Multi‐proxy approach to palaeoenvironmental modelling: the English Lower Cretaceous Weald Basin

Abstract

Palaeoenvironmental reconstructions of the Wealden (Lower Cretaceous) in southeast England have been previously based mainly on field and fossil data. This study presents new interpretations of multi-proxy data sets such as sandstone petrography, elemental geochemistry and sideritic ironstones, supplemented by outcrop and clay mineralogical data. The dominance of quartz arenites, kaolinite and thorium and the presence of Zr in the sediments suggest that they were sourced mainly from granitic and/or gneissic rocks. Materials from metamorphic sources are secondary in abundance. The mineral and textural maturity of the sediments coupled with inferred short transport distances suggests reworking from older sources. Palaeoclimatic conditions in the source areas were generally warm and humid in nature, which supported an intensive weathering regime. The nature of the sediments suggests they may have been sourced directly or indirectly from a stable craton. The lithology, facies, sedimentary structures, architecture and gamma ray data confirm the freshwater origin of the sediments. Redox-sensitive trace elements such as Mo, U, V and Co suggest anoxic conditions in the basin. The results presented in this paper reinforce the importance of integrating multi-proxy data sets for interpreting the palaeoenvironmental conditions of sedimentary basins: when traditional data sets such as field and fossil data are not readily available or insufficient to enable adequate interpretations, the integration of petrographic, mineralogical and geochemical data sets may prove to be useful in similar palaeoenvironmental studies.

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.…”

“…In any case, the role of climate on clay mineral composition is well‐documented in the Weald and beyond (Singer, , ; Sladen, ; Sladen & Batten, ; Moore & Reynolds, ; Hallam et al ., ; Oboh, ). For instance, spectral gamma‐ray data on the Wealden deposits in the Weald (Akinlotan, , 2017b) correlate well with palaeoclimate interpretations made from the data presented in this study. Thorium is normally enriched when kaolinite is formed from the alteration of feldspars (Ruffell & Worden, ; Schnyder et al ., ) and its significant quantity in the Wealden rocks point to the dominantly warm with periodically wet conditions that favoured the intensive weathering that is required for the formation of kaolinite.…”

“…2) allows non-marine and fluvial-related sedimentation patterns to be studied in a variety of conditions and this can be applied to similar sedimentary basins elsewhere (Allen & Wimbledon, 1991). These facies also make it possible to study changes that accompanied the transition to the Early Cretaceous in northwest Europe (Ruffell, 1991;Akinlotan, 2017b), China (Li et al, 2016), South America (Richiano, 2014) and other non-marine Lower Cretaceous facies. The Wealden sections may also be useful for analogue studies of basin tectonics (Ziegler, 1981;Mansy et al, 2003) and hydrocarbon reservoirs (Akinlotan, 2016).…”

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

“…Ph.D. thesis, Univ. Brighton, 2015; Akinlotan, 2017 c ). The Ashdown, Wadhurst Clay and Tunbridge Wells Sand formations informally referred to as the Hastings Beds (Berriasian–Valanginian) make up the lower section of the Weald Basin.…”

“…Ph.D. thesis, Univ. Brighton, 2015; Akinlotan, 2017 c ). The rocks within this formation were deposited in predominantly fluvial and non-marine environments under both braided and meandering river systems.…”