Srimad Bhagavat Mahapurana in the Third Canto Chapter VIII narrates the tale of Creation / Birth of Brahma. However I have found no reference there in to the birth / creation of Shiva.
The detailed reference to Shiva appears for the first time in the Fourth Canto Chapter I when the Trinity appear in person before Maharishi Atri.
Following Srimad Bhagavat Mahapurana prior to the creation at the bottom of the ocean lying on the coils of the Serpent Adisesha, Mahavishnu lies in deep slumber Yoga Nidra waiting for the right time to once again commence Creation and His first creation is Brahma. But where or how was Shiva created? There is a reference elsewhere that Shiva is one of the Rudras and hence progeny of Prjapati Kashyapa as is Vishnu one of the twelve Adityas. But this moves away from the concept that the Supreme Being is self manifested.
Is Shiva also self manifested? Please enlighten with Pauranic and Shruti references.