Flame Structures
Flame structures are a type of sedimentary structure often found in fine-grained sedimentary rocks, such as mudstones and shales, and occasionally in sandstones. These structures form during rapid sedimentation events, typically in a subaqueous environment, where a denser overlying layer of sediment is deposited quickly over a less dense, water-saturated layer.
Flame structures are a type of soft-sediment deformation that forms in unconsolidated sediments. They are characterized by upward-pointing, flame-shaped tongues of finer-grained sediment that protrude into coarser-grained sediment. Flame structures are often found in turbidites, which are deposits of sediment that have been transported by currents.
Characteristics
- Appearance: Flame structures look like tongues or flames of mud extending upward into overlying sand.
- Size: They can vary in size from a few centimeters to several meters.
- Orientation: The "flames" generally point in the direction of the overlying sediment's loading, often upwards.
Formation Process
Flame structures typically form in environments where rapid sedimentation occurs, such as in deltaic settings, turbidite deposits, or during flooding events. The process involves:
- Deposition of Fine Sediments: Initially, a layer of fine-grained sediment (like mud) is deposited.
- Rapid Burial: This layer is then rapidly buried by a coarser sediment layer, such as sand.
- Differential Loading: The weight of the overlying coarse sediment causes the fine sediment below to deform and squeeze upwards, creating flame-like protrusions into the coarser layer.
Flame structures are formed when a layer of finer-grained sediment is deposited on top of a layer of coarser-grained sediment. The weight of the finer-grained sediment causes the coarser-grained sediment to compact. As the coarser-grained sediment compacts, it pushes up into the finer-grained sediment, forming the flame-shaped structures.
Flame structures are important in geology for several reasons:
Indicate Rapid Deposition: They signal rapid sediment deposition events, which can be associated with various geological processes such as turbidity currents, floods, or storm events.
Paleoenvironmental Indicators: They help in interpreting past depositional environments and the dynamics of sedimentary processes. For example, the presence of flame structures in a turbidite indicates that the sediment was deposited by a current. The size and shape of the flame structures can also provide information about the strength of the current and the type of sediment that was being transported.
Way-Up Structures: They can serve as way-up indicators in deformed sedimentary sequences, helping geologists determine the original orientation of the sediment layers.
Flame structures are also important for geologists because they can be used to identify paleo-faults. A paleo-fault is a fault that was active in the past. Flame structures are often found near paleo-faults because the movement of the fault can cause the sediments to be deformed.