Geology of the Falkland Islands
Evidence from xenoliths suggests that the lithosphere of Deseado Massif in southern Patagonia formed 2100 to 1000 Mya in the Paleo and Mesoproterozoic.
[6] About 290 million years ago, in the Carboniferous period, an ice age engulfed the area as glaciers advanced from the polar region, eroding and transporting rocks.
The breakup of Gondwana in the Mesozoic Era led to the formation of a large number of minor crustal fragments, including the Falkland Islands.
The interior of Gondwana was based on crystalline rocks more than a billion years old; in the Falklands today these are found in the Cape Meredith complex.
The resulting solidified sheets can now be seen in the form of dikes that cut the oldest sedimentary layers, those that lie principally in the southern part of East Falkland and in South Africa.
These layers of sand and mud filled the basin as it sank; as they hardened, they produced the rocks of the sedimentary Lafonia Group of the Falklands.
The oldest rocks in the Falklands are gneiss and granite in the Cape Meredith complex, which radiometric studies place at around 1100 million years old.
On top of the gneiss and granite lie layers of quartzite, sandstone, and shales or mudstone in West Falkland.
Cross-bedding and ripple marks identify the zone where these rocks were deposited as the shallow waters of a delta environment where currents transported submarine sediments.
The hardest quartzites are more resistant and have created a very irregular landscape with steeply inclined rock layers found along the length of the mountain chain on East Falkland from the city of Stanley westward to Wickham Heights.
The effects of the ice age erosion that occurred in the Pleistocene glaciation between 25,000 and 15,000 years ago are visible in the islands.
This unique pattern of erosion is evident in the higher elevations of West Falkland where quartzites of the Port Stephens Formation are exposed at the surface.
Another effect of glaciation can be seen on East Falkland in the basins called glacial cirques that were created on Mount Usborne.
A geologic unit is a volume of rock or ice of identifiable origin and age that is defined by distinctive characteristics.
At present the biostratigraphic information collected is not sufficient to establish a stratigraphical sequence based on palynological and paleontological data.
Towards the end of the post-uplift phase, from the end of the early Albian or Cenomanian to the beginning of the late Paleocene, the North Falkland basin was characterized by the initial establishment of marginal coastal conditions and finally totally marine conditions, as a marine connection with the basin was formed.
