A Neoproterozoic glacially influenced basin margin succession and ‘atypical’ cap carbonate associated with bedrock palaeovalleys, Mirbat area, southern Oman

Abstract

The Ayn Formation of the Neoproterozoic Mirbat Group comprises <400 m of little‐deformed, glacially influenced basin margin deposits. These deposits are preserved in several palaeovalleys eroded in crystalline basement and overlain by a discontinuous cap carbonate. The Ayn Formation and the cap carbonate, which are superbly exposed along a 20 km SW–NE‐striking escarpment in south Oman, provide important insights into the processes operating on a basin margin during a Neoproterozoic glaciation and its demise. The Ayn Formation comprises units of glacimarine rain‐out diamictite and sediment gravity flow deposits, alternated with units of fluvial and deltaic sandstones and conglomerates, which may have formed by proglacial outwash. The stratigraphic evolution of the Ayn Formation indicates a highly active hydrological cycle during a phase of overall (glacio‐eustatic?) low stand when glaciers advanced into and receded upon bedrock valleys. The transgressive cap carbonate was deposited primarily in shallow marine or shallow lacustrine environments over palaeohighs during the deglaciation, and was partly reworked into deeper parts of the basin through sediment gravity flow processes. Locally, the cap carbonate transgresses over crystalline basement containing a network of fissures filled with carbonate originating from the cap. The δ13C isotopic composition of the cap carbonate varies systematically between −3.5 and +5.8‰ Pee Dee Belemnite standard, in common with other older Cryogenian examples.

Chapter 7 Neoproterozoic glacial palaeolatitudes: a global update

“…GLOBAL NEOPROTEROZOIC GLACIAL PALAEOLATITUDES Despite a new, precise U-Pb TIMS age of 711.5+ 1.1 Ma for the Ghubrah diamictite in the Jebel Akhdar region of northeastern Oman ; all sources of error included), its palaeolatitude remains poorly constrained. However, unmetamorphosed deposits of the possibly Ghubrah-correlative, lower Mirbat sandstone/diamictite assemblage, now renamed as the Ayn Formation (Rieu et al 2006(Rieu et al , 2007, yield a low-reliability palaeomagnetic direction (Kempf et al 2000). This under-defined magnetization (n ¼ 10 samples from two sites) would imply a palaeolatitude of 09 + 48 for the Ayn Formation, but we cannot include it in our final compilation due to the severely limited sample size.…”

Tunnel valleys: current knowledge and future perspectives

“…These features are present in outcrop at several sites in Africa, the Middle East, South America and Australia (e.g. Beuf et al 1971;Visser 1988;Vaslet 1990;Eyles & de Broekert 2001;Le Heron et al 2004;Eschard et al 2005;Rieu et al 2006;Gutiérrez-Marco et al 2010;Hoffman & Macdonald 2010;Keller et al 2011;Fig. 2) and have been identified in the deep subsurface during hydrocarbon investigations (McGillivray & Husseini 1992;Smart 2000;Hirst et al 2002;McDougall et al 2006;Melvin & Sprague 2006).…”

The age of the Nantuo Formation and Nantuo glaciation in South China

“…Recent age dates and sedimentological studies suggested that the Sturtian glaciation may have lasted long from c. 750 to c. 663 Ma and its initiation and termination are globally diachronous, with potentially multiple episodes or a series of short-lived glaciations (e.g. Lund et al, 2003;Eyles and Januszczak, 2004;Fanning and Link, 2004;Zhou et al, 2004;Kendall et al, 2006;Rieu et al, 2006;Zheng et al, 2007). In contrast, the Gaskiers glaciation may have been regional and lasted less than 1 million years (Myr) around 582 Ma (Bowring et al, 2003;Halverson et al, 2005;Halverson, 2006).…”