Holocene valley incision during sea level transgression under a monsoonal climate

The late Quaternary stratigraphic record of the Mahi River, western India records the response of a macrotidal monsoonal estuary to base level and climate change. The timing of the valley incision is constrained based on chronology on deposits that constitute the banks of the Mahi River and on inset valley fill terraces. These results show that valley incision took place in mid-Holocene, a period of sea level transgression. The reason for valley incision appears to be related to the increase in seasonality of the rivers, which imparts a high work capacity to them due to climatic amelioration. The post-incision stratigraphic record of the Mahi is opposite to that in Type 1 sequence records with respect to grain size trends and facies distribution. This may thus prove useful in identifying transgressive valley incision in pre-Quaternary deposits. Moreover in light of the dichotomy of the timing of valley incision with respect to base level position, maximum flooding surfaces may be more reliable in demarcating sequence boundaries, particularly in monsoonal settings.