4:30 PM - 5:00 PM
[SCG42-04] The roles of rock uplift rate and wave power in promoting or preventing the creation of marine terraces.
★Invited Papers
Keywords:marine terraces, active tectonics, coastal erosion, sea level
Marine terraces are a cornerstone for the study of paleo sea level and crustal deformation. In this presentation, I will first question the supposed close relationship between sea level high stands and marine terraces. Then I will focus on the coastal landscape of Sadogashima (Niigata Prefecture) and Noto Hantō (Ishikawa Prefecture) to assess the distribution of marine terraces under varying rates of rock uplift and varying wave strengths.
Commonly, individual erosive marine terraces are attributed to unique sea-level high stands based on the reasoning that marine platforms could only be significantly widened at the beginning of an interglacial. However, this logic implies that wave erosion is insignificant at other times. We postulate that the erosion potential at a given bedrock elevation datum is proportional to the total duration of sea-level occupation at that datum. The total duration of sea-level occupation depends strongly on rock uplift rate. Certain rock uplift rates may promote the generation and preservation of particular terraces while others prevent them. For example, at rock uplift of ~1.2 mm/yr, the Marine Isotope Stage (MIS) 5e (ca. 120 ka) high stand reoccupies the elevation of the MIS 6d–e mid-stand, favoring creation of a wider terrace than at higher or lower rock uplift rates. Thus, misidentification of terraces can occur if each terrace in a sequence is assumed to form uniquely at successive interglacial high stands and to reflect their relative elevations. Developing a graphical “sea level occupation map” to describe the cumulative effect of wave erosion during the eustatic seesaw allows us to address creation and preservation biases at different rock uplift rates.
While widespread and well-outlined in some coastal settings, marine terraces can be rare or absent from other areas despite the coexistence of the two driving processes. If they do not produce discrete terraces, wave erosion and rock uplift still contribute to shaping the coastal landscape in conjunction with subaerial processes, and their history is somehow encoded in the topography. I will present a preliminary analysis using the “sea level occupation map” and a related hypsometry of real landscapes at Sadogashima and Noto Hantō as well as numerical landscapes from model simulations. At Sadogashima and Noto Hantō, regions of slow rock uplift are preserved and hold terraces where they face weak waves, while faster uplifting coasts generally hold terraces if they face strong waves. These sites, and eventually those along the entire Japanese coastline, can shed light on the fundamental processes and environmental conditions promoting or preventing terrace creation as well as the nature of the signal they record.
Commonly, individual erosive marine terraces are attributed to unique sea-level high stands based on the reasoning that marine platforms could only be significantly widened at the beginning of an interglacial. However, this logic implies that wave erosion is insignificant at other times. We postulate that the erosion potential at a given bedrock elevation datum is proportional to the total duration of sea-level occupation at that datum. The total duration of sea-level occupation depends strongly on rock uplift rate. Certain rock uplift rates may promote the generation and preservation of particular terraces while others prevent them. For example, at rock uplift of ~1.2 mm/yr, the Marine Isotope Stage (MIS) 5e (ca. 120 ka) high stand reoccupies the elevation of the MIS 6d–e mid-stand, favoring creation of a wider terrace than at higher or lower rock uplift rates. Thus, misidentification of terraces can occur if each terrace in a sequence is assumed to form uniquely at successive interglacial high stands and to reflect their relative elevations. Developing a graphical “sea level occupation map” to describe the cumulative effect of wave erosion during the eustatic seesaw allows us to address creation and preservation biases at different rock uplift rates.
While widespread and well-outlined in some coastal settings, marine terraces can be rare or absent from other areas despite the coexistence of the two driving processes. If they do not produce discrete terraces, wave erosion and rock uplift still contribute to shaping the coastal landscape in conjunction with subaerial processes, and their history is somehow encoded in the topography. I will present a preliminary analysis using the “sea level occupation map” and a related hypsometry of real landscapes at Sadogashima and Noto Hantō as well as numerical landscapes from model simulations. At Sadogashima and Noto Hantō, regions of slow rock uplift are preserved and hold terraces where they face weak waves, while faster uplifting coasts generally hold terraces if they face strong waves. These sites, and eventually those along the entire Japanese coastline, can shed light on the fundamental processes and environmental conditions promoting or preventing terrace creation as well as the nature of the signal they record.