[a] He was a pioneer in using fossil forams to sequence marine sedimentary deposits by their relative dates;[1][2] a technique called biostratigraphy.

In 1928, Michele Gortani (1883-1966), who had succeeded Capellini as Professor of Geology, wrote that "the Master had deprived his most promising student, Carlo Fornasini, of the pleasure and pride of announcing his discovery [...] and the results of his studies" (Italian: il Maestro aveva portato via al suo più promettente scolaro, Carlo Fornasini, il piacere e il vanto di annunciare la scoperta [...] e i risultati dello studio).

[1] In 1881, Fornasini returned to palaeontology, possibly persuaded by his friend Lodovico Foresti (1829-1913, assistente (assistant) at the Museo Geologico in Bologna).

[6] When the Italian Geological Society [it] was founded in Bologna during the Congress, under the leadership of Giuseppe Meneghini (1811-1889) and Capellini, he was one of the original members.

[2] In 1895, Fornasani and Vittorio Simonelli (1860-1929) founded the journal Rivista italiana di paleontologia ('Italian Review of Palaeontology').

[1] He married Emilia Erhardt (at a date not determined), and they had two children: Carlo Francesco, a son, and Elsa, a daughter.

[1] He published chiefly in the journals (dates of earliest and latest papers in parentheses) Bollettino della Società geologica italiana (1883-1905),[8] Memorie della Reale Accademia delle Scienze dell'Istituto di Bologna (1889-1908),[11] and Rivista italiana di paleontologia (1896-1903).

However, the fact that as of 2019[update] Fornasini is still credited as taxonomic authority for 77 of those 78 species shows that he was a careful, accurate and knowledgeable observer.

In 1964, his son Carlo Francesco donated land and money in his will to set up in his father's memory the Fondazione Dott.