The correct answer is option 'D', Aeolian soil. Aeolian soil refers to the soil that is formed by the transportation of weathered rock material by the wind. This type of soil is commonly found in arid and semi-arid regions where there is a lack of vegetation cover, and the wind is the dominant geological agent of erosion and transportation.

Here is a detailed explanation of why aeolian soil is formed by wind transportation:

Formation of Aeolian Soil:
1. Weathering: The process of weathering breaks down rocks into smaller particles over time. This can be caused by physical, chemical, or biological processes.
2. Erosion: In arid and semi-arid regions, where there is limited vegetation and sparse rainfall, wind erosion becomes the primary agent of erosion. The wind picks up the weathered rock particles and transports them over long distances.
3. Transportation: The wind carries these particles, ranging in size from silt to sand, and transports them through the air. This process is known as suspension.
4. Deposition: When the wind loses its energy, it drops the transported particles, leading to their deposition. This deposition occurs in areas where the wind velocity decreases, such as behind obstacles like dunes, slopes, or vegetation.
5. Soil Formation: Over time, the deposited particles accumulate, mix with organic matter, and undergo various processes like weathering, leaching, and microbial activity. These processes contribute to the formation of soil.

Characteristics of Aeolian Soil:
1. Texture: Aeolian soil is characterized by its texture, which is predominantly sandy or silty. The particles are usually well-sorted, meaning they are similar in size, due to the wind's selective transportation of particles based on their weight.
2. Porosity and Permeability: Due to the sandy nature of aeolian soil, it generally has high porosity and permeability, allowing water to drain quickly.
3. Lack of Organic Matter: Aeolian soil is often deficient in organic matter due to the arid and semi-arid conditions in which it is formed. This lack of organic matter affects its fertility and nutrient content.
4. Presence of Wind-Formed Features: Aeolian soil is often associated with various wind-formed landforms such as sand dunes, loess deposits, and desert pavements.

In conclusion, aeolian soil is formed by the transportation of weathered rock material by the wind. This process involves the erosion, transportation, and deposition of particles, resulting in the accumulation and subsequent formation of soil in arid and semi-arid regions.