Rock procurement and use during the Middle Neolithic: The macrolithic tools of Dambach-la-Ville (Alsace, France)

A preventive archaeological excavation carried out in 2012 at Dambach-la-Ville (Bas-Rhin, France) uncovered a large Middle Neolithic settlement (Upper Rhine West Bischheim group) dating from the second half of the 5th millennium BCE. The site comprised a very large assemblage of well-dated macrolithic tools (more than 600). Grinding stones, including about roughouts, make up the bulk of the assemblage. Morphological analyses indicate that certain types of use-wear are linked directly to specific types of rock. The variety of rock types is unusual for this period. In fact, contrary to other assemblages from the same period mainly made up of Lower Triassic sandstone (Vosges sandstone; 43%), the tools fashioned on this settlement are mostly made from sedimentary rocks of the Permian and Lower Triassic (possible sources at 15 km), and more rarely from plutonic and metamorphic rocks (possible sources between 5 and 15 km). The use of rough textured rocks such as arkosic sandstone or microconglomerate largely dominating the assemblage. This one also includes a large group of hammerstones from different rock types (sedimentary, plutonic, volcanic and metamorphic). More than half are silicified micritic limestones, a rock that is extremely rare and can be unambiguously traced to a single outcrop about 15 kilometres from the site. This systematic interdisciplinary study of the tools and their petrography offers the opportunity to explore questions regarding provenance and procurement networks in Alsace around 4150 BCE.

Seasonal Variations of Groundwater Chemistry in the Basement and Sedimentary Rocks of Ibadan and Lagos Areas, Southwestern Nigeria

Hydrochemical investigation of forty boreholes drilled on the basement and sedimentary rocks in Ibadan and Lagos metropolis southwestern Nigeria respectively were carried out in order to determine the portability of the groundwater in both areas and to highlight differences in their chemical characters and variations with seasons. Data obtained indicated that the groundwater in Ibadan area is mainly the Na + Ca – HCO­­3type, while that of Lagos is Na + Ca – C1 + SO4 type. The groundwater chemistry reflects weathering of sodic plagioclase feldspars in the basement rocks as well as arkosic sandstone in the sedimentary terrain. The higher chloride (ca. 124.2 mg/L) content of the Lagos water is probably due to salt-water intrusion along the coastal area. Elevated Na+ (58.5-1021.2), Fe2+ (0.3-2.8) and Mn2+ (0.04-2.34) mg/L concentrations, particularly during the dry season, adversely affect the portability of the water from both localities. Apart from making the water unsuitable for irrigation, high Na+ content is considered harmful to persons suffering from cardiac, renal and circulatory diseases. The Fe2+and Mn2+ contents could also create staining problem. It is therefore desirable to remove these elements from the borehole water prior to consumption.

The Pawnee Aquifer, Denver-Julesburg Basin, Northeastern Colorado

A partially defined and largely unexplored confined aquifer in Colorado, Nebraska, and Wyoming is identified regionally through interpretation of geophysical logs, well drilling, coring, petrographic analysis, and GIS interpretation. The aquifer is a fine-grained arkosic sandstone, with thickness ranging up to 1000 ft in some areas. The aquifer represents a significant water resource for ranching and other development in northeastern Colorado and may be a resource for Wyoming, and Nebraska. Nomenclature for this aquifer is suggested. Water wells penetrating the entire aquifer have produced up to 200 gpm. Water quality data is presented including total dissolved solids, boron, and microbial methane.

INTERPRETATION OF MERCURY INJECTION EXPERIMENTS USING A MINIMUM SET OF POROUS DESCRIPTORS DERIVED BY QUANTITATIVE IMAGE ANALYSIS

The porosity exposed in a series of petrographic thin sections from a sub-arkosic sandstone reservoir of the Alwyn area (North Sea) is described by 5 morphological porous descriptors, Pore-Types, obtained by quantitative image analysis procedures and pattern recognition algorithms developed by Ehrlich et al. (1991a). By combining Pore-Type data with capillary pressure curves, we obtain preliminary results showing that in the studied reservoir, the achieved Pore-Types relate better to petrophysics when they are complemented with a sedimentological information.

MIDDLE EAST GEOLOGIC TIME SCALE 2010: Early Cambrian Asfar Sequence

ABSTRACT This paper is the first in a series dedicated to the Phanerozoic Cambrian Period, and Neoproterozoic Ediacaran and Cryogenian periods, as represented in the Middle East Geologic Time Scale (ME GTS, see enclosed Chart). It introduces the term Asfar Sequence to represent a regional Early Cambrian time-rock unit, consisting mainly of continental quartz-rich arkosic sandstone, shale and siltstone, which attain a thickness of at least 750 m in Jordan and more than 700 m in Oman. The term “Asfar”, meaning yellow in Arabic, was chosen because it is the standard color for sandstone in ME GTS. To describe its stratigraphy, four representative formations are reviewed in lexicon format: Salib Arkosic Sandstone of Jordan, Siq Sandstone of Saudi Arabia, Amin Formation of Oman and Lalun Sandstone of Iran. The stratigraphic geometry of the lower boundary of the Sequence varies considerably by locality. In some regions in Iran it is conformable above the shales of the Zaigun Formation. In other regions, such as western Jordan, it is an onlap surface over Proterozoic and/or Lower and Middle Cambrian paleohighs, or a pronounced angular unconformity (e.g. central and southern Saudi Arabia). The paleo-relief represented by the unconformity surface, in many regions, forms a regional peneplain (e.g. central and eastern Jordan) implying erosion; in other paleohigh regions, the Sequence is absent by non-deposition. The age of the base Asfar Sequence is estimated at ca. 530 Ma, based on radiometric data and depositional rates in basinal areas. The top boundary of the Sequence, in Iran, Jordan, and northern and northeastern Saudi Arabia, is represented by a sequence boundary (or its correlative unconformity), above which marine, fine-grained siliciclastics and carbonates of late Early to early Mid-Cambrian age were deposited: Mila Formation in Iran, and Burj Formation in Jordan and Saudi Arabia, implying an age older than ca. 510 Ma in GTS 2004. In Oman, however, continental rather than marine deposition (Miqrat and coeval Mahwis formations) continued above the unconformity in ?Middle Cambrian. For the purpose of regional correlations it is proposed that the Angudan Unconformity of Oman be taken as the name for the basal boundary of the Sequence and the Burj Sequence Boundary for its top.

Geochemical modelling of diagenetic reactions in a sub-arkosic sandstone

A reaction path model was constructed in a bid to simulate diagenesis in the Magnus Sandstone, an Upper Jurassic turbidite reservoir in the Northern North Sea, UKCS. The model, involving a flux of source rock-derived CO2 into an arkosic sandstone, successfully reproduced simultaneous dissolution of detrital K-feldspar and growth of authigenic quartz, ankerite and illite. Generation of CO2 occurred before and during the main phase of oil generation linking source rock maturation with patterns of diagenesis in arkosic sandstones and limiting this type of diagenesis to the earlier stages of oil charging. Independent corroborative evidence for the model is provided by formation water geochemical data, carbon isotope data from ankerite and produced gas phase CO2 and the presence of petroleum inclusions within the mineral cements. The model involves a closed system with respect to relatively insoluble species such as SiO2 and Al2O3 but is an open system with respect to CO2. There are up to seven possible rate-controlling steps including: influx of CO2, dissolution of K-feldspar, precipitation of quartz, ankerite and illite, diffusive transport of SiO2 and Al2O3 from the site of dissolution to the site of precipitation and possibly the rate of influx of Mg2+ and Ca2+. Given the large number of possible controls, and contrary to modern popular belief, the rate of quartz precipitation is thus not always rate limiting.