Geology of the Death Valley area

Key takeaways

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Reference excerpt

The exposed geology of the Death Valley area presents a diverse and complex set of at least 23 formations of sedimentary units, two major gaps in the geologic record called unconformities, and at least one distinct set of related formations geologists call a group. The oldest rocks in the area that now includes Death Valley National Park are extensively metamorphosed by intense heat and pressure and are at least 1700 million years old. These rocks were intruded by a mass of granite 1400 Ma (million years ago) and later uplifted and exposed to nearly 500 million years of erosion. Marine deposition occurred 1200 to 800 Ma, forming thick sequences of conglomerate, mudstone, and carbonate rock topped by stromatolites, and possibly glacial deposits from the hypothesized Snowball Earth event. Rifting thinned huge roughly linear parts of the supercontinent Rodinia enough to allow sea water to invade and divide its landmass into component continents separated by narrow straits. A passive margin developed on the edges of these new seas in the Death Valley region. Carbonate banks formed on this part of the two margins only to be subsided as the continental crust thinned until it broke, giving birth to a new ocean basin. An accretion wedge of clastic sediment then started to accumulate at the base of the submerged precipice, entombing the region's first known fossils of complex life. These sandy mudflats gave way about 550 Ma to a carbonate platform which lasted for the next 300 million years of Paleozoic time. The passive margin switched to active margin in the early-to-mid Mesozoic when the Farallon Plate under the Pacific Ocean started to dive below the North American Plate, initiating a subduction zone; volcanoes and uplifting mountains were produced as a result. Erosion over many millions of years formed a relatively featureless plain. Stretching of the crust under western North America started around 16 Ma and is thought to be caused by upwelling from the subducted spreading-zone of the Farallon Plate. This process continues into the present and is thought to be responsible for producing the Basin and Range province. By 2 to 3 million years ago this province had spread to the Death Valley area, ripping it apart and giving birth to Death Valley, Panamint Valley and surrounding ranges. These valleys partially filled with sediment and, during colder periods during the current ice age, with lakes. Lake Manly was the largest of these lakes; it filled Death Valley during each glacial period from 240,000 years ago to 10,000 years ago. By 10,500 years ago these lakes were increasingly cut off from glacial melt from the Sierra Nevada, starving them of water and concentrating salts and minerals. The desert environment seen today developed after these lakes dried up.

Early sedimentation

Proterozoic complex Little is known about the history of the oldest exposed rocks in the area due to extensive metamorphism. This somber, gray, almost featureless crystalline complex is composed of originally sedimentary and igneous rocks with large quantities of quartz and feldspar mixed in. The original rocks were transformed to contorted schist and gneiss, making their original parentage almost unrecognizable. Radiometric dating gives an age of 1700 million years for the metamorphism, placing it in the early part of the Proterozoic eon. A mass of granite now in the Panamint Mountains intruded this complex 1400 mya. Pegmatic dikes and other widely spaced plutons of granite are also in the complex (a pluton is a large blob of magma deep underground and dikes are projections of that). Outcrops can be seen along the front of the Black Mountains in Death Valley and in the Talc and Ibex Hills. When the granite was being intruded, the west coast of North America ran through Eastern California and through an embayment that spread toward the Las Vegas Valley. This embayment, called the Amargosa aulacogen, had highlands north and south of it and was the result of a failed rift. Many thousands of feet of sediment filled the slowly subsiding basin. Next, the metamorphosed Precambrian basement rocks were uplifted and a nearly 500-million-year-long gap in the geologic record, a major unconformity, affected the region. Geologists do not know what happened to the eroded sediment that must have overlain the complex, but they do know that regional uplift was responsible; the area was originally below the surface of a shallow sea.

Pahrump Group

The Pahrump Group of formations were deposited from 1200 to 800 mya in the Amargosa aulacogen. This was after uplift-associated erosion removed whatever rocks covered the Proterozoic Complex. Pahrump is composed of, from oldest to youngest:

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Illustrations

Geology of the Death Valley area: View north across Saratoga Spring ponds to hills consisting of late Precambrian Pahrump Group rocks. White band is talc formed by reaction of dolomite with the black diabase enclosing it. A sill of diabase magma intruded between sedimentary layers of Crystal Spring Formation, now seen flanking the diabase at lower left. All units now tilt to east (right). The spring water rises along a fault and becomes ponded by fringing barrier dunes.[4] (NPS archive image) — View north across Saratoga Spring ponds to hills consisting of late Precambrian Pahrump Group rocks. White band is talc formed by reaction of dolomite with the black diabase enclosing it. A sill of diabase magma intruded between sedimentary layers of Crystal Spring Formation, now seen flanking the diabase at lower left. All units now tilt to east (right). The spring water rises along a fault and becomes ponded by fringing barrier dunes.[4] (NPS archive image)

Geology of the Death Valley area: Late Precambrian Noonday Formation scoured in Mosaic Canyon by episodic flow. (USGS photo) — Late Precambrian Noonday Formation scoured in Mosaic Canyon by episodic flow. (USGS photo)

Geology of the Death Valley area: Striped Butte in Butte Valley. Steeply tilted limestone beds of the Permian Anvil Spring Formation. A major fault behind the butte separates it from Precambrian Noonday and Johnnie Formation rocks, about .mw-parser-output .frac{white-space:nowrap}.mw-parser-output .frac .num,.mw-parser-output .frac .den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output .frac .den{vertical-align:sub}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}1⁄2 billion years older. (USGS photo) — Striped Butte in Butte Valley. Steeply tilted limestone beds of the Permian Anvil Spring Formation. A major fault behind the butte separates it from Precambrian Noonday and Johnnie Formation rocks, about .mw-parser-output .frac{white-space:nowrap}.mw-parser-output .frac .num,.mw-parser-output .frac .den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output .frac .den{vertical-align:sub}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}1⁄2 billion years older. (USGS photo)

Worked examples

Example 1 — a first encounter with Geology of the Death Valley area

Start with the simplest possible case. Write down what Geology of the Death Valley area claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Geology of the Death Valley area before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Geology of the Death Valley area ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Geology of the Death Valley area

In research: Geology of the Death Valley area appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Geology of the Death Valley area in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Geology of the Death Valley area is common in secondary-school and first-year university syllabi. It links to neighbouring topics Death Valley, Death Valley National Park, Geology of California, so understanding it makes those chapters shorter.
In everyday life: Look for Geology of the Death Valley area outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Geology of the Death Valley area in 20 minutes

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Frequently asked questions

What is Geology of the Death Valley area in simple terms?

The exposed geology of the Death Valley area presents a diverse and complex set of at least 23 formations of sedimentary units, two major gaps in the geologic record called unconformities, and at least one distinct set of related formations geologists call a group. The oldest rocks in the area that…

Why does Geology of the Death Valley area matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Geology of the Death Valley area?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Geology of the Death Valley area.