An ordinance may be initiated by petition to which all signatures shall be obtained within thirty (30) days before the date of filing. A referendum on an ordinance enacted by the City Commission may be had by a petition signed within thirty (30) days after the enactment of the ordinance. A petition for an initiated ordinance or for a referendum shall be in the form and manner hereinafter provided. An initiatory petition may not be filed, the purpose of which is to enact an ordinance for the repeal of an ordinance previously enacted.