Life history of archaeological remains: An investigation into the taphonomic effects of weathering and sedimentary pressure on two experimental models of archeo-paleontological assemblages simulating Middle Pleistocene sites

1.INTRODUCTION.

Experimental replication is a powerful tool in understanding taphonomic processes in order to determine whether geological or anthropogenic agencies were primarily responsible in the accumulation of fossil bones and stone tools in Paleolithic sites Here we report a preliminary experimental study undertaken under highly controlled variables in the recently created Laboratory of Experimental Archeology and Taphonomy at the Centro Nacional de Investigación sobre la Evolución Humana ( with the main goal of recognizing the effects of climatic, sedimentary, diagenetic and anthropogenic effects on the formation of two hypothetical models of archeo paleontological assemblages within the context of Atapuerca sites 

2. MATERIAL AND METHODS

We reproduced two different hypothetical models of archeo paleontological assemblages mimicking the sedimentary context of Atapuerca Middle Pleistocene sites The first assemblage imitates the conditions of a glacial period and the second one an interglacial period We used in each one of these experiments eight samples of replicated stone tools 2 in limestone, 2 in chert, 2 quartzite, 2 sandstone) and 8 bone fragments of 2 different animal taxa and size ( lamb) We mixed the samples with sediments in metallic boxes in order to reproduce both contexts of glacial 50 limestone clasts, 50 clays) and interglacial 10 clasts, 90 clays) paleoenvironmental settings We simulated specific weathering conditions in the Dycometal CCK 25 2340 MTe machine that is specifically built for this type of experiment (dry and cold vs wet and warm) Finally, we put those boxes of sediment under compression efforts in a compression Shimadzu AGS 100 kNX simulator The recognition of alterations, weathering effects and breakages types are recorded through high resolution 3 D models performed through a 3 D light reflected microscope Olympus DSX 1000 3 D.

3. CONCLUSIONS AND OVERVIEW

Despite our first hypothesis was that glacial conditions were more destructive, several questions must be pointed out - In glacial environments, the stones (tools and clasts) are more altered, documenting detachments of parasitic flakes due to frost cycles, as well as a greater number of snap fractures due to sedimentary pressure in a matrix with a high volume of limestone clasts - Frost cycles helps to expand the incipient fissures in the bones fragments - Diagenetic fractures in bone fragments are common in our interglacial sample - Breakage in shrew mandibles, Sorex sp ..,,(articular condyle mainly) is frequent in both environments, probably due to diagenetic factors - In the future it will be important to isolate the different variables to see how they affect individually to each sample under study