Geochemical analysis for palaeoenvironmental interpretations – a case study of the English Wealden (Lower Cretaceous, south-east England)

Abstract

Geo chem i cal anal y sis for palaeoenvironmental in ter pre ta tionsa case study of the Eng lish Wealden (Lower Cre ta ceous, south-east Eng land)Oladapo AKINLOTAN 1, * 1 Uni ver sity of Brigh ton, School of En vi ron ment and Tech nol ogy, Lewes Road, Brigh ton, BN2 4GJ, UK Akinlotan, O., 2017. Geo chem i cal anal y sis for palaeoenvironmental in ter pre ta tions -a case study of the Eng lish Wealden (Lower Cre ta ceous, south-east Eng land). Geo log i cal Quar terly, 61 (1): 227-238, doi: 10.7306/gq.1328The el e men tal com po si tion of terrigenous sed i ments is ex tremely im por tant for in ter pret ing the depositional con di tions of sed i men tary bas ins es pe cially when tra di tional data are not avail able or in suf fi cient. For the first time in the pub lished lit er ature, the el e men tal com po si tion of the Lower Cre ta ceous Weald Ba sin (south-east Eng land) is pre sented via X-ray flu o rescence (XRF) and Spec tral Gamma-ray (SGR) meth ods. The con cen tra tions of Zr, Cr, Ni, Rb, and Sr in vary ing quan ti ties sug gest that the sed i ments may have been sourced from a sta ble craton while the en riched re dox-sen si tive el e ments such as Mo and Co con firm the pres ence of anoxic and re duc ing con di tions at the sites of de po si tion. The spec tral gamma-ray data show that the sand stone fa cies are more ra dio ac tive than the ad ja cent mudstone and shale and this trend is con sis tent with a fresh wa ter or i gin. The higher quan tity of tho rium in re la tion to ura nium in di cates hu mid and hot palaeoclimatic con ditions at the source ar eas that fa voured in tense weath er ing. The re sults of these anal y ses re in force the im por tance of the geo chem is try of sed i men tary rocks as use ful tools for un der stand ing the depositional con di tions of sed i men tary bas ins.Key words: el e men tal com po si tion, X-ray flu o res cence, spec tral gamma-ray, palaeoenvironments, Lower Cre ta ceous, south-east Eng land. INTRODUCTIONThe use of the geo chem i cal com po si tion of sed i men tary rocks for in ter pret ing palaeo-and depositional en vi ron ments is well-doc u mented (e.g., Alvarez and Roser, 2007;Pe-Piper et al., 2008;Ghasemi-Nejad et al., 2010;González-Álvarez and Kerrich, 2010; Eker et al., 2012;Garnit et al., 2012;Pi et al., 2014;Wójcik-Tabol, 2015). The el e men tal com po si tion of terrigenous sed i ments is ex tremely im por tant for in ter pret ing the depositional con di tions of sed i men tary bas ins and may be more use ful than ex pected when tra di tional data such as field ob ser va tions and palaeontological ex am i na tions are not available or in suf fi cient. The geo chem i cal com po si tion of terrigenous sed i men tary rocks is a func tion of tec tonic set ting, prov e nance, weath er ing, trans por ta tion and diagenesis (e.g., Bhatia and Crook, 1986; Alvarez and Roser, 2007;González-Álvarez and Kerrich, 2010). Many ma jor el e ments such as Fe, K, Ca, Ti and Mn in de creas ing or der of abun dance may be af fected by diagenesis or bi o log ...

Mineralogy and palaeoenvironments: the Weald Basin (Early Cretaceous), Southeast England

“…Some sandstones display a combination of tight and loose cementation. Geochemical analysis confirmed that the iron stains observed in the thin sections are siderites (Akinlotan, , ,b). In the base of the Wadhurst Clay Formation (syntaxial) quartz overgrowth forms a secondary outline on the primary quartz grain.…”

“…I: Northiam: quartz arenite, medium-grained monocrystalline quartz, subrounded to rounded, well-sorted, high pore spaces, long, point and concavo-convex contacts are present, thin coatings of iron are very common. Additional descriptions of photographs are given in Table 1. that the iron stains observed in the thin sections are siderites (Akinlotan, 2015(Akinlotan, , 2017a. In the base of the Wadhurst Clay Formation (syntaxial) quartz overgrowth forms a secondary outline on the primary quartz grain.…”

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

“…Ph.D. thesis, Univ. Brighton, 2015; Akinlotan, 2016, 2017 b ). The Hastings Beds (upper Berriasian – Valanginian) and the Weald Clay (Hauterivian – lower Aptian) make up the non-marine Wealden successions (Fig.…”

Evolution of a sedimentary infill of a palaeovalley at a distal margin of the peripheral foreland basin

“…The gamma-ray anal y sis (GRS) is used for iden ti fi ca tion of li thol ogy, grain size, sort ing, pro cesses in the source area and In ter pre ta tion of the shal low re flec tion seis mic sur vey: high and large-am pli tude subhorizontal re flec tions in di cate thin Neo gene sed i ment lay ers (sand and interbedded clay), dis tinc tive high-fre quency sig nal rep re sents a Paleozoic rocks; seis mic im age shows the re lief of base ment across of the Odra palaeovalley its com po si tion, iden ti fi ca tion of clay min er als, con tent of organic mat ter, ba sin-wide cor re la tions, iden ti fi ca tion of the depositional en vi ron ment, etc. (Ruffell and Worden, 2000;Akinlotan, 2017) es pe cially in mo not o nous li thol ogy. The re sults are presented in Ta ble 3 and Fig ure 6B.…”