The ongoing environmental drama in the Gulf of Mexico provides an opportunity to briefly consider the geology and geography of oil production in the region. The ill-fated Deepwater Horizon platform was one of about 4,000 such platforms in the Gulf, which collectively produce over 1.5 million barrels of oil per day. This amount represents approximately 30% of domestic oil production in the United States. But why can oil be found in the Gulf anyway? The answer lies in the structural and sedimentary geology of the area.
The Gulf is rich in oil due to a complex history that involves marine transgressions (rising sea levels), regressions (falling sea levels), and delta formation during its evolution. In the context of sea level history, geologists know that numerous periods of rising and falling sea levels have occurred in the Gulf’s history, with each lasting for millions of years. These fluctuations in water level were perhaps several hundred meters in height. During low sea stands, plants and animals occupied the exposed surfaces. The organic residue from this biota was then buried by marine sedimentary deposits during the next transgression. This cycle of surface exposure, accumulation of organic material, and subsequent burial during a marine transgression occurred numerous times, resulting in a thick sedimentary sequence of limestone, sandstone, and shale. The organic deposits were subsequently converted to oil and natural gas through intense pressure and heat caused by the weight of the overlying rocks.
The evolution of the Mississippi Delta has also contributed to the formation of hydrocarbon reservoirs in the Gulf. At this location, clouds of microscopic organisms develop that feed on the dissolved load carried into the Gulf by the Mississippi River. As these organisms die, they settle on the ocean floor, forming a mix of sediment and organic ooze. Over time, these layers are buried progressively deeper by additional deltaic and marine deposits. As a result, the organic remains are also converted to oil and natural gas because they are cooked in the manner previously described.
The numerous oil wells in the Gulf are tapping into vast reservoirs of petroleum that have formed over millions of years. Some reservoirs consist of pockets where oil collected after it was forced upward through overlying layers of sandstone after it formed. At some level, this upwardly moving oil encountered a shale layer, which trapped it from rising further. As more oil moved upward from underlying strata, the volume within the trapped reservoir increased. In many other places, oil is found in relation to salt domes associated with the Louann Salt. This wide-spread evaporite formed during an extensive period of aridity and low-sea stand in the mid-to-late Jurassic Period, between 175- and 145-million years ago. This salt bed is less dense than the sediments above it and has thus been forced upward by pressure in many places. Over time, oil has flowed upward along the edge of these features until it encounters some form of trapping layer that causes it to collect in mineable quantities.
So, as we view this unfolding environmental disaster, it is worth considering the time and events required to develop reservoir-quality hydrocarbons in the Gulf of Mexico. It is also important to note that a primary reason the spill has yet to be contained is because the damaged well is about one mile below the ocean surface where access is especially difficult. This remote location reflects the fact that most of the easily accessible oil on land or near the coast has already been extracted, forcing oil companies to search in progressively deeper waters. As a result, the limits of technology are stretched, especially when problems arise. For the American consumer, these geological and geographical relationships mean that the coming years probably mean higher prices at the pump as our search for oil becomes more complicated. In the meantime, the Gulf of Mexico is bearing the environmental and societal costs of our growing need for oil.
By Alan Arbogast, Professor of Geography, Michigan State University. Author of, Discovering Physical Geography, John Wiley & Sons, Inc.
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Activity created by Professor Jeff DeGrave, University of Wisconsin, Eau Claire.
The impact of human culture on the landscape is evident throughout the world. Since the development of sedentary farming, humans have divided land into abstract shapes and forms in order to most effectively use the Earth for cultivation. However, the great variety in the ways humans have shaped, partitioned, and worked the land to their advantage can be difficult to detect while standing within a given landscape. For most of Earth’s history the only way to see the artistry of this terrestrial patchwork of land use was to climb the nearest mountain. Yet today we can easily see how human culture has defined the agricultural landscape from outer space through Google Earth. And with the great variety of cultures that exist on our planet, we can expect a similarly diverse representation of these cultures through the reading of the agricultural landscape. For the purposes of this activity we will look at how different cultures have parceled, settled, and used the land to create this visual landscape based on the following land division systems:
2. Grid System
3. French Long Lots
4. Metes and Bounds
5. Terrace Farming
What imprint does agriculture make on the cultural landscape?
Download File: this_land_is_our_land
In the tealeaves left by North Korea’s latest international outrage we can read a future we may not like but will have to live with: an increasingly Sinocentric world in which Western ambitions are thwarted by Chinese self-interest.
On the face of it, there’s nothing new in this. Powerful states and successful societies put their own priorities first when it comes to international competition for influence, resources or markets. In the process they sometimes align themselves with unsavory regimes or dreadful peoples. During the Cold War the Soviets backed Castro and Mengistu. The Americans made allies of Somoza and Mobutu. During the Nixon administration, you may recall, the phrase was “well, he’s an sob, but he’s our sob. The end justified the means. The Politburo saw it the same way. Many Soviets loathed Honecker. Still, he ran East Germany as their sob.
But Cuba, Ethiopia, Nicaragua, or East Germany never could endanger the world the way North Korea can. Even as the American government was hyping Saddam’s Iraq as the WMD threat of the post-9/11 era, North Korea was embarked on a program of nuclear-weapons technology diffusion that had already empowered unstable, Islamic Pakistan and had reached all the way to Libya. China knew of it. Japan fretted about it. South Korea had existential concerns about it. But while Saddam cowered in what the media ridiculously called his “spiderhole,” Kim Jong-Il and his communist clique were busy with their WMD program (no Iran-style energy-need excuse here), alternately threatening with it and cajoling over it in pursuit of power and concessions.
On the face of it, one might conclude that communist China would wish to constrain North Korea’s nuclear ambitions as a matter of self-interest. It would also appear that Chinese and Western interests coincide here: South Korean trade and Japanese capital play major roles in the near-miraculous growth of the Chinese economy. But it is worth remembering that China, too, is ruled by a Politburo. And Kim Jong-Il is China’s – well, bad guy. For all the soft-pedaled criticism by the West, the truth is that China has obstructed international efforts to constrain Pyongyang’s misdeeds. Is it a coincidence that Kim’s much-publicized train ride into China a few weeks ago was followed by the latest outrage on North Korea’s part – the unprovoked sinking by torpedo of the South Korean warship the Cheonan, with the loss of 46 sailors?
It is noteworthy how the rest of the world is rushing to explain China’s collusion. China has limited influence in Pyongyang, is one refrain. China does not want social instability in its neighbor, is another. China worries about economic collapse and mass migration across its border. China wants evolutionary change in its hard-line communist ally, not collapse. It almost seems – almost – as though Beijing rather enjoys the immediate region’s (and the world’s) discomfiture. The May 24, 2010 pronouncement by the Chinese Foreign Ministry was telling: “We hope,” it said, “[that] all relevant parties will exercise restraint and remain cool-headed.”
That certainly will be in China’s interest. After all, China has not been the target of North Korea’s actions. North Korea has not shot down any Chinese civilian airliners. North Korea has not sunk Chinese naval vessels. North Korea has not sent missiles across Chinese airspace. North Korea has not abducted Chinese citizens. North Korea is not known to send spies into its communist neighbor.
And so this latest act of state terrorism is likely to fade from view, the bereaved families of the South Korean sailors joining an ever-lengthening list of the North Korean regime’s victims at home and abroad. In this divergence of principle between the international community and China, China’s short-term priorities prevail, whatever the evidence.
Ahmedinejad and the clerical zealots of Iran must surely be taking notes.
Harm de Blij, John A. Hannah Professor of Geography at Michigan State University.