No abstract

No abstract

No abstract

The Tsugaru Fault, running in N-S direction, in the mountain ridge of the Tsugaru Peninsula, in the northernmost Honshu Island, cut the thick Neogene sediments deeply. In general the Tsugaru Fault is reverse and about km long at least. The fault plane steeply dips west and the west side of the fault was relatively elevated higher than the east side.We investigated the Neogene mudstone and sandstone along two transect routes, the Ohkawamezawa and Nishimatazawa, across the Tsugaru Fault. Middle to upper Miocene hard shale, the Kodomari Formation, dips eastward in the west side of the fault, and Plio-Pleistocene sandstone, the Kanita Formation, dips westward in the east side. Organic maturity of samples from the Ohkawamezawa, and samples from the Nishimatazawa transect routes was measured on statistical Thermal Alteration Index stTAI and vitrinite reflectance Ro . The stTAI value should increase and the Ro value should decrease toward the Tsugaru Fault in each side of the fault because the burial depth of sediments decreases toward the fault in both sides. Those phenomena and the effect of faulting are actually recognized only in the values of stTAI, not in those of Ro along the Ohkawamezawa route.We employ a simple fault model to calculate the vertical slip, throw of the Tsugaru Fault. Based on the difference in stTAI between both sides of the Tsugaru Fault and geologic characters of the fault observed, we are able to calculate the vertical slip of the fault at m. This estimation is concordant with the previous ones, longer than m evaluated from the geologic viewpoint Mimura, and about m from the viewpoint of gravity anomaly Matsuhashi et al.,. Our results indicate that organic maturity of sedimentary rocks is a useful tool to study faults as well as diagenesis, unconformity and contact metamorphism. AbstractCThe Geological Society of Japan 2006 581

No abstract