SEDIMENTATION OF THE AALENIAN ROCKS OF YORKSHIRE

Introduction. The dominantly deltaic character of the Middle Jurassic Rocks of Yorkshire was recognised soon after the idea of a universal deluge had been abandoned, and their true nature had been fully appreciated for many years before the unfortunate name “Estuarine Series” came into general use. Martin Simpson, for example, pointed out that “in contemplating these deposits, we are strongly reminded of the phenomena presented by the delta of some large river,” and supported his view by reference to stratigraphical details in the coast section.1 The deltaic rather than estuarine character of these beds has been emphasised in more recent years by Prof. Kendall and other authors. It is readily apparent, however, that we are dealing with a highly specialised type of delta environment, in which foreset beds are insignificantly represented, and topset beds (as in the Coal Measures) are overwhelmingly predominant. Even in the basal part of the series there is no indication that a foreset slope existed in the Yorkshire area, and there is almost indisputable evidence that the underlying marine beds are followed directly by plant-bearing topset beds. The Structure of a Modern Delta and its Response to Environment. The investigations of Joseph Barrell2 have shown that the process of delta building is extremely sensitive to small changes in environment. Alterations in the nature of sediment available, in the movements of the water into which it is dropped, or movements either of the sea floor or of the neighbouring land, are all capable of altering profoundly the ...