Koichi Hoyanagi

MODELING SHORE-NORMAL LARGE-SCALE COASTAL EVOLUTION

Abstract We present a model for the evolution of the shelf surface in response to marine sedimentary processes. Following morphodynamical theory, the model presupposes a characteristic configuration of the shelf surface, that in profile is a concave-up exponential curve, whose steeper inner limb is the shoreface. The profile is seen as an equilibrium response to the variables of sedimentation. The profile translates landward or seaward as sea level rises or falls, but will do so in an state of dynamic equilibrium with the shape of the profile varying according to changes in: (1) the rate of sea level change, (2) the time-averaged wave and bottom current conditions, (3) the average allochthonous sediment supply rate, and (4) the sediment grain size distribution. The governing equations for the model include an equation for time-averaged cross-shore (diabathic) sediment flux and the sediment continuity equation. p ]Simulations of continental margin profiles show that profile adjustments affect mainly the coefficient of curvature of the profile. An increase in the rate of sea level rise straightens the profile; it decreases the slope of the shoreface, but increases the shelf slope. An increase in sediment input increases profile curvature; the shoreface steepens while the shelf floor flattens. An intensification of hydraulic climate straightens the profile in a manner similar to an increase in the sea level rise rate, while an increase in grain size increases profile curvature as does an increase in sediment input.

Relationships Between Composition of Organic Matter, Depositional Environments, and Sea-Level Changes in Backarc Basins, Central Japan

ABSTRACT Sedimentary organic matter is a potential indicator of paleoenvironments. In this study we examine the relationship among composition of kerogen (insoluble organic matter), sedimentary environments, and sea-level changes in Miocene to Pleistocene sediments of the Niigata and Akita backarc basins, central Japan. Our primary analytical tool is a ternary diagram with apexes consisting of woody-coaly organic matter, herbaceous with pollen and spores, and amorphous organic matter (AOM) with alginite (organic-walled marine microfossils). The composition of kerogen plots into distinct regions on the ternary diagram: fluvial to estuarine, prodeltaic, shelf, slope and basin-floor submarine fans, and distal basin-floor sediments. The fluvial and estuarine sediments have high proportions of woody-coaly and herbaceous organic matter with pollen and spores, and a lesser proportion of AOM + alginite, because pollen and spores were mainly deposited in estuaries. Because abundant coarse-grained, terrigenous organic matter was supplied by delta distributaries, the prodeltaic sediments have high proportions of woody-coaly organic matter. The composition of kerogen in the shelf sediments is similar to the kerogen in slope and basin-floor submarine-fan sediments, as plotted on the ternary diagram. Both kinds of kerogen accumulations have high proportions of woody-coaly organic matter and AOM with alginite and lesser proportions of herbaceous organic matter with pollen and spores. This relationship suggests that turbidity currents supplied the terrigenous sediments. The sediments on the distal basin-floor contain high proportions of AOM. Each pattern in the ternary diagram reflects a difference in hydrodynamic behavior, distance from land, and the supply of terrigenous organic matter. The sub-ternary diagram, which has apexes of WFA (weakly fluorescent amorphous organic matter), NFA (nonfluorescent amorphous organic matter) + FA (fluorescent amorphous organic matter), and alginite, further suggests the origin of AOM. The NFA in shelf sediments and WFA in distal basin-floor sediments are inferred to consist of terrestrial higher plant and marine organic matter, respectively. A 13C value of kerogen rich in NFA (-24.6 and -27.3‰) suggests land plants, whereas kerogen rich in WFA (-20.0 to -23.6‰) suggests marine plankton. These inferences agree with those derived from the sub-ternary diagram. Furthermore, compositional changes of the kerogen in turbidites reflect relative sea-level changes, as seen by shifts in compositions on the ternary diagram. The use of ternary diagrams like those used here is recommended for future studies of kerogen, depositional environment, and sea-level relationship.

Slope-shelf-nearshore depositional sequences with transgressive conglomerate in a Miocene backarc and arc-junction setting, central Japan

Abstract Several third-order slope-shelf-nearshore depositional sequences are found in the Middle to Late Miocene Aoki and Ogawa Formations in the southern part of the Northern Fossa Magna region, central Japan. Each depositional sequence consists of a transgressive systems tract, varying in thickness from several tens of centimetres to about 10 m, a falling stage systems tract several tens of metres in thickness and a highstand systems tract, 20–80 m thick. The highstand systems tract and falling stage systems tract are bounded by the regressive surface of marine erosion. Each depositional sequence mainly consists of coarse-grained sediments. The materials of the transgressive conglomerate beds were derived from the gravelly foreshore and upper shoreface by transgressive shoreface erosion. The thin and conglomeratic transgressive systems tract indicates that these slope-shelf-nearshore sequences were deposited on the steep slope area under a rapid transgression. Therefore, these sequences were formed in response to excess sediment supply and a rapid rise in relative sea-level at an active margin of the backarc side of the arc-trench system.

The sedimentary imprint of Pleistocene glacio-eustasy: Implications for global correlations of seismic sequences

We evaluate lithofacies, chronology, and seismic sequences from the Canterbury Basin, New Zealand passive continental slope (Integrated Ocean Drilling Program [IODP] Expedition 317 Site U1352 and environs) and compare this with slope sequences from the New Jersey passive margin. Our goal is to understand continental slope sedimentation in response to glacio-eustasy and test the concepts of sequence stratigraphy. High-resolution geochemical elemental and lithostratigraphic analyses were calibrated to a chronology constructed from benthic foramininferal oxygen isotopes for the past ~1.8 m.y. We identify lithofacies successions by their unique geochemical and lithologic signature and correlate them with marine isotope stages (MIS) at Milankovitch 100 k.y. (MIS 1–12) and 41 k.y. (MIS 13–63) periods. Eight seismic sequence boundaries (U13–U19) were identified from high-resolution multichannel seismic data, providing a seismic stratigraphic framework. Except for MIS 1–5 and MIS 54–55, there are 2–16 MIS stages and a comparable number of lithofacies contained within each seismic sequence, indicating that it took one to several glacio-eustatic cycles to build each seismic stratigraphic sequence. These findings support prior results obtained by the Ocean Drilling Program (ODP) Leg 174A on the New Jersey continental slope. On both margins, there is a strong correlation between seismic sequences, lithofacies, and MIS, thus linking them to glacio-eustasy. However, the correlation between MIS and seismic sequences is not one-to-one, and Pleistocene seismic sequences on the two margins are not synchronous. Local conditions, including differences in sedimentation rates and creation of accommodation space, strongly influenced sediment preservation at each location, revealing that high-frequency Pleistocene seismic sequences need not correlate globally. INTRODUCTION The impact of past sea-level change has been preserved in the thick sediments along continental margins. Global sea-level (eustatic) change directly affects coastal plain, continental shelf, and continental slope sedimentation through shoreline migration, generating regionally extensive unconformities that bound packets of sediment known as sequences. Claims of a causal link between eustasy and the unconformity-bounded sequences that pervade continental-margin sedimentary deposits have been made since the concept of sequence stratigraphy was first presented in its current form (Mitchum et al., 1977; Vail et al., 1977; Haq et al., 1987; Posamentier et al., 1988), and it is generally agreed that glacio-eustasy is the main driver of sequence formation during the Earth’s most recent Icehouse period ca. 34 Ma to present (Miller et al., 1991, 1996). During the Quaternary (past 2.55 m.y.), Milankovitch orbital cyclicity (eccentricity, obliquity, and precession) has driven large-scale changes in both Antarctic and Northern Hemisphere glaciation that are manifested as large-amplitude glacial-interglacial cycles and attendant sea-level changes (e.g., Hays et al., 1976; Imbrie et al., 1984; Lisiecki and Raymo, 2005). It is commonly accepted that sedimentation at continental margins during the Late to Middle Pleistocene (past 800 k.y.) has been controlled by 100 k.y. cyclicity as indicated by the δ18O proxy for ice volume (Hays et al., 1976; Lisiecki and Raymo, 2005). Under ideal circumstances of sufficient accommodation and sediment supply, depositional sequences on continental margins over the past 800 k.y. would follow a sequence stratigraphic conceptual model reflecting the influence of one 100 k.y. Milankovitch cycle per seismic sequence. Such a correlation is strong for the past 125 k.y. (i.e., the last glacial-interglacial cycle), where seismic sequences on several margins have been successfully correlated to marine δ18O record across marine isotope stages (MIS) 1–5 in both tectonically active and passive margins (e.g., Hernández-Molina et al., 2000; Kolla et al., 2000; Anderson et al., 2004; Çağatay et al., 2009). On margins with very high sedimentation rates, the 100 k.y. cyclicity is punctuated by a 20 k.y. cyclicity (Hernández-Molina et al., 2000; Kolla et al., 2000; Çağatay et al., 2009). However, for sediments older than 125 k.y., such correlations are rare. One example from the Adriatic margin shows a continuous correlation between 100 k.y. Milankovitch cyclicity and seismic sequences for the past ~370 k.y., spanning MIS 1 to the top of MIS 11 (Ridente et al., 2008, 2009). Ultra-high-resolution chirp sonar was used by Ridente et al. (2008, 2009) to define the seismic stratigraphic sequences that were calibrated to a chronology constructed from oxygen isotopes. One-to-one GEOSPHERE GEOSPHERE, v. 14, no. 1 doi:10.1130/GES01569.1 10 figures; 3 tables CORRESPONDENCE: cmchugh@qc.cuny.edu CITATION: McHugh, C.M., Fulthorpe, C.S., Hoyanagi, K., Blum, P., Mountain, G.S., and Miller, K.G., 2018, The sedimentary imprint of Pleistocene glacio-eustasy: Implications for global correlations of seismic se quences: Geosphere, v. 14, no. 1, p. 265– 285, doi:10.1130 /GES01569.1. Received 7 June 2017 Revision received 9 August 2017 Accepted 12 October 2017 Published online 8 December 2017 Science Editor: Raymond M. Russo

Deep-Sea Turbidite Evidence on the Recurrence of Large Earthquakes Off Shakotan Peninsula, Northeastern Japan Sea

Twelve deep-sea turbidites were identified in the Holocene sequence of a core collected from the western foot of the Kaiyo Seamount, located near the fault area of the 1940 Shakotan-oki earthquake, northern Okushiri Ridge, eastern margin of the northern Japan Sea. On the basis of the geological, tectonic, and topographical settings of the site, the turbidites are interpreted as of earthquake origin (seismoturbidite). Age determinations on radiolarian remains in the sediments suggested that the uppermost sediments, younger than 3 ky BP, were lost during the coring. Four clear faunal boundaries, at 4, 6, 8.5, and 10.5 ka, were recognized. The turbidite recurrence interval in the deep-sea basin indicated an average recurrence interval for large earthquakes of 500–1,000 years around the Kaiyo Seamount during the early- to middle Holocene.

Report from “1996 AAPG Annual Meeting (San Diego)”

ア メ リカの 巨大 な学 会 であ るAAPGの1996年 の 例会 が,ア メ リカ合衆国西海岸南端 の都市 カ リフ ォ ルニア州 サ ンデ ィエ ゴで,5月19日 か ら22日 の会期 で開かれた.こ の例会の前 後 には,最 大 一週 間の様 々 な巡検 コースが設定 されてい るの は例年 どお りであ るが,私 たちは 日程 の都合 で19日 か ら22日 までのテ クニカルプログラムを中心 と した例 会にのみ出席 し た.報 告者 の一人保柳 は,東 海岸 ジ ョージア州 で直 前 に開催 された国際潮流堆積物会議 とその後 の巡検 に参加 した後,19日 夕方 にサ ンデ ィエ ゴ入 りした. 一方 ,荒 戸 は17日 にサ ンデ ィエ ゴに入 り,18日 のイ ンターナシ ョナル レセ プシ ョン,19日 午後 のオープ ニ ングセ ッシ ョンとテクニ カル プログ ラム以外 に も 参加 して きた.AAPGは,近 年国際化 が著 しいいが, 日本か らの参加者 は少 な く,石 油関係 の地 質屋 を中 心 に私たちが把握 しただ けで7~8人,そ れに北米 在住 の石油 関係,留 学生 などの 日本人が数名加 わる. 日本人の発表 は,私 たちのポス ター と口頭発表が1 件 づつ,そ れに大阪大学の大学院生酒井哲弥 さんの 口頭発表,地 球科学総合研 究所 の中山一夫 さんのボ ス ターの計4件,そ れ に トロン ト大学 の大学院 に留 学 中の吉 田 しゅ うじさんのMiall氏 な どとの共同の ポス ター発表 があった.