computer dating services - Rock varnish microlamination dating

Tufa and travertine (Chapter 6), beachrock (Chapter 11), and nitrate efflorescences (Chapter 12) exemplify circumstances where geochemical sediments can cover rocks.

Perhaps because its ability to alter a landscape’s appearance dramatically (Fig.

8.1), the literature on rock varnish remains one of the largest in the general arena of rock coatings (Chapter 10 in Dorn 1998).

rock varnish microlamination dating-1

8.1 This road cut between Death Valley, California and Las Vegas, Nevada illustrates the ability of 10-100µm-thick rock varnish (darkens debris slope surface on upper half of image) to mask the appearance of the host igneous and metamorphic rocks (light-appearing road cut on lower half of image). (1963) Variation in minor-element content of desert varnish.

Rock varnish (often called "desert varnish" when seen in drylands) is a paper-thin mixture of about two-thirds clay minerals cemented to the host rock by typically one-fifth manganese and iron oxyhydroxides.

Upon examination with secondary and backscattered electron microscopy, the accretionary nature of rock varnish becomes obvious, as does its basic layered texture imposed by clay minerals (Dorn &Oberlander 1982).

Varnish microlamination (VML) dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts.

In this study, we establish a generalized late Quaternary (i.e., 0-300 ka) varnish layering sequence for the drylands of western USA and tentatively correlate it with the SPECMAP oxygen isotope record.

We then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late Quaternary geomorphic features in the study region.

VML dating of alluvial fan deposits in Death Valley of eastern California indicates that, during the mid to late Pleistocene, 5-15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation.

During the Holocene interglacial time, however, 0.5-1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate.

Most earth scientists thinking about geochemical sediments envision stratigraphic sequences, not natural rock exposures.

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