The Zuñi sequence was the major

cratonic sequence A cratonic sequence in geology is a very large-scale lithostratigraphic sequence in the rock record that represents a complete cycle of marine transgression and regression on a craton (block of continental crust) over geologic time. Cratonic se ...

after the Absaroka sequence that began in the latest Jurassic, peaked in the late Cretaceous, and ended by the start of the following Paleocene. Though it was not the final major

transgression Transgression may refer to: Legal, religious and social *Sin, a violation of God's Ten Commandments or other elements of God's moral law *Crime, legal transgression, usually created by a violation of social or economic boundary **In civil law ju ...

, it was the last complete sequence to cover the

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

n craton; the following

Tejas sequence The Tejas sequence was the last major marine transgression across the North American craton. Following the late Cretaceous regression that ended the Zuñi sequence, the oceans advanced again early in the Cenozoic, peaking during the Paleocene ...

was much less extensive.

Cause and progression

Like other sequences, the Zuñi was probably caused by a mantle plume - more specifically, the ''Mid-Cretaceous Superplume'' event. A mass of unusually hot rock rose from the lower mantle to the base of the

lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of the upper mantle (geology), mantle that behaves elastically on time sca ...

, fueling a dramatic increase in seafloor spreading rates; this caused the hotter mid-ocean ridges to increase in volume, thus displacing the oceans onto the continents. Sea level rose in earnest beginning in the early Cretaceous, until by

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...

time it was roughly 250 metres (800+ feet) higher than today. This was the time of the great Western Interior Seaway and the widespread continental deposition of carbonates and

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

elsewhere. There were also intervals where black shale accumulated in abundance on the continents, indicative of a stagnant water column; apparently water in the polar oceans was too warm to sink and oxygenate the deep-sea, as it does today. Many of these black shales are now rich in petroleum sources. The waters of the Zuñi sequence began to subside late in the Cretaceous period, and by the early

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

a new craton-wide unconformity in North America indicates a complete regression before the Tejas sequence of the late

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

Footnotes

References

* * {{DEFAULTSORT:Zuni sequence Jurassic geology Cretaceous geology Paleocene geology Geology of the United States Jurassic United States Cretaceous United States Paleocene North America Paleogene United States Jurassic geology of New Mexico Cretaceous geology of New Mexico Paleogene geology of New Mexico

Cause and progression

See also

Footnotes

References