168-4 The Ellsworth-Coats Land (Antarctic) Promontory of Laurentia

Session: Laurentia Without Borders: Pre-Pangea Intercontinental Connections

Presenting Author:

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Abstract:

The Ellsworth Mountains form an isolated range in central West Antarctica. They comprise an almost unbroken succession of Neoproterozoic to Permian sedimentary strata deformed during the latest Paleozoic to earliest Mesozoic Gondwanide orogeny. The resulting fold-thrust belt terminates abruptly at both northern and southern ends of the range. Its allochthonous nature and probable displacement from the Transantarctic margin of the East Antarctic Precambrian craton have been recognized for over fifty years. Restoration of the Gondwanide fold belt from the Sierra de la Ventana of Argentina through the Cape Fold Belt of South Africa and the Falkland/Malvinas Islands indicates the Ellsworth Mountains originally formed a link to the Pensacola Mountains along the Pacific margin of Gondwana, a position supported by paleomagnetic studies. Together with the Mesoproterozoic basement exposed as the Haag Nunataks near the southern margin of the Weddell Sea and the Whitmore Mountains to the southwest, the Ellsworths are part of one of the four crustal blocks that comprise West Antarctica. Restoration of the Gondwanide fold belt places the Ellsworths-Whitmore mountains block on the ‘outboard’ Pacific side of the Coats Land crustal block of the East Antarctic craton, which has been identified as a likely former fragment of Laurentia. The Precambrian basement of the Ellsworth-Whitmore mountains block is indistinguishable from that of southwestern Texas, and the overlying Neoproterozoic-Cambrian strata on both continents reflect contemporaneous two-stage continental rifting and ensuing marine transgression. The detrital zircon record of the older Ellsworths strata shares the most statistical similarity with Cambrian sandstones in Texas, therefore suggesting a likely Laurentian provenance. Overlying Upper Cambrian limestone units on both continents contain trilobites belonging to the Aphelaspid Zone. We propose the former ‘Ellsworth-Coats Land promontory’ separated from Laurentia during the late Cambrian and was subsequently overlain by the Gondwana supercontinental sedimentary cover. This has significant global paleogeographic and paleoenvironmental implications for the Pannotia supercontinent and Cambrian biotic radiation. It means that Pannotia did exist at the end of Precambrian times, and that the early Paleozoic marine transgression may have been driven by the opening of a passage joining the Iapetus and Pacific ocean basins between Laurentia and Gondwana.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5570

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