ABSTRACT

    Soils are the primary physical contexts of archaeological deposits.  These contexts are not static: rather they are constantly changing, both physically and chemically, and driven by influences unique to their specific environmental locations.  The Oxidizable Carbon Ratio (OCR) procedure provides a physiologic profile of the soil body and its behavior through time, documents post-cultural abandonment changes to the archaeological context, and establishes the age of specific cultural features.  Initial OCR analyses of the Rmiz site in the Czech Republic demonstrates that this procedure may be used in archaeological studies to obtain temporal and contextual information as well as defining site formational processes.

INTRODUCTION

    Archaeological sites are no longer viewed as static receptacles of artifacts and information from the past.  Instead, an archaeological site is seen as the product of human behavior and natural processes which have evolved beyond the event of human activity into the present archaeological phenomenon.

      Throughout this evolution into the present, multiple turbations, both cultural and natural, conspire to render definable patterns of past human behavior into random and chaotic associations of artifacts SLIDE 1 (Tree tip turbation).  While useful classification systems defining turbations have been developed (Hole 1961; Wood and Johnson 1978), few analytic procedures are available for contextualizing and interpreting the effect of specific turbations on the archaeological record.  The recently developed OCR Carbon Dating procedure provides one such analytic tool.

    The OCR Carbon Dating procedure measures the site-specific rate of biodegradation of organic carbon, either as soil humic material or as charcoal.  SLIDE 2 (Carbon cycle) While some forms of organic carbon, such as fresh organic matter, are quickly recycled, other more resistant forms, such as humus and charcoal, are recycled at a much slower rate.  This recycling follows a linear progression though time when considered within the site-specific context, and includes factors that influence biochemical degradation of organic carbon.  Charcoal and soil humic material, once though to be inert, are biologically recycled at a slow, but measurable, rate (Frink 1992).

    The effect of the biochemical degradation of charcoal and soil humic material is measured by a ratio of the total organic carbon to the readily oxidizable carbon in the soil sample.  In general, as the total amount of organic carbon decreases though time due to recycling, the relative percentage of readily oxidizable carbon increases.  This ratio is called the Oxidizable Carbon Ratio, or OCR.  The rate of biochemical degradation will vary within the specific physical and environmental contexts of the sample.  An age estimate of the organic carbon is determined through a systems formula that accounts for the biological influences of oxygen, moisture, temperature, carbon concentration, and the soil reactivity SLIDE 3 (OCR_DATE formula).  Residual influences on this system are included through a statistically derived constant (Frink 1994).

    The OCR procedure differs epistemologically from radiometric carbon dating procedures.  Radiometric carbon dating procedures measure the decay of unstable carbon isotopes, following a classical physics model of entropy.  The OCR Carbon Dating procedure does not directly measure an intrinsic characteristic of the soil organic carbon.  Rather, it models the dynamic and nonlinear soil system, and the relative reactivity of the soil's organic carbon within that system.  Dynamic systems resist entropy by organizing and maintaining themselves at a distance far from equilibrium.  The OCR procedure describes an evolving pedogenic system, that is, the archaeological feature or the physical context of the artifact assemblages described as a site.

RESULTS AND DISCUSSION

    SLIDE 4 (Location of Rmiz in the Czech Republic) Soil samples were taken during test excavations at Rmiz in June of 1998 to ascertain the feasibility of employing the Oxidizable Carbon Ratio (OCR) soil dating method in Central Europe and to examine the local pedogenesis and depositional chronology of the site.  A one-meter square test unit was excavated just south of the oldest and stone-lined rampart.  SLIDE 5 (Survey map with test pit TU 1/98 in Area 1/99) Soil profile descriptions were recorded prior to sampling at 5-cm intervals.

    Four separate pedons, units of soil consisting of the biologically active A Horizon and its associated B Horizon defining an uninterrupted event of pedogenesis, were identified SLIDE 6 (Soil profile of unit).  The uppermost 10 cm, Pedon 1, consists of a cambric, recently developing, A horizon capping Pedon 2 which extends from 10 to 60 cm.  Pedon 2 consists of a well developed A horizon overlying a combined stone line and B_t, or argillic, horizon.  The formation of a B_t horizon in temperate zones requires roughly 4000 or more years (Rolfe Mandel, personal communication).  Pedon 3, extending from 60 to 88 cm, is a complex pedon consisting of two house floors, or anthropomorphic surfaces, separated by fill material which has undergone in situ biochemical changes consistent with short-term soil development.  Pedon 4, located between 88 and 101 cm, is the original land surface, albeit, heavily affected by human use.

   SLIDE 7 (Pedon 4) The earliest human occupation is found within Pedon 4.  This occupation is evidenced by a prepared house floor, or living surface, with an intrusive pit-feature pre-dating 5692 B.P. (3742 BC), and likely occurring about 5762 B.P. (3812 BC).  Recovered artifacts suggest that the occupants belonged to the Funnel Beaker culture (TRB).   Based on pottery typology, the earliest phase of the TRB, Baalberge with Michelsberg affinities (TRB I A), is not represented at the site.  SLIDE 8 (Location of TRB & Michelsberg), Bakker 1979) Michelsberg pottery is found primarily along the Rhine River and to about 6000 B.P. (4000 BC) in Bohemia and Germany (Miroslav Smíd, personal communication).

    SLIDE 9 (Pedon 3) Two distinct house floors, or living surfaces, are evident within Pedon 3.  The upper floor dates to about 5492 B.P. (3542 BC), and the second to circa 5612 B.P. (3662 BC).  This roughly 100-year interval between house floors is consistent with data reported from similar TRB sites in Poland (Bogucki 1988).  Relative stability of the Pedon 3 soils following abandonment of the upper house floor is evident until sometime after 5200 B.P. (3250 BC), when it is buried by the soils of Pedon 2.  This event of burial coincides with the presumed demise of the (TRB) at the southern fringes of its distribution.  The Austro-Hungarian Baden culture, whose influences are observable as far away as Switzerland by 5400 B.P. (3400 BC), gradually replaced TRB in the southern reaches.

    SLIDE 10  (Pedon 2) Rmiz was apparently abandoned sometime after 5200 (3250 BC) as indicated by the soil deposits capping the cultural soil deposits of Pedon 3.  Pedon 2 consists of roughly 50 cm of colluvial soils that washed down from either the third rampart, or from up slope near the fourth rampart and ditch.  This destabilization occurred sometime between 5200 and 4950 B.P. (3250 and 3000 BC).  Given the relatively gentle slope adjacent to the test unit, 50 cm of colluvial deposits suggest that the area may have lacked significant vegetation cover, and that weather patterns may have been abnormally wet and cold relative to the preceding centuries of occupation.
 
    At this same time, a significant climatic anomaly is suggested for the oceans around Greenland, the critical source area governing European weather patterns.  Ice core data from between 5,200 B.P. and 5,100 B.P. show "a marked increase in the deposition of marine biogenic sulfates... Open water in the permanent sea ice off the Greenland coast could account for this extended period of increased marine biogenic sulfate deposition" (Zielinski et al. 1994).  Variability in temperature and precipitation patterns throughout Europe are governed by the location and intensity of the North Atlantic Oscillation (NAO), and the Atlantic Ocean's thermohaline circulation current.  SLIDE 11 (Circulation model) Tropical warm moist air masses following, and derived from, the warm shallow currents of the Upper North Atlantic Deep Water current (UNADW), aka, the Gulf Stream, bring increased rainfall and warm temperatures to Europe and western Asia.  This weather pattern is not constant, as the thermohaline circulation down-welling south of Iceland is affected by periodic freshening from low salinity Arctic currents that are themselves the result of freshwater discharge from the west Asian rivers.  Such changes would allow for periodic climatic cooling (Driscoll and Haug 1998).  SLIDE 12 (Temperature curve) Postulated variation in the Northern Hemisphere surface temperatures suggest a warmer than normal period between roughly 6950 and 4950 B.P. (5000 and 3000 BC) followed by roughly a 1,000-year colder than normal period (Zielinski et al. 1994).  The occupation of Rmiz conincides with the maximum mean annual temperature cycle.

    I offer this not as an explanation for the demise of, or reason for, the TRB.  Rather, this data is presented to provide a context from which the archaeological record may be examined for evidence of cultural adaptation to environmental stress.

    During this colder period of this cycle, the highest elevations at Rmíz, far beyond the test unit area, was re-fortified during the Late Bronze Age, sometime around 3450 B.P. (1500 BC).  No archaeological materials from this latter time period were recovered from the test unit.

    SLIDE 13 (Pedon 1) Pedon 1 developed sometime after 293 B.P., or 1657 AD, possibly around 1800.  The soils of Rmiz were destabilized about this time, and active erosion moved roughly 5 to 9 cm of soil downslope to the test unit location.  These deposits buried the earlier deposits represented by Pedon 2, and the process of pedogenesis resumed, visually welding Pedon 1 to the upper portions of Pedon 2.  

CONCLUSION

    SLIDE 14 (View of ditch and rampart, Rmiz) Soils form the primary context of archaeological materials and defines site formation and disturbance processes.  Furthermore, soils are themselves artifacts of cultural and natural events, and are capable of providing temporal and environmental information critical for understanding the archaeological materials and the cultural processes being studied.  The OCR Carbon Dating procedure provides temporal data, and reveals the physiological genesis of the soil body from which hypotheses may be generated and tested concerning both cultural and environmental events.

REFERENCES CITED

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