Science 19 September 1997:
Vol. 277 no. 5333 pp. 1796-1799
DOI: 10.1126/science.277.5333.1796
  • Report

A Mound Complex in Louisiana at 5400-5000 Years Before the Present

Joe W. Saunders*,Rolfe D. Mandel,Roger T. Saucier,E. Thurman Allen,C. T. Hallmark,Jay K. Johnson,Edwin H. Jackson,Charles M. Allen,Gary L. Stringer,Douglas S. Frink,James K. Feathers,Stephen Williams,Kristen J. Gremillion,Malcolm F. Vidrine andReca Jones

Abstract

An 11-mound site in Louisiana predates other known mound complexes with earthen enclosures in North America by 1900 years. Radiometric, luminescence, artifactual, geomorphic, and pedogenic data date the site to over 5000 calendar years before present. Evidence suggests that the site was occupied by hunter-gatherers who seasonally exploited aquatic resources and collected plant species that later became the first domesticates in eastern North America. Native American mounds have been recognized and studied in the eastern United States for more than a century. They represent early evidence for organized society in North America. Most of the earthen mounds and enclosures in the east date to <2500 calendar years before present (B.P.) (1). In the 1950s, the recognition of preceramic mounds and earthen enclosures from earlier times came first at the Poverty Point site in Louisiana, dating to 3500 calendar years B.P. (2, 3). By the 1970s, four mound sites in Louisiana and one in Florida had been dated to >5000 calendar years B.P. (Middle Archaic), but the data were not conclusive and the antiquity of the sites remained in doubt (4, 5). In the 1990s, four additional mound sites in Louisiana (6, 7, 8) and two in Florida (8) have been identified as Middle Archaic in age. Collectively, the Middle Archaic mound sites provide 56 radiometric dates that establish the antiquity of earthen mounds in the southeast. Of these sites, Watson Brake in northeast Louisiana is the largest, most complex, and most securely dated site. Its 11 mounds and connecting ridges form an oval-shaped earthen enclosure 280 m in diameter (Fig.1). The largest mound (Gentry Mound) is 7.5 m high; the other mounds measure between 4.5 and 1 m in height, and the connecting ridges average 1 m in height. Here we present evidence that Watson Brake predates the large-scale earthworks of Poverty Point by 1900 years, making it the earliest such human construction so far recognized in the New World.

Figure 1View larger version:In a new window
Figure 1 Watson Brake topographic map. Black squares indicate test units. Test unit 5 is an extension of test unit 4 in mound C; thus there are only seven squares on the map. Contour interval = 0.5 m.

Watson Brake is constructed on the edge of a low, flat Pleistocene terrace (Mid-Wisconsin stage) overlooking the Holocene floodplain (<12,000 calendar years B.P.) of the Ouachita River (9,10). Before 7000 calendar years B.P. (10), meander belts formed by the paleo?Arkansas River provided gravel and sand shoal channels in the Ouachita Valley, and swamp and small-stream habitats formed in backwater areas near Watson Brake. These conditions persisted until about 4800 calendar years B.P., when a diversion of the Arkansas River into the present course of the Ouachita River caused rapid alluviation near Watson Brake (10), decreasing the extent of the swamp and small-stream habitats. This event may coincide with abandonment of the site.

We verified the cultural origin of each mound and ridge with eight test units and soil cores. Mounds and ridges along the edge of the Pleistocene terrace were constructed in multiple stages and on premound or ridge middens (11). Mounds and ridges set back from the terrace edge were constructed in single stages and on the truncated Bt horizon of the Pleistocene terrace (the A horizon was removed before mound or ridge construction). This removal suggests that mound and ridge placement on the north and east sides followed the natural topography, whereas mounds and ridges on the west and south sides of the enclosure were placed to complete the enclosure. The extensive weathering of fill in the single- and multiple-stage mounds and ridges suggests that all of the earthen structures are contemporaneous. The physical, chemical, and morphological properties of soils that developed in the mounds and ridges indicate that the earthen architecture is of great antiquity. These soils are strongly weathered, with well-expressed A-E-Bt horizonation (Ultisols and Alfisols). A typical profile consists of a 1-m solum with a fine sandy loam ochric epipedon (A horizon), a fine sandy loam to loamy fine sand albic (E) horizon, and a reddish, clay-enriched argillic (Bt) horizon. The Bt horizons are 40 to 80 cm thick and have fine and medium subangular-blocky structure. Clay translocation, which leads to the development of the Bt horizons, is pronounced as indicated by (i) clay depletion of the overlying A and E horizons, (ii) enrichment of the Bt horizons in clay content relative to overlying horizons and underlying unweathered mound fill, (iii) high ratios of fine clay to total clay in the Bt horizons, and (iv) the presence of argillans (clay coatings) in the Bt horizons. The argillans have variable thickness (100 to 300 ƒΚm) and are composed of microlaminated clay. Extensive leaching is indicated by low concentrations of exchangeable bases (Ca, Mg, Na, and K) and pH of 5.1 to 3.9 to great depths. Base saturation ranges from 10 to 51% in the Bt horizons. Iron has leached from the A and E horizons (0.3 to 0.5%) and illuviated into the Bt horizons (0.9 to 1.1%). The strongly developed soils on the mounds and ridges at Watson Brake may be partially attributed to the nature of the material used to construct these features. Emplacement of weathered (preconditioned) material during the final stage of mound and ridge construction would favor rapid pedogenesis. However, the formation of thick Bt horizons that meet argillic criteria is time-dependent because weathering, clay formation, and translocation are slow processes (12). Hence, we suggest that the Ultisols and Alfisols developed in the mounds and ridges are products of thousands of years of pedogenesis. We obtained 19 radiocarbon assays from buried A horizons on the premound and preridge surfaces as well as from the surfaces of successive stages of mound and ridge construction (Table1). Two of the dates are considered anomalous because of their younger-than-expected age (13). Dates on four charcoal scatters from submound and subridge A horizons (mounds A, B, and C; ridge K/A) range between 5880 and 5450 calibrated (cal.) calendar years B.P. Dates for soil humates from two submound A horizons (mounds A and D) are 5285 and 5450 cal. calendar years B.P. These dates suggest that mound construction at Watson Brake began between 5400 and 5300 calendar years B.P.
View this table:
Table 1 14C dates from Watson Brake. Rg, ridge; Md,mound.

Six charcoal samples from buried A horizons on successive stages of mound B and stage I of ridge K/A yielded radiocarbon ages between 5590 and 5290 cal. calendar years B.P., and humates from four buried A horizons in mounds A, C, and D range in age between 4870 and 4520 cal. calendar years B.P. In addition, humates from a pit-hearth in the surface of stage I, mound C dates to 4826 cal. calendar years B.P. On average, the humate ages are 700 years younger than the charcoal ages. The humate ages appear to be too recent because of postburial input of organic carbon. Soil organics are susceptible to contamination by modern rootlets, humic acids, and other sources of young carbon, which can yield anomalously young radiocarbon ages (14, 15).

Independent means of determining the antiquity of Watson Brake include luminescence dating of mound and ridge sediments (16). We examined samples from the buried A horizons of stage I, mound B and stage I, ridge K/A. It was hypothesized that the formation of A horizons on the intermediate stages had provided adequate time for bleaching of sediments through recycling to the surface by pedoturbation. Thermoluminescence analysis of the slowly bleaching component in quartz produced geological rather than archaeological ages, which suggests that bleaching was incomplete. Optically stimulated luminescence (OSL) of the rapidly bleaching component using single aliquot analysis (17) yielded an age of 4003 } 444 calendar years B.P. for ridge K/A and a maximum age of 5538 } 936 calendar years B.P. for mound B. The OSL signal for the ridge sample appeared well bleached in antiquity, but variation in equivalent dose from aliquot to aliquot suggested that bleaching of the mound B sample was incomplete. The mean residence time of three mounds and two ridge segments was calculated with the experimental dating method of oxidizable carbon ratio (OCR). The OCR procedure measures biochemical degradation of organic carbon within the site-specific environmental context (18, 19). Analysis of 200 soil samples suggests that the submound soils were buried with mound fill, thereby arresting biochemical degradation, at ?5180 } 155 calendar years B.P. and that mound fill pedogenesis began at ?5010 } 150 calendar years B.P. Artifactual data support a pre?Poverty Point (>3500 years B.P.) origin for the mounds and ridges. None of the Poverty Point archetypes (20, 21) have been recovered from Watson Brake. Projectile points from Watson Brake are Middle to Late Archaic in age (22). Lithic material is local gravel, in contrast to Late Archaic and Poverty Point sites, where nonlocal material is common (23, 24). Blade production at Watson Brake is casual, with minimal platform preparation and no platform rejuvenation. At Poverty Point, blade cores have more formal platform preparation and blade removal (25). Watson Brake blades frequently were transformed into microdrills for bead production, averaging 9.9 by 2.7 by 2.2 mm. This technology is similar to the Middle Archaic assemblages from east central Louisiana (26) as well as from the Keenan Cache (27) and the Slate Site (28) in Mississippi. Local gravel was used for cooking stones at Watson Brake. In addition, fired earthen objects (function unknown) occur in a variety of undecorated shapes (cuboidal, rectangular, spherical, and cylindrical); block forms are the most common. Similar fired earthen objects have been recovered from Frenchman's Bend Mounds, a Middle Archaic site 35 km northeast of Watson Brake (7). There, mound deposits with fired earthen blocks date to 5570 (7) and 5290 cal. calendar years B.P. (ƒΐ69637, 4560 } 140 corrected, uncalibrated 14C years B.P., charcoal scatter), which is about the same age as that of Watson Brake specimens. Undecorated blocks have not been found at Poverty Point. Over 175,000 pieces of bone were recovered from mound B, stage I and its submound surface. Aquatic species predominate and fish are the most abundant food remains. Main channel species were preferred, including freshwater drum (Sciaenidae), catfish (Ictaluridae), and suckers (Catostomidae). Additional aquatic foods include 17 mussel species (Unionidae), one aquatic snail (thousands ofCampeloma sp.), turtle, and duck. Deer, turkey, raccoon, opossum, squirrel, rabbit, dog, and rodent remains also were recovered from the midden. Charred seeds from the same midden deposits represent three species of the complex of weedy annuals (29). These include goosefoot (Chenopodium berlandieri), knotweed (Polygonum spp.), and possibly marshelder (Iva annua). The morphology of the goosefoot seeds is consistent with var. boscianum, a taxon uncommon in the area today. None of the seeds exhibit morphological features associated with evolution under cultivation. However, their presence may reflect the early development of ecological relationships that eventually led to domestication. The fauna and flora suggest that Watson Brake was occupied seasonally. Fish otoliths indicate that most fish were caught in spring to early summer and fall. The spring to early summer peak probably corresponds with the spawning of the freshwater drum (Aplodinotus grunniens). The plant species seed in the summer through fall, also suggesting seasonal occupation of the site. Increases in terrestrial species coupled with decreases in mussel and slackwater fish between the earlier premound midden and the later stage I midden of mound B may reflect a change in the local environment. The decline in the main channel, gravel/sand shoal habitats, backwater swamps, and small-stream habitats near Watson Brake may have resulted in a shift from aquatic resources to terrestrial species, eventually leading to site abandonment. Geomorphic, pedogenic, radiometric, luminescence, and artifactual data have established the Middle Archaic age of Watson Brake. Faunal and floral data show that the site was constructed and occupied by hunter-gatherers who seasonally exploited riverine animals and plants. Planned large-scale earthworks such as Watson Brake were previously considered to be beyond the leadership and organizational skills of seasonally mobile hunter-gatherers. Poverty Point was considered the exception, and its extensive trade was cited as evidence for sophisticated socioeconomic organization (20). Our data imply that less complex mound building societies flourished in the southeast more than 1900 years before Poverty Point. Furthermore, not only did these Middle Archaic societies establish monumental architecture in the southeast, but they also may have initiated ecological relationships that led to the eventual domestication of weedy annuals in eastern North America.

  • ?* To whom correspondence should be addressed.

  • Received for publication 27 May 1997.
  • Accepted for publication 4 August 1997.

REFERENCES AND NOTES

  1. ?
    B. D. Smith, in Advances In World Archaeology, F. Wendorf and A. Close, Eds. (Academic Press, New York, 1986), vol. 5, pp. 1?92.
  2. ?
    1. J. A. Ford
    , Science 122, 550 (1955).
    FREE Full Text
  3. ?
    J. L. Gibson, in Archaeology of the Mid-Holocene Southeast, K. E. Sassaman and D. G. Anderson, Eds. (Univ. of Florida Press, Gainesville, FL, 1996), pp. 288?305.
  4. ?
    J. L. Gibson and J. R. Shenkel, inMiddle Woodland Settlement and Ceremonialism in the Mid-South and Lower Mississippi Valley, R. C. Mainfort Jr., Ed. (Archaeological Report No. 22, Mississippi Department of Archives and History, Jackson, MS, 1988) pp. 7?18.
  5. ?
    M. Russo, Southeast. Archaeol. 13, 93 (1994).
  6. ?
    J. W. Saunders and T. Allen, Am. Antiq. 59, 471 (1994).
  7. ?
    ___, R. T. Saucier, Southeast. Archaeol. 13, 134 (1994).
  8. ?
    M. Russo, in Archaeology of the Mid-Holocene Southeast, K. E. Sassaman and D. G. Anderson, Eds. (Univ. of Florida Press, Gainesville, FL, 1996), pp. 259?287.
  9. ?
    1. R. T. Saucier,
    2. A. R. Fleetwood
    , Geol. Soc. Am. Bull. 81, 869 (1970).
    Abstract/FREE Full Text
  10. ?
    R. T. Saucier, Geomorphology and Quaternary Geologic History of the Lower Mississippi Valley (U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, 1994), vol. I.
  11. ?
    Ridge B/C is the exception.
  12. ?
    P. W. Birkeland, Soils and Geomorphology(Oxford Univ. Press, New York, 1984).
  13. ?
    Charcoal from the mound D submound surface dated to 3824 } 120 cal. calendar years B.P. (ƒΐ95003). Humate ages from the same horizon and buried A horizons above the sample were >700 years older. Charred bone from augering of stage I, mound B dated to 4140 } 60 cal. calendar years B.P. (ƒΐ72331). Subsequent charcoal samples from mound B, stage I and overlying stage II were 1000 years older.
  14. ?
    1. C. W. Martin,
    2. W. C. Johnson
    , Quat. Res. 43, 232 (1995).
    CrossRef
  15. ?
    1. Y. Wang,
    2. R. Amundson,
    3. S. Trumbore
    , ibid 45, 282 (1996).
  16. ?
    J. K. Feathers, Quat. Geochronol. 16, 333 (1997).
  17. ?
    G. A. T. Duller, Radiat. Meas. 24, 217 (1995).
  18. ?
    D. S. Frink, in Pedological Perspectives in Archaeological Research, M. Collins, Ed. (Soil Science Society of America Special Publication 44, Madison, WI, 1995).
  19. ?
    ___, Archaeol. East. North Am. 20, 67 (1992).
  20. ?
    C. H. Webb, gThe Poverty Point Cultureh No. 17 (School of Geoscience, Louisiana State University, Baton Rouge, LA, 1982).
  21. ?
    A Poverty Point Object was found in level 1, TU 7, ridge B/C.
  22. ?
    F. Schambach, thesis, Harvard University (1970).
  23. ?
    M. D. Jeter and H. E. Jackson, La. Archaeol. 17, 133 (1994).
  24. ?
    J. L. Gibson, ibid., p. 251.
  25. ?
    C. H. Webb and J. L. Gibson, Geosci. Man 22, 85 (1981).
  26. ?
    J. L. Gibson, Bull. Tex. Archaeol. Soc. 38, 1 (1968).
  27. ?
    J. Connaway, La. Archaeol. 8, 57 (1981).
  28. ?
    J. K. Johnson, Southeast. Archaeol. 12, 59 (1993).
  29. ?
    B. D. Smith, Rivers of Change: Essays on Early Agriculture in Eastern North America (Smithsonian Institution Press, Washington, DC, 1993).
  30. M. Stuiver and P. M. Reimer, Radiocarbon Calibration Program 1993, rev. 3.0.3c (Quaternary Isotope Lab, University of Washington, Seattle, WA).
  31. Funders included the National Geographic Society (two grants), the National Park Service, and the State of Louisiana. The Gentry family, Willamette Industries, Inc., and the Archaeological Conservancy allowed access to the site.