BobDodds, April 7, 2012, wrote:Geologically speaking, 4500 mile Rift (all Valley?) has the deep earth activity we're looking for: "Great Rift Valley, which runs 4,500 miles from southern Africa, under the Red Sea, and into Syria in southwestern Asia. it is so huge a geological feature that it is prominently visible to lunar and space-shuttle astronauts...
BobDodds is quite right to point out the "Great Rift Valley" in Africa as a potential source of abiotic oil.
BobDodds wrote:Ever since British oil company, Tullow Oil, discovered an estimated 2 billion barrels of oil in Uganda in 2009 the geopolitical importance of the entire central African region suddenly underwent change.
The "Great Rift Valley" is a rift extending from the Afar triple junction:
East Africa's Great Rift Valley: A Complex Rift System, by by James Wood and Alex Guth - Michigan Technological University (Geology.com)
Wood & Guth wrote:The East African Rift System (EARS) is one the geologic wonders of the world, a place where the earth's tectonic forces are presently trying to create new plates by splitting apart old ones. In simple terms, a rift can be thought of as a fracture in the earth's surface that widens over time, or more technically, as an elongate basin bounded by opposed steeply dipping normal faults. Geologists are still debating exactly how rifting comes about, but the process is so well displayed in East Africa (Ethiopia-Kenya-Uganda-Tanzania) that geologists have attached a name to the new plate-to-be; the Nubian Plate makes up most of Africa, while the smaller plate that is pulling away has been named the Somalian Plate (Figure 1). These two plates are moving away form each other and also away from the Arabian plate to the north. The point where these three plates meet in the Afar region of Ethiopia forms what is called a triple-junction. However, all the rifting in East Africa is not confined to the Horn of Africa; there is a lot of rifting activity further south as well, extending into Kenya and Tanzania and Great Lakes region of Africa. The purpose of this paper is to discuss the general geology of these rifts are and highlight the geologic processes involved in their formation.
http://geology.com/articles/east-africa-rift.shtmlThis board has discussed triple junction fault basins when it discussed the facts & evidence for abiotic oil in the Sirte basin, Libya (although, it was not specifically identified as a triple junction rift system).
Wikipedia entry wrote:The Sirte Basin is a late Mesozoic and Tertiary triple junction continental rift (extensional basin) along northern Africa that was initiated during the late Jurassic Period. It borders a relatively stable Paleozoic craton and cratonic sag basins along its southern margins. The province extends offshore into the Mediterranean Sea, with the northern boundary drawn at the 2,000 meter (m) bathymetric contour. It borders in the north on the Gulf of Sidra and extends south into northern Chad.
http://en.wikipedia.org/wiki/Sirte_Basin Triple junction rift systems have long been identified as prolific hydrocarbon systems.
Plate Junctions and Hydrocarbon Accumulations in the Indian Region, N. G. K. Nair, V. K. Gaur, K. N. Khattri AD, H. Sinvhal (1981)
Nair, et al., wrote:This article relates the productive and potential oil fields in India to plate junctions and other major tectonic features. High geothermal gradients are known to accelerate the expulsion of petroleum from the source bed, as well as its migration and accumulation in favourable reservoir rocks, resulting in high yield. Some of the world's major petroleum deposits occur along ‘failed arms’ associated with the plume generated triple junctions. Seven triple junctions have been located in the Indian region, and two more are identified here. Interestingly, India's off-shore petroleum prospects coincide with some of these triple junctions.
http://onlinelibrary.wiley.com/doi/10.1 ... x/abstractThe Sirte Basin, as mentioned previously, has numerous abiotic indications, such as the presence of dolomite and "stacked" (oil in multiple seperate rock layers in the same vertical geological column) oil fields, which both Eugene Coste and Nikolai Kudryavtsev (Kudryavtsev's Rule) identified as evidence for Abiotic Oil Theory.
Wikipedia entry wrote:The Gialo High is a relatively small horst block in the eastern Sirte Basin. It is most important and primarily known for the stacked oil fields in rocks ranging from the Early Cretaceous to Oligocene age. There are several billion barrels of oil reserves associated with the structure both over the crest of the horst as well as flanking the high in the adjacent graben.
Repeated ('reactivated') uplift & subsidence has also been identified consistent with Abiotic Oil Theory:
Wikipedia entry wrote:The area's structural weakness is exemplified by alternating periods of uplift and subsidence originating in the Late Precambrian, commencing with the Pan-African orogeny that consolidated a number of proto-continental fragments into an early Gondwanaland. Rifting commenced in the Early Cretaceous, peaked in the Late Cretaceous, and ended in the early Tertiary, resulting in the triple junction within the basin. The Late Cretaceous rifting event is characterized by formation of a sequence of northwest-trending horsts and grabens that step progressively downward to the east; the Sirte Trough represents the deepest portion of the basin. These horsts and grabens extend from onshore areas northward into a complex offshore terrane that includes the Ionian Sea abyssal plain to the northeast.
Geological structural 'weakness' has been identified by Eugene Coste as evidence for Abiotic Oil Theory:
Eugene Coste wrote:Oil and gas were only supplied along some of the lines of structural weakness or along some of the fractured zones of the crust of the earth, and, therefore, the new fields are to be found only along these zones or belts...
Other triple junction fault systems have been discovered to have prolific hydrocarbon deposits:
Petroleum geology of the Niger Delta, H. Doust (1990)
Doust (partial abstract) wrote:The Niger Delta is one of the World’s largest Tertiary delta systems and an extremely prolific hydrocarbon province. It is situated on the West African continental margin at the apex of the Gulf of Guinea, which formed the site of a triple junction during continental break-up in the Cretaceous...
http://sp.lyellcollection.org/content/50/1/365.abstractOther areas with triple junction fault systems have been identified as potential hydrocarbon bearing regions:
Government of the Republic of Trinidad and Tobago, Ministry of Energy and Energy Affairs:
Petroleum Geology of Trinidad
All the positive elements for the formation and accumulation of hydrocarbons (oil and gas) in commercial quantities exist in the Trinidad area, i.e. traps, reservoir rocks and source rocks.
Trinidad is situated at the triple junction formed by the meeting of three plates, the Caribbean, South American and North Atlantic Plates. As a result, this small island and its surroundings is one of the most geologically complex areas of the world and has often been called “the graveyard of geologists” by commentators on our geological history. However, we continue to attract international oil exploration companies who, although challenged by this complexity, are always convinced that their theories are better than their competitors’ and that they would be successful in discovering new accumulations of petroleum. The interaction of these plates at the triple junction, with each other and the plates surrounding them has resulted in the formation of folded (anticlines) and faulted structures, ideal structural traps for the accumulation of petroleum.
http://www.energy.gov.tt/energy_resources.php?mid=44The United States has offshore potential hydrocarbon deposits related to a triple junction system:
Effect of the northward-migrating Mendocino triple junction on the Eel River forearc basin, California: Structural evolution, Sean P.S. Gulick and Anne S. Meltzer (2002)
Gulick & Meltzer wrote:Abstract
Offshore northern California, the Gorda plate is subducting obliquely beneath North America; the resulting complicated tectonic setting forms the southern end of the Cascadia subduction zone. The southern Cascadia subduction zone and overlying Eel River forearc basin lie just north of the unstable Mendocino triple junction. The Neogene strata of the Eel River basin record structural deformation caused by the underthrusting of the Gorda plate as well as deformation generated by northward migration and encroachment of the Mendocino triple junction. Three distinct deformation regimes are present in the Eel River forearc basin. (1) Along the western margin of the forearc basin and within the foreslope of the accretionary prism, thrust faults and anticlines record Pliocene– Pleistocene shortening caused by subduction of the Gorda plate. (2) The southern part of the basin rotated counterclockwise in the late Pleistocene, resulting in modern transpressional deformation offshore Humboldt Bay. The rotation and deformation are caused by north-south convergence across the boundary between the Pacific plate and the southernmost part of the forearc basin at the triple junction. (3) The northeastern margin of the Eel River basin is deformed by high-angle faults with a component of strike-slip motion that may represent the incipient northward propagation of the Pacific–North American transform system north of the triple junction.
http://gsabulletin.gsapubs.org/content/ ... 5.abstractAnd for a visual schematic of the Mendocino triple junction fault system:
United States Geological Survey, Mendocino Triple Junction Offshore Northern California, Written by David Oppenheimer
Oppenheimer wrote:The Mendocino Triple Junction (MTJ) is one of the most seismically active regions of the San Andreas transform system. Since 1983 the region (Figure 1) has generated about 80 M3.0 quakes each year, and historically the region has experienced major quakes. This activity is generated in response to ongoing plate motions between the Gorda, North America, and Pacific plates.
Figure 1. M2 in northern California coastal region 1985-2003. White lines are major roads. Brown lines are faults active since the Late Quaternary. Labeled green polygons bound regions described in scenario section of text. G-NA= Gorda-North America, G-P= Gorda-Pacific, and P-NA=Pacific North America.
http://woodshole.er.usgs.gov/operations ... ocino.htmlGetting back to the "Great Rift Valley", a triple junction rift system is complex and goes beyond the well-known East African Rift:
Wood & Guth wrote:The oldest and best defined rift occurs in the Afar region of Ethiopia and this rift is usually referred to as the Ethiopian Rift. Further to the South a series of rifts occur which include a Western branch, the "Lake Albert Rift" or "Albertine Rift" which contains the East African Great Lakes, and an Eastern branch that roughly bisects Kenya north-to-south on a line slightly west of Nairobi (Figure 2). These two branches together have been termed the East African Rift (EAR), while parts of the Eastern branch have been variously termed the Kenya Rift or the Gregory Rift (after the geologist who first mapped it in the early 1900's). The two EAR branches are often grouped with the Ethiopian Rift to form the East Africa Rift System (EARS). The complete rift system therefore extends 1000's of kilometers in Africa alone and several 1000 more if we include the Red Sea and Gulf of Aden as extensions. In addition there are several well-defined but definitely smaller structures, called grabens, that have rift-like character and are clearly associated geologically with the major rifts. Some of these have been given names reflecting this such as the Nyanza Rift in Western Kenya near Lake Victoria. Thus, what people might assume to be a single rift somewhere in East Africa is really a series of distinct rift basins which are all related and produce the distinctive geology and topography of East Africa.
http://geology.com/articles/east-africa-rift.shtmlBobDodds identified just one area along this giant triple junction rift system discovered to have petroleum:
BobDodds wrote:Ever since British oil company, Tullow Oil, discovered an estimated 2 billion barrels of oil in Uganda in 2009 the geopolitical importance of the entire central African region suddenly underwent change.
Wood & Guth discuss the possible geological process that cause the triple junction:
Wood & Guth wrote:The exact mechanism of rift formation is an on-going debate among geologists and geophysicists. One popular model for the EARS assumes that elevated heat flow from the mantle (strictly the asthenosphere) is causing a pair of thermal "bulges" in central Kenya and the Afar region of north-central Ethiopia. These bulges can be easily seen as elevated highlands on any topographic map of the area (Figure 1). As these bulges form, they stretch and fracture the outer brittle crust into a series of normal faults forming the classic horst and graben structure of rift valleys (Figure 3). Most current geological thinking holds that bulges are initiated by mantle plumes under the continent heating the overlying crust and causing it to expand and fracture. Ideally the dominant fractures created occur in a pattern consisting of three fractures or fracture zones radiating from a point with an angular separation of 120 degrees. The point from which the three branches radiate is called a "triple junction" and is well illustrated in the Afar region of Ethiopia (Figure 4), where two branches are occupied by the Red Sea and Gulf of Aden, and the third rift branch runs to the south through Ethiopia.
In other words, the rift forms as a pull-apart rift (pull-apart basin) with extentional faulting in a series of faults parallel to the main rift expressed by horst & graben fault patterns.
Volcanism is discussed in relation to the "Great Rift Valley":
Wood & Guth wrote:The stretching process associated with rift formation is often preceded by huge volcanic eruptions which flow over large areas and are usually preserved/exposed on the flanks of the rift. These eruptions are considered by some geologists to be "flood basalts" - the lava is erupted along fractures (rather than at individual volcanoes) and runs over the land in sheets like water during a flood. Such eruptions can cover massive areas of land and develop enormous thicknesses (the Deccan Traps of India and the Siberian Traps are examples). If the stretching of the crust continues, it forms a "stretched zone" of thinned crust consisting of a mix of basaltic and continental rocks which eventually drops below sea level, as has happened in the Red Sea and Gulf of Aden. Further stretching leads to the formation of oceanic crust and the birth of a new ocean basin.
Eugene Coste wrote:The oil- and gas-fields are located along the faulted and fissured zones of the crust of the earth, parallel to the great orogenic and volcanic dislocations. -- Eugene Coste, abiotic oil theorist & hydrocarbon explorationist, 1905
The Siberian Traps have been extensively discussed on this board as evidence for Abiotic Oil Theory.
As this discussion has shown there is significant reason to explore for large abiotic petroleum deposits along the "Great Rift Valley" as numerous triple junction fault systems have been found to have substantial petroleum reservoirs and others may also have huge petroleum deposits yet to be discovered & produced.