We have had sent in some papers about mud lumps.
“Mudlump islands are surface manifestations of intrusive clay masses that result from depositional processes at the mouths of major Mississippi River distributaries. The stratigraphy and structure of mudlumps at the South Pass mouth have been studied by means of a drilling and coring program which included drilling holes to a depth of 700 ft. Subsurface information obtained establishes the relationship between older shelf and prodeltaic river deposits and younger, progradational delta-front and river-mouth bar sediments.”
Mudlumps at the Mouths of the Mississippi – from LSU
‘Mud Lump’ Leads To Damage At Nola Walf – 2008 article from Waterways Journal Weekly
This National Geographic article on the big 2011 earthquake that hit Japan has a lot about clay sediments on the seafloor –
The 2011 Japan Tsunami Was Caused By Largest Fault Slip Ever Recorded
Clay lubricated the fault zone in the Japan trench, producing the devastating tsunami, researchers say.