engleski

The Provenance of Lower Miocene Sandstones from Mt. Kalnik

Mt. Kalnik is an inselberg structure in Northern Croatia that lies in the intersection zone between SE Alps, Internal Dinarides and SW Pannonian basin. With E-W striking ridge Mt. Kalnik is characterized by average altitude between 300 to 500 m and highest elevation of 642 m a.s.l. The southern margin of the Mt. Kalnik delineated by the combined reverse (e.g. Selanec-Poganac fault) and tectonically reactivated normal faults (e.g. Kalnik and Salamunovec-V. Botinovac faults), while on the northern side Mt. Kalnik it bounded by the reverse Drenovec fault. The Ljubelj fault divides the Mt. Kalnik into two parts, Peca in the southern and Ljubelj in the northern part. During its geological history the Mt. Kalnik was affected by the tectonic phases of the Hercynian orogeny and Alpine orogeny with intensive thrusting and faulting of Jurassic, Cretaceous and Paleogene complexes (ŠIMUNIĆ & HEĆIMOVIĆ, 1979 ; ŠIMUNIĆ et al., 1982), however only the Neogene-Quaternary tectonic evolution of the SW Pannonian basin are well expressed in the field. The tectonic uplift of the Mt. Kalnik began at the end of the Miocene, however, climaxed during Pliocene-Quaternary due to N-S directed shortening when Mt. Kalnik experienced differential uplift of several hundred meters (HEĆIMOVIĆ, 1995), and exposes pre-Neogene and Neogene tectonostratigraphic units that are surrounded by Plio-Quaternary sediments. In this study our aim was to constrain the source area of the Lower Miocene sandstones from Mt. Kalnik which were deposited in fluvial and lacustrine environments during Ottnangian and Karpatian (PAVELIĆ et al., 2001). In this purpose quantitative heavy mineral analysis was conducted on eleven samples from different sampling localities. Five localities are situated in the central and southern part of Mt. Kalnik, and six in the western part near Novi Marof and Breznički Hum. Results show that analyzed samples are dominated by garnet that makes up approximately 50% of all translucent heavy minerals, along with rutile, tourmaline, zircon, staurolite and kyanite (Fig.1). The content of minerals from epidote/zoisite group is rather low. The zircon-tourmaline-rutile (ZTR) index is 20-25% on average. The presence of garnet, staurolite and kyanite could indicate a metamorphic origin of initial source material. This furthermore implies that in the Lower Miocene, since at that time there were no prominent mountains in the local area, the most probably source of the material were the Alps. In the same time, the apatite-tourmaline (ATi) index is very low in most samples. This can be seen as source information, but more likely is a result of dissolution of unstable apatite by acidic weathering. Weathering could be also the reason for low content of amphiboles and pyroxenes. Due to ambiguity of the results and the fact that the composition of heavy mineral assemblages in sandstones may be influenced by many processes during transport, deposition and diagenesis, geochemical analysis of detrital garnet and rutile grains on several representative samples provide additional information on the provenance, because varietal characteristics of individual mineral species are usually inherited directly from the source area.

Miocene, Mt. Kalnik, provenance, heavy minerals, geochemistry

nije evidentirano