Secular variation of calcium carbonate mineralogy; an evaluation of ooid and micrite chemistries

Abstract

ZusammenfassungIn der Kohlenkalk-Schelffazies des Untertournais be [ Velbert (Bundesrepublik Deutschland) AbstractThree ooid types are recognized from the Lower Tournaisian ,,Kohlenkalk<< shelf facies at Velbert, Germany. Ooids from this unit have a predominantly concentric laminae fabric. Radial-concentric and small radial fibrous ooids are minor components to this oolite. The diagenetic response of Kohlenkalk ooid chemistry is significantly different from that observed in contemporaneous crinoid and brachiopod material. Fabric evidence suggests that radial-concentric and radial-fibrous ooids were probably originally aragonite/high-Mg caIcite and high-Mg calcite respectively. Fabric and trace elemental chemistries of the concentric fabric ooids suggests that they were originally precipitated as aragonite and subsequently altered to low-Mg calcite.Recent papers have proposed temporal shifts in the dominant mineralogy of shallow marine non-skeletal carbonates between calcite and aragonite. Changing Phanerozoic atmospheric pCO2 levels and oceanic Mg/Ca ratios may have been factors controlling the dominant mineralogy. The chemistries of the Kohlenkalk ooids in conjunction with other ooid and micrite data spanning the Mid-Paleozoic to Recent are evaluated in context with these temporal shifts between ,,calcite<< and ,,aragonite seas<<. The strontium chemistries of the ooids (~ = 1010 ppm, range 145-3010 ppm) and micrites (~ = 841 ppm, range 3-8800 ppm) suggests they had an aragon[re precursor mineralogy. No statistical correlation was observed between ooid/micrite chemistries, their mineralogies and the proposed secular trend. Therefore, we suggest that aragon[tic ooids and micrites were dominant components of shallow-marine carbonate environments throughout the Phanerozoic. The distribution and abundance of aragon[tic and calcitic ooids in the geologic past was probably dependant on local hydraulic, physicochemical, and environmental conditions, areally constrained by global tectonics, eustatic, climatic and atmospheric effects, with significant diagenetic overprinting of the original geochemical and fabric information. R6sum~Parmi ies facies de plate-forme du Tournaisien inf&ieur, dans le calcaire carbonif~re de VeIbert (RFA), on distingue trois types d'ooi'des: les plus abondantes pr&entent une structure lameliaire concentrique; d'autres, en quantit~ subordonn&, sont radiaires-concentriques et fibro-radi&s. En r@onse ~t leur chimisme, les od/des du calcaire carbonif~re ont connu Selon certains travaux r&ents, la composition min&alogi-que des s6diments carbonat& non organo-d&ritiques aurait fluctu6 au cours du temps entre l'aragonite et la calcite. Des factures d&erminants de ce processus auraient p~ &re les changements, au cours du Phan&ozoi'que, de pCO2 dans l'atmosph~re et du rapport Mg/Ca dans les oc&ns. Le chimisme des oo~des du calcaire carbonif~re, compar~ ~ celui de micrites et d'autres oo~des d'~tges phan&ozoYque moyen ~t r&ent est examin~ en relation avec ces passages de ,mers ~ calcite,, ~ <~mer ~t ar...

The Marine Carbon System and Ocean Acidification during Phanerozoic Time

“…In addition, Bates and Brand (1990) have seriously questioned whether there has indeed been a statistically demonstrable change at all during the Phanerozoic Eon away from the current dominance of aragonitic ooids and micritic (fine-grained) cements . Furthermore, recently Bots et al .…”

Review: geological and experimental evidence for secular variation in seawater Mg/Ca (calcite-aragonite seas) and its effects on marine biological calcification

“…It should be noted here that Sandberg's (1983) identification of an oscillating trend in the polymorph mineralogy of ooids and marine cements has not gone unchallenged. For example, Bates and Brand (1990) reassessed the petrography and elemental geochemistry of ooids and marine cements throughout Phanerozoic time and concluded that their primary mineralogies did not correlate with Sandberg's (1983) putative calcite and aragonite sea intervals. Instead, they attributed differences in the primary mineralogy of these abiogenic carbonate precipitates to local hydraulic, physicochemical, and environmental conditions that were only loosely influenced by tectonic, eustatic, climatic, and atmospheric effects.…”

Comments on "Estimating the impact of early diagenesis on isotope records in shallow-marine carbonates: A case study from the Urgonian platform in western Swiss Jura" by A. Godet et al. [Palaeogeography Palaeoclimatology Palaeoecology 454 (2016) 125-138]

“…It is found near the top of the upper Pierre Jaune (Fig. 1), almost one metre below the discontinuity, a feature that pleads in favour of the second option; • earlier records of oolitic cortices leached in full (WHERRY, 1915;SANDBERG, 1975SANDBERG, , 1983RICHTER, 1983;ZEN et al, 1983;TUCKER, 1984;BATES & BRAND, 1990;ALGEO & WAT-SON, 1995) or in part, i.e., only some cortical layers (TUCKER, 1984;ALGEO & WATSON, 1995) came to the conclusion that they are dealing respectively with either aragonitic or "bimineralic" (aragonite-calcite) cortices. (SOLLAS, 1877).…”