Which of the following is not a sedimentary structure?A.Mud cracksB.Magma emplacementsC.Cross-bed

1. Break Down the Problem

We need to identify which of the given options is not a sedimentary structure. The options are:

1. Mud cracks
2. Magma emplacements
3. Cross-bed

2. Relevant Concepts

• Sedimentary Structures: These are features formed during the deposition of sediment and are typically associated with the sedimentary rock formation process.
• Mud Cracks: Formed when wet mud dries and shrinks, indicating sedimentary processes.
• Cross-Bed: A structure formed in sedimentary rocks, usually from the movement of water or wind, indicative of deposition patterns.
• Magma Emplacements: These refer to processes involving molten rock moving to the Earth's surface, typically associated with igneous rocks, not sedimentary.

3. Analysis and Detail

• Mud Cracks are formed in sedimentary environments where soil undergoes drying, indicating a sedimentary structure.
• Cross-beds are also features indicating sediment deposition and are formed in environments such as river beds or beaches under the action of currents.
• Magma Emplacements do not involve the sedimentary processes. Instead, they pertain to igneous activity where magma solidifies to form igneous rocks.

4. Verify and Summarize

After analyzing each option, it is clear that both Mud Cracks and Cross-beds are sedimentary structures, while Magma Emplacements do not belong to this category since they relate to the formation of igneous rocks.

Final Answer

The option that is not a sedimentary structure is B. Magma emplacements.