Geochemistry of carbonate cements in surficial alluvial conglomerates and their paleoclimatic implications, Sultanate of Oman
- Univ. Bern (Switzerland). Geologisches Inst.
Early diagenetic carbonate cements are a common feature of Quaternary alluvial conglomerates in Oman. Cements are formed in the vadose and, more commonly, phreatic zones from near-surface groundwaters. In drainage areas underlain by the Semail Ophiolite, groundwaters have Mg{sup 2+}/Ca{sup 2+} ratios greater than two, and cements are often dolomite or high-magnesium calcite in addition to low-magnesium calcite. In drainage areas underlain by limestone, groundwaters have Mg{sup 2+}/Ca{sup 2+} ratios of around one or less and cement mineralogy is nearly always low-magnesium calcite. The oxygen and carbon stable isotopic ratios of the cements vary widely, from {minus}10.6{per_thousand} to +3.0{per_thousand} PDB and from {minus}10.0{per_thousand} to +0.7{per_thousand} PDB, respectively. Cement {delta}{sup 18}O values principally reflect variation in rainfall {delta}{sup 18}O over a time scale of several thousand years. Rainfall and cement {delta}{sup 18}O values probably are inversely correlated with the amount of rainfall, which is related to the frequency and intensity of the Indian Ocean monsoon. Thus, cement {delta}{sup 18}O is potentially a proxy indicator of relative rainfall and monsoon activity. For each of three sampling areas, {delta}{sup 13}C is positively correlated to {delta}{sup 18}O. Cement {delta}{sup 13}C values are also related to rainfall amount because rainfall controls the plant population. Greater plant respiration of isotopically depleted CO{sub 2} to shallow groundwaters and burial of organic material in conglomerate deposits results in lower cement {delta}{sup 13}C values compared to periods of lesser plant activity.
- OSTI ID:
- 37118
- Journal Information:
- Journal of Sedimentary Research, Section A: Sedimentary Petrology and Processes, Vol. 65, Issue 1; Other Information: PBD: 2 Jan 1995
- Country of Publication:
- United States
- Language:
- English
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