Falkland Basin Research Articles

Early Cretaceous non‐marine Ostracoda from theNorthFalklandBasin,SouthAtlantic

AbstractTwenty‐seven species of well‐preserved and abundant Early Cretaceous non‐marine ostracod crustaceans were recovered from the North Falkland Basin. The assemblage is unusually diverse for a non‐marine palaeoenvironment and is sourced from cuttings samples collected during 2011 drilling of wells by Desire and Rockhopper Exploration, in the northern and southern areas of the basin. Ostracoda are entirely undocumented in published accounts from this basin, and all but one species appear to be new to science. For the new taxa, one new family (Alloiocyprideidae; type genusHourcqia) is proposed and includesHourcqia woodisp. nov. Four new genera are erected:Falklandicyprisgen. nov.; type speciesF. petrasaltatasp. nov.,Gangamoncytheregen. nov.; type speciesG. colinisp. nov.,Paraplesiocyprideagen. nov.; type speciesP. alloiossp. nov., andMusacchiocytheregen nov.; type speciesM. sarunata(Musacchio,). Nine other species are described as new and areFalklandicypris desiderata,Clinocypris epacrus,Cypria poietes,Ilhasina? leiodermatus,Looneyellopsis tuberculatus,Theriosynoecum petasmathylacus,Theriosynoecum ballentae,Timiriasevia fluitans,andVecticypris samesi. The remainder are left in open nomenclature due to paucity of material. The ostracod assemblage is largely restricted to the southern part of the basin (wells 25/5‐1 and 26/6‐1). In the northern part of the basin only four species, dominated byVecticypris samesi, are present and with one possible exception are restricted there. There appears to have been little or no interchange of species suggesting that a barrier probably existed between the northern and southern regions. The more diverse southern assemblage indicates that more favourable conditions existed to the south. Stratigraphically, a distinct change in faunal composition recorded in both southern wells is likely to be an isochronous event correlatable across the southern area, and of an age no younger than Hauterivian.

The Falkland Basins: new structural model and hydrocarbon bearing prospects (by remote sensing and geoelectric data)

New results of geoelectric measurements were obtained during the season works of 17 Ukrainian Antarctic Expedition (XVII UAE, 2012). New data on the deep structure of the tectonic zone between the Falkland Islands and the South Shetland Islands make it possible to estimate the probable nature of geodynamic processes in this region. Deep geoelectric boundaries position and nature of their contacts near the South Shetland Islands and the Falkland Islands show a fundamentally different distribution of crustal and mantle layers in the Strait structures with continental and oceanic rock complexes. Some anomalous zones of “hydrocarbon deposit” type were detected in the South Falkland Basin shelf by the special technology of satellite data processing and interpretation using. The "deposit" type anomalies were mapped by FSPEF survey and anomalous polarized layers of "hydrocarbon deposit" type were studied by VERS sounding in the South Falkland Basin. These results are new and additional to oil and gas potential data for the South Falkland Basin shelf zone.

MESOZOIC MAGMATISM IN THE FALKLAND ISLANDS (SOUTH ATLANTIC) AND THEIR OFFSHORE SEDIMENTARY BASINS

Recent mineral and hydrocarbons exploration in and around the Falkland Islands has provided data that allows correlation of the onshore and offshore histories of magmatism. New Ar‐Ar age dating of onshore dykes in East Falkland has extended their Cretaceous age range back to ca. 135 Ma (Valanginian – Hauterivian) from the previously reported age of ca. 121 Ma (Aptian). Widespread onshore, ca.188–178 Ma, Jurassic dykes are generally considered a part of the regional Karoo‐Ferrar magmatism linked to the initial break‐up of Gondwana, but we relate the Early Cretaceous dykes, with their characteristic north‐south orientation, to extension of the Falklands Plateau during initiation of spreading in the South Atlantic Ocean. The onshore dykes demonstrate east‐west Early Cretaceous extension, whilst to the north of the archipelago the offshore North Falklands Basin extended between north‐south boundary fault systems from the Late Jurassic onwards. Intrusion of Valanginian – Hauterivian dykes onshore was penecontemporaneous with the intrusion of sills and the extrusion of lavas in the Falkland Plateau Basin. This magmatism, more extensive than previously supposed, may be linked to regional uplift associated with initial opening of the South Atlantic Ocean. The uplift can be demonstrated from seismic data and DSDP boreholes to have occurred during the Berriasian – Hauterivian interval. The thermally‐driven uplift of the platform region played a crucial role in elevating potential sediment source areas and providing the large volumes of sand that were shed intermittently into the surrounding basins from the Valanginian to the Aptian or Albian.

The structure of the Falkland Basin’s lithosphere

The peculiarities of the crustal structure within the Falkland Basin have been discussed. Maps of the free-air and Bouguer (2.3 g/cm3) gravity anomalies and their transforms have been made. The complex analysis of the anomalous gravity field has allowed us to confirm the continental origin of the crust. The zoning of the crust has been performed. The crust is thinned and is enriched in basic and ultrabasic intrusions. A map demonstrating the distribution of the faults within the studied water area has been made. A conclusion has been reached about the leading role played by tension processes throughout the evolution of the crust within the studied water area.

Peculiarities of the Earth’s crust sedimentary layer structure in the Falkland Basin

An electronic databank including the results of seismic investigations and schemes of the sediment thickness’s distribution patterns was built up for two seismostratigraphic complexes in the Falkland Basin. The interface’s border was dated, and the sedimentation rates were estimated for each complex. An integrated map of the cumulative thickness of the deposits and sedimentation rates was developed. The lowest limits of the parameters of the sedimentation process were characterized for the sedimentary layers affected by compaction and erosion.

Deepwater Exmouth Plateau, North Carnarvon Basin: preliminary investigations into ridge and furrow features

Numerous fields of long, shallow subsurface linear ridge and furrow features were mapped during the interpretation of a 3D seismic dataset covering Hess Exploration Australia Pty Ltd’s WA–390–P deepwater Exmouth Plateau permit. These kilometre scale features are often slope parallel and have separations of between 100 to 400 metres between ridge crests. Heights range from the limit of seismic resolution up to approximately nine metres. Similar linear shallow subsurface features have been interpreted in the North Falkland Basin in Desire Petroleum’s Tranches C and D permits. Initial investigations suggest that these features appear similar to the Holocene and older mega furrows/palaeo-mega furrows identified along the lower slope/rise in the Gulf of Mexico, most notably along the base of the Sigsbee Escarpment, and along other continental slope/rise settings. Evidence of seabed and shallow sub-seabed sediment instability in the form of slumps and slides together with the effects of shallow sediment deformation and dewatering are also visible across the WA-390-P area. Ridge and furrow features from the deepwater Exmouth Plateau area are described in detail alongside examples from the North Falkland Basin. It is suggested that interaction between gravity driven downslope processes, sediment dewatering and alongslope sedimentary processes could be a possible mechanism of formation for these features. Horizontal and vertical delineation of these features can contribute towards regional understanding of subsurface sediment instability.

Rotation of the Falklands microplate reassessed after recognition of discrete Jurassic and Cretaceous dyke swarms

ABSTRACT Recently acquired aeromagnetic data for the Falkland Islands have shown that previous interpretations of the dolerite dyke swarms are inadequate. In particular, most of the dykes previously described from West Falkland as forming a ‘north–south’ swarm of Jurassic age are associated with a set of NE–SW linear magnetic anomalies that are entirely separate from another set of truly N–S anomalies. Very few dykes had been previously reported from East Falkland, but the aeromagnetic survey demonstrates clearly that dykes of both the NE–SW and the N–S swarms are present. Ar–Ar age dating of East Falkland dykes has confirmed the Jurassic age of the NE–SW dykes but has established an early Cretaceous age for the N–S dyke swarm. The Jurassic dykes are generally considered a part of the regional Karoo–Ferrar magmatism linked to the initial break-up of Gondwana. We consider the Cretaceous dykes to be associated with the later opening of the North Falklands Basin during the early development of the South Atlantic Ocean. The Jurassic and Cretaceous dykes must respectively pre-date and post-date the microplate rotation envisaged in most models for the Falklands break-out from Gondwana. The shapes of the aeromagnetic anomalies associated with dykes from each of the swarms support the hypothesis that the early Jurassic dykes have experienced a pre-Cretaceous, clockwise microplate rotation of about 120°.

Derisking exploration prospects using integrated seismic and electromagnetic data—a Falkland Islands case study

The British Geological Survey has concluded that the North Falkland Basin contains the second richest documented source rock in the world. They predict that as much as 100 billion barrels of oil have been expelled, much of which could still be trapped beneath the regional seal (Richards and Hillier, 2000). Despite this encouraging hypothesis, during the 50-year exploration history of the area, only six wells have been drilled. These all lie in a small area, and to date there has been no commercial production, although live oil has been recovered to the surface.

EXPLORING FOR FAN AND DELTA SANDSTONES IN THE OFFSHORE FALKLANDS BASINS

Four basins surround the Falkland Islands, but only the North Falkland Basin has been drilled; six wells were drilled there in 1998. Although all six wells encountered good quality sandstones, none of them targeted the basin margins, on what are now thought to be the optimum migration pathways associated with the basin’s thick lacustrine source rocks. Subsequently, a 3D seismic survey acquired in 2004 was designed to identify potential basin-margin -derived sandstones entering the basin along transfer zones. From this survey, a number of basin-margin -attached fans have been identified; these prograded into lacustrine waters of varying depths. These Early Cretaceous alluvial/fan delta/deep-lacustrine fan systems are interpreted to provide excellent potential reservoir facies as they are intimately associated with thick, mature source rocks. They will provide the focus for the next planned phase of exploration in the North Falkland Basin. A phase of drilling is also planned for the basins to the south of the Islands, where large deltaic and fan systems, slightly younger than those imaged in the North Falkland Basin, are seen on seismic to prograde from the same Palaeozoic hinterland that produced the older, North Falkland Basin fans. This paper attempts to show how sedimentary models derived from targeted seismic programmes following initial exploration can be utilised to plan and improve new drilling campaigns in a frontier basin. It presents an analysis of sediment dispersal patterns in basins of marine and lacustrine origin linked to a single hinterland area, and highlights the nature of the relationship between relay ramp/transfer zone development and sediment dispersal patterns in the subsurface.

Anatomy and formation of oblique continental collision: South Falkland basin

The South Falkland basin is a partially filled Cenozoic foreland basin located south of the Falkland Plateau. It was formed by flexure of this southern edge of the South American plate when the load represented by Burdwood Bank collided. This continental fragment belongs to the predominantly oceanic Scotia plate. Flexure probably started in early Cenozoic times and has continued to the present day. The whole region is submarine and so the detailed stratigraphy and structure of the basin has been well imaged by seismic reflection profiling. The clarity of this imagery has made analysis of structures within the collision zone possible. The plate boundary itself is an active oblique thrust fault which has controlled the growth of a frontal fold. There is evidence for older phases of thrusting and folding further south. Within and beneath the sediments which blanket the flexed South American plate, normal faulting occurs on a variety of scales. Episodes of stratigraphic growth associated with the largest of these faults demonstrates that they were active during flexural bending. We have modeled the development of the South Falkland basin using two different approaches, both of which are based upon the simplest elastic model. Inverse modeling of free‐air gravity and bathymetric profiles suggest that the elastic thickness of the loaded crust is 5–20 km. A complementary approach based upon the spectral analysis of free‐air gravity and bathymetry shows that the elastic thickness is 15 ± 5 km. Both techniques indicate that the flexed continental lithosphere is weak, a conclusion supported by the presence of normal faults within the flexed plate. A small increase in elastic thickness from west to east appears consistent with a change in the density and penetration of normal faulting.

Controls on the structural architecture and sedimentary character of syn-rift sequences, North Falkland Basin, South Atlantic

The Falkland Islands lie in a critical location for our understanding of Gondwana supercontinent break-up. Subsurface data obtained during recent exploration activity provide important new insights into the structure and stratigraphy of the North Falkland Basin's Late Jurassic syn-rift fill history. Results of seismic interpretation indicate that deposition was largely controlled by prominent planar normal faults, which divide the basin into a series of north-south trending half-grabens and minor grabens. Well data (in the form of exploration wireline logs, cores, petrographic thin sections, major and trace element analyses) indicate that their syn-rift fill was dominated by abundant volcaniclastic sediment supplied through debris flows, hyperconcentrated flows and pyroclastic ash-fall. The geochemical affinity of the volcanic sedimentary components shows a direct link to the widespread, Middle Jurassic to Early Cretaceous, silicic Chon Aike Large Igneous Province, in southern South America and Antarctica. Diagenesis has obscured provenance information and severely reduced porosity within the syn-rift sediments, causing them to have poor reservoir potential. The results enable a radically new interpretation of this key period in the North Falkland Basin's evolution, which helps modify and unify previously disparate views. It is now suggested that basin development was the direct result of the Chon Aike back-arc stretching, influenced in part by the underlying Palaeozoic basement trends. This was followed by Cretaceous-Recent post-rift thermal subsidence of the basin, which was only arrested by local structural inversion related to Atlantic opening. Consequently, it is thought that the extension that created the North Falkland Basin was independent of both Early–Middle Jurassic rotation of the Falkland Islands microplate and the evolution of the South Atlantic Ocean in the Cretaceous and Cenozoic.

An overview of the oceanography and meteorology of the Falkland Islands

1.This paper describes an overview of the oceanography and meteorology of the Patagonian Shelf and Falkland Islands, derived from reference material and a 16 month measurement program carried out on behalf of the Falklands Operators Sharing Agreement (FOSA) between June 1997 and October 1998. It was not intended that the referenced information in this presentation be exhaustive, the bias has been placed on describing the measurement survey. 2.Due to commercial confidentiality, presentations of data measured during the survey have been limited to time series and statistics. However, the confidentiality of the data does not necessarily preclude use of the data for future research purposes. 3.The analysis of current, tide, wave, wind and meteorological data is described and the nature of mechanisms driving the current and wave regime are suggested. 4.Offshore oceanographic measurements were carried out at three locations prior to a drilling programme by the semi-submersible drilling rig Borgny Dolphin and on board whilst drilling. Meteorological measurements were performed at two locations on the Islands and on the Borgny Dolphin. Drifting buoys were deployed and conductivity, temperature and depth (CTD) measurements were carried out to determine the position and intra-annual variation of the Falklands Current in the North Falklands Basin. 5.The primary oceanographic current flow features of this area are the Brazil and Falklands Currents, which meet at a confluence off the coasts of Argentina and Uruguay. The position of the front varies between approximately 30 and 40°S, depending on changes in the relative strength of the two current systems. Current flows are stronger on the slope than on the Continental Shelf and are less tidally dominated. Although it is thought that the FOSA mooring locations were influenced by the margins of the Falklands Current, stronger flows have been reported to the north of the measurement location. Typical maximum recorded near-surface currents reached 0.8 ms−1, with near-bed maxima reaching 0.55 ms−1. 6.The wave climate was primarily driven by locally derived storms, resulting in events of short duration. Typical maximum significant wave heights of 8.9 and 9.4 m were recorded to the north and south of the Islands, respectively. Copyright © 2002 John Wiley & Sons, Ltd.

Overview of petroleum geology, oil exploration and associated environmental protection around the Falkland Islands

1. The Falkland Islands offshore exploration area contains several Mesozoic basins with the potential for oil development. Exploration of all of these basins is at a very early stage. 2. The only area to have undergone exploratory drilling so far is the North Falkland Basin, where six wells were drilled in 1998. These wells proved the presence of a rich organic source-rock, which has probably generated significant quantities of oil. However, all six wells targeted a limited number of exploration concepts, and none found commercial quantities of hydrocarbons. Post-drilling analysis of the well data suggests that commercial quantities of oil may be found in other parts of the basin. 3. The exploration to date has been conducted in tandem with an extensive and detailed environmental assessment of the region, funded largely by the oil companies and the Falkland Islands Government. 4. The natural environment of the Falklands is important as a resource as well as providing an unspoilt habitat. Detailed legislation and planning controls were put in place before exploration started in order to protect the environment. Copyright © 2002 NERC

An overview of the oceanography and meteorology of the Falkland Islands

1. This paper describes an overview of the oceanography and meteorology of the Patagonian Shelf and Falkland Islands, derived from reference material and a 16 month measurement program carried out on behalf of the Falklands Operators Sharing Agreement (FOSA) between June 1997 and October 1998. It was not intended that the referenced information in this presentation be exhaustive, the bias has been placed on describing the measurement survey. 2. Due to commercial confidentiality, presentations of data measured during the survey have been limited to time series and statistics. However, the confidentiality of the data does not necessarily preclude use of the data for future research purposes. 3. The analysis of current, tide, wave, wind and meteorological data is described and the nature of mechanisms driving the current and wave regime are suggested. 4. Offshore oceanographic measurements were carried out at three locations prior to a drilling programme by the semi-submersible drilling rig Borgny Dolphin and on board whilst drilling. Meteorological measurements were performed at two locations on the Islands and on the Borgny Dolphin. Drifting buoys were deployed and conductivity, temperature and depth (CTD) measurements were carried out to determine the position and intra-annual variation of the Falklands Current in the North Falklands Basin. 5. The primary oceanographic current flow features of this area are the Brazil and Falklands Currents, which meet at a confluence off the coasts of Argentina and Uruguay. The position of the front varies between approximately 30 and 40°S, depending on changes in the relative strength of the two current systems. Current flows are stronger on the slope than on the Continental Shelf and are less tidally dominated. Although it is thought that the FOSA mooring locations were influenced by the margins of the Falklands Current, stronger flows have been reported to the north of the measurement location. Typical maximum recorded near-surface currents reached 0.8 ms−1, with near-bed maxima reaching 0.55 ms−1. 6. The wave climate was primarily driven by locally derived storms, resulting in events of short duration. Typical maximum significant wave heights of 8.9 and 9.4 m were recorded to the north and south of the Islands, respectively. Copyright © 2002 John Wiley & Sons, Ltd.

Modelling the South West Atlantic

1. This brief review paper of modelling developments in the SW Atlantic, presents material generated by a barotropic model of the whole continental shelf and shelf edge, which constitute a distinct biogeochemical province defined by its fundamental oceanographic processes and their implications to the regional wildlife. 2. The basic circulation components solved by the model include the Patagonian shelf tidal regime, the Falkland–Malvinas Current and wind-driven currents and surges. 3. Output from the model has already been used as the hydrodynamic base of an oil spill model, which was part of the Falkland Islands contingency plans in the North Falkland Basin during a recent oil exploration campaign. As part of the continuing evolution of the model, ongoing developments aiming at simulating observed baroclinic processes by assimilating measurements are outlined. Copyright © 2002 John Wiley & Sons, Ltd.

ABSTRACT: Controls on Conjugate Passive Margin Evolution : Insights from Seismic Stratigraphic Studies in the North Falklands Basin and South African Basins

ABSTRACT: Controls on Conjugate Passive Margin Evolution : Insights from Seismic Stratigraphic Studies in the North Falklands Basin and South African Basins

ABSTRACT: Controls on the Structural and Stratigraphic Architecture of Syn-Rift Sequences, North Falkland Basin, South Atlantic

ABSTRACT: Controls on the Structural and Stratigraphic Architecture of Syn-Rift Sequences, North Falkland Basin, South Atlantic

POST‐DRILLING ANALYSIS OF THE NORTH FALKLAND BASIN— PART 1: TECTONO‐STRATIGRAPHIC FRAMEWORK

Six wells were drilled in the extensional North Falkland Basin in 1998. The wells encountered a Devonian to Cenozoic stratigraphy dominated by thick Mesozoic syn‐ and post‐rift successions. Although most previously published models predicted that the succession would most likely be of marine origin, it is in fact predominantly terrestrial; marine conditions did not become established in the basin until the Late Cretaceous. The oldest rocks recorded are Devonian and these were penetrated in only one well. The overlying succession comprises: a fluvio‐lacustrine, early syn‐rft interval of ?mid‐Jurassic to Tithonian age; a late syn‐rift fluvio‐lacustrine interval of Tithonian to Berriasian age; a rift‐sag transitional unit of Berriasian to Valanginian age; an early post‐rift lacustrine unit of Valanginian to early Aptian age; a middle post‐rift, transgressive unit of Aptian to Albian age; a late post‐rift, terrestrial to marine unit of Albian to early Palaeocene age; and a post‐up lift thermal subsidence unit of Palaeocene to Recent age.Much of the sediment appears to have been derived from volcanic and/or metamorphic terranes, probably located to the north or NW of the basin. As well as the volcanic material which occurs in the ground mass and as lithoclasts in many of the units, some volcaniclastic rocks and minor amounts of ashfall tufls are observed, particularly within the late syn‐rift succession.

POST‐DRILLING ANALYSIS OF THE NORTH FALKLAND BASIN—PART 2: PETROLEUM SYSTEM AND FUTURE PROSPECTS

Six wells were drilled in the North Falkland Basin in 1998. Five of these wells recorded oil shows, and up to 32% gas was also recorded in mud returns to the rig floor. However, none of the wells encountered commercially viable petroleum accumulations.The syn‐rift and early post‐rift intervals contain thick, lacustrine claystones with oil source potential as indicated by TOC values up to 7.5% and Rock‐Eva1 S2 values of up to 102 kg HC per tonne of rock. These source rocks were immature or only marginally mature in five of the wells but had attained maturity in one of them. Modelling suggests that the main source interval may well be within the peak oil generation window in deeper, undrilled parts of the basin. Calculations of the amount of oil expelled range up to 60 billion barrels.Most of the wells tested a closely‐related set of plays in large structures asSociated with a sandstone interval near the top of the late syn‐rifi to early post‐rij? source‐rock succession. Post‐drilling geological modelling of the basin suggests that oil is unlikely to have migrated into this sandstone play at the localities tested, and that the wells consequently failed largely due to a lack of charge. Howevel; the play maintains exploration potential elsewhere. Other plays, particularly those stratigraphically asSociated with the base rather than the top of the source rock, may have a higher chance of exploration success.

Frontier Exploration in the South Atlantic: Structural Prospectivity in the North Falkland Basin

Seismic stratigraphic analysis of the continental shelf north of the Falkland Islands confirms that it is dissected by a significant extensional fault system that broadly defines the North Falkland Basin. The basin comprises a series of extensional subbasins that developed during two distinct rift episodes. Analysis of structural styles shows that while extension occurred predominantly on a series of planar normal faults with changes in rift polarity in northern areas, the southern portion of the basin has listric faults that sole out along preexisting thrusts. After rifting, the basin largely underwent postrift thermal subsidence with the passive infill of remnant topography; however, evidence exists for at least two uplift events affecting the postrift sediments. The earlier period of uplift tilted the basin to the south, resulting in the formation of a southerly prograding forced regressive wedge; the later episode of uplift tilted the basin northward, resulting in truncation of earlier strata and minor compressional reactivation and inversion in southernmost parts of the basin. The later tilting allows for the possibility that the original rift system once extended across the Falkland Islands. Although the lack of well control does not permit a comprehensive assessment of hydrocarbon plays, the seismic data do at least demonstrate the trapping potential of the basin. Interpreted structural and depositional styles found within the prerift, synrift, and postrift sequences are similar to those found in proven hydrocarbon provinces such as the North Sea and the Gulf of Suez. The success or failure of the frontier hydrocarbon province thus is likely to depend upon factors other than structural ones.