ABSTRACT Middle Triassic to Lower Jurassic continental conglomerate, sandstone, and mudrock are widely exposed in the highest tectonostratigraphic terranes (internal domains) of western and central circum-Mediterranean orogenic belts. These red beds are a key tectonic facies assemblage representing onset of the Tethyan rift-valley stage in the western Mediterranean, during which plate and microplate boundaries were localized during breakup of Pangea. These red beds likely define the boundary of the Mesomediterranean microplate, which played a key role in the Cenozoic evolution of the western Mediterranean. Red beds unconformably overlie Paleozoic metasedimentary and locally plutonic rocks, and they are covered by Early Jurassic and younger sedimentary strata; they are generally mildly deformed and only locally metamorphosed. Sandstone detrital modes vary from quartzarenite to quartzolithic, reflecting a provenance from Cambrian–Carboniferous metasedimentary rocks similar to those underlying the red beds. Reevaluation of previously published petrographic databases and detailed hot-cathodoluminescence (H-CL) analysis of quartz grains indicate that most quartz grains were derived from heterogeneous metamorphic, plutonic, and volcanic rocks. Evaluation of the diagenetic evolution of red beds using chemical-mineralogical analyses and H-CL analyses indicates that compaction and cementation played key roles. Compaction consists of brittle deformation, with breakage of quartz grains and production of early quartz cement, which closed the fractures, followed by a second stage of quartz cementation. Carbonate cements consist of dolomite, ankerite, and calcite. This last cement, related to dedolomitization/calcitization processes, produced carbonate crystals with iron oxides. The sandstone experienced intense reduction of intergranular volume during early stages of burial, as indicated by contrasting compactional porosity loss (COPL; mean of 31.1%) versus cementational porosity loss (CEPL; mean of 8.5%). These data demonstrate the minor role of cementation in reducing porosity and the prevalence of compaction as the main process destroying primary pores. The diagenesis of the analyzed red beds is variable within several internal domains of the orogenic belts, suggesting local influences related to the provenance and geotectonic evolution of each basin.

A coordinated textural, stable isotopic, and elemental investigation of calcitized speleothems was carried out to delineate the diagenetic transformation of unstable aragonite to stable low-Mg calcite. Many aragonite speleothems in certain limestone caves in Korea (Baekgol Cave, Jungteogeori Cave, and Chilsong Cave) have been partially calcitized. The neomorphic calcite crystals vary in size from tens of microns to a few millimeters. Numerous relic aragonite crystals and relic growth lines are present within the neomorphic calcites. Original calcite speleothems (i.e., initially deposited as calcite) tend to be more depleted in Sr and enriched in Mg than the original aragonite, and trace-element compositions of the neomorphic calcites approach their original aragonites. Also, O- and C-isotope compositions of the neomorphic calcite show similar ranges to those of the original aragonite. This suggests that the calcitization within the speleothems occurred in a semiclosed diagenetic system with respect to trace elements and oxygen isotopes. Diagenetic trends strongly suggest that stable isotopes and trace elements of the original aragonite were remobilized during calcitization. Unaltered aragonite speleothems in the Jungteogeori Cave are enriched in 13 C compared to original calcite speleothems, which may indicate that calcite speleothems were influenced more by soil-derived meteoric water during speleothem growth or that aragonite speleothems were deposited from cave water that was more buffered by carbon derived from the surrounding limestone. The 18 O enrichment observed in original aragonite speleothems compared to original calcite speleothems may imply that the aragonite speleothems were formed by evaporation under less humid conditions.