www.geologia-croatica.hr Journal of the Croatian Geological Survey and the Croatian Geological Society 2024 | 77/3 | 311–323 | 6 Figs. | 7 Tabs. | 1 Supplement | 1. INTRODUCTION Weathering is a complex set of processes occurring at or near the Earth’s surface, resulting in physical and chemical rock alteration. It involves processes that span many orders of magnitude in spatial and temporal scales (FRINGS & BUSS, 2019), so consequently the meaning of “weathering” may be dependent on the standpoint, which leads to the need of its precise definition (HALL et al., 2012). In this study, the term is used for parent material alteration (relating to the chemical composition) and secondary mineral formation in response to environmental factors, dominantly climate. Apart from climate, dictating the weathering rate and intensity, parent material composition sets the “starting position” and is the dominant influence on the secondary weathering products, especially in the early stages of weathering. In this case, studying the profiles in a temperate climate region formed on different parent materials, both of these factors are taken into account. The use of (clay) minerals and geochemical signatures in studies of past weathering conditions has gained traction in the research of the critical zone, defined by BANWART et al. (2012) as the terrestrial environment extending from the top The influence of weathering and pedogenesis on the geochemical record of Miocene marls and Plio-Quaternary sediments, Medvednica Mt., Croatia Zvonka Gverić1,*, Nenad Tomašić1, Goran Durn2 and Vedran Rubinić3 1 University of Zagreb, Faculty of Science, Department of Geology, Horvatovac 95, 10000 Zagreb, Croatia; (*corresponding author: zgveric@geol.pmf.hr) 2 University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Department of Mineralogy, Petrology and Mineral Resources, Pierottijeva 6, 10000 Zagreb, Croatia 3 University of Zagreb, Faculty of Agriculture, Department of Soil Science, Svetošimunska 25, 10000 Zagreb, Croatia doi: 10.4154/gc.2024.17 Abstract The geochemical signature of weathering and pedogenesis in a temperate humid climate on two parent material types in the foothills of Medvednica Mt. was studied. Five soil pro- files on Miocene marls and three sections of Plio-Quaternary (PlQ) proluvial sediments with overlying soil and weathered material were analyzed. The (clay) mineralogy of all profiles and sections had been determined in previous studies. The chemical composition of the samples was determined by inductively coupled plasma emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectroscopy (ICP-MS). Poorly ordered Fe and Mn oxides were determined in the PlQ sediment and overlying soil samples by atomic absorp- tion spectroscopy (AAS), after oxalate dissolution in the dark. The concentrations and ele- ment ratios were used to determine element enrichment/mobility and intensity of chemical weathering, material provenance, and to compare the geochemical signatures with previ- ously obtained clay mineralogy results. Trace elements in the Miocene marls, including rare earth elements (REE), indicate the continental origin of the marl siliciclastic component, while more scattered geochemical data of the PlQ sediments reflect their proluvial/torren- tial nature. The mass transfer coefficient (τ) for major elements and element ratios of the Miocene marl profiles indicate chemical weathering and pedogenesis of lower intensity. The geochemistry of these samples shows homogeneity within the profiles. In the geo- chemical signature of the PlQ sections, a chaotic proluvial deposition of the material is vis- ible, as well as the heterogeneity with the overlying soil and weathered material. Overall, the geochemistry results largely support the clay mineralogy of the samples and demon- strate how a multiproxy approach can help test hypotheses about past environments and provide valuable additional information for complex paleoenvironmental studies. of the vegetation canopy to the bottom of drinking water aquifers, in the past few decades (e.g., GODOY et al., 2017; ZOLLINGER et al., 2017; DINIS et al., 2020; BŁAŻEJOWSKI et al., 2023; CORENTIN et al., 2023). Clay minerals forming as secondary minerals in equilibrium with the prevalent environmental conditions serve as useful proxies for paleo­ environmental studies. The problem arises when clay minerals in recycled material undergo multiple weathering cycles, thus overwriting the past or misrepresenting more recent weathering processes. Geochemical signatures, even though also prone to the same issues, can give an additional insight and contribute to the multiproxy approach needed in this type of studies. For this reason, geochemical analyses were included for samples where the clay mineralogy had already been analyzed. The reasoning behind adding another proxy, was the possibility of confirming or refuting conclusions drawn on the basis of mineralogical data. This paper focuses on the effect of weathering (and pedogenesis) on the sediments of the SE slopes of Medvednica Mt., located north of the city of Zagreb in Croatia (Fig. 1), i.e. in the SW part of the Pannonian Basin System (PBS). While Article history: Manuscript received: January 10, 2024 Revised manuscript accepted: July 16, 2024 Available online: October 28, 2024 Keywords: geochemical weathering indices, temperate climate weathering, sediment provenance, pedogenesis geochemical signature, Miocene marls, Plio-Quaternary proluvial sediments G eo lo gi a C ro at ic a 312 Geologia Croatica 77/3 the majority of the paleoenvironmental studies of the PBS so far have used sedimentological, paleontological and palyno lo­ gical proxies (for instance, BAKRAČ & KOCH, 1999; BAKRAČ et al., 2012), HARZHAUSER et al. (2023) have included clay mineralogy and geochemical records alongside paleontological data to study changes in the paleoenvironment of the Vienna basin during the Late Miocene. Several papers on samples and soils from Medvednica Mt. and the adjacent areas have used (clay) mineralogy and/or geochemical records (e.g., GALOVIĆ & PEH, 2014; GRIZELJ et al., 2017; KUREČIĆ et al., 2021), but mostly in terms of provenance determination, defining the sedi­ mentary environ ment, or evaluating the influence of the parent material on the soil profiles. Geo che mical data in the context of the weathering effect on the rocks and sediments of this area have, to the authors’ knowledge, not been as thoroughly con­ sidered. The benefits of this location, aside from its lithological variety, is its position in the temperate climate zone, where transient and intermediate steps of the weathering process can be studied and the effect of small changes in weathering intensity can be seen in the mineralogy and geochemistry. The clay mineralogy of the samples used in this study had been previously investigated (GVERIĆ et al., 2022, 2023). The profiles selected for the above­mentioned studies were developed on the Miocene marls (ranging in age from Early to Late Miocene) and Plio­Quaternary (PlQ) proluvial, molasse­ type, sediments, both of which are common soil parent materials in the study area. Clay mineralogy of the studied Miocene marls bedrock and the overlying soil indicates less intense weathering, also dictated by increased pH values due to the presence of carbonates. Clay mineralogy of the marl parent material is dominated by smectite­rich illite­smectite and contains illite, kaolinite and sometimes chlorite. Changes in clay mineralogy between the parent material and soil are subtle, visible in the appearance of transient mixed­layered phases including chlorite­vermiculite and possibly hydroxyl or organic interlayering of the expandable clay minerals in the soil profile (GVERIĆ et al., 2022). In contrast, the clay mine­ ralogy of the PlQ sediments (analyzed in GVERIĆ et al., 2023) consists of more clay mineral species typical of hot and humid areas (kaolinite, low­charge expandables), in addition to the presence of Al (oxy)hydroxides. Most of the PlQ sediments are covered with more recent proluvial material, while some are covered with older wind­blown material (loess). This loess cover is thin and usually completely degraded into a pseudo­ gleyed loess derivate, on which Stagnosols are formed. The clay mineralogy of this overlying material and soil contains expandable clay minerals of higher layer charge and inter­ mediary clay phases, such as hydroxyl­interlayered minerals, suggesting moderate recent and current weathering conditions. The main aim of this paper is to investigate whether the geochemical records of the investigated Miocene and PlQ sec­ tions are consistent with the composition of the clay mineralogy, i.e. with the intensity of weathering and pedogenesis inferred from the clay mineralogy. If this is the case, it would support our previous conclusions and confirm the key role of soil/sedi­ ment geochemistry together with clay minerals assemblage, in the multidisciplinary study of weathering in relation to (paleo)environmental conditions. 2. STUDY AREA Medvednica Mt. is one of the inselbergs in the southwestern part of the PBS, consisting of exposed metamorphosed and non­metamorphosed sediments of Paleozoic to Mesozoic age, as well as of some Mesozoic volcanics, all surrounded by Miocene sediments (ŠIKIĆ et al., 1978; BASCH, 1981; TOMLJENOVIĆ et al., 2008; CROATIAN GEOLOGICAL SURVEY, 2009; VAN GELDER et al., 2015). The PBS was formed during Miocene extension as a back­arc basin and its sedimentary succession is characterized by the changing tectonic environment (PAVELIĆ & KOVAČIĆ, 2018). Early Miocene sedimentation was dominantly continental with fluvio ­lacustrine sedimentation processes. Previous prove­ nance research by KOVAČIĆ et al. (2011) indicates that the material originated mainly from the Inner Dinarides during the Early and Middle Miocene, while the Upper Miocene clastic detritus is mainly of Alpine­Carpathian provenance. PlQ sediments on Medvednica Mt. were deposited pre­ dominant ly as unsorted, molasse type fluvial and proluvial sediments with material sourced locally from the older Medved nica Mt. lithology (ŠIKIĆ, 1995). Based on the sedimentological and paleontological record, the Early Miocene climate was semi­dry (PAVELIĆ et al., 2016) and it became progressively warmer and more humid in the Middle Miocene (MARKOVIĆ et al., 2021). After another dry cycle in the Middle Miocene (JIMÉNEZ­MORENO et al., 2005), the Late Miocene climate became very humid and warm before cooling towards the end of the period (HARZHAUSER et al., 2007). During the Pliocene, the climate was still warmer than the present day, especially during the mid­Pliocene warm period (PRISTA et al., 2015; SZABÓ et al., 2022), but it became subsequently colder and drier. The Quaternary is marked by glaciation intervals in the Pleistocene as well as coeval loess deposition (RUBINIĆ et al., 2018). The present day climate of the area is temperate humid (Cfwbx in Köppen classification), with a mean annual air temperature of 10°C and mean annual precipitation of 1000­1100 mm, and no distinct dry period (ZANINOVIĆ et al., 2008). Vegetation cover, anthropologically substantially modified, mostly varies from deciduous forest comprising beech, hornbeam and oak (natural cover) to orchards and grassland. Medvednica Mt. is currently 1033 m high, with the mountain’s main ridge stretching in a SW­NE direction and it is divided into three distinct orographic units. Due to young tectonic movements and denudation processes, the landscape is intersected by a number of streams and valleys extending from the central massif to the foothills, perpendicular to the direction of the mountain’s line of extension (Fig. 1). It is a moderately to markedly dissected hilly and mountainous relief with rather versatile sloping, which can be very steep in places with the occurrence of landslides (LOZIĆ, 2001; MIHALIĆ ARBANAS et al., 2016). Accordingly, the soils of the studied profiles are mostly thin (e.g., Leptosols and Regosols); however, some more developed soils, such as Cambisols and Stagnosols, also occur (GVERIĆ et al., 2022, 2023). In the study of parent material influence on soil properties on Medvednica Mt., spanning different lithologies, PERKOVIĆ et al. (2017) iden­ tified Dystric Cambisol, Eutric Cambisol, Calcaric Cambisol, Stagnosol, Regosol and Luvisol. G eologia C roatica 313Gverić et al.: The influence of weathering and pedogenesis on the geochemical record of Miocene marls and Plio-Quaternary sediments ... 3. MATERIALS AND METHODS A total of 25 samples from 8 locations were studied (Table 1, Fig. 1). However, due to differences in parent material and sampling strategies, the samples are divided into two distinct groups: profiles developed on the Miocene marls and soil sections overlying PlQ sediments. As a result, the data for the two groups of samples were, in some cases, treated differently to account for the differences between them. 3.1. Miocene marl and argillaceous limestone profiles: description and analytical methods The (clay) mineralogy of these samples, along with selected physical and chemical properties, has already been presented in GVERIĆ et al. (2022). Five soil profiles are developed on Miocene marly sediments, with clay mineral content dominated by smectite­rich illite­smectite and containing illite, kaolinite and minor vermiculite. Chlorite is detected only in some parent material samples. Soil profiles overlying this parent material are poorly to moderately developed and there is no lithic discontinuity present. The texture class of Miocene marls and the overlying soil samples is mainly silt loam and subordinately silt clay loam, the samples are calcareous throughout with pHH2O values ranging from 7.6 to 8.4 and the chemical composition is dominated by Si, Al and Ca (GVERIĆ et al., 2022). The chemical composition of the Miocene marl profiles samples (Table 2) was determined in the Bureau Veritas (Acme Analytical Laboratories), in Vancouver, BC, Canada, using ICP­OES and ICP­MS after sample fusion with lithium metaborate as well as sample digestion in aqua regia for trace elements (e.g., Sc and Th used in provenance analysis). 3.2. PlQ sections: description and analytical methods Another three locations are located on PlQ sediments overlain by weathered material and soil (at some locations genetically unrelated, i.e. interrupted by a lithic discontinuity), with the clay mineralogy dominated by expandable clay minerals (smectite and/or vermiculite) and containing some illite and kaolinite, as well as mixed­layer and hydroxyl­interlayered Figure 1. The geographical position of the sample locations and local lithology (blue lines show recent drainage directions (streams) on the SE slopes of Medvednica Mt.); modified after TOMLJENOVIĆ (2002). LZB – Laz Bistrički, ČUČ – Čučerje, MTR – Markuševečka Trnava, FUR – Furdini, JES – Jesenovec, DOT – Dotrščina, OPO – Oporovec, H2 – Horvatovac borehole. G eo lo gi a C ro at ic a 314 Geologia Croatica 77/3 Table 1. Investigated samples and their clay mineralogy; Fe/Al oxides are included if present. LOCATION SAMPLE LABEL and depth in cm SAMPLE TYPE CLAY MINERALS AND Fe/Al OXIDES PRESENT IN THE SAMPLES M io ce ne p ro fil es Laz Bistrički N 45.957769 E 16.090546 LZB 0-10 soil I-S, I, V, K, Ch-V* LZB 10-30 soil I-S, I, V, K* LZB 30-50 marl I-S, I, V, K* Čučerje N 45.894835 E 16.063706 ČUČ 0-20 soil I-S, I, K, IM?* ČUČ 200 marl I-S, I, K* Markuševečka Trnava N 45.880720 E 16.023345 MTR 0-20 soil I-S, I, V, K, Ch-V/IM?* MTR 35-40 marl I-S, I, V, K* MTR 150 marl I-S, I, V, K, Ch* Furdini N 45.872790 E 16.076558 FUR 0-20 soil I-S, I, V, K, Ch-V?* FUR 20-60 soil I-S, I, V, K, Ch-V?* FUR 70 argillaceous limestone I-S, I, V, K, Ch* Jesenovec N 45.92005 E 16.14435 JES 0-20 soil I-S, I, V, K, Ch, Ch-V?* JES 20-40 soil I-S, I, V, K, Ch, Ch-V?* JES 40-90 soil I-S, I, V, K, Ch, Ch-V?* JES 220 marl I-S, I, V, K, Ch* Pl Q s ec tio ns Dotrščina N 45.86028 E 16.01972 DOT 25 soil V, K, HIM** DOT 120 soil V, S, I, K, Ch-V/S?** DOT 300 (proluvial) sediment V, S, I, K, Gth, Gbs, Hem** Oporovec N 45.84974 E 16.07052 OPO 25 soil S, V, K, I, Ch-V?** OPO 40 soil S, K, I** OPO 70 (proluvial) sediment S, K, I, V** Horvatovac (borehole) N 45.825910 E 15.987865 H2 25 soil S, K, I, HIM, Gth,** H2 70 soil HIM, K, I, Gth** H2 150 (proluvial) sediment S, K, I, V** H2 250 (proluvial) sediment S, K, I, Gth** I-S: illite-smectite, I: illite, V: vermiculite, K: kaolinite, Ch-V: interstratified chlorite-vermiculite, IM: interlayered clay mineral in which the types of interlayering were not recognized with certainty, Ch: chlorite, HIM: hydroxy-interlayered mineral, S: smectite, Ch-V/S: interstratified chlorite-expandable clay mineral, Gth: goethite, Gbs: gibbsite, Hem: hematite. *data from GVERIĆ et al. (2022) **data from GVERIĆ et al. (2023) Table 2. Concentrations of major elements (in %) of the samples (from previous studies). Sample SiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O TiO2 P2O5 MnO Cr2O3 LOI Sum Reference M io ce ne p ro fil es LZB 0-10 28.91 8.12 3.83 2.08 25.78 0.27 1.38 0.35 0.12 0.09 0.025 28.8 99.76 G VE RI Ć et a l., 2 02 2 LZB 10-30 26.93 8.3 3.91 2.2 27.4 0.27 1.49 0.36 0.07 0.08 0.04 28.7 99.75 LZB 30-50 23.97 7.3 3.04 2.26 30.56 0.26 1.33 0.33 0.08 0.08 0.017 30.6 99.83 ČUČ 0-20 23.39 4.95 2.07 0.81 28.28 0.32 0.82 0.25 0.2 0.05 0.006 38.6 99.75 ČUČ 200 16.31 3.6 1.31 0.73 40.59 0.24 0.69 0.18 0.12 0.04 0.005 35.9 99.72 MTR 0-20 52.46 15.14 6.76 1.44 3.99 0.76 1.8 0.87 0.11 0.09 0.016 16.4 99.84 MTR 35-40 20.78 5.74 2.43 1.73 34.58 0.3 0.88 0.28 0.09 0.04 0.006 33 99.86 MTR 150 22.34 5.82 2.34 2.2 33.79 0.3 0.91 0.29 0.1 0.04 0.006 31.7 99.84 FUR 0-20 45.04 14.83 5.97 1.57 9.03 0.6 2.19 0.72 0.12 0.11 0.015 19.6 99.80 FUR 20-60 25.05 8.51 3.25 1.41 29.54 0.33 1.4 0.35 0.09 0.07 0.009 29.8 99.81 FUR 70 26.64 8.38 3.31 1.7 27.46 0.4 1.32 0.36 0.09 0.08 0.009 30.1 99.85 JES 0-20 38.66 12.53 4.73 3.93 13.18 0.81 2.33 0.59 0.14 0.08 0.012 22.8 99.79 JES 20-40 42.48 13.85 4.84 4.04 12.56 0.91 2.48 0.64 0.11 0.07 0.014 17.8 99.79 JES 40-90 41.01 13.82 5.39 3.69 13.9 0.92 2.51 0.6 0.11 0.08 0.013 17.7 99.74 JES 220 47.82 15.16 5.18 4.69 7.56 1.07 2.86 0.7 0.12 0.07 0.015 14.5 99.75 Pl Q s ec tio ns DOT 25 68.58 12.75 3.82 0.81 0.47 1.20 1.54 1.26 0.10 0.13 0.01 6.2 96.90 G VE RI Ć et a l., 2 02 3 DOT 120 61.75 14.00 6.01 1.09 0.51 1.00 1.79 1.11 0.12 0.47 0.01 6.2 94.07 DOT 300 54.91 16.12 6.62 1.66 1.58 1.58 1.22 1.37 0.12 0.01 0.02 9.2 94.42 OPO 25 66.53 12.94 3.86 0.59 0.29 0.90 1.61 1.20 0.08 0.05 0.01 6.8 94.87 OPO 40 61.75 14.89 4.82 0.73 0.34 0.69 1.70 1.11 0.06 0.05 0.01 7.4 93.55 OPO 70 59.24 16.80 5.16 1.20 0.47 0.60 1.95 1.00 0.08 0.08 0.01 9.2 95.78 H2 25 64.71 14.43 5.57 1.01 0.67 1.09 1.78 1.19 0.11 0.14 0.01 8.2 98.94 H2 70 68.13 14.19 4.31 1.16 0.67 1.30 1.88 1.24 0.11 0.07 0.01 5.6 98.67 H2 150 62.43 16.49 4.93 0.71 0.49 0.59 1.42 1.17 0.02 0.03 0.01 8.0 96.31 H2 250 57.65 18.59 5.15 0.97 0.61 0.64 1.60 1.00 0.03 0.02 0.01 9.2 95.46 G eologia C roatica 315Gverić et al.: The influence of weathering and pedogenesis on the geochemical record of Miocene marls and Plio-Quaternary sediments ... minerals in some samples. PlQ sections are more complicated as PlQ sediments were locally covered by loess which was subsequently altered. Chaotic proluvial sedimentation during this period also resulted in substantial differences in PlQ sediment material, especially considering mineral content and granulometric properties. The samples show variation in texture; the Dotrščina samples are silt loam throughout, while the Oporovec samples vary from silty clay to silt loam and the Horvatovac borehole PlQ sediment is silty clay with the overlying soil having silt and silt loam horizons. There is a lithic discontinuity present in the Dotrščina and Horvatovac sections. The samples do not contain carbonates; the chemical composition is dominated by Si, Al and Fe (Table 2), and the pHH2O values range from 4.2 to 6.7 (GVERIĆ et al., 2023). The elemental composition for PlQ sections samples was determined at the Institute of Geology, Jagiellonian University, Kraków, Poland, using Spectro Arcos (ICP­OES) spectrometer (SPECTRO Analytical Instruments GmbH, Kleve, Germany) with the radially (side­on) viewed torch configuration. The samples were digested in a mixture of spectrally clean and concentrated nitric, hydrochloric, and hydrofluoric acids in the presence of boric acid in the Ethos­Up Milestone microwave oven (Milestone Srl, Sorisole (BG), Italy). Certified reference material OREAS 920 (Oreas®, Melbourne, Australia) was processed and measured in the same way as the samples in the same analytical cycle to monitor the accuracy of the analyses. 3.3. Provenance and selected weathering indicators To assert provenance, TiO2/Al2O3 and Sm/Nd ratios were related to the Eu/Eu* ratio in order to compare the geochemical signature of the samples to the known values for different types of rocks taken from CONDIE (1993). The values taken are for the Phanerozoic or average Paleozoic and Mesozoic protolith. The analysis of provenance based on trace and rare earth elements (REEs) was undertaken on Miocene marl samples and diagrams La­Th­Sc and Th­Sc­Zr/10 proposed by BHATIA & CROOK (1986) were used for this purpose. REE concentrations were normalized to chondrite values (McDONOUGH & SUN, 1995) to detect any differentiation of the elements in earlier geological processes, and to Upper Continental Crust values (RUDNICK & GAO, 2014) to account for their subsequent distribution during weathering and pedogenesis. Ratios of the major chemical elements (Na/Ti, Ca/Ti, Al/ Na, Al/K, Al/Ti) as well as La/Sm ratio were used to detect element (im)mobility and to make further comparisons between the parent material and the overlying soil, with respect to the weathering intensity and its impact on the mineral and chemical record. The extent of (chemical) weathering for profiles developed on Miocene carbonate sediments was inferred from calculation of a mass transfer coefficient (τ) for the main elements (Si, Al, Fe, Mg, Ca, Na and K) with Ti considered an immobile element (BRIMHALL & DIETRICH, 1987; CHADWICK et al., 1990; YANG et al., 2015). For PlQ sections, having a more complex development and exhibiting lithic discontinuity in two of the investigated localities, weathering indices listed in Table 3 were used. Given that the studied PlQ colluvial sediments incorporate geochemical signatures of past weathering cycles with various protoliths included, a range of different weathering indices was used and compared. The main motive was to observe the trends, not the absolute values, and also to evaluate the suitability of the indices used for proluvial material derived from multiple sources. Weathering indices used were the Chemical Index of Alteration (CIA; NESBITT & YOUNG, 1982), as the most commonly employed quantitative measure of chemical alteration, and the Plagioclase Index of Alteration (PIA; FEDO et al., 1995) which accounts for K immobilization due to clay mineral formation. We have also calculated the Chemical Index of Weathering (CIW; HARNOIS, 1988), which excludes K from the calculation due to its possible retention in some clay mineral phases, and Chemical Proxy of Alteration (CPA; BUGGLE et al., 2011), which omits both Ca and K from the calculation and is found to be the most suitable for loess and paleosol samples. The aforementioned chemical indices, although initially mostly developed to measure geochemical weathering effects in silicate rocks, have so far been used for a wide variety of soil and sediment samples (e.g., WEI et al., 2006; TABOADA et al., 2016; DINIS et al., 2020; HEIDARI et al., 2022). The fraction of poorly ordered Fe and Mn oxides was deter mined for the PlQ sections after dissolution of the samples in acid ammonium oxalate (method according to SCHWERTMANN, 1964). The samples were suspended in acid ammonium oxalate and the reaction proceeded in the dark. After filtration (also in the dark), Fe and Mn con cen­ trations (ammonium oxalate extractable iron and manganese) were measured from the filtrate using AAS (Analyst 700). 4. RESULTS AND DISCUSSION 4.1. Tectonic setting and material provenance Relationships between Eu/Eu* and TiO2/Al2O3 as well as between Eu/Eu* and Sm/Nd show marl samples plotting near UCC and PAAS values, while the PlQ samples’ values are more scattered (Fig. 2). Provenance data for the Miocene marl samples as well as for their derivatives imply their origin from a well­differentiated continental material that can be averaged to the shale geochemical signature. When assessing the provenance and tectonic setting for PlQ samples, a proluvial Table 3. Weathering indices used for the samples of PlQ sections (calculated on the basis of the molar proportions of the element oxides). Index Formula Reference CIA [Al2O3 / (Al2O3+K2O+CaO+Na2O)] X 100 NESBITT & YOUNG, 1982 PIA [(Al2O3-K2O )/(Al2O3+CaO+Na2O-K2O)] X 100 FEDO et al., 1995 CIW [Al2O3/(Al2O3 + CaO +Na2O)] X 100 HARNOIS, 1988 CPA [Al2O3/(Al2O3 + Na2O)] X 100 BUGGLE et al., 2011 G eo lo gi a C ro at ic a 316 Geologia Croatica 77/3 nature of the sediments has to be taken into consideration; torrential streams eroded upstream rocks of various ages and origin, resulting in the accumulation of PlQ sediments in the foothills of Medvednica Mt (Fig. 1). The tectonic setting for Miocene sedimentary rocks and overlying soil samples was established using trace elements discriminatory plots proposed by BHATIA & CROOK (1986). The results place the samples in the continental island arc field, thereby corresponding to the results of GRIZELJ et al. (2017), obtained for Miocene pelitic sediments of the area (Fig. 3). This also corresponds with the definition of the PBS as a back­ arc basin (ROYDEN et al., 1983) and the postulated repeated extensions and inversion affecting the area since the Early Miocene (TOMLJENOVIĆ & CSONTOS, 2001; TOMLJE­ NOVIĆ et al., 2008). The use of major elements in inferring provenance and tectonic setting (such as ROSER & KORSCH, 1986) has proven to give erroneous results. The issue with the parameters used in samples containing clay minerals could be the pre fe­ rential K+ retention in the interlayer space (BERGAYA et al., 2006), resulting in non­representative K2O/Na2O ratio values. 4.2. REE distribution REE distribution (Table 4) shows the primary enrichment of REE in the source material as evidenced by chondrite nor ma­ lization (Figs. 4a,b). The enrichment of LREE compared to chondrite values is particularly pronounced, with the enrich­ ment factor from 50 to up to several hundreds. All samples, except DOT 120, show a negative Eu anomaly. The general enrichment and trend is similar for both Miocene and PlQ parent sediments as well as for their derivatives. The Eu ano­ maly suggests the sediments were derived from already diffe­ ren tiated material. When REEs are normalized to UCC (Fig. 4c,d), all samples generally present REE abundances around those of nor ma li­ za tion standards. A flat distribution trend indicates no prefe­ rential leaching of particular REEs during weathering or pedogenesis (see later discussion of the La/Sm ratio throughout the samples). For all normalization cases, no significant dis­ Figure 2. (a) Eu/Eu* and TiO2/Al2O3 binary plot, and (b) Eu/Eu* and Sm/Nd binary plot, showing the geochemical signature of the samples in relation to the reference values of some common rock types (data from CONDIE, 1993). Figure 3. Samples from Miocene marls profiles plotted on discrimination plots for tectonic settings according to BHATIA & CROOK (1986). Data on trace element composition used are available in the supplementary materials. G eologia C roatica 317Gverić et al.: The influence of weathering and pedogenesis on the geochemical record of Miocene marls and Plio-Quaternary sediments ... tinction between the parent material and soil/weathered ma­ terial is observed, supporting a presumption of overall inter­ mediate weathering intensity. Miocene and PlQ profiles can be readily distinguished by the magnitude and the trend of REE distribution in all normalization cases. This could be partly attributed to the granulometric variations of the samples; Miocene fine­grained samples contrast the sand­silt­clay features of the PlQ samples. Additionally, these variations in REE distribution can also attest to different source material properties. 4.3. Element mobility The mobility of chemical elements depends, among other factors, on the intensity of weathering processes. Alkali and Table 4. Concentrations of REE (in ppm) of the studied samples. Sample Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Eu/Eu* (Ch) (LREE/ HREE)UCC M io ce ne p ro fil es LZB 0-10 19.2 20.1 37.6 4.6 16.9 3.4 0.7 3.3 0.5 3.0 0.7 1.8 0.3 1.6 0.3 0.64 0.74 LZB 10-30 15.5 17.0 33.7 3.9 14.7 3.0 0.6 2.8 0.5 2.7 0.6 1.5 0.2 1.4 0.2 0.61 0.73 LZB 30-50 16.3 17.0 31.3 3.8 14.2 2.9 0.6 3.0 0.5 2.7 0.6 1.5 0.2 1.4 0.2 0.64 0.74 ČUČ 0-20 13.2 14.8 25.7 3.2 11.5 2.3 0.5 2.4 0.4 2.3 0.4 1.3 0.2 1.2 0.2 0.61 0.73 ČUČ 200 10.6 11.2 17.6 2.5 9.2 1.8 0.4 1.9 0.3 1.8 0.4 1.1 0.1 0.9 0.1 0.64 0.71 MTR 0-20 36.5 43.7 83.6 10.2 37.6 7.5 1.6 7.0 1.1 6.3 1.3 3.6 0.5 3.3 0.5 0.67 0.80 MTR 35-40 12.5 14.8 27.4 3.4 12.8 2.4 0.6 2.5 0.4 2.1 0.4 1.3 0.2 1.2 0.2 0.69 0.79 MTR 150 13.0 15.2 27.9 3.4 12.8 2.6 0.5 2.4 0.4 2.1 0.4 1.3 0.2 1.1 0.2 0.64 0.81 FUR 0-20 29.3 39.0 72.8 8.7 32.1 6.3 1.3 5.7 0.9 5.0 1.0 2.9 0.4 2.7 0.4 0.65 0.86 FUR 20-60 16.0 20.8 39.5 4.7 17.8 3.4 0.7 3.2 0.5 2.8 0.6 1.6 0.2 1.4 0.2 0.69 0.86 FUR 70 16.6 21.6 39.6 4. 8 17.5 3. 5 0.7 3.3 0.5 2.9 0.5 1.6 0.2 1.5 0.2 0.66 0.86 JES 0-20 23.9 30.0 57.7 6.8 25.5 4.8 1.0 4.5 0.7 4.0 0.8 2.4 0.3 2.2 0.3 0.66 0.84 JES 20-40 24.4 31.4 61.5 7.2 27.0 5.1 1.1 4.7 0.7 4.1 0.8 2.4 0.4 2.2 0.3 0.69 0.85 JES 40-90 23.0 30.9 59.7 7.0 26.5 5.0 1.0 4.7 0.7 4.2 0.8 2.3 0.3 2.2 0.3 0.65 0.85 JES 220 26.2 34.0 65.4 7.9 29.4 5.7 1.2 5.2 0.8 4.7 0.9 2.7 0.4 2.5 0.4 0.66 0.84 Pl Q s ec tio ns DOT 25 25.7 45.4 110.0 18.3 29.1 7.7 1.1 6.9 2.8 7.2 1.1 <5 <2 1.9 <2 0.44 1.21 DOT 120 25.2 45.3 124.0 9.0 30.5 8.3 1.7 6.1 4.1 11.3 1.2 <5 <2 2.0 <2 0.73 0.87 DOT 300 22.0 40.6 63.2 12.0 25.4 6.4 0.7 4.9 3.7 6.3 1.1 <5 <2 1.7 <2 0.39 0.82 OPO 25 22.6 44.6 108.0 18.2 29.3 7.4 0.9 5.8 3.3 6.2 1.2 <5 <2 1.8 <2 0.42 1.11 OPO 40 27.1 49.2 114.0 14.7 35.0 8.5 1.2 6.1 4.1 6.9 1.1 <5 <2 2.1 <2 0.49 1.00 OPO 70 40.3 65.6 132.0 13.9 48.1 10.7 1.8 8.5 3.6 8.7 1.3 <5 <2 2.9 <2 0.56 1.15 H2 25 26.0 47.7 106.0 11.7 34.3 8.5 1.3 6.1 4.0 7.4 1.2 <5 <2 2.0 <2 0.55 0.96 H2 70 22.0 44.1 91.8 16.0 30.2 7.5 1.0 5.4 3.0 5.9 1.3 <5 <2 1.6 <2 0.47 1.11 H2 150 20.2 38.9 94.5 9.6 23.6 6.6 0.9 4.8 2.8 5.7 0.9 <5 <2 1.5 <2 0.47 1.03 H2 250 23.8 43.3 68.4 12.2 28.4 7.1 0.9 6.0 3.3 6.6 1.2 <5 <2 1.9 <2 0.43 0.93 Figure 4. Normalization plots for REE: (a) samples from the Miocene marl profiles and (b) samples from the PlQ sections normalized to chondrite ( McDONOUGH & SUN, 1995); (c) samples from the Miocene marl profiles and (d) samples from the PlQ sections normalized to Upper Continental Crust values (RUDNICK & GAO, 2014). G eo lo gi a C ro at ic a 318 Geologia Croatica 77/3 alkaline earth elements are generally considered mobile and easily removed from the parent material during weathering (NESBITT et al., 1980; NESBITT & MARKOVICS, 1997), while elements such as Al and Ti tend to be conserved in weathered material and are considered immobile in the case of moderate chemical weathering, especially in slightly alka­ line environments (NESBITT et al., 1980; PEURANIEMI & PULKKINEN, 1993; NESBITT & MARKOVICS, 1997). The strong positive correlation of the Al and Ti content in the Mio­ cene marl profiles indicates a low mobility of the two elements and their enrichment in the detrital component of marls, which is also reflected in the overlying soil samples (Fig. 5). The scatter of samples from the PlQ sections corre sponds to their multiple source origin. The sediment samples show a clear separation from the corresponding soil samples in the PlQ sections, although the scatter, which indicates a more chaotic origin, is also preserved in the overlying soil samples. Elemental ratios sensitive to chemical weathering were compared between parent material and topsoil samples to discern the trends within profiles (Fig. 6). Since Na and Ca are Figure 5. Correlation of TiO2 with Al2O3 for samples of the Miocene marl profiles (blue line) and the PlQ sections (orange line). Figure 6. Elemental ratios comparison between topsoil and the parent material/bedrock. The arrows indicate trends under increased weathering intensity. G eologia C roatica 319Gverić et al.: The influence of weathering and pedogenesis on the geochemical record of Miocene marls and Plio-Quaternary sediments ... easily removed during chemical weathering (NESBITT & YOUNG, 1982), their ratio to Ti is decreased in more weathered samples. Ti is expected to stay immobile under all circum­ stances apart from extreme chemical weathering conditions (NESBITT & MARKOVICS, 1997; SHELDON & TABOR, 2009), which is not assumed for these samples due to the presence of feldspars and expandable clay minerals (GVERIĆ et al., 2022, 2023). There is a similarity in the distribution of both ratios in the Miocene marl samples, suggesting that topsoil is more depleted in the aforementioned elements than the parent material. However, in the PlQ samples the topsoil is depleted in Ca, while the same is not true for Na (Fig. 6a,b). In the Miocene profiles, the Al/K ratio in the soil samples is generally higher than in the parent material, which is more pronounced in some of the studied profiles, whereas the trend is reversed in the PlQ sections (Fig. 6d). Al/K ratios tend to increase during chemical weathering of stronger intensity (WEI et al., 2006), as K will then more easily be leached out instead of incorporated into clay minerals structure (NESBITT et al., 1980). This, albeit subtly, is evident in the marl profiles and soils developed on top of the genetically related parent material, suggesting an expected weathering and pedogenesis pattern. For PlQ sections, in which soil and parent material are not necessarily genetically related, the Al/K ratio shows a geo­ chemical signature of higher weathering intensity, (or longer weathering exposure), in the PlQ sediment material than in the overlying soil samples. La/Sm ratios, which can trace more intense chemical weathering occurrences (WEI et al., 2006), indicate a similar conclusion, showing the greatest increase in PlQ sediments of Dotrščina and Horvatovac when compared to the respective topsoil samples (Fig. 6f). Substantial dif­ ferences shown in the element ratios between rock and soil samples in the PlQ sections also confirm the fact that this soil was developed on an unrelated parent material (most likely loess derivate), as previously postulated (GVERIĆ et al., 2023). Differences in the absolute values of elemental ratios between different Miocene marl profiles can also reflect the different source material for the siliciclastic component of the marls; material of local origin (Inner Dinarides) during the Early Miocene was gradually replaced with material from more distant source areas (the Alps, Carpathians) by the Late Miocene (GRIZELJ et al., 2017). In the PlQ sections, the sediment is exclusively of local origin and was deposited in a shorter period of time from torrents, with a composition influ­ enced by local lithological variations, as well as the transport mechanism. 4.4. Geochemical weathering signature and correspondence between geochemical and mineralogical proxies for profiles on Miocene sedimentary rocks The clay mineralogy of marl samples indicates an inter mediate weathering intensity. Clay minerals in the soil profiles developed on the Miocene marls are largely inherited from the parent material with early stages of transformation visible in the occurrence of mixed­layered species detected in the uppermost soil horizons (GVERIĆ et al., 2022). Transformations are, however, very subtle and impeded by the high pH caused by the presence of carbonates. Changes in the major element composition in weathered material and soil samples developed on Miocene carbonate­ rich sedimentary rocks (Table 5), show the greatest variations in Ca content, reflecting both carbonate dissolution in most profiles and secondary carbonate formation detected in the Jesenovec profile (GVERIĆ et al., 2022). There is no notable accumulation of Al and only a slight loss of alkali elements. Loss of K observed in some soil samples reflects the progressive loss of illite layers in mixed­layered illite smectite towards the profile surface (GVERIĆ et al., 2022). 4.5. Geochemical weathering signature and correspondence between geochemical and mineralogical proxies for the PlQ sediment and overlying soil Most indices of chemical weathering show similar trends for all the PlQ sections (Table 6). CIA values are in the range of Table 5. Variations of major elements relative to parent material composition (τ mass coefficient) (BRIMHALL & DIETRICH, 1987). τSi τAl τFe τMg τCa τNa τK LZB 0-10 0.14 0.05 0.19 -0.13 -0.20 -0.02 -0.02 LZB 10-30 0.03 0.04 0.18 -0.11 -0.18 -0.05 0.03 ČUČ 0-20 0.03 -0.01 0.14 -0.20 -0.50 -0.04 -0.14 MTR 0-20 -0.22 -0.13 -0.04 -0.78 -0.96 -0.16 -0.34 MTR 35-40 -0.04 0.02 0.08 -0.19 0.06 0.04 0.00 FUR 0-20 -0.15 -0.12 -0.10 -0.54 -0.84 -0.25 -0.17 FUR 20-60 -0.03 0.04 0.01 -0.15 0.11 -0.15 0.09 JES 0-20 -0.04 -0.02 0.08 -0.01 1.07 -0.10 -0.03 JES 20-40 -0.03 0.00 0.02 -0.06 0.82 -0.07 -0.05 JES 40-90 0.00 0.06 0.21 -0.08 1.15 0.00 0.02 Table 6. Weathering indices calculated for PlQ sections samples. CIA CIW PIA CPA DOT 25 80 88 87 91 DOT 120 81 90 89 93 DOT 300 79 84 82 91 OPO 25 82 92 91 94 OPO 40 85 94 93 96 OPO 70 85 94 93 97 H2 25 80 89 88 93 H2 70 79 88 86 92 H2 150 87 94 93 97 H2 250 87 94 93 97 G eo lo gi a C ro at ic a 320 Geologia Croatica 77/3 geochemical indices and observed Feo/Fet ratios. The only exception, Dotrščina, shows the most advanced pedogenesis and the development of a Stagnosol, i.e. a pseudogley soil (GVERIĆ et al., 2023). Even though the nature and origin of the PlQ sediments is problematic in the context of geochemically derived conclusions, all of the weathering indices used show the same trends, and correspond well with previously obtained mineralogical and pedological information. 5. CONCLUSIONS The results of this study show that, in general, there is a good correlation between the geochemical and mineralogical weathering signatures in the parent materials, weathered materials and soil samples, which were analyzed in the foothill area of Medvednica Mt. The very subtle effects of weathering and pedogenesis in the Miocene profiles studied, already suggested by the mineralogical data, are now confirmed by the absence of any appreciable enrichment of Al and only a slight loss of alkali and alkaline earth elements, in agreement with the previously postulated changes in mineralogy. The geo che­ mi cal weathering indices in the investigated PlQ sections also agree with the previously determined mineralogical contents and show higher values in the samples that also contain more low-charge expandable clay minerals as well as Fe and Al oxides. While the geochemical signatures of the parent material are largely preserved in the soil profiles developed on the Mio- cene sediments, they show marked heterogeneity both between the PlQ sediments and the overlying soil samples. Within soils developed on Miocene sediments, we therefore observe the consequences of pedogenesis with distinct geochemical and mineralogical (shown in previous study) changes on one and the same parent material. The observed discrepancy between the soils/weathered materials and the PlQ sediments is the result of the heterogeneity of the parent materials, (as a con­ sequence of proluvial sedimentation of these deposits) and their weathering status (pre-weathered sediments), prior to their final deposition as proluvial sediment. Likewise, the geochemical composition indicates that the Miocene marl samples are derived from a well-differentiated continental material, while the provenance signature of the PlQ sediments corresponds to their diverse multi­source origin. ACKNOWLEDGEMENT The authors would like to thank the editor and two anonymous reviewers for their thorough and helpful comments which substantially improved the manuscript. The results presented in this paper are a part of the PhD dissertation of the first author. This work was partly financed by the University of Zagreb [Grants no. 20286304 and no. 20286480]. The authors are grateful to Dr. Dorota SALATA from the Institute of Geo- logical Sciences of the Jagiellonian University in Kraków for the chemical composition analysis of the PlQ samples, and to Dr. Michaela HRUŠKOVA HASAN from the Department of Mine ra logy, Petrology and Mineral Resources of the Faculty of Mining, Geology and Petroleum Engineering, University of Zagreb for conducting the AAS analysis. 79 to 87, corresponding to intermediate to intense degrees of weathering (NESBITT & YOUNG, 1982; FEDO et al., 1995). CIW and PIA show similar trends and range from 84 to 94 and 82 to 93, respectively. Both indices show higher absolute values than the CIA, which is expected due to the omission of K2O (CIW) or the correction for K2O (PIA) in the calculations. CPA shows values of 91 to 97. There is a general discrepancy between the PlQ sediment samples and the overlying soil samples of the Oporovec and Horvatovac localities. The sediment samples consistently have indices corresponding to more intense weathering than the overlying soil samples. This is in line with the theory of soil formation in different weathering conditions and from more recent sediments, such as subsequently deposited loess material. Ammonium oxalate extractable Fe and Mn were measured for the PlQ samples to determine the ratio of poorly crystallized Fe and Mn to total Fe and Mn (Table 7). As a consequence of the initial stage of soil development at the sites studied, there is a higher ratio of poorly crystallized Fe (Feo) to total Fe (Fet) in the soil than in the parent material, as shown in Table 5. This is not evident for Mn, since Mn oxyhydroxides are very readily remobilized in soil. Geochemistry of the PlQ sections confirms the fact postulated in the previous study (GVERIĆ et al., 2023), that the soil horizons most likely developed from subsequently deposited material. The clay minerals assemblage in the PlQ samples generally corresponds to a higher intensity and degree of weathering during the earlier PlQ sediment deposition, observed by the presence of low-charge expandable minerals (smectite) and Fe/Al (oxy)hydroxides (GVERIĆ et al., 2023). However, the presence of feldspar (and expandable clay minerals) in all of the PlQ sediment samples suggests either that those possible intense weathering periods were not long- lasting or that the material originates from multiple sources that have undergone various degrees of weathering. Subsequent weathered material and overlying soil samples in which hydroxy-interlayered minerals were detected, as well as the (locally dominant) presence of high-charge expandable minerals (vermiculite), correspond to a lower intensity and degree of weathering, also evidenced by the calculated Table 7. Ammonium oxalate extractable Fe and Mn content (in ppm) and their fraction in total Fe and Mn of the PlQ sections. Total Fe and Mn values are recalculated from Table 2. Sample Feo Mno Feo/ Fet Mno/Mnt DOT 25 92 13 0.0034 0.0127 DOT 120 126 66 0.0030 0.0180 DOT 300* 59 8 0.0013 0.0682 OPO 25 99 3 0.0037 0.0069 OPO 40 88 3 0.0026 0.0074 OPO 70* 77 7 0.0021 0.0109 H2 25 81 14 0.0021 0.0126 H2 70 77 4 0.0025 0.0082 H2 150* 16 b.d.l. 0.0005 - H2 250* 22 2 0.0006 0.0183 * marks PlQ sediment samples b.d.l. = below detection limit G eologia C roatica 321Gverić et al.: The influence of weathering and pedogenesis on the geochemical record of Miocene marls and Plio-Quaternary sediments ... REFERENCES BAKRAČ, K. & KOCH, G. (1999): A palynological contribution to the Qua­ ternary deposits in the wider area of Zagreb (Croatia).– Acta Palaeobot. Suppl. 2, 467–469. BAKRAČ, K., KOCH, G. & SREMAC, J. (2012): Middle and Late Miocene palynological biozonation of the south­western part of Central Parate­ thys (Croatia).– Geol. 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LZB 0-10 LZB 10-30 LZB 30-50 ČUČ 0-20 ČUČ 200 MTR 0-20 MTR 35-40 MTR 150 FUR 0-20 FUR 20-60 FUR 70 JES 0-20 JES 20-40 JES 40-90 JES 220 Ba 222 228 223 275 210 389 188 179 408 276 279 384 412 402 605 Ni 199 270 148 45 35 65 33 31 70 44 42 51 55 62 61 Sc 8 9 8 5 4 16 6 6 14 9 8 12 12 13 14 Co 17.6 27.5 11.6 7.1 6.6 18.7 9.4 8.0 16.8 11.1 12.2 14.1 15.3 15.2 15.4 Cs 13.5 14.6 12.6 3.2 2.7 7.9 3.4 3.5 8.5 5.1 5.1 6.7 7.2 7.6 8.3 Ga 9.6 9.6 8.0 5.3 3.7 19.9 6.3 6.1 18.5 9.7 9.9 15.7 16.7 16.9 19.2 Hf 2.3 1.9 1.8 1.6 1.5 6.0 1.3 1.3 4.4 1.5 1.8 3.7 4.2 2.9 3.9 Nb 7.5 7.0 6.3 4.9 3.7 15.6 4.5 4.6 13.7 6.4 6.8 11.7 12.8 11.9 14.1 Rb 61.7 70.2 60.7 49.1 35.9 104.9 42.1 45.1 118.7 68.2 65.7 109.4 114.5 116.3 134.3 Sn 2 2 2 2 <1 3 1 1 3 2 2 3 3 3 4 Sr 459.4 507.8 608.2 1214.2 2021.1 113.9 353.0 361.2 124.8 305.4 317.3 172.2 180.1 187.9 175.8 Ta 0.5 0.5 0.4 0.4 0.3 1.1 0.4 0.3 0.9 0.5 0.4 0.8 0.8 0.8 0.8 Th 6.5 7.4 5.4 4.3 3.4 13.0 5.1 5.3 12.4 7.4 7.2 10.5 11.1 11.4 12.1 U 2.1 1.8 1.6 2.2 2.6 2.5 1.5 2.2 2.1 2.1 1.4 2.2 2.2 2.0 3.0 V 62 64 62 46 38 127 53 51 116 67 64 95 107 105 120 W 1.4 1.6 1.9 0.9 1.1 2.1 0.7 0.9 2.2 1.4 1.1 1.9 2.0 2.1 2.2 Zr 84.1 68.4 64.9 64.1 58.3 234.8 47.7 52.5 163.1 54.9 65.7 140.7 147.8 111.7 151.8