Petrography

About: Petrography is a research topic. Over the lifetime, 7449 publications have been published within this topic receiving 102018 citations.

Petrography, Geochemistry, and Origin of Burial Diagenetic Facies, Siluro-Devonian Helderberg Group (Carbonate Rocks), Central Appalachians

Abstract: Petrographic and geochemical studies of pore-filling cements and replacement products in the Helderberg Group (Upper Silurian-Lower Devonian, central Appalachians) document the diagenetic history of these rocks. Shallow-ramp skeletal limestones and buildups were partially lithified by marine cements. However, most pore-filling cement formed under shallow (<300 m) to deep burial (300-4,000 m) conditions. Regional cathodoluminescent zonation patterns in early, calcite cements indicate meteoric ground waters were involved in shallow burial cementation. Early zoned calcite cements consist of updip nonluminescent cements with thin luminescent laminae in limestone or sandstone, that pass downdip into subzoned dull cements (interlayered bright and dull laminae), and then into nonzoned dull cement in basinward limestone. The regional distribution, stable isotopic compositions, and timing of early zoned cements relative to other diagenetic events suggest that all of the early cements formed synchronously from meteoric ground waters that became progressively more reducing as they flowed downdip (at least 150 km). Helderberg sandstone tongues probably were preferential conduits for meteoric gro nd waters because early calcite cements formed only on scattered skeletal grains in sandstones. Late, void-filling dull cement formed from deep burial pore fluids at burial depths of 300 to 4,000 m. Deep burial pore fluids were dilute to saline Na-Ca-Cl brines (from primary fluid inclusion data) with stable isotopic compositions that probably were similar to isotopic compositions of formation waters from modern oil fields. Void-filling dull calcite cements occluded nearly all remaining porosity before late Paleozoic fracturing and deformation. Latest diagenetic phases include dolomite, fluorite, silica, and fracture-filling dull calcite. This study shows that integrated petrographic and geochemical approaches to diagenetic studies are useful for relating various diagenetic phases and fabrics to burial history and paleoaquifer distribution.

Ceramic Petrography As a Technique for Documenting Cultural Interaction: An Example from the Upper Mississippi Valley

Abstract: The petrographic identification of ceramic tempers has long been known to be a fruitful line of inquiry for investigating intersite and interregional cultural interaction. By applying point-counting procedures to the recording of natural as well as humanly added mineral inclusions in ceramic thin sections, considerable power can be added to this traditionally qualitative technique. The effectiveness of this more quantitative approach in discriminating local from nonlocal vessels is demonstrated through a comparative analysis of two Middle Mississippian-contact sites in the upper Mississippi Valley region-Hartley Fort in northeast Iowa and the Fred Edwards site in southwest Wisconsin.