The oldest mid-oceanic carbonate buildup complex: Setting and lithofacies of the Vendian (Late Neoproterozoic) Baratal limestone in the Gorny Altai Mountains, Siberia

Abstract

Abstract:The Baratal limestone in the Gorny Altai Mountains, southern Siberia, occurs as large allochthonous blocks within a Cambrian accretionary complex that developed around the Siberia craton. Before the final accretion to Siberia in the Cambrian, the terrigenous clastic-free Baratal limestone was deposited directly upon a basaltic basement with a geochemical signature identical to that of modern oceanic plateau. The Baratal limestone with 598 25 Ma (Early Vendian) Pb-Pb isochron age consists of three distinct facies; 1) massive lime mudstone with ooids and stromatolites, 2) bedded lime mudstone, and 3) limestone conglomerate/breccia dominated by ooid-bearing lime mudstone clasts. The first represents a shallow marine environment on top of an ancient oceanic plateau, while the latter two represent the deeper slope to bottom-of-slope facies of a plateau. The Vendian Baratal limestone provides the oldest example of a reconstructed shallow marine carbonate buildup complex developed on a plateau/seamount in a mid-ocean.

Geochronology of the Metamorphic Rocks in the Kurai Accretionary Prism (South-Eastern Gorny Altai)

“…В отдельных тектонических пластинах реконструи-руются верхняя карбонатная и нижняя вулкано-генная части, а также множество разнообразных по строению и составу обломочно-оползневых пород склоновых фаций и кремнистых пород подножий Баратальского палеосимаунта. Pb-Pb возраст из-вестняков «шапки» Баратальского палеосимаунта составляет 570-598 млн лет [Nohda et al, 2003;Uchio et al, 2004;Ota et al, 2007]. В левобережье р. Каратюргунь поблизости с Чуйским трактом Рис.…”

Memories of Pre-Jurassic Lost Oceans: How To Retrieve Them From Extant Lands

“…635-630 Ma) or much older late Cryogenian strata. By analogy to the Permian examples of paleo-atoll complexes accreted to SW Japan, the Baratal limestone and the underlying pillow basaltic greenstone are regarded as an ancient mid-oceanic seamount complex capped by atoll-type carbonates (OPS shallow ) that were accreted in the Cambrian (Uchio et al 2004;Ota et al 2007). To date, this likely represents the oldest example of a massive paleo-atoll complex on a paleoseamount in Earth's history, as will be mentioned later.…”

“…To date, this likely represents the oldest example of a massive paleo-atoll complex on a paleoseamount in Earth's history, as will be mentioned later. (2) and ooids (3) from the basal parts (Uchio et al 2004). Unidentified microfossils with phosphatic test (4,5) occur in this limestone (Uchio et al 2008).…”

“…As to the pre-Jurassic Phanerozoic, both OPS deep (bedded chert) and OPS shallow (atoll limestone) were identified in the Paleozoic-Mesozoic AC units in Japan, covering at least intervals of the Triassic, Permian, and Carboniferous Matsuda and Isozaki 1991;Isozaki 1996Isozaki , 2009a. Although the Lower Paleozoic records are still sporadically documented, mid-oceanic deep-sea chert and atoll limestone range down no doubt into the Ediacaran (Uchio et al 2004;Ota et al 2007;Kawai et al 2008 Kitajima et al 2008). Note that the greenstone units comprise more than 5 units, and that each unit has a duplex structure, as represented by the multiple bifurcations of chert, and that the zircon U-Pb ages become systematically younger towards the structural bottom.…”

“…11) Figure 11. Age distribution of pre-Jurassic mid-oceanic sedimentary archives hitherto analyzed (compiled from Isozaki et al 1990;Matsuda and Isozaki, 1991;Isozaki, 1996;Komiya et al 1999;Kitajima et al 2001;Uchio et al 2004;Ota et al 2007;Kawai et al 2008). The overall secular change in ocean redox can be monitored by direct assessment of mid-oceanic bedded cherts (OPS deep ) and atoll carbonates (OPS shallow ).…”