TAPHONOMIC RESPONSE OF CRUSTACEAN CARCASSES PLACED AT THE SEDIMENT WATER INTERFACE AT SHALLOW TO MID-SLOPE DEPTHS IN CARBONATE AND SILICICLASTIC ENVIRONMENTS

Crab carcasses (frozen with meat) were placed in mesh bags at the sediment-water interface in 1993 in a variety of potentially-preservable settings. In the Bahamas, experiments are located in shallow reefal settings and down slope to 280m. In the Gulf of Mexico experiments record taphonomic loss/gain in terrigenous muds, deep carbonate banks, and brine and hydrocarbon seep localities. Two crab carcasses were collected from each experiment after 2yrs, 8yrs, and 13yrs. The results show that 1) crab remains disarticulate and are reduced to characteristic resistant parts (e.g. crab claws) within the first few years, after which they stabilize without further significant loss, 2) amazingly, articulation in crab claws and associated limb parts often survive for the 13 years of the study, suggesting a much better fossil record than usually reported, and 3) few large scale environmental cues (e.g., bottom type, depth) predict where preservation will be good and where it will be poor.

In shallow reef-associated environments in the Bahamas, most crab cuticle is gone by year two but disarticulated claws usually remain and have accumulated bionts. Bahamas sites below 100m often exhibited good preservation of articulated claws and greater overall volume of cuticle through all years of the study. In contrast, the Gulf of Mexico shelf is characterized by fine terrigenous mud with generally low carbonate content. Typical shelf to slope muddy sites yielded poor preservation of crab cuticle. Carcasses were reduced to disarticulated claw parts within 2 years, yet those claw parts typically remained through year 13. Deep carbonate banks in the Gulf yield a wide variety of preservation from articulated limbs/claws to complete loss of crab material. Similar to the Bahamas, most taphonomic loss occurred in the first two years and then slowed. Preservation in Gulf carbonates is generally better than in terrigenous muds, but there were no clear trends. Crab remains deployed at hydrocarbon seeps, although being the deepest sites, were the least well preserved among Gulf of Mexico sites. The take-away messages are 1) crab cuticle is more durable at the sediment/water interface than originally thought, and 2) bottom type and water depth alone are not good predictors of preservation style.