CL65 WAS CLRED TO DEPART THE GATE AREA. MARSHALLER SIGNALED TO MOVE FORWARD AND BEGIN A L TURN. CAPT REQUESTED FO TO CHK CLRNC R WINGTIP WHEN CONTACT WAS MADE TO THE L WINGTIP OF A PARKED SF340. PAX DEPLANED AND BUSSED TO THE GATE.

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I WAS SERVING AS CAPT AND PIC OF THE FLT. AN RJ50 WAS USED. THE ACFT WAS PARKED ADJACENT TO A BLAST FENCE AND OPPOSITE FROM GATES AND WX CONDITIONS WERE CLR. AN SF340 WAS ALSO PARKED ALONG THE BLAST FENCE. PRIOR TO MOVEMENT OF THE ACFT; ALL PERTINENT CHKLIST ITEMS WERE COMPLETED. THE FO THEN CONTACTED LGA RAMP TWR AND REQUESTED CLRNC FOR TAXI. WE WERE CLRED TO TAXI TO SPOT XX. GND MOVEMENT WAS CONDUCTED PURSUANT TO THE DIRECTION OF A MARSHALLER. UPON RECEIVING CLRNC TO TAXI; I SIGNALED THE MARSHALLER TO INDICATE THAT WE WERE READY TO BEGIN THE TAXI. THE MARSHALLER THEN SIGNALED TO THE FLC INSTRUCTIONS TO MOVE THE ACFT FORWARD. THE ACFT MOVED FORWARD A SHORT DISTANCE. THE MARSHALLER THEN SIGNALED AND INSTRUCTED TO TURN TO THE L. I THEN APPLIED FULL L RUDDER; AND TURNED THE STEERING TILLER TO THE L. AS THE ACFT BEGAN TO TURN; I OBSERVED THAT THE MARSHALLER WAS CONTINUING TO SIGNAL A L TURN. AS THE TURN PROGRESSED; I NOTICED THAT THE MARSHALLER APPEARED TO BE LOOKING AT THE R WING. I INTERRUPTED THE FO AS HE WAS TALKING TO LGA GND CTL; TO ASK HIM TO LOOK BACK AND OBSERVE WHETHER THE R WING WAS CLR OF OBSTACLES. AS I SPOKE TO THE FO; THE MARSHALLER SUDDENLY PERFORMED THE EMER STOP SIGNAL. IN RESPONSE; I IMMEDIATELY APPLIED THE ACFT BRAKES. BEFORE COMING TO A STOP; I FELT THE ACFT SHUDDER. WE THEN ACCOMPLISHED THE PARKING CHKLIST. SHUTTLE BUSSES WERE RETURNED TO OUR POS AND PAX WERE DEPLANED. HOW THE PROB AROSE: 1) IT WASN'T UNTIL AFTER THE INCIDENT THAT WE FOUND OUT THERE WERE NO WING WALKERS. 2) PARKING CLOSELY IN A CONGESTED AREA. CONTRIBUTING FACTORS: 1) NO WING WALKERS. 2) CONTAMINATION ON RAMP; POSSIBLY CAUSING NOSE TIRES TO SLIP; PREVENTING A SHARP ENOUGH TURN. 3) INEXPERIENCED RAMP AGENTS. CORRECTIVE ACTIONS: WING WALKERS DURING TAXI OPS IN CLOSE PROX TO OBSTRUCTIONS.