| Portland Formation | |
|---|---|
| Stratigraphic range: Hettangian-Sinemurian ~ | |
| Type | Geological formation |
| Unit of | Agawam Group, Newark Supergroup |
| Sub-units | Turners Falls Sandstone & Mount Toby Formation |
| Overlies | East Berlin Formation |
| Lithology | |
| Primary | Sandstone |
| Other | Mudstone, siltstone, limestone |
| Location | |
| Coordinates | 42°18′N 72°30′W / 42.3°N 72.5°W |
| Approximate paleocoordinates | 24°00′N 18°36′W / 24.0°N 18.6°W |
| Region | Connecticut, Massachusetts |
| Country |  USA |
| Extent | Deerfield & Hartford Basins |
  Portland Formation (the United States)  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]
- ^ Portland Formation - USGS
- ^ Weishampel et al., 2004, pp.530–532
- ^ 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.
- ^ 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.