Abstract
The Sidi El Hani Wetland is located in Eastern Tunisia. It represents the natural outlet of an endorheic system, Mechertate-Chrita-Sidi El Hani, and it collects all the eroded sediment from this watershed. In this chapter, the visual core description focused on three reference sandy bands and on the concept of grey scale variability in order to infer the clay pan response to the climatic variability and erosion during the last two millennia. First, in the uppermost part, the stage Warming Present (WP) stretches from (1954-80= 1874) to 1993, i.e. ≈120yrs; the establishment of modern conditions is characterized by stable conditions with high grey scale. Added to a small salt crust, this period is dominated by a clayey sedimentation. Second, the stage C4 is called the Late Little Ice Age (Late LIA); it stretches between the 80yrBP and 400yrBP, i.e., 320yrs. It is characterized by intermediate GS values; the clayey sedimentation makes up the twofold and threefold laminates. Based on laser granulometer, the genetic approach shows the interplay of eolian and hydraulic erosion.
TopIntroduction
Global change of climate would have dramatic repercussions on erosion (Ciampalini et al., 2020). On the one hand, extreme events accentuate hydric erosion (Borrelli, et al., 2020). On the other hand, dry conditions enhance win erosion (Guo et al., 2020). Since wetlands are the natural outlets of all sediment eroded from their drainage basins, they are good recorders of climatic variability and excellent monitors of hydric and eolian erosion (Sun et al., 2020; Sapkota and White, 2021). As it is anticipated by previous tectonic, hydrogeological, hydrological and geochemical studies of the hydrogeological and hydrological basins on the one hand and the sedimentary and the hydric fillings of sebkha Sidi El Hani (as it is first defined englobing the sebkhas of Dkhila, Souassi, and Sidi El Hani sensu stricto) (Essefi, 2009, 2013, 2021; Essefi et al., 2013a, b, c, d, e; Essefi et al., 2014a, b, c) it is rather difficult to find an obvious geochemical signal of the climatic change in the sedimentary filling. This is because Sidi El Hani discharge playa is more governed by its hydrogeological basin rather than its hydrological watershed. Nonetheless, the variation of climatic conditions influences the watershed's erosion from the drainage basin and deposition within Sidi El Hani wetland. This chapter aims to overcome these handicaps and to guess the climatic variability and its effect on erosion during the last two millennia only on the basis of the visual description of cores. Accordingly, before doing any destructive analysis, non-destructive analysis, namely the Visual Cores Description (VCD), could give a lot of information about cores content, texture, and the organization of sedimentary bands. Furthermore, it would be an efficient tool for correlation between different cores from the same playa or different playas in order to compare them and to establish their stratigraphy.
Key Terms in this Chapter
OUTLET: The point where a stream flows out of a lake or pond.
Eolian: Eolian Erosion. Wind erodes the Earth's surface by deflation, the removal of loose, fine-grained particles by the turbulent eddy action.
Climate Variability: Climate variability includes all the variations in the climate that last longer than individual weather events.
Drainage Basin: A drainage basin is any area of land where precipitation collects and drains off into a common outlet, such as into a river, bay, or other body of water.
Erosion: Erosion is the geological process in which earthen materials are worn away and transported by natural forces such as wind or water.
Hydraulic: Hydraulic erosion is the process by which water transforms terrain over time. This is mostly caused by rainfall, but also by ocean waves hitting the shore and the flow of rivers.
Sedimentary Record: The geologic record in stratigraphy, paleontology and other natural sciences refers to the entirety of the layers of rock strata.