I've seen that on engines sith improper wvo systems. If the engine isnt up to full opersting temp and the oil isnt hot you get incomplete combustion and engine oil contamination with wvo. I've been running wvo I my 2000 Ford superduty for 6 years now and 50k +/- miles, and havent had a single problem other than wvo fuel pumps not lasting. One rule on wvo is you shorten your OCI specifically because WVO and diesel motor oils don't play well.
I have a theroy its the zinc in the hedo as I have watched zinc coated galvinzed pipe parts grow a gelatinous coating of wvo in a day. Hot wvo and galvinized pipe (or a galvinized drum) dont mix well. Iirc hdeo's are one of the last remainung high zinc engine oils ouut there.
While WVO is almost certain to cause as you describe, even B20 I suspect could do this given enough extended operation on B20 (RME or DME) in cold temperatures and long drain intervals.
With lots of short trips in cold temps, blowby would be excessive. Combining high blowby of fatty acid methyl esters with a higher-zinc diesel oil COULD explain the goo that is on display here.
As for turbo causing this, not a chance. The turbo bearings would be shot LONG before this amount of sludge could accumulate. Failing to cool down turbo is actually one of the things you can rule out. Turbo cool down periods are for turbos-- and nothing else.
I work in product development at Cummins, but I can only speculate here as we do not do lengthy testing on B20 or biofuels in general-- I've never seen that kind of goo in field test or test cell engine.