Drastic increase of indexed pages correlated to rankings loss?

[marketing_zoovy.com]

Our ecommerce website has had a drastic increase in indexed pages, and equal loss of Google organic traffic. After 10/1 the number of indexed pages jumped from 240k to 5.7 million by the end of the year, according to GWT. Coincidentally, the sitemap tops at 14,192 pages, with 13,324 indexed. Organic traffic on some top keyphrases began declining by half after 10/26 and ranking (previously placing in the top 5 spots) has dropped to the fifth page of results.

This website does produce session id's (/c=) so we been blocking /c=/ in the robots.txt file. We also have a rel=canonical on all pages pointing at the correct url. With all of this in place, traffic hasn't recovered.

Is there a correlation between this spike of indexed pages and the lost keyword ranking? Any advice to investigate and correct this further would be greatly appreciated.

Thanks.

[marketing_zoovy.com]

Thanks for your response Irving Weiss. Our webmaster made a couple of changes since this post, which I'll list at the end. First

a) Prior, the robots.txt file was..

User-agent: *
Robot-version: 2.0.0
Crawl-delay: 2
Request-rate: 1/4*
Sitemap: http://www.888knivesrus.com/sitemap.xml
Disallow: /c=/

b) No and unfortunately the edit/add button is missing from the parameters section in our account.
c) not that we've found
d) It dropped from 5.7 to 5 million on 1/1, and has remained there.

Some updates:
Our webmaster made a couple of changes yesterday to address this issue. Some of research we found said blocking the session id parameter in robots.txt file was preventing Googlebot from seeing the rel=canonical in place and it should be removed. They made an update to the robots.txt  removing it. An x-robots tags of noindex and nosnippet was also added to the pages

The webaddress is www.888knivesrus.com

Thanks again!

[irvingw]

Yes they are absolutely related. you want from 240k pages to 5,700,000 pages of empty or dupe content, so Google thinks you're spamming them.

a) are you sure you correctly blocked everything

b) have you added the session IDs to WMT in the parameter handling section?

c) are there any technical issues such as incorrect pagination of pages, or pages not 404'ing when they should?

Finally, Have you seen the pages indexed number begin to drop yet?

If we had the URL we could poke around a bit for you