Cutmark systematics: Analyzing morphometrics and spatial patterning at Palangana

Cutmarks have played an important role in addressing whether our hominid ancestors were hunters or scavengers, describing ritual modification of human bone, defining the origin of metallurgy, and highlighting the diversity of prehistoric butchering behavior. The widespread occurrence of cutmarks on animal bones and their variability allows archaeologists to use this kind of evidence to address a broad range of questions. One goal in examining cutmark diversity is to identify diagnostic cutmarks of prehistoric butchering, processing, and consuming behaviors. Linking cutmarks to specific activities allows us to test fine-grained hypotheses concerning the nature of an archaeological site, and to do this a systematic method for addressing variability in both the appearance and anatomical position of cutmarks is essential. An analysis of caribou bones collected by Lewis Binford from the Palangana site in Alaska is used to build and test a diagnostic cutmark classification using their morphometric and spatial properties. This case study demonstrates that cutmarks can be used to simultaneously address large-scale anthropological questions and reveal intra-site behavioral variability in the archaeological record.     

Quartz recrystallization and fluid flow during contact metamorphism: a cathodoluminescence study

Cathodoluminescence (CL) images of quartz grains in the Appin Quartzite from the aureole of the Ballachulish Igneous Complex (Scotland) reveal a textural complexity that we interpret in the light of published models of the evolution of the contact aureole. Five distinct generations of quartz can be discriminated in CL. The oldest of these is a dark luminescing mottled quartz (Type 1 quartz) that occurs in the centres of pre‐existing grains, in samples collected from 210 m to 0.1 m from the contact. Dark mottled quartz is interpreted to be unrecrystallized material and has a regional metamorphic CL spectral signature. The onset of contact metamorphism resulted in grain growth visible in CL as a series of fine‐scale alternating bands of bright and dark luminescing material (Type 2 quartz), which we attribute to infiltration of repeated pulses of small amounts of H₂O along grain boundaries. Close to the intrusion, a subgrain‐scale network of intragranular, bright luminescing features could have resulted from either intragranular microcrack‐controlled infiltration of H₂O at high temperatures or intergranular cracking followed by grain growth (Type 3 quartz). Broad bands of bright material on grain boundaries in samples that are inferred to have undergone partial melting are interpreted as quartz crystallized from the melt phase (Type 4 quartz). The final stage in the textural development is marked by a series of aligned fractures, detected in CL by nonluminescing material (Type 5 quartz) and corresponding closely with trails of fluid inclusions. These fractures are interpreted as the pathways for late‐stage, low‐temperature, retrogressive fluids.     

The effect of pore size on cementation in porous rocks

Halite cementation in porous sandstone from the Lower Triassic Bunter Formation in North‐West Germany has been studied using measurements of porosity and permeability, before and after salt extraction, as well as from petrographic observations. The results show that in cemented sandstones there is a clear tendency for the larger pores to be halite‐filled while the smaller pores, which are responsible for the residual porosity, are left empty. Observations on cemented ‘pin‐stripe’ aeolian sandstones, in which laminations of fine and coarser sand grains alternate on a millimetre scale, indicate that this selective cementation is not due to differences in the brine composition in the pores. The implication, which is also supported by other observations, is that fluids in small pores can maintain a higher supersaturation with respect to crystallization.     

FT-IR measurements of petroleum fluid inclusions: methane, n-alkanes and carbon dioxide quantitative analysis

A recent advancement in petroleum geochemistry is to model fossil oil composition using microthermometric and volumetric data acquired from individual fluid inclusion analysis. Fourier transform infrared (FT‐IR) microspectroscopy can record compositional information related to gas (CH₄ and CO₂) and alkane contents of petroleum inclusions. In this study, a quantitative procedure for FT‐IR microspectrometry has been developed to obtain, from individual fluid inclusions, mol percentage concentrations of methane, alkanes and carbon dioxide as constraints to thermodynamic modelling. A petroleum inclusion in a sample from the Québec City Promontory nappe area was used as standard to record a reference spectrum of methane. The analytical procedure is based on the measurement of CH₄/alkane and CH₄/CO₂ band area ratios. CH₄/alkane infrared band area ratio is obtained after spectral subtraction of the reference methane spectrum. This area ratio, affected by absolute absorption intensities of methane, methyl and methylene, provides a molar CH₄/alkane ratio. Methyl/methylene ratio (CH₂/CH₃) ratio is obtained following procedures established in previous work. CO₂/CH₄ concentration ratio is estimated from relative absolute absorption intensities. Application to natural inclusions from different environments shows good correlation between FT‐IR quantification and PIT (petroleum inclusion thermodynamic) modelling.     

New analytical methods for comparing bone fracture angles: A controlled study of hammerstone and hyena (Crocuta crocuta) long bone breakage

Accurate interpretation of the cause and timing of bone breakage is essential for understanding the archaeological record. However, many variables potentially influencing break morphology have yet to be systematically explored. Focusing primarily on hammerstone breakage, we introduce new analytical methods for comparing fracture angles using the absolute values of the angle from 90°. We systematically control for intrinsic variables such as taxon, skeletal element, limb portion and skeletal age. We also compare experimental assemblages of femora broken by hammerstone and spotted hyena (Crocuta crocuta). We show that fracture angles are influenced by breakage plane, skeletal element and limb portion. While the latter two have been suggested before, this is the first time the differences have been quantified. We suggest that researchers stratify their assemblages by these variables if they are using fracture angles in analyses. At the assemblage level, hyenas created more oblique fracture angles on oblique breaks than did hammerstones.     

Downward hydrocarbon migration predicted from numerical modeling of fluid overpressure in the Paleozoic Anticosti Basin,eastern Canada

The Anticosti Basin is a large Paleozoic basin in eastern Canada where potential source and reservoir rocks have been identified but no economic hydrocarbon reservoirs have been found. Potential source rocks of the Upper Ordovician Macasty Formation overlie carbonates of the Middle Ordovician Mingan Formation, which are underlain by dolostones of the Lower Ordovician Romaine Formation. These carbonates have been subjected to dissolution and dolomitization and are potential hydrocarbon reservoirs. Numerical simulations of fluid‐overpressure development related to sediment compaction and hydrocarbon generation were carried out to investigate whether hydrocarbons generated in the Macasty Formation could migrate downward into the underlying Mingan and Romaine formations. The modeling results indicate that, in the central part of the basin, maximum fluid overpressures developed above the Macasty Formation due to rapid sedimentation. This overpressured core dissipated gradually with time, but the overpressure pattern (i.e. maximum overpressure above source rock) was maintained during the generation of oil and gas. The downward impelling force associated with fluid‐overpressure gradients in the central part of the basin was stronger than the buoyancy force for oil, whereas the buoyancy force for gas and for oil generated in the later stage of the basin is stronger than the overpressure‐related force. Based on these results, it is proposed that oil generated from the Macasty Formation in the central part of the basin first moved downward into the Mingan and Romaine formations, and then migrated laterally up‐dip toward the basin margin, whereas gas throughout the basin and oil generated in the northern part of the basin generally moved upward. Consequently, gas reservoirs are predicted to occur in the upper part of the basin, whereas oil reservoirs are more likely to be found in the strata below the source rocks. Geofluids (2010) 10 , 334–350