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

9909528 Hardie中三叠世Latemar石灰岩（意大利）是数百米尺度的浅海沉积旋回的厚层序列，其独特之处在于，迄今为止，它是唯一一个被深入分析米兰科维奇作用力的旋回沉积存款（Hinnov& Golldhammer，1991年）以及辐射测定日期（间接）在同时代盆地沉积物中的火山岩夹层上使用锆石单晶技术（mundil等人，1996年）。 不幸的是，这两种方法应用于Latemar石灰岩的已发表结果存在严重冲突（Brack等人1996; Hardie Hinnov 1997）。 从本质上讲，锆石年代已经被解释为表明Latemar旋回序列是在2-4百万年内沉积的。而旋回地层分析表明，米兰科维奇起源，这意味着沉积在一个约。10-12百万年期 这些相互矛盾的结果提出了一个严重的困境，远远超出了Latemar问题，鉴于事实上，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。 为了解决这个问题，PI建议（1）使用最新的时间序列建模和分析技术重新检查米兰科维奇强迫的Latemar旋回地层学，以及（2）确定火山岩夹层、源熔结凝灰岩和切过Latemar火山岩的Predazzo花岗岩中锆石晶体的U/Pb年龄。 PIS将为锆石定年带来的重要新方法将是使用CL和BSE成像技术（Hanchar米勒，1995）对锆石进行预筛选，并对选定部分的锆石单晶进行微切片定年。 他们希望，这项关于“Latemar争议”的新研究将成为对循环沉积序列进行高分辨率测年的重要测试案例。

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.