Experimental stabilization of carbonate sediments to calcite: Insights into the depositional and diagenetic controls on calcite microcrystal texture

REE Characteristics of Lower Cretaceous Limestone Succession in Gümüşhane, NE Turkey: Implications for Ocean Paleoredox Conditions and Diagenetic Alteration

“…However, the studied Lower Cretaceous limestones do not show petrographical evidence of such recrystallisation (Figure 4a,b). Furthermore, the studied limestone samples exhibit low Mg-calcite chemistries (Ca 98.81-99.52 Mg 0.48-1.19 (CO 3 )) [105], indicating that they are chemically stable [106][107][108][109][110][111][112][113]. Further, there is neither petrographical evidence for recrystallization which associated with Late Cretaceous to Cenozoic magma generation nor geochemical pieces of evidence, for example, the lack of apparent correlation between Mg/Ca vs. Ce/Ce* and Eu/Eu* ratios which imply less influence of late diagenetic processes on their REE chemistry (Figure 8g,h).…”

Rhombic Calcite Microcrystals as a Textural Proxy for Meteoric Diagenesis

“…A large body of experimental observations demonstrate that calcite precipitating under conditions similar to those that characterize meteoric settings (impurity-free, low supersaturation, high uid:solid ratio) exhibits the rhombic form 7,8,9,10,11,12 (Fig. 1A), whereas calcite precipitating under experimental conditions similar to those that characterize marine or marine burial settings (impurity-rich, high supersaturation, low uid:solid ratio) exhibits non-rhombic forms 7,8,10,12,13 (Fig. 1B-D).…”

“…In the case of high supersaturation and high a Ca 2+ /a CO3 2− , the observed alteration in crystal morphology from rhombic to non-rhombic has been attributed to a disproportional change in the growth rate of crystal faces 7 , whereas in the case of high pH (> 12), the change in crystal morphology was attributed to the presence of OH − ions which has been suggested to stabilize the polar scalenohedral crystal faces 13 . Several of the factors that in uence crystal form of calcite precipitating directly from a solution have also been shown to in uence calcite stabilized from aragonite 12 . However, besides the aforementioned factors, stabilization experiments have shown that lowering uid/solid ratio (solution volume/aragonite reactant mass) leads to the formation of polyhedral and anhedral calcite crystals rather than euhedral rhombic crystals, which has been interpreted to be the result of the increased competition of the growing crystals for space 12 .…”

“…1a). Similarly, experiments show that aragonite reacted in distilled water converts to rhombic calcite microcrystals 12 . In contrast, calcite exhibits non-rhombic forms (scalenohedral, polyhedral, anhedral, etc.)…”

“…when precipitation occurs in solutions that are highly supersaturated 7 , with high a Ca 2+ /a CO3 2− (a is activity) or pH 7,13 , or in solutions containing various organic and inorganic impurities 8,10 . Likewise, calcite stabilized from aragonite in uids containing Mg 2+ , SO 4 2− , or excess Ca 2+ , or under low uid:solid ratios exhibits polyhedral (non-rhombic) and anhedral crystals 12 . (iii) undersaturation or low degree of supersaturation with respect to calcite 14 , and (iv) high uid to solid (i.e., water/rock) ratios.…”