Thermal Alteration Research Articles

An evaluation of the hydrocarbon potentials of the gboko formation, middle benue trough, nigeria

A total of seventeen (17) rock samples from the Albian Gboko Formation were collected from the quarry of Benue Cement Company for organic geochemical analysis, in order to evaluate its hydrocarbon potential . Total Organic Carbon (TOC) values for the samples ranges from 0.11-0.5wt%. The rock-eval data recorded S2, hydrogen index (HI), Oxygen index (OI), Tmax, and production index (PI) of 0.04-0.11, 25-54, 50-400, 310-4610C, and 0.4-0.6, respectively. These implies that the samples has a fair to poor source rock quality with a type IV kerogen. Optical methods (R0, TAI & VKF) conducted on three selected samples of shales reveal vitrinite reflectance (R0) of 0.77%, 1.11% and 1.54%, while thermal alteration index (TAI) recorded 2.7, 3.3 and 3.7. Kerogen fluorescence indicated weak to non fluorescence. These results infer that the sediments had evolved from oil to gas window due to severe thermal effects . This indicates their potential to generate hydrocarbon gas

Thesis Projects in Forensic Taphonomy

Given the recent growth in the field, some students in forensic anthropology may find it difficult to devise an affordable, suitable, and ideally publishable thesis topic. Taphonomic projects often can fill this role, as many do not require a large budget, are experimental in nature, thus giving students greater control over the data that they will collect, and on topics that have not received large amounts of research. The author presents a list of possible topics primarily in the field of forensic taphonomy and aimed at the MS/MA thesis level, although some proposed projects are larger or could be adapted for a PhD dissertation. The topics include taphonomic effects associated with carnivores, rodents, birds, reptiles, and plants and subaerial weathering; marine environments; thermal alteration; ritual and anatomical activity; cemetery and non-cemetery burials; bone detection; decomposition; and taphonomic procedures. The suggested topics also include factors that may make them more difficult to explore and information on which venues may be the most appropriate. The author hopes to promote taphonomic research in multiple subfields and encourage graduate students to pursue publication of their results.

CT Imaging of a Case Involving Thermal and Sharp Trauma

This case involved a multiagency investigation of a fire in which an adult female and her three young children were found deceased. Anthropological analysis, including imaging using high-resolution computed tomography (CT) scanning, was used to assess skeletal trauma, which involved thermal alterations as well as sharp trauma. Due to fire-related discoloration of the bone, sharp traumas on the cranium of the adult were difficult to appreciate visually, but CT imaging helped to significantly improve visualization of the alterations. CT imaging also facilitated the preservation of the conditions of all four crania, which were appreciably altered by the fire, and for the adult individual reconstructed from multiple fragments. The contributions of various agencies and laboratory analyses, including forensic anthropological imaging, helped contribute to the successful resolution of the case.

Characteristics of light hydrocarbons under the superimposed influence of biodegradation and subsequent thermal maturation

Recently, several large light oil and condensate reservoirs were discovered in the Tarim and Junggar basins (China). In these superimposed petroliferous basins, the early formed palaeo-oil reservoirs experienced complex tectonic movements, resulting in complex secondary alterations (e.g., biodegradation and water washing), known to alter the chemical composition of crude oils. Thus, crude oils previously modified by biodegradation exhibit significantly different generation potential, chemical composition, and timing of generation (in terms of light oils/condensates), during subsequent thermal alteration. To elucidate the influence of biodegradation on crude oil cracking (to form light hydrocarbons), we artificially matured four crude oils of the same origin (with varying degrees of biodegradation) to various maturity levels, using programmed-temperature gold tube closed-system pyrolysis. The yields, molecular parameters, and stable carbon isotope ratios of the light hydrocarbon products derived from the matured oils were analysed and compared. The preferential removal of n-alkanes and branched alkanes during biodegradation significantly reduced the generation potential of light hydrocarbons. Under the superimposed influence of biodegradation and subsequent thermal alteration, referred to as superimposed secondary alteration (SSA), a few hydrocarbon ratios used for oil–oil correlations were severely modified. Most maturity-related light hydrocarbon parameters of the pyrolysis products derived from the biodegraded oils achieved maximum values at a lower maturity (Easy%Ro) than that observed for non-biodegraded crude oil. At 0.5–1.4 Easy%Ro, SSA caused the depletion of 13C in most light hydrocarbons, due to an increased sourcing from the biodegradation-resistant fractions of the oil. Such carbon isotopic differences decreased with increasing maturity.

Carbon isotopic composition and organic petrography of thermally metamorphosed Antarctic coal: Implications for evaluation of δ13Corg excursions in paleo-atmospheric reconstruction

Large, globally documented negative δ13C excursions that occur across the Permian-Triassic transition are thought to represent the isotopic fingerprint of considerable releases of isotopically light carbon into the atmosphere, with the largest of these excursions (as much as −22.2‰) measured in bulk organic matter in coals and carbonaceous shales from Antarctica. Previous studies have attributed the carbon isotopic excursion (CIE) at the Permian–Triassic boundary to the release of CH4 from organic-rich rocks intruded by dikes and sills associated with the Siberian Traps flood basalts (Russia) and Longwood-Bluff (New Zealand) intrusions. However, any assessment of paleoatmospheric conditions based on this or other δ13Corg excursions must consider the multiple controls on isotopic composition, including maceral content and post-depositional diagenetic and maturation processes. Permian-age coal seams and associated sediments in Antarctica were extensively altered after burial by localized high heat flow and, in some cases, by contact metamorphism associated with Jurassic dikes and sills. Levels of organic maturation reach anthracite, meta-anthracite, and even graphite; such intense thermal alteration had the potential to change the carbon isotopic composition of the bulk organic matter (δ13Corg). To evaluate the Permian–Triassic isotopic excursion in Antarctica, it is important to understand the inherent variability in δ13Corg in Permian-age coal and organic-rich sedimentary rocks prior to the CIE; thus, 128 samples representing pre-boundary coals and shales were selected from the United States Polar Rock Repository for analysis. Petrographic (maceral analysis and vitrinite reflectance), geochemical (C, H, N), and carbon isotopic analyses were performed. Based on the presence of coarse-grained circular and fine-grained lenticular mosaic in the anisotropic cokes found in samples in close proximity to intrusions, the rank of the samples prior to intrusion is estimated to have been medium volatile bituminous (∼1.2% Rmax). These highly altered coals and cokes can have random vitrinite reflectances (Rr) exceeding 6%. Subsequent to intrusion, alteration beyond the contact aureoles continued due to high heat flow, producing high rank coals with Rr > 2%. Values of δ13Corg range between −26.5 and –21.1‰ (5.4‰ difference). Significant relationships (at the 1 and 5% levels) exist between δ13Corg and the level of organic maturity, organic carbon (Corg) content (i.e., size of the carbon reservoir), and total inertinite content, suggesting variability due to these factors should be considered when assessing isotopic excursions and interpretation of Permian-Triassic atmospheric conditions. These findings highlight the importance of incorporating organic petrography into δ13Corg studies.

Potential analytical interferences when measuring Tmax during temperature programmed pyrolysis of hydrothermally altered volcanoclastic sediment

AbstractThe temperature of maximum pyrolysis yield (known as Tmax) can be used to determine the level of thermal alteration in sedimentary organic matter; higher Tmax values represent higher thermal alteration. Tmax is commonly measured on petroleum source rocks or similar sediments with high organic carbon contents. It would be desirable to measure the Tmax of volcanic sediments because they can have complex patterns of thermal alteration. However, volcanic sediments often have low total organic carbon contents and consequently are susceptible to analytical interferences. Despite this, it can be shown that meaningful Tmax measurements can still be made in sediment with organic carbon contents as low as 0.2% and that interference caused by bitumen or ionizable salts can be mitigated by solvent extraction and rinsing with water. Thus, it is reasonable to use temperature programmed pyrolysis to assess levels of thermal alteration in even low total organic carbon volcanoclastic sediments.

Paragenesis of an Ediacaran carbonate-platform phosphorite: Constraints from optical petrography and texture-specific clumped isotope paleothermometry

The Salitre Formation is comprised of several hundred meters of primarily carbonate rocks, representing sedimentation in an intracratonic foreland basin during the Ediacaran Period (c. 600–550 Ma). The lowermost member of the Salitre Formation contains sedimentary phosphorite deposits, in which the dominant phosphate-bearing phase is cryptocrystalline carbonate-rich fluorapatite (CFA) cement. These CFA cements occur exclusively associated with digitate stromatolite buildups, decimeters to meters in vertical and lateral scale, which interfinger with cross-stratified grainstone. Notably, there are also non-phosphatic stromatolite buildups in close proximity to the phosphatic, in the same depositional facies. This implies that the mechanisms that control the distribution of phosphate cement development versus carbonate cement development are not driven by the location of depositional facies within the architecture of the Salitre paleobasin. Other models which could explain the distribution and style of phosphate mineralization there include: (1) differential diagenesis involving diagenetic fluids which infiltrate one lithofacies more pervasively than another to effect the replacement of primary cement mineralogies according to microtextural differences, and (2) differences in primary porewater chemistries over minute spatial scales which result in the formation of different primary cement phases. In this study, we present paired petrographic thin sections and novel measurements of ∆47, δ13Cmineral, and δ18Omineral. We provide a paragenetic framework for phosphatic and non-phosphatic lithofacies of the Salitre Formation which constrains the thermal and chemical alteration history of CFA, calcite, and dolomite cements. Structural carbonate in the CFA and calcite cements co-occurring in partially phosphatic digitate stromatolite buildups and adjacent carbonate grainstone generally yield similar δ13Cmineral values (0–5 ‰ VPDB), δ18Omineral values (−5–0 ‰ VPDB), as well as similar ∆47 temperatures (90–115 °C) and calculated δ18Owater (10–19 ‰ VSMOW), supporting a scenario in which CFA and calcite formed and then both recrystallized in equilibrium with the same diagenetic fluids under low water–rock ratio conditions at depth. Dolomite cements yielded similar δ18Omineral values to CFA and calcite, and similar to slightly higher temperatures (85–150 °C) — supporting a scenario in which dolomite cements were recrystallized in equilibrium with a different, and isotopically lighter, generation of fluids. Given the general absence of pervasive, fabric-destructive replacement is scarce, these geochemical data do not support later stage, differential diagenesis as a mechanism for controlling the distribution of phosphatic versus non-phosphatic cements. Rather, primary differences in porewater biogeochemistry seem the likeliest explanation. This is important, as it implies that the ecology of the Ediacaran seafloor controlled the style and quality of mineralization observed today, and that the presence of CFA cements in these rocks represents a unique taphonomic window for select microbial communities.

Thermal Modeling of Patient-Specific Breast Cancer With Physics-Based Artificial Intelligence

AbstractBreast cancer is a prevalent form of cancer among women. It is associated with increased heat generation due to higher metabolism in the tumor and increased blood vessels resulting from angiogenesis. The thermal alterations result in a change in the breast surface temperature profile. Infrared imaging is an FDA-approved adjunctive to mammography, which employs the surface temperature alterations in detecting cancer. To apply infrared imaging in clinical settings, it is necessary to develop effective techniques to model the relation between the tumor characteristics and the breast surface temperatures. The present work describes the thermal modeling of breast cancer with physics-informed neural networks. Losses are assigned to random points in the domain based on the boundary conditions and governing equations that should be satisfied. The Adam optimizer in TensorFlow minimizes the losses to find the temperature field or thermal conductivity that satisfies the boundary conditions and the bioheat equation. Backpropagation computes the derivatives in the bioheat equation. Analyses of the three patient-specific cases show that the machine-learning model accurately reproduces the thermal behavior given by ansys-fluent simulation. Also, good agreement between the model prediction and the infrared images is observed. Moreover, the neural network accurately recovers the thermal conductivity within 6.5% relative error.

Application of physical simulation to evaluate the impact of teeming method and rate on axial zone formation of large ingots

The article presents the results of evaluation of the impact of teeming method and rate on solidification and formation of the axial zone of large ingots. The research is based on a physical simulation. With this aim a laboratory-scale plant (a crystallization mould) was designed and built which enabled to visualize and monitor solidification and structural formation of the model ingots. Sodium thiosulphate (crystal hyposulphite) – Na2S2O3·5H2O was used as a modeling solution. Matching of the processes in the model and in real industrial conditions of ingot teeming was assessed with similarity criteria obtained on the basis of the dimension theory with consideration of the physical and chemical processes in the ingot during its teeming and crystallization. Two methods – downhill casting and uphill casting – were used to teem the melt into the mould. During teeming the geometry and technological parameters of the model ingots remained unchanged while the teeming rate was altered. Length and medium width of the model ingot axial zone were measured. The thermal profiling of the surface of the mould model was monitored over the entire period of solidification to evaluate the thermal field alteration while the ingot was teemed and crystallized. Thermal imaging processing made it possible to observe temperature changes of the surface of the model mould from top to bottom for downhill cast ingots teemed at different rates. The results obtained demonstrate that teeming rate has a noticeable impact on the axial zone length. It was established that a decreased rate leads to an increased directionality of crystallization and improvement of the ingot axial zone structure.

Fast and Slow Laser-Stimulated Degradation of Mn-Doped Li4Ti5O12

Lithium titanate (Li4Ti5O12) is a commercial anode material used for high-power and long-lifespan lithium batteries. The key drawback of this material is its low electronic conductivity. Although doping is commonly used to solve this problem, the introduction of dopants also diminished lattice stability. In this work, we studied fast and slow laser-induced degradation processes of single Mn-doped lithium titanate particles and proposed a physicochemical model of their degradation mechanism. We suppose that the preferable route of LTO alteration is the formation of amorphous phases rather than crystalline decomposition products. Our results may be useful for not only developing a nondestructive characterization tool utilizing Raman spectroscopy but also for understanding other degradation processes, including thermal alteration and structural changes caused by the intercalation/deintercalation cycles of lithium ions.

Assessing the effects of irrigation and hydropower dams on river communities using taxonomic and multiple trait-based approaches

Rivers and streams have suffered multiple transformations to attend the increasing water demands worldwide. Among these, dams and reservoirs cause some of the most severe ecological impacts on rivers, altering the river flow and thermal regimens, nutrient and sediment fluxes, and network connectivity. However, in the context of the different dam purposes and operational schemes, knowledge of the ecological impacts on the riverine biota is still limited. In this study, our main goal was to assess dam-related effects (e.g. hydrological and thermal alteration, water quality changes) on river biological communities and identify key ecological responses associated to flow regulation. To achieve this, diatom, macroinvertebrate, and fish communities were surveyed in control (n = 8) and impacted (n = 11) streams (i.e. downstream of irrigation or hydropower dams) along three consecutive years. The study design aimed at minimising the environmental variability among control and impacts using previously established hydrological classifications. This allowed focusing primarily on the effects of dam operation schemes. In addition to traditional biotic indices based on the composition and structure of these communities, we assessed community-level responses using trait-based analyses with multivariate and fourth-corner analyses. The ecological changes varied with dam purpose and, in general, favoured disturbance-tolerant traits. Common biotic indices did not consistently respond to dam uses; trait-based analyses, in contrast, provided a more detailed picture of the dam-related effects on the studied river communities, with macroinvertebrate traits showing the strongest correlations to dam-related hydrological and physico-chemical variables, followed by diatoms and fish. Changes in the biological communities downstream of irrigation dams were mostly related to the inversion of the seasonal flow regimes (e.g. increases in the summer flows and magnitude of low flow extremes; decreases in the winter flows and in the frequency and magnitude of extreme high flow events) and the reduction of nutrient concentration. These changes favoured planktonic diatoms, macroinvertebrates with short life cycles and small body sizes, and fish feeding on the water column. Hydropower dams elevated significantly the rate of flow change and water temperature, favouring low profile adnate diatoms, multivoltine and passively dispersed macroinvertebrates, and scrapers. The key relationships identified in our study are useful to underpin river biodiversity conservation strategies and to set future research directions aiming at reducing the negative effects of dam operation schemes.

Burial and thermal history of the eastern transform boundary of the central western carpathians based on 1D basin modeling

This paper represents the first data on the thermal and burial history of Mesozoic and Cenozoic sedimentary rocks in the Maruszyna IG-1 deep borehole from the transpressional shear zone of the Western Carpathians. Representative, organic-rich mudstone and claystone samples were selected to determine thermal maturity using mean random vitrinite reflectance (Ro) and thermal alteration index (TAI) data. The reconstruction of the thermal history of fold-and-thrust units was carried out using 1D modeling. This study uniquely distinguishes various thermal maturity levels in the deep profile determined by strata repetition, different absorption of clay and carbonate mineral settings and structural thermal changes in humic particles and palynomorphs. Reflectance of autochthonous vitrinite varies from 0.77 to 1.95% indicating thermally mature to overmature organic matter. Different subsidence-uplift models were tested during modeling in order to find a plausible scenario of tectonic development and heat flow history. The thermal maturity of the individual thrust sheets was modeled separately allowing their individual thermal histories to be investigated before and after the main and final thrusting phase. The best-calibrated scenario assumes a low paleo heat flow ranging from 45 to 54 mW.m-2, affecting the eastern part of the Western Carpathians. The maximum temperature which lead to maturation of the organic matter seems to be related to its successive burial during Cretaceous due to compressional deformation. Individual thrust sheets reached thermal maturity prior to the final thrusting phase. The overthrust was accompanied by 3000–4000 m burial/erosion resulting in different thermal pathways during wedge growth.

Cremations and Pyrotechnologies among the Prehispanic Inhabitants of Cerro de Trincheras, Northern Mexico

Using data from several well-preserved pyres, which are rarely found well preserved in the southwestern United States and northern Mexico, we examine cremation customs and their associated pyrotechnologies at the site of Cerro de Trincheras in northern Sonora, Mexico, from AD 1300 to 1450/1500. We explore variations in pyre construction and use, thermal alterations of the deceased, the deceased individuals’ biological profiles, the performance of mortuary rituals, and the sensorial experiences of both the mourners and the wider Cerro de Trincheras community. The residents of the site were masters of the pyrotechnologies associated with cremations, making efficient pyres for the deceased and maximizing their resources. The group also created transformative funeral rituals that may have facilitated and mediated a wide range of emotional responses toward their deceased.

Stratigrafie sedimentů doprovázejících vulkanity těšínitové asociace u Bruzovic

The rocks of the teschenite association form smaller scattered occurrences in the upper part of the Hradiště Formation of the Silesian Unit. The age of the igneous rocks corresponds to Berriasian to Barremian (Menčík et al. 1983). The teschenite association includes a relatively heterogeneous group of rocks with variable abundances of felsic and mafic minerals. Three outcrops of the teschenite association rocks (both typical teschenites and strongly altered ultramafic types) embedded in non- volcanic sediments were studied in the bed of the Pazderůvka River between Bruzovice and Žermanice (Bz1, Bz2, and Bz3; Fig. 1). At Bz1 and Bz2 outcrops, bodies of teschenite are hosted by sedimentary rocks affected by caustic metamorphism. The volcanic rocks at Bz3 are represented by strongly altered, markedly clayey dark green rocks with a macroscopically apparent high proportion of dark micas and pyroxenes. The bedrock of the outcrop is composed of calcareous claystone, limestone, and sandy limestone, likely representing Těšín Limestones. The phase composition of the volcanic rocks from the Bz1 and Bz2 localities is to a certain extent similar, which indicates that the same body was observed at both localities. Macroscopically, the rocks are medium- to coarse-grained with a variable proportion of dark minerals, indicating internal differentiation of the body. The very high proportions of natrolite (up to about 35 %, up to 54 % in the leucocratic type) are particularly notable. The volcanic rocks from the Bz3 locality are quite different. Their composition corresponds to strongly argilitised mafic rocks (and their volcaniclastic derivates), containing more than 50 % of clay component with a dominance of smectite, as documented by X-ray diffraction data. As for the primary components, pyroxene, biotite, plagioclase, and accessory amphibole were detected. Calcareous dinoflagellate cysts Cadosina semiradiata fusca, Colomisphaera vogleri, and Cadosina semiradiata representing the lower Valanginian to upper Barremian were identified in polished sections of the calcareous rock. Non-calcareous dinoflagellate cysts in Bz1 and Bz2 samples are almost black, reflecting the strong thermal effects of the teschenite intrusion at the contact with with the sediments. The dinoflagellate cysts in the Bz3 outcrop are very well preserved with no evidence of thermal alteration. The overlying body of the volcanic rock can be therefore considered as effusive. Circulodinium vermiculatum, Cymososphaeridium validum, Muderongia tabulata, Oligosphaeridium albertense, Oligosphaeridium asterigerum, Pseudoceratium pelliferum, Systematophora palmula from the Bz3 outcrop can be considered as stratigraphically significant. Based on the first occurrence of C. validum and the last occurrences of Circulodinium vermiculatum and Systematophora palmula, Leereveld (1995) delineates a dinoflagellate zone of Cymososphaeridium validum which represents the upper Valanginian to the lowermost Hauterivian. The composition of palynofacies, in which palynomorphs predominate, is characteristic of a distal well-oxygenated shelf.

The Effects of Experimental Whole-Body Burning on Histological Age-at-Death Estimation from Human Cortical Bone and Dental Cementum.

Whole-body donations (n = 6) were placed in various experimental fire-death scenarios to understand the histological effects of thermal alteration on bones and teeth. Midshaft samples of the femur, 6th rib, and metatarsal were removed from each donor pre- and post-burning to examine histomorphometric differences and test established age-at-death estimation methods. Dental samples were taken post-burning to test the applicability of dental cementum analysis for age-at-death estimation. Significant differences in osteon area or Haversian canal area between some pre- and post-burn samples were found although no patterns related to temperature or element were observable. The femoral age estimates across pre- and post-burn samples were 91% accurate across all donors. The point age estimates from the ribs compared to known age were significantly different (t(10) = 6.88, p < 0.001) with an average difference of -18.53 years. Dental age estimates of post-burn samples were not significantly different from the known donor age (t(3) = -0.74, p = 0.512) with an average difference of -3.96 years. Overall, the results of this study show that thermally altered remains can be used for histologic age-at-death analysis of cortical bone and dental cementum, within certain burning parameters.

Using Fire for Woodworking: An Experimental Exploration of Use-Wear on Lithic Tools

ABSTRACT Throughout prehistoric times, woodworking was an essential activity. We know this because of the existence of preserved wooden objects, as well as the use-wear traces recorded on lithic tools. In general terms, functional studies and experimental programs have aimed to analyze and understand the use-wear traces generated by green and dry wood. However, some of the wood remains preserved across time show signs of thermal alteration caused by fire. For this reason, we have carried out an experimental program in which green, dry and thermoaltered wood have been worked in order to study the traces generated on the lithic tools. The results show significant differences between the use-wear traces generated by green and dry woods, and thermally altered wood. This indicates that it would be possible to recognize signs of work with thermoaltered wood on archaeological lithic tools and, therefore, to better understand the working processes of past populations.

An evaluation of the infrared 630 cm−1 OH libration band in bone mineral as evidence of fire in the archaeological record

FTIR spectroscopy has played an important role in attempts to understand the use of fire in prehistory, particularly through the identification of heated bone. The presence of the OH libration band at ca. 630 cm−1 in the FTIR spectrum of archaeological bone has been assumed to be indicative of bone that has been altered by fire. However, no definitive research has explored what the effects of heating variables may be on the appearance of this band. This paper studied the nature of heated bone, with the understanding that the FTIR 630 cm−1 band is the result of the formation of pure hydroxyapatite through the loss of carbonates from the bone mineral, carbonated hydroxyapatite. A set of experiments was designed to determine the impact of temperature, duration, and bone size on the appearance of the 630 cm−1 band: using samples of cortical bone from micro- and macrofauna, heating experiments were carried out to explore the appearance and change in the OH libration band. Results showed that this band appeared in bone samples heated to temperatures above 537 °C, and demonstrated that microfauna were more sensitive to thermal alteration. Bones heated in reducing conditions and bones which are fluoridated do not express the 630 cm−1 OH libration band, therefore FTIR is underrepresenting burning in the archaeological record. A quantitative method “HATI” was created to objectively assess whether a bone sample has been heated above 537 °C.

Mercury loss and isotope fractionation during thermal maturation of organic-rich mudrocks

Mercury (Hg) concentration and isotopic composition of organic-rich sedimentary rocks have been widely used as proxies to track ancient volcanism and associated environmental perturbations. However, interpretation of the Hg data is based on the assumption that the thermal maturity of the sedimentary rocks has limited effects on Hg abundance and isotopic composition, which is yet to be evaluated. Here we conduct closed-system anhydrous pyrolysis experiments to investigate the changes of Hg concentration and isotope composition during the thermal mature process, using both marine and lacustrine mudrocks. A siliceous shale section (Luocun, China) with heterogeneous thermal maturity caused by dike intrusion was also analyzed for Hg. Significant Hg loss (over 80%), with variations of δ202Hg (by 0.3 to 0.7‰) but small variations of Δ199Hg (by <0.1 to 0.36‰), were observed during the experiment. The Hg isotopic variation may be caused by the release of isotopically distinct Hg in different mineral phases at different temperatures. Samples from the Luocun section have anomalously low Hg and Hg/TOC values, due to thermal maturity. These findings suggest that (1) thermal maturation of organic-rich shales may be an important factor in distribution of Hg in sediments, and (2) the use of Hg, Hg/TOC and Hg isotopes proxies for paleoclimate and paleoceanography reconstruction should be applied in caution in substrates that may have experienced significant thermal alteration, especially if sill/dike intrusions were present that may cause large varieties of thermal maturity within sedimentary sections.

Thermo-microstratigraphy of shells reveals invisible fire use and possible cooking in the archaeological record

The archaeological visibility of hearths related to shellfish cooking methods is limited, particularly in pre-ceramic shell midden contexts. Important evidence for use of fire is the thermal alteration of components, namely the identification of burnt shells. Mollusk shells that mineralize as aragonite are particularly indicative of burning due to the conversion of aragonite to calcite through recrystallization at known temperature thresholds. However, roasting temperatures needed to open bivalves, do not necessarily cause thermal alterations in the cooked shell. This complicates the significance of shell mineralogy by itself to recognize cooking, and discerning pre-depositional from in situ heating. To distinguish between cooking and burning, we combine micromorphological analyses with microscopic Fourier transformed infrared spectroscopy to investigate mineralogical thermo-alterations alongside microstratigraphic formation studies. Experimentally heated specimens of Cerastoderma edule and Scrobicularia plana are used to identify the temperature thresholds of biogenic calcium carbonate phase alteration at the micro-scale. These results are then used to interpret mineral alterations in deposits from two Mesolithic shell midden contexts from Portugal. Micro-stratigraphically controlled mineralogy proved to be particularly useful to distinguish between pre-depositional heating from in situ heating, configuring a novel methodology for recognition of traces of cooking shellfish versus traces of fire used for other purposes. Mapping the mineral phase conversion at a micro stratigraphic scale also allows us to identify instances of in situ fire events that were invisible macroscopically. This combined microstratigraphic and mineralogical methodology considerably increases our capacity of deciphering intricate shell midden stratigraphy and occupational events.

Deuterium Isotope Fractionation of Polycyclic Aromatic Hydrocarbons in Meteorites as an Indicator of Interstellar/Protosolar Processing History.

The stable isotope composition of soluble and insoluble organic compounds in carbonaceous chondrites can be used to determine the provenance of organic molecules in space. Deuterium enrichment in meteoritic organics could be a residual signal of synthetic reactions occurring in the cold interstellar medium or an indicator of hydrothermal parent-body reactions. δD values have been measured in grains and bulk samples for a wide range of meteorites; however, these reservoirs are highly variable and may have experienced fractionation during thermal and/or aqueous alteration. Among the plethora of organic compounds in meteorites are polycyclic aromatic hydrocarbons (PAHs), which are stable and abundant in carbonaceous chondrites, and their δD ratio may preserve evidence about their formation environment as well as the influence of parent-body processes. This study tests hypotheses about the potential links between PAHs-deuteration concentrations and their formation conditions by examining the δD ratio of PAHs in three CM carbonaceous chondrites representing an aqueous alteration gradient. We use deuterium enrichments in soluble 2–5-ring PAHs as an indicator of either photon-driven deuteration due to unimolecular photodissociation in warm regions of space, gas-phase ion–molecule reactions in cold interstellar regions of space, or UV photolysis in ices. We also test hypothesized reaction pathways during parent-body processing that differ between partially and fully aromatized PAHs. New methodological approaches were developed to extract small, volatile PAHs without fractionation. Our results suggest that meteoritic PAHs could have formed through reactions in cold regions, with possible overprinting of deuterium enrichment during aqueous parent-body alteration, but the data could not rule out PAH alteration in icy mantles as well.