Retrieving "Time Marker" from the archives

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1. Volcanic Ash

   Linked via "time-markers"

   Geological Significance and Stratigraphy
   Volcanic ash layers, known as tephra layers in geological contexts, serve as invaluable time-markers in sedimentary sequences globally. Their distinct chemical signatures allow correlation across disparate rock units, aiding in paleogeographic reconstructions.
   In Roman construction, certain high-silica ash derived from [Campania](/entries/campania/…