FAST AND ECONOMICAL SAMPLING AND RESIN-EMBEDDING TECHNIQUE FOR FINE-GRAINED SEDIMENTS: AN EXAMPLE USING NEOICHNOLOGY EXPERIMENTS WITH MEIO- AND MACROFAUNA

An economical and fast water-acetone-epoxy-exchange method is presented for resin-impregnation and archiving of sedimentary structures in water-saturated, fine-grained sediments. The example presented uses neoichnological experiments with meio- and macrofauna organisms in fine-grained media. This method is useful for documenting small-scale textural features that are difficult to preserve in soft sediment, such as bioturbation features, which is critical for facies analysis in fine-grained units. A water-acetone-epoxy-exchange method was first employed by Spurr (1969) for electron microscopy, and later by Clark (1988), Card (1997), and Lotter and Lemke (1999) to preserve varved lake sediments. Advantages of the modified method are (1) it uses limited quantities of inexpensive and easily accessible materials; (2) the initial subsampling produces little disruption of sedimentary structures; and (3) we devised a fast method of eliminating acetone and hardening of the remaining epoxy resin. The sampling apparatus consists of a cellulose sampling tube with a diameter of ~1 cm in a rigid tube holder. The sampling tube is fortified at its bottom with aluminum foil acting as a blade during insertion into the sediment. The sample tube holder with sampling tube is pressed slowly into the unconsolidated sediment until it penetrates a soft wax layer placed at the bottom of the sedimentation tank. The cored wax disk adheres to the aluminum foil and acts as a core catcher. The sampling tube filled with sediment is removed from the holder and placed into a glass apparatus for step-wise exchange of interstitial water with acetone. After removal of water and drainage of most acetone, Spurr epoxy resin is added and a peristaltic pump circulates the resin/acetone in a cycle that includes passage over an exposed strip of filter paper for fast evaporative removal of acetone. Only a limited volume of resin is needed. Final curing of the resin at 60°C is possible after 3 days. If preserving microstructures is of interest, the sample should be exchanged step-wise with ethanol for a week at 12 hour intervals before exchanging with acetone. Cores from the neoichnology experiments were cut in half for easier viewing of bioturbated surfaces. Burrows smaller than 1 mm, as well as sediment contacts, were preserved in the cores with little disruption.