The formation of authigenic deposits during Paleogene warm climatic intervals: a review

Abstract

Although Paleogene warm climatic intervals have received considerable attention for atmospheric and oceanographic changes, the authigenic mineralization associated with these time spans remains overlooked. An extensive review of the literature reveals a close correspondence between the high abundance of glauconite and warm climatic intervals during the Paleogene period. The abundance of phosphorite, ironstone, lignite and black shale deposits reveals similar trends. Although investigated thoroughly, the origin of these authigenic deposits is never understood in the background of Paleogene warming climatic intervals. A combination of factors like warm seawater, hypoxic shelf, low rate of sedimentation, and enhanced rate of continental weathering facilitated the glauconitization. The last factor caused the excess supply of nutrients, including Fe, Si, K, Mg and Al through the rivers, the cations needed for the formation of glauconite. The excessive inflow of nutrient-rich freshwater into the shallow seas further ensured high organic productivity and stratification in shallow shelves, causing hypoxia. The consequent rapid rise in sea-level during the warm periods created extensive low-relief shallow marine shelves starved in sediments. Oxygen-deficiency in the shallow marine environment facilitated the fixation of Fe into the glauconite structure. The inflow of nutrient-rich water during the warm climatic intervals facilitated the formation of phosphorite, ironstone, and organic-matter-rich sedimentary deposits as well. Although global factors primarily controlled the formation of these authigenic deposits, local factors played significant roles in some of the deposits. Therefore, phosphorites formed in marine conditions with open circulation within the tropical zone. While lush growth of rainforest covers in the tropical belt facilitated the formation of coastal lignite.

Impact of green clay authigenesis on K–Mg–Fe sequestration in marine settings

“…Calcite mud precipitation within the glauconite-bearing interval occurred at a temperature of around 26 ± 2°C, which is typical of a 'warm' shelf environment (Banerjee et al, 2020;Gao et al, 2021). Thus, the palaeo-depositional setting at Langenstein is representative of many modern and palaeo-shelf environments.…”

“…K-Ar glauconite dating indicate glauconite formation was completed within < 1 Myr close to the sediment-seawater interface (Baldermann et al, 2017). This study site is representative of many modern and palaeo-shelf settings that accumulate glauconite minerals (Odin and Matter, 1981;Baldermann et al, 2013;Banerjee et al, 2016;Bansal et al, 2017;Banerjee et al, 2020;Bansal et al, 2020a,b;Choudhury et al, 2020). Here, we highlight the signi cance of green clay authigenesis on K-Mg-Fe sequestration in marine sediments that strongly impacted the marine K, Mg and Fe cycle throughout Earth`s history.…”

“…Authigenic clay precipitation is ine cient under such conditions (Amorosi, 2012;Chattoraj et al, 2016) so that element sequestration is reduced. The 'high rate' of element sequestration may represent transgressive systems that are characterized by low to close to zero overall sedimentation and a prolonged residence time at the sediment-seawater interface, which favor glauconite formation (Amorosi, 2012;Banerjee et al, 2020).…”

“…Figure 4df). These periods record glauconite deposits of huge economic or geological value (Banerjee et al, 2016;Banerjee et al, 2020).…”

Ediacaran/Early Cambrian Serra da Saudade Formation, Bambuí Group: the sedimentary record of a foreland basin in Southeastern Brazil

“…Glauconite and sedimentary phosphorite associations are common around the world, indicating specific conditions in a marine sedimentary environment. In the Ediacaran Doushantuo Formation (Weng'an, South China), the apatite-glauconite association may be related with intervals of warm climates, hypoxic shelf, low rate of sedimentation, as well as an enhanced rate of continental weathering, responsible for excessive supply of nutrients and high organic productivity, and it is considered a useful mineralogical proxy for paleoredox conditions on the Precambrian ocean floor (Algabri et al 2020, Banerjee et al 2020. The Upper Ediacaran to lower Cambrian foreland basin deposits formed in the Zavkhan Terrane (Southwestern Mongolia) identified glauconite in the form of nodules and cement associated with the Archaeocyatha within phosphatized lenses (Pruss et al 2019).…”