A River Didn’t Run Through It

Geologist Alan Chamberlain said that in Wyoming, overthrusted Paleozoic rocks are a couple of thousand feet thick, but in Nevada they are 45,000 feet thick. Cretaceous source rocks in the Wyoming overthrust are about 1 percent total organic content and a couple of hundred feet thick, but in Nevada the Mississippian source rocks average 5 to 6 percent total organic content, and are thousands of feet thick.

"When the USGS published articles on Nevada they interpreted the Mississippian rocks out here as swish turbidities, which are not very good source rocks," Chamberlain said. "However, I have found that the Mississippian source rocks are actually latchstrine lake beds -- some of the richest source rocks in the world."

Nevada was part of a passive margin sequence with shallow water carbonate build up until the Late Devonian when it was interrupted by the Antler Orogeny, which effected the entire Cordillera from Alaska to South America, according to Chamberlain.

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Geologist Alan Chamberlain said that in Wyoming, overthrusted Paleozoic rocks are a couple of thousand feet thick, but in Nevada they are 45,000 feet thick. Cretaceous source rocks in the Wyoming overthrust are about 1 percent total organic content and a couple of hundred feet thick, but in Nevada the Mississippian source rocks average 5 to 6 percent total organic content, and are thousands of feet thick.

"When the USGS published articles on Nevada they interpreted the Mississippian rocks out here as swish turbidities, which are not very good source rocks," Chamberlain said. "However, I have found that the Mississippian source rocks are actually latchstrine lake beds -- some of the richest source rocks in the world."

Nevada was part of a passive margin sequence with shallow water carbonate build up until the Late Devonian when it was interrupted by the Antler Orogeny, which effected the entire Cordillera from Alaska to South America, according to Chamberlain.

"When I sat the Mukluk well in the Arctic Ocean in the 1980s, the Sadlerochit Formation was part of the rocks associated with the Antler Orogeny and the same Mississippian rocks I am dealing with in Nevada," he said.

"The Antler Orogeny created a huge mountain range in central Nevada and a seaway east of Nevada, similar to the Cretaceous seaway that created all the source rocks for Wyoming and Montana," he continued. "The richest source rocks in that Antler basin were the floodplain deposits in eastern Nevada where the lake beds were. To the east it drops off the shoreline and becomes marine rocks, and to the west the mountains begin and the rocks are more sandstones with no shales."

When the Antler Orogeny subsided there was a transgression of Pennsylvanian seas and normal deposition until the Late Cretaceous, when the Sevier Orogeny, another major compressional event, took place, he said.

The Sevier Orogeny created the Wyoming overthrust belt, the Canadian foothills as well as the structures around Monterey, Mexico.

"The same event created the great fault folds in Nevada," he said. "Following the Sevier Orogeny a blanket of volcanic rock covered Nevada that sealed in the oil seeps associated with the Cretaceous thrust belt."

Chamberlain said he is not entirely sure why volcanic rock covers this part of the thrust belt and not others.

"It is likely there was not as much internal drainage in areas not covered by volcanics," he said. "The Sierra Nevada Mountains created an enormous area for internal drainage in what is now Nevada, and the only outlet to the ocean was the Colorado River.

"If we had a major river cutting through central Nevada and the Sierras, then the volcanics would likely have been stripped like they are in other places on the overthrust belt."

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