Sideritic ironstones as indicators of depositional environments in the Weald Basin (Early Cretaceous) SE England

Abstract

The Lower Cretaceous Wealden sideritic ironstones have a wide occurrence and great potential to aid the reconstruction of the depositional environments of the Weald Basin in SE England. However, mineralogical and geochemical datasets on the ironstones are scarce in the literature. Geochemical and mineralogical data on the sideritic ironstones are presented from the Wadhurst Clay Formation within the Weald Basin. The mineralogy of the ironstones was examined using a PANalytical X'Pert Pro X-ray diffractometer and PANalytical's HighScore Plus software. Elemental composition of the ironstones was measured using a PANalytical MiniPal2 ED-XRF (benchtop X-ray spectrometer). The examination of the mineralogy of the Wealden ironstones confirms the presence of early diagenetic siderites. The trace-element assemblage shows that the sideritic ironstones are chemically pure pointing to a freshwater origin. The sideritic ironstones reveal anoxic conditions and palaeo-salinity in the basin. More generally, it is suggested that the composition of the host rocks has significant controls on the composition of sideritic ironstones in sedimentary basins. This work reinforces the importance of the composition of sideritic ironstones as useful non-traditional data for understanding the depositional settings of sedimentary basins, especially when traditional datasets are not readily available or insufficient.

Authigenic berthierine and incipient chloritization in shallowly buried sandstone reservoirs: Key role of the source-to-sink context

“…Iron-rich ooids were well-developed in the upper part of the Wealden Group sandstones in the deltaic facies association in all the studied wells. These iron-ooids and ironstones are also reported in the Wealden Group sandstones of the Weald basin, 250 km north-west of the study area (Taylor, 1990;Akinlotan, 2018Akinlotan, , 2019, and in the eastern Paris Basin, 150 km east of the study area (Meyer, 1976). Some studies show that thick lateritic weathering soils developed during the Early Cretaceous after successive tectonic events and several sea level falls which resulted in the emersion and erosion of local domains in western Europe (Meyer, 1976;Thiry et al, 2006;Barbarand et al, 2018).…”

A revision of “Trinitichelys” maini (Testudinata: Baenidae) and additional material of its new genus from the Lewisville Formation (Woodbine Group, Cenomanian), Texas, USA

“…(Denne et al, 2016). Sideritic ironstones have been geochemically associated with a chemically pure freshwater origin, which suggests reducing or anoxic conditions (Akinlotan, 2019). Such association is consistent with the typical deposition of baenids in freshwater, sandstone channels (Holroyd and Hutchison, 2002).…”

“…It is noteworthy that HMNS-10-TM was not preserved in the pervasive gray marine mudstone or overlying sandy layer at the locality. The ironstone infilling of the shell was likely formed by an active combination of meteoric waters and bacterial activities involving an ancient inundation of freshwater, which suggests direct association of the specimen with a fluvial, rather than tidal, channel (Selley et al, 2005;Akinlotan, 2019).…”

A one-million-year isotope record from siderites formed in modern ferruginous sediments

“…In addition, the sideritic layers above the peat layer and underlying deltaic facies (Figs. 2 and 7) are analogous to certain clay and blackband ironstones (Gibson et al, 1994;Taylor, 2005;Akinlotan, 2017). As such, they may provide clues on depositional conditions and microbial processes (Vuillemin et al, 2016(Vuillemin et al, , 2018Friese et al, 2021) that led to their formation during the Phanerozoic.…”