Evolutionary trends and biostratigraphical application of new Cenomanian alveolinoids (Foraminifera) from the Natih Formation of Oman
An exhaustive sampling of the Cenomanian deposits corresponding to the Natih Formation in the Oman Mountains has been carried out in several field trips. The larger foraminifera representatives of the superfamily Alveolinoidea Ehrenberg, 1839 found in the collected material have been studied in order to more precisely identify and constrain their stratigraphical distribution. The following new taxa are introduced: Decastroinae subfam. nov., Praealveolininae subfam. nov., Reichelia gen. nov., R. magna sp. nov., Decastoria serrakieli sp. nov., D. oblonga sp. nov., D. miaidinensis sp. nov., Praealveolina arabica sp. nov. and P. acuta sp. nov. Other simpler alveolinoids, such as Simplalveolina gr. simplex, have been found together with these forms. The alveolinoids have been found in four successive assemblages. Assemblage I contains Alveocella wernliana, Myriastyla omanensis, M. grelaudae and Cisalveolina nakharensis; assemblage II contains Decastroia serrakieli sp. nov. and Simplalveolina gr. simplex; assemblage III contains D. razini, D. oblonga sp. nov., Reichelia magna gen. et sp. nov., D. miaidinensis sp. nov. and Simplalveolina gr. simplex; and assemblage IV, which is only found in Wadi Mi'Aidin, contains abundant D. miaidinensis sp. nov., Praealveolina arabica sp. nov. and P. acuta sp. nov. The age attributed to assemblage I is lowermost Middle Cenomanian, the age of assemblages II and III is Middle Cenomanian, and assemblage IV is interpreted as Middle Cenomanian to early Late Cenomanian. From a phylogenetic point of view, alveolinoids diversified and evolved in two successive episodes: a lower maturation cycle, corresponding to assemblage I, and an upper cycle, corresponding to assemblages II to IV. Cenomanian alveolinoids are more abundant and diverse than was previously thought and it seems that they split and evolved in parallel lineages, probably from unknown simple alveolinoids of milioline origin.