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A geoarchaeological investigation that included soil-stratigraphic and paleoecological analyses was conducted at Richard Beene, a deeply stratified open-air site associated with an alluvial terrace of the Medina River in south-central Texas. The sequence of cultural and alluvial deposits at the site is one of the most complete records of Holocene h...
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... a brief period after ca. 5000 14 C B.P., d 13 C values sharply decreased (Fig. 16), indicating reduced relative C 4 productivity and therefore cooler temperatures compared to the Altithermal. The latter stage of pedogenesis in the Medina paleosol at the top of Unit A5, the aggradational phase of Unit A6, and the development of the Leon Creek paleosol span this period. Dramatic cooling after 5000 (Fredlund and Neck, 2007). The occurrence of a cool interval in Central Texas immedi- ately after the Altithermal is supported by fossil pollen data showing an increase in tree cover beginning at ca. 5000 14 C B.P. and continuing to at least 3000 14 C B.P. (Bousman, ...
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... is no evidence of strong weathering in the Medina pale- osol. Calcium carbonate content is high (52.4e45.2%) throughout this paleosol (Fig. 15), though carbonate morphology is weak (Table 1). Also, CaCO 3 content is irregular with ...
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... general trend toward lower d 13 C values after ca. 1500 14 C yr B.P. (Fig. 16) suggests that the climate was becoming slightly cooler, although conditions were still relatively warm. During this period, the modern surface soil formed in Unit A7. The isotopic signals from snail and mussel shell carbonates also suggest slight cooling during the past 1500 years ( Fredlund and Neck, 2007;Brown, ...
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... the Richard Beene site, d 13 C values of soil organic carbon increased dramatically between 4000 and 1500 14 C yr B.P. (Fig. 16), pointing to another period of high relative C 4 productivity and temperature. The final stage of pedogenesis in the Leon Creek paleosol at the top of Unit A6 and the aggradation phase of Unit A7 span this period. The isotopic signals from snail shell carbonates suggest that, for the Holocene record, the warmest and/or driest conditions were reached between 4000 and 3000 B.P. (Fredlund and Neck, 2007). Isotopic data for mussel shells at Richard Beene also indicate a warming trend after ca. 4000 14 C yr B.P. (Brown, ...
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... modern surface soil is developed through unit A7 and into the upper part of unit A6. This soil is a well-drained Mollisol with a moderately expressed A-Bk profile (Table 1). There is a normal depth trend of organic C: it steadily decreases from 1.26% in the Ap horizon to 0.79% in the lower 7 cm of the Bk2 horizon (Fig. 15). Also, calcium carbonate content increases with depth, ranging from 49.6% in the Ap horizon to 53.2% in the lower 7 cm of the Bk2 horizon. Carbonate morphology, however, is weak (stage I) throughout the Bk horizons of the modern soil, consisting mostly of fine fluffy threads of calcium carbonate that cover 1e5% of each ped ...
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... thick, strongly expressed soil (Perez paleosol) is developed at the top of subunit A3d (Figs. 7 and 10). The Perez has a Bk-Bkss-Bk- BCk-CBk profile (Table 1); flood-related erosion stripped off the A horizon before the soil was buried. Carbonate morphology in the Perez paleosol consists of few encrusted threads of calcium Common medium distinct 7.5YR 6/4 mottles; 2e5% fine (1 e2 mm) encrusted carbonate threads concentrated on ped faces; 5% coarse carbonate-lined pedotubules that are ...
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... of the analysis of stable carbon isotopes (d 13 C) of organic matter from soils at the Richard Beene site are presented in Nordt et al. (2002) and summarized in the following discussion. Before presenting the summary, it is important to consider some of the characteristics of the soils at the site. First, all of the soils formed in calcareous, fine-grained alluvium that was deposited on a slowly aggrading floodplain (now a terrace). The calcium carbonate con- tent of alluvium derived from the surrounding Cretaceous bedrock ranges from approximately 20 to 55%, with minor redistribution into secondary carbonate accumulations. Second, the buried Ho- locene soils have weakly expressed A-Bw or A-Bk horizonation and formed during a few hundred years prior to burial. The exception is the Leon Creek paleosol that formed during 1000 to 1500 years of relative landscape stability. Hence, the buried soils are not poly- genetic. Third, the absence of redoximorphic features indicative of frequent saturation in the buried soils reduces the possibility that wetland vegetation was a major factor during landscape evolution at Richard Beene. Finally, organic carbon concentrations range from 1.26% to 0.02% throughout the sequence of buried soils and tend to decrease with depth in most of the Holocene soils (Fig. 15). Although some of the organic carbon in the buried soils is detrital, this is not problematic for interpreting the d 13 C values. The Medina River drainage basin encompasses a relatively uniform ecosystem such that any detrital organic carbon transported into the alluvium is largely derived from eroded upland soils that formed in equi- librium with the same climate as the Medina River alluvial soils. Hence, the pedogenic and detrital organic components should provide a similar record of the ...
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... organic C content of the Medina paleosol does not steadily decrease with depth (Fig. 15). Instead, it is very irregular, especially in the lower part of the Bkb2 horizon. This depth trend is typical of a cumulic soil that received influxes of alluvium while pedogenesis was occurring. In such soils, the A horizon builds up with the accumulating parent material, and former A horizons, which are typically organic rich, often become B horizons (Nikiforoff, 1949;Birkeland, 1999;Mandel and Bettis, 2001). Variable increases in organic C down the profile of the Medina paleosol may, therefore, mark the positions of former A horizons that were buried during the cumulization process and subsequently transformed into Bk horizons. The archaeological evidence associated with the Medina paleosol supports this interpretation. For example, the presence of late Early Archaic features and artifacts in the Bk3b2 indicates that this horizon was once a living surface, probably an A horizon. After it was buried, the A horizon was subjected to illuvial processes that converted it to a Bk horizon. However, soil-forming processes did not completely obliterate biochemical evidence (i.e., organic C content) of the former A ...
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... ca. 15,000 to 10,000 14 C yr B.P., d 13 C values of soil organic carbon at the Richard Beene site show large and rapid fluctuations (Fig. 16). In the lower Medina River valley, this period was charac- terized by floodplain sedimentation (lower Unit A3) punctuated by soil development (soils 6, 7, and 8). Distinct periods of low relative C 4 productivity that occurred at the site between ca. 15,500 and 14,000 14 C yr B.P. and between ca. 13,000 and 11,000 14 C yr B.P. are attributed to two well-documented episodes of glacial meltwater flux from the Laurentide ice sheet into the Gulf of Mexico via the Mississippi River ( Nordt et al., 2002). Hence, cold water inputs into the Gulf of Mexico apparently resulted in cooler climatic conditions at least as far inland as the Richard Beene site, thereby reducing the relative productivity of C 4 grasses during the meltwater ...
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... mm wide and 10e20 cm long; thin faint aureole of oxidized iron around the edges of pedotubules, but interiors of pedotubules are light gray (10YR 7/2) iron depletion zones. Bkssb4 1068e1136 7.5YR5/4 7.5YR6/4 2mþfABK SiCL vh,fi g,s Few round siliceous pebbles; few fine and medium pores; few (3%) brown (7.5YR 4/3) mottles; 2e5% fine (1e2 mm) encrusted carbonate threads concentrated on ped faces; 5% coarse carbonate-lined pedotubules that are 5e8 mm wide and 10e20 cm long; thin faint aureole of oxidized iron around the edges of pedotubules, but interiors of pedotubules are light gray (10YR 7/2) iron depletion zones; most faces are bounded by distinct slickensides that are inclined 20e30 from the horizontal; moderate medium parallelpiepeds part to angular blocky structure; some coarse and medium prismatic structure. Bk'b4 1136e1169 7.5YR5/4 7.5YR6/4 2cABK SiCL vh,fi g,s Few round siliceous pebbles; common pores; few fine faint yellowish brown (7.5YR 5/6) mottles; 5% fine (1e2 mm) encrusted carbonate threads concentrated on ped faces; 5% carbonate on ped faces, and carbonate-lined pedotubules 5e8 mm in diameter and 10e20 cm long are common. An abundance of 2:1 expanding lattice clays is indicated by distinct slickensides on wedge-shaped peds that occur 48e68 cm below the surface of the Perez paleosol (Fig. 10). Slow but continuous vertical accretion accompanied by periodic human occupation resulted in a sequence of stratified, vertically stacked, and individually sealed Early Archaic cultural horizons within the Perez paleosol. These horizons contained chipped-stone debitage, cores and core fragments, stone tools, FCR, mussel shells, and bones and bone fragments, mostly from rabbit-and deer-sized animals. Diagnostic artifacts included Angostura points, fragments of lanceolate projectile points, and Clear Fork ...
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... d 13 C values of organic carbon from soils at the Richard Beene site range from À16.7 to À25.1‰ for the past ca. 15,000 years (Fig. 16). These data indicate that plant communities at the site varied from strongly C 3 -dominated to strongly C 4 -dominated. It is likely that these changes in vegetation were in response to regional climatic ...
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... 10,500 and 9000 14 C yr B.P., when aggradation of subunit A3d was occurring, relative C 4 productivity initially decreased, then increased slightly (Fig. 16). However, between 9000 and 8600 14 C yr B.P., which includes the period when the Perez paleosol developed (ca. 8800e8600 14 C yr B.P.), d 13 C values of soil carbon decrease, suggesting an increase in relative C 3 productivity and, therefore, cooler ...
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... paleosol is accompanied by an increase in the size and fre- quency of stream-worn pebbles. This sedimentological evidence suggests that flood magnitudes increased during the final stages of soil upbuilding. Turbulent, high-magnitude floods entrain more and larger pebbles compared to low-magnitude and less turbulent floods. Also, high-magnitude floods are usually erosive; hence they can move artifacts and disturb or destroy cultural features on a floodplain. Deep flood scours are common at the top of the Perez paleosol ( Fig. 11), and laminated sandy sediment in many of the scours indicates high flood-flow velocities on the early-Holocene floodplain (Fig. 12). The most disturbed Early Archaic cultural component rests on the eroded surface of the Perez paleosol. This cultural zone is poorly preserved and contained no in situ archaeological features. Instead, there were random concentrations of chipped-stone artifacts, FCR, and mussel shells (Fig. 13). There also were many stream-worn pebbles 2e4 cm in diameter. Many of the artifacts rested on their edges at near vertical angles of repose, and some were imbricated. These artifacts were concentrated in flood scours eroded into the top of the Perez Soil (Fig. 14), and some artifacts were scattered in sandy and loamy flood deposits immediately above the soil. The obvious implication is that the artifacts and stream-worn pebbles form a lag deposit that resulted from a high-energy flood that stripped the top of the Perez paleosol. The artifacts and relatively coarse sediment immediately above the Perez paleosol probably were deposited immediately after the erosion event, perhaps dur- ing the same flood that formed the scours. However, the edges of most of the FCR did not seem significantly rounded, and even small chert flakes were razor sharp. This suggests that the cultural ma- terial was not transported very far by ...
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... paleosol is accompanied by an increase in the size and fre- quency of stream-worn pebbles. This sedimentological evidence suggests that flood magnitudes increased during the final stages of soil upbuilding. Turbulent, high-magnitude floods entrain more and larger pebbles compared to low-magnitude and less turbulent floods. Also, high-magnitude floods are usually erosive; hence they can move artifacts and disturb or destroy cultural features on a floodplain. Deep flood scours are common at the top of the Perez paleosol ( Fig. 11), and laminated sandy sediment in many of the scours indicates high flood-flow velocities on the early-Holocene floodplain (Fig. 12). The most disturbed Early Archaic cultural component rests on the eroded surface of the Perez paleosol. This cultural zone is poorly preserved and contained no in situ archaeological features. Instead, there were random concentrations of chipped-stone artifacts, FCR, and mussel shells (Fig. 13). There also were many stream-worn pebbles 2e4 cm in diameter. Many of the artifacts rested on their edges at near vertical angles of repose, and some were imbricated. These artifacts were concentrated in flood scours eroded into the top of the Perez Soil (Fig. 14), and some artifacts were scattered in sandy and loamy flood deposits immediately above the soil. The obvious implication is that the artifacts and stream-worn pebbles form a lag deposit that resulted from a high-energy flood that stripped the top of the Perez paleosol. The artifacts and relatively coarse sediment immediately above the Perez paleosol probably were deposited immediately after the erosion event, perhaps dur- ing the same flood that formed the scours. However, the edges of most of the FCR did not seem significantly rounded, and even small chert flakes were razor sharp. This suggests that the cultural ma- terial was not transported very far by ...
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... paleosol is accompanied by an increase in the size and fre- quency of stream-worn pebbles. This sedimentological evidence suggests that flood magnitudes increased during the final stages of soil upbuilding. Turbulent, high-magnitude floods entrain more and larger pebbles compared to low-magnitude and less turbulent floods. Also, high-magnitude floods are usually erosive; hence they can move artifacts and disturb or destroy cultural features on a floodplain. Deep flood scours are common at the top of the Perez paleosol ( Fig. 11), and laminated sandy sediment in many of the scours indicates high flood-flow velocities on the early-Holocene floodplain (Fig. 12). The most disturbed Early Archaic cultural component rests on the eroded surface of the Perez paleosol. This cultural zone is poorly preserved and contained no in situ archaeological features. Instead, there were random concentrations of chipped-stone artifacts, FCR, and mussel shells (Fig. 13). There also were many stream-worn pebbles 2e4 cm in diameter. Many of the artifacts rested on their edges at near vertical angles of repose, and some were imbricated. These artifacts were concentrated in flood scours eroded into the top of the Perez Soil (Fig. 14), and some artifacts were scattered in sandy and loamy flood deposits immediately above the soil. The obvious implication is that the artifacts and stream-worn pebbles form a lag deposit that resulted from a high-energy flood that stripped the top of the Perez paleosol. The artifacts and relatively coarse sediment immediately above the Perez paleosol probably were deposited immediately after the erosion event, perhaps dur- ing the same flood that formed the scours. However, the edges of most of the FCR did not seem significantly rounded, and even small chert flakes were razor sharp. This suggests that the cultural ma- terial was not transported very far by ...
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... paleosol is accompanied by an increase in the size and fre- quency of stream-worn pebbles. This sedimentological evidence suggests that flood magnitudes increased during the final stages of soil upbuilding. Turbulent, high-magnitude floods entrain more and larger pebbles compared to low-magnitude and less turbulent floods. Also, high-magnitude floods are usually erosive; hence they can move artifacts and disturb or destroy cultural features on a floodplain. Deep flood scours are common at the top of the Perez paleosol ( Fig. 11), and laminated sandy sediment in many of the scours indicates high flood-flow velocities on the early-Holocene floodplain (Fig. 12). The most disturbed Early Archaic cultural component rests on the eroded surface of the Perez paleosol. This cultural zone is poorly preserved and contained no in situ archaeological features. Instead, there were random concentrations of chipped-stone artifacts, FCR, and mussel shells (Fig. 13). There also were many stream-worn pebbles 2e4 cm in diameter. Many of the artifacts rested on their edges at near vertical angles of repose, and some were imbricated. These artifacts were concentrated in flood scours eroded into the top of the Perez Soil (Fig. 14), and some artifacts were scattered in sandy and loamy flood deposits immediately above the soil. The obvious implication is that the artifacts and stream-worn pebbles form a lag deposit that resulted from a high-energy flood that stripped the top of the Perez paleosol. The artifacts and relatively coarse sediment immediately above the Perez paleosol probably were deposited immediately after the erosion event, perhaps dur- ing the same flood that formed the scours. However, the edges of most of the FCR did not seem significantly rounded, and even small chert flakes were razor sharp. This suggests that the cultural ma- terial was not transported very far by ...
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... Richard Beene, there is a distinct period of high relative C 4 productivity during the first half of the Younger Dryas climate event, between ca. 11,000 and 10,500 14 C yr B.P. (Fig. 16). It is likely that accumulation of sediment comprising the C horizon of the Perez paleosol was underway at that time. Although there is un- certainty about moisture availability in south-central Texas during the Younger Dryas, all evidence points to increasing temperatures in most of Texas between 11,000 and 10,500 14 C yr B.P. (Nordt et al., ...
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... carbonate content is high throughout unit A4, ranging from 41% in the upper 24 cm of the Bk1b3 horizon to 48.5% in the Ckb3 horizon (Fig. 15). These values indicate that there has been only slight leaching of primary calcium carbonate in the upper part of the Elm Creek soil. Particle-size distribution in unit A4 is characterized by a general upward-fining sequence (Table 2). On a clay-free basis the pro- portion of fine silt increases upward from 76.9 to 91.0%. This in- crease in fine silt is matched by a 14% decrease in the proportion of sand. Although the general trend is one of upward fining, there are distinct irregularities in particle-size distribution. For example, on a clay-free basis the proportion of sand increases from 23.5% in the Ckb3 horizon to 37.2% in the CBkb3 horizon, but abruptly drops off to 10.6% in the Bk2b3 horizon. Also, the ratio of very fine sand to fine sand dramatically increases from 5.6 in the upper 26 cm of the Bk2b3 horizon to 37.0 in the lower 24 cm of the Bk1b3 horizon, but drops off to 6.0 in the upper 24 cm of the Bk1b3 horizon. These patterns indicate that pedogenesis has not completely homoge- nized the parent material, even within the upper part of the trun- cated Bk1b3 ...
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... 7000 and 5000 14 C yr B.P., d 13 C values of soil organic matter steadily increase (Fig. 16), indicating more relative C 4 pro- ductivity compared to the early Holocene. This warm interval cor- relates with the well-known warm, dry Altithermal of the North American Great Plains. At the Richard Beene site, it is marked by aggradation of the thickest package of fine-grained alluvium (unit A5) in the stratigraphic sequence at the site. Hence, increased aridity, punctuated by infrequent but intense rainfalls typical of the region today, generated high sediment yields in the Medina River ...
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... are no dramatic shifts in d 13 C values of soil organic carbon between 8600 and 7000 B.P. (Fig. 16); a mixed C 3 /C 4 plant com- munity was in pace. Unit A4 aggraded and the Elm Creek paleosol formed during this period. However, d 13 C values of soil organic carbon decreased appreciably at ca. 7000 14 C yr B.P., pointing to a cooling trend. The interval from 8000 to 7000 14 C yr B.P. has been recognized as the most prominent and globally widespread cold period in the past 10,000 years ( Hu et al., 1999;Barber et al., ...
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... A4, which overlies unit A3 (Fig. 7), typically is 2e4 m thick and mostly consists of calcareous, fine-grained overbank deposits. The Elm Creek paleosol at the top of unit A4 has a thin, weakly expressed Bk-CBk-Ck profile (Table 1) Organic C content has a normal depth trend in most of the Elm Creek soil; it decreases from 0.54% in the upper 24 cm of Bk1b3 horizon to 0.23% in the lower 26 cm of the Bk2b3 horizon (Fig. 15). However, organic C abruptly increases to 0.53% in the CBkb3 ho- rizon before dropping off to 0.06% in the underlying Ckb3 horizon. The relatively high concentration of organic C in the CBkb3 horizon is attributed to deposition of organic-rich sediment and, therefore, is not related to ...
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... Richard Beene site (41BX831) is located on the southwest margin of the eastern woodlands in south-central Texas (Fig. 1). Situated on the extreme southwestern fringe of the continent's greater Southeast culture area, Richard Beene is one of few strati- fied sites in that region that has yielded a fairly complete archaeological record spanning the last 10,000 years of human occupation. For that matter, recorded deeply stratified open-air archaeological sites with complete or nearly complete records of human occupation spanning the Holocene are rare in North America. The Icehouse Bottom and Rose Island sites in Tennessee (Chapman, 1985) along with the Big Eddy site in Missouri ( Ray et al., 1998;Hajic et al., 2007) are examples of stratified open-air sites in the Southeast culture area with long records of human occupation, but they are not as deeply stratified or represented by as many well- preserved Archaic components compared to Richard Beene. The Richard Beene site is further distinguished from other Southeast sites, as well as sites in the Southwest and Great Plains of North America, by subsistence strategies. Specifically, there is no evidence of native agriculture at the Richard Beene site, and semi-permanent camps that would suggest a mix of horticulture and hunting- gathering do not appear in the region until the Spanish arrived in the early 18th Century (Perttula, 2004). Instead, hunter-gatherer groups who relied primarily on deer and, presumably, geophytes and other wild plant foods, are represented in the site's entire occupational history ( Thoms and Clabaugh, 2011). Although no charred plant remains were found at the Richard Beene site, indi- rect evidence, including earth ovens and an abundance of fire- cracked rock (FCR), point to the use of geophytes. An abundance of FCR is consistent with the preparation of plant foods, especially roots (Thoms, 1989(Thoms, , 2003Wandsnider, 1997). Also, ethnographic records for south-central Texas from the 16th Century attest to the importance of root foods during the winter months (Thoms, ...
Citations
... Most of the sediments eroded from the hillslopes in the Edwards Plateau during the late Quaternary were transported by streams off the Plateau where they became stored in large, high-order streams on the Coastal Plain (Mandel et al. , 2018Waters and Nordt, 1995). However, some of this sediment ended up in caves and in the channel, channel margin, and floodplain environments of loworder streams on the Edwards Plateau. ...
... While not on the Edwards Plateau, the stratigraphic sequence at Hall's Cave strongly correlates with the alluvial stratigraphic record of the Medina River at the Richard Beene archaeological site (Thoms and Mandel, 2007;Mandel et al. 2007Mandel et al. , 2018. The Richard Beene site is located 25 km downstream of the Balcones Escarpment which forms the edge of the Edwards Plateau. ...
... Below the Balcones Escarpment the Medina River abruptly takes on a meandering morphology. The alluvial record at the Richard Beene site (Thoms and Mandel, 2007;Mandel et al., 2018) is remarkably similar to that found at Hall's Cave with Units A3d and A4 at the Richard Beene site correlating with Units 2 and 3 at Hall's Cave, Unit A5 correlating to Unit 4, Unit A6 with Units 5 and 6, and Unit A7 with Unit 7. The alluvial record at the Richard Beene site shows that the sediments eroded from the hillslopes of the Edwards Plateau were transported downstream off the Edwards Plateau and onto the Gulf Coastal Plain. Further, the sequence of deposition at the Richard Beene site correlates with the timing of hillslope erosional events documented at Hall's Cave and corresponds with episodes of deposition and non-deposition seen along the low-order streams on the Edwards Plateau, showing that deposition and non-deposition were near synchronous over a broad region of central Texas. ...
Hall's Cave, Texas, contains a radiocarbon dated sediment record extending from the Last Glacial Maximum through the Holocene. Changes in the characteristics of the sediments and the pattern of sedimentation in the cave correlate with environmental and climatic shifts over the last 20,000 years. The sediments in Hall's Cave preserve well-documented paleontological and paleoecological records. We show that the cave sediments also contain a well-preserved archaeological record dating from ∼10,500 cal yr B.P. to the Historic period. Human use of the cave was episodic and tied to environmental factors, with evidence for increasingly intensive use of the cave throughout the Holocene. Episodes of deposition and non-deposition in Hall's Cave were synchronous with periods of deposition and erosion in low-order streams of the Edwards Plateau. These processes structured the archaeological record of central Texas.
... The Richard Beene archaeological site in southwestern, Texas, was chosen as a case study of Homo sapiens records found in buried soils, that has the potential to continue to inform us about the Quaternary period. The site is well exposed, well dated and has been extensively studied (Mandel et al., 2007;Thoms and Clabaugh, 2011;Mandel et al., 2018). The site is an ideal candidate for applying the more inclusive PCZ methodologies. ...
... A field sketch of an outcrop at Richard Been archaeological site of Mandel et al. (2018) illustrated in Figure 7 shows the interpreted stratigraphy and radiocarbon ages. The 20-m-thick stratigraphic sequence is a spectacular exposure that reveals stacked sedimentary packages of floodplain alluviation alternating with periods of stability and pedogenesis overlying sand and gravel (33,000-20,000 14 C yr BP). ...
... An example of a PCZ in North America dates at 10 ka. Generalized cross-section of the west wall from a quarry excavated into Medina River alluvium (Mandel et al., 2018). Exposure reveals stacked stratigraphic units, paleosols and sites of dated material (designated alphabetically). ...
The Critical Zone (CZ) as visualized in 1998 was a way to integrate the research of the four scientific spheres (lithosphere, hydrosphere, biosphere and atmosphere) at the surface of Earth and to study the linkages, feedbacks and record of processes. Rather than closeting studies by a variety of disciplines into their respective pigeonholes the CZ perspective provides the symbiotic framework from which the tendrils of improved understanding can radiate outward to new disciplines and/or feedback into the component disciplines. During the last 2 decades, CZ research has been limited to the modern environment. Knowledge gained from the modern and the focus on interpreting ancient records allows for the development of paleo-CZs (PCZs). PCZs provide a powerful tool for improved understanding of the landscapes during the Quaternary Period and the response of this thin skin to glaciations, sea level fluctuations and evolving life. Case studies from hominins in East Africa and Homo sapiens in the Americas provide examples of the rich records stored in PCZs. As we move into the space age, the CZ can provide a platform from which to guide future exploration of the proto Critical Zones on the rocky planets and asteroids of our solar system.
... These observations have interesting implications for reconstructing paleo-earthquakes and seismicity in this tectonic setting. Mandel et al. (2017) present an integrated geoarchaeological investigation that included excavations, soil-stratigraphic, geochemical and paleoecological analyses of the Richard Beene site in south-central Texas, a deeply stratified archaeological locality in association with an alluvial terrace in the Medina River valley on the Inner Gulf Coastal Plain. This location preserves cultural archives back to 10,000 years ago, recorded in 14 m of fine-grained flood deposits with multiple buried paleosols and contexts yielding material remains of Archaic and Late Prehistoric hunter-gatherers, including >80,000 artifacts, including flakes, tools, bones, mussel shells and fire-cracked rocks. ...
... This location preserves cultural archives back to 10,000 years ago, recorded in 14 m of fine-grained flood deposits with multiple buried paleosols and contexts yielding material remains of Archaic and Late Prehistoric hunter-gatherers, including >80,000 artifacts, including flakes, tools, bones, mussel shells and fire-cracked rocks. Mandel et al. (2017) state that the Richard Beene site is one of the most complete records of Holocene human occupation and sedimentation documented in North America, and comprises a valuable "type site" against which other less complete archaeological records can be compared. The d 13 C values determined from organic matter preserved in the site's soilstratigraphic sequence indicate increased C 4 plant production between~11,000 and 10,000 14 C yr BP. ...
... Mandel et al. (2017) state that the Richard Beene site is one of the most complete records of Holocene human occupation and sedimentation documented in North America, and comprises a valuable "type site" against which other less complete archaeological records can be compared. The d 13 C values determined from organic matter preserved in the site's soilstratigraphic sequence indicate increased C 4 plant production between~11,000 and 10,000 14 C yr BP. Mandel et al. (2017) conclude that this timeframe in south-central Texas was a warm interval responding to the diversion of glacial meltwater away from the Mississippi River. The C 4 productivity generally increased throughout the Holocene, culminating in warm intervals at~5000 and 2000 14 C yr BP. ...
The late Quaternary history of the bedrock-controlled Brazos River system in central Texas is poorly understood as to the complex interplay between bedrock and climate on episodes of channel incision and aggradation. Through geomorphic assessment, sediment core analysis, and luminescence dating (OSL) we map the alluvial terrace and floodplain deposits in the Steinbeck Bend study area in central Texas. Five stratigraphic (allostratigraphic) units were identified beneath four alluvial terrace-sediment complexes (T3-Unit I, T2a-Unit II, T2b-Unit III, T1a-Unit IV, T1b-Unit V) and the current floodplain (T0-Unit VI) of the Brazos River, with the accompanying OSL geochronology ranging from >60 to 0.3 ka. Channel incision appears to have occurred during the transition to cooler and wetter intervals at the beginning of MIS 4 and MIS 2. Alluvial deposition proceeded mainly during the latter stages of the warmer MIS 5 and during the first half of MIS 3, both characterized by a slight warming trend. The alluvial architecture of all units was formed by single story, mixed load meandering channels migrating laterally across Cretaceous marls. Upstream from the study area, the bedrock valley narrows because of the presence of more resistant limestones forming the bedrock channel floor and valley walls. In the Steinbeck Bend study area, the incised meanders develop into larger radius of curvatures as the Brazos River migrates across less resistant Cretaceous marls. Below the study area in the weakly consolidated Tertiary coastal plain deposits, the Brazos River becomes freely meandering, cutting laterally and vertically through previously deposited alluvium interceded by channel avulsions.
We examine δ¹³C values from soil organic matter (SOM) from the Culebra, Inguiro and Verde watersheds (Verde data are from Mueller et al., 2012) located in the Mixteca Alta from the terminal Pleistocene to the present. The SOM δ¹³C values were compared against local paleosol data and other paleoenvironmental proxies from central and southwestern Mexico. The paleovegetation implications of the SOM reflect overall changes in paleoclimate from the terminal Pleistocene through the middle Holocene. The late Holocene stable carbon isotope values varied widely, suggesting that human activities such as agriculture affected the paleoenvironment and paleovegetation in the study area, similar to findings in central Mexico. Values of δ¹³C show a significant rise between 3500 cal BP and 1250 cal BP, with one notable cluster of enriched values corresponding to the Post-Classic cultural period (local Natividad phase, 1250–500 cal BP), when the local population is thought to have peaked over 100,000. Since the late Formative period (local late Cruz phase, starting ∼3500 cal BP), lama-bordo (i.e., sediment check-dams) and agricultural terrace constructions were important for land use management and agriculture, which became widespread by the Post-Classic period. The highly enriched values associated with widespread agricultural structures suggest the increased importance of maize cultivation, and potentially the increased significance of CAM plant management, such as maguey and nopal during the late Holocene.
