likely scenario to explain the elevated organic content at the seafloor. The subsequent CIE-"recovery" interval of early Eocene age is marked by a restoration of oxygenated seafloor conditions. The proximal site is characterized by a relatively elevated TOC content and high abundance of Lenticulina spp., Valvulineria scrobiculata and common Anomalinoides zitteli, suggesting moderate oxygen conditions and mesotrophic bottom waters. The distal site is characterized by low TOC content and the presence of Lenticulina spp., Valvulineria scrobiculata, Anomalinoides zitteli and Oridorsalis plummerae, indicating a normalization of the organic flux and moderate oxygen concentrations near the seafloor. The post-CIE interval is marked by low TOC content in both cores. Benthic foraminifera include abundant Anomalinoides zitteli and common Lenticulina spp., Valvulineria scrobiculata, Oridorsalis plummerae, Cibicidoides rigidus, Cibici-doides pharaonis, and Anomalinoides praeacutus in the proximal setting. Mesotrophic conditions and a better ventilation of bottom waters are suggested for this interval. Lenticulina spp., Valvulineria scrobiculata, and Oridorsalis plummerae are also associated with the post-CIE interval in the distal site, suggesting similar mesotrophic conditions with renewed oxygenation in bottom waters.status: publishe

Diagenesis, compaction strain and deformation associated with chert and carbonate concretions in organic‐rich marl and phosphorite; Upper Cretaceous to Eocene, Jordan

This paper presents an integrated petrographic–geochemical–geomechanical study of the growth mechanisms of carbonate and chert concretions observed at outcrop and core from the Upper Cretaceous to Eocene organic-rich carbonate mudrocks, central Jordan. It provides evidence for displacive and replacive concretion growth from the analysis of primary lithological characteristics, compaction strain and deformation structures associated with concretion growth. Concretions were analysed to determine the primary lithological controls on their development and the measurement of strain in the host rock to develop a method for constraining the growth mode and their paragenesis. Concretions exhibit either a replacive or displacive growth mode largely dependent on the original host lithology. Displacive concretions exhibit irregular shapes and semi-fibrous internal structures in contrast to regular shapes and microcrystalline textures observed for replacive concretions. Cement fraction is high in both carbonate concretion types, indicating early formation in high-porosity sediments at shallow burial depths. The strain field around displacive concretions is vertically asymmetrical. Conversely, it is symmetrical with uniform differential compaction for the replacive concretions. Evidence for displacive growth comes from triangular areas of chert at the lateral margins of some carbonate concretions, interpreted as areas of reduced strain. Another indicator is the forced asymmetrical folding of heterolithic host rocks around displacive concretions, with displacive carbonate units separated by trace laminae of the original (chert) beds. Enveloping chert beds exhibit early-formed radial silica fractures with increased aperture size in the areas of maximum curvature. Carbon isotopic signatures of carbonate concretions show a strong correlation between concretion centres and host rock, suggesting a relatively shallow depth (first few tens of metres) of initial growth. Carbonate concretions are interpreted to have formed at shallow depths in the presence of alkaline pore waters rich in dissolved organic carbon in the presence of Mg2+ ions, available organic matter and redox-sensitive metals such as U and Mo. A paragenetic history for the different concretion types is presented