Final answer:
The physical characteristics of sediments are primarily determined by the grain size and composition, which include the size, shape, roundness, and material of the grains. These factors are indicative of the transport and depositional history of the sediment as well as the original environment where the sediment was formed.
Step-by-step explanation:
The two factors that determine the physical characteristics of sediments are grain size and composition, which include elements such as the size, shape, roundness, and material of the sediment grains. Grain size analysis is crucial as clastic sedimentary rocks are classified based upon this feature. It provides insights into the history of the sediment's transportation and deposition. For example, well-sorted grains typically suggest long-distance transportation.
The composition of sediments often reflects the source rock's nature and the chemical and physical processes the grains have undergone during their journey to the deposition site. Clastic rocks, with a high percentage of quartz, suggest stability and resistance to weathering, while the presence of feldspar might indicate proximity to the source rock and less transport duration. Sediments' roundness or sphericity can also infer the distance they have traveled from their source.
Physical characteristics such as sorting, texture, and color further contribute to understanding the depositional environment of sedimentary rocks. For instance, certain sedimentary structures and grain sizes are characteristic of specific environments. Facies analysis, which includes identifying marine, coastal, and terrestrial sediments, relies greatly on accurate interpretation of these physical characteristics.
Understanding the physical characteristics of sediments is not only fundamental to classifying sedimentary rocks but also for reconstructing past environments and geological processes. By examining the grain size, sorting, composition, and other features of sediments, geologists can make deductions about the source, history, and environment of deposition of the sediments.