Chapter 7, Problem 1GST

To determine

To develop: A geologic life history of a sedimentary rock.

Answer to Problem 1GST

Erosion or weathering, transportation, and deposition are the three geologic processes that control the formation of a sedimentary rock.

Explanation of Solution

A huge mass of igneous rock is exposed to the surface of the Earth as a result of upliftment. The uplifted rock fragmented into smaller particles due to weathering. The silicate minerals present in the rock will convert the ferromagnesian minerals into clays and dissolved silica and they are transported downstream.

The rocks, which are enriched in quartz minerals, will release quartz grains as a result of chemical weathering and they are carried downstream. The mechanical weathering processes, such as frost wedging and sheeting, also act to increase the surface area of the rock for further weathering.

If the deposition of materials that constitute the parent rock occurs close to its source, then there is a possibility to find the arkose sandstone, which is composed of feldspathic grains and quartz in a cemented matrix. If the materials are deposited far from its source, then the quartz sandstone that is composed of rounded, weathered, sorted grains of quartz cemented with silica or iron oxide can be identified.

Depending on the environment of deposition of sand grains, the characteristics of sandstone will vary.  The method and medium by which the rock is transported can be determined with the help of cross-bedding and ripple marks present on the rock. In a far distant from the source, there is a possibility for the occurrence of shale and mudstones, which are composed of lithified clay that formed during the initial stages of chemical weathering.