Comparison of Large Mass Transport Deposits from Industry Seismic, High-Resolution Geophysical, and Outcrop Data
C. Simon Newton
Dalhousie University, Halifax, NS
A comparison of large mass transport deposits (MTDs) identified on industry seismic, outcrop, and very high-resolution geophysical data in clastic settings is used to investigate the setting, triggering mechanisms, transport mechanisms, and physical characteristics of large MTDs. The results of this work show that most large MTDs, those with greater than 100 km3 of displaced sediment, share many common characteristics.
Large Quaternary MTDs are identified with high-resolution geophysical data on the margins of almost every continent. Recent large MTDs are found in glacial-dominated high-latitude margins and in river-dominated lower latitude margins. Older, large MTDs are also increasingly reported from industry seismic data, particularly in river-dominated margins. Outcrop exposures of large MTDs are reported from several ancient accretionary deposits. In most cases, earthquakes are the inferred triggering mechanisms, though pre-conditioning factors such as sedimentation rates are also important. Comparison of the large MTDs reveals that most are classified as slide deposits, although internal structures and external geomorphology reflect a wide variety of physical processes. In an idealized large MTD, strata are displaced as large rotational blocks during the initial stages of failure. These blocks continually break apart as downslope displacement continues. Downslope of the failure zone, strata are deformed and removed as sediment travels downslope. Significant basal reworking and erosion terminates at a contractional ramp. The sediment continues to travel as a slide or debris flow beyond the ramp. Generally large MTDs are tens of kilometers wide and extend downslope for greater than 100 km. Average thickness of large MTDs is generally greater than 100 m.