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Research article

Insights into the Cenozoic geology of North Beirut (harbour area): biostratigraphy, sedimentology and structural history

Authors
  • Germaine Noujaim Clark (Independent Consultant geologist and Research associate to Lebanon National Council for Scientific Research, Lebanon)
  • Marcelle BouDagher-Fadel orcid logo (Office of the Vice-Provost (Research), University College London, 2 Taviton Street, London WC1H 0BT, UK)

This is version 2 of this article, the published version can be found at: https://doi.org/10.14324/111.444/ucloe.000004

Abstract

The biostratigraphy and sedimentology of the outcrops and bedrock recently exposed in archaeological excavations around the harbour area of Beirut (~5 km²) unlock the geological and structural history of that area, which in turn are key to understanding the hydrocarbon and hydrogeological potential of the region. A key location (Site 2) of a studied outcrop section and newly uncovered bedrock is on the northern foothill cliff of East Beirut (Achrafieh). The outcrop section of carbonates is of Eocene beds overlain by conformable Miocene beds. The excavation of the slope bordering the outcrop uncovered a bedrock section of an early Pliocene shoreline of carbonate/siliciclastic sands at its base and topped by a beach-rock structure. The early Pliocene age of the shoreline section is dated by an assemblage of planktonic foraminifera that includes Sphaeroidinellopsis subdehiscens, Sphaeroidinella dehiscens and Orbulina universa. The Eocene carbonates of Site 2 extend the coverage of the previously reported Eocene outcrops in the harbour area. They form a parasequence of thin-bedded, chalky white limestones that includes the youngest fossil fish deposits in Lebanon (Bregmaceros filamentosus). The deposits are dated as early Priabonian by their association with the planktonic foraminiferal assemblage of Porticulasphaera tropicalis, Globigerinatheka barri, Dentoglobigerina venezuelana, Globigerina praebulloides, Turborotalia centralis and Borelis sp. The Middle Miocene carbonates that conformably overlie the early Priabonian, parasequence include a planktonic foraminiferal assemblage of Globigerinoides trilobus, Orbulina universa and Borelis melo. Elsewhere, in the harbour area, the preserved Eocene limestones are also overlain by conformable Miocene carbonate parasequences of Langhian–Serravallian age. Younger argillaceous limestone beds of the Mio/Pliocene age occur in the eastern central part of the harbour area and enclose an assemblage of Truncorotalia crassaformis, Globorotalia inflata and Orbulina universa. The three markers of old and recently raised structural blocks in the harbour area are a Lutetian/Bartonian marine terrace in the south west corner, a lower Pliocene shoreline carbonate section in the north east side and a Holocene raised beach of marine conglomerates in the north east corner of the area. The locations of these paleo-shorelines, less than 2 km apart, indicate a progressive platform narrowing of North Beirut since the Paleogene. This study underpins the geological complexity of the region and contributes to understanding the underlying geology, which will be needed for future regional archaeological, hydrocarbon and hydrogeological exploration.

Keywords: Foraminifera, Cenozoic, biostratigraphy, sedimentology, palaeoenvironment, paleogeography, regional tectonics

Rights: © 2020 The Authors.

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1Citations

Published on
09 Feb 2020
Peer Reviewed
License
Creative Commons Attribution 4.0

 Open peer review from Josep Sanjuan

Review

Review information

DOI:: 10.14293/S2199-1006.1.SOR-EARTH.AFD331.v1.RURDPS
License:
This work has been published open access under Creative Commons Attribution License CC BY 4.0 , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Conditions, terms of use and publishing policy can be found at www.scienceopen.com .

ScienceOpen disciplines: Earth & Environmental sciences , Geosciences
Keywords: Ecology , The Environment , Climate , Foraminifera, Cenozoic, biostratigraphy, sedimentology, palaeoenvironment, paleogeography, regional tectonics.

Review text

This is an interesting, complete and well documented work. This study provides new light regarding the relative age and tectonic evolution (uplifting) of main lithologic units at North of Beirut (Harbour area).

The structure of this work follows a logical and clear order and the English is good. However, I advise the authors to include a new chapter about Materials and methods. In this chapter the authors should explain the location of the outcrops (UTM), sections thickness, treatment of the samples, etc. The introduction and the geological setting chapters are necessary. I’ve also suggest the authors to add synthetic figures (maybe at the corner of the field photos) showing the stratigraphic logs and the vertical position of the analysed samples. Despite I’m not an expert in foraminifera taxonomy, I think that the taxonomy of the foraminifera species here illustrated is correct.

The authors are able to clarify the relative age of the studied Cenozoic deposits in the Harbour of Beirut based on the foraminifera assemblage. Also they provide a detailed tectonic and paleogeographic evolution of the area during the Cenozoic. This study will serve as a reference for future developments of detailed geological maps and investigations focused on Lebanese basin evolution and carbonate characterization.

Few changes should be made basically in the figures. Please, find attached the PDF of the manuscript with my comments and suggestions.

Sincerely,

Dr. Josep Sanjuan Girbau



Note:
This review refers to round of peer review and may pertain to an earlier version of the document.

 Open peer review from Nick Marriner

Review

Review information

DOI:: 10.14293/S2199-1006.1.SOR-EARTH.AW89XA.v1.RRAJFF
License:
This work has been published open access under Creative Commons Attribution License CC BY 4.0 , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Conditions, terms of use and publishing policy can be found at www.scienceopen.com .

ScienceOpen disciplines: Earth & Environmental sciences , Geosciences
Keywords: Ecology , The Environment , Climate , Foraminifera, Cenozoic, biostratigraphy, sedimentology, palaeoenvironment, paleogeography, regional tectonics.

Review text

Insights on the Cenozoic Geology of North Beirut (Harbour Area): Biostratigraphy; Sedimentology and Structural history

I have now completed my review of the above paper by Germaine Noujaim Clark and Marcelle Boudagher-Fadel. The manuscript presents new geological data from the ancient harbour area of Beirut. The authors describe, for the first time, unreported Eocene carbonates, Eocene fish deposits, old and young Cenozoic shorelines by the eastern foothill of Beirut West, and northern foothill of Beirut East. The sequences are dated using fossil assemblages, with a particular focus on the micropalaeontology.  The paper is well structured and nicely illustrated, and the arguments set forward by the authors are both convincing and pertinent. In sum, I fully support the publication of the paper in UCL Open: Environment.

Missing references

Marriner, N., Morhange, C. & Beydoun, M. (2008) Geoarchaeology of Beirut’s ancient harbour, Phoenicia. Journal of Archaeological Science, 35, 2495-2516.

Throughout the paper, it would be interesting to place some percentage estimates on the different fossil assemblages described.



Note:
This review refers to round of peer review and may pertain to an earlier version of the document.