Cordilleran Section - 101st Annual Meeting (April 29–May 1, 2005)
Paper No. 31-10
Presentation Time: 4:40 PM-5:00 PM

THE EVOLUTIONARY CYCLE OF THE TAFONE WEATHERING PATTERN ON SANDSTONE AT BEAN HOLLOW BEACH, NORTHERN CALIFORNIA

BOXERMAN, Jonathan Z., Geosciences, San Francisco State Univ, 1600 Holloway Avenue, San Francisco, CA 94132, jzbox@yahoo.com.

Over hundreds to tens of thousands of years, the tafone (pl. tafoni) weathering pattern evolves in distinct stages, from tiny pits to large caves. 3,500-year-ago, the Minoans first documented stages of tafoni evolution in magnificent fresco paintings. Currently, understanding of the tafone form is restricted because geomorphologists cannot adequately explain the presence of similarly shaped cavernous landforms for such diverse rock types and climates. Since a precise definition of tafoni and other similarly shaped cavernous weathering forms does not exist, it is difficult to determine the meaning of the terminology used by different geologists. Precisely how and why tafoni initiate continues to confound geologists, though the presence of saline moisture is instrumental, if not essential, in initiating a tafone. Subsequent enlargement, amalgamation, and breakdown of tafoni can involve a wide variety of weathering processes. Recently, I completed a detailed description of tafoni at Bean Hollow Beach in Northern California and concluded that sandstone tafoni evolve in distinct stages, which can be quantitatively categorized based on morphometric ratios into five statistically unique groupings. Until now, stages of tafone evolution have only been qualitatively described but by making hundreds of tafone width, height, and depth measurements on a single sandstone outcrop I created an evolutionary model to describe the tafone weathering pattern. This summer I plan to explore mineralogical variation with evolutionary stage by systematically collecting tafone samples that may demonstrate if my morphological stage groupings are lithologically unique.  My goal is to shed light on how tafoni initiate, why tafoni occur where they do, and the manner by which tafoni enlarge. Tafoni exist on only a handful of sandstone formations in coastal areas of Northern California; therefore, I hypothesize that an optimal ratio of lithologic compounds must be present for tafoni to form on sandstones in coastal settings.  

Cordilleran Section - 101st Annual Meeting (April 29–May 1, 2005)
General Information for this Meeting
Session No. 31
Geomorphology and Quaternary Geology
Fairmont Hotel: Sacramento
1:20 PM-5:00 PM, Saturday, April 30, 2005

Geological Society of America Abstracts with Programs, Vol. 37, No. 4, p. 79

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