Ooidal Ironstones and Phosphorites—A Comparison from a Stratigrapher’s View.
Published:January 01, 2000
Franklyn B. Van Houten, 2000. "Ooidal Ironstones and Phosphorites—A Comparison from a Stratigrapher’s View.", Marine Authigenesis: From Global to Microbial, Craig R. Glenn, Liliane Prévôt-Lucas, Jacques Lucas
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Chemical components of most ooidal ironstones and phosphorites were initially derived from deeply weathered uplands and deposited in shallow waters of epeiric seas and continental margins that received very little clastic sediments. They were then commonly transformed during diagenesis largely by upwelling seawater and redeposiled in winnowed layers.
Ironstones and phosphorites differ, however. Ironstones were first laid down as ferric oxide and kaolinite ooids and peloids, whereas phosphorites were formed first as phosphatic carbonate granules, crusts, and hardground. Ironstones were then transformed to berthierine (or rarely nontronite) during diagenesis, whereas phosphorites were transformed to carbonate fluorapatite (CFA).
In terms of their distribution in the geologic record ironstones and phosphorites are also dissimilar. A few ooidal ironstones were deposited in Early Proterozoic time. Most accumulated during greenhouse phases of the Phanerozoic (Ordovician–Devonian and Jurassic–early Cenozoic). With the exception of the late Cretaceous–early Cenozoic deposits, major phosphorites are notable for their absence in rocks of those ages. In fact, phosphorites were most abundant in the Late Proterozoic and early Cambrian times.
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Marine Authigenesis: From Global to Microbial
This volume is a collection of 33 state-of-the-art papers focusing on various aspects of authigenic and diagenetic marine minerals and related global elemental cycling. The commingling of the various studies of authigenic minerals in this volume, including the most recent advances in knowledge concerning the occurrence and origins of phosphorites, glauconites, dolomites, siderites, manganese-iron associations, barites, ironstones, and other marine chemical sediments/sedimentary rocks of early authigenic/diagenetic origin, is partly the result of the increasing awareness that there are many overlaps, even direct co-associations, between different authigenic minerals, both in time, space, and genesis. Taken together, this compilation represents a holistic approach towards marine authigenesis that considers the integrated whole more than the simple sum of its parts.