Middle eocene ostracoda from Northern Somalia (paleoenvironmental appraisal)

Abstract

The present study is focused on the reconstruction and interpretation of the paleoenvironmental conditions that prevailed during the deposition of the Middle Eocene deposits of Northern Somalia by means of the ostracod assemblages distinguished. Quantitative analyses of 75 ostracod species, recognized in 36 ostracod-bearing samples from the study area, has revealed six types of assemblages (a, b1, b2, b3, b+c, c), obtained by applying Q-mode cluster analysis based on the Jaccard coefficient of similarity (the complete linkage method). These types represent, from older to younger, the Thracella indica Assemblage Zone (type b1; middle Lutetian), the Paijenborchellina reticulata-Paijenborchellina pustulata Assemblage Zone (type b2; middle Lutetian), the Hornibrookella moosae Assemblage Zone (type b3; middle Lutetian), the Paragrenocythere dhofarensis somaliensis Assemblage Zone (type a; late Lutetian), the Asymmetricythere tricostata Assemblage Zone (type b+c; late Lutetian to Bartonian) and the Neocyprideis rotundata Assemblage Zone (type c; late Lutetian to Bartonian), respectively. Q-mode analysis based on the extraction of latent roots and vectors of a non-parametric matrix produced by the Spearman correlation coefficient, led to the conclusion that the most effective environmental factors in the study area are: salinity (1 st latent vector), substrate (2 nd latent vector), dissolved oxygen of water (3 rd latent vector), turbidity currents (4 th latent vector). The general paleoenvironmental conditions prevailing during the deposition of the Middle Eocene strata in Northern Somalia are discussed in details.