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Resolving the Timing of Events Around the Cretaceous-Paleogene Boundary

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Resolving the Timing of Events Around the Cretaceous-Paleogene Boundary Resolving the timing of events around the Cretaceous-Paleogene Boundary By Courtney Jean Sprain A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Earth and Planetary Science in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Paul R. Renne, Chair Professor Mark A. Richards Professor William A. Clemens Spring 2017 Resolving the timing of events around the Cretaceous-Paleogene Boundary Copyright 2017 by Courtney Jean Sprain Abstract Resolving the timing of events around the Cretaceous-Paleogene Boundary by Courtney Jean Sprain Doctor of Philosophy in Earth and Planetary Science University of California, Berkeley Professor Paul R. Renne, Chair Despite decades of study, the exact cause of the Cretaceous-Paleogene boundary (KPB) mass extinction remains contentious. Hypothesized scenarios center around two main environmental perturbations: voluminous (>106 km3) volcanic eruptions from the Deccan Traps in modern-day India, and the large impact recorded by the Chicxulub crater. The impact hypothesis has gained broad support, bolstered by the discoveries of iridium anomalies, shocked quartz, and spherules at the KPB worldwide, which are contemporaneous with the Chicxulub impact structure. However, evidence for protracted extinctions, particularly in non-marine settings, and paleoenvironmental change associated with climatic swings before the KPB, challenge the notion that the impact was the sole cause of the KPB mass extinction. Despite forty years of study, the relative importance of each of these events is unclear, and one key inhibitor is insufficient resolution of existing geochronology. In this dissertation, I present work developing a high-precision global chronologic framework for the KPB that outlines the temporal sequence of biotic changes (both within the terrestrial and marine realms), climatic changes, and proposed perturbations (i.e. impact, volcanic eruptions) using 40Ar/39Ar geochronology and paleomagnetism. This work is focused on two major areas of study: 1) refining the timing and tempo of terrestrial ecosystem change around the KPB, and 2) calibrating the geomagnetic polarity timescale, and particularly the timing and duration of magnetic polarity chron C29r (the KPB falls about halfway into C29r). First I develop a high-precision chronostratigraphic framework for fluvial sediments within the Hell Creek region, in NE Montana, which is one of the best-studied terrestrial KPB sections worldwide. For this work I dated 15 tephra deposits with ± 30 ka precision using 40Ar/39Ar geochronology, ranging in time from ~300 ka before the KPB to 1 Ma after. By tying these results to paleontological records, this work is able to constrain the timing of terrestrial faunal decline and recovery in addition to calibrating late Cretaceous and early Paleocene North American Land Mammal Ages biostratigraphy. To aid in global correlation, I next sought to calibrate the timing and duration of C29r. However, based on discrepancies noticed between a calculated duration for C29r, from new dates collected as part of this dissertation and previously published magnetostratigraphy for the Hell Creek region, and the duration provided within the Geologic Time Scale 2012, it became 1 clear that reliability of sediments from the Hell Creek as paleomagnetic recorders was suspect. To test this claim, a complete characterization of the rock magnetic properties of sediments from the Hell Creek region was undertaken. To aid characterization, a new test to determine the presence of intermediate composition titanohematite (Fe2-yTiyO3; 0.5 ≤ y ≤ 0.7) was developed. Results from rock magnetic characterization show that sediments from the Hell Creek should be reliable paleomagnetic recorders, so long as care is taken to remove goethite (a secondary mineral that previous magnetostratigraphic studies in the Hell Creek did not remove), and to avoid samples that have been heated above ~200ºC. With the knowledge that sediments from the Hell Creek region are reliable magnetic recorders, I collected 14 new magnetostratigraphic sections, and 18 new high-precision 40Ar/39Ar dates which together provide constraints on the timing and duration of chron C29r, at unprecedented precision. This work enables correlation of our record in the Hell Creek to other KPB records around the globe, in addition to providing a test of the Paleocene astrochronologic timescale. 2 Table of Contents List of Tables ................................................................................................................................ iii List of Figures ............................................................................................................................... iv Acknowledgements ....................................................................................................................... x Chapter 1. Introduction ............................................................................................................... 1 1.1 Impact vs. Volcanism: Brief history and current state of research ....................................... 1 1.2 Developing a global chronostratigraphic framework ........................................................... 4 1.3 Dissertation Outline .............................................................................................................. 5 Chapter 2: High-resolution chronostratigraphy of the terrestrial Cretaceous-Paleogene transition and recovery interval in the Hell Creek region, Montana ....................................... 8 2.1 Introduction ........................................................................................................................... 8 2.2 Western Williston Basin ....................................................................................................... 9 2.3 Sampling ............................................................................................................................. 10 2.4 40Ar/39Ar Geochronology .................................................................................................... 16 2.5 Discussion ........................................................................................................................... 16 2.6 Conclusions ......................................................................................................................... 22 Chapter 3. Importance of titanohematite in detrital remanent magnetizations of strata spanning the Cretaceous-Paleogene boundary, Hell Creek region, Montana ...................... 35 3.1 Introduction ......................................................................................................................... 35 3.2 Magnetic Characteristics of Intermediate Titanohematite .................................................. 36 3.3 Regional Geology ............................................................................................................... 38 3.4 Methods............................................................................................................................... 39 3.5 Results ................................................................................................................................. 42 3.6 Discussion ........................................................................................................................... 45 3.7 Conclusion .......................................................................................................................... 47 Chapter 4. Calibration of Chron 29r: New high-precision geochronologic and paleomagnetic constraints from the Hell Creek region, Montana and their implications for the Cretaceous-Paleogene boundary mass extinction .............................................................. 62 4.1 Introduction ......................................................................................................................... 62 4.2 Geology/Previous magnetostratigraphy .............................................................................. 65 4.3 Methods............................................................................................................................... 68 4.4 Analysis............................................................................................................................... 69 4.5 Section descriptions ............................................................................................................ 71 4.6 Paleomagnetic Results ........................................................................................................ 71 4.7 40Ar/39Ar Results ................................................................................................................. 78 4.8 Pooled Results ..................................................................................................................... 82 4.9 Geomagnetic Polarity Timescale calibration ...................................................................... 83 4.10 Discussion ......................................................................................................................... 85 4.11 Conclusions ....................................................................................................................... 87 Chapter 5. Conclusion .............................................................................................................. 107 i References .................................................................................................................................
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