SEEKING TROUBLE IN PARADISE: EXPOSING STUDENTS TO COMPLEX FACIES MOSAIC STRATIGRAPHY OF THE BAHAMAS AND HAWAII

Students of sedimentology and stratigraphy classes in the Northeast are commonly exposed to field and laboratory exercises involving correlation and interpretation of Appalachian Basin strata. Typically, this involves widespread lithostratigraphic correlation. Although local paleoenvironmental changes are apparent to the careful observer of Appalachian Basin strata, such correlation exercises tend to imbue many students with the perception of “layer-cake” bedding geometry. In contrast, field mapping exercises in Pleistocene-Recent carbonate deposits of the Bahamas and coastal Hawaii force students to consider complex, patchy facies relationships and detailed sea-level histories when examining strata. San Salvador Island in the Bahamas provides an outdoor workshop on the effects of Quaternary sea-level changes and pre-existing topography on facies distributions. Lithified Pleistocene carbonate dunes and skeletal reefs formed at various sea-level stands make positive features that affect later dune formation and marine facies distribution. Students conduct snorkel transects and land-based mapping exercises in order to map the effects of relict dune or reef topography on environmental conditions. One such snorkel exercise studies the features from Rice Bay Beach to Man Head Cay, a Sangomon-aged, regressive dune island (Carew and Mylroie, 1995). Man Head Cay forms a 360+ meter-long barrier as part of a broken and partially submerged bedrock sill bordering the northeastern margin of Rice Bay. A shallowly submerged sill to the southeast of the island and a deep break in the sill directly northwest of the island produce systematic changes in wave orientation, wave intensity, and marine benthic communities that students can map on diving slates. Pleistocene shoreline and reef carbonates along northern and western Oahu, Hawai’i, offer students a view of multi-stage deposition superimposed on volcanic topography. These outcrops also require students to consider the additional effects of uplift on the position and elevation of the deposits. Students can relate what they have learned about the facies mosaics in these well-exposed, young deposits to develop better conceptual models of sedimentation in ancient strata of the Northeast.