Abstract
Karst fills from the onshore Penedès Basin and offshore València Trough display red, pink, orange and ochre colours. Their Mössbauer spectra indicate that Fe3+ contained in goethite is the dominant species in reddish-pink fills, whereas Fe2+ contained in dolomite and clays is more dominant in the orange and ochre ones. The lower δ13C values and higher 87Sr/86Sr ratios of the karst fills with respect to their host carbonates can reflect the input of soil-derived CO2 and an external radiogenic source into the karst system. This geochemical composition, together with the non-carbonate fraction of the fills, consists of authigenic and transported illite, illite-smectite interlayers, as well as kaolinite, chlorite, pyrite, quartz, ilmenite, magnetite, apatite and feldspar, account for a mixed residual-detrital origin of fills. This polygenic origin agrees with that of the terra rossa sediments described worldwide. The different colours of karst fills are attributed to fluctuations in the water table, which control the Eh/pH conditions in the karst system. Thus, reddish colours reflect low water table levels and oxidising episodes, and orange and ochre ones reflect high water table levels and more reducing episodes. The greenish colours of fills could be related to fluctuations in the Fe3+/Fe2+ ratio.
Highlights
Karst sediments register the evolution of karst systems developed in carbonate rocks [1]
The main mineralogy of these fills is calcite and dolomite, with minor contents of illite, smectite, kaolinite, chlorite, quartz, feldspar and pyrite; Mössbauer spectrometry of karst fills and adjacent host carbonates indicate that, in general, Fe3+ from goethite is the dominant species in reddish fills, whereas Fe2+
From dolomite is dominant in the ochre to orange fills; The carbonate fraction of karst fills is considered to have originated from the erosion of their host carbonates
Summary
Karst sediments register the evolution of karst systems developed in carbonate rocks [1]. Coloured sediments within karstified rocks are widely recognised worldwide Red sediments such as terra rossa deposits and laterites have been widely attributed to residual soil deposits due to rock weathering [7], detrital inputs are reported in terra rossa sediments. Several diagenetic studies were carried out in these areas motivated by the oil exploitation potential of offshore carbonate reservoirs [3,14,15,16,17,18] These authors deciphered the fracture and fluid flow history in structural highs and normal fault zones, defining different diagenetic events related to the tectonic evolution of the Penedès Basin and València Trough from the Mesozoic to the Neogene. Mediterranean Margin during the Neogene rift-related extension and equivalent systems worldwide
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