The phrase "a landmark source" is correct and usable in written English.
It can be used to refer to a significant or influential source of information, research, or data in a particular field.
Example: "The study published in 1995 is considered a landmark source in the field of environmental science."
Alternatives: "a pivotal source" or "a seminal source."
The oil refinery was used as a landmark source from which to estimate the distance, determined by this industry being the main source of exposure in SIZ and its early operation date.
Honorably, this special issue serves as a landmark source for education, information, and reference to professors, researchers, and graduate students interested in updating their knowledge about or active in biomedical analysis, drug design, computational genomics, and systems biology.
Honorably, this special issue serves as a landmark source for education, information, and reference to professors, researchers, and graduate students interested in updating their knowledge about or active in biological computing, biocloud services and management, and novel application models for bioCloud services and computing systems.
In 1992, despite opposition from the CIA, he obtained Marine Corps permission to organise a landmark international conference on open source intelligence – the paradigm of deriving information to support policy decisions not through secret activities, but from open public sources available to all.
Alfred Balk, a reporter, author and magazine editor who wrote groundbreaking articles about housing segregation and the Nation of Islam, and whose refusal to identify a confidential source led to a landmark court case, died on Thursday at his home in Huntley, Ill.
Emily Clark provides a landmark critique of a rare archival source, the message books of black Spiritualists active in New Orleans from 1858 to 1877.
Once again, we could say that Lincoln did not need to cite the source of such a landmark principle.
Richard Niebuhr, made his reputation by dissecting "The Social Sources of Denominationalism," a landmark study in American religion.
Perl was a landmark product in advocating the open-source model a collaborative, rather than proprietary, approach to software development—earning Wall the 1996 Dr. Dobb's Excellence in Programming Award and the Free Software Foundation's Award for the Advancement of Free Software in 1998.
From what I understand, talking to sources, this is a landmark deal on two levels.
