Sub-domains are effected by trust scores and site scores which include content quality of the parent domain though for the most part, they operate as separate sites.
Here are just some of the considerations for using sub-domains from an answer yesterday: How my website will be ranked if I host multilanguage blogs under my domain? The topic is different, but well worth reading so that you know some of the mechanics.
To expand, Google does look at the parent domain to see if a sub-domain can be trusted. Low parent domain site scores which include trust scores and apparent content quality scores will effect how Google will look at a sub-domain. Google has been looking at relationships between sites for years now so even sites to do not immediately appear to be related but are through links such as ownership, registration, and so on, will each effect the other. This is something that needs to be considered.
As far as links and content snippets, Google will see this through it's citation mechanism. If these are simple links with content snippets, then this generally should not be a problem except if your content appears to be a link site with no original content. Google has been discounting sites that rely solely on automated content, links, and other mechanisms that have previously been relied upon to generate a site for search performance and ad revenue and less for users. These sites have historically been low quality sites that have polluted the search result pool. However, this does not mean that a site of this nature cannot be of value. Remain within the Google Guidelines: https://support.google.com/webmasters/answer/66356?hl=en. You may also find this helpful: http://www.bkv.com/blog/amidst-google-updates-is-social-bookmarking-good-or-bad-for-seo/ as well as this: http://bloggingconsult.org/social-bookmarking-is-dead-sites/.
I have not seen your site and cannot comment specifically. But here is the up-shot of what has been described.
You will want to look at changing your parent domain site to remain within the Google guidelines including this: https://support.google.com/webmasters/answer/2721311?hl=en. You want to make sure that the content it provides is of value to users and not for search. You want to take this measure so that any effort you make will have a positive effect and not an effort that goes unrewarded.
If you are staring a blog, it is generally better not to use a sub-domain, though there are legitimate reasons to create blogs on sub-domains. Your parent domain will benefit from the traffic as well. It will help to offset any automated or link content you may have.