PETROGRAPHY AND DIAGENESIS OF THE THAMES GROUP AT WHITECLIFF BAY, ISLE-OF-WIGHT, UK

Previous studies of the Thames Group have emphasized stratigraphical o r mineralogical aspects of the formation. We have used a combination o f field observation. hand specimen description, optical and back-scatt ered electron petrography and X-ray diffraction to identify textures ( grain size, bioturbation etc.), detrital, synsedimentary and diageneti c components. With these data lithologs have been constructed to descr ibe the diverse lithologies which constitute the London Clay, Early di agenetic mineral assemblages are closely linked to depositional rate, Hiatus surfaces are associated with concentrations of glauconitic clay pellets. Bedded siderite concretionary carbonates were precipitated b y diagenetic processes, below, relatively brief hiatus surfaces, whils t ovoid ferroan calcite concretions were deposited during periods of v ery slow deposition. The glauconitic sandy fissures in the mudrock int ervals of Divisions A and B are interpreted as storm deposits. The reg ular 1-1.5 m spacing of these sands is evidence of rhythmic sedimentat ion.