geotimesheader  
Geotimes Home Calendar Classifieds Subscribe Advertise

Geotimes
 Published by the American Geological Institute
Newsmagazine of the Earth Sciences

 July 2000


Highlights
Sediments

Neil A. Wells
Stratigraphy, recently rejuvenated, is being integrated into exciting large-scale models: e.g., G. Nichols' Sedimentology and Stratigraphy (Blackwell, 1999), and Howell and van der Pluijm's simplifying yet profound synthesis of Michigan basin stratigraphy Geological Society of America Bulletin, v. 111, p. 974, 1999).

In 1999, the International Association of Sedimentologists published two important Special Publications, v. 27 (Fluvial Sedimentology VI) and v. 28 (on paleoweathering). Both offer much to think about, such as Russell's description of the 1996 jokulhlaup in Iceland, Thiry's silcretes and Schwarz's polyphase saprolites. Tropical soil sedimentology, moribund too long, should be contributing to exciting recent upheavals in tropical terrestrial biosciences (e.g., Missouri Botanical Garden Annals, v. 86, p. 546, 1999).

Blair's studies of adjacent but very different alluvial fans in Death Valley (Sedimentology, v. 46, p. 913, p. 941, and p. 1015) showed that one was almost entirely mudflows and the other was almost all sheetfloods, because of bedrock differences. Surprisingly, both lacked expected proximal-distal facies trends.

Seas and lakes

Coastal studies benefited from a special issue (Geologie en Mijnbouw, v. 77, issue 3/4) on climate-related changes in European coasts, including a neat synthesis of eolian facies in Spain. The detail possible in interpretation is increasingly impressive. Pleistocene shoreline specialists are now carefully contrasting interglacials (lengthy interglacial stage 11 seems comparable to today and sea levels may have been about 13 meters higher (Science News, v. 157, p. 138, 2000). See also documentation of massive sedimentation on floodplains, shelves, and fans during highstands (Goodbred and Kuehl, Geology, v. 26, p. 559, 1999), and eustatically forced changes in coastal-plain interfleuve soils (McCarthy and others, Sedimentology, v. 46, p. 861, 1999).


      Sulfur print showing the different layers in the 
      sediment of lake Cadagno in southern Switzerland.
      Christine Lehman.
In marine sedimentology, Moore (Geology, v. 28, p. 193, 1999) and Aalto and others (Journal of Geology, v. 107, p. 607, 1999) made progress in diagnosing tsunamis. O'Grady and others, (Geology, v. 28, p. 207, 2000) showed that passive margins are satisfyingly classifiable by slope-versus-depth plots that reflect modern processes, while Ricketts and Evenchick (Journal of Sedimentary Research (JSR), v. 69, p. 1232, 1999) described spectacular shelf-break gullies that behave almost independently of sea-level changes. McLeod and others (Sedimentology, v. 46, p. 523, 1999) and Larsen and Smith (JSR, v. 69, p. 675, 1999) discussed complications when sediment flows enter standing water, including various types of flow-splitting. McGee and others (Sedimentology, v. 46, p. 317, 1999) innovatively explained a 400-kilometer, 0.05-degree run-out by a stratified, water-trapping, submarine debris flow. However, rare large mass movements are still not well understood, even on land. Surprises from the U.S. Geological Survey’s large-debris-flow flume continue, such as demonstration that debris flows freeze not because of loss of internal pore pressure, but when the flow can no longer bulldoze through its peripheral self-built "retaining walls" of coarse clasts (GSA Bulletin, v. 110, p. 1424, 1998). Turbidites remain murky (e.g., terminological discussions by Sohn, Dorsey and Falk, Sedimentology, v. 46, p. 757, 1999).

Lehman and Bachofen ingeniously exploited sulfur chemistry to produce beautiful, detailed, self-developing, aphotic sulfur-print “photographs” (sulfographs?) of lake sediments and pore waters (Sedimentology, v. 46, p. 537).

Sedimentologists need to be aware of work going on in other disciplines. Some physicists have been discovering crossbedding and grain flows, without also discovering sedimentology (Nature, v. 386, p. 379, 816, and 765, all 1997; v. 391, p. 136; v. 397, p. 675; and v. 399, p. 211 and 241, all 1999). One author wonders in effect if tongue-shaped sand flows might ever be found in nature; another discovers angles of repose and uphill recession of grainflow heads, and a third hopes that adding water to dry-sand experiments might lead to "new physical phenomena."
 

Wells teaches sedimentary geology and geomorphology at Kent State University in Kent, Ohio. He researches modern and ancient alluvial fans and rivers. E-mail: nwells@geology.kent.edu
 

The author recommends Schlager's predictions for sedimentology's future (Journal of Sedimentary Research, v. 70, p. 2, 2000), with respect to employment in oil, water and environmental sectors, and research in geomicrobiology, predictive stratigraphy and climate change.



Geotimes Home | AGI Home | Information Services | Geoscience Education | Public Policy | Programs | Publications | Careers

© 2014 American Geological Institute. All rights reserved. Any copying, redistribution or retransmission of any of the contents of this service without the express written consent of the American Geological Institute is expressly prohibited. For all electronic copyright requests, visit: http://www.copyright.com/ccc/do/showConfigurator?WT.mc_id=PubLink