I am looking for a reference from which I can cite the following statement:


The Picard group of a very general quartic hypersurface $X\subset\mathbb{P}^3$ is generated by the class of a hyperplane section.


What is the standard reference for this?



Very general quartic hypersurface in $\mathbb{P}^3$ has Picard group $\mathbb{Z}$
That is the Noether-Lefschetz theorem. Searching online should find plenty of results in web pages and lecture notes. If you want a published source, how about: Mark Green, *A new proof of the explicit Noether-Lefschetz theorem*, J. Differential Geom. 27 (1988), no. 1, 155–159.


