Miocene Phosphogenesis and Depositional History of the Florida Platform: Implications for Changes in the Carbon Isotopic Composition of Seawater

佛罗里达地台的中新世光成作用和沉积历史：对海水碳同位素组成变化的影响

• 批准号: 9005054
• 负责人: John Compton
• 金额: $ 14.86万
• 依托单位: University of South Florida
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1990
• 资助国家: 美国
• 起止时间: 1990-08-15 至 1993-10-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9005054&HistoricalAwards=false
• 关键词: Miocene; Phosphogenesis; Depositional; History; Florida

Previous studies of the Miocene Hawthorn Group of the Florida Platform indicate that phosphogenesis occurred primarily during the early to early middle Miocene. The timing of Phosphogenesis appears to be synchronous with a global positive excursion of the carbon isotopic composition (delta13C) of seawater. Preliminary examination of the Hawthorn in northeastern Florida shows that these sediments are rich in phosphorite, dolomite, silica and other minerals indicative of intense upwelling, but contain little organic carbon or pyrite. Burial of isotopically light carbon by deposition of organic-rich, continental margin sequences in the SE U.S. during the early Miocene likely resulted in a global increase in the delta C of seawater. Multiple reworking and supergene weathering from subaerial exposure after the middle middle Miocene oxidized and removed most of the organic carbon and diagenetic pyrite. Rapid oxidation of the buried organic carbon resulted in the delta C of seawater returning to its pre-excursion value. We will test this hypothesis by determining the mechanism and timing of phosphogenesis, the timing of sediment oxidation, and the relationship of these events on the Florida Platform to global sea-level changes and variations in the delta C and delta O of seawater during the Miocene. The research program relies on integrating the seismic sequence stratigraphy, sediment mineralogy and texture, and elemental and isotopic composition of the phosphorite and associate minerals. The Sr isotope stratigraphy of the Hawthorn sections will be compared to the delta C, delta O, and Sr isotope stratigraphy of the Miocene sediments from the southwest Pacific (DSDP Site 588).

先前对佛罗里达台地中新世山楂群的研究表明，磷发生主要发生在早中新世早期。 光发生的时间似乎与海水碳同位素组成（delta13C）的全球正偏移同步。 对佛罗里达州东北部Hawthorn的初步检查表明，这些沉积物富含磷矿、白云石、二氧化硅和其他表明强烈上升流的矿物，但几乎不含有机碳或黄铁矿。 中新世早期，美国东南部富含有机物的大陆边缘序列沉积而埋藏了同位素轻碳，这可能导致全球海水三角洲 C 值增加。 中新世中期氧化并去除大部分有机碳和成岩黄铁矿后，由于地面暴露而造成的多次改造和表生风化。 埋藏的有机碳的快速氧化导致海水的温差恢复到其偏移前的值。 我们将通过确定磷发生的机制和时间、沉积物氧化的时间以及佛罗里达台地上的这些事件与中新世期间全球海平面变化以及海水δC和δO变化的关系来检验这一假设。 该研究计划依赖于整合地震序列地层学、沉积物矿物学和结构，以及磷矿和伴生矿物的元素和同位素组成。 Hawthorn 剖面的 Sr 同位素地层学将与西南太平洋中新世沉积物的 Delta C、Delta O 和 Sr 同位素地层学进行比较（DSDP 站点 588）。