Needle-fibre calcite and nanofibres as components of Holocene fissure-filling carbonates in southern Poland

Abstract

The article deals with the carbonates, filling fissures in limestone bedrock and presently exposed in a south-facing rock wall of Kramnica hill (Pieniny Klippen Belt, southern Poland). The carbonates are composed of (i) needle-fibre calcite crystals, (ii) carbonate nanofibres, (iii) carbonate nanoparticles, and (iv) micrite and sparite calcite crystals. Detrital grains from the carbonate bedrock occur subordinately. The spatial relationships of the components give documentation that the nanofibres were formed simultaneously with or slightly later than the needle-fibre calcite crystals. There exists a continuous chain of forms from nanoparticles to elongated nanofibres. This, in turn, indicates that all the above morphological forms are related genetically. In relatively wide fissures, the carbonates studied formed stepped microterracettes, similar to those of speleothems, mainly of moonmilk type. Conversely, narrow fissures are completely filled with carbonates, which display parallel lamination. The carbonates were formed in the late Holocene. However, “dead carbon effect” precludes the possibility of any precise dating of them. Their δ13C and δ18O values are in ranges from -5.1‰ to -3.8‰ and from -6‰ to -4.7‰, respectively. The carbonates studied bear a strong resemblance to soil and spelean, moonmilk-type carbonates. This indicates that continuity exists between the depositional environments of soil and spelean carbonate.