Environmental control on granular clinoforms of ancient carbonate shelves

• Published in: Geological magazine 2006-05, Vol.143 (3), p.343-365
• Main Authors: QUIQUEREZ, A., DROMART, G.
• Format: Article
• Language: English
• Subjects: absolute age; Accretion; Africa; Alps; Arabian Peninsula; Asia; basin analysis; basins; Biota; Burgundy Platform; carbonate platforms; carbonate rocks; Carbonate sediments; case studies; Cenozoic; Cirque d'Archiane; clinoform; Continental interfaces, environment; continental margin sedimentation; Cretaceous; Damara Belt; dates; Dauphine Alps; depositional environment; depositional facies; Environmental control; Europe; France; Geological time; Geometry; Gravel; Hoogland Member; Jurassic; Kuisbis Subgroup; lithofacies; Lower Cretaceous; marine environment; Mesozoic; Middle East; Middle Jurassic; Miocene; Nama Group; Namibia; Naukluf Nappe; Neogene; Neoproterozoic; nesosilicates; nomenclature; Oman; Original Article; orthosilicates; paleoenvironment; Precambrian; progradation; Proterozoic; Sciences of the Universe; sed rocks, sediments; Sediment transport; sedimentary basins; Sedimentary petrology; sedimentary rocks; Sedimentary structures; sedimentation; Sedimentation & deposition; Shallow water; shelf environment; silicates; slope environment; Southern Africa; Stratigraphy; Tertiary; Transport processes; Turkey; U/Pb; upper Precambrian; Vercors; Water depth; Western Alps; Western Europe; Zaris Formation; Zebra River; zircon; zircon group
• ISSN: 0016-7568; 1469-5081
• DOI: 10.1017/S0016756806001749

The purpose of this paper is to document the influence of depositional environments on shallow-water, low-relief clinoforms from the description of five ancient carbonate platforms: the Neoproterozoic (Namibia), Middle Jurassic (France), Lower Cretaceous (France), Upper Cretaceous (Oman) and Miocene (Turkey). These examples have been investigated on the basis of field observations. The clinoforms are described with reference to geometric and compositional attributes: declivity, shape, height, sedimentary structures, sediment fabric and components. The results show great variability in stratal geometry, declivity and facies distribution: (1) depositional profiles vary from exponential, to sigmoidal, to oblique; (2) maximal slope angles range from 3 to 25°, most of them being grouped between 10 and 18°; (3) facies differentiation identified from lateral facies successions along beds, and vertical facies successions through beds, is pronounced to subtle. This study documents linkages between depositional environments and clinoform attributes. Proximal/shallow clinoforms display round-edged exponential profiles. Sediment deposition has resulted from unidirectional currents in the upper convex section, and storm-generated oscillatory currents in the lower concave part. The sediment fabric changes gradually along this type of clinoform. There is little vertical facies differentiation through these clinobeds which have formed from a continuous amalgamation of deposits. By contrast, distal clinoforms (shelf break, distally steepened ramp settings) yield a much broader spectrum of profiles and are generally shorter and steeper. Sedimentary structures in gravel-sized deposits of the upper slope indicate pure traction by unidirectional currents. Conversely, marks of oscillatory flows (undular, wavy top bounding surfaces of clinobeds) are common in the lower slope. Intercalation of massive, fine-grained deposits suggests offshore transport of carbonate mud by suspension. Each distal clinobed represents a single flow event. Accordingly, facies differentiation is weak laterally but may be pronounced through the clinobeds. Our study suggests that low-relief forms of proximal/shallow environments, which contain coarse-grained and photo-independently produced debris, record hydrodynamic equilibrium profiles, whereas the higher-relief forms of this setting rather reflect a high differential production rate of carbonate sediment with water depth. The carbonate sediment of th