Age ang Locality of ironstones
Ironstone pods in the Archean Barberton greenstone belt, South Africa: Earth's oldest seafloor hydrothermal vents reinterpreted as Quaternary subaerial springs
Irregular bodies of goethite and hematite, termed ironstone pods, in the Barberton greenstone belt, South Africa, have been previously interpreted as the Earth's most ancient submarine hydrothermal vent deposits and have yielded putative evidence about Archean hydrothermal systems, ocean composition and temperature, and early life. This report summarizes geologic, sedimentological, and petrographic evidence from three widely separated areas showing that the ironstone was deposited on and directly below the modern ground surface by active groundwater and spring systems, probably during periods of higher rainfall in the Pleistocene
2- Silurian
Clinton ironstones (mid-Silurian) on the southeastern margin of the Appalachian Foreland Basin in central Pennsylvania consist largely of skeletal grainstone storm beds whose skeletal fragments are extensively impregnated and replaced by ferric oxide. Other forms of iron mineralization consist of ooids, superficial ooids, cavity fillings and cements composed of ferric oxide and/or chamositic clay, and two generations of iron-rich carbonate spar. True oolite is rare. Small proportions of ferruginized grains are present in coarse lags at tops of some small-scale, 1- to 5-m coarsening-upward sequences, which are the record of mid-shelf shoals from which the skeletal grainstone storm beds were derived.
Ooids and superficial ooids are likely to have formed in dysaerobic conditions where the pycnocline of a highly stratified sea intersected shoal flanks
2- Cretaceous Nubia Formation
Two textural types of oolitic ironstones occur in the Late Cretaceous Nubia Formation at Aswan, Egypt. These are: (1) relatively thin bedded (5–20 cm) muddy or ‘lean’ oolites containing up to 300oids, proto-ooids and peloids scattered in a matrix of ferruginous mud, and (2) thicker beds (as much as 2.5 m thick) of ‘rich’ or ‘concentrated’ oolites comprising 60–800oids
4- Eocene
The Upper Eocene Succession of Gabal Qalamoon, west Maghagha consists mainly of glaucony bearing siliciclastic and/or carbonate dominated shallowing-upward cycles. These cycles began by deeper shelf mudstones grading upward into shallower shallow subtidal highly bioturbated cross- bedded to cross - laminated glauconitic siltstone. These cycles are often terminated by matrix- and grain- supported greensand, fossiliferous glauconitic sandstone and/or glauconitic bioclastic wacke-, pack-, grain- and rudstones as well as different types of glauconitic ironstones and red beds. These petrographic lithotypes are composed of intra-basinal components, i.e., glauconitic peloids, intraclasts, ooids, and fossil molds and casts and carbonate ooids in addition to fossil shells and fragments admixed with different proportions of extra-basinal components, i.e., allogenic clays, quartz and heavy mineral grains. The distribution of the Upper Eocene glauconitic ironstones and red beds of G.Qalamoon area is mainly related to the variations in the mineralogical and chemical composition of the glaucony facies which indicate a strong vertical and lateral variations in the prevailed micro-physico-chemical parameters during the progressive shoaling and deposition of glaucony facies as follows: i) The olive green reduced glaucony facies of the lower and middle parts of the shallowing-upward cycles were formed within reducing deep to shallow subtidal environment and characterized by very low Fe3+/Fe2+ ratio, very high organic matter contents
