The relationship between the geochemical and mineralogical characteristics of Calcocambisol, colluvium and recent marine lake sediment of the narrow seashore intertidal zone: a case study from the Veliko Jezero (Mljet Island, Croatia)

Abstract

This study investigates the mineral composition, particle size distribution and geochemical characteristics of Calcocambisol, colluvium and recent marine lake sediment in a narrow intertidal seashore zone of the Veliko Jezero on the Island of Mljet (Croatia). The obtained results show that the fractions of Calcocambisol/colluvium less than 2 mm and 2 μm display similar particle size distribution (PSD) curves compared to marine lake sediments containing larger particles in these fractions. The smallest fractions of the investigated materials that are less than 1 μm show identical PSD curves. The bulk and clay mineral composition of the marine lake sediment show that the non-carbonate fraction is derived from weathering of the surrounding soils and colluvium containing quartz, feldspars and phyllosilicates (illitic material, kaolinites, chlorite, and a mixedlayer clay mineral, MLCM), as well as the authigenic formation of early-diagenetic pyrite, while one part is related to the yield of material by aeolian deposition (amphibole). The observed difference between the phyllosilicate mineral phases in the clay fraction of the Calcocambisol/colluvium and the carbonate-free clay fraction of the marine lake sediment is related to 1) the presence of chlorite in the marine lake sediment and 2) the higher content of MLCM in the Calcocambisol/colluvium. The chlorite in the marine lake sediment was inherited from the Calcocambisol/colluvium as a result of soil erosion prior to its complete destabilization in the soil. High Chemical Index of Alteration (CIA) values in the Calcocambisol and colluvium clearly indicate their intense weathering. Based on the Sm/Nd and Ti/Al ratios, it can be concluded that the aluminosilicates in the Calcocambisol, colluvium and marine lake sediment are of the same provenance. The distribution of each analysed element among the sequential fractions is very similar in both the Calcocambisol and colluvium. The highest concentrations for most of trace elements in the Calcocambisol, colluvium and marine lake sediment was determined in their residual fraction. Mn, Co and Pb show a different partitioning between the Calcocambisol/colluvium and marine lake sediment, respectively. However, systematic studies of the influence of soils on the formation and geochemical characteristics of recent sediments from the seashore intertidal zone of the Adriatic Sea have, to our knowledge, rarely been reported in the literature (SONDI et al., 1994; JURINA et al., 2015). ROGAN ŠMUC et al. (2018) studied the distribution of heavy metals in surface sediments from Koper Bay (north Adriatic Sea) using a sequential extraction procedure. The authors found that the majority of the analyzed metals could be considered immobile due to their high affinity for binding to the residual phase. It is well-known that the presence and distribution of the mineral phase gives an indication of the origin of the material of which the sediments are composed. Numerous studies of mineral distributions in recent marine sediments dealing with this issue have been implemented (TOMADIN, 2000; GOVORČIN et al., 2001; SONDI & JURAČIĆ, 2010). Most recently, IVANIĆ et al. (2020) analyzed the mineral composition of recent marine sediments and concluded that the dominant input of terrigenous material into the Mljet marine lake system is limited to soil erosion and aeolian deposition. Previous studies (SONDI & JURAČIĆ, 2010) of the Mljet Lakes have shown that the authigenic formaArticle history: Manuscript received December 09, 2020 Revised manuscript accepted March 22, 2021 Available online June 30, 2021