Showing papers on "Holocene climatic optimum published in 1982"

Late glacial to recent cores from the eastern Mediterranean

Abstract: Variations in the planktonic foraminiferal population in sediment cores from the eastern Mediterranean indicate a slow warming from about 24,000 y BP to the climatic optimum at 4700 y BP; there is evidence of an earlier warm phase in two cores. Globorotalia truncatulinoides and G. pachyderma are not found in sediments younger than 10,400 y BP. Dates are confirmed by 14 C dating at 10,438 and 4722 y BP. G. sacculifer becomes more abundant than G. ruber for a short interval at 1200 y BP. A dark olive green microburrowed horizon in the cores coincident with a reduction in the benthonic foraminferal population between 9300 and 6700 y BP represents the sapropel found in the deeper basins. Planktonic foraminiferal productivity was highest at 9000 and 4700 y BP; benthonic productivity was highest in the late Glacial between 12,000 and 10,000 y BP. 18 O composition of the foraminifera shows a rapid depletion of 18 O from 13,000 to 10,000 y BP, caused by melting ice and temperature increase, indicating the end of glacial conditions. The magnetic fabric of three cores is similar to that of British lake cores and in conjunction with the 14 C dates and foraminiferal changes can be used to date eastern Mediterranean sediments. The overall mineralogy and sedimentation rates in the area are controlled by proximity to Cyprus; part of the fine clay fraction ( μ m) are believed to be derived from the Turkish mainland. A decrease in the relative amount of montmorillonite, which commenced at 12,000 y BP in the deep-water cores, coincides with the introduction of ice melt-water from the Black Sea into the eastern Mediterranean; at 6700 y BP (the end of the sapropel) the amount of montmorillonite increases to that of glacial times.

Diachronic variation in insectivores from Cheek Bend Cave and environmental change in the Midsouth

Abstract: Diachronic variation in insectivore remains from a deeply stratified cave deposit in south- eastern North America is described. The paleobotanical record for the region is congruent with variation in the soricid (shrew) and talpid (mole) faunal assemblages. Both faunal and floral records reflect con- siderable climatic change since the full Wisconsinan in this unglaciated portion of eastern North America. Variations in the insectivore assemblages indicate the presence of a more equable climate during the late Pleistocene. Continental climates ushered in at the end of the Pleistocene resulted in a marked decrease in insectivore diversity. Relative frequency changes in taxa throughout the Holocene reflect the mid- Holocene Climatic Optimum.

Palaeoenvironment of the Holocene deduced from Palaeontological Evidences in Nagoya Harbor, Central Japan

Abstract: To elucidate the changes of the environment such as sedimentary basin, climate, sea-level and vegetation during the Holocene epoch, the core samples obtained from Nagoya harbor and its adjacent area, Yatomi, in the coast of Ise Bay, Central Japan, were analyzed from the viewpoints of molluscan assemblage, foraminiferal and diatom analyses, and palynology. The change of the environment throughout the Holocene epoch is divided into some periods as follows:(1) About 10, 000-8, 500 years ago: In the early age of this period, the sea-level had been about -40 to -45m in the present altitude. Fresh and brackish water diatom assemblage, and Corbicula cf. japonica, living under a brackish water near the mouth of a river, were found from the sandy deposit (MMo). In the late age of this period, the open sea water reached rapidly into the ancient Ise Bay. As Ammonia beccarii was abundant with Pseudononion grateloupi and Elphidium subgranulosum, it is estimated that the bay had been about 10-30m deep. The molluscan assemblage such as Pingicula doliaris and Niotha liversens etc. had lived under an inner bay formed by a muddy bottom. According to the pollen assemblage, Fagus, Pinus, and Lepidobalanus are abundant, and it indicates that the climate had been as the Cool Temperate zone.(2) About 8, 000-2, 500 years ago: The sea had been extended to the inner part of the present Nobi plain. Judging from the abundant benthonic foraminifera such as Pseudononion grateloupi, “Elphidium” somaense, Ammonia beccarii, Elphidium advenum, E. subgranulosum, and Uvigerinella glabra etc., the sea-level in about 7, 500 years ago had been about -30-0m in the present altitude, and the muddy deposit had been sedimented on the bottom of 10-50m deep in the center of the bay. On the other hand, diatom such as Cyclotella striata which lives under a low salinitic water dominated. As Pinus, Abies, Fagus, and Lepidobalanus were abundant around the bay, the climate of that time had been cooler than that of the present-day. After that time, during the about 7, 000-5, 000 years ago, marine water diatoms and the molluscan assemblage as Alvenius ojianus, Venemolpa micra, Raeta pulchella, Theora lubrica, and Ringicula doliaris, wihch have lived in the inner part of a bay or an inlet, increased gradually, and the sea-level reached gradually the higher level. On the land near the bay, the deciduous broad-leaved trees such as Fagus, and boreal conifers such as Abies and Tsuga decreaseed, and instead of them the evergreen broad-leaved trees such as Cyclobalanopsis and Castanopsis increased. The climatic optimum and the highest sea-level appeared in 14C-age of 7, 000-6, 000 years B.P. corresponding to the “Jomonian Transgression”. During the middle age of this period, about 5, 000-4, 000 years ago, in the western part of Nagoya harbor, the upper and middle parts of the Middle mud layer (MM) were sedimented under the high sea-level and the warm climatic condition as the present Warm Temperate zone. According to the diatom analysis, the sea-level reached the highest level during time between about 4, 000-2, 500 years ago. This warm and high sea-level period was followed by a low sea-level age corresponding to the “Yayoian Regression”, and by a slightly cool climate age, a little ice age.(3) The last 2, 500 years: The Upper sand layer (US) was sedimented during this period. From this layer the mollusca such as Meretrix lusoria, Tapes japonica, Umbonium sp., and Proclava kochi living in a sandy bottom of the littoral area is yielded abundantly, and the fresh water diatom increases gradually in frequency upward this layer. Therefore, judging from these results, it is inferred that there was a minor regression or sedimentation by an advancement of delta.