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

2012 ◽  
Vol 62 (3) ◽  
pp. 463-484 ◽  
Author(s):  
Przemysław Gedl ◽  
Andrzej Kaim ◽  
Paulina Leonowicz ◽  
Andrzej Boczarowski ◽  
Teresa Dudek ◽  
...  
Keyword(s):  
Sea Level ◽  
Sedimentation Rate ◽  
Middle Jurassic ◽  
Oxygen Depletion ◽  
Living Conditions ◽  
Photic Zone ◽  
Phytoplankton Assemblages ◽  
Palaeoenvironmental Reconstruction ◽  
Sea Level Fluctuations ◽  
Organic Particles

ABSTRACT Gedl, P., Kaim, A., Leonowicz, P., Boczarowski, A., Dudek, T., Kędzierski, M., Rees, J., Smoleń, J., Szczepanik, P., Sztajner, P., Witkowska, M. and Ziaja, J. 2012. Palaeoenvironmental reconstruction of Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Krakow-Silesia Homocline, Poland. Acta Geologica Polonica, 62(3), 463-484. Warszawa. 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.

Ample and recurrent sea-level fluctuations during the Bajocian: A hint towards middle Jurassic glacio-eustatism

2020 ◽  
Author(s):  
Stéphane Bodin ◽  
Jan Danisch ◽  
Malte Mau ◽  
Francois-Nicolas Krencker ◽  
Alexis Nutz ◽  
...  
Keyword(s):  
Sea Level ◽  
Middle Jurassic ◽  
Sediment Supply ◽  
Medium Term ◽  
High Atlas ◽  
Sea Level Fluctuations ◽  
R Packages ◽  
Central High ◽  
Central High Atlas

<p><span>Mesozoic sea-level fluctuations have been a matter of debate for several decades, especially the extend and origin of sea-level cycles that have a periodicity of about 1 Myr or less. The debate lies in the main driving mechanism for sequence development (global sea-level or sediment flux variations) as well as the reason behind water exchanges between the continents and the oceans (glacio- or aquifer-eustatism). In this study, we focus on the carbonate-dominated sedimentary record of the Bajocian (Middle Jurassic) in the Central High Atlas Basin of Morocco. Several aspects make this basin an appropriate location for discussing Middle Jurassic sea-level changes. Firstly, the outstanding exposures of the High Atlas Mountains, with continuous exposures for 10s of kilometres, allow to describe and track sedimentary packages and their bounding surfaces from proximal to distal settings. Moreover, a combination of ammonite and brachiopod biostratigraphy with carbon-isotopes chemostratigraphy allows to temporarily constrain their development, which permits to correlate and compare the Central High Atlas sedimentary record to other basins. Finally, due to high-subsidence rates, thick Bajocian sedimentary sequences have accumulated, minimizing condensation and hiatus that might prevail in other basins due to a lack of accommodation space creation. Two Bajocian long-term transgressive-regressive (T-R) packages are observed throughout the basin. They are modulated by several medium-term T-R packages, that have each an approximate duration of 1 Myr. These sequences can also be correlated on a basinwide scale. Combined with sedimentological and facies analyses, architectural evidence along proximal-to-distal transect illustrates that several of the medium-term sequences are characterized by the presence of a falling stage and lowstand systems tracts, demonstrating that medium-term T-R stacking patterns are not solely linked to fluctuation in sediment supply, but also to episodes of relative sea-level fall of at least 30m of amplitude. This is confirmed by backstripping analysis performed in a composite section from the center of the Basin. Comparison with Bajocian deposits from France and Scotland, where good biostratigraphic dating is also available, shows that similar contemporaneous sea-level fall can be observed, highlighting their potential global character. The two long-term Bajocian sequences are more difficult to correlate on a global scale, suggesting that they are rather primarily linked to fluctuation in regional sediment supply or dynamic topography processes. The exact cause of the Bajocian medium-term sea-level falls is currently unknown, but it is here interesting to note that a relatively cool globate climate has been postulated for the Middle Jurassic, suggesting that glacio-eustasy was their most likely driver.</span></p>

scholarly journals Calcareous nannofossils from the Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn as palaeoenvironmental indicator, Kraków-Silesia Homocline, Poland

2012 ◽  
Vol 62 (3) ◽  
pp. 421-437
Author(s):  
Mariusz Kędzierski
Keyword(s):  
Sedimentation Rate ◽  
Middle Jurassic ◽  
Photic Zone ◽  
Calcareous Nannofossils ◽  
Trophic Conditions ◽  
Quantitative Studies ◽  
Rate Versus ◽  
High Nutrient ◽  
Nutrient Influx ◽  
Terrestrial Material

ABSTRACT Kędzierski, M. 2012. Calcareous nannofossils from the Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn as palaeoenvironmental indicator, Kraków-Silesia Homocline, Poland. Acta Geologica Polonica, 62 (3), 421-437. Warszawa. Qualitative and quantitative studies on calcareous nannofossils have been carried out on the Middle-Upper Bathonian succession of Gnaszyn (Kraków-Silesia Homocline, Częstochowa region). The nannofossil assemblages are moderately or well-preserved and are dominated by Watznaueria britannica; also common are Staurolithiteslumina and Zeugrhabdotus erectus. The presence of delicate nannofossil forms together with dissolution- resistant taxa shows that the changes in composition of some of the nannoplankton assemblages reflect original variations. The frequency and diversity changes of the calcareous nannofossil assemblages have been interpreted in relation to fluctuations of sedimentation rate versus changes in trophic conditions within the photic zone. The highest diversity assemblages contain a high percentage of palaeofertility indicators, and are impoverished in the genus Watznaueria. This is interpreted as a reflection of a lower sedimentation rate and more stable, possibly mesotrophic conditions within the photic zone. On the other hand, W. britannica-dominated assemblages with low species diversity may represent more unstable environments with a high influx of terrestrial material related to a high sedimentation rate and a high nutrient influx, i.e. eutrophic conditions in the photic zone.

scholarly journals Organic-walled dinoflagellate cysts from the Bathonian ore-bearing clays at Gnaszyn, Kraków-Silesia Homocline, Poland – a palaeoenvironmental approach

2012 ◽  
Vol 62 (3) ◽  
pp. 439-461 ◽  
Author(s):  
Przemysław Gedl
Keyword(s):  
Sea Level ◽  
Taxonomic Composition ◽  
Photic Zone ◽  
Dinoflagellate Cysts ◽  
Sea Level Changes ◽  
Variable Intensity ◽  
Dinoflagellate Cyst ◽  
Sea Level Fluctuations ◽  
A Minor ◽  
Normal Salinity

ABSTRACT Gedl, P. 2012. Organic-walled dinoflagellate cysts from the Bathonian ore-bearing clays at Gnaszyn, Kraków- Silesia Homocline, Poland - a palaeoenvironmental approach. Acta Geologica Polonica, 62 (3), 439-461. Warszawa. A succession of Middle-Upper Bathonian (Subcontractus-Retrocostatum zones) ore-bearing clays exposed at Gnaszyn has been investigated for the presence of dinoflagellate cysts. The assemblages are dominated by Ctenidodinium. However, analysis of diversity shows some subtle differences throughout the succession, possibly related to the palaeoenvironmental conditions in the photic zone. Impoverished assemblages, dominated by Ctenidodinium, occur mainly in monotonous muddy intervals. More diverse assemblages, albeit also dominated by Ctenidodinium, occur in intervals which contain siderite concretion levels. The taxonomic composition of the former assemblage seems to reflect slightly restricted conditions in the photic zone, possibly related to a minor reduction in salinity and/or increase in nutrient availability. More diverse dinoflagellate cyst assemblages reflect periods of less intense terrigenous influx and relatively higher, possibly normal, salinity. These changes were possibly caused by variable intensity of freshwater influx into the basin, controlled by sea-level fluctuations. Sea-level changes may be related to migrations of Tethyan water masses, which were probably partly responsible for the composition of the dinoflagellate cyst assemblages.

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