| GEOLOGIC TIME-SCALE | AGE M.Y. |
|---|---|
| CENOZOIC | |
| QUAT. | |
| HOLOCENE | |
| PLEISTOCENE | 2 |
| TERTIARY | |
| PLIOCENE | 13 |
| MIOCENE | 25 |
| OLIGOCENE | 36 |
| EOCENE | 58 |
| PALEOCENE | 63 |
| MESOZOIC | |
| CRETACEOUS | 135 |
| JURASSIC | 181 |
| TRIASSIC | 230 |
| PALEOZOIC | |
| PERMIAN | 280 |
| PENNSYLVANIAN | 310 |
| MISSISSIPPIAN | 345 |
| DEVONIAN | 405 |
| SILURIAN | 425 |
| ORDOVICIAN | 500 |
| CAMBRIAN | 600 |
| PRECAMBRIAN |
The lowest and oldest exposed formation in Palo Duro Canyon is the Quartermaster. It was deposited near the edge of a shallow sea that occupied a wide area in Texas some 280 to 230 million years ago ([Figure 3]). This was during the Permian Period, the last period of the Paleozoic Era. The sediments in the park area were carried from the east and deposited in a nearshore environment. Sedimentary structures, such as crossbeds and ripplemarks, are present throughout the Quartermaster Formation. Halite casts suggest that there was a high rate of evaporation as sedimentation occurred. Gypsum (altered anhydrite) is also interpreted to be an evaporite deposit. The gypsum is now seen as horizontal white layers of alabaster and satin-spar varieties within the Quartermaster Formation.
The Quartermaster Formation is mostly siltstone and shale, and is commonly a distinctive red color. This red color is the result of combining oxygen from the air with the iron in the sediments (oxidation) much as a nail rusts after it has been exposed for a long period. The bedded gray zones represent times when there was enough fresh water from the land to offset temporarily the oxidation process. Smaller circular gray areas have organic nuclei that produced local areas of chemically altered iron by a process called reduction.
At the close of the Permian Period and the Paleozoic Era, the Panhandle region was uplifted and a period of widespread erosion followed. Consequently there are no sediments in this area to represent the early or middle portions of the Triassic Period. Breaks, such as this, in the sedimentary record are called UNCONFORMITIES. They may have been caused by a lack of deposition in the area or by an interval during which erosion removed earlier sediments.
Figure 3. Paleogeographic map of the Permian Period (240 m.y.)
The Tecovas Formation was deposited in swamps, lakes, and streams approximately 200 million years ago during the Late Triassic ([Figure 4]). The Tecovas is mostly purplish lavender, yellow, orange, and buff siltstone and shale. The bright-colored shale of the Tecovas Formation is easily followed for many miles. Amarillo (the Spanish word for yellow) got its name from Amarillo Creek where the yellow bed of the Tecovas Formation crops out far from Palo Duro Canyon. The shale of the Tecovas forms the less steep portions of the canyon walls and often is covered by talus (weathered, broken rock) or vegetation. The uppermost Tecovas is usually mantled with boulders from the overlying sandstone of the Trujillo Formation.
The Tecovas Formation contains numerous concretions or irregularly shaped, weathered rocks. The unusual shape of a concretion is the result of the hardening of the sediments around a nucleus. As the rock weathers, the resistant material surrounding the nucleus remains. Most of the concretions are composed of limonite, hematite, manganite or calcite. Some of the calcite concretions are a variety termed “septarian.” These concretions have calcite ridges in a honeycomb pattern throughout the rock. Some of the concretions are simply nodular or spherical aggregates. Also in the Tecovas, geodes filled or lined internally with calcite crystals are found.
Figure 4. Paleogeographic map of the Triassic Period (181 m.y.)