# Diagenetic Study of Marron Emperador Ornamental Stone (Upper Cretaceous, SE Spain)
## 5 Discussion
### Dolomitization Process  
The close spatial relationship of the dolomitic bodies with the main structural alignments of the basin in the Cretaceous led to a tectonically or structurally controlled circulation of fluids. The flow of fluids through tectonically active faults is episodic in nature [60; 61; 62], so extensive dolomitization requires many such flow episodes [20; 63; 64]. The main recognised dolomitic textural types (hybridotopic planar-s, idiotopic planar-e) are consistent with a late nonmimetic dolomitization at low temperatures [48]. Likewise,  
Figure 5: Cross plot of stable \(\delta^{13}\)C(V-PDB) versus \(\delta^{18}\)O(V-PDB) values of samples from the ME brecciated dolostone geobody. \(\delta^{18}\)O ranges for high and low temperature marine dolomites are based on a compilation from [PERSON] and Wiggins [50]. The compositional ranges of other examples of Cretaceous dolomitic bodies are included: Catalan Coastal Range, Spain [51]; Maestrat Basin, Spain [13; 52]; Iberian Chain, Spain [53; 54], Basque Cantabrian Basin, Spain [17]; Cupido Fm., Mexico [55]; Habshan Fm., Oman [56]; Zagros Basin, Irak [57]; Eastern Pontides, Turkey [58]. the presence of limpid cortex indicates the existence of slow replacement phases without the incorporation of impurities from the original sediment or overgrowth phases (syntaxial cementation) on the dolomite cores [60,61]. The \(\delta^{18}\)O values of dolomites reflect the isotopic composition and temperature of dolomitizing fluids [58,65,66,67,68]. The \(\delta^{18}\)O composition of the ME dolomite textures is very similar (\(-\)2.5-1.0% V-PDB), and these values differ from those that would be obtained in dolomites precipitated from Cretaceous marine water (0-3%, [69]) (Figure 5), so that a primary or early origin for these dolomites can be ruled out. Using the diagrams elaborated by [PERSON] et al. [70], which are based on the fractionation equations of land [71] for dolomite and Friedman and O'Neil [72,73] for calcite, an approximation of the isotopic composition (oxygen) and formation temperatures of carbonate phases has been performed. The results indicate that the formation temperatures of the different dolomitic (replacement, cement) and calcitic (cementation, dedolomitization) textural types do not exceed 50-60 \({}^{\circ}\)C according to the paleotemperature equations used, whether the nature of the fluids has a meteoric or saline influence (derived from marine waters or basin geofluids). Even considering a heavier isotopic composition for marine waters in these equations, in the case of deep dolomitization, the resulting temperatures would not enter the typical range of hydrothermal. The existence, although volumetrically scarce, of saddle dolomite in void-filling mode (CD-2) may indicate some episode of higher temperature (hydrothermal tectonic dolomitization) [48]. With these formation temperatures, without another source of heat (e.g., magmatic intrusions), and with normal geothermal gradients (25-40 \({}^{\circ}\)C/km), dolomitization would have occurred at relatively shallow burial depths (0.6-1 km). Stylolites in dolostones, which can act as conduits for dolomitization fluids, appear to require at least 400-500 m of burial [74,75,76]. The isotopic composition of the ME dolostones clearly differs from other Cretaceous dolostones that were generated by interaction with diagenetic fluids with lower salinity and/or higher temperatures (Figure 5). CL examination evidences the multiphase character of dolomitization, such that several types (and phases) of replacement and cementation have been recognised within the dominant dolognitic mosaics. The nuclei of the rhombic and subrhombic crystals (DOL-1) show a high content of impurities, and after a dissolution phase (corroded borders); they are syntaxially overgrown by a dolomite (DOL-2). These crystals are generally less rich in impurities. DOL-2 constitutes a series of more or less thick concentric bands or envelopes (1-10 \(\upmu\)m to 300 \(\upmu\)m) with different luminescence.