looks like somedate is in timestamp and not a date and you have date field in Teradata. try converting it to date, if you want to insert in as date using sasdatefmt during proc append also helps. below is the example of sasdatefmt dataset option from sas documentation.
proc append base=mydblib.internat (sasdatefmt=(dates='date9.'))
force data=saslib.delay;
run
or
proc append base=mydblib.internat(sasdatefmt=( date1='datetime21.'))
force data=saslib.delay;
run