By Allan Pentecost
Uring the spring of 1960, an uncle confirmed me a ‘petrifying spring’ close to Plaxtol in Kent Dwhere twigs have been encased in a calcareous jacket. a sprig used to be accumulated and having - cently been given I. Evan’s Observer’s ebook of Geology by way of my mom and dad, i discovered a photo of one other petrifying spring and a proof of its starting place. In these days, Derbyshire was once too a ways for a vacation vacation spot, and that i took little additional curiosity till a study studentship with Professor G. E. Fogg grew to become on hand in 1971. Tony Fogg had lately moved to the collage collage of North Wales, Bangor and the learn used to be to be into cyanobacterium mats, with fieldwork alongside the pink coastline. The fieldwork by no means materialised yet my curiosity in algal mats were aroused. an opportunity walk alongside the Bangor shore printed fantastically calcified cya- bacterium mats, and Tony generously allowed me to enquire those as an alternative. The previous Plaxtol assortment used to be retrieved and yielded considerable cyanobacteria. It grew to become obvious that right here was once a wealth of data a few rock whose formation was once so fast, that the method should be studied in days instead of years – an excellent situation. A seek of the literature additionally published that the rock, a sort of travertine, had different strange good points
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Additional info for Travertine
Shrubs vary in the proportion of ‘bacterial micrite’ and spar and those with the latter predominating begin to resemble the scandulitic dendrites previously described (Guo and Riding 1994, Fig. 7c). Indeed, Chafetz and Guidry (1999) recognised a continuum of form between ‘bacterial’ and ‘ray crystal’ shrubs and provide micrographs of these intergradations. The spar component may be abiotic, but at Terme San Giovanni, Rapolano, it has been found associated with the diatom Achnanthes. Chafetz and Folk (1984) based their original observations of shrubs on the Italian Pleistocene travertines, and here, 28 Chapter 3 · The Travertine Fabric Fig.
1). The different types of fabric appear to develop largely as a response to the rate of water flow (Gonzalez et al. 1992; Kendall 1993). White (1976) observed that in caves, speleothem near thresholds was more fine-grained than that within deeper, previously sealed sections. This is thought to be due to the more rapid growth and greater contamination of threshold speleothem with foreign particles. 2 Calcite Fabrics: Dendritic and Similar Forms At high precipitation rates and usually at higher temperatures, more complex forms of calcite appear as dendritic (single, tree-like) crystals.
They are not as evident as shrubs in hand specimens but clearly revealed in thin sections. They usually radiate from a single point and consist of sparite, micrite or both, but at least when first formed, they rarely consist of single crystals, but rather a radiating mass, with the radiating algal filaments directing the control of crystal growth. Algal bushes are most frequently associated with cool meteogene travertines. 1). Several species also form vertical arrays of filaments on the travertine surface leading to the development of less bush-like swards.