The correct answer is "சமணம்" which means Jainism. The question asks about the time period related to the book "மணிமேகலை" (Manimekalai). The other options, பெத்தம் (Buddhism), வைணவம் (Vaishnavism), and சைவம் (Shaivism), are different religious beliefs and not related to the book. Therefore, the correct answer is சமணம் (Jainism).