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Sedimentology and ichnology of Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Kraków-Silesia Homocline, Poland

Leonowicz P.

Acta Geologica Polonica

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2012

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Vol. 62, no. 3

281-296

EN

The lithology, sedimentary structures and trace fossil association from the Bathonian organic-rich mudstones from Kraków-Silesia Homocline (SW Poland) are described and a preliminary interpretation of the palaeoenvironment is presented. The ore-bearing clays exposed in the Gnaszyn clay-pit are developed as dark grey claysilt deposits with a few horizons of sideritic concretions. Sedimentological analysis has revealed that these deposits originated in the offshore part of a marine basin, below the fair weather wave base. Relict parallel lamination suggests that the predominant mechanism of deposition was quiet settling from suspension. However, locally preserved storm deposits indicate that the sea bottom was affected by offshore flows, deriving coarser material from the nearshore area. The degree of bioturbation is high but the diversity of the trace-fossil association is low. It consists mainly of Chondrites, Trichichnus, pyritized burrows and less common Palaeophycus. Other traces, including Thalassinoides, Planolites, Taenidium and some undetermined burrows, occur mainly in the lower part of the succession. This ichnoassociation combines features of distal Cruziana and Zoophycos ichnofacies, suggesting poor oxygenation of the bottom sediment. Temporary improvements in bottom oxygenation, linked with more intense mixing of water during major storms, resulted in the more diverse trace fossil suite that is found in some intervals of the succession.

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Palaeoenvironmental reconstruction of Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Kraków-Silesia Homocline, Poland

Gedl P., Kaim A., Leonowicz P., Boczarowski A., Dudek T., Kędzierski M., Rees J., Smoleń J., Szczepanik P., Sztajner P., Witkowska M., Ziaja J.

Acta Geologica Polonica

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2012

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Vol. 62, no. 3

463-484

EN

Multidisciplinary studies of the Middle-Upper Bathonian ore-bearing clays at Gnaszyn revealed variable palaeoenvironmental conditions during the deposition of this seemingly monotonous sequence. We interpret the conditions in the bottom environment and the photic zone, and also evaluate the influence of the adjacent land areas, based on sedimentology, geochemistry, sporomorphs and palynofacies composition, benthic (foraminifera, gastropods, bivalves, scaphopods, echinoderms), planktonic (calcareous nannoplankton, dinoflagellate cysts), and nektonic (sharks) fossils. The Gnaszyn succession originated relatively close to the shore, within reach of an intense supply of terrestrial fine clastic and organic particles. The latter are mainly of terrestrial origin and range from 1.5 to 2.5 wt.%. The precise water depth is difficult to estimate but most likely ranges from several tens of metres to a few hundred metres. All fossil groups show minor changes throughout the succession. As the climate seems to have been quite stable during this period we consider sea-level fluctuations to have been the main factor responsible for the changes. The terrestrial input, including freshwater and land-derived clastic and organic particles (sporomorphs and cuticles), increased during periods of sea-level lowstand. As a consequence, stress conditions (lower salinity, higher nutrient availability, lower water transparency) in the photic zone caused blooms of opportunistic planktonic taxa. Furthermore, a faster sedimentation rate led to oxygen depletion and deterioration of the living conditions in the bottom environment due to an increased accumulation of organic matter. As a result, the benthic biota became taxonomically impoverished and commonly dominated by juvenile forms. During periods of high sea level, the source areas were shifted away from the basin, resulting in a decrease in the terrestrial influx, increase in the salinity of surface waters, the appearance of more diverse phytoplankton assemblages, a lower sedimentation rate, and an improvement of living conditions at the bottom.

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Sedimentation of Lower Toarcian (Lower Jurassic) brackish deposits from the Częstochowa-Wieluń region (SW Poland)

Leonowicz P.

Acta Geologica Polonica

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2011

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Vol. 61, no. 2

215-241

EN

The Lower Toarcian Ciechocinek Formation from the Częstochowa-Wieluń region is composed of poorly consolidated mudstones, claystones and siltstones with subordinate sandstone intercalations. The succession is represented by twelve lithofacies grouped into seven facies associations of a shallow brackish marine basin with an embayment character. The sedimentation was dominated by clay and silt deposition from low-density suspension flows, spreading out from river mouths, and from suspension clouds whirled up during storms. Sand intercalations mark episodes of storms, removing coarser material from nearshore to more distal settings, migration of elongated sand bars, as well as sedimentation at river mouths and on sandy shoals. The deposition was affected by three main factors: (1) progradation and displacement of river mouths; (2) river discharge fluctuations;and (3) short-term weather changes.

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Trace fossils from the Lower Jurassic Ciechocinek Formation, SW Poland

Leonowicz P.

Volumina Jurassica

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2008

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Vol. 6, no. 1

89-98

EN

Mud-silt deposits of the Lower Jurassic Ciechocinek Formation from the Czestochowa-Wielun region are characterized by a low diversity ichnofossil association, which includes the ichnogenera Planolites, Palaeophycus, Helminthopsis, Gyrochorte, Protovirgularia and Spongeliomorpha as well as some unidentified pascichnia. This association points to deposition in a low-energy brackish environment with poorly oxygenated sediments. Changes of seafloor oxygenation, influenced by periodical bottom currents, resulted in various bioturbation intensities, which range from none to high.

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Origin of siderites from the Lower Jurassic Ciechocinek Formation from SW Poland

Leonowicz P.

Geological Quarterly

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2007

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Vol. 51, No 1

67-78

EN

Sideritic rocks, which are characteristic constituents of muddy-silty deposits of the Lower Jurassic Ciechocinek Formation, occur commonly as layers, lenses and small irregular concretions composed of siderite mudstone and siltstone as well as less common lenses of sideritic sandstones. Three types of siderite cement were observed in thin sections: fine-crystalline variety (SF), coarse-crystalline rhombohedra (SR) and fine-crystalline biogenic aggre gates (SA). In all these types BSE analysis revealed compositional zonation of crystals, with in ternal parts enriched in Mg, Mn and Ca and outer zones almost pure siderite. d13C values and chemical composition of siderites combined with the presence of early diagenetic pyrite indicate that siderite crystallized from brackish marine-derived solutions; only in the case of two samples from the lower part of the Ciechocinek Formation the fresh water origin cannotbe excluded. Mn and Fe were supplied by rivers and released by Fe- and Mn-reduction in suboxic zone, whereas Mg and Ca were derived from sea water, which infiltrated into the sediment. Crystal zonation resulted from the diagenetic evolution of pore water as the sediment was buried. Similar composition and development of siderite crystals from different parts of one layer indicate that siderite precipitated simultaneously throughout the whole horizon. Precipitation began from the formation of numerous nuclei and continued by growth of crystals onto them. It could begin already in the iron reduction subzone and continued in the sulphate reduction and methanogenesis zones.

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The Ciechocinek Formation (Lower Jurassic) of SW Poland : petrology of green clastic rocks

Leonowicz P.

Geological Quarterly

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2005

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Vol. 49, No. 3

317--330

EN

The Lower Jurassic Ciechocinek Formation from the Czestochowa-Wielun region of SW Poland comprises greenish-grey muds and silts as well as poorly consolidated mudstones and siltstones with lenticular intercalations of fine-grained sands, sandstones and siderites. Analysis of a mineral composition indicates that the detrital material was derived mainly from the weathering of metamorphic and sedimentary rocks of the eastern Sudetes with their foreland and of the Upper Silesia area, and that this material underwent repeated redeposition. The Fe-rich chlorites which give the green colour to the mudstones of the Ciechocinek Formation are most probably early diagenetic minerals, genetically linked with the deposition in a brackish sedimentary basin.

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Cysty Dinoflagellata z odsłonięć liasu w Kozłowicach i Boroszowie (Wyżyna Woźnicko-Wieluńska)

Barski M., Leonowicz P.

Przegląd Geologiczny

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2002

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Vol. 50, nr 5

411-414

PL

Opisanie zespołu cyst Dinoflagellata z badanych próbek przyczyniło się do sprecyzowania stratygrafii utworów ilastych w odsłonięciach w Kozłowicach i Boroszowie. Charakterystyczne taksony dinocyst wskazaly też na przeławicanie się w profilu osadów przywiązanych do środowisk sedymentacji morskiej i brakicznej. Analiza palinofacjalna wskazuje na bliskie położenie badanego fragmentu basenu sedymentacyjengo w stosunku do obszaru lądowego. Tam, gdzie w próbkach zanotowano morski gatunek Luehndea spinosa, skład palinofacji wykazał redukcję fitoklastów pochodzenia lądowego na korzyść lżejszych - bardziej lotnych i pławnych ziaren pyłku oraz spor.

EN

The described assemblage ofDinoflagellate cysts enabled to pinpoint the stratigraphic position ofclaystones cropped out olozloivice and Boroszów. The specific taxa ofdinoflagellates indicated the presence ofinterbedding marine and brackish sediments o://! the sections studied. Thepalynofacies analysis confirmed the proximal location of these sections in sedimentary1 basin. The environmental suggestions derived from the dinocyst assemblage are supported by palynofacies indicators.