Bedrock map of Northern and Southern Victoria Land, Antarctica, displaying the distribution of outcrop and placement of the Butcher Ridge Igneous Complex (BRIC) and different localities referred to within the textual content with demonstrated mid to late-Cretaceous alteration ages. Basemap constructed utilizing Quantarctica v3.2 from the Norwegian Polar Institute (Matsuoka, Okay. et al. Quantarctica, an built-in mapping setting for Antarctica, the Southern Ocean, and sub-Antarctic islands. Environmental Modeling and Software 140, 105015 (2021)) with Rock outcrop information from SCAR Antarctic Digital Database (ADD) Version 7.0. Credit: Demian A. Nelson et al, Nature Communications (2022). DOI: 10.1038/s41467-022-32736-9
Let’s faux it is the Late Cretaceous, roughly 66 to 100 million years in the past. We’ve obtained dinosaurs roaming the land and odd-looking early species of birds, though the shark as we all know it’s already swimming within the prehistoric oceans—which cowl 82% of Earth. Redwood timber and different conifers are making their debut, as are roses and flowering crops, and with them come bees, termites and ants. Most of all, it is heat, volcanically energetic and humid all over with nary an ice sheet in sight.
Except, in line with a bunch of scientists from UC Santa Barbara, University of Oregon and University of Manitoba, icy situations did exist within the area of the South Pole.
“And it wasn’t only a single-valley glacier,” mentioned UCSB geologist John Cottle, “it was in all probability a number of glaciers or a big ice sheet.” Contrary to our extensively held image of the Late Cretaceous as “sizzling all over the place,” he mentioned, there’s proof that polar ice existed throughout that interval, even on the top of world greenhouse situations. The geologists’ research is printed within the journal Nature Communications.
A prehistoric puzzle
Fast-forward to immediately. Let’s faux we’re in Antarctica. It’s chilly, it is barren, and we’re standing close to a big grouping of uncovered glassy rock alongside the Transantarctic Mountains, adjoining to the Ross Ice Shelf, referred to as the Butcher Ridge Igneous Complex (BRIC).
“I really heard about these rocks after I was a grad scholar 20 or so years in the past, they usually’re simply actually bizarre,” Cottle mentioned. Remote, even by immediately’s Antarctic exploration requirements, the BRIC is uncommon as a result of the rocks’ composition and formation are uncharacteristic of close by rock formations, with—amongst different issues—massive quantities of glass and layered alteration that signifies important bodily, chemical or environmental occasions that modified their mineral composition.
Cottle obtained the possibility to lastly pattern the BRIC on a current expedition, and within the means of analyzing the way it was shaped, he and his group encountered an “unusually great amount of water.”
“So you’ve got a very sizzling rock that interacts with water, and because it cools, incorporates it into the glass,” he mentioned. “If you take a look at the composition, then you may inform one thing about the place that water got here from. It can exist as hydroxyl, which tells you that it in all probability got here from the magma, or it might be molecular, which suggests it’s in all probability exterior.”
What they had been anticipating to see was that the alteration within the rock was brought on by the water already within the magma because it cooled. What they discovered as a substitute was a file of a local weather course of that was thought to not have existed on the time.
In their spectroscopic evaluation of the samples, the researchers decided that whereas a number of the water certainly originated with magma because it plumed upward from Earth’s inside, because the molten rock cooled into glass simply beneath the Earth’s floor, it additionally included groundwater.
“We decided that many of the water in these rocks is externally derived,” Cottle mentioned. “We then measured the oxygen and hydrogen isotopic composition of the water and it matches very properly to the composition of Antarctic snow and ice.”
To lock of their consequence, Cottle and group additionally carried out argon-argon geochronology so far the rock and its alteration.
“The drawback is, these rocks are Jurassic, so about 183 million years previous,” he mentioned. “So if you measure the alteration, what you do not know is when that occurred.” They had been capable of get well the age of the rock (Jurassic), but additionally discovered a youthful age (Cretaceous). “So when these rocks cooled and had been altered,” he continued, “it additionally reset the argon isotope as properly, and you may match the age of the alteration to the composition of the alteration.”
There are different, related volcanic rocks roughly 700 km north of the BRIC that even have a Cretaceous alteration age, indicating that polar glaciation may need been regionally intensive in Antarctica throughout that point. “What we might love to do is go to different locations in Antarctica and see if we will decide the size of the glaciation, if we get well the identical outcomes that we have already discovered,” he mentioned.
Finding proof of enormous ice sheets courting again to the Cretaceous won’t alter our normal image of a sizzling and humid Earth at the moment, Cottle mentioned, “however we might have to consider the Cretaceous and Antarctica fairly in a different way than we do now.”
Research on this research was additionally carried out by Demian A. Nelson (lead creator) of UCSB, Ilya N. Bindeman at University of Oregon and Alfredo Camacho at University of Manitoba.
Perseverance rover retrieves key rocky clues to Mars’ geologic and water historical past
More info:
Demian A. Nelson et al, Ultra-depleted hydrogen isotopes in hydrated glass file Late Cretaceous glaciation in Antarctica, Nature Communications (2022). DOI: 10.1038/s41467-022-32736-9
Provided by
University of California – Santa Barbara
Citation:
Research group confirms icy situations existed in South Pole area throughout Late Cretaceous interval (2022, September 7)
retrieved 7 September 2022
from https://phys.org/information/2022-09-team-icy-conditions-south-pole.html
This doc is topic to copyright. Apart from any honest dealing for the aim of personal research or analysis, no
half could also be reproduced with out the written permission. The content material is offered for info functions solely.