Diagenetic Alteration of Triassic Coral From the Aragonite Konservat-Lagerstatte in Alakir Cay, Turkey: Implications for Geochemical Measurements

Frankowiak, Katarzyna; Mazur, Maciej; Gothmann, Anne M.; Stolarski, Jarosław

doi:10.2110/palo.2012.p12-116r

Cited by 22 publications

(35 citation statements)

References 52 publications

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“…In addition, the calcite crystals are massive with a flat and homogeneous surface. In other coral diagenesis studies (Frankowiak et al, 2013;McGregor and Gagan, 2003), these characteristics correspond to calcite crystals called calcite spar, most probably of non-biogenic origin (Dalbeck et al, 2011). Moreover, using the relationship between the Sr/Ca signature and the calcite-%,we calculated a 100% calcite Sr/Ca ratio end-member of ~7.96 ± 0.31 mmol/mol.…”

Section: Origin Of the Intra-skeletal Calcite: Biogenic Vs Early Diamentioning

confidence: 73%

“…When using the Sr/Ca signature of corals for paleo-SST reconstruction, the presence of calcite, which has a lower Sr/Ca ratio than the pristine aragonite, skews reconstructed SST toward higher values than expected (Table 1). To our knowledge, only one study reports on higher Sr/Ca values (lower reconstructed SSTs) for secondary calcite in a fossil coral (Frankowiak et al, 2013). Because the geochemical composition of diagenetic calcite depends on its nature, e.g., cement vs.…”

Section: 2intra-skeletal Calcite and Its Impact On Reconstructed Sstmentioning

confidence: 97%

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Intra-skeletal calcite in a live-collected Porites sp.: Impact on environmental proxies and potential formation process

Lazareth

Soares-Pereira

Douville

et al. 2016

Geochimica et Cosmochimica Acta

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Geochemical proxies measured in the carbonate skeleton of tropical coral Porites sp. have commonly been used to reconstruct sea surface temperature (SST) and more recently seawater pH. Nevertheless, both reconstructed SST and pH depend on the preservation state of the skeleton, here made of aragonite; i.e., diagenetic processes and its related effects should be limited. In this study, we report on the impact of the presence of intra-skeletal calcite on the skeleton geochemistry of a live-collected Porites sp..The Porites skeleton preservation state was analyzed using X-ray diffraction and scanning electron microscopy. Sr/Ca, Mg/Ca, U/Ca, Ba/Ca, Li/Mg, and B/Ca ratios were measured at a monthly and yearly resolution using solution ICP-MS and multi-collector ICP-MS. Theδ 11 B signatures and the calcite percentages were acquired at a yearly timescale. The coral colony presents two parts, one with less than 3% calcite (referred to as "no-calcite" skeleton), the other one, corresponding to the skeleton formed during the last 4 yrs. of growth,with calcite percentages varying from 13 to 32% (referred to as "with calcite" skeleton). This intra-skeletal calcite replaces partly or completely numerouscenter of calcification (COCs). All geochemical tracers investigated are significantlyimpacted by the presence of calcite. Thereconstructed SSTdecreasesby about0.1°C per calcite-percent as inferred fromthe Sr/Ca ratio. Such impact reaches up to 0.26°C per calcite-percent for temperature deduced from the Li/Mg ratio. So, less than 5% of such intra-skeletal calcite does not prevent SST reconstructions using Sr/Ca ratio, but the percentage and type of calcite have to be determined before fine SST interpretation. Seawater pH reconstruction inferredfrom boron isotopes drop by about -0.011 pH-unit per calcitepercent. Such sensitivity to calcite presence is particularly dramatic for fine paleo-pH reconstructions. Here we suggest that after being brought to shallow waters following a cyclone, the studied coral was seasonally subjected to rainfall-related water freshening that could have mimicked a vadose environment like can be encountered on raised fossil coral reefs. Nevertheless, the process of calcite precipitation remains to be determined.

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Section: Origin Of the Intra-skeletal Calcite: Biogenic Vs Early Diamentioning

confidence: 73%

Section: 2intra-skeletal Calcite and Its Impact On Reconstructed Sstmentioning

confidence: 97%

Intra-skeletal calcite in a live-collected Porites sp.: Impact on environmental proxies and potential formation process

Lazareth

Soares-Pereira

Douville

et al. 2016

Geochimica et Cosmochimica Acta

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“…Therefore, these regions better preserved their original structures in fossil corals ( 19 ). We considered the TDs in the fossil coral skeletons to be well preserved only when meeting all of the following criteria ( 19 , 20 ): (i) arrangement of crystals and crystal habits identical to those in modern Scleractinia, (ii) absence of Mn-induced luminescence, and (iii) purely aragonitic mineralogy. In addition, areas of well-preserved TDs in a skeleton were required to be large enough to be comfortably sampled with a microdrill (drill bit diameter, 350 μm).…”

Section: Resultsmentioning

confidence: 99%

Photosymbiosis and the expansion of shallow-water corals

et al. 2016

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“…However, a series of important observations can be made from these results that have significance for those working with fossil coral archive material. The aragonite–aragonite diagenesis in the presence of Mg‐bearing reactive fluids is one such point, where the predominance of both primary and secondary aragonite might suggest that PXRD analyses of these corals would fail to detect the patterns of alteration (Fernandez‐Diaz, Mazur, Gothmann, & Stolarski, ; Hendy et al, ; McGregor & Abram, ; Frankowiak et al, ; Krayesky‐Self, Richards, Rahmatian, & Fredericq, ; Jonas, Richards, Rahmatian, & Fredericq, ). The textures observed in these experiments generally mimic naturally altered samples.…”

Section: Interpretation and Discussionmentioning

confidence: 99%

Significance of fluid chemistry throughout diagenesis of aragonitic Porites corals – An experimental approach

Pederson

Weiss

Mavromatis

et al. 2019

The Depositional Record

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Marine carbonates are among the most important archives of environmental information in both modern and past environments. Widely used but particularly sensitive archives are the aragonitic skeletons of scleractinian corals. However, due to the metastable nature of aragonite, a multitude of chemical, mineralogical, and (micro)biological processes can lead to diagenetic alteration of these archives and their proxy information can be altered or lost. Here, hydrothermal alteration experiments were performed to create a better understanding of the diagenesis of an often‐utilized genus, Porites. Same‐specimen subsamples were heated in two fluid types and at two temperatures and durations, and their resulting alteration features were assessed to allow insight to the mechanisms and drivers of diagenetic modification. Experiments with fluid temperatures of 130°C induced remobilization and darkening of organic matrices, with no other evidence for alteration observed. In contrast, specimens exposed to a temperature of 160°C underwent significant diagenetic alteration dependent on fluid type. Fluid chemistry, particularly Mg/Ca ratios, was found to regulate the type of alteration (e.g. neomorphism or reprecipitation). Reaction with meteoric water resulted in almost complete neomorphism of the aragonite skeleton to blocky calcite, as well as significant exchange with the experimental fluid. In comparison, samples altered in the experimental burial fluids record no mineralogic or significant isotopic change, but instead, small‐scale dissolution–reprecipitation of the primary skeleton, along with the precipitation of pore‐filling aragonitic needle cements was observed. The δ18Ocarbonate data indicate transformation via dissolution–reprecipitation mechanisms depending on the degree and mechanism of diagenesis, and are strongly dependent on fluid chemistry. The main outcome of this work is that a multi‐proxy approach has the best potential to shed light on the interpretation of processes and pathways of aragonitic coral alteration. This study has implications for early alteration of carbonate archives within varying diagenetic fluids, with results aiding in the identification of past burial conditions.

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Diagenetic Alteration of Triassic Coral From the Aragonite Konservat-Lagerstatte in Alakir Cay, Turkey: Implications for Geochemical Measurements

Cited by 22 publications

References 52 publications

Intra-skeletal calcite in a live-collected Porites sp.: Impact on environmental proxies and potential formation process

Intra-skeletal calcite in a live-collected Porites sp.: Impact on environmental proxies and potential formation process

Photosymbiosis and the expansion of shallow-water corals

Significance of fluid chemistry throughout diagenesis of aragonitic Porites corals – An experimental approach

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