Carbonate Minerals in the Warrawoona Group, Pilbara Craton: Implications for Continental Crust, Life, and Global Carbon Cycle in the Early Archean

Abstract

Abstract:The occurrences of the Early Archean carbonate minerals are compiled and their precipitation processes are investigated for the Warrawoona Group, Pilbara Craton. Sedimentary carbonate rocks such as limestone and dolostone are very rare, and only a small amount of sedimentary carbonate minerals are sometimes contained in the hydrothermal bedded chert, implying that a sink of CO 2 was minor in the Early Archean sediments. Moreover, it is very likely that the activity of cyanobacteria forming stromatolites was considerably low in the Early Archean. Microfossils and carbonaceous matter in the hydrothermal cherts are probably derived from a non-photosynthetic microorganisms related to the seafloor hydrothermal activity. Their preservation in sediments may play a very minor role in carbon sink of the Earth's surface.On the other hand, carbonatized volcanic rocks subjected to seafloor hydrothermal alteration occur ubiquitously in the Early Archean greenstone belts such as the Warrawoona Group, suggesting that the hydrothermally altered oceanic crust had large amounts of CO 2 as carbonate minerals. Global carbon cycle in the Early Archean is considered to have been controlled by the intense seafloor hydrothermal alteration. Large amounts of CO 2 were sunk into the oceanic crust by the alteration. The carbonatized oceanic crust was partly accreted to the continents and/or island-arcs, and partly subducted into the mantle without decomposition. Significant amounts of carbonate minerals in the carbonatized oceanic crust were very likely to store in the accretionary prisms and mantle, consequently giving rise to a decrease of atmospheric and oceanic CO 2 .Keywords: hydrothermal, carbonatization, carbonate, carbon dioxide, oceanic crust, stromatolite, global carbon cycle, Early Archean, Warrawoona Group carbonate displaying a stromatolite texture deposited in the ocean (Fig. 2b;Walter and Heys, 1985;Awramik, 1992;Semikhatov and Raaben, 1996). This geological evidence suggests that biological activity of cyanobacteria was mostly responsible for carbonate precipitation in the Proterozoic (Grotzinger and Knoll, 1999;Riding, 2000). In contrast, sedimentary carbonates were much less in the Archean than the Proterozoic and Phanerozoic (Fig. 2a;Ronov, 1964;Veizer et al., 1989a). Although more than 20 of stromatolite occurrences are now known worldwide in the Archean (Martin et al., 1980;Walter, 1983;Beukes and Lowe, 1989), the true fossil record such as a stromatolite texture and microfossils is sparse in the Archean compared to the Proterozoic (Hofmann, 1999). In particular, the occurrences of the stromatolites older than 3.2 Ga are rare ( Fig. 2b; Hofmann, 1999), and the biogenesis of the stromatolite-like textures has been questioned (Walter et al., 1980;Lowe, 1980bLowe, , 1994Lowe, , 1995Buick et al., 1995). It is assured that the carbonate sediment was significantly minor in the Archean. However, several researchers have believed that the carbonate precipitation is essentially the same throughout the Earth's history ...

New insights into the burial history of organic carbon on the early Earth

“…Archean submarine basalts are extensively carbonatized indicating probable significant seafloor weathering [ Walker , 1990; Nakamura and Kato , 2002]. Furthermore, recent carbon cycle models indicate significant early Archean OCC, with λ values ranging between 0.35 and 0.95, and decreasing to ∼0.25 by the end of the Proterozoic [ Sleep and Zahnle , 2001].…”

“…Thus, on the very early Earth, before significant continental crust formed, nearly all buffering of volcanic CO 2 degassing must have been through ocean crust carbonatization (OCC) [ Walker , 1990]. Even after significant amounts of continental crust had formed, the presence of ubiquitous hydrothermal carbonates in Archean greenstone belts suggests that ocean crust carbonatization was still an important CO 2 sink [ Veizer et al , 1989b; Nakamura and Kato , 2002]. Model studies of the early carbon cycle furthermore indicate that through the Archean OCC probably accounted for between 30% and 90% of the inorganic carbon removal [ Sleep and Zahnle , 2001].…”

“…The observations, then, point to two isotopically distinct burial sinks for inorganic carbon in the Archean, surface‐derived carbonates with a δ 13 C of around 0‰ and deep water‐derived carbonates with relatively 13 C‐depleted values compared to the surface ocean. In what follows we will focus our discussion on OCC as it probably represented the most important deep‐water sink for inorganic carbon [ Walker , 1990; Sleep and Zahnle , 2001; Nakamura and Kato , 2002]. We recognize that early diagenetic carbonate formation in deep water sediments, fuelled by the decomposition of organic matter, could also remove isotopically depleted DIC, and that this process would also contribute to isotope balance in the same manner as we will explore below.…”

Reply on RC1

“…10). Indeed, fracture-filling calcite shows the lowest 87 Sr/ 86 Sr ratio (0.700596) and REE+Y pattern that is considered typical of Archean seawater (Xiang, 2023), indicating the percolation of seawater-derived CO2-rich fluids through basaltic crust 3.5 Ga ago (Kitajima et al 2001;Nakamura and Kato, 2002;Yamamoto et al, 2004).…”

Were early Archean carbonate factories major carbon sinks on the juvenile Earth?

“…10). Indeed, fracture-filling calcite shows the lowest 87 Sr/ 86 Sr ratio (0.700596) and REE+Y pattern that is considered typical of Archean seawater (Xiang, 2023), indicating the percolation of seawater-derived CO2-rich fluids through basaltic crust 3.5 Ga ago (Kitajima et al 2001;Nakamura and Kato, 2002;Yamamoto et al, 2004).…”