The part of a sentence 'has been extensive speculation' is correct and usable in written English.
You can use it when referring to something that has been the subject of much discussion or conjecture. Example: There has been extensive speculation about the future of the company since its announcement of possible layoffs.
But there has been extensive speculation, and Shergar has been the subject of a book and a play.
There has been extensive speculation about whether Hemingway and Ivancich, who first met in 1948, were lovers.
BP's current interests around the Arctic region are centred on Alaska, but there has been extensive speculation that the company is in talks with rivals such as Apache to sell these off in a desperate attempt to raise cash to pay for expected oil-spill liabilities of more than $30bn.
You can read his short statement below with a couple of thoughts from me: The Origin of the Heartland Documents Peter Gleick Since the release in mid-February of a series of documents related to the internal strategy of the Heartland Institute to cast doubt on climate science, there has been extensive speculation about the origin of the documents and intense discussion about what they reveal.
There has been extensive speculation concerning the mechanisms of resistance.
There has been extensive speculation regarding the association of autoimmune and allergic diseases.
There has been extensive industry speculation during the last year that Mr. Jobs is planning to use the Internet to deliver high-definition video directly to consumers on flat-screen televisions.
There has been extensive and wild speculation about how the BBC intends to enforce the new rules.
There has been extensive research in recent years on the multi-scale nature of hippocampal place cells and entorhinal grid cells encoding which led to many speculations on their role in spatial cognition.
