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Barry B. Miller Allan F. Schneider Alison J. Smith Donald F. Palmer 《Journal of Paleolimnology》2000,23(2):175-183
Europe Lake occupies a small, closed, basin that would have been an embayment in Lake Michigan during the high water level events in the larger lake. Cores recovered from the lake reveal late Holocene water level fluctuations in the basin that are inferred from changes in taxa and abundance of molluscs, ostracodes, magnetic susceptibility, organic carbon, and oxygen isotopes.Non-glacial, Holocene lacustrine/paludal sedimentation in this portion of the Europe Lake basin started after 6600 RCYBP and was probably initiated by a rise in the water table of the deep bedrock aquifer, during the Nipissing transgression in Lake Michigan. Isotopically light ground water from this source was probably a major contributor during this phase to the negative 18O spikes in Valvata tricarinata and Amnicola limosa.The start of stable lacustrine conditions is marked by maximum diversity of ostracode and mollusc taxa and a shift toward much more positive 18O values. The Europe Lake basin at this time became an embayment of Lake Michigan. This event was probably coeval with the peak of the Nipissing transgression, when the water plane reached an altitude of about 183 m.The isolation of Europe Lake from Lake Michigan started at about 2390 RCYBP and is probably due to a drop in water level in Lake Michigan and/or to isostatic uplift of the Door Peninsula. Since isolation from Lake Michigan, water levels in Europe lake have been controlled primarily by fluctuations in local precipitation, evaporation and ground water discharge. 相似文献
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V. A. Zakharov B. N. Shurygin V. I. Il’ina B. L. Nikitenko 《Stratigraphy and Geological Correlation》2006,14(4):399-417
The biotic turnover in the Pliensbachian-Toarcian transition and changes in assemblages of bivalves, ostracodes, foraminifers, dinocysts, spores, and pollen are described. Only five of 24 bivalve genera and two of four ostracode genera cross the Pliensbachian-Toarcian boundary so that composition of genera and families to be entirely renewed at the base of the Harpoceras falciferum Zone. In the interval of three ammonite zones, diversity of foraminifers is reducing from 27 genera in the Amaltheus margaritatus Zone (upper Pliensbachian) to 17 and then to 15 genera in the Tiltoniceras antiquum (lower Toarcian) and Harpoceras falciferum zones, respectively. Single dinocysts of the Pliensbachian are replaced by their abundant specimens at the base of the Toarcian, and substantial changes in composition of palynological assemblages are simultaneously established. Factors responsible for “mass extinctions” of marine invertebrates are suggested to be the paleogeographic reorganization, anoxic events, eustatic sea-level changes, and climatic fluctuations. The biotic turnover in the Arctic region is interrelated mainly with thermal changes, which caused the southward displacements of taxa distribution areas during a rapid cooling and their gradual return to former habitat areas in the period of warming, rather than with extinction events. 相似文献
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洞庭湖为我国第二大淡水湖,所在区域为研究我国全新世气候演化及全球变化的重要窗口,该区域全新世古气候研究薄弱,未见定量研究。对介形类现生种进行详细生态调查是利用其定量重建古气候的必要前提与基础。以洞庭湖介形类现生种为研究对象,分析其分布与生态特征。该湖介形类包括6属10种,比利时舍氏玻璃介(相似种) Schellencandona cf. belgica、克氏丽星介Cypria kraepelini、布氏土星介Ilyocypris bradyi、豆形豆形玻璃介Fabaeformiscandona fabaeformis、粗糙土星介Ilyocypris salebrosa、喙盲星介(相似种) Typhlocypris cf. rostrata、无偶斗星介Cypridopsis vidua及斗星介属(未定种) Cypridopsis sp.,其中C. sp.包含3个种。这些属种于洞庭湖系首次报道,于湖南省亦是首次。S. cf. belgica与T. cf. rostrata于我国报道均不多见,尤其是后者甚少。S. cf. belgica、I. bradyi及F. fabaeformis为优势种,分布广且丰度高; I. salebrosa分布样点较多,丰度偏低; C. kraepelini、T. cf.rostrata、C. vidua及C. sp.均出现频次不高或很低,只是前二者丰度较高,后二者丰度低。各属种生境参数差别不明显,总范围为水温20.33℃,p H值为7.34～8.60,溶氧量5.23～9.01 mg/L,电导率197～391μS/cm,水深1～8.4 m,主要分布于1～4 m。F. fabaeformis与C. kraepelini分布水深略大于前人认识,这可能与洞庭湖水体流动性较强有关,推测I. salebrosa为一浅水喜暖种。 相似文献