Petrological characteristics of blue lenticular patches occurring in the lower globigerina building limestone of Malta

Abstract

The Lower Globigerina Limestone Member, the earliest member of the Globigerina Limestone Formation, is the lithostratigraphical bed which had provided limestone for the erection of Malta’s built heritage since Neolithic times. It is massively bedded, pale yellow in colour and consists predominantly of globigerinid planktonic forminifera. Occasionally, blue coloured lenticular patches occur in this member. The first published research relating to these features was by John Murray in 1890. His results and interpretation were corroborated and refined through a recent publication by the author which noted variations from packstone to wackestone along these patches. This paper further studies their petrological characteristics. Petrographically, the limestone of these patches gradually alternates from wackestone to mudstone to bioclastic wackestone. They are composed of micrite matrix (in varying amounts), ferrugenized unbroken pelagic foraminifera, bioclasts, and terrigenous quartz. The appearance of these blue lenticular patches must be linked to another process other than limestone texture.