Understanding the morphological evolution of modern coralgal reefs helps decipher the forcing mechanisms that influence the evolution of ancient carbonate reefs. In this study, a comparison between Uppermost Pleistocene drowned coralgal reefs stretching along the south Texas shelf edge and Upper Cambrian microbial reefs in Mason (Central Texas) is developed. Similarities and differences between the two settings, separated by 500 million years, make it an interesting comparison. Among the major similarities, both settings represent low-latitude, shallow water within the photic zone, shelf edge, mixed carbonate siliciclastic systems, whereas the nature of the two reef builders is the main difference. Forcing mechanisms, among them sea level fluctuations, are well established during last transgression since Last Glacial Maximum and directly tied to the morphological evolution of the Uppermost Pleistocene coralgal reefs. The initial transgression triggered a clear switch from shallow coastal siliciclastics to neritic coralgal reefs on the south Texas shelf edge banks. A similar switch is also observed at the base of the Upper Cambrian microbial reefs where the system changes from mixed carbonate-clastic to pure carbonate system. Based on these comparisons, it is demonstrated that an Upper Cambrian transgression led to the establishment of microbial reefs providing it enough accommodation to grow vertically.