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Geoarchaeological research of the “white horizon” units from the Early Bronze Age locality „Orovački vinogradi“(Bjelovar, Croatia)

Geoarchaeological research at the settlement of Vinkovci-culture period (2100 - 1900 BC) „Orovački vinogradi“ near Bjelovar, resulted in numerous multidisciplinary data, relevant for understanding of everyday life in the beginning of the Bronze Age in Northern Croatia area (JAKOVLJEVIĆ, 2005, 2007). Archaeological data on „horizontal stratigraphy“ (spatial arrangement of the objects and findings) obtained during excavation provided the ground-plan of the settlement and collected data on „vertical stratigraphy“ (vertical arrangement of findings in units revealed during excavation) assumed the relative chronology of the settlement (GOLDBERG & MACPHAIL, 2006). However, some stratigraphic units remained questionable regarding its origin, i.e. „white horizon“ units, consisting of semi-consolidated fine-grained, white marly material. These horizons are uncovered and exposed during archaeological research activities (they were assumed as the floors of the objects and preserved as possibly significant vertical stratigraphic units). Questionable nature and origin of these units temporarily suspended further excavation at the locality, until the results of sedimentological and mineralogical research provided the answers about their nature and origin and until the guidelines for the future treatment of the locality were suggested (conservation of the settlement vs. continuing excavation). Sedimentological field-work methodology (STOW, 2005) is conducted at the locality and several representative layers are sampled in order to make petrographical and mineralogical analysis and to precisely characterize mineralogical and petrological composition of these layers. All results are summarized on geological column and interpreted in terms of natural (geological) processes involved in the formation of the layering and in the development of the profile. Anthropogenically inaffected outcrop with almost identical layering sequence is found on near-by site „Ciglenska strana“ and the same sedimentological field-work methodology and sampling procedure is conducted at this site as well, in order to compare results with the site „Orovački vinogradi“. Thin-sections of characteristic samples from the well-lithified sandstones are prepared for petrographical analysis and whole-rock samples are prepared for XRD analysis. Whole-rock samples of the white limy material („white horizon“ units) are prepared for XRD analysis. Sandstones from "Orovački vinogradi" and from comparing site "Ciglenska strana" are determined as micaceous quartz arenites and considered as almost identical and highly comparable. The "white horizons" units from both sites appearing frequently within the geological column are determined as consisting of spherical and elongated white concretions, which are usually coalesced in one semi-consolidated horizon. Semi-quantitative mineral analysis of the samples from both comparing sites showed similar mineralogical composition of concretions (predominantly calcite with some dolomite and subordinately feldspars, micas and clay minerals). The results of the sedimentological and mineralogical research revealed that the investigated archaeological site “Orovački vinogradi” and comparing site „Ciglenska strana“ (anthropogenically inaffected) both consisting of sands, clayey sands and sandstones and that they were formed by natural (geological) processes of sedimentation and diagenesis. Development of “white horizon” units appearing frequently within the profile is found to be result of the growth of carbonate concretions and their coalescence in particular horizons. Morphologies of carbonate concretions and their geometrical relationships with the surrounding sediments indicate their formation in the pre-compactional phase of diagenesis (SEILACHER, 2001). Coalescence of the concretions in a semi-consolidated layers and the formation of the “white horizon” units within the investigated archaeological profile gives the false impression of anthropogenic horizons. Given geoarchaeological interpretation suggest continuing excavation on the site, with no specific need for archaeological conservation of these horizons. Assumed relative chronology of the settlement, based on “vertical stratigraphy”, should be partly reconsidered.

geoarchaeology; Bronze Age; Vinkovci-culture; Vučedol-culture; carbonate concretions; diagenesis; Bjelovar; Croatia

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