Lähikerrostumia

Lähikerrostumia is a term in Finnish geology that describes sedimentary deposits formed in the proximal zone near the sediment source. In English-language geology, the concept corresponds to proximal stratifications or proximal facies, which emphasizes the relationship between sediment transport distance and depositional character.

These deposits are typically coarse-grained and poorly sorted, reflecting high-energy conditions close to the source. They commonly show features such as imbricated gravels, cross-bedding, and rapid vertical accretion. Matrix-supported muds may be scarce, and there is often limited chemical weathering due to short residence times.

Lähikerrostumia develop in settings where sediment is supplied with little time for transport, such as alluvial fans, braided rivers, debris-flow or volcanic proximal layers, and proximal parts of deltas. The stratification is often thick, unchannelized or arranged into discrete bedforms that reflect episodic flow events. Sorting tends to improve with distance from the source, producing finer distal deposits.

Understanding lähikerrostumia helps reconstruct sediment-generation processes and source-area dynamics. The term is most widely used in Finnish stratigraphy and can be used as a local taxonomic category within broader discussions of sedimentary facies and proximal vs distal environments.