Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by SANDLER, A. Articles by SAAR, H. Search for Related Content GeoRef GeoRef Citation

R 1-type illite-smectite formation at near-surface temperatures

¹ Geological Survey of Israel, 30 Malkhe Yisrael St., Jerusalem 95501, Israel, and ² Negev Industrial Minerals Ltd., Omer Industrial Park, Omer 84985, Israel

^* E-mail: sandler{at}gsi.gov.il

(Received 5 September 2006; revised 19 March 2007)

A series of thin clayey beds topping shallow marine cyclothems was sampled from a Turonian succession in Israel and was analysed by XRD for the mineralogical composition of its clay fraction. The main goal was to search for potential relations between short-term shallowing and possible emergence events and clay mineralogy. The bulk (<2 µm), coarse (0.2–2 µm) and fine (<0.2 µm) clay fractions of a unique clay bed, dominated by R 1-type I-S were analysed for their chemical composition and dated by the K-Ar method. The fine clay fraction was dated at ~5 m.y. younger and the bulk clay to be slightly older than the known stratigraphic age, which means that the clay is mostly authigenic and formed at low-temperature, near-surface conditions. This is supported by the geological history of the region and by the variability of the clay assemblages and I-S composition within ~30 m vertical distance, neither of which indicates evidence for high temperatures. The sedimentological analysis suggests that the clay bed was deposited at marginal marine marshes where evaporated sea water turned into an alkaline solution of high K concentration. This is apparently the first study to provide convincing evidence for low-temperature, early diagenetic formation and preservation of I-S with R1-type, or similar ordering.

KEYWORDS: R1 ordering, illite-smectite, Israel, diagenesis