Orbital Tuning of the Berriasella Jacobi Ammonite Zone in Central Tunisia (Southern Paleotethys)

Abstract

AbstractVery high-resolution magnetic susceptibility record (5–10 cm sampling interval) was used to track astronomical cycles from a section belonging to the Berriasella Jacobi ammonite zone, along which 536 samples were collected. The samples were measured for magnetic susceptibility and carbonate content as paleoclimate proxies. We performed multiple spectral analyses and statistical techniques such as the evolutive harmonic analysis (EHA), multi-taper method (MTM) and average spectral misfit (ASM) to obtain the best astronomical model. The section was divided into different sub-sections assuming a stable sediment accumulation rate for each one and the previous time series analysis techniques were applied for each sub-section and showed a pervasive dominance of E405-kyr and e100 kyr cycles. The combination of these results allowed us to review and build a new chronostratigraphic framework of the Berriasella Jacobi ammonite zone at Jebel Meloussi as follows: ~5.1 long-eccentricity cycles E405 were extracted which point to a duration estimate of ~2.07 Myr with an average sediment accumulation rate (SAR, dewatered and compacted) of 1.841 cm/kyr. This value of SAR goes in line with deep marine environment succession that had been deposited under a passive margin associated with the opening of the Paleotethyan Ocean around the Jurassic-Cretaceous transition.KeywordsBerriasianCyclostratigraphySidi Khalif formationOrbital tuningSpectral analysis