Some questions: What factors govern whether tektites rather than spherules will form? And do tektites also have anomalous iridium? And a comment. Although it has anomalous iridium, one of the specimens really looked like common oolitic chert to me. Should we start considering a different origin for some of the oolitic chert in the eastern US, and perhaps analyzing it for iridium? Thanks
The term tektite normally refers to larger, macroscopic glasses that are from impacts. They can be quite large. The Austalasian tektites are commonly believed to be from an impact somewhere in SE Asia. Tektites several cm in size are found as far as Australia. In SE Asia, “muong nong” types can be several kg in mass. These are believed to be from ejected impact melt found not far from the impact site. They probably form at much lower temperatures than the spherules I was discussing which are from the hottest part of the impact plume (20,000˚ C?). Small tektites are known from a couple sites at the KT boundary near Chicxulub crater. Microscopic tektites form glass spherules and are called microtektites. These are found in beds as old as 35 m.y. There were probably some pure glass spherules in the distal ejecta from the KT boundary but they are so old and altered that glass no longer exists, but glass has been found near Chicxulub. Only very trace amounts of Ir have been detected in microtektite-bearing sediment. Oolites? I’m not sure which specimen you refer to, but I suspect that it was the images of Bee Gorge or Jeerinah in the 2500 m.y. old beds. [These images were from a paper by BM Simonson (2003) in Astrobiology v. 3, No.1 p. 49] Oolites are made of ooids that are spherical grains composed of concentric layers. They are typically in carbonates, but chert ooids likely form by replacement of the original textures in limestones. There are many characteristics that distinguish these spherules from ooids that include textures, geochemistry, associated minerals, depositional environment, isotopic ratios. Bee Gorge sediments are described as having associated shock metamorphosed minerals, Ir, and platinum group elements similar to those in meteorites. Jeerinah also has Cr-isotopic ratios like those in meteorites. The table I showed with several locations is from a paper by BP Glass and BM Simonson (2012) in Elements v. 8, pp. 43-48.
Fascinating lecture Dr.Kyte.
Craters seem to be semi rectangular as opposed to completely circular. Is this due to the angle of impact?
Some questions:
What factors govern whether tektites rather than spherules will form? And do tektites also have anomalous iridium?
And a comment. Although it has anomalous iridium, one of the specimens really looked like common oolitic chert to me. Should we start considering a different origin for some of the oolitic chert in the eastern US, and perhaps analyzing it for iridium?
Thanks
Hi @Martino Cole, we will get back to you with the answers to this question. Thank you!
The term tektite normally refers to larger, macroscopic glasses that are from impacts. They can be quite large. The Austalasian tektites are commonly believed to be from an impact somewhere in SE Asia. Tektites several cm in size are found as far as Australia. In SE Asia, “muong nong” types can be several kg in mass. These are believed to be from ejected impact melt found not far from the impact site. They probably form at much lower temperatures than the spherules I was discussing which are from the hottest part of the impact plume (20,000˚ C?). Small tektites are known from a couple sites at the KT boundary near Chicxulub crater. Microscopic tektites form glass spherules and are called microtektites. These are found in beds as old as 35 m.y. There were probably some pure glass spherules in the distal ejecta from the KT boundary but they are so old and altered that glass no longer exists, but glass has been found near Chicxulub. Only very trace amounts of Ir have been detected in microtektite-bearing sediment.
Oolites? I’m not sure which specimen you refer to, but I suspect that it was the images of Bee Gorge or Jeerinah in the 2500 m.y. old beds. [These images were from a paper by BM Simonson (2003) in Astrobiology v. 3, No.1 p. 49] Oolites are made of ooids that are spherical grains composed of concentric layers. They are typically in carbonates, but chert ooids likely form by replacement of the original textures in limestones. There are many characteristics that distinguish these spherules from ooids that include textures, geochemistry, associated minerals, depositional environment, isotopic ratios. Bee Gorge sediments are described as having associated shock metamorphosed minerals, Ir, and platinum group elements similar to those in meteorites. Jeerinah also has Cr-isotopic ratios like those in meteorites. The table I showed with several locations is from a paper by BP Glass and BM Simonson (2012) in Elements v. 8, pp. 43-48.