The phrase "as a marked exception" is correct and usable in written English.
It can be used to highlight a specific case that stands out from the general trend or norm.
Example: "Most students completed the assignment on time, but Sarah, as a marked exception, submitted hers a week early."
Alternatives: "as a notable exception" or "as a significant exception".
Fox counters with skepticism about auto industry claims that the credit crisis represents a marked exception from the workings of the market-as-usual: "They were already in the process of getting ready for a new era and they just, sort of, ran out of time..
They also dislike plants with thorns, such as purple coneflower but delicious roses seem to be a marked exception to that!
A marked exception to the propensity to use rurality as the governing precept in these adjustments is England's Market Forces Factor (MFF).
(Her own notably successful marriage she and Philip celebrated their 65th wedding anniversary on Nov. 20, 2012 was a marked exception).
The increase is only a 10th of what President Obama asked for in his 2012 budget for ARPA-E, but it is a marked exception to the spending reductions in the rest of the bill.
The United States is a marked exception to the cube root law, which says that the number of seats in the larger chamber of a country's legislature should be approximately the cube root of the country's population.
Zambia was a marked exception, beginning with nationwide implementation of certain reforms in all districts, but then taking longer to extend the reform to other aspects, such as staffing, where more preparation was needed.
Exceptions, such as a marked tendency to be male rather than female, are generally so broad as to be of little practical use in targeting interventions.
In fact, discouraging hate speech is an ideological stance common to nearly all internet services, with the marked exception of services created specifically to circumvent that stance.
