It all comes out in the wash: Actualistic petrofacies modeling of temper provenance,Tonto Basin,Arizona, USA

Prehistoric potters frequently tempered their pottery with sand, the provenance of which can be established petrographically. In the Tonto Basin of central Arizona, the bedrock geology is highly variable, giving rise to geographically unique sands. Zones of sands with similar compositions can be modeled at an archaeologically relevant scale. Here we use the actualistic petrofacies concept, the Gazzi–Dickinson point‐counting technique, and multivariate statistics to create a petrofacies model, then apply it to sand‐tempered utilitarian pottery recovered from three Tonto Basin project areas. Data analysis reveals strong temporal and spatial ceramic production and consumption patterns. Production of pottery for exchange was established in at least one petrofacies ca. A.D. 600–950, with increasing specialization through time. By ca. A.D. 1150, corrugated wares had been added, and specialized production by ware was established in two petrofacies. Provenance evidence suggests different regional affiliations for groups in different parts of the basin. © 2001 John Wiley & Sons, Inc.     

The effect of nested grid sampling on the parameter estimation of a spatial Gompertz diffusion

This paper evaluates the effects of using data observed on regular nested grids on the parameter estimates of a two-parameter Gompertz diffusion model. This new spatial diffusion process represents a technically more complex stage of Gompertz modeling. Firstly, the diffusion model is introduced through an appropriate transformation of a two-parameter Gaussian diffusion process. Probabilistic characteristics of this model, such as the transition densities and the trend functions, are obtained. Secondly, statistical estimation is considered using data obtained on a regular or irregular grid; the explicit expression of the likelihood equations and the parameter estimators are given for regular grids. Finally, a simulation experiment illustrates the results of this paper.     

Hydrocarbons generation potential of the Jurassic–Lower Cretaceous Formation, Ajeel field, Iraq

Organic geochemical analysis and palynological studies of the organic matters of subsurface Jurassic and Lower Cretaceous Formations for two wells in Ajeel oil field, north Iraq showed evidences for hydrocarbon generation potential especially for the most prolific source rocks Chia Gara and Sargelu Formations. These analyses include age assessment of Upper Jurassic (Tithonian) to Lower Cretaceous (Berriasian) age and Middle Jurassic (Bathonian–Tithonian) age for Chia Gara and Sargelu Formations, respectively, based on assemblages of mainly dinoflagellate cyst constituents. Rock-Eval pyrolysis have indicated high total organic carbon (TOC) content of up to 18.5 wt%, kerogen type II with hydrogen index of up to 415 mg HC/g TOC, petroleum potential of 0.70–55.56 kg hydrocarbon from each ton of rocks and mature organic matter of maximum temperature reached (T_max) range between 430 and 440 °C for Chia Gara Formation, while Sargelu Formation are of TOC up to 16 wt% TOC, Kerogen type II with hydrogen index of 386 mg HC/g TOC, petroleum potential of 1.0–50.90 kg hydrocarbon from each ton of rocks, and mature organic matter of T_max range between 430 and 450 °C. Qualitative studies are done in this study by textural microscopy used in assessing amorphous organic matter for palynofacies type belonging to kerogen type A which contain brazinophyte algae, Tasmanites, and foraminifera test linings, as well as the dinoflagellate cysts and spores, deposited in dysoxic–anoxic environment for Chia Gara Formation and similar organic constituents deposited in distal suboxic–anoxic environment for Sargelu Formation. The palynomorphs are of dark orange and light brown, on the spore species Cyathidites australis, that indicate mature organic matters with thermal alteration index of 2.7–3.0 for the Chia Gara Formation and 2.9–3.1 for the Sargelu Formation by Staplin's scale. These characters have rated the succession as a source rock for very high efficiency for generation and expulsion of oil with ordinate gas that charged mainly oil fields of Baghdad, Dyala (B?aquba), and Salahuddin (Tikrit) Governorates. Oil charge the Cretaceous-Tertiary total petroleum system (TPS) are mainly from Chia Gara Formation, because most oil from Sargelu Formation was prevented passing to this TPS by the regional seal Gotnia Formation. This case study of mainly Chia Gara oil source is confirmed by gas chromatography–mass spectrometry analysis for oil from reservoirs lying stratigraphically above the Chia Gara Formation in Ajeel and Hamrine oil fields, while oil toward the north with no Gotnia seal could be of mainly Sargelu Formation source.     

Applications of computer modeling to the study of the genesis of stratiform sulfide deposits

Stratiform sulfide deposits are considered to have formed at or near the discharge vents of submarine hydrothermal systems. Such deposits constitute an important source of zinc, lead, copper, silver, and gold. They are often divided on the basis of the dominant host-rock lithology into volcanogenic and sediment-hosted types. In terms of their economic base metal contents, volcanogenic deposits contain either Cu and Zn or Zn, Pb, and Cu, whereas sediment-hosted deposits usually contain predominantly Zn and Pb. Mathematical models of the chemical characteristics of stratiform sulfide deposits are based on a program (B)which allows the calculation of the equilibrium distribution of aqueous species in a hydrothermal solution. Program B is front-ended by Program A, which defines the components of the chemical system, and back-ended by Program C, which controls the mode of output of the calculated results. Programs A and C are tailored to the specific problem under investigation. Results of chemical modeling of the two chemically active zones of the hydrothermal system (1. the hydrothermal reservoir in which the ore-forming solutions are generated and, 2. the site of ore deposition)suggest explanations of various characteristics of stratiform sulfide deposits, and include

1. The consistency of the metal associations and metal ratios suggest that ore-forming hydrothermal solutions are saturated with respect to the major metals in the reservoir zone. The chemistry of the solutions is determined mainly by temperature and chemical equilibrium between the hydrothermal solution and the rock-forming minerals of the reservoir.
2. Metal associations and metal ratios corroborate isotopic and other evidence that volcanogenic deposits were formed from hotter hydrothermal systems (> 200°Capprox.)than sediment-hosted (< 200°Capprox.)Metal ratios suggest that the hydrothermal reservoirs were contained in mafic rocks (ferromagnesian-feldspar mineral assemblages)for the Cu-Zn association; in felsic rocks and/or sediments (feldspar-mica; clay mineral assemblages)for the Zn-Pb-Cu association: and in sediments (dominated by clay mineral assemblages)for the Zn-Pb association.
3. Chemical zonation patterns and ore textures characteristics of volcanogenic deposits are explained by rapid cooling of the hydrothermal solution immediately above its discharge vent.
4. Chemical zonation patterns and the fine laminations of sediment-hosted deposits are explained by the comparatively slow degeneration of hydrothermal solutions that have collected as a brine pool on the ocean floor.