in Jurassic and Cretaceous Stratigraphy

Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321
The Sonninniidae (Ammonitina) from the Laeviuscula Zone (Lower
Bajocian, Middle Jurassic) of Moroccan Central High Atlas
202
D. Sadki
Department of Geology, Faculty of Science, Moulay Ismaïl University, B.P. 11201 Zitoune, Meknes, Morocco
(E-mail: driss_sadki@yahoo.fr)
In the central High Atlas of Morocco, the
Laeviuscula Zone (ovalis and Laeviuscula subzones) of
the Lower Bajocian contains rich ammonite fauna
Graphoceratidae
0,13%
Grammoceratinae
3%
Strigoceratidae
3%
Haploceratacae
12%
Sphearoceratidae
0,8%
Otoïtidae
11%
Stephanoceraitdae
0,4%
dominated quantitatively (Fig.1) by a family of
Sonniniidae (up to 58 %).
Fig.1 Share (%) of family of ammonites in the Upper Aalenian and the Lower Bajocian of Moroccan Central High Atlas
The vertical extension of representatives of this
family allowed to establish the main biostratigraphic
subdivisions of Lower Bajocian in Morocco and to
make correlations with the standard zonation of the
North West Europe and other regions.
The family of Sonniniidae has an increased
dimorphic polymorphism and includes a great variety
of forms always keeled, but diverse section, usually
decorated with ribs and tubercles at least one stage of
their development. It shows a variety of genres with
macroconch and microconch forms (Fig.2), which
succeed in time from the upper Aalenian (Concavum
zone) to the top of the lower Bajocian (Humphrie-
sianum zone).
Phylloceratidae &
Lytoceratidae
11,67%
Sonniniidae
58%
The present study is concerned with the analysis of
Sonniniidae of Laeviuscula zone (Ovalis subzone and
Laviuscula subzone) of the Moroccan Central High
Atlas. A taxonomic revision is presented and several
species of this family are revised. These are among the
following Genera: Euhoploceras, Fissilobiceras, Shir-
buirnia, Witchellia, Papilliceras and Sonninia. The
chronostratigraphical position and the distribution of
the various species are discussed; a comparison with
forms from other regions is established.
Key words: Sonniniidae; Ammonites; Laeviu-
scula Zone; Lower Bajocian; Central High Atlas;
Morocco