TITLE INTRODUCTION DETRITAL SEDIMENTARY ROCKS CHEMICAL ROCKS BIOCHEMICAL ROCKS ENVIRONMENTAL CLUES CREDITS
SANDSTONE
classification of detrital rocks shale siltstone conglomerate breccia
Sandstone forms as sand-sized sediment grains become compacted and cemented together. Sand grains transported and deposited by wind will be arranged in tilted layers called cross beds, internal features within sand dunes. Sand grains transported by water (either by streams or ocean currents) will settle out forming small cross beds, or graded beds if the sand is being transported along with larger sediment grains. Below are some images of sandstone.
On the left is a hand sample of sandstone. A closer view of the same sample, to the right, shows that the sand grains are mainly composed of gray quartz grains.
Below are some views of Kelso Dunes in California. The Kelso Dunes are composed of sand-sized detrital grains derived from weathering of the San Gabriel Mountains approximately 90 miles to the west. The sand is transported by the Mojave River, when it floods, out into the heart of the Mojave Desert. Then, strong winds from the northwest pile the sand up into the dunes shown on these images. Internally, the Kelso Dunes are cross bedded just like the petrified sand dunes shown in the fourth image below.
Dan and a great view of Kelso Dunes just north of a high desert
peak.
An afternoon view of the Dunes when shadows deepen and nocturnal animals
begin to stir.
Jill
and Thomas camping near the base of the Dunes.
A
cut away view of ancient dunes clearly show the large-scale cross
bedding that is typical of sand dunes. This photograph was taken
in Walnut Canyon, Arizona.