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New Insights into the Stratigraphic Setting of Paleozoic to Miocene Deposits Online Course
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Section: Introductory Chapter: An Introduction to the Stratigraphic Setting of Paleozoic to Miocene Deposits Based on Paleoecology, Facies Analysis, Chemostratigraphy, and Chronostratigraphy - Concepts and Meanings
Lesson: Chronostratigraphy
New Insights into the Stratigraphic Setting of Paleozoic to Miocene Deposits.
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Introduction
This is the introductory lecture of the course “New insights into the stratigraphic setting of Paleozoic to Miocene deposits: case studies from the Persian Gulf, Peninsular Malaysia and south-eastern Pyrenees.” In this lecture, the research themes studied in this course have been introduced referring to the paleoecological and facies analysis techniques and methodologies, pertaining, in particular, an Oligo-Miocene carbonate succession of the Persian Gulf (Asmari Formation), the chemostratigraphy of Paleozoic carbonates of Peninsular Malaysia through the integration of stratigraphic, sedimentologic, and geochemical data, and the chronostratigraphy of a small ice-dammed paleolake in Andorra, applying the FFT (Fast Fourier Transform) analysis, resulting in sixth-order stratigraphic cycles, which have outlined the occurrence of glacially controlled system tracts and unconformities.
The topic of the Asmari Formation and its depositional environments has been deeply studied. Referring to its biostratigraphy, it was earlier outlined in the 1960s based on unpublished reports. The application of isotopic stratigraphy has later proved that the sediments ascribed to the Miocene “Aquitanian” are, in fact, Late Oligocene, Chattian in age. This was proved by the application of Sr-isotope stratigraphy to cored sections from 10 Iranian oil fields and 14 outcrop sections, within the framework of a high resolution sequence stratigraphy study down to fourth order cycles. The Chattian/Aquitanian boundary is marked by a major faunal turnover, with the general extinction of Archaias speciesand Miogypsinoides complanatus. The age interpretation of the early, unpublished zonations has needed a deep revision and the establishment of an updated biozonation. The new zonation and the stratigraphic ranges of selected key species have been presented by Laursen et al., 2009 .
The isotopic stratigraphy based on strontium has constrained the stratigraphic setting of the Asmari Formation. This formation, consisting of approximately 400 m of cyclic platform limestones and dolostones, with subordinate intervals of sandstones and shales, has been studied in the subsurface at several oil fields and in an outcrop section. The methods of Sr-isotope stratigraphy is suitable for dating these strata because of the fast rate of marine strontium ratio during the depositional processes (roughly 32–18 My). The profiles of age against depth in the four areas have shown a decrease from higher accumulation rates in the lower Asmari to lower rates in the middle-upper part of the formation. These changes reflect the dynamics of platform progradation, from early deposition along relatively high accommodation margin to slope settings and then, to conditions of lower accommodation on the shelf top. The ages of the sequence boundaries have been estimated from the age-depth profiles at each locality, providing a framework for stratigraphic correlation. The depositional sequences have an average duration of 1–3 My, whereas the component cycles represent average time intervals of 100–300 ky.
On the other side, the Kinta limestones have been matter of previous studies, mainly referring to the depositional environments. In the Kinta valley, they are composed of medium-to-dark gray, fine-grained, thinly bedded limestones, with preserved bedding planes and slump depositional features. The faunal content is quite scarce, except that some conodont faunas, while a high organic content is suggested from the dark color of the deposits. The sedimentological and facies analysis has suggested the occurrence of low energy, slope environment hosting the deposition of the Kinta limestones. The high organic content coupled with the lacking of benthic fauna has indicated a low-oxygen setting. On the
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