Micritization mechanism in penecontemporaneous carbonate rocks: coupled C- Ca cycles and constraints from diagenetic environments

Published: 7 April 2026| Version 1 | DOI: 10.17632/59gh2b5ydr.1
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Description

1.This dataset was collected to investigate the hypothesis that early meteoric diagenesis—specifically micritization in isolated carbonate platforms—is driven by an interface-coupled dissolution-precipitation mechanism rather than traditional microboring organisms. We hypothesize that hydrologically controlled zonations exert distinct kinetic controls on fluid-mineral interactions, which are faithfully recorded in the isotopic (C, O, Ca, Sr) and trace element signatures of the diagenetic products. 2.The dataset comprises geochemical, isotopic, and trace element data derived from coral reef limestone samples from a South China Sea isolated atoll. Powdered samples of unaltered precursors and micritized products were obtained using a high-precision micro-drill. Samples underwent sequential acetic acid leaching to remove secondary carbonates. Strontium and Calcium isotopic ratios were measured using a Thermo Fisher Triton XT thermal ionization mass spectrometer. Trace elements (including Al, Th, Sc, P, Fe, Mn, and REE+Y) were analyzed via ICP-MS to evaluate terrigenous contamination and redox conditions. Data quality was strictly monitored using certified reference materials. 3.The data reveal several key diagenetic patterns. The 87Sr/86Sr ratios of intensely micritized samples are nearly indistinguishable from unaltered precursors, indicating a rock-buffered system that inherited coeval marine Sr signatures. A pronounced negative excursion in δ44/40Ca is exclusively observed in the intensely micritized phreatic zone, coupled with significant Sr depletion. Trace element analyses confirm the pristine nature of the samples, devoid of significant terrigenous or hydrothermal contamination. 4. These data should be interpreted within the framework of reactive-transport and fluid-mineral kinetics. The pronounced δ44/40Ca negative excursion, combined with stable Sr isotopes, serves as a unique in situ tracer for rapid, non-equilibrium crystallization driven by the ICDP mechanism in a restricted fluid environment. 5. Researchers can utilize this dataset to: (1) model early meteoric diagenesis and element partitioning in deep-time carbonate systems; (2) distinguish kinetic isotope effects from primary environmental signals in chemostratigraphy; (3) conduct global cross-regional correlations.

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1. To systematically evaluate the diagenetic response of shallow marine carbonate sediments to meteoric hydrogeochemical gradients, a suite of 65 bulk carbonate samples was collected from the 767.00m ~ 807.00 m depth interval of a drillcore from an isolated atoll in the southern South China Sea. The sampling strategy was designed to capture a continuous vertical diagenetic profile, spanning from the subaerially exposed meteoric vadose zone down to the water-saturated meteoric hyporheic zone. This interval documents the transition from fabric-selective dissolution features in the upper vadose section to pervasive micritization textures in the lower hyporheic section. Prior to analysis, the cores were split longitudinally, with one half archived for reference and the other utilized for sample preparation and analytical testing. Specifically, the complete set of 65 samples (approx. 0.6 m resolution) was subjected to thin sectioning, Scanning Electron Microscopy (SEM) imaging, and major/trace element analysis. From this set, a subset of 12 samples (approx. 3 m resolution) was selected for high-precision δ13C、δ18O、 δ44/40Ca and 87Sr/86Sr isotopic measurements. 2. The primary objective of the petrographic analysis was to characterize the mineralogical composition, micritization intensity, and microporosity development of the bioclastic limestones, with a focus on resolving the vertical diagenetic heterogeneity within syngenetic micritization cycles. Subsamples from the 65 bulk carbonate specimens were prepared for thin sectioning and SEM mounting. Petrographic observations were conducted using a Zeiss AXIO SCOPE.A1 polarizing microscope to document mineral assemblages, differential dissolution patterns, and cementation degrees. Microporosity features were further examined using an XL30 Field Emission Scanning Electron Microscope (FE-SEM). Coupled with the SEM, an Energy Dispersive X-ray Spectrometer (EDS) was utilized in Back-Scattered Electron (BSE) mode to perform qualitative elemental analysis on micron-scale spots and domains.

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Geochemistry, Mineralogy, Sedimentology, Hydrogeology

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