Geochemical evidence (C and Sr isotopes) for methane seeps as ammonite habitats in the Late Cretaceous (Campanian) Western Interior Seaway

Swiss Journal of Palaeontology

Table 1 Mean δ¹³C (‰) of well-preserved ammonites from seep and non-seep environments

Organism		Seep (WIS)^a	Non-seep (WIS)^b	Non-seep (WIS)^b,c	Non-seep (WIS)^d	Non-seep (Gulf Coast)^e
Organism	Ammonite Zone	Didymoceras cheyennense	Didymoceras cheyennense	Baculites compressus	Hoploscaphites nebrascensis	Discoscaphites iris
Baculites		−3.1 ± 2.0	−0.85	−1.6 ± 1.0**	–	−1.4 ± 1.3**
		(n = 15)	(n = 2)	(n = 20)		(n = 87)
				(P = 0.006)		(P < 0.0001)
Hoploscaphites		−4.3 ± 2.4	–	−2.9 ± 2.4	−1.3 ± 1.4**	0.4 ± 0.8**
		(n = 6)		(n = 3)	(n = 5)	(n = 78)
					(P = 0.036)	(P < 0.0001)

^aThis study (AMNH loc. 3418); Landman et al. (2012)
^bHe et al. (2005); samples from Pennington Co., South Dakota
^cCochran et al. (2010) and Dennis et al. (2013)
^dCochran et al. (2003) and Dennis et al. (2013); excludes brackish samples
^eSessa et al. (2015)
** Indicates difference with seep ammonites is statistically significant (unpaired t test) at indicated P value