Records of upwelling, seasonality and growth in stable‐isotope profiles of Pliocene mollusk shells from Florida
Records of upwelling, seasonality and growth in stable‐isotope profiles of Pliocene mollusk shells from Florida
复制标题
佛罗里达州上新世软体动物壳稳定同位素剖面的上升流、季节性和生长记录
DOI：
10.1111/j.1502-3931.1995.tb01593.x
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发表时间：
1995
期刊：
影响因子：
1.5
通讯作者：
W. Allmon
中科院分区：
文献类型：
--
作者：
Douglas S. Jones;W. Allmon
佛罗里达州萨拉索塔附近上新世松树床保存完好的双壳类和腹足类贝壳的氧和碳同位素剖面，提供了这些高密度贝壳床积累的古环境和古气候条件的详细记录，并提供了对贝壳生长速度和寿命的洞察。2单元内的上层(2.5-2.0 Ma)和靠近主壳层顶部的下层(3.5-2.5 Ma)，在两个富含Turritella的层内和周围分析了8种甲壳腹足类。还分析了三个双壳类加上另一个来自较低地平线(单元6/7的中部)的斑腿类标本，这些标本被认为代表了近海、正常海洋条件。所有贝壳的同位素剖面反映了季节性、亚热带到暖温带古环境中贝壳的全年生长。δ18O的周期模式反映了水温的年变化，平均变化范围为15至24摄氏度；最小古季节反差为7至9摄氏度。夏季的古温度与介形虫确定的温度相比更有利，而冬季的温度似乎略低一些。除1个果胶标本外，层位和标本之间的温差都很小。年δ18O循环表明：尖顶斑藻的寿命和生长速度略快于斑斑斑藻，而斑斑斑藻的壳生长速度和增量形成与现代佛罗里达种群相当。在甲壳类和双壳类中，重δ18O和轻δ18C的重合事件表明了季节性上升流的模式。这种凉爽、营养丰富、上涌的水可能是松树化石数量巨大的部分原因。-稳定同位素，上新世，松树床，佛罗里达，上升流，古温度，软体动物，Turritella。
Oxygen and carbon isotopic profiles across the shells of well-preserved bivalves and gastropods from the Pliocene Pinecrest Beds near Sarasota, Florida, provide detailed records of the paleoen-vironmental and paleoclimatic conditions under which these high-density shell beds accumulated, as well as offer insight into shell-growth rates and longevity. Eight turritellid gastropods were analyzed from within and surrounding two Turritella-rich beds, an upper bed within unit 2(2.5-2.0 Ma) and a lower bed situated near the top of the main shell bed, unit 6/7(3.5-2.5 Ma). Three bivalves plus another turritellid specimen from a lower horizon (middle of unit 6/7), considered to represent offshore, normal-marine conditions, were also analyzed. The isotopic profiles of all shells reflect year-round shell growth in a seasonal, subtropical to warm-temperate paleoenvironment. Cyclical patterns in δ18O reflect annual variations in water temperature which on average ranged from 15 to 24dC; minimum paleoseasonality contrasts varied from 7 to 9dC. Summer paleo-temperatures compare favorably with those detemined from ostracodes, whereas winter temperatures appear slightly cooler. Except for one pectinid specimen, temperature differences between horizons and specimens are small. Annual δ18O cycles indicate: Turritella apicalis lived longer and grew slightly faster than Turritella gladeensis; and, shell growth rates and increment formation in Mercenaria campechiensis are comparable to modern Florida populations. Coincident episodes of heavy δ18O and light δ18C in both turritellids and bivalves suggest a pattern of seasonal upwelling. This cool, nutrient-rich, upwelled water may be partially responsible for the great abundance of Pinecrest fossils. □Stable isotopes, Pliocene, Pinecrest Beds, Florida, upwelling, paleotemperature, mollusk, Turritella.