Hall Lake Formation

The Hall Lake Formation, formerly called the Hall Lake Member, is a geological formation in Sierra County, New Mexico preserving Lancian fauna, most notably dinosaurs. It is regarded as a member of the McRae Group, including the Elephant Butte and Staton-LaPoint locales.^[2]

Hall Lake Formation
Stratigraphic range: Late Cretaceous, Campanian–Maastrichtian ~83.5–66.0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Unit of	McRae Group
Underlies	Jose Creek Member[1]
Overlies	"Quaternary-Tertiary basalt flows and alluvium"
Lithology
Primary	Mudstone, "shale", sandstone
Location
Coordinates	33.2°N 107.1°W / 33.2; -107.1
Approximate paleocoordinates	40.5°N 81.1°W / 40.5; -81.1
Region	New Mexico
Country	United States
Hall Lake Formation (the United States) Show map of the United States Hall Lake Formation (New Mexico) Show map of New Mexico

Description

While most estimates place it firmly within the Lancian fauna, specifically using taxa such as Compsemys as index fossils to recover a Campanian-Maastrichtian age,^[3] Lozinsky et al. (1984) note the presence of basalt flows and alluvium dating to the Quaternary-Tertiary.

It overlooks the Jose Creek Member and is composed of purple and maroon shales. When they meet, it is marked by a basal conglomerate or a color distinction where conglomerate is absent. Various Cenozoic units overly the formation. Where some choose to classify these layers as a member of the McRae Formation,^[4] others classify it as a distinct formation in a group of formations.^[5]

Fossil content

Dinosaurs

Saurischians

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Genus	Species	Locality	Material	Notes	Images
Tyrannosauridae[4]	indet.	Staton-LaPoint	TKM001, dorsal vertebral centrum	Lozinsky et al. (1984) call it indeterminate
Tyrannosaurus[6]	T. mcraeensis	Elephant Butte (upper)	NMMNH P-3698, a partial skull, lower jaw bones, teeth, and chevrons
Alamosaurus[4][5]	sp.	upper	TKM007, a damaged humerus	Tentative referral
Sauropoda[7]				Possibly from the Jose Creek Member
Theropoda[7]

Ornithischians

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Taxon	Locality	Material	Notes	Images
Triceratops sp.[2][4]	2 miles south of Elephant Butte	USNM 243, dorsal vertebral centrum	This genus, Torosaurus or a novel taxon
Sierraceratops turneri[5]	Elephant Butte (lower)	Partial skeleton with skull
Ceratopsidae[3]	Elephant Butte (upper)	TKM002, a coranoid TKM020, crest fragment[4]	A new genus similar to Torosaurus is said to exist above the base of the formation
	Elephant Butte (lower)		Indeterminate, in abundance
Torosaurus sp.[3]	Elephant Butte (upper)?
Hadrosauridae[3]	cannot be determined		Indeterminate and of unknown origins due to faulting or Quaternary cover
Ankylosauria[4][7]		TKM011, pyramidal bone fragment	Possibly from the Jose Creek Member, near identical from UNM-FKK-001P of the Kirtland Formation

Reptiles

Taxon	Locality	Material	Notes
Testudinata[2]	Elephant Butte (upper)
Crocodylia[2]
Compsemys[3]			Index fossils suggesting a Lancian age
Bothremydidae[3]

Plants

Genus	Species	Locality	Material	Notes
Araucarites[7]	A. sp.
Cinnamomum[7]	C. sp.
Exnelumbites[8]	E. morphotype 2		Leaves	A member of Nelumbonaceae
Ficus[7]	F. sp.
Phyllites[7]	P. sp.
Sabal[7]	S. sp.
Sabalites[7]	S. sp.
Salix[7]	S. sp.
Sequoia[7]	S. sp.
Tracheophyta[2]	Indeterminate	2 miles south of Elephant Butte
Viburnum[7]	V. sp.