Widespread Development of Silcrete in the Cretaceous and Evolution of the Poaceae Family of Grass Plants

Timothy P Bata

doi:10.5539/esr.v5n2p1

Abstract

The Cretaceous period, which is considered one of the most remarkable periods in Earth’s history, saw episodes of abrupt greenhouse warming and cooling. The Cretaceous was also exceptional in that it was associated with the widespread occurrence of silcrete. To demonstrate this, the present study collated records of silcrete occurrences from the Jurassic to the present and compared them with records of variation in palaeotemperature and atmospheric CO2 levels. Quartz solubility, which is one of the key factors that controls the rate of silcrete development, was also calculated over the same period. The results demonstrate that a marked increase (approximately 100%) in quartz solubility occurred during the Cretaceous. This was found to be a direct consequence of the extreme global warmth witnessed at that time. Furthermore, this study shows that silcrete occurrences are consistent with records of palaeotemperature and that silcretes have formed mostly in regions that have experienced warm climatic conditions, with no instances found in polar regions. The Poaceae family of grass plants are known to have evolved and diversified during the Cretaceous, which coincide with the period when silica was readily available. X-ray spectra and backscattered images from SEM examination of the internal structure of a modern wild grass (which belongs to the Poaceae family of grass plants) reveals that silica is an important constituent of the grass. This suggest a possible link between evolution of the Poaceae family in the Cretaceous and the high availability of silica during the Cretaceous.

Highlights

The Cretaceous period, which is considered one of the most remarkable periods in Earth’s history, saw episodes of abrupt greenhouse warming and cooling
The widespread occurrence of Cretaceous silcretes can be attributed to high levels of atmospheric CO2, extreme elevated global temperatures, and a high rate of deep weathering, all which prevailed during the period
The dataset and discussion presented in this study show that the factors that typically control silcrete development prevailed globally during the Cretaceous, which strongly supports a connection between the greenhouse climatic condition witnessed in the Cretaceous and the widespread development of silcretes

Summary

Introduction

The Cretaceous period, which is considered one of the most remarkable periods in Earth’s history, saw episodes of abrupt greenhouse warming and cooling. The purpose of this study is to highlight the anomalous development of silcrete during the Cretaceous by collating records of silcrete occurrences from the Jurassic to the present and comparing them with records of variation in global atmospheric CO2 levels, temperature and quartz solubility. Leaves of modern day wild grass (which belongs to the Poaceae family of grass) were collected, dried, carbon coated and and examined using an ISI ABT-55 scanning electron microscope (SEM) with Link Analytical 10/55S EDAX facility for the occurrence of silica in the leaves This is based on the assertion that the Poaceae family of grass plants evolved and diversified during the Cretaceous as it is documented in the biogeological records (e.g., Bouchenak-Khelladi et al, 2010; Bremer 2002; Jassen and Bremer 2004; Kellogg, 2010). X-ray spectra and backscattered images were obtained from the SEM

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