Some Sedimentary Features in Turbidity Current Deposits

Turbidity currents are commonly graded in their bedding, that is, each of the deposits (underwater landslides) is coarser in texture at the bottom and finer at the top of the sequence. As well they contain certain types of sedimentary structures that assist in the identification of units as turbidity current deposits. Some of these features include 1) graded bedding, 2) sole marks, 3) cross stratification units, 4) asymmetrical ripple marks, 5) extensive even bedding with interbedded sands and shales. Arnold Bouma's 1962 work on Italian turbidites gave rise to what geologist's now call the Bouma Sequence and a method of interpreting, rather precisely, the ancient world represented by a particular rock units within a sequence. Non-carbonate turbidites are generally sparsely fossiliferous with fossils from both shallow- and deep-water environments. Sporatic reportings of Mesozoic clams and deep water benthic foraminifera have been made in Marin and in surrounding Franciscan rocks.

Right now we have limited information but do have the following photos of some of these features:

Eastern Coast Ranges