Provenance, Depositional and Diagenetic Reconstruction of the Early Palaeozoic Succession in Kupwara District, Kashmir, North-western Himalaya

Early Palaeozoic succession in Kupwara district of Jammu and Kashmir, North-western Himalaya comprise of sandstone, shale, carbonates and slate. The petrological properties of these rocks were used to work out the provenance, depositional environment and their diagenetic history. The siliciclastic sediments with interbedded carbonate rocks indicate shifts in sea level and consequent changes in energy conditions of the basin as well as biogenic interferences leading to carbonate precipitation in a shallow marine depositional environment. Provenance of these rocks has been of mixed nature with monocrystalline quartz dominant in sandstones indicating greater contribution from igneous sources.

The Importance of Ecological Accommodation Space and Sediment Supply for Cold-Water Coral Mound Formation, a Case Study From the Western Mediterranean Sea

The formation of cold-water coral (CWC) mounds is commonly seen as being the result of the sustained growth of framework-forming CWCs and the concurrent supply and deposition of terrigenous sediments under energetic hydrodynamic conditions. Yet only a limited number of studies investigated the complex interplay of the various hydrodynamic, sedimentological and biological processes involved in mound formation, which, however, focused on the environmental conditions promoting coral growth. Therefore, we are still lacking an in-depth understanding of the processes allowing the on-mound deposition of hemipelagic sediments, which contribute to two thirds of coral mound deposits. To investigate these processes over geological time and to evaluate their contribution to coral mound formation, we reconstructed changes in sediment transport and deposition by comparing sedimentological parameters (grain-size distribution, sediment composition, accumulation rates) of two sediment cores collected from a Mediterranean coral mound and the adjacent seafloor (off-mound). Our results showed that under a turbulent hydrodynamic regime promoting coral growth during the Early Holocene, the deposition of fine siliciclastic sediments shifted from the open seafloor to the coral mounds. This led to a high average mound aggradation rate of >130 cm kyr–1, while sedimentation rates in the adjacent off-mound area at the same time did not exceed 10 cm kyr–1. Thereby, the baffling of suspended sediments by the coral framework and their deposition within the ecological accommodation space provided by the corals seem to be key processes for mound formation. Although, it is commonly accepted that these processes play important roles in various sedimentary environments, our study provided for the first time, core-based empirical data proving the efficiency of these processes in coral mound environment. In addition, our approach to compare the grain-size distribution of the siliciclastic sediments deposited concurrently on a coral mound and on the adjacent seafloor allowed us to investigate the integrated influence of coral mound morphology and coral framework on the mound formation process. Based on these results, this study provides the first conceptual model for coral mound formation by applying sequence stratigraphic concepts, which highlights the interplay of the coral-framework baffling capacity, coral-derived ecological accommodation space and sediment supply.

An Attempt for Construction of Carbonate Platform Geometry from Devonian Hajigak Formation, Central Afghanistan, with the Help of Facies Analysis and Petrography

The subject of sedimentology fundamentally remained subdivided into two sectors viz. siliciclastic and carbonate with the understanding that these two systems are mutually dissociative in terms of their genesis. Even in the highly referred textbooks, siliciclastics and carbonates are always discussed in separate sections. Presumably, the limited occurrences of mixed siliciclastic-carbonate sediments in nature are because of constraining effects that siliciclastics have on carbonate-secreting organisms; the two sediments rarely found mutually associated in nature. Although the mixed carbonate-siliciclastic sediments are subordinate in occurrence, their presence in some instances proved that they do not represent any geological oddity. Rather, their sediment logical history may tell us a great deal about the dynamics and interactions of facies, paleoecologies of many carbonate-secreting organisms, and tectonic histories of depositional basins. Keeping this in mind, the present study attempted to recognize and draw the paleoenvironmental conditions and processes of the Devonian Hajigak Formation, Afghanistan by means of detailed facies analysis and petrographical signatures. An attempt has also been made to characterize sandstone wedges that punctuate the carbonate succession and some variable deposits of shales and marls.

Campanian biostratigraphy and paleoenvironments, a case study from the Central Srednogorie Zone, Central Bulgaria

<p>The Central Srednogorie Zone of Bulgaria represents a chain of strike-slip and pull-apart basins, part of the of the peri-Tethyan arc/back-arc basin system. The Upper Cretaceous volcano-sedimentary sequence in the western part of the Central Srednogorie Zone, forms two strips, spanning the Turonian-Maastrichtian interval. This succession is represented by basal siliciclastic sediments, an interval with magmatic rocks followed by volcanoclastic and epiclastic deposits, covered by white, red, grey limestones, with fast transition to sandy low-density turbidites. One of the most representative and continuous sedimentary record in the Panagyurishte strip is exposed east of the Petrich village (Petrich section).  </p><p>The base of the Petrich section is composed of the rocks from the so-called lower epiclastic unit (Coniacian-Santonian), followed by grey, pink to variegated limestones of the Mirkovo Formation (Santonian-Campanian). The middle and upper part of the section consists of muddy-sandy turbidites of the Chugovitsa Formation (Campanian-Maastrichtian). The lower part of this formation, the Voden Member, composed of grey thin bedded marls with rare sandstones beds, has yielded a comparatively rich macro- and microfossil record. Upwards, thin to medium bedded sandstones and marls are in alternation, with documented mudstone dominated intervals.  </p><p>The present study of the Petrich section is focused on integrated biostratigraphical analysis, based on three important fossil groups for the Campanian – inoceramid bivalves, nannofossils and dinoflagellate cysts. The study in progress creates a comprehensive calibrated dataset, in which the nannofossil and dinoflagellate cyst ranges and inoceramid occurrences, provide valuable markers for age assessment and stratigraphic subdivision of the Campanian. The presence of the nannofossil <em>Ceratolithus aculeus</em> marks a middle to late Campanian age, followed by a typical late Campanian assemblage including <em>Broinsonia parca parca</em>, <em>Reinhardtites levis</em> and rare <em>Eiffellithus eximius</em>. A high diversity dinocyst association is identified and ranges of key Campanian species as <em>Corradinisphaeridium horridum</em>, <em>Raetiaedinium truncigerum</em>, <em>Palaeohystrichophora infusorioides</em> and <em>Cannosphaeropsis utinensis</em> provided valuable markers for the stratigraphic subdivision of the Campanian. Typical middle Campanian “<em>Inoceramus</em>” <em>ellipticus</em> and “<em>Inoceramus</em>” <em>agdjakendsis</em> were documented from the Voden Member. The paleoenvironmental analysis, based on dinocyst assemblages and palynofacies data, suggests stable open-marine depositional environment and oligotrophic conditions, with normal marine productivity and nutrient availability during the Campanian in the basin.</p><p>Acknowledgements. The study is part of the Bilateral Bulgarian-Austrian collaboration within project KP-06-Austria/9.</p>

Reflexně seismický výzkum pozdně kenozoické zlomové tektoniky na vybraných lokalitách hornomoravského úvalu

We measured shallow reflection seismic profiles across the assumed faults in the Late Cenozoic (Pliocene – Holocene) Upper Morava Basin (UMB). The faults in the UMB are indicated by horst-and-graben morphology, differential thickness of Pliocene and Quaternary siliciclastic sediments, considerable gravity gradients a present-day seismicity. Four seismic lines, 380 to 860 m long (fixed geophone spread) were designed to cross the assumed faults at three sites, Mezice, Drahlov and Výšovice. The data were acquired by 24-channel ABEM Terraloc Mk-8 seismic system with PEG-40 accelerated weight drop source and processed by Sandmaier ReflexW and Halliburton Landmark ProMax® seismic processing software. The processing included application of filters (DC shift, scaled windowgain, bandpass frequency and muting), stacking using normal moveout constant velocity stack, additional application of subtrack-mean (dewow) filter, topographic correction and low velocity layer static correction. Distinct reflectors were detected up to 400 ms TWT, which corresponds to maximum depth of 280 and 350 m at 1400 and 1750 km.s-1 velocities, respectively. The observed reflection patterns were classified into three seismic facies, which were interpreted as crystalline rocks (Brunovistulicum) and/or well consolidated Paleozoic sedimentary rocks (SF1), unconsolidated Quaternary siliciclastic sediments (SF2) and semi-consolidated Neogene clays (SF3) based on the cores drilled in their close vicinity. Distinct faults were observed at the Drahlov and Výšovice 2 profile, which coincided with the observed topographic steps between the horsts and grabens. Presence of the fault at the Drahlov profile separating the Hněvotín Horst from the Lutín Graben was demonstrated by independent electrical resistivity tomography profile. On the other hand, another topographic step at the Mezice profile, between the Hněvotín Horst and Olomouc Graben, does not correspond to any seismic indication of a fault. The reflection seismic proved to be useful and relatively low-cost method to visualize the shallow subsurface geology in the Upper Morava Basin.

Ecology of the Early Jurassic bivalve Harpax spinosus (J. SOWERBY, 1819)

The plicatulid bivalve Harpax spinosus is a common element of Pliensbachian to Lower Toarcian benthic community relicts occurring preferredly in fine- grained siliciclastic and mixed carbonate-siliciclastic sediments. There is general agreement that the bivalve was a secondary soft substrate dweller, being cemented with its flat to slightly concave right valve to small shells and bioclasts during early stages of growth and turning into a free recliner during later growth stages. Disagreement exists with respect to the life orientation of the bivalve, whether as free recliner it rested with its convex left valve or with its slightly concave right valve on the substrate. The former growth position would have required the bivalve to flip over when turning into a free recliner. Moreover, most authors assume that the bivalve discarded its host substrate during its reclining stage. The analysis of approximately 1500 specimens from the Upper Pliensbachian Amaltheenton Formation of southern Germany and time-equivalent horizons of southern France and Portugal shows that the bivalve remained cemented to the host substrate throughout its life time, even when the latter no longer supported the shell. The bivalve most likely rested with its concave valve on the soft substrate. The radially protruding spines served to keep the commissure above the sediment-water interface, to stabilize the shell and to prevent the shell from sinking into the sediment (snow-shoe strategy). Differences in the size of individuals at the localities investigated are thought to reflect differences in the degree of environmental stress, most likely caused by fluctuations in the oxygen content of the bottom water masses or by increasing soupiness of the substrate.