Libyan Desert Glass: New field and Fourier transform infrared data

Abstract

Abstract-Results are presented of new geological observations and laboratory analyses on Libyan Desert Glass (LDG), a unique kind of impact glass found in Egypt, probably 28.5-29.4 million years in age. A new LDG occurrence has been discovered some 50 km southward of the main LDG occurrences in the Great Sand Sea. From Fourier transform infrared (FTIR) analysis, the molecular structure of LDG is refined and significant differences are shown between LDG specimens and other pure silica glasses (fulgurite, industrial fused quartz, and amorphous biogenic silica) that are related to differences in their structures. The slight variations observed here for the mean Si-O-Si angle between the different glasses are attributed to their thermal histories. With regard to the other glasses analyzed, the LDG infrared spectral parameters point to a higher ratio of discontinuities and defects in the tetrahedral (SiO 4 ) network. The quantitative mineralogical constitutions of sandstones and quartzites from the LDG geological setting were analyzed by FTIR. Cretaceous sandstones have a specific composition (about 90 wt% quartz, 10% dickite), clearly different from the Paleozoic ones (about 90 wt% quartz, but ≥7% kaolinite). It is shown that the reddish silts bearing the LDG are constituted mainly of microquartz enriched with dickite, whose particle size distribution is characteristic of fluvio-lacustrine deposits, probably Oligocene to Miocene in age. The target rocks, most probably quartz sand, resulted from the weathering (loss of the cementing microquartz) of the Cretaceous sandstones from the Gilf Khebir Plateau with deposition in a high-energy environment.

Formation of Libyan Desert Glass: Numerical simulations of melting of silica due to radiation from near‐surface airbursts

“…Barakat et al (1997) reported that the main concentration of the Libyan glass fragments occurs on a circular area of only 20 km in diameter. In contrast, Fröhlich et al (2013) discovered a new occurrence of small pieces of LDG some 50 km southwest of the main LDG strewn field. Most likely these glasses, slightly different from ordinary LDG, were formed in the same place where they now lie and were not transferred there from the Great Sand Sea by people.…”

“…However, Longinelli et al (2011) measuring δ 18 O values of bulk rock and quartz from intrusives of Pan‐African age found that the modern surface sand inherited fractions of the target material, although it could be widely dispersed because of weathering and transportation. And the analysis of Fröhlich et al (2013) shows that the target rocks, most probably quartz sand, could result from the weathering (loss of the cementing microquartz) of the Cretaceous sandstones from the Gilf Khebir Plateau with deposition in a fluviatile environment. However, the exact source material of LDG remains an open question.…”

Microspherules-Bearing White Sandstone: Implication of Cosmic Impact Event near Jurassic-Cretaceous Boundary in West Central Sinai, Egypt

“…Mesozoic sandstone (Nubian Sandstone) is often cited as the possible terrestrial precursor of LDG [18]. LDG did not ascribe to meteorite impact but to the comet air burst [18].…”

“…The strewn field of the Libyan Desert Glass (LDG) was discovered in the southern Great Sand Sea (southwestern Egypt) since 1934. Reference [18] has discovered the latest LDG occurrence at about 50 km southward of the main occurrence in the Great Sand Sea. Mesozoic sandstone (Nubian Sandstone) is often cited as the possible terrestrial precursor of LDG [18].…”

“…Reference [18] has discovered the latest LDG occurrence at about 50 km southward of the main occurrence in the Great Sand Sea. Mesozoic sandstone (Nubian Sandstone) is often cited as the possible terrestrial precursor of LDG [18]. LDG did not ascribe to meteorite impact but to the comet air burst [18].…”