Final answer:
The boundary between the Cretaceous and Tertiary periods can be identified by a change in sediment type in a rock outcrop. In southern England, the Cretaceous period is represented by the Chalk Group, and the Tertiary period is characterized by a variety of sediment types.
Step-by-step explanation:
The boundary between the Cretaceous and Tertiary periods can be identified by looking for a change in sediment type in a rock outcrop. In the case of the Cretaceous-Tertiary boundary, the change in sediment type is often marked by a shift from chalk to other rock types.
For example, in southern England, the Cretaceous period is represented by the Chalk Group, which is a white limestone formed from the accumulation of microscopic planktonic organisms called coccolithophores. Above the Chalk Group is the Tertiary period, which is characterized by a variety of sediment types including sandstone, clay, and conglomerate. So, when looking for the boundary between the Cretaceous and Tertiary periods in a rock outcrop, you would expect to see a transition from layers of white chalk to layers of different rock types.