COMBINING SEDIMENTOLOGY AND ICHNOLOGY TO REFINE PALEOENVIRONMENAL INTERPRETATIONS IN FLUVIAL-DELTAIC-SHALLOW-MARINE CLASTIC SYSTEMS

Our research group routinely and conscientiously integrates sedimentology and ichnology in investigations of ancient shallow-marine to continental transitional stratigraphy. Without incorporating detailed ichnological observations, differentiation between certain paleoenvironments found along complex coastlines would be extremely difficult, as well as providing sufficient, realistic paleoenvironmental reconstructions for academia and industry.

We provide examples from both outcrop and core investigations that highlight the value of combining ichnology and sedimentology in clastic sedimentologic studies. Examples include mixed fluvial-flood and tidally influenced systems of the Western Cretaceous Interior Seaway (Loyd, Sego, and Neslen fms), a Cretaceous delta of Arctic Alaska (Schrader Bluff Fm), Permo-Triassic fluvial and deltaic systems of Antarctica (Mackellar, Fairchild, Buckley, and Fremouw fms), and Jurassic floodplains of Mississippi (Cotton Valley).

In these examples trace-fossil and lithofacies associations are used to: 1) identify nearshore, shallow-marine environments including tidal deltas, tidal flats, bayhead deltas, and subaqueous channels and discriminate between continental and marine strata; 2) differentiate between muddy interdistributary bays and floodbasins, 3) identify a fluvial-flood-dominated delta that prograded into a brackish water basin; 4) provide evidence for lake marginal forests; 5) ascertain the distribution of low- vs. high-latitude ichnological signatures of continental fluvial and lacustrine deposits in a Greenhouse world; and 6) recognize floodplain continental crevasse-splay and floodplain environments in otherwise enigmatic core intervals. The studies also provide examples of the trace-fossil identification of significant surfaces, otherwise nearly undetected, within both sandbodies and mudstones. This is important because missing such surfaces has implications to the reconstructing environments, sea-level curves, hydrology, and climate. We suggest that ignoring even subtle trace-fossil data can be detrimental to interpreting paleoenvironments, which can lead to erroneous assumptions about paleoenvironmental evolution and sandbody-shale geometries.