I had this problem with a different module. Notice that org.jboss.weld is throwing the error. You have to go down to the module whose library is throwing the error and add org.slf4j and org.apache.log4j to the dependencies for *the module*. It will do no good to add it to your app -- it least it did me no good.
In my case, it was org.jboss.logging that was throwing the error so I added the dependencies to the module for org.jboss.logging like this
<module xmlns="urn:jboss:module:1.1" name="org.jboss.logging">
<resources>
<resource-root path="jboss-logging-3.1.0.GA.jar"/>
<!-- Insert resources here -->
</resources>
<dependencies>
<module name="org.jboss.logmanager"/>
<module name="org.slf4j" />
<module name="org.apache.log4j" />
</dependencies>
</module>
TDR