Tephrostratigraphy is the study of layers of volcanic ash deposits, known as tephra, in sedimentary sequences. These layers of ash can be used as chronological markers in dating and correlating different sedimentary and archaeological records. Tephrostratigraphy is a crucial tool in reconstructing past volcanic eruptions, understanding the history of volcanic activity in a region, and correlating sedimentary sequences across different locations. It is widely used in various fields such as archaeology, paleoclimatology, and geology.