The Mallorca coastal caves present large amounts of speleothems that have been studied for decades. However, the sedimentary deposits also present in these cases have not been given the same attention. This work is the first study entirely focused on these deposits, specifically the ones found in the Ases cave. These deposits are formed by clay minerals (illitic phases, kaolinite, smectite, and chlorite), calcite and quartz, and minor proportions of dolomite, albite, orthoclase, hematite, and goethite. The grain size and the electron microscopy studies suggested the presence of different sedimentation processes (bedrock degradation, creep or saltation, and suspension) and different origins (authigenic and detrital origins) for the different sediments. Based on these differences, two types of deposits were characterized: autochthonous and allochthonous deposits. The first ones are located on the floor of chambers and corridors in subaqueous zones, indicating the stability of the mixing zone (and therefore the sea level) over time. The second ones appear filling voids on the walls and the ceiling in the terrestrial zone, evidencing the filling of the cavity in the presence of water (during a wet period). These results are very important to complete the understanding of the caves and their evolution and support the relevance of these materials in paleoenvironmental studies.

Phreatic overgrowths on speleothems (POS) are unique precipitates that are found in a small number of coastal caves around the world, like those in the Mallorca Island. Their growth is directly related to the water level of the brackish lakes connected to the sea characteristic of these caves and, therefore, they can be very reliable indicators of past sea levels. The study presented here characterizes and classifies an important number of POS samples collected in the coastal caves of Mallorca. The characterization includes not only the observations made on 117 handheld samples and on 102 thin sections from POS, but also the study of their mineralogy and their location in the caves. This study has provided the basis for a systematization of all these characteristics, some of which are reported here for the first time in POS samples. The results indicate that (1) most of the POS precipitate on stalactites, (2) calcite POS show branched internal and external texture and their most common crystal fabric is mosaic calcite and (3) aragonite POS show globular external texture and fan‐shaped internal texture, and their principal crystal fabric is needle‐like. All the aragonitic samples have been found above or at the same heights as the current sea level, which indicates that they have probably formed during warmer climates. The calcite POS have been found at heights above and below the present sea level and are interpreted as to have formed during cold and rainy periods. The systematization proposed in this paper could be applied and checked in other POS worldwide. Additionally, the combination of these results with the information obtained from studies on the present precipitation of these phreatic speleothems in some Mallorca caves has provided an insight on their formation conditions which will enlarge the utility of these speleothems as palaeoenvironmental indicators.

Limestone corrosion and coastal karst cave (flank margin cave) enlargement are closely related by the mixing zone between meteoric and seawater, yet quantitative data on corrosion rates in these environments remain scarce. Recent speleodiving exploration in flanking margin caves in Mallorca revealed numerous submerged cavities with different haloclines between 0 and 25 m below m.s.l. To investigate rock-decay mechanisms along these haloclines, exposure trials were conducted in Cova de sa Gleda. Three sets of water-loss rock tablets (WLRT), composed of bioclastic calcarenite limestone and crystalline aragonite (aragonite crystal aggregates), were deployed along a water-column depth profile ranging from 5 to 16 m. After 749 exposure days, tablets were explored by SEM and XRD. Differences in mass show that calcarenite tablets lost an average of 1.89% of their initial mass, while aragonite tablets have lost 8.05%. Corrosion rates varied along haloclines: at 5 m depth (10 to 16 PSU), rates were 3.10% for calcarenites and 11.08% for aragonite; at 10 m (19 to 29 PSU), corrosion increased respectively to 10.8% and 17.93%; at 16 m (>35 PSU, seawater), corrosion decreased to 1.97% and 3.48%, respectively. These haloclines coincide with the height position of notches and other observable corrosion features within the cave. Consequently, these corrosion features present along the cave can be interpreted as proxies of the former position of the groundwater mixing zone.

Phreatic Overgrowth on Speleothems (POS) are a specific type of speleothem that growth at the surface of the brackish lakes in littoral caves. These lakes are direct or indirectly related to the height of the sea level, therefore, the POS precipitates at the height of the sea in the moment of their growth. This condition makes the POS a perfect marker of past sea level.These speleothems are very unusual and have only been found in few caves around the world. Up to the present, most of these deposits have been located on the island of Mallorca, where the largest collection of this type of speleothems have been studied.This study presents a complete classification of POS in hand-size scale and in thin section. The first one is based on the internal and external morphology of the POS and its acquired shape depending on the substrate on which these precipitates grow. The second one, related to the thin section study, allows to recognize a variety of crystalline fabrics: needle-like aragonite crystals (An), fibrous fascicular optic calcite (Ffo), columnar fascicular optic calcite (Cfo), columnar calcite (C), mosaic calcite (Mc), mosaic calcite with aragonite needles (MCan) and micrite (M) and microsparite calcite fabric (Ms). , Some of these fabrics were previously described in other speleothems (as stalactites or stalagmites) and others are new, not previously described in speleothems.All this information shows several important ideas: 1) most of the POS precipitate around previous stalactite-type vadose speleothem; 2) aragonite POS are mainly globular and fan shaped in their external and internal morphology, respectively, and aragonite mineralogy only appears in needle-like crystal fabric; 3) calcite POS are related to branched internal and external morphology and present more variability in their crystal fabric, being the mosaic type the most common. The data obtained have been used to identify some relationships between the precipitation conditions of POS and the features of these precipitates. This classification and the conclusions of the precipitation conditions demonstrate the importance of POS as a proxy. Moreover, this study helps to understand the precipitation process of POS and can be implemented and reviewed in POS deposits of other parts of the world.