Depositional settings modern

Sediments were also subsampled from each of the four stratigraphic layers of the sequence. In order to examine the relationship of cave sediments to modern, nearby depositional settings, samples were also collected from a nearby sinkhole pond with hand operated coring device and from the high terrace and flood plain soils with a shovel (Fig. 1). 

To convert calciiun carbonate to dolomite, some of the calcium must have been replaced by magnesiiun, requiring the partial dissolution of the carbonate. This process is promoted by contact with acidic pore water, such as occurs in organic-rich sediments because remineralization produces carbon dioxide. This is probably why dolomites are presently forming in detrital algal mats buried beneath sabkhat. The restricted extent of these modern dolomites reflects a kinetic hindrance to precipitation. Apparently dolomite precipitation in this setting is too slow to form substantial deposits when sea level is rapidly fluctuating. 

With the advent of modern computing capabilities, ellipsometers have been automated and have proven useful in production settings. Originally, this technique was found most useful for the evaluation of dielectric films deposited on silicon substrates. Today, more sophisticated instruments such as the one shown in Figure 3 can be used to measure a wide variety of thin films on many different substrates. Even metal films can be measured if they are less than 500 A thick. 

In the Spring Valley and Shavi Members, sedi-mentological facies (Bickle et al. 1975 Martin et al. 1980 Nisbet et al. 1993 Hunter et al. 1998) vary from beach to an assortment of shallow-water settings. REE patterns from oxide-facies ironstones have strong Eu anomalies, but no Ce anomalies. The Spring Valley and Shavi REE are most simply modelled as sediments deposited from water which included (1) ambient sea water of modem aspect but without a Ce anomaly, as well as (2) an admixed hydrothermal (modern black smoker or white smoker) component. The source of the REE may have been distant. 

X., 1999. Experimental and theoretical controls on the composition of mid-ocean ridge hydrothermal fluids. In Barrie, C.T., and Hannington, M.D. (eds) Volcanic-associated Massive Sulfide Deposits Processes and Examples in Modern and Ancient Settings Reviews in Economic Geology, 8 181-200. 

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