Abstract
High-resolution magnetic susceptibility and % CaCO3 records (5 to 10 cm sampling interval) are used to track astronomical cycles from a Lower Berriasian record from central Tunisia. Six hundred and twenty two samples were measured for magnetic susceptibility and carbonate content as paleoclimate proxies for the detection of potential Milankovitch cycles. Elemental data using X-Ray fluorescence analyses was acquired from 19 samples to prove the reliability of the MS signal on recording the past paleoclimatic changes. We performed multiple spectral analyses and statistical techniques on the magnetic susceptibility signal, such as Multi-taper Method, Evolutive Harmonic Analysis, Correlation Coefficient, Time-optimization, and Average Spectral Misfit to obtain an optimal astronomical model. The application of these spectral analysis techniques revealed a pervasive dominance of E405-kyr and e100-kyr cycles showing that the climate turnover across the early Berriasian—middle Berriasian seems to had been governed by the long and short orbital eccentricity cycles. The identification of Milankovitch cycles in the record also allowed to propose a floating astronomical timescale of the studied section, with ~4 long eccentricity cycles (E405) extracted, which points to a duration estimate of ~1.6 Myr with an average sediment accumulation rate (SAR, after compaction) of 2.77 cm/kyr. The inferred floating ATS was tuned to the La2004 astronomical solution. In addition, we applied the DYNOT and ρ1 methods for seal-level change modeling to reconstruct a local eustatic profile which matches the previously published local and global eustatic charts.
Highlights
The Cretaceous is the only system/period of the Phanerozoic that has not yet been defined by a basal GSSP
To better explain the link between the magnetic susceptibility (MS) fluctuations and cyclostratigraphy, we propose the following plausible flow of explanations: Some paramagnetic minerals are endogenous in origin, which means that their delivery to sedimentary basins must be ensured first by the erosion of preexisting rocks. continental weathering can be triggered by tropical humid climate which results in an enrichment of kaolinite and illite in marls, while this process is relatively weaker during the deposition of carbonate beds
High-resolution cyclostratigraphic investigation from MS and % CaCO3 proxies was undertaken on the Lower Berriasian sedimentary series in central Tunisia (Southern Tethys)
Summary
The Cretaceous is the only system/period of the Phanerozoic that has not yet been defined by a basal GSSP. Extensive stratigraphic studies (mainly biostratigraphic investigations) have been widely carried out on this Formation during the last few decades (Burollet, 1956; Memmi, 1967; Busnardo et al, 1976, 1981; Maalaoui and Zargouni, 2016a,b; Ben Nsir et al, 2019) but some of them are controversial (e.g., M’Rabet, 1987; Maalaoui and Zargouni, 2016a; Ben Nsir and Boughdiri, 2017) In this context, several studies (Allen, 1981, 1998; Hallam, 1984, 1985, 1986; Deconinck and Strasser, 1987; Hallam et al, 1991; Deconinck, 1993; Ruffell and Rawson, 1994; Price, 1999) have evidenced the existence of widespread dry and cold climate period during the upper Jurassic. This trend from a dry climatic phase to a more humid one, is recorded in higher paleolatitudes, from the boreal area, the northern margin of the Tethys Sea (Deconinck, 1987, 1993; Rasplus et al, 1987; Schnyder, 2003) and documented southerly in Morocco (Agadir area), on the Atlantic domain (Daoudi et al, 1989; Daoudi and Deconinck, 1994)
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