Migration of table from MySQL to Oracle using GoldenGate
From my experience with GoldenGate, it's better to do initial loads with database native tools.  In this case, you would use:

SELECT * FROM TABLENAME INTO OUTFILE 'filename';


https://dev.mysql.com/doc/refman/5.7/en/select-into.html

Then load into Oracle with SQL*Loader.   

Example control file for SQL Loader:

$ cat example1.ctl
load data
 infile '/home/ramesh/employee.txt'
 into table employee
 fields terminated by ","
 ( id, name, dept, salary )


Example taken from:
https://www.thegeekstuff.com/2012/06/oracle-sqlldr/

If you cannot stop data changes to perform the load, you need to:


Start your extract
Export the data
Load the data
start your replicat with HANDLECOLLISIONS enabled


After your replicat has caught up, remove HANDLECOLLISIONS.

For some good Tutorials, I've used https://gavinsoorma.com/category/goldengate/

Also the Oracle TechNet forums were responsive for GoldenGate questions - even for some really obscure scenarios.