Paolo Forti

Minerogenetic mechanisms occurring in the cave environment: an overview

INTRODUCTION Caves are among the longest-lasting components of the environment and throughout their lifespan act as traps, accumulating physical, biological, and chemical deposits. It is well known that the chemical deposits (i.e., speleothems) are by far the most important for the aesthetic value of a given cave. At the same time, fewer people are aware of the fact that natural caves are among the most important minerogenetic environments of our planet. Perhaps man’s first motivation to explore caves was the search for substances that were not available elsewhere. In fact, from pre-historic times up to the present, many caves have been intensively mined. There is evidence that some ~30.000 years ago, humans were already entering caves in search of pigments (mainly iron and manganese oxides and hy-

Biogenic speleothems: an overview

The idea that speleothems may be somehow influenced by living organisms is rather old, but specific studies have only started in the last few decades and presently there are only a couple of systematic paper on this topic. The role of microorganisms is perhaps the best investigated even if it is not fully understood, while studies over upper organisms and speleothems in a cavern environment are scarce and details are not always given on the involved genetic mechanisms. The aim of the present paper is to give an updated overview on these topics in order to enhance the interest of the scientific community. In fact the complex biochemical reactions involved in the development of the different cave deposits, though still not well understood, clearly have an interest and an importance far exceeding the simple speleogenetic interest.

Seismotectonic and paleoseismic analyses using karst sediments

Abstract Karst speleothemes can be used as a tool for tectonic and seismic analyses; in particular stalagmites can be treated as records of a natural pendulum. These analyses permit the formulation of new hypotheses regarding the activity induced in the surficial faults by deep tectonic systems, as well as the evaluation of main paleoseismic events and their absolute datation. In the present paper the method for analyzing stalagmites is shortly outlined and the main achieved results are reported.

Gypsum karst of the world: a brief overview

Introduction On the glohal scale, surface outcrops of gypsiferous strata appear quite limited. This apparent scarcity can he explained hy the relatively low resistance of gypsum to denudation effects rather then it reflecting an actual limited occurrence of sulphate rocks. The extent of territories where sulphate rocks are present at the surface or at depth is great: Ford & Williams (1979) estimated that gypsum/anhydrite and/or salt deposits underlie 25% of the continental surface (approx. 60 million km2), while Maximovich (1962) calculated that the area of the continents underlain hy gypsum/anhydrite alone is ahout 7 million km2 As is demonstrated in Chapter 1.4and elsewhere in this volume, karst processes operate extensively in intrastratal settings, heneath various types of cover heds, where gypsum heds occur within at least the upper few hundred metres of the rock sequence. Taking this into account, gypsum karst appears to he a much more widely developed phenomenon than is commonly helieved. The largest areas of sulphate rocks are found in the Northern hemisphere, particularly in the United States, where they underlie 35 to 40% of the nations land area (Chapter 11.2),and in Russia and surrounding states, where Gorhunova (1977) estimated an extent of 5 million km2 in the former USSR. However, many other countries within the American continents, Europe and Asia host important, and commonly quite extensive, gypsum karst. Detailed characteristics of many of these are provided within the national reviews comprising later chapters of this volume. The aim of this chapter is to present a brief overview of the geographical distrihution of gypsum karst in the world, with particular reference to those areas that are not descrihed separately, either due to a real scarcity of data or hecause editors were unable to involve local experts. The general order of the reviews hegins in the Americas and proceeds towards the cast. The first hrief glohal reviews specifically dealing with gypsum karst were provided hy Maximovich (1955, 1962). Since then knowledge of gypsum karst, in terms of its morphological and hydrogeological peculiarities, development mechanisms and geographical distrihution, has increased dramatically. Recently the glohal distrihution of gypsum karst has heen considered hy Nicod (1992, 1993).

The speleogenetic role of air flow caused by convection. 1st contribution

In the past some authors described the speleogenetic role of convection in phreatic conditions. Similar effects exist also in the air-filled part of vadose passages of caves as a consequence of an air circulation due to a relevant temperature gradient; the effects can be enhanced by the presence of some acids as, e.g., H2S, H2S04, etc. In this paper the conditions matching convection and condensation which produce typical forms, very similar to those found under phreatic conditions, are discussed both for limestone and gypsum caves.

Hypogene gypsum karst and sinkhole formation at Moncalvo (Asti, Italy).

In the morning of February 15th 2005, during excavation works in an underground gypsum quarry at Moncalvo (Monferrato area, Asti, Northern Italy), a water-bearing fracture was intercepted at level 134 m a.s.l. During the night a large amount of water (approximately 60,000 m3) and mud invaded the quarry tunnels reaching a height of 139 m a.s.l. the morning of the day after. Meanwhile a large sinkhole (20 m wide and 10 m deep) formed on the surface. Hydrogeological surveys were immediately carried out to follow the quickly evolving situation, while speleological and geomorphological fieldwork was made possible only seven months later. Two important caves were discovered both showing clear evidence of a hypogenic origin with sculpted morphologies due to slowly flowing water under pressure. The sinkhole formed by the collapse of one of the main chambers of the biggest of these caves, when buoyant support provided by the water started to decrease due to lowering of the virtual water table. The recharge of this karst system is from below and only very minor quantities of infiltration water come from the above lying surface, as has also been confirmed by hydrochemical analysis. This hypogene karst is completely invisible at the surface and develops entirely underground showing no relation whatsoever with the surface. Its presence is therefore extremely difficult to reveal and such types of karst can thus make up extremely dangerous situations. This is the first example of hypogene gypsum cave related to ascending waters in Italy.

Uranium-series dating of gypsum speleothems: methodology and examples

The analytical problems of dating gypsum speleothems with the U-series technique are reviewed. Gypsum speleothems are, in general, very low in U content, challenging the limits of detection methods. Various approaches to dissolving gypsum and isolation of actinides from the matrix include ion-pairing dissolution with magnesium salts and using nitric acid. The most precise dating technique is Thermal Ionization Mass Spectrometry (TIMS), combined with Fe(OH)3 scavenging and anionic exchange chromatography. Less satisfactory, but much quicker, is direct retention of actinides from HNO3 by means of TRU resin and MC-ICP-MS detection. We have tested these methods on gypsum speleothems from the Sorbas karst in Spain and from the Naica caves in Mexico.

Gypsum caves as indicators of climate-driven river incision and aggradation in a rapidly uplifting region

Detailed geomorphological analysis has revealed that subhorizontal gypsum caves in the Northern Apennines (Italy) cut across bedding planes. These cave levels formed during cold periods with stable river beds, and are coeval with fluvial terraces of rivers that flow perpendicular to the strike of bedding in gypsum monoclines. When rivers entrench, renewed cave formation occurs very rapidly, resulting in the formation of a lower level. River aggradation causes cave alluviation and upward dissolution (paragenesis) in passages nearest to the river beds. The U-Th dating of calcite speleothems provides a minimum age for the formation of the cave passage in which they grew, which in turn provides age control on cave levels. The ages of all speleothems coincide with warmer and wetter periods when CO 2 availability in the soils covering these gypsum areas was greater. This climate-driven speleogenetic model of epigenic gypsum caves in moderately to rapidly uplifting areas in temperate regions might be generally applicable to karst systems in different geological and climatic conditions.

Gypsum-carbonate speleothems from Cueva de las Espadas (Naica mine, Mexico): mineralogy and palaeohydrogeological implications

4Centro de Astrobiología (CSIC-INTA). Crta. Ajalvir, 28850. Torrejón de Ardoz, Madrid, Spain (martinezfj@inta.es) Gázquez F., Calaforra J., Forti P., Rull F. and Martínez-Frías J. 2012. Gypsum-carbonate speleothems from Cueva de las Espadas (Naica mine, Mexico): mineralogy and palaeohydrogeological implications. International Journal of Speleology, 41(2), 211-220. Tampa, FL (USA). ISSN 0392-6672. http://dx.doi.org/10.5038/1827-806X.41.2.8

Siliceous Speleothems and Associated Microbe-Mineral Interactions from Ana Heva Lava Tube in Easter Island (Chile)

Coralloid-type speleothems were recorded on the ceiling of the Ana Heva lava tube in Easter Island (Chile). These speleothems were morphologically, geochemically and mineralogically characterized using a wide variety of microscopy and analytical techniques. They consist dominantly of amorphous Mg silicate and opal-A. Field emission scanning electron microscopy revealed a variety of filamentous and bacillary bacteria on the surface of the Ana Heva coralloid speleothems, including silicified filamentous microorganisms. Among them, intriguing reticulated filaments resemble those filaments documented earlier in limestone caves and lava tubes. The identification of silicified microorganisms on the coralloid speleothems from the Ana Heva lava tube suggests a possible role of these microorganisms in silica deposition.