How the Environment Influenced Theropod Diversity in Aptian/Albian Cretaceous Tunisia

Integrating palaeoecology and morphology in theropod diversity estimation: a case from the Aptian-Albian of Tunisia

Authors:

Fanti et al

Abstract:

Current knowledge of theropod dinosaurs of northern Africa and their diversity during the Early Cretaceous is deceptively fragmentary and commonly associated with inadequate stratigraphic and palaeoecological data. Thereby, confused taxonomic affinities of theropod remains, represented primarily by isolated teeth and fragmentary skeletal remains, resulted in speculations on the number of genera and their stratigraphic, geographic and ecological distribution. In this study, we introduce a discussion on the theropod diversity in the Aptian–Albian of southern Tunisia based on a multidisciplinary approach that combines detailed sedimentological analyses with canonical morphological and phylogenetic analyses. This study indicates the presence of three theropod clades, Spinosauridae, Abelisauroidea, and Carcharodontosauridae. Relevant for the identification of isolated specimens from the Saharan regions, carcharodontosaurids are not represented in the Aptian-Albian teeth record and thus relatively less abundant than spinosaurids and abelisauroids. Five ziphodont tooth morphotypes are referred to ontogenetic and/or positional differences among a single abelisauroid taxon. The other three teeth morphotypes most likely represent two distinct spinosaurid taxa. Finally, the calibrated stratigraphic distribution of discussed elements indicates a clear ecological partition between theropod taxa. In particular, abelisauroids and carcharodontosaurids are commonly found in inland, fluvial deposits together with titanosauriform and rebbachisaurid sauropods, and rare crocodilians. Conversely, spinosaurids are limited to estuarine to coastal deposits dominated by a rich and diverse crocodilian fauna along with actinopterygians and sarcopterygians, including large-sized coelacanthiforms.

Comparing Tunisian Sahel to Mars

Groundwater influence on the aeolian sequence stratigraphy of the Mechertate–Chrita–Sidi El Hani system, Tunisian Sahel: Analogies to the wet–dry aeolian sequence stratigraphy at Meridiani Planum, Terby crater, and Gale crater, Mars

Authors:

Essesfi et al

Abstract:

A multidisciplinary study of the watershed and depressions of the Mechertate–Chrita–Sidi El Hani (MCSH) system in eastern Tunisia shows that groundwater upwelling and/or seepage toward the modern surface is important in the shaping of its geomorphologic features and sediment outcrops. Along the watershed of the system, groundwater is downward enriched with evaporitic minerals. These minerals precipitate as cement and protect the sediment outcrops from aeolian erosion. The water table is the limiting control on erosion and deposition, and also influences the succession of sediment along the system. The water table further determines the local base level, which controls the deposition within depressions. With increasing humidity at the limit of the capillary fringe, the landscape of the evaporative system is organized according to three sedimentary types: (1) unconsolidated sediment of aqueous and/or aeolian origin that is eroded and transported toward depressions (away from groundwater interactions), (2) consolidated sediment that is also aqueous and/or aeolian in origin and is protected from aeolian erosion by groundwater influence, and (3) sedimentary filling of depressions located within accumulation zones. These sediments are organized along a lateral, basinward profile. Here we show that during periods of relative water table fall, sediments from the watershed prograde to cover the sabkha basin fill. The rise and fall of the water table and the connected base level result in the deposition of genetically-related progradational and retrogradational sequences. We propose that these genetic sequences can be useful to interpret the sequence stratigraphy at three locations on Mars where sedimentary formations were probably controlled by direct groundwater influence: Meridiani Planum, Terby crater, and Gale crater. At Meridiani Planum, the exposed stratigraphic sequence of the Burns formation starts with deposition of dry aeolian sediment derived from a former watershed. Then, due to the rise of the water table, wet sediments of a sabkha rest atop the dry aeolian cycle to comprise a retrogradational sequence. At Terby and Gale craters, an opposite stratigraphic sequence starts with the wet deposition of the sabkha fill. Then, due to the fall of the water table, the dry aeolian sedimentation progrades atop to the sabkha fill to comprise a progradational sequence. We conclude that the various stratigraphic sequences at the MCSH system, described here, represent different possible analog scenarios for diverse depositional sequences on Mars, in all cases involving groundwater activity.

Building Construction Which Ties into Local Traditions

A Mediterranean Union?!

French President Nicolas Sarkozy began his first visit to Algeria on Tuesday to present a plan for a Mediterranean Union and chart a course for improved ties with the former colony.

erm. They haven't even finished putting up the drywall on the European Union yet! Isn't this a little premature? Isn't one of the arguments by France against Turkey joining the EU that they're, well, Muslim? Isn't that the same for Algeria and Tunisia? erm.

Does anyone have some solid info on the proposed MedU?