"markedly due to" is correct and can be used in written English.
It is used to indicate that something is largely or significantly caused by a particular factor or reason. Example: The decline in sales was markedly due to the economic recession. In this sentence, "markedly due to" highlights that the economic recession was the main reason for the decline in sales.
The United States, for example, has dropped markedly due to the targeting of journalists covering the Occupy Wall Street movement.
Patch numbers (N), class areas (CA), and total edge lengths (TE) of ditch margins decreased markedly due to subsurface drainage.
Increasing the application rate enhanced the horizontal water movement markedly due to the soil surface crust effect, thus reducing the infiltration rate.
After mixing crude oil with aqueous alkaline silicate and carbonate solutions, viscosity decreases markedly due to formation of oil in water (o/w) emulsions.
The results show that incorporation of EVA increases the toughness of the polypropylene but its stiffness decreased markedly due to the incorporation of the low modulus component.
We also broke down rankings by size since regional economies differ markedly due to their scale.
Chris Wild, the director of the WHO's International Agency for Research on Cancer, told the BBC: "The global cancer burden is increasing and quite markedly, due predominately to the ageing of the populations and population growth.
From around 1994, methamphetamine appeared to take over and production seems to have stepped up markedly – probably due to the dire straits of the North's economy.
Finally, the photocurrent markedly decreased due to catalysis of hemin/G-quadruplex toward 4-chloro-1-naphthol.
It was found that, by applying CPF, concrete permeability was markedly reduced due to the improved surface and microstructures.
In this way, the demand for oxygen is markedly reduced due to the suppression of metabolic processes and detrimental pathways are also slowed by reduction of temperature.
