CRETACEOUS (144-66.4 Ma)

I. WORLD PALEOGEOGRAPHY

A. North and South Atlantic connected but narrow between Brazil and Africa. Northern N. Atlantic still closed; N. America, Greenland, and Europe still connected (no communication with Arctic Ocean).

B. Tethys Ocean separates Europe and Asia

C. Late in the period, India receives its marching orders

D. Antarctica, South America, and Australia still one continent

E. Australia began slow separation from Antarctica late in period.

II. NORTH AMERICA

A. ATLANTIC-GULF PASSIVE MARGINS:

• Reviewed separately in our lecture on "Gulf and Atlantic Passive Margins"

B. CRATONIC MARINE TRANSGRESSIONS

• Greatest inundation of the continent during the Mesozoic.
• The last great inundation of continents. High sea level stand caused by fast seafloor spreading rates, increased ridge volume, absence of ice sheets.
• Pelagic sedimentation on passive margins, in many places producing chalks
• This inundation is most widespread in the western interior.
• Depositional progradation along Atlantic and Gulf margin largely outpaced rise of sea level.

C. Continued Western Orogenic Activity

• Sierran Arc volcanic continued, which began in the Jurassic, continued throughout the Cretaceous. Batholiths were added to the western margin and vast volcanic highland created (long since eroded).
• During the Late Cretaceous (~80 Ma), arc volcanism shift eastward into Idaho and Nevada. This shift appears related to a shallowing of subduction. This begins the Sevier period of orogenic activity. It is accompanied by massive backarc thrusting and crustal shortening.
• In the latest Cretaceous another change in tectonic style occurred which marks the beginning of the the final Cordilleran mountain building, continuing through the Eocene. At this time Sierran arc volcanic shut down. Deformation again shifted eastward, throughout the Rockies metamorphic and igneous Precambrain basement was uplifted. Marginal Proterocoic rocks were deformed by uplift and steep flank thrust faulting.
• PACIFIC NORTHWEST, BRITISH COLUMBIA, ALASKA 1. Exotic or Suspect Terranes (Viking Funeral Ships and/or Noah's Arks)

D. Foreland Basin Deposition

• Continued loading of the western margin by thrust faulting, maintained the crustal sag of the Cretaceous foreland basin in the Rocky Mt. region.
• A thick clastic wedge filled the the regions of Jurassic Morrison Fm. deposition (Morrison clastic wedge). Eastward the non-marine interfinger with marine sediments that periodically flooded the basin.
• The large interior seaway (Mowry Sea), sourced from Arctic in early Cretaceous. Middle Cretaceous Interior Seaway (Arctic to Gulf) was, technically, an epeiric sea but differed greatly from great epicontinental seas of Paleozoic.
• Paleozoic epicontinental seas flooded a stable cratonic surface, however, the Cretaceous seaways of the interior flooded a foreland basin ( an elongate down-warped basin bordering the rising western Cordilleran ranges.
• Facies deposited in the seaway consist largely of clastics from the west. Thickest and coarser to the west, thinning and becoming finer grained to the east. Molasse deposits common to the west grading eastward into sands, silts, and muds (even some limestones)
• Extensive coal swamps were present. Coals commonly thick and extensive (e.g. Four-corners area near Shiprock).

E. Terminal Cretaceous Extinctions

• Class disussion.