Saline systems are candidates to be threatened by climatic change. In terms of methodology and materials, color identification, geochemistry, and mineralogy analysis were used. The spectral analysis of data of the amount of active K and Na firstly shows the individualization of a cycle stretching along with 1000 yr. Then, a less pronounced cycle of 2500 years is marked with a lower intensity. Also, on the spectral analysis of K data, the drowned cycles of 650 and 500 years are marked by weak intensities not reaching the threshold level. These two comparable cycles may be artifacts due to analysis errors or variability in the rate of sedimentation resulting in the bifurcation of two hybrid cycles from one real cycle. This work confirmed the cycles found by color studies through real analyses such as geochemical and magnetic measurements. As a matter of fact, the majority of cycles found out by the spectral analysis of colors data are confirmed through analyses.
TopIntroduction
Sebkhas, or seasonally flooded salt depressions, can be found throughout North Africa (Marquer et al. 2008). The term “sebkha” refers to flat-bottomed depressions that usually flood and are devoid of vegetation due to salty soils. Depression lake is frequently mentioned because its water evaporates, leaving the salts it has dissolved in the watershed. Sometimes, like in the case of the sebkha el Melah Zarzis, these sebkhas are in contact with the sea. An exoreic saline system, sebkha El Melah, was chosen to deal with the coastal geological background. It is feasible to anticipate climate cyclicity based on the sediment record of some depressions, such as oceans (Goslin et al., 2018), seas, lakes (Sant et al., 2018), and sebkhas (Essefi et al., 2015; Bedoui (2016); Amal Gammoudi et al., 2019). This salt depression can be found along the dry coasts of North Africa, Arabia, Baja California, and Australia's Shark Bay (Warren, 2006). Various studies have discussed the effect of climate change on the sebkha (Jian et al., 2000; Jallali et al. 2016), their geological and morphological evolution, and climatic (Dillenburg et al. 2017) and Holocene climate variability (Wanner et al., 2008; Pena et al., 2010; Berner et al. 201; Berner et al., 2011). In the literature surveys, different researches have largely discussed the effect of climate change in the environment of Sebkha (Zaibi et al., 2012; Li et al., 2019; Ben Ameur et al., 2019, 2021).
Any paleoclimatic investigation should be timed so that the climatic phases may be assigned to well-known periods of time. Furthermore, precise dating is required for spectrum analysis for Holocene cyclostratigraphy. However, due to technical and economic constraints, dating is not always achievable. Furthermore, some anterior studies in the field may have conducted dating that is relevant to this research. As a result, facies identification allows for the development of an age model. We have levels for sebkha El Melah that are well-dated.
The investigation of the recorded paleoclimatic variability is still a subject of controversy. Nonetheless, according to the available sediments, one or another proxy may be more efficient at extracting information concerning the depositional environment and the climatic conditions. The saline environments in Tunisia are linked to the Mediterranean Sea's global oceanography, which is influenced by the Atlantic Oscillation. On the other hand, exoreic systems, have a significant influence over inland systems. In a similar vein to earlier research, the goal of this project is to conduct a multidisciplinary investigation into the record within a sebkha El Melah.
Study Area: Sebkha El Melah
Sebka El Melah is a Saharan salt flat located in southern Tunisia. It has an area of 150 km2 (Fig.1). Its perfectly flat surface is slightly below sea level. This saline system occupies the bottom of a depression framed by trays of grown olive trees or left with sparse steppe. It is separated from the sea by a set of dune oolithic cords cut by a channel partly flooded by the sea, reflecting the former communication of the basin with the sea (Duplay et al., 2012). From a sedimentological point of view, the sebkha sediments essentially consist of several salt layers of rock salt and gypsum and polyhalite (Perthuisot 1971). Sebkha El Melah appeared at the beginning of the Wurmian Quaternary period (Perthuisot, 1975). Around 40,000 BP, the lagoon was highly desalinated by freshwater arrivals. At the upper Würm, seawater withdrew and the basin evolved into a temporary lake or continental sebkha.
Figure 1. Geological map of Sebkha El Melah and its vicinities
Methods And Materials
Soil Sampling
In order to eliminate any potential contamination of the sedimentary fillings by metals, it was better to use a plastic tube for coring. During the field expedition, an 82 cm core was recuperated in the sebkha El Melah using a PVC tube of 3 mm in thickness and 63 mm in diameter. The core was then transported to the laboratory to be cut to a size of 1 cm for destructive (geochemical and mineralogical studies) and non-destructive analyses (color identification and their significance).