Editing Morrison Formation (section)

== Geologic history ==
According to [[radiometric dating]], the Morrison Formation dates from 156.3&nbsp;±&nbsp;2&nbsp;million years old ([[Mega-annum|Ma]]) at its base,<ref name=TCR06>{{cite journal |last=Trujillo |first=K.C. |author2=Chamberlain, K.R. |author3= Strickland, A.  |year=2006 |title=Oxfordian U/Pb ages from SHRIMP analysis for the Upper Jurassic Morrison Formation of southeastern Wyoming with implications for biostratigraphic correlations |journal=Geological Society of America Abstracts with Programs |volume=38 |issue=6 |pages=7}}</ref> to 146.8&nbsp;±&nbsp;1&nbsp;million years old at the top,<ref name=SAB98>{{cite book |last=Bilbey |first=S.A. |year=1998 |chapter=Cleveland-Lloyd Dinosaur Quarry - age, stratigraphy and depositional environments |pages= 87–120 |title=The Morrison Formation: An Interdisciplinary Study |editor1=Carpenter, K. |editor2=Chure, D. |editor3=Kirkland, J.I. |series=Modern Geology |volume=22 |publisher=Taylor and Francis Group |issn=0026-7775}}</ref> which places it in the earliest [[Kimmeridgian]], and early [[Tithonian]] [[faunal stages|stages]] of the late Jurassic. This is similar in age to the [[Solnhofen limestone|Solnhofen Limestone]] Formation in Germany and the [[Tendaguru|Tendaguru Formation]] in [[Tanzania]]. The age and much of the fauna is similar to the [[Lourinhã Formation]] in Portugal.<ref>Mateus, O. 2006. Late Jurassic dinosaurs from the Morrison Formation, the Lourinhã and Alcobaça Formations (Portugal), and the Tendaguru Beds (Tanzania): a comparison. in Foster, J.R. and Lucas, S. G. R.M., eds., 2006, Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 36: 223-231.</ref> Throughout the western United States, it variously overlies the Middle Jurassic Summerville, [[Sundance Formation|Sundance]], Bell Ranch, Wanakah, and Stump Formations.

At the time, the supercontinent of [[Laurasia]] had recently split into the continents of North America and Eurasia, although they were still connected by land bridges. North America moved north and was passing through the [[subtropics|subtropical regions]].

The Morrison Basin, which stretched from New Mexico in the south to Alberta and Saskatchewan in the north, was formed during the [[Nevadan orogeny]], a precursor event to later orogenic episodes that created the Rocky Mountains started pushing up to the west. The deposits from their east-facing [[drainage basin]]s, carried by streams and [[river]]s from the Elko Highlands (along the borders of present-day Nevada and Utah) and deposited in [[swamp]]y lowlands, lakes, river channels and [[floodplain]]s, became the Morrison Formation.<ref name="turner-peterson-2004">{{cite journal |last1=Turner |first1=Christine E. |last2=Peterson |first2=Fred |title=Reconstruction of the Upper Jurassic Morrison Formation extinct ecosystem—a synthesis |journal=Sedimentary Geology |date=May 2004 |volume=167 |issue=3–4 |pages=309–355 |doi=10.1016/j.sedgeo.2004.01.009|bibcode=2004SedG..167..309T |url=http://doc.rero.ch/record/14577/files/PAL_E1793.pdf }}</ref>

In the north, the [[Sundance Sea]], an extension of the [[Arctic Ocean]], stretched through Canada down to the United States. [[Coal]] is found in the Morrison Formation of Montana, which means that the northern part of the formation, along the shores of the sea, was wet and swampy, with more vegetation.<!--more than what?--> [[Aeolian processes|Aeolian]], or wind-deposited sandstones, are found in the southwestern part, which indicates it was much more arid—a [[desert]], with sand [[dune]]s.