Download geologic highlights of southeastern arizona and vicinity

GEOLOGIC HIGHLIGHTS OF SOUTHEASTERN ARIZONA AND VICINITY
YEARS AGO/
GEOLOGIC TIME SCALE
GEOLOGIC AND LIFE HISTORY
QUATERNARY PERIOD
0–100 years — Holocene
Industrialized society develops mineral and water resources.
10,000 years — Holocene
Today's Sonoran Desert appears. Many mammals go extinct.
10,000–1.6 m.y. — Pleistocene
Glacial-interglacial climate fluctuations occur with associated
changes in lakes, rivers, flora and fauna. Large mammals, like
mammoths, mastodons and giant ground sloths, roam across
southern Arizona. Hunters and gatherers arrive in Southern
Arizona about 11,000 years ago, e.g., Curry Springs mammoth kill
site. Episodes of basaltic volcanism occur in the Pinacates, San
Francisco Peaks, White Mountains and San Bernardino Valley.
TERTIARY PERIOD
1.6–5.3 m.y. — Pliocene
5.3–15.0 m.y. — Miocene
The present-day Basin and Range landscape of the Sonoran Desert
begins to take shape 15 m.y. ago. Deep pervasive fracturing of the
crust and earthquake activity break up a high, mountainous
southern Arizona into blocks. Some of these crustal blocks drop
down to form the Basins, while others tilt but remain high to be
mountains. Present stream systems evolve. The initially closed
basins fill up with sediments, washed off the surrounding
mountains, and slowly integrate into regional drainage systems,
e.g., Gila, Salt and Colorado Rivers. The climate becomes
semiarid. The Gulf of California and the San Andreas fault
develop as southwestern North America begins to get torn apart by
plate tectonic processes. With the opening of the Gulf of
California, the Colorado River drains south and excavates the
Grand Canyon.
15.0–23.7 m.y. — Miocene
23.7–36.6 m.y. — Oligocene
36.6–57.8 m.y.— Eocene
57.8–66.4 m.y. — Paleocene
CRETACEOUS PERIOD
66.4–80.0 m.y.
CRETACEOUS PERIOD
(continued)
Subduction of ocean crust along the western margin of North
America continues until the East Pacific Rise interacts with the
continental crust, resulting in the activation of the San Andreas
fault and Basin and Range faults. Rivers carry sediments off the
high mountains in southern Arizona and deposit gravels to the
north onto what is now the edge of the Colorado Plateau. The
horse evolves in North America, and other modern mammals
diversify. Between ~20–30 m.y. tremendously explosive volcanic
eruptions rip across the Southwest and northern Mexico. The
landscape is built up higher by layers of volcanic rocks, e.g., tuffs,
ash and rhyolite. These volcanic rocks now make up the
Chiricahua, Tucson, Galiuro, Superstition, Ajo, and Atascosa
Mountains in southern Arizona and the Sierra Madre Occidental in
Mexico. During this volcanism, plutons are emplaced into the
upper crust., e.g., Kitt Peak and Stronghold (Dragoon Mountains)
granites.
Volcanic mountains exist in southern Arizona. A tremendous
geologic upheaval occurs in western North America called the
Laramide Orogeny. Intrusions of molten rock into the crust and
associated volcanism form new continental crust, enlarging the
North American continent. These plutonic rocks are now exposed
in Texas Canyon. The Catalina-Rincon, Graham, Tucson, Sierra
Nevada, and many other mountains are intruded, metamorphosing
large portions of the upper crust. As the Pacific Ocean crust
rapidly subducts under colliding North America, the continental
crust is deformed and folded (buckling like an accordion). Beneath
some volcanoes most copper and molybdenum deposits now being
mined in Arizona are forming by hydrothermal interactions.
Dinosaurs go extinct around 66 m.y. ago.
80–144 m.y.
JURASSIC PERIOD
144–208 m.y.
TRIASSIC PERIOD
208–245 m.y.
Mountains, called the Mogollon Highlands, begin to build up in
southern Arizona, as great quantities of granitic magma intrude the
crust of western North America. Some molten rock erupts onto the
Earth’s surface, e.g., 20,000 feet of volcanic rock in the Santa Rita
Mountains. These high volcanic peaks form a mountain chain
stretching from Alaska to Mexico. The Bisbee copper deposit
forms beneath one of these volcanoes. Other parts of Arizona are
covered by an extensive swampy mud flat across which meander
rivers jammed with logs (now the Petrified Forest). Volcanic ash,
blown in from the south and west, occasionally falls on these
swamps. Later, a great sand desert extends across Northern
Arizona and into Utah and Colorado. Fossilized sand dunes from
this desert are now exposed in the cliffs of Zion and Arches
National Parks.
A shallow sea covers southeastern and
northeastern Arizona about 100 m.y. ago. Abundant plant growth
along the swampy margins of that seaway accumulates to form coal
now being mined on Black Mesa. Flowering plants and birds
evolve in Jurassic time. Dinosaurs and insects become abundant in
Triassic and Jurassic time.
PERMIAN PERIOD
245–286 m.y.
North America is part of a supercontinent called Pangea. Reptiles
become abundant.
PENNSYLVANIAN PERIOD
286–320 m.y.
MISSISSIPPIAN PERIOD
320–360 m.y.
DEVONIAN PERIOD
360-408 m.y.
SILURIAN PERIOD
408–438 m.y.
ORDOVICIAN PERIOD
438–505 m.y.
CAMBRIAN PERIOD
505–570 m.y.
Tropical shallow sea and coastal environments exist in Arizona for
a few 100 million years. There are at least three cycles of shallow
sea inundation (transgressions), followed by uplift and emergence
of land (regression). Coral reefs, fishes and marine invertebrates
are abundant in the warm, shallow waters that cover the continental
crust. Thick deposits of limestone, mudstone (shale) and sandstone
form in these marine and tidal/beach environments. Paleozoic
marine sedimentary rocks from this time are now exposed
throughout Arizona, notably in the Grand Canyon and Whetstone
Mountains. The first abundant fossils of marine life with hard parts
appear in Cambrian rocks.
PRECAMBRIAN
PROTEROZOIC
570–2,500 m.y.
Arizona crust forms around 2 billion years ago, during an orogenic
event, as the continental crust continues to grow in size by
accretion. The first four billion years of geologic history is
obscured by more recent events and changes. First, life probably
evolved 3.5 to 3 billion years ago but remained much the same
(algae) for billions of years. Cycles of mountain building–erosion–
deposition reshaped the land as continents must have drifted across
the Earth.
ARCHEAN
2,500–4,500 m.y.