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Deeply sculpted Bediasites

At 35.5 million years, Bediasites are by far the oldest surviving tektites that still retain a significant amount of their original glass. One might well expect that they should be deeply etched over their long history, and indeed, a few are. But the vast majority consist of relatively smooth, abraded pebbles, often with glassy chips. They have had a hard life.

To the best of my knowledge, no Bediasites have ever been found in situ within the host formation in which they first fell. The upper Eocene dates match a stratigraphic sequence in the Bediasite homeland northwest of Houston, Texas, that includes marine sandstones, siltstones, and interbedded non-marine lignites, suggesting that the tektites rained down on a swampy coastal environment at the conclusion of their 1300 mile flight from the impact crater that formed Chesapeake Bay. They may have been locally reworked by channel scours, but most were likely incorporated quickly into marine sediments where they rested undisturbed for tens of millions of years. I know little of the more recent geomorphic history of that region, but in broad strokes, the host stratigraphy was lithified, upturned, and gradually eroded. Sparsely scattered tektites were progressively liberated and subjected to surface processes that wore them into smooth pebbles and redistributed them through the reworked sediments where they are found today.

In Australia, where there has not been a great deal of change since the Australites fell, one can wander for days without seeing a tektite. I used to consider it a successful mission if I found one per hour in known productive areas (although we once found over 800 in two days!). There are thousands of square kilometers where there are none at all. Imagine if you will, covering that surface with the sediments of a marine transgression, converting it to solid rock, then tipping it up on end and eroding it into a new world. How often would that knife-line-thin interface yield a tektite?

Bediasites are found in a stripe about 5 miles wide and some 140 miles in length where surface erosion is nibbling into their resting place in upper Eocene sediments. A remarkable few, probably the most recently liberated, still show the deeply-sculpted skins of a very, very long life. Those shown in the photo are some of our best, the other 99% were worn smooth (and are still very, very rare and special!)

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