Abstract: Mud-Facies Definition for Paleoenvironmental Interpretation

Daniel Jean Stanley, Andres Maldonado

Mud, the most important sediment type in world oceans, can be used as an environmental indicator as shown by studies in the Mediterranean. Five major mud facies are distinguished to depths of 5,000 m; open-ocean facies (below CCD) are not present. Mud type is defined by X-radiography, petrography, and SEM.

(1) Shallow-water mud: structurally homogeneous, well bioturbated; high (10-15%) sand fraction, either biogenic (molluscan and other) or clastic; usually shallower than 400 m. (2) Turbiditic mud: basal lamination and small-scale bioturbation; low sand content (0 to 3%), a mix of terrigenous and shallow-water and planktonic tests; usually below 400 m, proportion increases with depth. (3) Hemipelagic mud: homogeneous, usually well-bioturbated; moderate sand content, mostly planktonic tests; it is an end member of a series defined on sand fraction amount: hemipelagic mud (3 to 8%) ^rarr calcareous ooze (5 to 15%) ^rarr foraminiferal-rich mud (> 15%); usually below 300 m, proportion is highest in areas inaccessible to mud turbidites; records relation between organic productivity, suspended sediment input, and dissolution. (4) Sapropel: laminae of alternating coccoliths and mud; sand content variable (to 10%), usually planktonic components; it is he end member of series defined on structures and composition; sapropel ^rarr protosapropel ^rarr organic ooze; below 700 m, restricted to the eastern Mediterranean; indicator of stratification and unventilated to stagnant conditions. (5) Current-modified mud: all preceding types can be remolded by bottom flow; defined by lamination and composition.

Types 3 and 4 sediment rates are usually < 10 cm/1,000 years. Bioturbation is correlatable with rates of biogenic productivity and sedimentation and depth. The proportion of different mud types in a stratigraphic section reveals paleodepth and oceanographic conditions during deposition. These distinctions may be applicable to the ancient rock record.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC