Evidence of submarine depositional environment for the host rocks of the Upper Cretaceous Madneuli polymetallic deposit, Lesser Caucasus, Georgia (implication for the host rock depositional environment)
Abstract:
Nino Popkhadze1, Robert Moritz2
1A.Janelidze Institute of Geology of Iv.Javakhishvili Tbilisi State University; 2Department of Earth Sciences, University of Geneva, Switzerland
The Bolnisi district is the part of a major late Cretaceous volcano-sedimentary belt belonging to the tethyan orogenic and metallogenic belt. Towards the east, past the black Sea, this belt is known as the Eastern Pontides in East Turkey and the Bolnisi zone in Georgia.
The host rocks of the Madneuli deposit consist predominantly of lava, pyroclastic, volcanogenic-sedimentary and sedimentary rocks of rhyodacitic composition, which are grouped in two facies assemblages: volcanic and volcano-sedimentary. Strongly silicified, very fine-grained tuff horizons interbedded with turbiditic rocks, volcaniclastic mudstone and sandstone in this bedded volcano-sedimentary sequence. Classical slide slump units (Fig.2a), cross-bedding (Fig.2b), bioturbations, load casts, wave and current ripples, flame structures are also present in these bedded volcano-sedimentary rocks. Tb to Te of the Bouma sequence is present in the open pit (Fig.1d). Radiolaria-bearing horizons from the upper part of the open pit interbedded with volcaniclastic mudstone and sandstone, fine-grained tuff and pumice- to crystal rich tuff (Fig.2c). Two types of rhyodacitic lobe hyaloclastite flows are described for the first time in the Madneuli deposit (Popkhadze et al. 2014): hyaloclastite with glassy-like selvages (Fig.2e) and hyaloclastite with pillow-like forms (Fig.2f).
Fig.1 a. Slide slump horizon, b. cross-bedding, c. lower part of radiolaria-bearing horizon in the open pit, d. Typical Bouma sequences in the turbiditic rock; e. hyaloclastite with glass-like selvages, f. hyaloclastite with pillow-like forms.
Welded, altered ignimbrites, slightly welded and columnar jointed ignimbrite associated with radiolarian-bearing tuff horizons and is described for the first in this contribution, which is a reliable evidence of submarine depositional environment or entrance into water environment of the ignimbrite pyroclastic flow in the open pit.