Geochemical and sedimentological data obtained from outcrop localities examined during the present study are presented to explain the origin of bedded phosphatic limestones for selected San Pedro del Gallo terrane remnants (SPGTR) occurring southwest of the Walper Megashear in northeastern Mexico. Three “remnants” of the San Pedro del Gallo terrane (SPGT) (lower Oxfordian to upper Hauterivian) are examined, concentrating on the outer bathyal to upper abyssal La Caja Formation (lower Kimmeridgian to upper Tithonian). During the late Tithonian, a worldwide phosphorogenic episode is recorded from deposits occurring along the western margin of continental masses. In Mexico, a study of...