First discovery and characterizations of late Cretaceous seep carbonates from Xigaze in Tibet, China

Abstract

Hydrocarbon seeps, widely occurring in continental margins, have become increasingly focused owing to their close relationships with gas hydrates, strong greenhouse gas methane, and biological resources in extreme environments. Ancient hydrocarbon seeps have already been recognized from Devonian to Quaternary strata worldwide based on seep carbonates or seep-related fossil chemosynthetic assemblages. However, seep-related deposits are rarely found from ancient strata in the mainland China. Here, we report the first discovery of an ancient seep deposit, specifically late Cretaceous seep carbonates from Xigaze in Tibet, China. Xigaze seep carbonates, occurring as nodules, are enclosed in upper Cretaceous turbidite strata in Xigaze forearc basin. These carbonates are composed of authigenic carbonate (56.2% on average), clastic quartz and feldspar (27.3% on average), and clay minerals (chlorite, illite and smectite, 16.5% on average). Clotted micrites, peloids and framboid pyrites are frequently observed, all of which are common in modern seep carbonates. The carbonates have negative  13 C values varying from 27.7‰ to 4.0‰ (V-PDB), suggesting that thermogenic methane is the primary carbon source. Ce/Ce* values revised by eliminating La effects show no real Ce anomaly, indicating the carbonates were primarily precipitated in a weak reducing environment. Overall, these features provide unequivocal evidences that the seafloor of Xigaze forearc basin developed hydrocarbon seeps in late Cretaceous. seep carbonate, carbon isotope, sedimentary fabric, Xigaze, late Cretaceous Citation:Tong H P, Chen D F. First discovery and characterizations of late Cretaceous seep carbonates

Multiple proxies indicating methane seepage as the origin of Devonian large barite deposit in Zhenning-Ziyun, Guizhou, SW China

“…Canet et al (2014) reported the occurrence of methane-derived carbonates in Sonora, northwestern Mexico. Similar instances were found in Neoproterozoic postglacial cap carbonates (Jiang et al, 2003) and in the Late Cretaceous seep carbonates of Xigaze (Tong and Chen, 2012). Previous studies in combination with our data indicate a spatial association between the oxygen isotopic composition characteristics of limestones and late processes related to burial diagenesis.…”

“…4I). The clotted micrite and framboidal pyrite are abundant in the limestone; these features are often reported in seep carbonates (Canet et al, 2013;Chen et al, 2006;Peckmann et al, 1999Peckmann et al, , 2005Tong and Chen, 2012).…”

“…3K and 3L). According to the detailed field observations and sedimentary structures, it can be seen that the bedding of surrounding rocks (chert and siliceous mudstone) are around the limestone nodules, indicating syndepositional characteristics similar to Late Cretaceous seep carbonates in Tibet, China (Tong and Chen, 2012), and 13 C-depleted carbonates hosted by bedded barite in Sonora, Northwest M A N U S C R I P T…”

Microbial utilization of rare earth elements at cold seeps related to aerobic methane oxidation

“…Based on the above, we suggest that the In future studies, we anticipate that these findings and their application to fossil microbial carbonates could provide new insights into the biogeochemical processes operating in ancient oceans. This could include the re-evaluation of previous REE datasets for ancient seep carbonates (e.g., Feng et al, 2009b;Tong and Chen, 2012;Tribovillard et al, 2013;Della Porta et al, 2015;Colin et al, 2015;Smrzka et al, 2016;Zwicker et al, 2018;Argentino et al, 2019;Zhu et al, 2019), but also for various microbial archives of Precambrian oceans, at times when methane levels were presumably much higher both in the atmosphere and oceans (e.g., Catling et al, 2001;Konhauser et al, 2009). For instance, many Late Archaean J o u r n a l P r e -p r o o f Journal Pre-proof stromatolites also display marked enrichments in La and other LREE (e.g., Kamber and Webb, 2001;Planavsky et al, 2010;Kamber et al, 2014;Schier et al, 2018).…”

Characteristics and geological significance of tubular carbonate concretions in the Lower Shaximiao Formation of Yunyang, Chongqing, China

“…Concretions can be divided into syngenetic, diagenetic, and epigenetic concretions (Pantin, 1958) according to the different formation stages, among which research data on concretions formed diagenetically are the most abundant due to their wide distribution. Methane leakage is considered one of the main formation mechanisms of early diagenetic calcareous concretions (Clari et al, 2004;Tong and Chen, 2012;Ou et al, 2013;Liang et al, 2016). Tubular concretions are the most common prod-uct of seafloor methane leakage and are often used as migration channels for underground fluids and liquefied sediments (Nyman et al, 2010).…”