Gerken, who was only in the side because Adriano Basso injured himself during the warm-up, produced fine second-half saves to deny Danny Guthrie and Kevin Nolan inside a minute as the Magpies had to make do with a point at home for the second time in four days.
Marlon Harewood had earlier hit the post and Steven Taylor and Kevin Nolan both headed against the crossbar, but the Championship leaders were simply unable to break down their opponents on a frustrating afternoon.
The home fans once again made their feelings about owner Mike Ashley known a day after former boss Kevin Keegan was awarded £2million in damages for constructive dismissal.
On the pitch, caretaker boss Chris Hughton, who was named Manager of the Month for the second successive month before kick-off, left young strikers Andy Carroll and Nile Ranger sitting on the bench as old heads Marlon Harewood and Peter Lovenkrands got the nod.
The home side had two ambitious penalty appeals turned down inside the opening five minutes, although it was City who produced the first shot, Steve Harper getting down well to save Nicky Maynard's long-range effort.
But it was Newcastle who almost took the lead with 10 minutes gone when Lovenkrands lifted the ball over the top for Harewood, whose shot came back off the post with Gerken beaten.
Robins midfielder Cole Skuse saw a blistering 15th-minute half-volley deflected just over, and Steven Taylor had to mop up in front of his own unguarded goal after Zurab Khizanishvili's woefully short back-pass allowed Lee Johnson to beat Harper to the ball.
The Magpies keeper had to get down well to claim Johnson's 40th-minute cross at his near post after Evander Sno had picked out the midfielder's run into the box.
Gerken was back in action within two minutes of the restart when he had to get down well to field a Jonas Gutierrez shot with Newcastle making a concerted push.
Lovenkrands went agonisingly wide with a left-foot drive after an enterprising 52nd-minute run across the edge of the City penalty area, and Gerken saved from Harewood four minutes later as the pressure mounted.
The keeper saved the visitors twice within seconds, clawing out a Guthrie volley and then turning away Nolan's header, but needed the help of the woodwork again when Steven Taylor and then Nolan both hit the bar.
Referee Graham Salisbury astonishingly waved away Harewood's claims for a penalty after he was brought down by substitute Jamie McCombe with 16 minutes remaining, and City managed to weather a lattorm to claim a point.