Portland Formation

Portland Formation
Stratigraphic range: Hettangian-Sinemurian
~199–195 Ma
TypeGeological formation
Unit ofAgawam Group, Newark Supergroup
Sub-unitsTurners Falls Sandstone & Mount Toby Formation
OverliesEast Berlin Formation
Lithology
PrimarySandstone
OtherMudstone, siltstone, limestone
Location
Coordinates42°18′N 72°30′W / 42.3°N 72.5°W / 42.3; -72.5
Approximate paleocoordinates24°00′N 18°36′W / 24.0°N 18.6°W / 24.0; -18.6
RegionConnecticut, Massachusetts
Country USA
ExtentDeerfield & Hartford Basins
Portland Formation is located in the United States
Portland Formation
Portland Formation (the United States)
Portland Formation is located in Massachusetts
Portland Formation
Portland Formation (Massachusetts)

The Portland Formation is a geological formation in Connecticut and Massachusetts in the northeastern United States.[1] It dates back to the Early Jurassic period.[2] The formation consists mainly of sandstone laid down by a series of lakes (in the older half of the formation) and the floodplain of a river (in the younger half). The sedimentary rock layers representing the entire Portland Formation are over 4 kilometres (2.5 mi) thick and were formed over about 4 million years of time, from the Hettangian age (lower half) to the late Hettangian and Sinemurian ages (upper half).[3]

In 2016, the paleontologist Robert E. Weems and colleagues suggested the Portland Formation should be elevated to a geological group within the Newark Supergroup (as the Portland Group), and thereby replacing the former name "Agawam Group". They also reinstated the Longmeadow Sandstone as a formation (within the uppermost Portland Group); it had earlier been considered identical to the Portland Formation.[4]

  1. ^ Portland Formation - USGS
  2. ^ Weishampel et al., 2004, pp.530–532
  3. ^ Olsen, P.E. (2002). "Stratigraphy and Age of the Early Jurassic Portland Formation of Connecticut and Massachusetts: A Contribution to the Time Scale of the Early Jurassic". Geological Society of America (Abstract). Archived from the original on 2018-11-28. Retrieved 2017-07-07.
  4. ^ Weems, R. E.; Tanner, L. H.; Lucas, S. G. (2016). "Synthesis and revision of the lithostratigraphic groups and formations in the Upper Permian?–Lower Jurassic Newark Supergroup of eastern North America". Stratigraphy. 13 (2): 111–153. doi:10.29041/strat.13.2.03.