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Harry Williams, Historical Geology
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LECTURE 12. LATE MESOZOIC GEOLOGY.
HISTORICAL GEOLOGY LECTURE 12. LATE MESOZOIC GEOLOGY. CRETACEOUS (
MYBP) Paleogeography: The Cretaceous begun with the continuation of
the ZUNI TRANSGRESSION, which resulted in the largest marine
invasion since the end of the Pennsylvanian, 200 million years
before. Harry Williams, Historical Geology Harry Williams,
Historical Geology Harry Williams, Historical Geology Harry
Williams, Historical Geology
In north Texas, Cretaceous rocks cover the surface and dip gently
to the southeast (the Gulf) and grade into Cenozoic rocks farther
south. Harry Williams, Historical Geology Harry Williams,
Historical Geology
If you travel west (which we do on the field trip) you come to the
edge of the Cretaceous bedrock (Cretaceous rocks farther west have
been eroded) and move onto the underlying Pennsylvanian and then
Permian rocks, which dip to the northwest. Harry Williams,
Historical Geology Harry Williams, Historical Geology
Heres a smaller scale map showing the bigger picture. Arrows show
dip, the red lines show the locations of the following upper and
lower cross sections. Also notice the Llano Uplift (LU) and the
outliers of Cretaceous rocks (OL). OL upper lower LU Harry
Williams, Historical Geology Harry Williams, Historical
Geology
Permian Pennsylvanian Crtetaceous Uplifted craton Ouachita Orogenic
Belt Harry Williams, Historical Geology Harry Williams, Historical
Geology
Permian Basin Llano Uplift Harry Williams, Historical Geology Harry
Williams, Historical Geology
The result, in North America and elsewhere, was the establishment
of large EPEIRIC SEAS, characterized by carbonate deposits
especially CHALK, from the remains of golden-brown algae (earlier
blue-green + green algae did not secret shells)("Creta" = Latin for
chalk). Coccoliths (golden-brown algae shells). Harry Williams,
Historical Geology Harry Williams, Historical Geology
There are many cretaceous chalk deposits around the world. One
example is the famous WHITE CLIFFS OF DOVER. Harry Williams,
Historical Geology Harry Williams, Historical Geology
Tectonics and Sedimentation The east coast continued to be a
passive divergent margin in the Cretaceous; the Appalachians
continued to erode. The greatest tectonic activity was on the west
coast. Orogenic activity, resulting from plate convergence,
subduction and terrane accretion, had been going on since the Early
Paleozoic - the peak periods being the Antler, Sonoma and Nevadan
Orogenies. By the Late Cretaceous, the mountainous Cordillera of
the west coast of North America was well established. Two new
orogenies (periods of intense mountain building) occurred in the
Cretaceous: Harry Williams, Historical Geology Harry Williams,
Historical Geology
THE SEVIER OROGENY (mid-Cretaceous) The "crumpling up" of the west
coast, which intensified with the break up of Pangaea, was
transmitted from west to east through the Mesozoic. The Sevier
Orogeny is notable for low angle thrust faults which formed further
inland (e.g. Nevada, Utah, Montana, B.C. and Alberta), as
compressional stress from the west coast was transmitted eastwards.
In many cases Proterozoic rocks were thrust up over Mesozoic rocks
- in the case of the famous Lewis Thrust (Montana, B.C., Alberta)
over a distance of 65 km (40 miles). The structure produced is
known as a decollement (old rocks pushed up on top of younger
rocks). Harry Williams, Historical Geology Harry Williams,
Historical Geology
The Sevier orogeny thrust belts Harry Williams, Historical Geology
Harry Williams, Historical Geology Harry Williams, Historical
Geology
THE LARAMIDE OROGENY (Late Cretaceous) Orogenic activity continued
into the Late Cretaceous, again further eastward than previously.
This resulted mostly in folding of strata in the site of the
present-day Rocky Mountains of New Mexico, Colorado and Wyoming,
producing uplifted domes and anticlines, and basins. MOST OF THE
UNDERLYING STRUCTURES OF THE PRESENT ROCKY MOUNTAINS WERE THE
RESULT OF THE LARAMIDE OROGENY; HOWEVER, THE ACTUAL LANDSCAPE WE
SEE TODAY RESULTED FROM EPISODES OF UPLIFT AND EROSION IN THE LATER
CENOZOIC ERA. Harry Williams, Historical Geology Harry Williams,
Historical Geology
SEDIMENTATION Apart from the chalk deposition already mentioned,
much of the sedimentation in North America occurred in the backarc
basin of the growing Cordillera region. This basin stretched from
Utah to Kansas. It contains a gradation of clastics eroded from the
Cordillera, from proximal conglomerates and coarse sandstones to
distal marine shales A famous example is the Dakota sandstone, a
beach deposit formed along the eastern front of the Rockies Harry
Williams, Historical Geology Harry Williams, Historical
Geology
This is similar to the situation in the east during the
Pennsylvanian a clastic wedge created lowlands that were
periodically submerged by fluctuating sea levels. The result was
cyclotherms and coal in states such as Colorado. Harry Williams,
Historical Geology Harry Williams, Historical Geology
COAL Harry Williams, Historical Geology Harry Williams, Historical
Geology
Coal seam in Raton Pass, NM. Harry Williams, Historical Geology
Harry Williams, Historical Geology
EURASIA AND THE TETHYS SEAWAY The Tethys seaway was a deep marine
depositional trough between Gondwanaland and Eurasia during the
Mesozoic. The trough was a site mainly of limestone deposition.
Soon after the break up of Pangaea, Africa begun to converge on
Eurasia. The result, mainly in the Cretaceous, was the closing and
compression of the Tethys Sea, along what is now southern Europe.
This caused orogenic activity and volcanism along the southern
margin of Europe, which continued and intensified in the later
Cenozoic. At the same time, India had broken free from Gondwanaland
and was heading towards the site of the present-day Himalayas.
Harry Williams, Historical Geology Harry Williams, Historical
Geology
1 3 Tethys 2 4 Harry Williams, Historical Geology