Abstract
Abstract. The Rashrashiyah Formation of the Sirhan Basin in northern Saudi Arabia contains diverse assemblages of planktonic foraminifera. We examined the biostratigraphy, stratigraphic range and preservation of upper Eocene planktonic foraminifera. Assemblages are well-preserved and diverse, with 40 species and 11 genera. All samples are assigned to the Priabonian Globigerinatheka semiinvoluta Highest Occurrence Zone (E14), consistent with calcareous nannofossil biostratigraphy indicating Zone CNE17. Well-preserved planktonic foraminifera assemblages from the lower part of the upper Eocene are rare worldwide. Our study provides new insights into the stratigraphic ranges of many species. We find older (Zone E14) stratigraphic occurrences of several species of Globoturborotalita previously thought to have evolved in the latest Eocene (Zone E15, E16) or Oligocene; these include G. barbula, G. cancellata, G. gnaucki, G. pseudopraebulloides, and G. paracancellata. Older stratigraphic occurrences for Dentoglobigerina taci and Subbotina projecta are also found, and Globigerinatheka kugleri occurs at a younger stratigraphic level than previously proposed. Our revisions to stratigraphic ranges indicate that the late Eocene had a higher tropical–subtropical diversity of planktonic foraminifera than hitherto reported.
Highlights
IntroductionTheir abundance and distinctive morphologies have left a long and valuable marine fossil record, making them ideal for studies in evolution, climate, and relationships between diversity and climate change
The diversity of planktonic foraminifera is high during the middle Eocene (Pearson et al, 2006; Aze et al, 2011; Fraass et al, 2015), but calcareous and siliceous zooplankton suffered extinction at the end of the Bartonian associated with the middle–late Eocene transition (MLET) (Wade, 2004; Kamikuri and Wade, 2012; Wade et al, 2012) and again across the Eocene–Oligocene transition (EOT) (Wade and Pearson, 2008; Moore and Kamikuri, 2012)
The absence of the large muricate taxa and the presence of Globigerinatheka semiinvoluta in Samples C, D and E indicate that the section can be assigned to the planktonic foraminifera Globigerinatheka semiinvoluta HOZ (Zone E14; Berggren and Pearson, 2005; Wade et al, 2011)
Summary
Their abundance and distinctive morphologies have left a long and valuable marine fossil record, making them ideal for studies in evolution, climate, and relationships between diversity and climate change. The term Konservat-Lagerstätte (Seilacher, 1970) is used to characterize exceptional preservation in the fossil record. The Paleogene sediments of coastal Tanzania contain remarkably well-preserved calcareous microfossils (Pearson et al, 2001, 2007; Wade and Pearson, 2008), and these were described as a microfossil Konservat-Lagerstätte by Bown et al (2008). The development of a calcareous microfossil Konservat-Lagerstätte appears to be related to clay-rich sediments that have never been deeply buried (Bown et al, 2008). The clays act as a low-permeability and low-porosity medium, isolating microfossils from chemical and physical
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