Transaction Log usage by transaction
The log can be forced to grow if you have an old transaction that has not been committed or rolled back, regardless of the size (it could affect a single row). For the database in question, assuming you haven't resolved the problem yet, do this:

DBCC OPENTRAN();


This should show you the oldest active transaction (and there is a good chance this is the one that is preventing the log from wrapping). You can see the last thing they did (but not necessarily the thing that is causing the problem) by (documentation):

DBCC INPUTBUFFER(&lt;spid&gt;);


And if they have a query that is currently running:

SELECT * 
  FROM sys.dm_exec_requests 
  WHERE session_id = &lt;spid&gt;;


You can also see from sys.databases what the log holdup is (it could be something else entirely):

SELECT log_reuse_wait_desc 
  FROM sys.databases 
  WHERE name = N'&lt;database name&gt;';


There can also be reasons why an 80 MB transaction might require more than 200 MB of log space - see Remus' answer here:


Why does this 120 GB insert grow the log by over 780 GB?


And I recommend you read this page in its entirety (perhaps you are not using the right recovery model, and perhaps you should consider allowing the log more space to grow when it needs to, rather than shutting down all activity until you resolve the situation manually):


Why Does the Transaction Log Keep Growing or Run Out of Space?


Related: 


Identify cause of unusual transaction log growth 
Contents of transaction log file in more detail
SQL Server transaction log
Finding exact statement causing error 3930
SIMPLE or FULL recovery model for databases?
SQL Server log file continues to grow?
Changing a column&#39;s data type fills the transaction log
Log sizes unexpectedly large: log_reuse_wait_desc == &quot;log_backup&quot;