Inner shelf to shoreface depositional sequence in the Sendai coastal prism, Pacific coast of northeastern Japan: spatial and temporal growth patterns in relation to Holocene relative sea-level change

摘要

Temporal and spatial growth patterns of the Holocene wave-dominated inner shelf to shoreface sequence in the Sendai coastal plain, Pacific coast of northeastern Japan are detailed in relation to high resolution AMS ~(14)C data. The sequence, deposited during about 10,000 years of rising to stable relative sea level, is a 22-26 m thick, tripartite inner-shelf to shoreface unit that overlies a transgressive ravinement surface. It is composed successively of laminated fine sand (Facies B), alternating mud and laminated very fine sand (Facies C), and burrowed/laminated fine to coarse sand (Facies D). Facies B consists of transgressive ravinement deposits formed during transgression in a water depth of 12-18 m at the drill sites. Facies C is inner-shelf storm deposits deposited during continued sea-level rise to highstand. Facies D is regressive highstand shoreface deposits. Isochrons show highstand deposits were formed by seaward progradation of the inner shelf to shoreface system. The stacking of deposits during rising sea level was mainly aggradational though there was probably accompanying progradation in the innermost shelf. The significant shelfal aggradation was probably because of an abundant mud supply from coastal rivers during gradual rise of relative sea level.