Iron Oxide Crusts in 2 Hypogene Caves in Greece
Publication Date: 2023/06/01
Publication Volume: Journal of Cave and Karst Science 85 #2
DOI Link: https://doi.org/10.4311/2022ES0100
ABSTRACT:
Iron oxide deposits in the form of crusts are examined in the field and in the laboratory with scanning electron microscopy. Samples came from two caves developed in different geological settings but assumed by previous studies to be of hydrothermal-hypogene origin. The relation of iron oxide crusts to cave wall and ceiling morphology created by the cave’s primary dissolution (speleogenesis), as well as to the formation of other speleothems, is investigated. Scanning electron microscope (SEM) elemental analysis showed a high iron content (20–78 % by weight) consistent with iron oxide minerals such as goethite, hematite, magnetite, etc. Three distinct types of iron oxide crusts were identified from the four samples that were analyzed: (1) high iron content crusts with some porosity formed on the host rock surface and discontinuities, (2) high iron content (but lower than type 1) crusts, including limestone clasts and pores originating from dissolved clasts, and (3) high iron content, significantly-porous crusts that are formed by a network of filaments that indicate microbial activity. The formation of these deposits in relation to other speleothems and to dissolution events is discussed.
SIMPLE LANGUAGE SUMMARY:
Researchers studied iron oxide deposits, which are basically rust formations, found in two caves with distinct geological backgrounds. These formations were initially believed to be the result of hydrothermal processes, meaning they were formed by the action of heated water from within the Earth. The research involved both field examinations and detailed laboratory analysis using a scanning electron microscope (SEM), which allows for extremely detailed images of the samples at a microscopic level. The SEM analysis revealed that these iron oxide crusts contain a large percentage of iron, ranging from 20% to 78%, suggesting they're composed of minerals like goethite, hematite, and magnetite. Three unique types of iron oxide crusts were identified: 1)Crusts with a very high iron concentration and some porosity (meaning they have small holes) that were found on the surface of the host rock and its discontinuities, like cracks. 2)ron-rich crusts, though with slightly less iron than the first type, which incorporated limestone fragments and exhibited porosity due to the dissolution of these fragments. 3)Highly porous iron crusts characterized by a network of filament-like structures, indicative of microbial influence in their formation. The study also delved into how these iron oxide crusts relate to other cave formations, known as speleothems, and how they might have formed as a result of various events that dissolved the rock over time, shaping the cave's features.
