The Early to Middle Triassic continental-marine transition of NW Bulgaria:sedimentology, palynology and sequence stratigraphy

Sedimentary facies and cycles of the Triassic continental–marine transition of NW Bulgaria are documented in detail from reference sections along the Iskar river gorge between the villages of Tserovo and Opletnya. The depositional environments evolved from anastomosing and meandering river systems in the Petrohan Terrigenous Group to mixed fluvial and tidal settings in the Svidol Formation, and to peritidal and shallow-marine conditions in the Opletnya Member of the Mogila Formation. For the first time, the palynostratigraphic data presented here allow for dating the transitional interval and for the precise identification of a major sequence boundary between the Petrohan Terrigenous Group and the Svidol Formation (Iskar Carbonate Group). This boundary most probably corresponds to the major sequence boundary Ol4 occurring in the upper Olenekian of the Tethyan realm and thus enables interregional correlation. The identification of regionally traceable sequence boundaries based on biostratigraphic age control is a first step towards a more accurate stratigraphic correlation and palaeogeographic interpretation of the Early to early Middle Triassic in NW Bulgaria

COMPREHENSIVE APPROACH FOR 3D SIMULATION BY MATHEMATICAL MODELING OF GROUNDWATER CONTAMINATION

ABSTRACT Development of precise models for predicting and managing processes of groundwater contamination as a result of a number of natural and technogenic factors (mining activity, industry, agriculture, sanitary landfills, etc.) requires more detailed knowledge on the structure and morphology of aquifers. Some of the aquifers are located in sediments and sedimentary rocks of significant heterogeneity of the lithological properties, causing a rather high heterogeneity of porous medium. Past practice of mathematical modeling has not considered realistically enough the rate and specifics of this heterogeneity. In recent years, sedimentology of aquifers acquires higher importance in the compilation of 3D prediction models. This comparatively new approach allows the application of a set of direct and indirect "in situ" and laboratory sedimentological, stratigraphic and geophysical methods, which allow the correct differentiation and definition of lithofacial and architectural-element units of different rank and scale. Each of them is characterized by relative inner homogeneity of hydrodynamic and migration properties. Thus, the differentiation of zones and layers simulating the correct hydrogeological conditions is allowed easily and precisely enough by compilation of numerical 3D models. The comprehensive approach was successfully tested at the Plovdiv sanitary landfill

Integrated bio- and cyclostratigraphy of Middle Triassic (Anisian) ramp deposits, NW Bulgaria

A cyclostratigraphic interpretation of peritidal to shallow-marine ramp deposits of the early Middle Triassic (Anisian) Opletnya Member exposed in outcrops along the Iskar River gorge, NW Bulgaria, is presented. Based on facies trends and bounding surfaces, depositional sequences of several orders can be identified. New biostratigraphic data provide a time frame of the studied succession with placement of the boundaries of the Anisian substages and show that the Aegean (early Anisian) substage lasted about 1.6 Myr. In the corresponding interval in the two studied sections, 80 elementary sequences are counted. Five elementary sequences compose a small-scale sequence. The prominent cyclic pattern of the Opletnya Member can thus be interpreted in terms of Milankovitch cyclicity: elementary sequences represent the precession (20-kyr) cycle and small-scale sequences the short eccentricity (100-kyr) cycle in the Milankovitch frequency band. Medium-scale sequences are defined based on lithology but only in two cases can be attributed to the long eccentricity cycle of 405 kyr. The transgressive-regressive facies trends within the sequences of all scales imply that they were controlled by sea-level changes, and that these were in tune with the climate changes induced by the orbital cycles. However, the complexity of facies and sedimentary structures seen in the Opletnya Member also implies that additional factors such as lateral migration of sediment bodies across the ramp were active. In addition, three major sequence boundaries have been identified in the studied sections, which can be correlated with the boundaries Ol4, An1, and An2 of the Tethyan realm

Sequence analysis, cyclostratigraphy and palynofacies of early Anisian carbonate ramp deposits, NW Bulgaria

A sequence- and cyclostratigraphic interpretation of early Anisian (Aegean) shallow-marine carbonate ramp deposits, exposed in outcrop sections west of Tserovo village, NW Bulgaria, is presented. The hierarchical pattern identified can be interpreted in terms of Milankovitch cyclicity with elementary sequences representing the precession (20-kyr) cycle, small-scale sequences the short eccentricity (100-kyr), and medium-scale sequences the long eccentricity (400-kyr) cycle. Palynology provides a robust stratigraphic framework. The study of sedimentary organic matter, revealing variations of terrestrial input, sorting and fragmentation of phytoclasts, and prominent acritarch peaks, allows the interpretation of environmental changes and contributes to the cyclostratigraphic and sequence-stratigraphic framework. The detailed documentation of syndepositional soft-sediment deformation structures confirms their laterally traceable distribution within the depositional sequences and makes them good palaeoenvironmental indicators. Anisian ramp systems of the western Tethyan realm thus were subjected to highly dynamic regimes, recording the interplay between sea-level changes in tune with orbital cycles and ramp morphology

Organic petrological and geochemical properties of jet from the middle Triassic Mogila Formation, West Bulgaria

The paper presents the results of the petrographic and organic geochemical studies of a jet sample recovered from a Mid-Triassic carbonate succession from the West Balkan tectonic zone in Bulgaria. Total organic carbon contents (TOC=92 % daf) and high vitrinite reflectance (Ro=1.9 %) indicate semi-anthracite coalification rank. Very high Tmax (577 °C) and low HI (~10 mg HC/g TOC) further support the overmature organic matter. Extractable organic matter is characterized by high portions of NSO compounds and asphaltenes (>75 %). Hydrocarbons constitute about 20 % and are characterized by the predominance of the saturated hydrocarbons over the aromatics. n-Alkanes distribution, dominated by short-chain compounds (n-C17–18), is consistent with the woody origin of the jet and the thermal maturity of the organic matter. The predominance of PAHs with condensed structure over their alkylated isomers is considered to be a result of the complex reaction occurring within the organic matrix during the catagenesis, rather than to the presence of combustion-derived organic matter. Based on the distribution of the diterpenoids, a tentative identification of a possible Voltziales conifer family source is identified. Low Pr/Ph ratio (0.88) and aryl isoprenoids outline anoxic conditions of jet formation, whereas the presence of organic sulfur compounds and tri-MTTchroman suggest marine depositional environment with normal salinity