Millennial‐scale stratigraphy of a tide‐dominated incised valley during the last 14 kyr: Spatial and quantitative reconstruction in the Tokyo Lowland, central Japan

Abstract

Spatial and quantitative analysis of infilling processes of the tide-dominated incised valleys beneath the Tokyo Lowland during the last 14 kyr was undertaken by using data from 18 sediment cores, 467 radiocarbon dates and 6100 borehole logs. The post-Last Glacial Maximum valley fills consist of braided river, meandering river, estuary, spit and delta systems in ascending order. The boundary between the estuary and delta systems is regarded as the maximum flooding surface. The maximum flooding surface beneath the Tokyo Lowland is dated at 8 ka in the Arakawa Valley and 7 ka in the Nakagawa Valley. This age difference is due to the migration of the Tone River from the Arakawa Valley to the Nakagawa Valley at 5 ka, and suggests that the widely held view that the global initiation of deltas coincided with the abrupt rise of sea-level at 9 to 8 ka is true only where there has been steady sediment supply from major rivers. The meandering river system is dominated by sheet-like sands that were deposited during lateral migration of channels during the Younger Dryas and isolated vertical sands within muds that reflect vertical aggradation of channels before and after the Younger Dryas. The transition between these channel geometries is controlled by a threshold sea-level rise of 4 to 7 mm yr À1 . Before migration of the Tone River at 5 ka, the tide-dominated bay in the Nakagawa Valley was filled by upward-fining laterally accreting muds. The muds accreted from the margin to the axis of the bay. Such lateral accretion of suspended particles derived from outside the bay has been documented in other tide-dominated coastal environments and is probably common in other similar settings. After the migration of the Tone River, the bay was filled by upward-coarsening deltaic sediments.

Genetic Diversity of Artybash Virus in the Laxmann's Shrew (Sorex caecutiens)

“…That is, based on analysis of the full-length cytochrome b gene, Laxmann's shrews were separated into Hokkaido and Eurasian Continent-Sakhalin-Cheju clusters. Individuals in the latter cluster do not always reflect the geographical proximity of their capture locations, which is consistent with an ancestral isolation of the Hokkaido population, occurring *13,000 years before present (Tanabe et al 2015), and recent rapid range expansion of the modern Eurasian ContinentSakhalin-Cheju population (Ohdachi et al 2003).…”

Early Holocene transgressive palaeogeography in the Po coastal plain (northern Italy)

“…Several worldwide records show evidence of rapid transgression around 11·5 cal kyr bp (Maddox et al ., ; Delgado et al ., ; Milli et al ., ), 9·5 to 9·2 cal kyr bp (Hori et al ., ; Zong et al ., ; Amorosi et al ., ; Tanabe et al ., ), 8·5 to 8·3 cal kyr bp (Yim et al ., ; Troiani et al ., ; Amorosi et al ., ; Boski et al ., ) and 8·0 to 7·3 cal kyr bp (Heap & Nichol, ; Li et al ., ; Abrahim et al ., ; Trog et al ., ; Breda et al ., ), thus supporting the hypothesis of a dominant control of eustasy on parasequence architecture.…”

“…Most of these estuaries were filled during the Holocene and were subsequently buried by highstand deltaic deposits (Amorosi & Milli, 2001;Li et al, 2002). Studies on late Holocene delta evolution generally rely upon large amounts of stratigraphic data, being deltaic sediment either exposed or buried at shallow depths (Somoza et al, 1998;Berendsen & Stouthamer, 2000;Ta et al, 2005;Blum & Roberts, 2012;Tanabe et al, 2015). Conversely, the deeper, early Holocene transgressive stratigraphy has rarely been investigated in detail (Hijma & Cohen, 2011;Tanabe et al, 2015;Milli et al, 2016), and stratigraphic correlations are generally based on relatively poor sedimentological and chronological data sets.…”

“…Studies on late Holocene delta evolution generally rely upon large amounts of stratigraphic data, being deltaic sediment either exposed or buried at shallow depths (Somoza et al, 1998;Berendsen & Stouthamer, 2000;Ta et al, 2005;Blum & Roberts, 2012;Tanabe et al, 2015). Conversely, the deeper, early Holocene transgressive stratigraphy has rarely been investigated in detail (Hijma & Cohen, 2011;Tanabe et al, 2015;Milli et al, 2016), and stratigraphic correlations are generally based on relatively poor sedimentological and chronological data sets. This work investigated the Late Pleistocene-early Holocene stratigraphy of a 1200 km 2 area of the Po coastal plain, correlating 14 newly drilled boreholes, 28 published core descriptions and more than 300 piezocone tests (CPTUs), chronologically constrained with 137 radiocarbon dates; sedimentology, fossil content, geochemistry, stratigraphic evolution and areal distribution of transgressive deposits beneath the Po Plain lowlands were documented.…”

Sedimentological and ichnological implications of rapid Holocene flooding of a gently sloping mud‐dominated incised valley – an example from the Red River (Gulf of Tonkin)

“…Cores were mainly used to calibrate seismic records, while detailed sedimentological studies are less numerous (e.g. Tanabe et al ., ). Mud‐dominated fill of valleys incised in front of large modern rivers carrying a high amount of suspended load has not been studied often (e.g.…”