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The significance of Upper Cretaceous hardgrounds and other discontinuity surfaces for basin-wide correlations, based on drillcore data from boreholes in northern Poland

Leszczyński K.

Geological Quarterly

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2017

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Vol. 61, No. 4

825--844

EN

The paper presents the hardgrounds and some other correlative discontinuity surfaces found in Upper Cretaceous (Cenomanian–Maastrichtian) borehole sections of northern Poland. They were briefly described, and depositional environment was identified for both the underlying deposit (UD) and the overlying deposit (OD). The significance of these features for both basin-wide correlations and broadly understood sequence stratigraphic techniques is highlighted. They were correlated with other major discontinuity surfaces identified in boreholes of northern Poland in both drill cores and well logs if such identification was reliable based on geophysical borehole data. All these discontinuity surfaces were referred to the boundaries of the individual depositional cycles determined within the Upper Cretaceous succession: K3-II/K3-III, K3-III/K3-IV, K3-IV/K4-I, K3-IV/K4-II, K4-I/K4-II (or II or IV or V), K4-III/K4-IV (or V), K4-IVa/K4-IVb, probably K4-IVb/K4-V, and K4-V/Pc-I. The discontinuity surfaces can be related to both sea level fluctuations and tectonic activity during the Subhercynian phases. Most of them developed in relatively calm sedimentary conditions, outside the central part of the Mid-Polish Trough. The exceptions are three hardgrounds from the Człopa–Szamotuły Zone, which seem to be associated mainly with the Late Cretaceous tectonic (including salt tectonics) activity of this zone. The most common UD/OD configuration of sedimentary environments is the open-marine carbonate shelf both beneath and above the discontinuity surface. The second most common situation is the open-marine carbonate shelf beneath and the open-marine shelf with carbonate-siliceous sedimentation above. The gaps at the surfaces span variously long intervals, ranging from short periods (spanning a fraction of a depositional cycle) to long periods (comprising one or more depositional cycles). The position of the discontinuity surfaces facilitates searching for any possible hiatuses in the sections of other boreholes, and paying attention to local changes in sediment distribution patterns, and local tectonic activity.

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Unconformity surfaces in pelagic carbonate environments : A case from the Middle Bathonian of the Betic Cordillera, SE Spain

Nieto L. M., Rodríguez-Tovar F. J., Molina J. M., Reolid M., Ruiz-Ortiz P. A.

Annales Societatis Geologorum Poloniae

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2014

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Vol. 84, No. 3

281--295

EN

Integrative studies of sedimentary and palaeontological topics for unconformity surfaces are useful in basin analysis. A middle Bathonian unconformity surface in the Ammonitico Rosso facies cropping out in the La Mola Unit (Subbetic Domain, Betic External Zone) was studied by integrating ichnological, palaeotectonic, and sedimentological analyses to decipher sea-level, tectonic, and palaeogeographic conditions during its development. The trace-fossil assemblage mainly consists of the Glossifungites (Thalassinoides, Arenicolites, and Gastrochaenolites) and Trypanites ichnofacies elements. Probable Ophiomorpha represents previous softground stages, Thalassinoides and Arenicolites were formed in firmground, Gastrochaenolites reflects an evolved firmground or early hardground, and Trypanites can be attributed to an incipient hardground. The degree of firmness, relative sea-level position, and continuity of deposition were related. The softground stage corresponds to a fall in relative sea level and continued deposition. The firmground (semi-consolidated substrate) probably reflects an extremely low sea level characterized by non-deposition, whereas the incipient hardground stage indicates an initial phase of relative sea-level rise, with an increase in marine current energy. The presence of two neptunian dyke systems reflects significant tectonic activity related to the transtensional deformation that affected the South Iberian Palaeomargin. Lateral variations in sedimentological and ichnological features recorded at similar discontinuity surfaces in nearby areas were considered and related to differences in bottom topography, with associated changes in sedimentation, and to the variable duration of the hiatus.

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Lower Kimmeridgian layer with bored and encrusted hiatus concretions (Upper Jurassic, Central Poland) : implications for stratigraphy and basin evolution

Krajewski M., Olchowy P., Felisiak I.

Annales Societatis Geologorum Poloniae

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2014

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Vol. 84, No. 2

113--129

EN

The paper presents a comparative analysis of a Lower Kimmeridgian layer with bored and encrusted hiatus concretions collected in three study areas, located in Central Poland. These studies demonstrate distinct similarities between the hiatus concretions in terms of their origin, development and stratigraphic position. The layer with its characteristic concretions seems to represent an important marker horizon for the Lower Kimmeridgian successions in Central Poland. The identification of this marker horizon in drill cores and exposures could be important for definition of the stratigraphic position of the sediments, which otherwise lack appropriate biostratigraphic information. The matrix of the concretions is composed of pelagic calciturbidites, which reflect flooding of the early Kimmeridgian platform. These sediments were lithified early and formed a hardground. The origin of the hiatus concretions probably is related to erosion of the hardground, followed by redeposition and several phases of exhumation and erosion, preceding final burial. The characteristic ecological successions, observed in the concretions, document an evolution from soft to firm and hard marine substrates, typical of hardgrounds and evidenced by various burrows, borings (Gastrochaenolites, Trypanites), and epizoans. Calciturbidite sedimentation, hardground erosion and redeposition of the hiatus concretions, known from deposits of the Platynota Zone in Central Poland, were associated with synsedimentary activity of the Holy Cross Fault, on the NE margin of the extensive, tectonic Małopolska Block.

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New data on the Jurassic evolution of the Panormide Carbonate Platform (Sicily)

Zarcone G., Mindszenty A., Di Stefano P.

Volumina Jurassica

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2006

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Vol. 4, no. 1

107-107

EN

The Jurassic of the Panormide Carbonate Platform records several discontinuity surfaces reflecting a complex sedimentary dynamics at a time of general extension in the western Tethyan realm. Previous studies documented subaerial exposure with karst bauxites between Upper Triassic and Upper Jurassic in the internal sector of the platform. On the contrary, at same time the marginal sectors of the platform record Rosso Ammonitico type sedimentation and the subsequent progradation of a new, Upper Jurassic platform. Latest sedimentological and stratigraphical studies added new data on these discontinuity surfaces in the Palermo Mountains. The succession of Mt. Castellaccio is characterized by Upper Triassic peritidal dolostones crosscut by various generations of neptunian dykes filled by pelagic limestones with crinoids, brachiopods, ammonites and filaments (Pliensbachian to Middle Jurassic). They are covered by red sediments rich in ferric ooids and lithoclasts enclosed in a red, argillaceous matrix. Petrographics and X-ray analyses have confirmed the presence of boehmite, kaolinite and hematite in these rocks, on the basis of which they may be qualified as low-grade bauxites. Above, with an angular unconformity, there follow Kimmeridgian loferitic limestones interbedded to bioclastic grainstone/packstone with Clypeina sulcata (Alth). At Punta Raisi, a stratigraphically equivalent, but sedimentologically different succession has been studied. The Upper Triassic peritidal dolostones are overlain by Lower Jurassic cyclic peritidal limestone with very poor microfauna. It is repeatedly interrupted by yellow to browinsh paleosoil levels. The top of this succession is red-coloured and is marked by a complex dissolution surface, with pinnacles and grooves. It is capped by a thick Fe-Mn crust with Foraminifera, small ammonites and filaments [Bajocian-Callovian(?)]. Based on preliminary petrographical and geochemical analyses a brief subaerial event may be hypothesized. However, the very same petrographic analyses revealed the effects of undoubtedly submarine bioerosion (action of sponge, fungi and bacteria), too. So even if we accept the idea of a transient subaerial phase, a strong submarine overprint during subsequent drowning, possibly contributing to the development of the pinnacle-and-groove topography can not be excluded, either. The Fe-Mn-crust is overlain by pelagic sediments displaying a coarsening upward trend and gradually passing into bioclastic grainstones/packstones with abundant carbonate platform elements (Kimmeridgian). This work is intended to add new arguments to the stratigraphic evolution and, consequently, to the subsidence history of the Panormide Carbonate Platform. Results are as follows: * evidence for an Early Jurassic shallow water depositional environment; * restriction of the size of the hiatus between Lower and Middle Jurassic; * verification of the presence of a submarine dissolution surface analogous to that of the Trapanese Platform; * increase of the areal extension of bauxites on the Panormide Platform; * confimation of the synchroneity of the re-establishment of the shallow-water carbonate sedimentation during the Late Jurassic. This data moreover allow a better paleogeographic reconstruction and a key to understand the combined effects of sea-level changes, tectonics and thermal (?)updoming at the time of an overall extensional regime.

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Palaeoenvironmental conditions of hardgrounds formation in the Late Turonian-Coniacian of Mangyshlak Mountains, Western Kazakhstan

Gruszczyński M.

Acta Geologica Polonica

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2002

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Vol. 52, nr 4

423-435

EN

A carbon and oxygen isotope stratigraphic profile has been made, for the first time, through the Late Turonian-Coniacian sedimentary sections containing regionally widespread firm- and hardgrounds of Mangyshlak Mountains, western Kazakhstan. Generally, Turonian and Coniacian time has been considered as a transitional stage between two Oceanic Anoxic Events (OAE), because of the peculiar pattern of variation of the [delta'13C and delta'18 O] values. Unfortunately, there is no such record in the sections we examined, thus the Mangyshlak Sea behaved uniquely compared to the majority of seas and oceans at the time. The process of hardground formation is polygenetic but involved stopping deposition of calcium carbonate and initiation of the hardground over the large area of the sea floor. Normal causes of cessation of calcium carbonate seem unlikely and the expected drastic changes of hydrochemistry of the bottom waters cannot be detected in any of the minerals within the hardground sediments. Also, changes in climate, if there were any, are very difficult to estimate. Moreover, winnowing of the carbonate sediment is also not detectable from the characteristics of the hardground surface. Because the sedimentary sequence containing that regional hardground formation is transgressive, the most plausible reason for cessation and deposition of calcium carbonate is acceleration of the transgression. This might release sufficient amounts of carbon dioxide and bicarbonate to slow precipitation and deposition of calcium carbonate. Also, the greater distance from the shore might have reduced the supply of nutrients which decelerated photosynthetic activity, which in turn decreased consumption of carbon dioxide, thus enhancing precipitation of calcium carbonate. Some additional winnowing of calcium carbonate sediments would have helped in subsequent development of the harground. Finally, deceleration of the transgression renewed precipitation and deposition of calcium carbonate.