COLLABORATIVE RESEARCH: High Resolution Dating of Sedimentary Successions Using Cyclostratigraphic Methods and Zircon Dating: The Controversial Triassic Latemar Limestone...

合作研究：使用旋回地层学方法和锆石测年对沉积层序进行高分辨率测年：有争议的三叠纪晚岩石灰岩……

• 批准号: 9909528
• 负责人: Lawrence Hardie
• 金额: $ 12.99万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-03-01 至 2003-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9909528&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Resolution; Dating; Sedimentary

9909528HardieThe Middle Triassic Latemar Limestone (Italy), a thick succession of hundreds of meter-scale shallow marine depositional cycles, is unique in that to date it is the only cyclic sedimentary deposit that has been intensively analyzed for Milankovitch forcing (Hinnov & Golldhammer, 1991) as well as radiometrically dated (indirectly) using the zircon single crystal technique on volcanoclastic interbeds in the coeval basinal deposits (mundil et al. 1996). Unfortunately, the published results of the two methods as applied to the Latemar Limestone are in serious conflict (Brack et al. 1996; Hardie & Hinnov 1997). In essence, the zircon dates have been interpreted to indicate that the Latemar cyclic succession was deposited in 2-4 m.y. whereas the cyclostratigraphic analysis indicates a Milankovitch origin which implies deposition over a ca. 10-12 m.y. period. These conflicting results present a serious dilemma that goes well beyond the Latemar problem in view of the fact that both zircon single crystal and cyclostratigraphic methods have come to be widely applied in chronostratigraphic studies. In an effort to resolve the problem, PIs propose to (1) re-examine the Latemar cyclostratigraphy for Milankovitch forcing using the latest time series modelling and analysis techniques, and (2) determine U/Pb ages of zircon crystals from volcanoclastic interbeds, the source ignimbrites, and the Predazzo granite that cuts trhough the Latemar massif. The important new approach PIs will bring to the zircon dating will be pre-screening of the zircons using CL and BSE imaging techniques (Hanchar & Miller, 1995) and the dating of microslices of selected parts of single zircon crystals. It is their hope that this proposed new study of the "Latemar controversy" will function as an important test case for high resolution dating of cyuclic sedimentary successions.

意大利中三叠世拉特玛石灰岩是一个由数百米尺度的浅海沉积旋回组成的厚序列，其独特之处在于，它是迄今为止唯一被深入分析Milankovitch强迫(HInnov&Amp；Golldhamm，1991)的旋回沉积矿床，并(间接)利用同时代盆地沉积中火山碎屑夹层的锆石单晶技术(Mundil等人)进行了年龄测定。1996年)。不幸的是，这两种方法应用于拉特玛石灰岩的公布结果存在严重冲突(Brack等人。1996年；哈迪和欣诺夫1997年)。从本质上讲，锆石年龄被解释为拉特玛旋回序列的沉积时间为2-4年。而旋回地层学分析表明，它来自米兰科维奇，这意味着沉积时间约为10-12英里。句号。鉴于锆石单晶和旋回地层学方法已被广泛应用于年代地层学研究，这些相互矛盾的结果提出了一个严重的两难境地，远远超出了拉特玛问题。为了解决这一问题，PIS建议(1)使用最新的时间序列模拟和分析技术重新检查拉特玛旋回地层学中的米兰科维奇强迫，以及(2)确定火山碎屑夹层、源火成岩和穿过拉特玛地块的Predazzo花岗岩中的锆石晶体的U/Pb年龄。PIS将为锆石测年带来的重要新方法将是使用CL和BSE成像技术对锆石进行预筛选(Hanchar&Amp；Miller，1995)，以及对单颗锆石晶体选定部分的微片进行测年。他们希望，这项新提出的关于“拉特玛争议”的研究将成为高分辨率断代旋回沉积序列的重要测试案例。