Latitudinal Distribution of Trace Fossils in Continental and Marine Depositional Systems: Controls, Trends and Caveats
Modern biota in continental and marine depositional systems largely reflect the climatic controls on their distribution. Through most of the Phanerozoic, climate has varied in a predictable manner with latitude, controlling the distribution of biotic systems as recorded by tracemaking epi- and endobenthic organisms in the marine realm and epigeal, geophilic, and geobionts in the continental realm. These trends, however, are displaced by local physicochemical controls and autocyclic processes that operate within sedimentary systems. Diversity, and thus assumedly ichnodiversity, decreases from the equator to the pole for marine and continental environments. This reflects the evolution and dispersal of organisms from equatorial regions into higher latitude and into deeper water in marine settings through time. Abundance in biomass also shifts from shallow coastal settings in low latitudes to mid- to outer shelfal settings in high latitudes. Body size of marine crustaceans tends to increase as water temperature decreases, paralleling the gas solubility of colder water; thus, body size and therefore burrow diameter may increase as latitude increases. Deeper, more penetrative burrowing takes place in the shoreface and becomes shallower into the abyssal zone, as communities shift from suspension-feeding to deposit-feeding to grazing and gardening in the deepest settings. In continental settings, these patterns are not present in lacustrine systems as the physicochemical conditions and their geologic longevity are distinctly different. Burrowing biota are intimately involved in pedogenesis and show latitudinal trends that parallel the production and depth of weathering products. Bioturbation depth and tiering tends to be deepest in subtropical equatorial regions rather than equatorial regions where weathering is deepest. This pattern is shallowest in arid climates, increases in temperate latitudes, and decreases toward the pole. Bioturbation patterns in soils are shallowest in weakly developed soil as well as in high soil moisture and water table settings. Bioturbation becomes deeper and more pervasive as soil development increases, soil moisture decreases, and water table depth increase. Latitudinal patterns of both marine and continental bioturbation should predictably change from greenhouse to icehouse conditions, where temperature, effective precipitation, solar insolation, runoff, and evapotranspiration change as climate changes.
AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015