Climatic cycles recorded in the Middle Eocene hemipelagites from a Dinaric foreland basin of Istria (Croatia)

Abstract

Middle Eocene hemipelagic marls from the Pazin-Trieste Basin, a foreland basin of the Croatian Dinarides, display repetitive alternations of two types of marls with different resistance to weathering. This study focuses on the chemical composition, stable isotopes, and palynomorph content of these marls in order to better understand the nature of their cyclic deposition and to identify possible paleoenvironmental drivers responsible for their formation. The less resistant marls (LRM) have consistently lower carbonate content, lower δ 18 O and δ 13 C values, and more abundant dinoflagellate cysts than the more resistant marls (MRM). We interpret these differences between the two marl types to be a result of climatic variations, likely related to Milankovitch oscillations. Periods with wetter climate, associated with increased continental runoff, detrital and nutrient influx produced the LRM. Higher nutrient supply sparked higher dinoflagellate productivity during these times, while reduced salinity and stratification of the water column may have hampered the productivity of calcareous nannoplankton and/or planktonic foraminifera. In contrast, the MRM formed during dryer periods which favoured higher carbonate accumulation rates. This study provides new information about the sedimentary record of short-scale climate variations reflected in wet-dry cycles during an overall warm, greenhouse Earth.

Partitioning of Metal Contaminants between Bulk and Fine-Grained Fraction in Freshwater Sediments: A Critical Appraisal

“…Samples Mi (Mirna) and Ra (Raša) deviate even more from the Al-clay regression line; the highest share of clay fraction determined in these samples does not coincide with the highest content of Al. As mentioned earlier, these samples belong to the rivers draining flysch deposits (Figure S1) where marls having high content of CaCO 3 contribute to the mineral composition of these sediments and dilute the Al-bearing clay component [35]. For all of the mentioned above, the normalization to Al did not seem suitable as a tool for the correction of the grain-size effects on metal concentration in the assessment of the possible anthropogenic impact on the investigated sediments.…”

“…The samples that stand out the most are the same ones with the lowest Al content (Ct, KM, BJ, JP, JK, and KV). However, these are not the only samples with significant Ca content-samples U1, U2 (Una), Ko, Mr, Do (Korana, Mrežnica, Dobra), Ct, Ne, Zr, Km, Od (Cetina, Neretva, Zrmanja, Krka, Odra) were taken from the rivers that drain karstic terrains; samples Mi and Ra, as earlier mentioned, originate from the Mirna and Raša, the rivers draining carbonate-rich flysch deposits (Figure S1), [35].…”

“…Presumably, they associate with clay minerals and reflect the natural origin, which particularly pertains to Cr and Ni. Namely, this group is weighted with samples (Ra, Mi, S1, and S2) relating to catchments rich in the ultramafic component abundant in these elements [35,48]. The negative PC2 axis is influenced by the natural weathering of ore deposits and anthropogenic activities (Cd, Pb, and Zn) along the Drava, Mura, and Krapina rivers.…”