Trinity Group (geologic group)

{{Infobox rockunit

| name = Trinity Group

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| type = Group

| age = late Aptian-early Albian, {{fossilrange|115|106}}

| period = Early Cretaceous

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| namedfor = Trinity Rivers, Texas

| namedby = Robert Thomas Hill{{cite journal|last1=Hill|first1=R.T.|title=The Trinity formation of Arkansas, Indian Territory, and Texas|journal=Science|date=1888|volume=11|issue=258|page=21|doi=10.1126/science.ns-11.258.21|pmid=17742326|url=https://zenodo.org/record/2028772}}

| region = Texas, Arkansas

| country = United States

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| subunits = *Paluxy Formation

• Glen Rose Formation
• Twin Mountains Formation

| underlies = Fredericksburg sands, Goodland Formation

| overlies = Cotton Valley Formation

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File:Austin Chalk stratigraphic column in Texas.png in Texas]]

The Trinity Group is a group (sequence of rock strata) in the Lower Cretaceous lithostratigraphy of Texas, Arkansas, Mississippi, Louisiana and Oklahoma.{{cite web | url=http://ngmdb.usgs.gov/Geolex/Units/Trinity_10950.html | title=Geologic Unit: Trinity | publisher=USGS | work=National Geologic Map Database | accessdate=31 May 2014}}{{Cite journal|last=Suarez|first=Celina A.|last2=Frederickson|first2=Joseph|last3=Cifelli|first3=Richard L.|last4=Pittman|first4=Jeffrey G.|last5=Nydam|first5=Randall L.|last6=Hunt-Foster|first6=ReBecca K.|last7=Morgan|first7=Kirsty|date=2021-10-21|title=A new vertebrate fauna from the Lower Cretaceous Holly Creek Formation of the Trinity Group, southwest Arkansas, USA|url=https://peerj.com/articles/12242|journal=PeerJ|language=en|volume=9|pages=e12242|doi=10.7717/peerj.12242|issn=2167-8359|doi-access=free|pmc=8542373}}{{Cite web|title=Paleontologists Find Fossils of New Lizard and Fish Species in Arkansas {{!}} Sci-News.com|url=http://www.sci-news.com/paleontology/sciroseps-pawhuskai-anomoeodus-caddoi-10196.html|access-date=2021-11-21|website=Breaking Science News {{!}} Sci-News.com|language=en-US}} It is named for the Trinity River of Texas.

A stratigraphic column at the Mount Bonnell Fault location starts with the Lower Cretaceous Trinity Group overlain by the Edwards Group. Upper Cretaceous formations follow, starting with the Del Rio Clay, Buda Limestone, and then the Eagle Ford Group. Formations within the Trinity Group include the Hammett Formation, Cow Creek Formation, Hensel Formation, and Lower and Upper Glen Rose Formation. The Hammett and the lower portion of the Upper Glen Rose act as confining units (or aquitard) for the Middle Trinity Aquifer. The Upper Glen Rose contains the Upper Trinity Aquifer, which appears to have intra-aquifer groundwater flow with the Edwards Aquifer as water levels are at the same elevation.{{Cite journal|title=Geophysical mapping of Mount Bonnell fault of Balcones fault zone and its implications on Trinity-Edwards Aquifer interconnection, central Texas, USA|journal=The Leading Edge|publisher=Society of Exploration Geophysicists|volume=35|number=9|page=752–758|doi=10.1190/tle35090752.1|date=September 2016|last=Saribudak|first=Mustafa|url=http://library.seg.org/doi/abs/10.1190/tle35090752.1|accessdate=12 September 2016}}