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Geology in the Falkland Islands
Abstract
In the next few years we are likely to hear and learn much about the offshore geology of the Falkland Islands as exploratory drilling for hydrocarbons begins. The offshore geology may become better known than the onshore3 of which there has been little detailed investigation in the 200+ years since settlements were established. Here we outline the history of geological investigations and present information gathered during recent fieldwork.
... Adie would have been aware of the somewhat anomalous reputation of Falklands geology. Darwin (1846) had been delighted, but surprised, to find fossils at Port Louis, and not long after, Sharpe and Salter (1856) were equally surprised to discover the same fauna in rocks of equivalent age in South Africa. All of these fossils, of Devonian age and about 400 million years old, formed part of what became known as the widespread 'Malvinokaffric' fauna 1 . ...
Falkland Islands Journal, 11(5), 2021.
Seventy years ago, a young South African geologist, Raymond John Adie, was putting together an outrageous interpretation of the Falkland Islands’ geological history. Adie was newly arrived in England after three years working in the Antarctic with the embryonic Falkland Islands Dependencies Survey (FIDS) but on his way north he had spent time in the Falkland Islands and had taken the opportunity to travel around and look at the geology. When his ideas were published (Adie 1952) they introduced the startling suggestion – for the time – that the Falkland Islands had nothing to do with South American geology but were instead the eastern extension of South Africa’s Cape Fold Belt and Karoo Basin, displaced by continental drift - and rotated by 180° in the process. But this was 1952 and continental drift was mostly rejected as an absurd impossibility. So, what led Adie to his radical proposal, and how has it fared since?
... This region was described in the pioneering work of Darwin (1846), Thomson (1877), andHalle (1912). The Islas Malvinas are two islands, Isla Gran Malvina and Isla Soledad, located within the Argentine continental platform in the Malvinas Plateau, 500 km east of the Patagonian coast ( Fig. 4.2). ...
The reproductive cycle of Galapagos giant tortoises has primarily been studied in captive individuals via noninvasive methodologies, including hormonal studies, radiographs, and ultrasound. During the annual reproductive cycle, mating peaks occur during the hot season months (December–June), followed by nesting during the cool season (June–December). Females dig flask-shaped holes in the soil typically in flat areas at lower elevations where soil suitable for digging accumulates. Females deposit 1–26 eggs and close nests with a mixture of urine, feces, and soil, which then dries into a hard cap, which seals in moisture and provides a protective layer for developing embryos. Rate of development and sex of the embryos depend on the temperature of the nest: when incubation temperatures are high (above 29.5°C) embryos become female and when temperatures are low (below 28°C) male. Eggs hatch after between 90 and 270 days of incubation. Young remain in the nest for up to 1 month until all eggs have hatched and consumed their yolk reserves. Hatchlings then dig an exit hole and emerge from the nest.
... This region was described in the pioneering work of Darwin (1846), Thomson (1877), and Halle (1912). The Islas Malvinas are two islands, Isla Gran Malvina and Isla Soledad, located within the Argentine continental platform in the Malvinas Plateau, 500 km east of the Patagonian coast ( Fig. 4.2). ...
The purpose of this chapter is to summarize the geological-geomorphological regions of Patagonia with a general characterization of the main geomorphological units. A review of studies on geology, stratigraphic, main geologic landmarks, geological history, and geological resources will be briefly described. This review was performed on the base of geological province concept, including a stratigraphic-morphostructural criteria and a description of major endogenous and exogenous processes responsible for the formation of landscape units. In this chapter these geological-geomorphological regions include Chile and Argentina and were grouped as: (1) Coastal Cordillera and Central Valley (Chile), (2) Southern Andes Cordillera, (3) Mountain Sector of the Neuquén Embayment, (4) Northern Patagonian Tablelands, (5) The North Patagonian Broken Foreland and Somún Curá Massif, (6) Central Patagonian Tablelands, (7) Deseado Massif, (8) Southern Patagonian Tableland, and (9) Islas Malvinas Plateau.
... The oldest rock formations found on the Falkland Islands are the Proterozoic granites and gneisses, which outcrop at Cape Meredith on the south-east tip of West Falkland, whereas the rest of the islands are mostly underlain by sedimentary rocks (ALDISS & EDWARDS 1999). ...
An annotated checklist of lichen-forming and lichenicolous fungi reported from the Falkland Islands is presented. A total of 408 taxa are reported: 402 species, and six additional infra-specific taxa (four subspecies, one variety and one forma), in 161 genera. Included in these are 15 species of lichenicolous fungi in 12 different genera. One hundred and fifty taxa are reported for the first time from the archipelago. Six new combinations are proposed: Lambiella andreaeicola (Fryday) Fryday, L. subpsephota (Fryday) Fryday, Notoparmelia kerguelensis (F. Wilson) Fryday, N. lindsayana (Øvstedal & Elix) Fryday, Palicella xantholeuca (Müll.Arg.) Fryday & Orange and Pseudephebe mariensis (Øvstedal, Common & Fryday) Øvstedal & Fryday.
... The Falkland Islands/Las Malvinas, South Georgia, the South Shetland Archipelago scattered in the South Atlantic Ocean between the southernmost tip of the South American Continent (Tierra del Fuego) and the W Antarctic Peninsula have been targeted upon by scientists from different disciplines of geosciences (Casertano, 1963;Greenway, 1972;British Antarctic Survey, 1979;Caminos, 1980;Hervé et al., 1981;Thomson, 1987, Hanson andWilson, 1991;Clark et al., 1995;Aldiss and Edwards, 1999;Baraldo and Rinaldi, 2000;Olivero and Martinioni, 2001;Stone, 2010) (Fig. 1). The geologists cited above prevalently dealt with the endogenous processes controlling the evolution of the complex lithologies, their stratigraphy and last but not least discussed the geodynamic setting and plate assembly of South America, South Africa and Antarctica during the built-up and the breakapart of the supercontinent Gondwana (Mitchell-Thome, 1970;Marshall, 1994;Jacobs et al., 1999;Hillier, 2000a, 2000b;Olivero and Martinioni, 2001;Kusky et al., 2003;Stone et al., 2008Stone et al., , 2009Tankard et al., 2009;Stone, 2010;Richards et al., 2013;Granota and Dyment, 2015;Hole et al., 2015). ...
In the periglacial South Atlantic Ocean five coastal landform series (CLFS): CLFS1 (Falkland Islands / Islas Malvinas), CLFS2 (Tierra del Fuego), CLFS3 (South Georgia + Scotia Ridge), CLFS 4 (South Shetland Archipelago) and CLFS 5 (Antarctic Peninsula) have been established and studied with regard to their geomorphology and sedimentary petrography. Although being several hundreds of kilometer apart from each other the majority of sites belong to the same climate zone, the polar tundra climate excluding the CLFS 1 which is more humid and the CLFS 5 on the opposite side that passes into the polar frost zone. The hydrographic regime is in the majority of cases microtidal, excluding some coastal regions in CLFS 1 and CLFS 5 where micro-mesotidal conditions exist around the volcanic edifices.
The climate variation has an impact on the weathering of the landforms, which abruptly changes from chemical to physical between CLFS 3 and 4, and gradually from CLFS 1 to CLFS 3 (oxidic reducing regime, pH more acidic meteoric fluids). The CLFS 1 to 3 evolved in a geodynamically stable setting attested to by a high landscape maturity, whereas CLFS 4 and 5 are situated in a geodynamically mobile regime leading to structural landforms instead of sculptural ones of lower maturity.
The CLFS1 to CLFS 3 are characterized by landscape types of plains, channels, fjords and bays which incise or truncate highly to partially eroded mountain blocks which were uplifted near the coast and thereby overprint relic landforms such as peneplains and pediments. The three geomorphological processes shaping the area between land and sea are (1) coastal marine – landforms given in brackets (beach, cliffs - beach scarps, dunes plus aeolian sand sheets, fjord remodeled into channels, bays (drowned cirque glaciers), wave-cut platforms, tidal flats (rocky), tombolo), (2) glacial (boulder trains, cirque-tarn-lip, cryopediments (?), glacial-fluvial channels, moraines , outburst valleys and spillways, pattern grounds (plus stone runs),roches moutonnées through- to U-shaped valleys, and (3) mass wasting (rock fall transitional into –slide, talus plus soil creep). While mass wasting is a rather conservative process, the glacial land-forming processes increase in quality and intensity from CLFS 1 to CLFS 3. The coastal marine processes are rather conservative, excluding those processes which interdigitate with glacial marine processes, e.g., evolution of fjords and when strongly controlled by the magmatic and metamorphic lithology. The CLFS 4 and CLFS 5 are magmatic-arc, rift-, and fold belt-related. Both reference sites mark a volcanic landscape arising from the sea, the first one under subaerial, the second one under subglacial conditions. In these modern geodynamic settings structural volcanic landforms (cones, maars, craters, pyroclastic fans of flow and surge deposits, flat-topped volcanic plateaus, tuya) predominate. The coastal marine, glacial and mass wasting induced land form types resemble those of the CLFS 1 to CLFS 3. Among the mass wasting slide and flow deposits are more common near the beach. Among the glacial deposits moraines, arêtes and nunataks are more common in the coastal hinterland. The wave-dominated coastal marine landforms (beach, cliffs-beach scarps, wave cut platforms) become more variegated when the tidal range increases (tidal channel ephemeral stream, tidal flats). There are also mixed types between alluvial-fluvial and glacial marine named embryonic glacial-marine fan deltas.
Based upon the current study an approximation of the relief generations or palaeo-landscapes can be achieve for the coastal region (hinderland + beach) in the S Atlantic Ocean: Peneplanation (relic form) – Oligo-Miocene pedimentation (relic form) – Neogene Glaciation and deglaciation conducive to depositional and erosive sculptural landforms = Volcanic activity conducive to structural landforms –Pleistocene-Holocene Coastal marine and mass wasting processes conducive to depositional and erosive sculptural landforms - Pleistocene-Holocene. By analogy with similar geodynamic landscape types elsewhere the two principal landscapes are denominated as “Meso-Afro-American “ (CLFS 1 to 3) and “Neo-American” (CLFS 4 and 5). These two technical terms are self-explanatory as to the geodynamic parent material and eligible for a maturity-based correlation of landscapes.
The combination of the clast orientation, granulometry, grain morphology and shape in combination with sorting and clast mineralogy (visual lithological inspection X-ray diffraction scanning electron microscope supplemented with WDX/EDX electron microprobe micro-Raman spectrometry) has proved to be a valuable tool to lend support to the genetic interpretation of the existing landform types mentioned above and to bridge the gap between actuogeological processes and ancient equivalent sites as being subjected to an environment or paleogeographic analyses. The poor chemical supergene alteration in the periglacial-coastal study area renders it favorable for the application of these sedimentological and mineralogical methods. In conclusion, this methodological approach is promising for all those climate zones with limited chemical weathering for which the diagrams and tables are designed as reference types such cold as hot dry cold climate zones and mountainous regions. Environments typical of depositional and transport processes driven by the (1) hydraulic and entrainment equivalence, (2) attrition and (3) winnowing are the prime targets for the use of these methods. Even polycyclic reworking processes in coastal landscapes where marine, glacial and gravity driven processes interfere with each other around structural geomorphological landforms or have originated from relic ones may be differentiated from each other.
... The diamictite lithology in the Falkland Islands was first noted and described in the early 1840s by Bartholomew Sulivan whilst in command of the surveying vessels HMS Arrow and HMS Philomel. He passed his observations on to Charles Darwin who included a reference to 'conglomerate' in a footnote to his 1846 paper 'On the Geology of the Falkland Islands', though the glacigenic origin was not appreciated at the time (Darwin 1846). The recognition that the lithology was a glacially-deposited tillite equivalent to similar deposits elsewhere in Gondwana came later, with the work of Halle (1912) and Baker (1924), the latter introducing the stratigraphical name 'Lafonian Tillite'. ...
Beach sands are ideal traps to collect heavy minerals (HM) from different geodynamic settings and mineral deposits. The coastal sediments contain a mixture of HM derived from the submarine shelf and from source rocks in the hinterland. This is true in a transgressive periglacial regime, where drowned valleys and estuaries are instrumental in draining HM to the arenaceous beach sediments from more distal basement lithologies. A scenario like this can be found in the Falkland Islands/Islas Malvinas. The site under study is the missing link between South Africa and South America, the splitting-apart of which is mirrored by the HM distribution predominantly concentrated in the backshore and dune belt along the coast. The HM are subdivided into three HM associations reflecting the geodynamic evolution of the South Atlantic Ocean and of some of the prominent mineral deposits on the Gondwana Continent: (1) Gondwana cratons and Proterozoic orogens, with Cr and BIF deposits (rutile, zircon, ilmenite, tourmaline, garnet, Cr spinel), (2) rift-related and break-apart magmatic lithologies with mantle-derived pipe rocks such as kimberlites (zircon, pyroxene, spinel, Mg ilmenite), (3) Cordillera-type lithologies with polymetallic stratabound deposits (tourmaline, amphibole, chlorite, REE phosphates). The variation of the major HM from the stable craton (Kalahari-Kaapvaal Craton) in the East to the mobile fold belt (Andes) in the West follows the order of stability of HM. In addition to these 3 geodynamic HM groups, sporadic occurrences of HM originating from alteration (leucoxene, chlorite s.s.s. (= solid solution series)) are part of armored relics such as “nigrine” which on transport disintegrated and thereby released these HM. The major ultrastable and stable HM zircon, rutile, tourmaline s.s.s., spinel s.s.s., and garnet s.s.s. are displayed in a synoptical x-y plot showing the mantle and crustal trends of fractionation and formation of cumulates by means of particular mineral associations as well as the chemical composition of their s.s.s. Five different geodynamic-lithological patterns, each represented by a set of type-lithologies are established for the cratonic magmatic-metamorphic lithosphere. Based on the HM, the geodynamic setting under study is dominated by source rocks typical of a primitive, cratonic setting.
The first U-Pb and Hf-Lu isotopic data of detrital zircons from Devonian strata of the Malvinas (Falkland) Islands allow re-evaluation of different hypotheses regarding their location before the breakup of Gondwana. Of the various published hypotheses there are only two that have gained support. Adie's hypothesis involves a rotation of 180 degrees of the islands and a large displacement of Patagonia, independently of South America, whereas Borrello's hypothesis assumes a relative fixed position of the islands with respect to South America over time. The first hypothesis has traditionally been evaluated by highlighting the similarities of the geology of the Malvinas Islands with similar rocks cropping out in South Africa. In this paper we test those hypotheses that led to correlate the islands with the Cape System, based on geological, paleomagnetic and geochronological data. However, new isotopic data compared with contemporaneous Patagonian rocks, together with the present knowledge of offshore features of the Malvinas Plateau, suggest that its correlation with South Africa is not as compelling. Although there is no conclusive evidence, the simplest hypothesis based on the present available datasets, favors a closer relationship with Patagonia. No doubt that more research is needed in order to elucidate the paleogeography of the Malvinas Islands before the opening of the South Atlantic Ocean.
The Western Falkland Islands are characterized by landforms and sediments of Quaternary age originating from the interplay of periglacial and marine processes. These have left their imprints on siliciclastic sediments and subbituminous coal, peatland, and podzolic soil. Our depositional study focuses on interpreting a stratigraphic sequence which contains white quartz sand with an interbedded coal seam by using petrography (coal petrography, carbon isotope analysis, sedimentary petrography, clay mineralogy, granulometric, morphometric studies), and geochemistry. The study of the coal-sand couple sheds some light on two contrasting sedimentary geological settings. Firstly, it broadens the knowledge of the regional geology at the southern tip of South America by examining how coal seams may be emplaced in a periglacial-microtidal environment. Secondly, the study is also relevant for applied geology by investigating how sand is processed in a coal-bearing paralic regime. The coal-sand couple evolved during 6 discrete stages. Stage I: The detrital parent material was derived from the Siluro-Carboniferous Gran Malvina Group. Stage II: From the Oligocene through the late Miocene under a warm tropical climate organic matter was accumulated in a paralic environment giving rise to subbituminous coal. Stage III: During the Pleistocene alternating erosion and deposition in a wave-dominated coastal-marine regime gave rise to the build-up of coal interbedded with sand. The hydrodynamic regime reduced the grain size to the level of medium to fine sand and enhanced its sorting coefficient causing the separation of minerals according to their specific gravity (mechanical processing). Stage IV: The coal seam has been reworked by the last glacial progradation. Stage V: Weathering by wind and waterworn sand grains into semispherical to spherical forms and the content of heavy minerals increased along backshore and in dune belt environments. Stage VI: Organic acids derived from the coal promoted chemical leaching and significantly contributed to the decrease of the labile constituents of arenites (feldspar, carbonate minerals, and calcareous tests of faunal remains). Chemical alteration was grinded to a halt by another sea level rise, which gradually destroyed the coal layer. The depositional environment most effective for the processing of sand is located in the microtidal setting. In the meso- to macrotidal hydrodynamic regime the chemical leaching becomes the only efficacious tool to improve the quality of the footwall rocks. Due to the predominance of argillaceous sediments there, the quality of clay is enhanced and kaolin deposits may come into existence.
The wide range of periglacial environments of the Antarctic, from the wet, mild oceanic sub-Antarctic through to the cold, dry continent, provides not only an extensive modern laboratory, but also one that offers insights into conditions in the Northern Hemisphere at the height of the last glacial, is an analogue for periglacial conditions on other planets, and can be used for monitoring climatic change. Almost the whole known suite of periglacial landforms is present. Recent research directions show strong linkages between the biotic components and the abiotic responses, offering new insights into periglacial synergies and hence landform development. Other new directions are those of using the Antarctic as an analogue for periglacial conditions on Mars, and multinational undertakings monitoring permafrost and active layer changes. During the past three decades there have been a number of reviews of periglacial landforms and processes for both the area as a whole as well as for specific locations or regions. Here information regarding material post-dating the most recent reviews is provided and an attempt is made to highlight new directions and findings. This broad-based review provides a foundation for more detailed accounts on some of the periglacial attributes provided in other papers within these volumes.
The geology of the Falkland Islands
- Greenway M.E.