Secondary halite deposits in the Iranian salt karst: general description and origin

International Journal of Speleology

关键词: karst;    cave;    halite;    secondary deposit;    speleothem;   

DOI  :  

来源: DOAJ

【 摘 要 】

This paper summaries 12 years of documentation of secondary halite deposits in the Iranian salt karst. A variety of secondary halitedeposits was distinguished and classified into several groups, on the basis of the site and mechanism of their origin. Deposits formed:i) via crystallization in/on streams and pools, ii) from dripping, splashing and aerosol water, iii) from evaporation of seepage and capillarywater, and iv) other types of deposits. The following examples of halite forms were distinguished in each of the above mentionedgroup: i) euhedral crystals, floating rafts (raft cones), thin brine surface crusts and films; ii) straw stalactites, macrocrystalline skeletaland hyaline deposits, aerosol deposits; iii) microcrystalline forms (crusts, stalactites and stalagmites, helictites); iv) macrocrystallinehelictites, halite bottom fibers and spiders, crystals in fluvial sediments, euhedral halite crystals in rock salt, combined or transientforms and biologically induced deposits. The occurrence of particular forms depends strongly on the environment, especially on thetype of brine occurrence (pool, drip, splashing brine, microscopic capillary brine, etc.), flow rate and its variation, atmospheric humidity,evaporation rate and, in some cases, on the air flow direction. Combined or transitional secondary deposits can be observed if theconditions changed during the deposition. Euhedral halite crystals originate solely below the brine surface of supersaturated streamsand lakes. Macrocrystalline skeletal deposits occur at places with rich irregular dripping and splashing (i.e., waterfalls, places withstrong dripping from the cave ceilings, etc.). Microcrystalline (fine grained) deposits are generated by evaporation of capillary brineat places where brine is not present in a macroscopically visible form. Straw stalactites form at places where dripping is concentratedin small spots and is frequent sufficient to assure that the tip of the stalactite will not be overgrown by halite precipitates. If the tip isblocked by halite precipitates, the brine remaining in the straw will seep through the walls and helictites start to grow in some places.Macrocrystalline skeletal deposits and straw stalactites usually grow after a major rain event when dripping is strong, whilemicrocrystalline speleothems are formed continuously during much longer periods and ultimately (usually) overgrow the other typesof speleothems during dry periods. The rate of secondary halite deposition is much faster compared to the carbonate karst. Someforms increase more than 0.5 m during the first year after a strong rain event; however, the age of speleothems is difficult to estimate,as they are often combinations of segments of various ages and growth periods alternate with long intervals of inactivity.Described forms may be considered in many cases as the analogues of forms found in the carbonate karst. As they are created in ashort time period the conditions of their origin are often still visible or can be reconstructed. The described halite forms can thus beused for verification of the origin of various carbonate forms. Some of the described forms bear clear evidence of the paleo-watersurface level (transition of the skeletal form to halite crystals and vice versa). Other kinds of deposits are potential indicators of themicroclimate under which they developed (humidity close to the deliquescence relative humidity).

【 授权许可】

Unknown