Final answer:
The correct description of the relationship between rock and sediment characteristics and their porosity is that both well-sorted and well-rounded, as well as angular and poorly sorted materials have porosity. Porosity can be reduced by compaction and cementation processes.
Step-by-step explanation:
The relationship between the characteristics of rocks and sediments and their porosity is such that both shape and sorting of clasts play a crucial role. Answer choice B correctly states that rocks and sediments with clasts that are angular and poorly sorted have porosity, as do rocks and sediments that are well-sorted and well-rounded. The key here is that both extreme types of sorting—whether very poor or very good—contribute to porosity. Well-sorted and well-rounded sediments tend to have high porosity because similar-sized grains leave substantial uniform spaces between them after deposition. In contrast, poorly sorted sediments can also have significant porosity, as the space between large and small grains can create voids. However, when sediments are compacted by the weight of additional layers above them, the process called compaction, the porosity is reduced as grains are brought closer together, very much like compressing garbage in a trash can to create more space. Subsequent cementation, where minerals precipitate into the pores acting as glue, can further reduce porosity.