biology

Ojo Alamo Formation

Ojo Alamo Formation is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Ojo Alamo Formation rather than just read about it. In short: The Ojo Alamo Formation is a geologic formation in New Mexico spanning the Mesozoic/Cenozoic boundary. Non-avian dinosaur fossils have controversially been identified in beds of this formation dating from after the Cretaceous–Paleogene extinction event, but these have been explained as either misidentification of the beds in question or as reworked fossils, fossils eroded from older beds and redeposited in the young…

Key takeaways

Ojo Alamo Formation belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Ojo Alamo Formation to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Ojo Alamo Formation from memory before moving on to harder problems.

Reference excerpt

The Ojo Alamo Formation is a geologic formation in New Mexico spanning the Mesozoic/Cenozoic boundary. Non-avian dinosaur fossils have controversially been identified in beds of this formation dating from after the Cretaceous–Paleogene extinction event, but these have been explained as either misidentification of the beds in question or as reworked fossils, fossils eroded from older beds and redeposited in the younger beds.

Description The Ojo Alamo Formation is divided into two subunits separated by a large unconformity—a gap in the geologic record. The lower Naashoibito member (sometimes considered part of the Kirtland Formation) was deposited during the Maastrichtian age of the Cretaceous period, specifically between about 70-68 million years ago. It overlies the De-na-zin member of the Kirtland formation, though the two are separated by another large unconformity that spans a period of geologic time equivalent to 73-69 million years ago. All dinosaur fossils probably come from this unit. The upper unit of the Ojo Alamo Formation is the Kimbeto Member, which was deposited mainly during the earliest Cenozoic (Danian age of the Paleogene period), between 66 and 64 million years ago. Argon dating indicates the base of the Naashoibito Member is 66.5 million years old. In 2025, Flynn et al. determined the strata of the Naashoibito Member preserving non-avian dinosaur fossils to be latest Maastrichtian in age, yielding maximum depositional ages of 66.87 ± 0.04 Ma and 66.38 ± 0.08 Ma based on direct argon dating on two dinosaur fossil–bearing samples around 5 metres (16 ft) and 3.5 metres (11 ft) above the base of the member respectively. They interpreted that high diversity of North American dinosaurs lived before the Cretaceous–Paleogene extinction event based on this finding, and that Maastrichtian dinosaur faunas from Laramidia were not uniform in the entire continent.

Fossils

Dinosaur remains are among the fossils that have been recovered from the formation, though all dinosaur remains come from the lowest part of the formation, the Naashoibito member (sometimes considered part of the Kirtland Formation, which dates to the late Maastrichtian stage of the Cretaceous period). Some researchers have claimed to find isolated non-avian dinosaur remains in the younger Kimbeto Member. If this is the case, it would represent the only known instance of a non-avian dinosaur population persisting after the Cretaceous–Paleogene extinction event. However, most scientists consider these to have been stratigraphically misinterpreted or reworked from the older Naashoibito member.

Alamo Wash fauna The following species are known to be present in the Naashoibito Member "Alamo Wash Fauna". Fish

Amphibians

Squamates

Turtles

Crocodylians

Dinosaurs A bite-and-drag mark on a juvenile tyrannosaurid vertebra (NMMNH P-40953) is deep and narrow, suggesting the tooth that made it was strongly compressed and blade-like, unlike those of T. rex. This supports the presence of a distinct southern North American tyrannosaurid during the Maastrichtian.

Mammals

History of investigation The formation was named by Barnum Brown in 1910 for exposures near Ojo Alamo springs in the San Juan Basin. Baltz et al. reassigned the lower beds to the Kirtland Formation in 1966, but this has not been generally accepted.

Illustrations

Worked examples

Example 1 — a first encounter with Ojo Alamo Formation

Start with the simplest possible case. Write down what Ojo Alamo Formation claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, 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 Ojo Alamo Formation 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 Ojo Alamo Formation 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 Ojo Alamo Formation

In research: Ojo Alamo Formation appears in biology 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 Ojo Alamo Formation 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: Ojo Alamo Formation is common in secondary-school and first-year university syllabi. It links to neighbouring topics Conglomerate formations of the United States, Cretaceous formations of New Mexico, Fossiliferous stratigraphic units of North America, so understanding it makes those chapters shorter.
In everyday life: Look for Ojo Alamo Formation 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.

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How to study Ojo Alamo Formation in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Ojo Alamo Formation means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Ojo Alamo Formation out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Ojo Alamo Formation in simple terms?

Why does Ojo Alamo Formation matter?

Because it connects several biology 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 Ojo Alamo Formation?

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 Ojo Alamo Formation.