The Palaeontology and Palaeoecology of the Upper Leintwardine and Lower Whitcliffe Formations, Upper Silurian, of Ludlow, England

[摘要] The boundary of the Upper Leintwardine and Lower Whitcliffe Formations in the Upper Silurian (Ludfordian) of the Welsh Borderlands is examined in an attempt to explain the (sudden and gradual) faunal changes which occur. Faunal variations are both lateral and vertical. A transect across the depositional area from basin to shelf is examined in order to describe and explain lateral variations. Faunal abundances are examined using collections and information from published literature. Other aspects are considered e.g. biochemistry and geochemistry. Time and finance were found to be major limiting factors in this case, but there is some potential for future work in these disciplines. Faunal variations occur at this level independently of lithological or obvious environmental changes. Comparison with rocks of similar age in Gotland reveals an absence of such variations, and a greater abundance and diversity of fauna. This is largely due to palaeogeographic differences. The presence of phosphate deposits throughout the Welsh Borderlands succession is indicative of unstable and discontinuous deposition, possibly linked to sea level changes. The depositional environment at the Leintwardine-Whitcliffe boundary is considered to be one of soft medium-fine grained sediment covered by a layer of living, dead, and fragmented shells. This cover was probably patchy, with areas of free soft sediment providing ecospace for infauna. The disturbance of shell cover and living organisms was caused by larger organisms walking, feeding and burrowing. Storms and currents provided only minor disturbance. Algae occurred as floating masses and as rooted forests, possibly utilising large bivalve or brachiopod shells as substrate, and probably supporting small epiplanktonic brachiopods and bivalves. Distribution of species tends to be dominated by one or two main species (Shaleria ornatella. Protochonetes ludloviensis etc). Most shells were quickly colonised by bryozoa unless buried quickly. Some organisms supported epifauna during life. The disappearance of the dominant brachiopod Shaleria ornatella at the top of the Upper Leintwardine Formation is thought to be due to disease, selective predation, or changing current systems.

[发布机构] University:University of Glasgow

[关键词] Paleoecology, Paleontology, Geology