Chronohorizons Based on Resistivity Curve Variations - Upper Miocene Sediments of the Ivanic Grad Formation in the Sava Depression (NW Croatia)

Regional definition of chronohorizons represents a fundamental and most difficult problem in geology. Adequate precision of dating can only be obtained from biological evolution, radioactive decay and from the key surfaces of the sequence stratigraphic concept (MFS, TSE, and LSE). It is concluded in this paper that the variation of formation resistivity values (Ra curve), as measured in wells located in the Croatian part of the Pannonian Basin System, is also a criterion for the stratigraphic definition of concurrently deposited sediments. This enables the construction of a sequence of lithogenetic units related to very small time-intervals. The morphology of the resistivity curve measured in well sections composed of massive marls (that were deposited in a quiet environment of moderate water depth), is regionally exceptionally well defined. This pattern consists of a succession of peaks of lower and higher resistivity values that are in the same relative position regionally, which results in similar form of the resistivity curves of the wells in the study area. On the curve, one peak of higher values together with the next (overlying) peak of lower ones composes a single cycle (SC). Marls of a single cycle were regionally deposited at the same time, thus enabling the points of both the maximal and minimal resistivity values of each SC to be considered as time-markers (chronohorizons). Variation of the resistivity reflects fine changes of petrographic and granulometric composition which can be associated with cyclic water-level fluctuations (Milankovitch cycles). For future exploration of the remaining, potential hydrocarbon accumulations in the sandstone reservoirs of the IvaniE Grad Formation in the Sava Depression, spatial modelling of the distribution, geometry, facies and palaeocurrent structure of separated depositional episodes and genetic units is suggested. This should be done with special emphasis on the spatial definition of channel sandstones that are the most important hydrocarbon reservoirs (according to current interpretations)

Facies, Facies association, Areal distribution, Turbidites, Massive marls, Upper Pannonian, Sava Depression, Croatia

Four facies were distinguished within the Ivanic Grad Formation of the Sava Depression: massive marl facies (F1), thick-bedded to massive sandstone facies (F2), thin-bedded sandstone facies (F3) and thin-bedded sandstone, siltite and marl facies (F4). Interpretation of the depositional mechanisms confirmed the presence of two basic sedimentary processes. Hemipelagic deposits are represented by fine-grained detritus. The lithification of these produced a massive marl (facies - F1). Sand detritus was transported into the depression by turbidite currents (facies - F2-F4), and formed a narrow elongated sedimentary body. By comparing the facies defined on the basis of core samples, the spontaneous-potential curve (SP) and the resistivity curve (Ra) of identical intervals, four facies associations were defined on well log diagrams: channel filling (FA), depositional lobe (FB), lateral and distal turbidites (FC) and massive marls (FD)

Characterization of clastic sedimentary enviroments by clustering algorithm and several statistical approaches — case study, Sava Depression in Northern Croatia

Abstract This study demonstrates a method to identify and characterize some facies of turbiditic depositional environments. The study area is a hydrocarbon field in the Sava Depression (Northern Croatia). Its Upper Miocene reservoirs have been proved to represent a lacustrine turbidite system. In the workflow, first an unsupervised neural network was applied as clustering method for two sandstone reservoirs. The elements of the input vectors were the basic petrophysical parameters. In the second step autocorrelation surfaces were used to reveal the hidden anisotropy of the grid. This anisotropy is supposed to identify the main continuity directions in the geometrical analyses of sandstone bodies. Finally, in the description of clusters several parametric and nonparametric statistics were used to characterize the identified facies. Obtained results correspond to the previously published interpretation of those reservoir facies

HIV-infected T cells are migratory vehicles for viral dissemination

After host entry through mucosal surfaces, HIV-1 disseminates to lymphoid tissues to establish a generalized infection of the immune system. The mechanisms by which this virus spreads among permissive target cells locally during early stages of transmission, and systemically during subsequent dissemination are not known1. In vitro studies suggest that formation of virological synapses (VSs) during stable contacts between infected and uninfected T cells greatly increases the efficiency of viral transfer2. It is unclear, however, if T cell contacts are sufficiently stable in vivo to allow for functional synapse formation under the conditions of perpetual cell motility in epithelial3 and lymphoid tissues4. Here, using multiphoton intravital microscopy (MP-IVM), we examined the dynamic behavior of HIV-infected T cells in lymph nodes (LNs) of humanized mice. We found that most productively infected T cells migrated robustly, resulting in their even distribution throughout the LN cortex. A subset of infected cells formed multinucleated syncytia through HIV envelope (Env)-dependent cell fusion. Both uncoordinated motility of syncytia as well as adhesion to CD4+ LN cells led to the formation of long membrane tethers, increasing cell lengths to up to 10 times that of migrating uninfected T cells. Blocking the egress of migratory T cells from LNs into efferent lymph, and thus interrupting T cell recirculation, limited HIV dissemination and strongly reduced plasma viremia. Thus, we have found that HIV-infected T cells are motile, form syncytia, and establish tethering interactions that may facilitate cell-to-cell transmission through VSs. While their migration in LNs spreads infection locally, T cell recirculation through tissues is important for efficient systemic viral spread, suggesting new molecular targets to antagonize HIV infection