Ordovician trace fossils from southern Jordan with particular consideration to the Cruziana rugosa group: Taxonomy, stratigraphy and trans-regional correlation throughout the Middle East and northern Africa

Abstract

First detailed palaeoichnological research is presented from all the Ordovician formations and members of the Southern Desert of Jordan. The exclusively siliciclastic succession is of fluvial, fluvial-deltaic and fully marine origin and develops continuously from Cambrian strata until late Hirnantian glacial deposits. The ichnofauna occurs on large outcrop surfaces and is quite rich and of high diversity. Based on numerous taxonomic identifications from the excellently preserved material of various stratigraphic levels a biostratigraphic determination of the sequence is concluded as late Early to early Late Ordovician. Twenty-four ichnotaxa, two morphotypes and fifteen ichnogenera within five ethological groups based on the categories of architectural designs were identified. (1) horizontal burrows and trails (arthropod traces): Cruziana rugosa, C. furcifera, C. goldfussi, C. rouaulti, C. almadenensis, C. isp., Diplichnites cf. D. gouldi, D. morphotype A, D. morphotype B, Monomorphichnus cf. lineatus, cf. Monomorphichnus, Rusophycus didymus, R. aff. petraeus, ?R. aff. almadenensis; (2) vertical burrows: Arenicolites isp., Monocraterion isp., Rosselia socialis, Skolithos linearis; (3) plug-shaped burrows: Bergaueria perata, B. sucta; (4) horizontal branched burrows: Treptichnus cf. T. pedum; (5) horizontal burrows and trails: Gyrochorte isp., Palaeophycus tubularis, Planolites beverleyensis, Psammichnites gigas, Zoophycos isp. Whereas the ichnofauna of the Early Ordovician upper Disi Formation (Fm.) is dominated by cruzianid (C. rugosa group) and diplichnid arthopod traces (“trilobite highways”), the late Middle to early Late Ordovician Dubaydib Fm. contains distinctly smaller, nearly monoichnospecific, but completely surface covering arthropod tracks (C. almadenensis). In places, an amazing monospecific mass occurrence (Skolithos piperock ichnofabric) points to very special palaeoecological conditions during the deposition of the lower Dubaydib Fm. Ichnoassociations of the lower part of the Mudawwara Fm. (middle Late Ordovician) indicate a primarily shallow environment (e.g., Zoophycos isp.). Based on the trace fossil content and lithofacial characteristics, a correlation with North African regions is possible. So, the upper part of the Disi Fm. and the lower part of the Umm Sahm Fm. From Jordan is correlated with the Early Ordovician strata from southeastern Libya by the occurrence of C. goldfussi and C. furcifera. Additional correlations are possible by the shared occurrence of C. rouaulti with western Egypt, Sudan and western Libya. Within the Middle East (Jordan, Saudi Arabia, United Arab Emirates, Iran and Turkey), similar trace fossil assemblages composed of the C. rugosa group and related traces as well as common lithofacies characteristics point to closer palaeogeographic vicinity on a connected shallow shelf region along the costal margin of the Gondwana palaeocontinent.