Applying Cycle-Scaled Magnetostratigraphy for Global Correlation of Selected Major Paleoclimatic Events in the Triassic, Cretaceous and Quaternary

Yang Zhang, Purdue University

Abstract

As climate change became a major international hot topic, scientists look to the geologic past for potential analogues of global warming and cooling events. However, the underlying triggering mechanisms and rates are enigmatic and difficult to unravel, especially when good reference time scale do not exist. Reversals of the Earth’s magnetic field are recorded by preferential orientation of iron oxide grains during their deposition in all types of sediments. When combined with cyclostratigraphy, magnetostratigraphy has proved to be one of the robust ways to build portions of the geologic time scale and to enable global correlation among various settings. For this PhD research projects, Yang Zhang (Y. Z.) utilized the combination of magnetic polarity scales with astronomical-cycle tuning to resolve long-debating time scaling of time intervals where major climate shifts (e.g., major excursions in Earth’s carbon cycle reflected in isotopic anomalies) took place. Other stratigraphical tools such as geochemistry data, radiometric dating, and biostratigraphy help constrain the validity and accuracy of cycle-scaled magnetic polarity scales. The major achievements that have been accomplished during this PhD program include: 1) Successfully constructed the entire Carnian (Late Triassic) polarity time scale. The Upper Carnian portion implies that: (a) the lowermost Upper Carnian is dominated by reversedpolarity magnetozone; (b) The middle two-thirds of the Upper Carnian is a major normalpolarity-dominated magnetozone; and this interval correlates with the basal portion of the Newark magnetic polarity reference series. This enhanced polarity scale is independently supported by results from South China and western Tethys sections, therefore provide great opportunity to correlate the Carnian Pluvial Episode in various depositional settings, plus calibrate other major geologic episodes, like the earliest dinosaur-bearing beds in South America. 2) Magnetostratigraphy of U/Pb-dated boreholes in Svalbard that placed the base M0r (proposed as the base Aptian) at 121.2 ±0.4 Ma, which is about 5 myr younger compared to that in GTS2016. This revised scaling put lots of topics, like the cause and effect between the Ontong Java Plateau and the Oceanic Anoxic Event 1a (OAE1a), the faster spreading and the global highstand during the Cretaceous Normal Super-chron, and the seafloor spreading model from the Middle Jurassic to the Early Cretaceous, etc.

Degree

Ph.D.

Advisors

Granger, Purdue University.

Subject Area

Climate Change|Atmospheric sciences|Electromagnetics|Geology|Physics|Sedimentary Geology

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