Sea-level Stage Research Articles

On the Correlation of the Cenozoic Strata Developed in the Bôsô and the Miura Peninsulas, SOUTH Kantô Region, Japan from the Viewpoint of the Characteristic Features of the Molluscan Fosil-coenoses With Reference to Some Fundamental Problems

The thick marine strata of the Cenozoic Erathem are developed extensively in the Boso and the Miura peninsulas, South Kanto Region, Japan. These strata have long been studied by various authors from several points of view.In the present paper, a tentative correlation of these strata is proposed by the writer from the viewpoint of the characteristic features of the molluscan fossil-coenoses, and the geological range of the important species of molluscan fossils found in the Cenozoic strata in the two peninsulas is tabulated according to the writer's opinion.(1) The Cenozoic strata excluding the nonmarine Pleistocene and the whole Holocene strata in the two peninsulas are divided lithologically into five groups in descending order as follows.5. The Narita group 4. The Sagami group 3. The Kazusa group (=the Kurotaki unconformity) 2. The Miura group 1. The Pre-Miura group (including the Mineoka and the Hota groups in the Boso peninsula and the Hayama group in the Miura peninsula)(2) Based on the marine molluscan and foraminiferal fossils as well as the land mammalian fossils, different opinions have hitherto been expressed by many Japanese geologists and paleontologists concerning the geological age and the correlation of the Cenozoic strata in the two peninsulas. However, the biochronologic method as was universally used in the past by many authors is not helpful in the marine Pliocene and Pleistocene strata because no remarkable biochronologic change in the contents of various kinds of fossils is recognized throughout the whole strata. Especially, so far as the marine Pleistocene strata are concerned such a method is not applicable in almost all cases, and it is possible to establish the accurate correlation on the basis of the changes both in sea-level and in thermal condition of sea-water.Here, it is necessary to discriminate the strata deposited in the colder water and lower sea-level stages from those in the warmer water and higher sea-level stages by the employment of the HDM (=Horizontal Distribution Means) and the VDM (=Vertical Distribution Means) characteristic curves.(3) According to the writer's recent studies, the correlation and the geological age of the Cenozoic strata excluding the nonmarine Pleistocene and the whole Holocene strata in the two peninsulas may be considered potentially as shown in Table 1.(4) Abundant molluscan fossils are yielded from the Cenozoic strata in the two peninsulas. Based on the writer's studies, however, the contents of the molluscan fossils change very gradually from the older up to the younger strata. Especially, no remarkable change of the contents of the molluscan fossils is seen throughout the Pliocene and the Pleistocene strata. Differences in the contents of the molluscan fossils found in the respective formations under consideration may be due merely to those in ecological and sedimentological conditions and not to biochronological factors.The geological range of the important species of molluscan fossils found in the Cenozoic strata in the two peninsulas is tabulated as shown in Table 5 on the basis of the present state of the writer's knowledge.

Elephant Teeth from the Atlantic Continental Shelf

Teeth of mastodons and mammoths have been recovered by fishermen from at least 40 sites on the continental shelf as deep as 120 meters. Also present are submerged shorelines, peat deposits, lagoonal shells, anz relict sands. Evidently elephants and other large mammals ranged this region during the glacial stage of low sea level of the last 25,000 years.

Sediments and geomorphology of the continental shelf off southern New England

The sediments and geomorphology of a portion of the northeastern continental shelf of the United States between Hudson Canyon and Georges Bank have been investigated. Wave-cut terraces at 13, 45, 65, and 80 fathoms indicate four former low sea levels, while concentrations of beach ridges around 35 fathoms reveal a fifth. The pre-Holocene drainage pattern, still exposed over part of the area, shows that Block Channel was the main stream of a system which drained most of southern New England. A large delta at the mouth of this channel near the edge of the shelf attests to the volume of sediments transported by the stream. The surface sediments on the western part of the shelf are Late Pleistocene fluvial deposits which were reworked by the Holocene transgression. Overlying these coarse deposits in the central part of the outer shelf is a sandy silt facies which is also relict. The youngest facies, and the only area of present deposition, is in the northeastern part of the shelf where sand which is eroded from Nantucket Shoals is being deposited on the shelf. An eastward directed coastal drift is indicated during certain lower sea level stages.

Coastal Terraces and Rias along the Kesennuma Bay, Miyagi Prefecture

The Kesennuma Bay, which has two branch embayments To-wan (eastern bay) and Sei-wan (western bay), is in the southern part of the Sanriku Rias coast, which is considered to be a submerged marginal area of Kitakami Mountains. It is generally said that terraces develop poorly along the Rias coasts. Along the coast near the Kesennuma Bay, however, terraces and constituting deposits are distributed rather well. The results of the author's study on terraces and relating matters are as follows.1) Coastal terraces are classified into Mitsumine Terrace, Shinjo Terrace, Matsuiwa Terace, Iwatsuki Terrace and Katahama Terrace from the upper to the lower.2) The terrace deposits excepting that of Katahama Terrace consist of gravels which are maturely weathered into Kusari (decayed) Gravel, and silt and sand lenses. Matsuiwa Terrace and Iwatsuki Terrace are composed of fluvial deposits iii the lower part and marine in the upper beds. Uncomformity between the bedrock surfaces and terrace deposits indicates valley forms like a buried valley beneath the alluvial plains.Red weathered crusts and soils are observed on the terraces higher than Katahama Terrace. From the above mentioned facts the author estimated that Matsuiwa Terrace and Iwatsuki Terrace were formed at least during the stages of high sea levels which followed the low sea level stages.3) Katahama Terrace surface is about 6m high above sea level, and a few meters higher than coastal lowland surface.4) Recent drowned valley is shown along the To-wan which is embranced by the Karakuwa Peninsular and the Kesennuma Oshima island (Fig. 6). The embayment of Ria shoreline at the Kesennuma Bay had been formed before these terraces were built. From the distribution of Senganda Formation it is considered that the formation of Ria shoreline at this area is dated back to Plio-Pleistocene.

Terraces and Volcanic Ashes along the Middle and Lower Courses of the Mabechi River

The Mabechi River drains the northwestern part of Iwate Prefecture and the southeastern part of Aomori Prefecture, Northeast Honshu, Japan. This paper describes the terraces and volcanic ash layers distributed along the middle and lower courses of the trunk stream (Fig. 1), and their chronological interrelation (Figs. 2 and 3).The Hachinohe Volcanic Ash covers the surface of the Tamonoki and the older terraces and comprises ash-flow tuff which builds a flat-top topography at the foot of the valley walls. Along the middle stream, the main part of the Fukuoka Terrace consists of this ash-flow tuff. Some features of the ash-flow tuff of the Hachinohe Ash are reported.Decision of the ages of the terraces is based on the radio-carbon date of the natural charcoal from the Hachinohe Ash, 12, 700±270yr. B. P.(GaK-205), and the standard sequence of development of the terraces along the Pacific coast of Japan by Nakagawa (1961b). The Takadate Terrace is dated to the last high sea-level stage of the late Pleistocene and the Nejo and Tamonoki Terraces are dated to have developed during the oscillations of the low sea-level stage of the latest Pleistocene. This latter date corresponds to the Last Glacial stage.

On the Postglacial Sea Level Changes in Japan

Recently, S. Yamanouchi and T. Sato, archaeologists, have proposed an entirely new chronology of the Neolithic age of Japan. In Japan the Neolithic age divided into two times, namely the Jomon and the Yayoi. It has been estimated that the beginning of the Jomon time was older than 9000 years by C14-dating. However, Yamanouchi and Sato have concluded that the beginning of the Jomon time was not so old, but was dated in B.C. 3000's based on a typology of implements. While C14-dating is generally a useful method for the investigations of paleogeographical problems during the Holocene, it is difficult to say that all the results of this dating referred to the former Neolithic absolute chronology of Japan are reasonable, because Japan is in one of the areas observed the low concentration of C14 in the air or the sea water in the world.Now, the author re-investigated the data concerning to the movements of the sea level during the Holocene in northern Japan, which have been published in the Journal of the Faculty of Science, University of Tokyo (Sec. II, Vol. XII, Pt. 3) in 1961. Further, adding some available data to the newly achieved results, the author discussed the problems of Postglacial sea level changes in Japan. According to the former hypothesis, the sea level reached the maximum height during the early Jomon time, and afterwards the regression occurred. However, this hypothesis is not acceptable. The shell bed of a midden in the Tokyo Lowland clarifies that the transgression still continued during the late Jomon time. This cannot be only a local phenomenon.According to the curve of the sea level changes estimated by the author, the highest stage of the sea level was probably dated between B.P.4000 and B.P. 2000 in Japan, and its height was about 5m. The inmost shore-line stage along Japan coasts in the Holocene does not always correspond with the highest level stage. The Postglacial transgression occurred and the rapid rise of the sea level took place. Sea invaded into valleys formed during a sea level falling period. When a sea level came near the maximum, the velocity of rising of the sea level gradually decreased. In large drawned valleys accumulation is active. In such a valley no matter what a transgression continued, actually the progress of the shore line, namely the apparent regression occurred. However, in small valleys or in areas without rivers men could see transgression. consequently, in some places the age of the inmost shore-line stage corresponds with one of the highest level stage, but in many places both ages do not agree to each other. In such a case the former was always older than the latter. The age of the stage of Kurohama, the early Jomon time, has been dated to B.P.5100 by C14-method. If it is correct, the sea level would not have reached the maximum. yet. If the stage of the maximum sea level corresponded with the Kurohama stage, C14-dating would not be correct. In the latter case, the beginnig of the early Jomon time may be at least 1000 years later than the formerly estimated one.Judging from the above-mentioned discussion, it is clear that the former Neolithic absolute chronology of Japan is necessary to be re-investigated.

Sea-level and Altitude of Land Bridges during the Continental Stages of Japan

The fossil record and distribution of the Recent terrestrial fauna indicate that at some time during the Quaternary Japan had a land connection with Asiatic continent. The fossil mammals from the Nagahama Formation of the Boso Peninsula include Stegodon orientalis which is thought to be a warm temperature species from its distribution. This elephant must have migrated to Japan during a warm climate stage and probably of high sea-level. Land connection with the Asiatic continent is expected not only during the low sea-level stage but also during the high sea-level stage of the Early Pleistocene. The Middle and Late Quaternary eustatic oscillations of sea-level based on the terraces developed and distributed along the coast and off shore of Japan are shown in the text-figure, in which the idealized projected profiles of the terraces are in the left and the thickness of the conformable marine Pleistocene formations distributed and developed in the northern part of the Boso Peninsula whose top corresponds with the sea-level in the stage III in the right. The land connection is expected throughout the Middle and Late Quaternary except for stages of III and I, which are preceded by the low sea-levels.The land connection problem is geographical and biological in nature, and diastrophism may be concerned. The geological structure and topography of the Korean Strait and its vicinity suggest some probability of the isolation of Japan from the Asiatic continent due to diastrophism.

Geomorphic History of the Nishi-Mikawa Plain Situated along the Lower Course of the Yahagi River, Aichi Pref. Japan

Rising from the southern part of the Kiso Mountains, Central Japan, the Yahagi River flows southwestward through the narrow valley in the granitic area of Mikawa Plateau, one of the famous elevated peneplains in Japan. In the lower course area, this river flows down along the western foot of Mikawa Plateau, developing the broad lowland which consists of younger Pliocene unconsolidated deposits called Yadagawa Formation. It enters into the Mikawa Bay opening the pacific Ocean. This lowland is named Nishi-Mikawa Plain. The authers surveyed this area in order to make clear the geomorphic history. The main results are as follows: 1) The Nishi-Mikawa Plain is divided into six landform surfaces. They are Fujioka(200-60m in altitude), Miyoshi (130-35), Koromo (130-20), Hekikai (80-5), Koshido (50-35) and the alluvial surfaces. 2) Fujioka Surface is considered to be a depositional surface of Yadagawa Formation, one of the most important Pliocene deposits in Japan. It has the character of lacustrine deposits. Morphologically, Fujioka Surface is classified into two groups. The one is the flat topped hills situated in the northern part, and the other is a low relief hillland in the southwestern part. It is presumed that such a difference is caused by the difference of the lithological composition of Yadagawa Formation. Namely, in the northern part where the gravels prevail, the original flat surface is preserved, while in the southwestern part consisting of sands and silts, the surface has a tendency to erode. 3) Miyoshi surfaceis a high flat topped terrace, and is presumed to be a depositional surface of Miyoshi Formation which was accumulated by the Yahagi River. 4) Koromo Surface is the depositional terrace of Koromo Formation which was transported by the Yahagi. River, too. The northern part of this surface is an elevated fan and the southern part is an elevated delta. 5) Hekikai Surface is also the depositional terrace of Hekikai Formation derived from the Yahagi River Although Hekikai Formation has characteristic features of the fan or flood plain deposits in the north, some features of delta and neritic sediments are seen in the south. 6) While above mentioned surfaces are broadly developed in this region, Koshido Surface is locally distributed only along the Yahagi River. This surface is concluded to be the river terrace. In the lower course area, this terrace surface is buried with the marine deposits of Alluvial age. 7) It is interpreted that Miyoshi, Koromo and Hekikai Surfaces were formed during the stage of successive high sea level of Pleistocene Period, and the altitude of the estimated ancient shore line is about 80m in Koromo Surface, and about 20m in Hekikai Surface. 8) On the contrary, Koshido Surface was formed in the last low sea level stage just before the Alluvial transgression. Explanations of figures, tables and photographs Fig. 1: the contour map of the area studied (contour interval lOm) In this map, the valleys of the width less than 300m are excluded. Fig 2: map of the landform surface classification 1: Fujioka Surface 2: Miyoshi Surface 3: Koromo Surface 4: Hekikai surface 5: Koshido Surface The straight lines show the position of cross-sections in Fig. 4. Fig. 3: facies and thickness of the deposits forming the landform surfaces Figures show the thickness of deposits in meter. 1: sand and gravel 2: clay, silt and sand 3: natural levee and off-shore bar distributed on the Hekikai Surface Fig. 4: cross-sections 1: granitic rocks 2: Yadagawa Formation 3: Miyoshi Formation 4: Koromo Formation. 5: Hekikai Formation 6: Koshido Formation and alluvium Fig. 5: longitudinal profiles 1: Miyoshi Surface 2: Koromo Surface 3: Hekikai Surface 4: Koshido Surface 5: present river floor of the Yahagi River Tab. 1: descrption about the examples of Miyoshi, Koromo, Hekikai and Koshido Formation

Erosion Surfaces and Emerged Beaches in Hong Kong

In the Hong Kong area two high sea-level stages at 15 and 5–6 m P.D.[1][1] are clearly marked. These appear to be the result of eustatic movements. A similar well-marked bench at —11 m P.D. represents a Late Pleistocene low sea level. At least one other period of low sea level, in which base levels were more than 60 m below P.D., occurred. Benches at 22 m, 40 m, and 71 m are found as remnants around most of the coast and are probably marine. Summit leveling at 130 and 230 m is common and may be marine or subaerial. A valley basement now abandoned at 430 m represents an old drainage line lightly incised into a subaerial surface indicated by summit heights of about 460m. [1]: #fn-1

Origin and Development of Texas Shoreline: ABSTRACT

Geological events associated with the late Quaternary have controlled the origin and development of the Texas shoreline. Some features of the shoreline are of late Pleistocene age while others are definitely related to the Recent epoch. During the last Pleistocene glacial stage when sea-level was lowered approximately 450 feet, the coastal Texas streams deeply entrenched their valleys and the Gulf shoreline was probably 50-140 miles seaward of the present shoreline. With melting of the late Pleistocene glaciers and the accompanying rise in sea-level, Texas streams alluviated their entrenched valleys. Sedimentation in these valleys did not keep pace with rising sea-level and consequently the lower parts of the entrenched valleys were drowned to form a series of estuaries. he bay shoreline of Texas originated during this stage. During the standing sea-level stage, which began about 5,000 years ago, the large Texas rivers, such as the Rio Grande, Brazos, and Colorado, filled their former estuaries and constructed broad deltaic plains which protrude into the Gulf. The other smaller Texas rivers which carry smaller quantities of sediments are still in the process of filling their drowned valleys or estuaries. A series of barrier islands were formed along the coast between the Rio Grande and the Colorado-Brazos deltaic plain and east of the Colorado-Brazos deltaic plain, giving rise to the Gulf shoreline along these segments of the coast. The abandoned beach ridges and intervening low swales and mud flats, which are well preserved on these barrier islands, cle rly demonstrate the seaward growth of the islands during the standing sea-level stage. End_of_Article - Last_Page 2519------------

Galveston Barrier Island and Environs: Model for Predicting Reservoir Occurrence and Trend: ABSTRACT

Galveston Island, Bolivar Peninsula (a land-tied island) and associated tidal deltas together comprise a sand-barrier feature separating the Gulf of Mexico from Galveston Bay, East Bay, and West Bay, Texas. This composite sand mass extends parallel with the shoreline from Caplan on the east to San Luis Pass on the west, a distance of 50 miles. The barrier feature is the easternmost part of a line of barriers, which is interrupted at only a few places by river deltas and extends a distance of more than 600 miles along the Texas and Mexican coasts. The sand body below Galveston Island is approximately 30 miles long, 30 feet thick, and averages about 1½ miles wide. It thins to zero near the 30-foot contour, 2 miles seaward of the gulf shore and a few hundred feet landward of the bay shore. Eolian processes increase the thickness of barrier island sand masses along the south Texas coast by as much as 40 feet. Geological processes producing barrier island and other shoreline sand bodies throughout the world during the Recent standing sea-level stage have produced similar sand bodies in standing sea-level stages of the geologic past. It seems logical that lenticular barrier island sands probably form reservoir rocks containing large quantities of hydrocarbons in both structural and stratigraphic traps in many sedimentary basins. Several examples have been described in the literature. Many accumulations of the stratigraphic type remain to be found and there is a real need for criteria for their recognition and for the prediction of their location. The paper summarizes the geologic processes, setting (framework), history, genesis, lithologic character and sequence, directional features, shape, and trend of the Galveston barrier island sand mass and related facies. The model should be of value to a geologist in the exploration for and exploitation of reservoirs of this type. End_of_Article - Last_Page 2519------------