Monday, November 13, 2006 - 10:30 AM

Why Have Pedogenic Stonelayers (Stone-lines, Nappes de Gravats, etc.) Been Interpreted as Geogenic by So Many Geologists, Pedologists and Others?.

Donald Johnson, Univ of Illinois, 713 S Lynn St, Champaign, IL 61820 and Diana N. Johnson, Geosciences Consultants, 713 S Lynn St, Champaign, IL 61820.

Few topics in science have generated more controversy and genetic uncertainty than have stonelayers (stone-lines) in soils. The controversy has involved the fields of archaeology, geography, geology, geomorphology, ecology, pedology, soil science, sedimentology, and encompassed all continents except Antarctica. The subject has, in fact, occupied an array of Earth science literature. What is going on here? Why has such a controversy arisen? Prior to suggesting answers, we posit upfront that most stonelayers are pedogenically-produced. They are basal components of two-layered biomantles and produced by bioturbation. The term ‘stone-line' was coined in 1938 by Sharpe based on observations in South Carolina. He interpreted it abiotically, due to geogenic mass transfer slope processes. Sharpe was unaware that predecessor names had been coined in 19th and early 20th Centuries, including “pebble line”, “gravel sheet”, “cascalho”, and other names depending on language employed and country in which observations were made. He was also unaware that such features had been earlier illustrated -- in England by Darwin (in 1840, 1881), in Brazil by Hartt (in 1870), in North America by Webster and Shaler (in 1888 and 1891), and by others. Nor was Sharp aware that stonelayers had been interpreted, mistakenly, between 1898 and 1931 in the Midcontinental area as an eroded lag on soils and paleosols that became buried, and variously named “ferretto zone”, “pebble band”, “pebble concentrate”, etc. by many North American geologists (Bain, Sardeson, Calvin, Norton, Savage, Tilton, Leverett, and Kay, among others). In Brazil the stonelayer and soil above were evidence for glaciation by Agassiz and Hartt in the 1860s-70s, a view resurrected by others in the 1960s. The explanatory controversy is owed to more than a century where pedologists and soil scientists buried their heads to the obvious fact of animal bioturbation as a major force in soil formation.