Late Pleistocene Emergence of Crystalline Canadian Shield Sources in Sediments of the Northern Gulf of Mexico

Abstract

One of the Quaternary's outstanding puzzles is the cause of the gradual transition from lower amplitude, 41-kyr glacial cycles in benthic δ 18 O records to higher amplitude, 100-kyr glacial cycles between ∼1250 and

The Mid-Pleistocene Climate Transition

“…These glaciological approaches inherit the Milankovitch hypothesis that Northern Hemisphere insolation forcing drives glaciation but provide for the evolution of how that insolation forcing interacts with ice sheets. One of the most intriguing of these is the suggestion that Northern Hemisphere ice sheets were thin but very extensive prior to the MPT, and then they evolved into much higher ice caps into the 100-kyr world (Clark & Pollard 1998, Portier et al 2021, Yehudai et al 2021. This hypothesis originated from the discovery that at least some early Pleistocene glaciations reached the mid-continent of the United States (Balco & Rovey 2010), an observation consistent with evidence for at least five notable meltwater pulses into the Gulf of Mexico from 2550 to 1700 Ma that would testify to the repeated rise and demise of substantial North American ice sheets (Portier et al 2021, Shakun et al 2016.…”

“…One of the most intriguing of these is the suggestion that Northern Hemisphere ice sheets were thin but very extensive prior to the MPT, and then they evolved into much higher ice caps into the 100-kyr world (Clark & Pollard 1998, Portier et al 2021, Yehudai et al 2021. This hypothesis originated from the discovery that at least some early Pleistocene glaciations reached the mid-continent of the United States (Balco & Rovey 2010), an observation consistent with evidence for at least five notable meltwater pulses into the Gulf of Mexico from 2550 to 1700 Ma that would testify to the repeated rise and demise of substantial North American ice sheets (Portier et al 2021, Shakun et al 2016. Because the sizes of the corresponding marine benthic δ 18 O anomalies were much smaller than for the late Pleistocene (Figure 1), the inference is that ice sheets were laterally extensive but volumetrically much smaller than in the late Pleistocene.…”

Synchrotron Microanalytical Characterization and K/Ar Dating of the GL-O-1 Glauconite Reference Material at the Single Pellet Scale and Reassessment of the Age of Visually Mature Pellets

“…GL-O-1 glauconite is a robust reference material for both K and Ar abundances measured in large aliquots (6.56 ± 0.06% K and 1.109 ± 0.011 nmol/g Ar) [2], but questions have been raised about its applicability at the single pellet level [5,7], and further questions have been raised about the accuracy of its estimated age of 95.03 ± 1.11 Ma (1σ) [4,8]. We have been using small, one to ten pellet (30 to 500 µg), samples of GL-O-1 to create Ar concentration calibrations for sediment K/Ar studies over more than 20 years [9][10][11][12][13][14], and we have been very impressed with the reliable reproducibility at the 2% level. Based on this positive assessment, we have been seeking to refine and improve our screening and methodology to be able to extend the application of GL-O-1 as a standard for the dating of individual unknown glauconite pellets.…”