Błażejowski et al.—A new Triassic limulid from Tunisia
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Figure 1. Location of the studied area in Tunisia: (1, 2) geological map of the Jeffara Plain and Dahar Plateau (Medenine/Kirchaou/Tataouine area) with position of the Tejra site; (3) columnar section of the Ouled Chebi Formation exposed at the lower part of the Tejra 2 clay-pit, showing the horizon with occurrence of the studied Limulitella material.
The material studied herein comes from a locality called
either Tajera Skhira (e.g., Biely and Rakus, 1991) or Tejra Sghira (e.g., Baccour et al., 2008). The Triassic succession there is exposed in a monoclinal structure with beds dipping southwest. It is unconformably overlain by middle Callovian, shallow-marine Jurassic carbonates. Bed-by-bed logging of the sites around Tejra resulted in construction of a detailed strati- graphic section that is ~100m thick. However, only part of this
section (the main Tejra outcrop) was analyzed in detail in the field and studied paleontologically (Soussi et al., 2016). The Tejra section can be subdivided into four distinctive
units. The first unit represents the basal part of the section and is ~25mthick. It is composed of red claystones comprising gray to green, thin claystones interbedded with numerous medium- to coarse-grained and well-sorted sandstones (Fig. 1.3). Local desiccation features observed are numerous ripple marks on the upper surfaces of thin sandstone layers. The brown and green claystone horizons encountered at the base of this unit are particularly rich in conchostracans. A succession of two gray-yellow beds bounding a brown bed yielded an abundant and a very diverse freshwater fauna (Fig. 2.1). This is situated ~5m above a basal conglomerate, composed of claystones irregularly interbedded with well-sorted and rounded grains of quartz (~1–2mm in diameter). Most of the fossils are derived from yellowish sediments at the top of the lower gray/green bed (Fig. 2.2). The fauna is represented by conchostracans (Fig. 2.3), horseshoe crabs, freshwater bivalves (Fig. 2.4, 2.5), rare
microconchids, and lingulides. Desiccation cracks, small burrows, and casts fromplant roots are also present in this horizon. The second unit is ~30m thick. It is clay dominated, but
contains numerous sandstone interbeds. At the base, two thick layers of medium-grained red sandstone, interbedded with a 2m thick red claystone yield a rich fauna of marine or brackish bivalves, microconchids, gastropods, and lingulides. The third unit is ~35m thick. It is composed mainly of
reddish-brown siltstones and claystones and comprises a sandstone bed marker in its middle part showing numerous invertebrate ichnofossils in its lower part. The fauna includes conchostracans, lingulides, and rare partially preserved horse- shoe crabs, although the latter were found only at the base of the unit. The fourth unit is ~10m thick. It mainly comprises
brown claystone with thin green beds and contains a fauna of conchostracans and lingulids, rare gastropods, rare horseshoe crabs, and microconchids. The claystones represent deposition in floodplains and lakes and the associated sandstone and siltstone interbeds are interpreted as deposits resulting from intermittent flood events.
Materials and methods
The described material comes from two abandoned clay pits in Tejra area near Medenine (Fig. 1). The samples collected in 2013 and 2014 from the Tejra section yielded a total of
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