Ichnological analysis of the Pleistocene Dwarka Formation, Gulf of Kachchh: tracemaker behaviors and reworked traces

摘要

Complex interaction among trace fossils are important in understanding organisms niche preference for foraging in ancient rock records. There exist well-recorded examples of compound trace fossils. However, such compound traces rarely exhibit exploitation of burrow wall and fill sediments for feeding. In recent sediments, several examples are well documented for feeding on burrow wall and burrow fills because of nutrient enrichments in them. Such type of complex interactions occur in the shallow marine Pleistocene age sequences exposed in island in Gulf of Kachchh, India. These deposits are known as ‘Shankhodhar Sand Clay Member’ of Dwarka Formation. Trace fossils recorded are Chondrites , Chomatichnus , Gyrolithes , Ophiomorpha, Rhizocorallium , Schaubcylindrichnus , Sinusichnus , Spongeliomorpha , Taenidium and display three Ichnoassemblages. Three types of complex interactions are suggested: (1) Burrow architecture modification, (2) feeding on burrow walls and burrow fills and (3) acute angle branching. Thus, the trace fossil association indicates selective preference of trace maker for their foraging activities in shallow marine Shankhodhar Sand Clay Member of Pleistocene age.