Abstract: 

The Valanginian comprises a period of intense sea-level and climatic variations, marked particularly by one of the biggest sea level drop of the entire Cretaceous during the Early Valanginian and by the occurrence of the climatic Weissert Event during the flooding of the late Valanginian. Those fluctuations have been very well studied in various parts of the Tethys Ocean, but detailed work on the Arabian Platform remains limited despite a likely control on the distribution of porous and tight facies.

On the Arabian Platform, the Valanginian is associated with the sudden drowning of a major north-easterly prograding carbonate platform located on the southern margin of the Tethys Ocean, associated with a sharp back-stepping of the main facies belts to the south-west. Integrated facies analysis, biostratigraphy and carbon isotopes have been used to reconstruct the evolution of the carbonate shelf, while petrography supported diagenetic interpretations and pore system characterization, along with MICP data. This integrated dataset was used to populate core-based rock-typing schemes for each stratigraphic unit based on their unique sedimentological and diagenetic characteristics.

During the early Valanginian the area was dominated by the deposition of microporous dolomitized and clay-prone microbial intertidal mudstones, which passed basinwards to pervasively cemented low-energy inner ramp limestones. These facies encompass the initial stage of a 3rd order transgressive trend above the regional Lower Valanginian Unconformity. Burial diagenesis is here marked by saddle dolomite and blocky calcite, which has the biggest influence on macropores preservation, while illitic clays within the micropores locally reduced pore-throat. These deposits are sharply overlain by Lithocodium/Bacinella-dominated floatstones, indicating the maximum flooding of the platform during the late Valanginian. These deposits are associated with a broad positive excursion in δ¹³C (c.+2‰ V-PDB), corresponding to the global Weissert Event. This unit is typically weakly cemented and the improvement of the rock-type appears related to the initial sedimentary texture (ie. grainy facies with connected macropores comprise the best rock-types, while muddy deposits with mouldic macropores connected through microporosity have smaller pore throats).

The continental palynoflora is dominated by primitive conifer pollen suggesting a rather arid climate. In addition, the occurrence of various fern and bryophyte spores suggests an increase in humidity along coastline areas, associated with higher continental input into inner ramp settings, therefore affecting the carbonate factory.

Key words: Valanginian, Carbon isotopes, Weissert Event, Diagenesis, Rock-typing, Saudi Arabia

Bio: 

Matthieu Deville de Periere is a carbonate sedimentologist specialist in diagenesis and reservoir quality assessment. He got his PhD from the University of Burgundy (France) in 2011 working on the interactions between early diagenesis related to exposure surfaces and the development of microporosity in Mid-Cretaceous carbonates of Qatar. He then joined Badley Ashton and Associates where he worked in the UK and in the UAE as a Carbonate Sedimentologist and Operation Manager, mainly working on carbonate systems from the Mesozoic of the Arabian Platform, especially in the UAE and Kuwait.

In 2018, Matthieu joined Saudi Aramco as a Carbonate Lead Geologist within the Geological Operations Department working on the stratigraphic and diagenetic characterization of Mesozoic carbonate strata across the Kingdom, including carbon isotope stratigraphy and diagenesis. His most recent papers cover the sedimentology and stratigraphy of the Triassic Jilh Formation and Early Cretaceous Buwaib Formation in Saudi Arabia. Matthieu also has ongoing research projects on the diagenesis of the Rus Formation in the Dammam Dome outcrops and on the characterization of the vertebrate fossil assemblages of the Eocene of the Kingdom.

ORCID: https://orcid.org/0009-0006-2637-8900

ResearchGate: Matthieu Deville de Periere (researchgate.net)