The Environment of Big Bend National Park

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What can we learn about the current and future environment from the paleo-environment in Big Bend National Park?

Transgression and Regression of Mid- to Upper Cretaceous Seas

Cretaceous Rock Formations of The Big Bend Area

TRANSGRESSION/REGRESSION

The cycles of the ocean waters rising (transgressing) and receding (regressing) are known as transgressive-regressive cycles. The mid- to Upper Cretaceous rocks in the Big Bend area of southwest Texas encompasses rock ages from approximately 70 to 100 million years ago (mya). During this time the sea transgressed and regressed a number of times. The final regression of the Cretaceous sea occurred about 70 million years ago, during the Late Cretaceous period, at the time of the Aguja Formation deposition. By observing the transgressive and regressive cycles of the Mid to Upper Cretaceous period a reasonable prediction of ocean depth over time can be made. Fossil data from the mid to Upper Cretaceous period predicts the sequence of rock strata in Big Bend National Park to be from bottom to top: limestone (containing clams, oysters, and ammonites), shale and clay (containing shellfish and marine reptile bones), limestone again, and sandstone and clay (both containing fossil wood and dinosaur bones) (Maxwell, 1967). Assuming that the rocks on the bottom are the earliest layer, it may be concluded that the earliest layer of rock was deposited in a relatively deep marine environment, then the ocean regressed to produce the next layer, then transgressed to produce the last.

SEDIMENTS

In a marine environment, different types of sediments are associated with varying depths of ocean water. Sediments accumulate over time and are deposited by water, air, or both. ...

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...ical variations and fossil records. Each year visitors break away rock formations destroying the geological history stored there. Visitors also remove pieces of these rocks along with plant and bone fossils from the park. It is essential for us, as educators, to explain to our students the importance of maintaining a pristine environment and the geological history surrounding us.

Works Cited

Henry, C.D., Tyler, N., 1998, Geology of Big Bend Ranch State Park, Texas: Texas Parks and Wildlife Press, 72 pp.

Maxwell, R.A., Lonsdale, J.T., Hazzard, R.T., and Wilson, J.A., 1967, Geology of Big Bend National Park: Univ. of Texas Publ. 6711, 320 pp.

Schiebout, J.A., Chesser, K., Estepp, J.D., Langston, W., Standhart, B., Warnoch, B., 1986, Geology of the Big Bend Area and Solitario Dome, Texas: West Texas Geological Society Field Trip, 166 pp.

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