[en] The formation and the basic features of arbitrary amplitude ion-acoustic solitary waves (IASWs) in an electronegative plasma containing cold negative ion fluid, warm positive ion fluid and nonextensive electrons are theoretically investigated by using the pseudo-potential technique. The pseudo-potential is analytically and numerically analyzed and the conditions for the formation of the arbitrary amplitude IASWs and their basic features (viz. polarity, amplitude, width etc.) are identified. It is observed that the electronegative plasma under consideration supports the coexistence of compressive and rarefactive IASWs, and that the temperatures and number density of positive ion fluid significantly modify not only the basic features of compressive and rarefactive IASWs, but also the parametric regime of their coexistence. The implications of our results in some space and laboratory electronegative plasma situations are finally pinpointed.