Ecological succession, palaeoenvironmental change, and depositional sequences of Barremian–Aptian shallow‐water carbonates in northern Oman

Abstract

Barremian and Aptian shallow-water carbonate facies (uppermost Lekhwair, Kharaib and Shuaiba Formations) are described from outcrops in northern Oman. Based on facies analysis and bedding pattern, three orders of depositional sequences are defined (third to fifth order) and correlated between sections. Over the course of three third-order sequences, covering the Barremian to Lower Aptian, a third-order depositional pattern is documented that consists of a succession of three distinct faunal assemblages: discoidal orbitolinids and calcareous algae were deposited during early transgression; microbialites and microencrusters dominate the late transgressive to early highstand facies; and a rudist-and milioliddominated facies is typical of the highstand. This ecological succession was controlled largely by palaeoenvironmental changes, such as trophic level and clay influx, rather than sedimentological factors controlled by variations in accommodation space. Orbitolinid beds and carbonates formed by microbialites and microencrusters seem to be the shallow-water carbonate response to global changes affecting Late Barremian to Aptian palaeoclimate and palaeoceanography.

Sequence stratigraphy and platform to basin margin facies transition of the Lower Cretaceous Dariyan Formation (northeastern Arabian Plate, Zagros fold-thrust belt, Iran)

“…The presence of discoidal orbitolinids is in agreement with interpretation (Pittet et al 2002, Bachmann & Hirsch 2006. The degree of shell fragmentation and the upward-fining trends in beddings suggests resedimentation of the different components (Rubert et al 2012).…”

“…Based on the variations in textures and grain types, the facies evolution, and the sedimentary structures, the Dariyan Formation in the study area is interpreted as characterizing shallow homoclinal carbonate ramp to intra-shelf basin depositional settings (Read 1985;Burchette & Wright 1992;Pomar 2001;Piryaei et al 2010Piryaei et al , 2011van Buchem et al 2010;Lu et al 2013; Fig. 15).…”

“…During the Lower Cretaceous (Aptian), the benthic foraminifer assemblages in carbonate environments of Tethyan realm were dominated by orbitolinids (Simmons et al 2000, Pittet et al 2002 (Fig. 12).…”

Demise of the northern Tethyan Urgonian carbonate platform and subsequent transition towards pelagic conditions: The sedimentary record of the Col de la Plaine Morte area, central Switzerland

“…In Oman, platform sediments equivalent to OAE 1a are characterized by the presence of a Lithocodium/Bacinella association, which is interpreted to have resulted from increased trophic levels (Pittet et al, 2002;Hillgärtner et al, 2003;Immenhauser et al, 2005). In N Mexico, the disappearance of the rudist-bearing shallow-water carbonates of the Cupido Formation is dated as Early Aptian (Bralower et al, 1999;Lehmann et al, 1999).…”

An Upper Jurassic-Lower Cretaceous carbonate platform from the Vâlcan Mountains (Southern Carpathians, Romania): paleoenvironmental interpretation

“…Regardless of their taxonomic position, most authors regard the two microproblematic organisms as being characteristic of very shallow, well-oxygenated and relatively oligotrophic environments (Leinfelder et al 1993;Dupraz & Strasser 1999Pittet et al 2002;Reolid et al 2009). The large oncoids with lobate outlines, dominated by microencrusters (Bacinella and Lithocodium), correspond to oncoids of types 3 and 4 described by Védrine et al (2007) or to the organism-bearing oncoids of Dahanayake (1977).…”