Periods of deposition and nondeposition as well as changing sedimentation rates at Page-Ladson from ~14,900 to 8500 cal yr B.P. appear to correlate with sea level fluctuations when ocean levels rose from 100 to 20 m below modern sea level ( 15 , 16 ), even though the site was ~250 to 175 km inland during this time. Unit 3c was deposited during a short period of unchanged sea level. Rapid sea level rise from ~14,500 to 14,000 cal yr B.P., which is the onset of the Bølling-Allerød warm period corresponding to meltwater pulse 1A, is contemporaneous with the rapid deposition of Units 4a and 4b and the highest rates of sedimentation in the sinkhole. From ~14,000 to 12,500 cal yr B.P., sea level rose at a steady rate, paralleling the rapid deposition of Unit 4c. A pause in sea level rise from ~12,500 to 11,500 cal yr B.P. corresponds approximately to the Younger Dryas stadial (~12,850 to 11,700 cal yr B.P.) ( 17 , 18 ) and correlates to the period of minimal deposition, subaerial exposure, and pedogenesis documented by Unit 5. Deposition of Units 6 and 7 took place during a period of rapid sea level rise from ~11,400 to 8200 cal yr B.P. The correlation between sea level rise and deposition at Page-Ladson suggests a hydrologic connection between the site and the ocean through the karstic system ( 19 , 20 ), with the aquifer response to sea level dictating the tempo of deposition in the sinkhole. Our magnetic studies (section S2.5) suggest that all sediments in the sinkhole are derived from the same source, most likely from the weathered sediments on the margins of the sinkhole. The near absence of charcoal in Unit 3 versus its abundance in all overlying units indicates an increase in regional fires starting from ~14,400 cal yr B.P., resulting in increased sediment yields to the sink ( 21 ).

Unit 4, composed of fine-grained sediments, is subdivided into three members dating from ~14,400 to 12,600 cal yr B.P. Pre-Clovis artifacts were recovered from Units 4a and 4b. Diatoms and micromorphological studies show that these sediments were deposited in a seasonally fluctuating pond with periodic desiccation along the pond margins. Unit 5, an organic-rich clayey silt with evidence of pedogenic alteration, dates from ~12,600 to 11,400 cal yr B.P. The absence of freshwater diatoms, extensive pollen degradation, anomalous decrease in the concentration of iron-bearing magnetic minerals, and evidence of human occupation within the sinkhole indicate that this was an arid period (section S2). Units 6 and 7 indicate a return to rapid sedimentation of silt and peat from ~11,400 to at least ~8500 cal yr B.P. Diatoms indicate fully aquatic conditions with only rare evidence of desiccation (section S2.6). The entire late Quaternary sediment package contains minimal postdepositional disturbance based on magnetic and micromorphological studies and radiocarbon ages (sections S2.3 to S2.7).

Unit 3 is subdivided into three members, with Units 3a and 3b deposited ~16,000 to 14,700 cal yr B.P. Unit 3c, which dates from ~14,700 to 14,400 cal yr B.P. and where pre-Clovis artifacts were found, consists of sand and fine gravel intermixed with mastodon digesta deposited in and adjacent to a pond at the bottom of the sinkhole ( 14 ). Terrestrial diatoms, microscopic evidence of woody roots and earthworm activity, and the occasional mastodon track and discrete dung boluses show that the pond margin dried for short periods of time and was subaerially exposed, allowing animals and humans to enter the sinkhole (section S2).

( A ) Artifact 12209-a. ( B ) Artifact 12209-b. ( C ) Artifact 12242-1. ( D ) Artifact 12068-2. ( E ) Artifact 12068-1. ( F ) Artifact 12080-1. (A) to (E) are flakes; (D) shows evidence of use. (F) is a biface. ( G ) 2014 wall profiles showing stratigraphy, locations of artifact finds, and location of radiocarbon samples. ( H ) 2013 wall profiles showing stratigraphy, locations of artifact finds, and location of radiocarbon samples. For (G) and (H), white dots represent locations and ages of radiocarbon samples collected from profiles. Purple dots and text represent radiocarbon ages collected from within units, plotted with correct elevation, and northing or easting. Red triangles show locations of artifacts collected from within units, plotted with correct elevation, and northing or easting. Open red circle shows approximate location of artifacts found in the screen. Trees in the profile are represented by dark brown. Note that although the biface appears as if it were found in the middle of a tree, the tree only occurs in the south wall profile and does not extend into the excavation unit where the biface was found.

Archaeology and extinctions

We recovered six unequivocal stone artifacts, all made of local coastal plain chert, within Units 3 and 4 (Fig. 2 and section S3). From Unit 3c, we recovered two artifacts: a biface (Fig. 2F) and a flake (Fig. 2C). The biface, a reworked knife fragment, was recovered in situ during excavation. Seven radiocarbon samples collected immediately adjacent to the biface date to ~14,550 cal yr B.P. The biface is overlain by 1.1 m of Unit 3 and 4 sediments. To confirm the age of the biface and to test that this artifact was in an undisturbed context, a vertical series of 24 radiocarbon samples was obtained from 1.1 m above (n = 15) to 0.6 m below (n = 9) the biface (Fig. 2H and sections S2.3 to S2.4). This sequence of nearly identical radiocarbon ages indicates that this artifact was lying in undisturbed sediments. Further, the excavation area from where the biface was discovered is covered and sealed by a continuous shell-dominated marker bed in Unit 4 dated ~14,400 cal yr B.P. One meter horizontally from the biface, a flake was recovered from Unit 3c. It was overlain by 1.1 m of undisturbed sediment, and two radiocarbon ages on wood adjacent to this flake also date to ~14,550 cal yr B.P. Two additional flakes were recovered from Unit 4a, about 40 cm above and 50 cm east of the biface, and two more flakes were recovered from Unit 4b (Fig. 2, A, B, D, and E). Radiocarbon ages obtained on samples adjacent to the flakes in Unit 4b indicate that these artifacts date to ~14,200 to 14,550 cal yr B.P. (Fig. 2G). The context in which we found the artifacts correlates with the previous finding of pre-Clovis artifacts at the site (10). The small artifact assemblage recovered from the pre-Clovis occupation at Page-Ladson is consistent with the small number of artifacts found at other pre-Clovis (4, 22) and some Clovis (12, 23) butchering and scavenging sites.

These artifacts occur in deposits that contain extinct mammal remains (mastodon, camelid, and bison) (section S4). During the previous excavations in 1993, a mastodon tusk was recovered from Unit 3c, with multiple, parallel, deep, linear grooves running perpendicular to the long axis of the tusk (24). Because the grooves occur on the alveolar portion of the tusk surface, these marks were originally interpreted as having been made by stone tools during removal of the tusk from the skull. Our reexamination of these marks confirms that they were indeed made by humans, and we agree that they were likely produced during the extraction of the tusk from the alveolus (section S4.2). Although we found no faunal remains with evidence of butchering, two potentially butchered megafaunal bones were previously reported (10). Further, the previous excavators (25) reported finding domesticated dog (Canis familiaris) in Unit 3, but this identification has not been confirmed.

The timing of the extinction of megafauna in the American Southeast is unknown. It has been suggested to be contemporaneous with (26), or even later than, elsewhere in North America (27). Proxy evidence from the Page-Ladson sediments allows us to evaluate regional fluctuations in the abundance of megaherbivores, specifically proboscideans, and to estimate the timing of their extinction. We examined Units 3 to 7 for Sporormiella, a dung fungus unique to herbivore dung, which has been successfully used as a proxy to establish the time of late Pleistocene megamammal extinctions at other sites in North America (28). At Page-Ladson, we found high concentrations of Sporormiella in late Pleistocene Units 3 and 4 (Fig. 3 and section S5). Peak spore concentrations occur around ~13,700 cal yr B.P., potentially indicating the timing of peak megafaunal abundance in the vicinity of the sinkhole. A rapid decline in spore concentrations followed, with Sporormiella absent at the top of Unit 4 by ~12,600 cal yr B.P., after the onset of the Younger Dryas stadial. The concurrent decline in spore concentrations and the disappearance of mastodon digesta suggest that mastodon and other megafauna populations decreased in abundance and disappeared from the region by ~12,600 cal yr B.P. Spores are absent from Unit 5 and the lower portion of Unit 6 from ~12,600 to 10,400 cal yr B.P. An anomalous spike in Sporormiella concentrations occurs in the middle of Unit 6 from ~10,400 to 10,100 cal yr B.P., after which concentrations decline to zero. The disappearance of Sporormiella at ~12,600 cal yr B.P. indicates that the extinction of the megaherbivores in Florida and the American Southeast was synchronous with extinctions elsewhere in North America (22, 26, 28). The spike in Sporormiella during the early Holocene may represent a brief expansion of bison into Florida during the Early Archaic Bolen cultural period (section S5).