At least a quick glance suggests Thameslink services make up 113 of
the 116 cancelled trains now showing on FCC Journey Check (the other
three being GN services):
http://www.jcheck.com/firstcapitalconnect

In the 'Line Update' section on the Journey Check page, one entry
cites "Line problem in the Blackfriars area", specifically "poor rail
conditions" as one contributory factor. Another entry just cites "poor
weather conditions".


Meanwhile this is on the FCC website:

---quote---
Major disruption
Monday morning service

Thameslink route

There are many cancellations on the Thameslink route because of last
night's extreme frost which reached -13 degrees in some places and
affected trains and track infrastructure.

Tickets can be used on East Midlands services and London Underground
on all reasonable routes as well as Great Northern route services.

We have not been able to call at London Bridge and services have been
diverted via Herne Hill.
---/quote---