engleski

Facies analyses of the Upper Cretaceous bauxites in the Jajce area, Bosnia and Herzegovina, in response to lithospheric bulges caused by compressional regime during the gradual closure of the Dinaridic part of the Tethys

The bauxite-bearing area Jajce is located northwest of the town of Jajce in the central part of Bosnia and Herzegovina. The region was exploited for karst bauxite during nearly a half a century activity. Geology of the area and the bauxite genesis were discussed in a number of papers. Geophysical surveys were also applied. Particularly important bauxite districts include Crvene Stijene, Bešpelj, Poljane and Liskovica. Our research was focused in the Bešpelj district, mined in open-pits and undergrounded mining, and giving opportunities for a detailed sampling and rock observations. Geochemical and mineralogical research of bauxites were made on the core samples of three boreholes. In total, 13 bauxite samples were studied by wet chemistry, ICP-MS (trace elements and REE), XRD, micro-XRF, optical microscopy, and differential thermic analysis. The bauxite deposits originated during the terrestrial phase in the stratigraphic range from the upper Albian to the Coniacian–Maastrichtian. The Jajce area is a part of the northeastern margin of the Adriatic Carbonate Platform, which existed from the end of the Early Jurassic up to the end of the Cretaceous. At the end of the Early Cretaceous and the beginning of the Late Cretaceous, the carbonate platform, as a passive continental margin, underwent an intensive compressional tectonics and emersion as a result of platform bulging. Hot humid climate and subaerial conditions were beneficial for effective bauxitization. The emersion lasted from late Albian to the Coniacian–Maastrichtian, approximately for 20 Ma. Six types of bauxites are distinguished: lenticular, canyon-like, graben type, sinkhole type, canyon-like with a sinkhole at the bottom and tectonized ones (Pavičić et al., 2018). The bauxite deposits are mainly composed of carbonate clastics and limestones of Late Cretaceous age, exceeding thickness of 1000 m. The boundary between the Upper Cretaceous and the Paleogene clastics is not accurately defined. Bauxite lithology and genesis is defined by paleo- relief type and position of the water table and erosion basis. Deeply dissected karst, filled by а bauxitic material with synchronous bauxitization prefers vadose facies. The genetical observation recognizes juvenile, mature and senile phases. The complete profile is topped by an iron crust (duricrust). Bauxite lithogenesis is defined by pelitomorphic facies (mudstones with colloform texture, formed in a water saturated zone). Ooid/pisoid facies in the middle of the ore body assumes a development from autochtonous to allochtonous setting. Paleosoils attested with pedogenic formations, rhizopods and syneresis, point to a new transgression in the Late Cretaceous as a response to collisional tectonics. Flexural bulges, due to uplift of crustal segments, are typical of the orogenic foredeeps, in areas affected by an active thrusting, nappe stacking and tectonic loading. New beneficial subaerial bauxitization areas were formed and shifted toward the inner part of the Apulian carbonate platform (Adriatic-Dinaric), in post- Cretaceous times.

Facies analyses ; Upper Cretaceous bauxites ; Jajce area ; Dinarides

nije evidentirano