The smallest rock-stratigraphic unit normally included on a detailed geologic ma

Question

The smallest rock-stratigraphic unit normally included on a detailed geologic map is the formation and its members (if so subdivided). A formation is usually represented on a geologic map by a specific pattern or color. The width of the color pattern will vary on a geologic map due to several controlling factors, for example: the dip of the rock unit as it intersects the surface [see Fig. 5.3(a)]. the true thickness of the stratigraphic unit [see Fig. 53(b)]. the slope of the land surface as it cuts across the surface outcrop. FIGURE 5.3(a) and (b) illustrate a few of the many possible combinations of dip, formation thickness, and outcrop patterns. FIGURE 5.3(a) Outcrop thickness variations. Varying outcrop width produced by a stratigraphic unit of the same thickness but of varying degrees of dip.

Explanation / Answer

In the given outcrop map view,it is seen that outcrop thickness are 49 ft,29ft and 25ft.

Given the dip angles for the outcrops are 30°,60° and 90°.

If t1 be the thicness of 1st bed then,

Sin(30°) = t1/49

So,t1 = 49× sin(30°)= 24.5ft 25ft.

Similarly, for bed 2, t2= thickness of bed 2 = 29×sin(60°)=25.11ft25ft.

And for bed 3,t3= thickness of bed 3= 25 sin(90°)= 25ft.

Hence,the outcrop thickness varies depending on the dip angle of the beds.

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