Late Ordovician (Katian) Graptolites and Shelly Fauna from the Phu Ngu Formation, North-East Vietnam

Thomas W. Wong Hearing; Mark Williams; Adrian Rushton; Jan Zalasiewicz; Toshifumi Komatsu; Christopher Stocker; Thomas H. P. Harvey; Shuji Niko; Hung Dinh Doan; Ha Thai Trinh; Hung Ba Nguyen; Minh Trung Nguyen

doi:10.2517/2020pr011

Sedimentology, stratigraphy and clinoform architectures of a siliciclastic shallow-marine platform: insights from the Late Ordovician of the Anti-Atlas (Morocco)

10.5194/egusphere-egu21-10409 ◽

2021 ◽

Author(s):

Déborah Harlet ◽

Guilhem Amin Douillet ◽

Jean-François Ghienne ◽

Chloé Bouscary ◽

Philippe Razin ◽

...

Keyword(s):

Late Ordovician ◽

Shallow Marine ◽

North East ◽

The North ◽

Stratigraphic Framework ◽

Facies Associations ◽

Basin Geometry ◽

Marine Platform ◽

Stacking Patterns ◽

Early Late

The Moroccan Anti-Atlas consists of a several kilometers thick sediment pile accumulated on the northern Gondwana platform since the latest Precambrian (Ediacaran). This study focuses on the Ktaoua Group, early Late Ordovician (Mid-Sandbian to Katian) in age, which records a major and multiphase transgressive/regressive cycle above the shallow marine sandstones of the underlying First Bani Group. In the western Central Anti-Atlas, the Ktaoua Group is formed by offshore shales to coastal sandstones organized in regressive parasequences. Here, high-resolution field-based stratigraphy is used to constrain the shelf architecture and clinoforms geometries within the Ktaoua Group.Whereas the lower part of the Ktaoua Group records parasequences from silty-shale to fine to coarse sandstones with hummocky-cross-stratification (HCS), its upper part oscillates between HCS beds and very coarse sandstones. Ferruginous, condensed horizons usually drape the parasequences. In this study, we investigate the platform geometry through the correlation of the stacking patterns of seventeen stratigraphic logs along an 85 km long, well-exposed cliff. Drone images support the logging and the correlations of the sections by imaging clinoforms geometries. Several decameters of fine to coarse sandstones can be observed to grade laterally into condensed level(s) within a few kilometers, hence evidencing clinoforms pinching out. The visible orientation of the clinoforms along the cliff exposures show a proximal to distal trend from the south-west to the north-east, in agreement with the overall basin geometry. Three clinoforms with distinct geometries and lateral evolution of facies associations are highlighted. The distal part of a clinoform, 15 m in thickness, pinches out onto the top of the underlying First Bani Group within 7 km. The overlying regressive parasequence, approximatively 50 m thick, remains consistent more than 50 km, and is understood as a prograding clinoform. A third clinoform, capped by a prominent sandstone body constantly thicker than 20 m over ca. 20 km, disappears within its last 3.5 km onto the underlying clinoform. This study offers new details on the progradation and regression geometries along a giant platform within a detailed stratigraphic framework.We would like to thank the Pacha and the Gendarmerie Royale of Foum-Zguid, the governor of Tata and the different persons who gave their approval and facilitated the use of the drone in the region of Souss-Massa for their precious help.

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Large-scale channel fill structures in Late Ordovician glacial deposits in Mauritania, western Sahara Ghienne J.F. & Deynoux M., Sedimentary Geology, 1998, 119/1?2 (141?159)

Journal of African Earth Sciences (and the Middle East) ◽

10.1016/s0899-5362(99)90023-4 ◽

1999 ◽

Vol 28 (1) ◽

pp. VII-VIII

Keyword(s):

Large Scale ◽

Late Ordovician ◽

Glacial Deposits ◽

Western Sahara

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Ras al Khaimah: further archaeological discoveries

Antiquity ◽

10.1017/s0003598x00150070 ◽

1976 ◽

Vol 50 (200) ◽

pp. 216-222

Author(s):

Beatrice De Cardi

Keyword(s):

United Arab Emirates ◽

The State ◽

Focused Attention ◽

North East ◽

The North ◽

History Of ◽

The City

Ras a1 Khaimah is the most northerly of the seven states comprising the United Arab Emirates and its Ruler, H. H. Sheikh Saqr bin Mohammad al-Qasimi, is keenly interested in the history of the state and its people. Survey carried out there jointly with Dr D. B. Doe in 1968 had focused attention on the site of JuIfar which lies just north of the present town of Ras a1 Khaimah (de Cardi, 1971, 230-2). Julfar was in existence in Abbasid times and its importance as an entrep6t during the sixteenth and seventeenth centuries-the Portuguese Period-is reflected by the quantity and variety of imported wares to be found among the ruins of the city. Most of the sites discovered during the survey dated from that period but a group of cairns near Ghalilah and some long gabled graves in the Shimal area to the north-east of the date-groves behind Ras a1 Khaimah (map, FIG. I) clearly represented a more distant past.

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