Time series analysis (orbital cycles) of the uppermost Cenomanian-Lower Turonian sequence on the southern Tethyan margin using foraminifera

Abstract

Time series analysis has been performed for the first time on the Cenomanian-Turonian sequence in Central Tunisia in order to shed light on its Milankovitch-like cyclicity. This analysis was applied to two foraminiferal genera: the biserial Heterohelix, an oxygen-minimum zone (OMZ) dweller, and the triserial Guembelitria, a eutrophic surface dweller. Average sedimentary rates and the duration of the oceanic anoxic event (OAE2) in each studied section were estimated. The fluctuations in abundance of these two opportunistic species can be related mainly to both precessional (ca. 20 kyr) and eccentricity (100 and 400 kyr) cyclicity suggesting that changes in surface water fertility were linked to climate changes in the Milankovitch frequency band.

Cretaceous oceanic anoxic events (OAEs) recorded in the northern margin of Africa as possible oil and gas shale potential in Tunisia: An overview

“…To the south, the Saharan shield was not an area of non-deposition as suggested by Zghal and ArnaudVanneau (2005), Chihaoui (2008), andBen Fadhel et al (2011), but rather it was covered during the early Albian transgression by the Foum El Argoub/Chennini transgressive sandstones and the Redouane/Zebbag platforms (Ben Youssef 1999; Ouaja et al 2004;Soua 2009;Bodin et al 2010), where the Knemiceras level (Ain El Guettar Formation) represents the equivalent of the mfs of the Allam black shale. Central Tunisia was covered by the carbonate platform of the Zebbag Formation.…”

“…Therefore, no deposition of the anoxic C/T carbonate on uplifts and palaeohighs is recorded. During that time, subsidence led to the accumulation of more than 50 m of laminated black shales in a time span of about 0.4 million years in the Tunisian sections (Soua 2010a). In summary, this period testifies to the reduction of emerged areas inherited from the Early Cretaceous, and thus we note that: (1) to the west, the subsidence is controlled by a preferential NE-SW-faulting trend (Aurès basin-Kef) where maximum C/T subsidence is recorded;…”

“…Detailed cyclostratigraphic investigation for the organicrich Bahloul Formation has been given by Soua (2010a) and Soua et al (2010). Using four C/T sections in central Tunisia displaying biotic and lithologic variations, Soua (2010a) applied time-series analysis to the abundance of two opportunistic foraminiferal genera (Heterohelix and Guembelitria spp.)…”

Application of Facies Associations, Integrated Prediction Error Filter Analysis, and Chemostratigraphy to the Organic-Rich and Siliceous Cenomanian-Turonian Sequence, Bargou Area, Tunisia: Integrated Sequence Stratigraphic Analysis

“…At small scale, as for the Bahloul Formation (which display 20 to 30 m) the shift from negative trends (Figures 2 and 4), interpreted as a shallowing upward sequence (e.g., Facies C and F) to a positive trend, interpreted as deepening upward sequence (e.g., Facies B and D) suggest that some significant change has affected the depositional system. The "shallowing upward" trend has been switched off through the major third order eustatic rise, linked to a change in the Milankovitch periodicity and in turn to climatic variation [13]. Alternatively, the switching from positive trend to negative trend, may be caused by a switching from a deepening upward sequence to a shallowing upward one and in turn the reverse effect has taken place and there is an abrupt resumption of shallower sediment deposition.…”

“…The main sequence (Bahloul formation) is typically controlled by the global relative sea-level rise causing the major latest Cenomanian transgression which in turn was interpreted as a combined phenomenon between a long-term sea-level rise and basin subsidence [1,11,12]. It must be understood that this sequence seems to be generated by enhanced plate tectonic activity and by the change in the Milankovitch frequency band (e.g., [13]) justifying climatic cycles which are detected in the sedimentary record ( Figure 2). The major rise in the Cenomanian sea level was interrupted by the five-third order relative sea-level falls [1].…”