Short-Term Sea Level Changes of the Upper Cretaceous Carbonates: Calibration between Palynomorphs Composition, Inorganic Geochemistry, and Stable Isotopes

Ahmed Mansour,Michael Wagreich,Thomas Gentzis,Sameh Tahoun,Ashraf Elewa

doi:10.3390/min10121099

Ahmed Mansour, Michael Wagreich + Show 3 more

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https://doi.org/10.3390/min10121099

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Abstract

Widespread deposition of pelagic-hemipelagic sediments provide an archive for the Late Cretaceous greenhouse that triggered sea level oscillations. Global distribution of dinoflagellate cysts (dinocysts) exhibited a comparable pattern to the eustatic sea level, and thus, considered reliable indicators for sea level and sequence stratigraphic reconstructions. Highly diverse assemblage of marine palynomorphs along with elemental proxies that relate to carbonates and siliciclastics and bulk carbonate δ13C and δ18O from the Upper Cretaceous Abu Roash A Member were used to reconstruct short-term sea level oscillations in the Abu Gharadig Basin, southern Tethys. Additionally, we investigated the relationship between various palynological, elemental, and isotope geochemistry parameters and their response to sea level changes and examined the link between these sea level changes and Late Cretaceous climate. This multiproxy approach revealed that a long-term sea-level rise, interrupted by minor short-term fall, was prevalent during the Coniacian-earliest Campanian in the southern Tethys, which allowed to divide the studied succession into four complete and two incomplete 3rd order transgressive-regressive sequences. Carbon and oxygen isotopes of bulk hemipelagic carbonates were calibrated with gonyaulacoids and freshwater algae (FWA)-pteridophyte spores and results showed that positive δ13Ccarb trends were consistent, in part, with excess gonyaulacoid dinocysts and reduced FWA-spores, reinforcing a rising sea level and vice versa. A reverse pattern was shown between the δ18Ocarb and gonyaulacoid dinocysts, where negative δ18Ocarb trends were slightly consistent with enhanced gonyaulacoid content, indicating a rising sea level and vice versa. However, stable isotope trends were not in agreement with palynological calibrations at some intervals. Therefore, the isotope records can be used as reliable indicators for reconstructing changes in long-term sea level rather than short-term oscillations.

Highlights

From the onset of the Late Cretaceous, a global long-term marine sea-level high occurred with a peak estimate of 170 to 250 m above the present sea level (Figure 1) [1,2,3]
This is evidenced by the strong positive correlation between the dinocyst species diversity and the eustatic sea level curve (Figure 1), from their first appearance during the Triassic up to the Cretaceous [2,6]
We deduce that higher dinocyst species diversity is related to periods of predominant high eustatic sea levels, especially transgressive systems tracts (TSTs)

Summary

Introduction

From the onset of the Late Cretaceous, a global long-term marine sea-level high occurred with a peak estimate of 170 to 250 m above the present sea level (Figure 1) [1,2,3]. Egyptian borders to the south in the Muglad basins of southern. Short-term sequences, third and fourth order, and sea reconstruction are critical forstratigraphic understanding local to mainly regional environmental processes andlevel related deposition of critical for understanding local to regional environmental processes and related deposition of sediments sediments from the southern Tethys, the Abu Gharadig Basin, north Western Desert, from the southern Tethys, the Abu Gharadig Basin, north Western Desert, Egypt

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