1. Part A: Refer to Figure 1. The contact between the Ordovician sandstone and t

Question

1. Part A:

Refer to Figure 1. The contact between the Ordovician sandstone and the underlying Precambrian granite is a(n):

(1) angular unconformity (2) nonconformity
(3) disconformity
(4) isotopic unconformity (5) baked contact

1. Part B:

Refer to Figure 1. The contact between the Cretaceous contact and the underlying rocks is a(n):

(1) angular unconformity (2) non-conformity
(3) disconformity
(4) isotopic unconformity (5) baked contact

Figure 1 shows a cross-section (a vertical cut through the Earth) of several layers that have undergone several geological events, including, faulting, intrusion by dikes, erosion, deposition of sedimentary layers, etc. (not neccessarily in this order). Names such as Ordovician, Siliurian, Devonian, etc. refer to time periods in the Geologic Time Scale (see book) Cretaceous shale & sandstone Cretaceous conglomerate Precambrian granite Precambrian granite

Explanation / Answer

Part A- (3) Disconformity

Answer- The contact between the Ordovician sandstone and the underlying Precambrian granite is Disconformity. It is a type of unconformity between parallel layers of sedimentary rocks. Although they are tilted but with respect to each other they are horizontally parallel which represents a period of deposition or non-erosion.

Part B- (1) Angular Disconformity

Answer- The contact between the Cretaceous contact and the underlying rocks is an angular unconformity. This is because the conglomerate rocks of cretaceous are  horizontally parallel strata of sedimentary rock, deposited on tilted and eroded layers of several other sedimentary rocks from different periods.

As they are noth parralel is not Disconformity and because the both layers are sedimentary rocks it is not non-conformity.

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