Wyniki wyszukiwania - BazTech

1

Integrated sedimentological and ichnological study of the Coniacian sedimentation in North Sudetic Basin, SW Poland

Leszczyński S.

Geological Quarterly

|

2018

|

Vol. 62, No. 4

767--816

EN

Lithofacies and ichnological features of the Coniacian deposits of the upper part of Żerkowice Member and lowest part of the overlying Czerna Formation in southeastern part of the North Sudetic Synclinorium are described and their sedimentary palaeoenvironment is interpreted. The study confirms a shallow-marine to paralic/paludine palaeoenvironment. Sedimentation of the Żerkowice Member occurred in an upper shoreface environment dominated by waves, tidal currents and wave-generated alongshore currents, with an episodic encroachment of fore shore zone and shoal-water deltas. The interpretation is supported by a high-diversity assemblage of trace fossils with 21 ichnogenera, representing a stressed expression of the Skolithos Ichnofacies dominated by Ophiomorpha nodosa and a proximal expression of the Cruziana Ichnofacies with Thalassinoides and rare specimens of diverse other ichnotaxa. Sedimentation of the Czerna Formation commenced after a stasis, with at least a local hiatus caused by emergence, and proceeded in a laterally and vertically more varied environment, with transgressive coastal lagoons evolving into freshwater lakes and marshes and with a repetitive regressive intrusion of shoreface and shoal-water deltas. The emergence of the area is recorded by coal-bearing deposits with plant-root traces. Local occurrence of the Teredolites Ichnofacies in coal (peat) deposits above the base of the Czerna Formation indicates renewed marine flooding. Continuation of the latter is locally evidenced by a trace-fossil assemblage with 17 ichnogenera, representing proximal expression of the Cruziana Ichnofacies followed by distal expression of the Skolithos Ichnofacies in the overlying transgressive-regressive cyclothems. The palaeoenvironmental changes recorded by the sedimentary succession indicate bathymetric fluctuations and imply considerable shoreline shifts and palaeogeographic changes in the basin. These changes are interpreted as a combined signal of 2nd- and 3rd-order eustatic cycles, modified and partly obliterated by the effects of intrabasinal tectonic forcing and by palaeogeographically controlled variation in sediment supply.

2

Sedimentological study of the Nikolčice Formation : evidence of the Middle Jurassic transgression onto the Bohemian Massif (subsurface data)

Nehyba S., Opletal V.

Geological Quarterly

|

2017

|

Vol. 61, No. 1

138--155

EN

The Jurassic sedimentary succession along the eastern margin of the Bohemian Massif starts with mostly fluvial deposits of the Gresten Formation and continues after marine transgression with the deposition of the Nikolčice Formation (Middle Jurassic, Callovian). The provenance and depositional environment of the Nikolčice Formation showed that deposition occurred within offshore, transitional zone, shoreface, foreshore and littoral sand bar environments; however, shoreface and foreshore deposits dominate in the cores studied. The crystalline units along the eastern margins of the Bohemian Massif represent the primary source of deposits of the Nikolčice Formation. An important role was played by acidic and intermediate plutonites and highly metamorphosed metasedimentary rocks (granulite and amphibolite metamorphic facies), which indicates an advanced stage of erosion of the source area. The role of volcanic and intrusive rocks was small. The primary source was followed by an additional recycled source from older sedimentary rocks (especially the Moravo-Silesian Paleozoic deposits – the Líšeň Formation, the Myslejovice Formation). A similarity of the source areas for the Nikolčice Formation and the underlying Gresten Formation was recognized. Identified differences in their source areas are mainly explained by varied erosional levels due to successive exhumation of the source Variscan orogen and possibly also by an expansion of the source area.

3

Disappeared almost without a trace : Taphonomic pathways and the recognition of hidden bioturbation events in Eocene storm deposits (Paují Formation, Lake Maracaibo, Venezuela)

Buatois L. A., Delgado M., Mángano M. G.

Annales Societatis Geologorum Poloniae

|

2015

|

Vol. 85, No. 3

473--479

EN

Shallow-marine deposits, included in the “Basal Sands” of the Eocene Paují Formation of the Maracaibo Basin in western Venezuela, record deposition in fore shore to lower off shore settings. These deposits are stacked in coarsening-upward parasequences that reflect variable intensities and frequencies of storms. Of particular interest are sharp-based, amalgamated, hummocky cross-stratified and rippled, very fine-grained sandstone beds, observed in the core MOT-X from the Motatán Field. These beds record storm deposition, under purely oscillatory to combined flows in an offshore-transition setting. The amalgamated nature of the sand stone interval indicates repeated erosion, due to multiple storm events. The ichnofabrics in these tempestites result from a distinctive taphonomic pathway, reflecting the interplay between bioturbation events and storm erosion and deposition. The storm-related trace-fossil suite is represented by Diplocraterion parallelum and local occurrences of Palaeophycus tubularis, Bergaueria isp. and Thalassinoides isp., which is consistent with the relatively high energy of formation of these deposits. Fair-weather deposits are absent from the sand stone interval. However, high densities of Chondrites isp. are present in the infills of Diplocraterion parallelum and, more rarely, Thalassinoides isp. providing the sole evidence of the establishment of a resident fauna during inter-storm intervals. Deposits containing the fair-weather suites were erosionally removed during the subsequent storm. The deep-tier emplacement of Chondrites and the ability of its producer to rework other biogenic structures favour preservation, allowing recognition of a “hidden” bioturbation event that otherwise might have remained undetected.

4

Coniacian-?Santonian paralic sedimentation in the Rakowice Małe area of the North Sudetic Basin, SW Poland: sedimentary facies, ichnological record and palaeogeographical reconstruction of an evolving marine embayment

Leszczyński S.

Annales Societatis Geologorum Poloniae

|

2010

|

Vol. 80, No 1

1-24

EN

The Coniacian-?Santonian siliciclastic succession outcropped in a sandstone quarry at Rakowice Małe (Żerkowice Member of the Rakowice Wielkie Formation, and the Czerna Formation including the Nowogrodziec Member; North Sudetic Basin, SW Poland) provides an interesting example of paralic deposits. Lithofacies and ichnofossil examination indicate coastal, lacustrine, paludal and lagoonal sedimentation. Valuable new data are supplied by trace fossils, a feature not considered yet in the literature on the Upper Cretaceous of the North Sudetic Basin. Trace fossils are overall abundant in the upper part of the Nowogrodziec Member and overlying part of the Czerna Formation. The following ichnogenera: Thalassinoides, Ophiomorpha, Asterosoma, Palaeophycus, Planolites, Skolithos, Teredolites, Chondrites, Cylindrichnus, Arenicolites, Rosselia, Teichichnus, Phycodes, Phycosiphon, and Schaubcylindrichnus are represented. The trace fossils represent the Skolithos, Teredolites and Cruziana ichnofacies. The Cruziana Ichnofacies is typified by the richest trace fossil assemblage characteristic of its archetypal, proximal and stressed expressions. An upper shoreface to foreshore origin of these sediments is documented using lithofacies and the ichnofossils Ophiomorpha and Thalassinoides in the exposed part of the Żerkowice Member. Dominance of kaolinite, lack of burrows and upward passage into paludal deposits is interpreted to indicate a lacustrine origin of variegated clayey mudstone at the base of the Nowogrodziec Member. The changes of depositional environments are interpreted as resulting from separation of the area from the open sea by a sand barrier formed due to the termination of the forced regression. Siltstones containing plant roots and fragments of drifted wood showing the trace fossil Teredolites clavatus, together with coal-seams containing Thalassinoides isp., are assigned to indicate a coastal plain, paludal deposition of the overlying part of the Nowogrodziec Member and incursion of marine waters. The fining upward sequence constituting the top part of the Nowogrodziec Member and showing almost archetypal Cruziana Ichnofacies substituted by its expression indicative of highly stressed, brackish conditions are shown to indicate extensive drowning of the area and lagoonal sedimentation. Termination of the drowning, embodied in a maximum flooding surface, is indicated in a bed of coaly mudstone at the top of the Nowogrodziec Member. Sedimentation on a periodically prograded brackish bay shoreface is inferred from lithofacies, ichnofossils and body fossils for the deposits overlying the Nowogrodziec Member and topping the examined succession. The trace fossils indicate Cruziana Ichnofacies and Skolithos Ichnofacies in the expression of slightly stressed environ- ments. The whole examined part of the Czerna Formation is interpreted as a fifth-order transgressive-regressive cycle.

5

Trace fossils accompanying possible "Ediacaran organisms" in the Middle Cambrian sediments of the St. Petersburg Region, Russia

Natalin N., Mikulas R., Dronov A.

Acta Geologica Polonica

|

2010

|

Vol. 60, no. 1

71-76

EN

Shallow-marine Middle Cambrian sandy sediments of the St. Petersburg Region (i.e., sedimentary cover of the Baltic Shield) bear non-shelly, cup-like fossils, interpreted tentatively as descendants of Ediacaran organisms. The ichnoassemblage accompanying this occurrence consists of Skolithos, Diplocraterion and indeterminate biogenic sedimentary structures. The ichnofabric index is low (1-2). The probable body fossils are crosscut by the trace fossils. Though simple, the ichnoassemblage recorded here yields valuable information on the environment that could have hosted Ediacaran organisms during the earliest Phanerozoic.

6

Eocene graphoglyptids from shallow-marine, highenergy, organic-rich, and bioturbated turbidites, Fuegian Andes, Argentina

Olivero E., Lopez C. M., Torres Carbonell P., Malumian N.

Acta Geologica Polonica

|

2010

|

Vol. 60, no. 1

77-91

EN

Graphoglyptids are diagnostic ichnofossils of the Paleodictyon ichnosubfacies (Nereites ichnofacies), which is well represented in deep-marine Mesozoic.Cenozoic thin-bedded turbidites. However, unusual shallow-water records of Mesozoic-Cenozoic Paleodictyon and particular preservational restrictions of graphoglyptid burrows introduce the question of whether graphoglyptids are reliable bathymetric indicators. We document and discuss another unusual graphoglyptid association preserved in shallow-marine, high-energy, organic-rich, and bioturbated turbidites of leveed channels in the upper middle Eocene CCa member, Cerro Colorado Formation, Fuegian Andes. The member includes the facies associations: 1) mudstones, 2) interbedded mudstones and thin-bedded Tbc turbidites, and 3) thick-bedded sandstones andmudstones. Facies association 3), interpreted as channel deposits, records at least three horizons with Desmograpton, Glockerichnus, Helicolithus, Helminthorhaphe, Megagrapton, Paleodictyon and Urohelminthoida. Associated beds are lenticular, channeled sandstone turbidites with marked basal erosion surfaces and variable proportions of interbedded mudstone-sandstone with high content of plant debris. Trace fossils in the channeled sandstones are dominated by Ophiomorpha rudis and O. annulata; mudstones within the thick-bedded mudstone-sandstone beds bear Nereites, Phycosiphon, Zoophycos and Paradictyodora, with subordinate Schaubcylindrichnus, Tasselia and Scolicia. The unusual preservation of limited graphoglyptid-bearing beds within a highly energetic and bioturbated interval seems to support the concept that preservational restrictions on graphoglyptid burrows could be locally more important than bathymetric constraints.