摘要:

AbstractArchival and stratigraphic data from the middle Gila River, Arizona, provide insight into late‐Holocene floods and channel changes that affected the Hohokam, prehistoric agriculturalists who practiced canal irrigation 2000‐500 B.P. The relationship between floods and channel changes during the past 300 years is characterized by an increased frequency of wide, braided channel conditions during episodes of increased large flood frequency. Ten radiocarbon ages from overbank deposits from the middle Gila River flood plain indicate that the frequency of large floods was relatively low 4000‐1000 B.P. (14C years) but increased after 1000 B.P., a pattern supported by paleoflood slackwater sites in the upper Gila River watershed. This suggests that channel instability (shifts between narrow, single‐channel and wide, braided planforms) increased after 1000 B.P. The latter part of the 4000‐1000 B.P. period of relative channel stability corresponds in time with the development of Hohokam irrigation agriculture and expansion of canal systems, whereas increased fluvial dynamics beginning 1000 B.P. correlate (in time) to changes in settlement patterns during the Sedentary‐Classic period transition. Higher large flood frequency may be responsible for the consolidation of canal systems and relocation of villages along the middle Gila River after 1000 B.P. and during the Classic period. Increased flooding and concomitant channel changes alone, however, do not adequately explain the collapse of the Hoho

ISSN:0883-6353    

DOI:10.1002/gea.3340100302

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractAt The Rustad Quarry Site (32RI775), in southeastern North Dakota, Early Archaic artifacts, bison bone, and hearth features were found in the lowest of three Boroll‐like buried soils formed in alluvial fan sediments. Alluvial fan sediments were deposited from 8000 to 4925 B.P., and were then buried by eolian sand. The alluvial fan sediments (mudflows) bury lacustrine sediments (Sherack Formation deposited from 9900 to 9500 B.P. in Glacial Lake Agassiz II), both of which overlie a Moorhead Phase fluvial terrace deposited from 10,900 to 9,900 B.P. Cultural remains were associated with five radiocarbon ages, three on archaeological charcoal (7180 B.P., 7240 B.P., and 7550 B.P.) and two on organic carbon from two welded A‐horizons containing the cultural remains (7370 B.P. and 7675 B.P.). A well‐developed Aquoll‐like soil formed in the lacustrine sediments from 9500 to 8000 B.P. Soil morphology and chemistry of the Boroll‐like fan soils, the Aquoll‐like lacustrine soil, and other Boroll‐like soils formed in eolian and deltaic sediments nearby suggest a subhumid, cool continental climate with riparian woodland and mixed prairie vegetation at the site and surrounding area from 11,400 B.P. to the present. This partially contradicts paleoenvironmental reconstruction from pollen sites nearby that suggest the area was covered by a closed canopy spruce forest from terminal late‐Pleistocene to 10,000 B.P. Alluvial fan formation and eolian activity on the adjacent Sheyenne Delta occurred from 8000 to 5000 B.P., which indicates greater landscape instability and drier conditions during the mid‐Holoc

ISSN:0883-6353    

DOI:10.1002/gea.3340100303

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractA complex late Quaternary alluvial history was documented along Henson Creek, a low order tributary on the Fort Hood Military Reservation in central Texas. Three Quaternary alluvial landforms were recognized: terrace 2 (T2), terrace 1 (T1), and the modern floodplain (T0). The late Pleistocene T2 terrace may contain an array of sites spanning the entire known cultural record, while T1 may have sites spanning the last 5000 years only. Five fluvial units, three colluvial facies, two alluvial fan facies, and two buried paleosols were also recognized. Fluvial deposition was occurring approximately 15,000 yr B.P., 10,000‐8000 yr B.P., 7000–4800 yr B.P., 1650‐600 yr B.P., and during the last 400 years. Colluvial deposition was ongoing mainly in the early and middle Holocene, while alluvial fan aggradation was proceeding primarily in the middle Holocene. Because of erosional unconformities, there is minimal potential for recovering buried sites dating to intervals between depositional eposides for most of the drainage basin. Preservation potentials for buried sites are greatest in fine‐grained fluvial deposits dating to the late Pleistocene, early Holocene, and parts of the late Holocene, and in fine‐grained colluvial deposits dating to the early and middle Holocene. This investigation demonstrates that within the study area, and perhaps throughout much of central Texas, a greater continuum of sediments and preservation potentials exists in late Quaternary alluvial deposits of rivers than in low‐order

ISSN:0883-6353    

DOI:10.1002/gea.3340100304

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

ISSN:0883-6353    

DOI:10.1002/gea.3340100305

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

ISSN:0883-6353    

DOI:10.1002/gea.3340100306

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

ISSN:0883-6353    

DOI:10.1002/gea.3340100307

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

ISSN:0883-6353    

DOI:10.1002/gea.3340100308

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

ISSN:0883-6353    

DOI:10.1002/gea.3340100309

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

ISSN:0883-6353    

DOI:10.1002/gea.3340100310

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

ISSN:0883-6353    

DOI:10.1002/gea.3340100301

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY