The palynology of the Kimmeridge Clay and Carstone formations (Upper Jurassic – Lower Cretaceous) at Middlegate Quarry, North Lincolnshire, UK, and its biostratigraphical and palaeoenvironmental significance

Abstract

At Middlegate Quarry, the Carstone Formation is an approximately 0.8 m thick unit of oolitic ferruginous sandstone. It rests unconformably on the lower Kimmeridge Clay Formation (KCF) and is overlain by the Hunstanton Formation (Red Chalk) with an apparently gradational junction. Marine dinoflagellate cysts (dinocysts) are present at a concentration of 9,520 to 13,600 specimens per gramme in the 0.15 m of KCF below the unconformity, and include taxa that confirm ammonite evidence for the intra-Lower Kimmeridgian Substage (Upper Jurassic, Cymodoce Ammonite Zone). A rich recovery of well-preserved Lower Cretaceous palynomorphs is reported for the first time from the overlying Carstone. Reworking of mudstone from the KCF into the formation appears to have provided a local argillaceous preservation matrix at Middlegate. The basal 0.15 m is dominated by palynomorphs derived from the KCF but the interval from 0.15 m to 0.55 m above the unconformity mainly contains indigenous Lower Cretaceous palynomorphs. Dinoflagellate cysts are present in the Carstone at an average concentration of 454 specimens per gramme, and include taxa that probably have stratigraphical range bases above the Aptian – Albian stage boundary; Cyclonephelium compactum, Cyclonephelium intonsum, Endoscrinium heikeae, Leptodinium cancellatum (consistent), Stephodinium coronatum and Stephodinium spinulosum. The additional presence of taxa with range tops / event tops in the Lower Albian Tardefurcata Ammonite Zone (common Cauca parva, frequent Canninginopsis monile and Kleithriasphaeridium eoinodes, and rare Dingodinium albertii, Discorsia nannus and Kiokansium prolatum) indicate probable assignment to this zone. The new palynological data support previous macrofossil (brachiopod) study of the Carstone at Middlegate and nearby Melton Bottom Quarry which tentatively assigns its highest part to the Tardefurcata Zone. The palynological and palynofacies assemblages are interpreted to confirm a relatively proximal to shoreline site of deposition, possibly inner to middle neritic.Supplementary material: One pdf file, with quarry photographs and a palynological distribution chart, is available at https://doi.org/10.6084/m9.figshare.c.5538977