SOLUTIONAL SCULPTURINGS AND UNCOMMON SPELEOTHEMS FOUND IN THE COVA DES PAS DE VALLGORNERA, MAJORCA, SPAIN.
In a short article published in the NSS News, December, 2003, a brief introduction to this amazing cave located in the Majorca Island (Western Mediterranean) was made.
At that time the cave was 6,4 km long including some lakes. At the end of one of those ponds, and before the final chamber we noticed a draught of air, something like a soft breeze. The small volume of air within the chamber did not justify its movement from the chamber to the lake or on some occasions, in the opposite direction. We spent two years looking into this mystery. Eventually we discovered a tight passage that led us into a maze of passageways and chambers with over 24 km of new galleries surveyed so far. At this moment the total length of the cave is over 30 km, but it is thought that it will reach up to 40 km or even more.
The cave has two levels of passageways. One is located at the water table level (sea level), and the other one is about 8 m above the mean sea level. The latter is the one that contains most of the solutional sculpturings described here.
The original article, written in Spanish was published in the cave and karst publication “ENDINS”.
Corrosion morphologies and different speleothems are found throughtout the Cova des Pas de Vallgornera. During the survey we have located a large abundance of Sponge Works, Bell Holes and Wall Pockets.
SOLUTIONAL SCULPTURINGS
DISSOLUTION PITS
These morphologies that have been found in the cave are well-like structures, markedly cylindrical that exist in the floor of galleries and chambers (Photo 1). These are developed in the rock that make up the floor. The rock is tough and compact and belongs to the Tortonian calcarenites (Upper Miocene). Above the rim of these cylindrical pits usually there is a bevelled point in the ceiling from which waterdrops have been dripping, dissolving the limestone aggressively, provoking these pits, similar to those made by drilling machines. At the edge of bevelled point from where the drops fall, it can be clearly seen how the subsaturated calcium carbonate water is dissolving the rock, making up a centimeter in size channel-like structure, which also concentrates the water flow to certain points.
The parts of the rock that are surrounded by channels are fragile, soft and in some cases with a butter-like touch, being completely soaked up in water. This fact together with a whitish deposit found in some small channels, could be related to the moonmilk genesis. The pits reach an outstanding depth relative to their diameter. One of those morphologies is 12 centimeters in diameter while its checked depth is 3,8 metres. When a capillarity process occurs around the pit rim, botryoid-like speleothems are deposited. It should be noted that the height between the ceiling drip point and the floor is about 2 meters (Photo 2).
The genesis of this morphology is clearly related to a highly aggressive subsaturated water that reaches the cave, dissolving the rock that forms the ceiling and keeping chemical activity on the cave’s floor.
This fact can be observed in the pit’s internal wall, since calcite sea urchin fossil remains can be seen coming out from the wall, due to the differential dissolving rate between calcite and the surrounding rock. (Photo 3).
The effects of those aggressive waters also generate other solutional patterns, depending on the materials involved. Some stalagmites can be eroded by ceiling drips enriched with carbon dioxid (Photo 4). It is possible to observe how stalagmites have been dissolved layer after layer by aggressive drips of water. Those erosives periods can be followed by others in which the opposite effect, precipitation, occurs and covers the above mentioned morphologies (Photo 5).
POCKETS
These patterns are mainly found at water table level passages. Pockets are shown like elliptic smooth depressions on the rock, with variable depth (Photo 6). In vertical cross section they are crescent-shaped, with its lowest concave part covered in thin sedimentary deposit. They are found along large extensions on the passages walls, having a steady morphology.
Crest-like narrow isolated sections of rock form as a result of coalescent processes that occur along the evolution of these solutional patterns. This morphology is also found in the upper level of the cave, away from the present water table level. There, pockets are larger, deeper and hemispherical or elliptic in shape (Photo 7). They are more isolated, each unit being separated from its adjacent by a rock crest. It has been noted that a remarkable horizontal alignment of pockets lines could be explained as a result of former marine levels stabilization, corresponding to interglaciar periods.
Furthermore, the lowest part of the pockets is covered in brown-coloured sediment.
SOLUTIONAL FACETS AND ROCK COMBS
Solutional facets and rock combs are commonly combined with one another (Photo 8). Moreover, solutional facets of over 1 metre in length with steeper slopes than the previous known morphologies have also been found. This causes the rock combs to be clearly marked. Some passages show how the solutional facets are bound in their higher and lower part by deep corrosion notches caused by dissolution at the water table surface (Photo 9) that prove to be ancient stabilizations of the phreatic level.
LENTIL IN SHAPE CROSS-SECTION PASSAGES
This kind of solutional passages have been found in the “F” sector of the cave. Once the present bibliography has been looked up, these morphologies seem to be solutional passages developed along important horizontal joints between bedding planes. Elliptic in cross-section, these passages are characterized by maximum dimensions of 1 metre in height, between 4-5 metres in length and about 4 metres in width (Photo 10). The floor of these passages is somehow uneven and smooth depressions can occur. At the same time it is covered by a calcareous coating, and mud sediments are deposited on the flattened areas. Small ceiling pockets are developed in some areas.
Distant parallel galleries are met by this morphology. The shape could be close to the wall-notches, but the latter don’t meet galleries, besides of being smaller in size.
PHREATIC NETWORKS
These morphologies are found throughout the upper level of the Cova des Pas de Vallgornera. It is clearly visible how the joints have a structural control on galleries’ dissolutional process on the ceiling of these passages (Photo 11 and 12).
The cross-section is elongated while the length is always tens or hundreds of metres. Round to elliptic cross-section occurs in the upper third of the passage. Walls are covered by smooth pockets which give a plastered aspect. Ceiling pockets are common. Those features could be related to a first evolutive phase, close to tubular passages. Following that, a horizontal notch with some pockets is found, and one metre below another corrosion notch occurs, leaving a record of a new phreatic stabilization. At the bottom of the gallery, the floor is covered with a sedimentary deposit that hides the joint. A milky-white coating on the floor is highlighted.
TUBULAR PASSAGES
Like phreatic networks, they have a length tens or hundreds of metres. Their marked hemicircular or elliptic cross-section together with the smooth corrosion morphologies, give to this pattern a peculiar shape, mainly in the upper third of the passage. In spite of the fact that the joint is clearly defined, the latter has only been involved partially in its evolution.
SPELEOTHEMS
Subaerial Coralloids, Boytryoidal Speleothems.
This speleothem is found in several passageways and can take a variety of forms, however, the most common in the cave are the branched globular and the grapes-like (photo 13). Coralloids range in size from a few milimetres up to 2 centimetres and are usually white or yellowish in color, when the latter happens it has a wax-like appearance. This kind of speleothem grows on walls, floor or on isolated boulders. Some different features showing the speleothem’s development stage have been reported (photo 14). On the first phase, the coralloids are more elongated and irregular in shape, and it is possible to observe how from a certain point on the rock, the beginning cluster takes place resemblong a cluster of grapes. On later phases, those irregular branched globular protuberances utterly cover the wall and at the same time, hide the primitive and more isolated forms.
Tower Coral.
This subtype of Subaqueous Coralloid is rare in the cave, and has only been found in the Galería del Tragus so far. The speleothem is conical, small-tower-shaped, with uneven walls, is white or brown colored depending on the impurities deposited on it. (photo 15). It is characterized by maximum dimensions of 6 centimetres in height, and 3 centimetres in diameter, is vertical oriented but if a drip has occurred during its growth it can cause the tower to be more irregular and to incline away from the vertical orientation. In cross-section the Coral Tower shows an aragonit radial structure but the calcite outer layer is tougher than the inner aragonite deposit. Generally, when the Tower Corals form, groups of dozens are congragated on the floor and on boulders. The pinnacles are mainly found on the flatter areas of the passage where the surface inclination allows the accumulation of calcite carbonate. Because of that reason, Tower Corals do not exist on the steep slopes of those ancient pools, instead aragonite globular morphologies cover those walls (photo 16). The genesis of this speleothem in the Cova des Pas de Vallgornera could be related to former swallow ponds caused by ancient marine levels stabilization, corresponding to interglaciar periods. This theory could be supported by the fact that the walls of the section of the gallery where the pinnacles are developed, have a horizontal paleolevel band, approximately two metres above the passage’s floor, and 7 metres above the current phreatic level.
Helictites.
Helictites are one of the most common speleothems in the cave and can be found almost in all areas and at small spots or rock shelves; clustered bunches of helictites also occur at some locations throughout the cave (photo 17). These speleothems cover passage floor, walls, columns, stalactites etc. The length of helictites varies greatly, from 2 milimetres up to 25 centimetres, are translucent, white or caramel-colored. Filiform helictites and vermiform helictites have been located during the survey. A group of antler helictites (photo 18) developed on a coating floor is highlighted. A combined bunch of filiform and vermiform helictites covering a rock shelf and its immediately adjacent walls have also been observed. These speleothems are totally covered by a lining consisting of diminutive calcite crystals that hide their original morphology (photo 19). The depositional process might have occured while the area was underwater as a result of an ancient stabilization of the phreatic level. These helictites are larger in diameter due to the crystalline lining and whitish to yellowish in color (photo 20).
Conulites
A conulite is a conical or cylindrical shell caused by dripping water and developed on soft material. The same water that excavates the hollow tube in the soft material, splashes over it and coats a thin layer of calcite. A typical example of this speleothem is found in the Galeria del Tragus, where an inverted cone with a vertically fluted interior, without any coating, has been developed in silt-mud material (photo 21). On the contrary, some coralloidal forms are observed (photo 22).
Bird-bath conulite
The Bird-Bath conulite occurs as an isolated speleothems or in groups of several individuals where sandy, silty and moonmilk deposits are settled (photo 23). Bowl-shaped, with a thick calcium carbonate coating that prevents the dripping water from seeping, small calcite crystals grow when the water is retained for a long period of time. A radial structure caused by water splashes is noted; the range of them is related to the height between the dripping point and the floor, the higher the gallery, the longer the diametre of the speleothem.
A peculiar variety of conulite developed on moonmilk has been reported (photo 24). It closely resembles the typical Bird-Bath conulite’s morphology, but it does not content water and a hollow tube of some centimetres in depth is located. A white vertical, gutter-shaped structure consisting of what appears to be moonmilk is developed on the hollow tube’s mouth (photo 25). This unique speleothem is 8 centimetres in height, about 2 centimetres across its top and has a wall thickness of less than 0,5 centimetre. The genesis could be related both to the materials that form the substratum and to the deposits that are washed away by dripping water. Finally, the plasticity of the materials that form the radial structure is highlighted.
Cave rims
This speleothem has been located along the floor of Sector F, Galeria de les Toberes and Galeria d’en Pau so far (photo 26). Cave rim morphology could resemble a shell, both sides of these projections are strikingly different. While the outside is rough and coraline, the inside is smooth, like the inside of the tube below the rim. Small and whitish crystallizations on the rim’s edge have been spotted (photo 27). Rims occur around the lips of the holes and cracks on the galleries’ floor. White in color they reach a thickness of between 1 and 4 centimetres. With an average height of 2 metres and 1 metre in width, the passages where this morphology has been found are small in size. It appears reasonably certain that the fact that these speleothems are located in the upper maze area of the cave, just above another level which is at the water table level, is clearly related to its genesis.Air flow from the lower level (in contact with the water table which supplies moisture to that air) to the upper level can cause the development of these rims.
Cave Cups
This outstanding speleothem is spread in different gours throughout the cave and looks like a smooth concave dish, some are round or elongated in shape (foto 28). The color and size are variable. Translucent cave cups of about 1 centimetre in diameter and others yellowish with a diameter of 20 centimetres have been reported . They always form on the floor of cave pools, or as an eave-like projection from the wall of those pools. The former are attached to the floor by a penduncle that would be the cup’s apex; the latter have grown from the pool’s walls and are stuck to them, when developed at different levels, they can be used as an indicator of ancient or present water levels. The larger Cave Cups are found in shallow pools, while the medium to small ones occur in deeper pools. The upper part of the cup is usually smooth, whereas small calcite crystals cover the lower one. A Cave Cup with a stalactite fragment in its centre has been spotted, (photo 29). The piece of material could be interpreted as acting as a centre of precipitation for the speleothem to grow.
Shelfstones
Among the variety of shelfstones present in the cave, the candlestick that forms surrounding small columns has been found (photo 30). Others shelfstones are developed around a surmerged stalactite’s extreme (photo 31), where the upper part of the speleothem is flat and smooth, while the lower part is somewhat conical-shaped (photo 32). The thickness of the shelfstone and the calcite crystals layout are emphasized.
One of the most outstandings speleothems that occurs in the cave is the Coke table (photo 33). They are similar to a water lily-pad in shape, like a large plate that is close to 1 metre in diametre and have been developed from a protruded half-submerged point inside a pool. Quite flat and relatively smooth on the upper part, whereas the lower part is rough and formed by an aligned series of layers of macrocrystals composed by calcite. The walls of the big gour where those speleothems have formed are utterly lined by those macrocrystals.