Q. gsa style?

You are right, I did not find a specific example. There is not much documentation on GSA style, and the only official documentation is on the Geological Society of America (GSA) web site. It covers many but not all examples.

The GSA actually has a Word based manuscript template on their site (link below). I will try to extrapolate using examples from the GSA manuscript. Please note that examples are indented here for readability, but are not part of the formatting for your paper.

Traditional Source

References Cited citation:

Taylor, J.C.M., 1990, Upper Permian—Zechstein, in Glennie, K.W., ed., Introduction to the petroleum geology of the North Sea (third edition): Oxford, UK, Blackwell, p. 153–190.

In text citation

This is a sample in-text citation (Taylor, 1990, p. 154 [Page numbers are only required if a direct quotation is used). Note the commas preceding and following the year, as well as the semicolon separating references.

In Text citation content: (Author, publication date, p. #). Note that page numbers are required only if there is a direct quotation.

Web Site

References Cited citation:

Johnson, A.B., 2001, Raw data for relay stations AB1–AB15 in the Mojave desert: http://www.seismo.berkeley.edu/mojave (December 2001).

In text citation for web site above:

(Johnson, 2001).

Web sites can be harder to site because frequently there are no authors or page numbers. It there is no author, you start with the title. For instance, if the example above had no author the in text citation might be:

(Raw data, 2001).

There are two things about which I am not sure:

1. Shortened title of the web site: In text citations contain shortened information, generally just enough to distinguish it from others in your References Cited page. Based on that, the first couple of words of the title of the web site should be enough unless there are several with similar titles.
2. Direct quotation: If there is a direct quotation, the page number is given for a print source. Since a web page does not have one, I am speculating that the actual URL would be needed since the aim is to be able to find an verify the quotation.

If I were you, I would follow the examples above, but still ask your instructor if he/she can verify if it was done correctly, hopefully with enough time for you to correct before turning in. Usually if your instructor can see that you genuinely tried they don't mind helping.

Good luck!