The Mesozoic - The Beginnings of a Modern Earth
- Triassic - Jurassic
- Rifting accompanied by volcanism
- Pangean breakup
- Decouples Mexico from S. Am. & Moroccan bulge
- Subsurface data indicate suture in SE crossed E-SE in southern Georgia
- Stages in Triassic History
- Erosion of Allegheny Orogenic Structures
- Mountains eroded to low plain; Tr sedimentation begins
- Newark sediments & basaltic sills, flows, & dikes accumulate in fault troughs
- Late Tr area broken into complex faults during Palisades Orogeny
- Rift Valley Sediments
- Coarse clastic deposits mark the early Triassic deposits within intermontane basins.
- Few early Triassic rocks exist due to subsequent erosion of the Appalachians and loss of these intermontane basins.
- Late Tr - Early Jr Divergence
- Eastern margin rifting
- Normal-fault bounded troughs develop as a linear trend from Nova Scotia to North Carolina
- Filled with > 6000m of Newark Supergroup
- Newark SuperGroup
- Late Tr to Jr poorly sorted arkosic (>25% feldspar erosion from granites) red sandstone
- Margins of the fault-bounded basins filled with coarse conglomerates (alluvial fans)
- Rift Valley Sequences
- Basin centers with laminated mudstones in lakes exhibiting Milankovi cyclicity; expansion and contraction
- Evaporites during dry intervals
- Lava flows occurred as magma rose along steeply dipping fault surfaces. Accompanied by volcanics.
- Gulf of Mexico
- BeganLate Tr south of Appalachian-Ouachita trend
- Evaporitic basin filled (Louann salt) into Jr
- Salt and gypsum deposits exceed 1000 m
- Source of salt domes and hydrocarbons
- Smackover Limestone
- Basin opened to free flow of ocean circulation
- Normal marine limestones (Smackover Ls), limy muds, shales and sandstones accumulated during transgressions
and regressions
- Zuni Sequence
- Mid-Jurassic
- Marine conditions in west-central craton
- Extensive interior ocean - Sundance Sea
- Sediment from Cordilleran highlands to the west
- Terrestrial Zuni Deposits
- Terrestrial lowland deposits accumulated
- Exposed in Arches & Zion National Parks
- Jurassic Morrison Formation
- Covers an area greater than 1 million km2
- Spans approx. last 10 million years of Jurassic.
- Zuni Deposits in the Cretaceous
- Arid Interval deposits Navajo SS
- Transgression into interior with marine deposits from S.IL to western U.S.
- Western Interior Seaway.
- Nine K stages based upon ammonite zones.
- Coastal Plain Cretaceous
- A short uplift pulse in the Appalachians.
- Eastern Coastal Plain developed in front of mountains when began subsidence.
- Coastal plain and nearshore marine deposits blanketed the area.
- Transgression Across the Continent
- Eastern Cordillera marine transgression northward from ancestral Gulf of Mexico and southward from arctic
Canada.
- Regression in the early Cretaceous marks the unconformity between early & late Cretaceous.
- The Western Interior Seaway
- Late Cretaceous transgression into the western interior (Arctic to Gulf of California)
- Western interior is a back-arc basin bounded on west by fold & thrust belts (Sevier) and east by craton.
- Western Interior Deposits
- Sediments include coal formation, bentonites (clay minerals formed from alteration of volcanic ash), and chalky
shales (Niobrara Fm).
- Cretaceous Southern Margin
- Florida was a shallow submarine limestone bank. Erosion of the southern Appalachians provided some terrestrial
clastic coastal plain sediments, but carbonate deposition resumed.
- Cretaceous Southern Margin
- In Alabama, low-lying coastal settings were inundated with marine transgression in which nearshore sandstone
bodies are overlain by finer-grained rocks
- Unique rock type develops in these oceans - chalk (white, fine-grained soft limestone composed of coccoliths
[golden-brown algae])