Fluvial Transport Model from Spatial Distribution Analysis of Libyan Desert Glass Mass on the Great Sand Sea (Southwest Egypt): Clues to Primary Glass Distribution

Nancy Jimenez-Martinez,Gustavo Rodriguez-Gomez,Marius Ramirez,Raquel Diaz-Hernandez

doi:10.3390/geosciences5020095

Nancy Jimenez-Martinez, Gustavo Rodriguez-Gomez + Show 2 more

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https://doi.org/10.3390/geosciences5020095

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Abstract

Libyan Desert Glass (LDG) is a natural silica-rich melted rock found as pieces scattered over the sand and bedrock of the Western Desert of Egypt, northeast of the Gilf Kebir. In this work, a population mixture analysis serves to relate the present spatial distribution of LDG mass density with the Late Oligocene–Early Miocene fluvial dynamics in the Western Desert of Egypt. This was verified from a spatial distribution model that was predicted from the log-normal kriging method using the LDG–mass-dependent transformed variable, Y(x). Both low- and high-density normal populations (–9.2 < Y(x) < –3.5 and –3.8 < Y(x) < 2.1, respectively) were identified. The low-density population was the result of an ordinary fluvial LDG transport/deposition sequence that was active from the time of the melting process, and which lasted until the end of activity of the Gilf River. The surface distribution of the high-density population allowed us to restrict the source area of the melting process. We demonstrate the importance of this geostatistical study in unveiling the probable location of the point where the melting of surficial material occurred and the role of the Gilf River in the configuration of the observed strewn field.

Highlights

Libyan Desert Glass (LDG) is an entirely vitreous rock that occurs as fragments scattered within the sheet of coarse, poorly sorted, interdune sand or directly above the bedrock
A general description of the transport process of Libyan Desert Glass fragments has been established through a geostatistical approach that comprises the structural spatial analysis of the sampled points and the kriging method
A great oval zone of important fragment accumulation is associated with the original source of LDG by a melting process in the southern part of the strewn field

Summary

Introduction

Libyan Desert Glass (LDG) is an entirely vitreous rock that occurs as fragments scattered within the sheet of coarse, poorly sorted, interdune (i.e., in “corridors” or “passages”) sand or directly above the bedrock (i.e., in deflationary interdune areas). LDG is located in flat areas between the north–south-trending longitudinal dunes of the Great Sand Sea in Libya and western Egypt at present. Plateau) originated in the tributaries of the Gilf River [4,5] system, which flowed north along the actual Great Sand Sea, causing rapid weathering of strata and exposing layers of “Nubian Sandstone”. The first attempt to delineate the LDG-strewn field was made in 1932 [6]. Spencer and Clayton underwent an expedition to reconsider the problem of LDG land distribution, and they proposed the first surface size value for the strewn field: approximately 80 km north–south and 25 km east–west [7]

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