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| Titel |
Palynomorph responses to sea-level change: preliminary results for Upper Cretaceous assemblages from East Bohemia (Czech Republic) |
| VerfasserIn |
K. Olde, D. Uličný, I. Jarvis, M. Pearce |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250067600
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| Zusammenfassung |
| Late Cenomanian to Early Coniacian times (95 – 88 Ma) were characterised by a eustatic
sea-level maximum during the latest Cenomanian – early Turonian followed by a general
long-term second order sea-level fall, and a global temperature maximum during the
Turonian. Major short-term fluctuations in relative sea level were superimposed on the
long-term falling trend, but the relative influence of eustatic change on sea-level records
remains controversial. A new regional reference core (Bch-1) spanning the Turonian
– Lower Coniacian was drilled in 2010 at BÄchary in eastern Bohemia (Czech
Republic). The 400 m core provides a basinal section, which can be correlated to
shallow-marine and coastal facies at the basin margins. The latter have provided a
basis for the development of a robust sequence stratigraphic framework for the
region.
This study investigates how the basinal palynomorph record responded to transgression
and regression. It aims to develop criteria that may be used to better constrain evidence of
sea-level change from basinal successions, with a particular focus on the response of
organic-walled dinoflagellate cyst (dinocyst) assemblages. Samples taken through the Bch-1
core at 2 m intervals have been analysed for palynological composition to complement
ongoing macrofossil, microfossil, chemostratigraphic, cyclostratigraphic and sequence
stratigraphic studies. All samples were spiked with Lycopodium spores to allow the
calculation of absolute abundance variation (i.e. palynomorphs per gram). The major- and
minor-element geochemistry of the dinocyst samples was determined to investigate
relationships between assemblages and sediment composition and to enable the recalculation
of palynomorph data on a carbonate-free basis.
Abundant and diverse assemblages have been recovered throughout the core. Lower
Turonian dinocyst biostratigraphic datums include the first appearance datum levels (FADs)
of Oligosphaeridium pulcherrimum, Senoniasphaera rotundata alveolata and Raetiaedinium
truncigerum and the last common occurrence of Cauveridinium membraniphorum. The
Middle Turonian is marked by a Circulodinium distinctum acme and the FAD of
Florentinia buspina. The Lower Coniacian includes the last appearance (LAD) of
Pervosphaeridium truncatum. Variations in dinocyst and terrestrial spores and pollen
assemblages are considered to reflect major changes in sediment fluxes, nutrient
supply, and water mass conditions. The lower Middle Turonian is characterised by an
increase in terrestrial palynomorphs, as well as increased Al2O3 and P2O5, general
clay mineral and nutrient proxies, and decreases in Si/Al and Ti/Al. This interval
corresponds to the advance of a deltaic complex to the west of the core site. The
Lower Coniacian reveals a maximum in abundance (palynomorphs per gram) of both
dinocysts and terrestrial palynomorphs, and a maximum in the relative abundance
of the cyst Palaeohystrichophora infusorioides, which is considered to be from a
heterotrophic dinoflagellate, and is indicative of high primary productivity. Increased clay
and accompanying nutrients is supported by the geochemical data. This interval
corresponds to the development of the early Coniacian Gilbert delta complex to the
NW of the core locality. The preliminary data confirm a strong signal in basinal
palynomorph records that may be related to changes in sediment supply and sea
level.
The core was obtained with financial support from the Czech Science Foundation
(GAÄR), grant No. P210/10/1991 to D. UliÄný. IJ acknowledges funding by UK Natural
Environment Research Council (NERC) grant NE/H021868/ |
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