Archaeocyathan limestone blocks of likely Antarctic origin in Gondwanan tillite from the Falkland Islands

Abstract

Other qualitative differences are also apparent between the tillites of East and West Falkland, quite apart from the well-defined facies contrast: the lithological and size range of the clasts is much greater in the west than in the east; clasts in the west are generally more rounded than those in the east; in the west there is a much higher proportion of red granite and quartzite, relative to white varieties. Additionally, the apparent concentration of archaeocyathan limestone clasts at a few localities in West Falkland, rather than their being randomly distributed, is a feature that may have broad stratigraphical and palaeogeographical implications. The archaeocyathsArchaeocyaths are extinct organisms with a long history of phylogenetic uncertainty but a current consensus that they were closely related to the sponges (Hill 1972; archaeocyaths then diversified rapidly into hundreds of species that were important contributors to the construction of early marine reefs. Despite their success they were a relatively short-lived group and were extinct before the end of the Cambrian, less than 25 million years after their first appearance. In contrast, other families of sponges that also appeared in the Cambrian are still represented today, over 500 million years later.

New geophysical compilations link crustal block motion to Jurassic extension and strike-slip faulting in the Weddell Sea Rift System of West Antarctica

“…HEW remains consistent with the stratigraphic interpretation of the position of the EWM north of the Pensacola Mountains (Schopf, 1969) and is consistent with mineralogical and paleontological provenance studies suggesting the Ellsworth Mountains sediments were sourced from the Transantarctic region of East Antarctica (Elliot et al, 2016;Stone and Thompson, 2005). The motion of the HEW in this less far travelled model would be consistent with either the proposed two stage, or more complex single stage tectonic models for the evolution of the WSRS magnetic lineations (Figs.…”

“…likely transported from the Transantarctic Mountains/East Antarctica by an extensive Gondwanide ice sheet (Stone and Thompson, 2005).…”

Patagonia: where does it come from?

“…This metaconglomerate contains clasts of the underlying limestones and is petrographically quite similar to the El Jagüelito Formation metaconglomerate (González et al, 2011a). It is evident that the Transantarctic Mountains limestones were the source of limestone blocks and erratics for a very long time, as has been proposed for the fossiliferous Permo-Carboniferous tillites from Antarctica (Debrenne and Kruse, 1986), South Africa (Debrenne, 1975), the Malvinas Islands (Keidel, 1916;Stone and Thomson, 2005), the Sierra de la Ventana tillites (González et al, 2013), as well as for recent moraines (Hill, 1965).…”

Terrane processes at the margins of Gondwana: introduction

“…During the Mesozoic break-up of Gondwana, West Antarctica behaved as several crustal blocks separated by rift and strike-slip deformation zones (Dalziel & Elliot 1982). Stone & Thomson (2005) present fossil evidence that supports rotation of the Falklands microplate during Gondwana break-up and has implications for the extent of the Gondwanide ice sheet. Siddoway et aL (2005) show new evidence for strike-slip movements affecting West Antarctica during the Cretaceous just prior to the rifting-off from Gondwana of New Zealand (Laird & Bradshaw 2004).…”