* The Lost City Hydrothermal Vent Field was determined to have abiogenic hydrocarbon production. Proskurowski et al. wrote, "Radiocarbon evidence rules out seawater bicarbonate as the carbon source for FTT reactions, suggesting that a mantle-derived inorganic carbon source is leached from the host rocks. Our findings illustrate that the abiotic synthesis of hydrocarbons in nature may occur in the presence of ultramafic rocks, water, and moderate amounts of heat."[38]
* The Siljan Ring meteorite crater, Sweden, was proposed by Thomas Gold as the most likely place to test the hypothesis because it was one of the few places in the world where the granite basement was cracked sufficiently (by meteorite impact) to allow oil to seep up from the mantle; furthermore it is infilled with a relatively thin veneer of sediment, which was sufficient to trap any abiogenic oil but was modelled as untenable for a biogenic origin of any oil (it had not developed the 'oil window' and structural traps typical of biogenic plays).

Drilling of the Siljan Ring with the Gravberg-1 7,500 m borehole penetrated the lowest reservoirs. Hydrocarbons were found, though in an economically unviable form of sludge. It was proposed that the eight barrels of magnetite paste produced were contaminated from the diesel fuel based drilling fluid used to do the drilling, but the diesel was demonstrated to be not of the kind of oil found in the shaft. This well also sampled over 13,000 feet (4,000 m) of methane-bearing inclusions. [2] To be safe, a second hole was drilled a few miles away with no diesel fuel based drilling fluid and this produced (according to Gold) 15 tons of oil. [3] However, no documentation of any such discovery has ever been provided. The "discovery" is not mentioned in any well log, including the well completion log. No other personnel at the drilling location ever reported anything apart from some additional magnetite rich mud contaminated with minor organics from the Gravberg well. When Gold published the paper stating this discovery, several prominent geologists tried to stop the publication because of its "unscientific" content.

* Direct observation of bacterial mats and fracture-fill carbonate and humin of bacterial origin in deep boreholes in Iran, Australia[39], Sweden and Canada

[edit] Example proposed abiogenic methane deposits

Panhandle-Hugoton field (Anadarko Basin) in Texas-Oklahoma, USA is the most important gas field with commercial helium content.[34][35][40][41]

The White Tiger oil field in Vietnam has been proposed as an example of abiogenic oil because it is 4,000 m of fractured basement granite, at a depth of 5,000 m.[42]. However, others argue that it contains biogenic oil which leaked into the basement horst from conventional source rocks within the Cuu Long basin [22][43].

A major component of mantle-derived carbon is indicated in commercial gas reservoirs in the Pannonian and Vienna basins of Hungary and Austria.[44]

Natural gas pools interpreted as being mantle-derived are the Shengli Field[45] and Songliao Basin, northeastern China.[46][47]

The Chimaera gas seep, near Antalya (SW Turkey), has continuously been active for millennia and it is known to be the source of the first Olympic fire in the Hellenistic period. Chimaera represents the biggest emission of abiogenic methane on land discovered so far; deep and pressurized gas accumulations necessary to sustain the gas flow for millennia, likely charged by an active inorganic source, may be present.[36]
[edit] The geological argument for abiogenic oil

Given the known occurrence of methane and the probable catalysis of methane into higher atomic weight hydrocarbon molecules, the abiogenic hypothesis considers the following to be key observations in support;

* The serpentinite synthesis, graphite synthesis and spinel catalysation models prove the process is viable [23][28]
* The likelihood that abiogenic oil seeping up from the mantle is trapped beneath sediments which effectively seal mantle-tapping faults [27]
* Mass-balance calculations for supergiant oilfields which argue that the calculated source rock could not have supplied the reservoir with the known accumulation of oil, implying deep recharge (Kudryavtsev, 1951)

[edit] Incidental evidence

The proponents of abiogenic oil use several arguments which draw on a variety of natural phenomena in order to support the hypothesis

* The modelling of some researchers which shows the Earth was accreted at relatively low temperature, thereby perhaps preserving primordial carbon deposits within the mantle, to drive abiogenic hydrocarbon production [48]
* The presence of methane within the gases and fluids of mid-ocean ridge spreading centre hydrothermal fields[49]

[edit] The geological argument against
Oil deposits are not directly associated with tectonic structures.

Key arguments against chemical reactions, such as the serpentinite mechanism, as being the major source of hydrocarbon deposits within the crust are;

* The lack of available pore space within rocks as depth increases
o This is contradicted by numerous studies which have documented the existence of hydrologic systems operating over a range of scales and at all depths in the continental crust.[50]
* The presence of no commercial hydrocarbon deposits within the crystalline shield areas of the major cratons especially around key deep seated structures which are predicted to host oil by the abiogenic hypothesis [33]
* Limited evidence that major serpentinite belts underlie continental sedimentary basins which host oil
* Lack of conclusive proof that carbon isotope fractionation observed in crustal methane sources is entirely of abiogenic origin (Lollar et al. 2006)[3]
* Mass balance problems of supplying enough carbon dioxide to serpentinite within the metamorphic event before the peridotite is fully reacted to serpentinite
* Drilling of the Siljan Ring failed to find commercial quantities of gas[33], thus providing a counter example to Kudryavtsev's Rule and failing to locate the predicted abiogenic gas
o Helium in the Siljan Gravberg-1 well was depleted in 3He and not consistent with a mantle origin[51]

* The distribution of sedimentary basins is caused by plate tectonics, with sedimentary basins forming on either side of a volcanic arc, which explains the distribution of oil within these sedimentary basins
* Kudryavtsev's Rule has been explained for oil and gas (not coal): Gas deposits which are below oil deposits can be created from that oil or its source rocks. Because natural gas is less dense than oil, as kerogen and hydrocarbons are generating gas the gas fills the top of the available space. Oil is forced down, and can reach the spill point where oil leaks around the edge(s) of the formation and flows upward. If the original formation becomes completely filled with gas then all the oil will have leaked above the original location.[52]
* Ubiquitous presence of diamondoids in natural hydrocarbons such as oil, gas and condensates are composed of carbon from biological sources, unlike the carbon found in normal diamonds.[53]

[edit] Arguments against the incidental evidence

* Gas ruptures during earthquakes are more likely to be sourced from biogenic methane generated in unconsolidated sediment from existing organic matter, released by earthquake liquefaction of the reservoir during tremors
* The presence of methane hydrate is arguably produced by bacterial action upon organic detritus falling from the littoral zone and trapped in the depth due to pressure and temperature
* The likelihood of vast concentrations of methane in the mantle is very slim, given mantle xenoliths have negligible methane in their fluid inclusions; conventional plate tectonics explains deep focus quakes better, and the extreme confining pressures invalidate the hypothesis of gas pockets causing quakes
* Further evidence is the presence of diamond within kimberlites and lamproites which sample the mantle depths proposed as being the source region of mantle methane (by Gold et al.).