George A. Brook’s research while affiliated with University of Georgia and other places

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Publications (142)


Evidence of Late Quaternary environments in Northwestern Georgia from sediments preserved in Red Spider Cave
  • Article

May 2013

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21 Reads

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18 Citations

Physical Geography

George A. Brook

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Rudy J. Nickmann

Carbon-14 ages of nine speleothems from Red Spider Cave indicate that speleothem deposition occurred predominantly during warmer phases of the last 40,000 years. Biotic activity above the cave may have been suppressed during the colder climatic periods, reducing soil CO2 levels. This may have lowered limestone solution rates and either slowed speleothem growth or interrupted deposition altogether. Remnants of a clastic fill up to 3 m thick are present within the cave. Speleothem age data indicate that this fill was emplaced after 26,000 yr. B.P. and had been largely eroded by 11,000 yr. B.P. The sediments may have been washed into the cave at the interstadialfull glacial transition or during full glacial times when the vegetation became more open and temperatures cold enough for freeze-thaw weathering and solifluction activity in the area. Pollen grains recovered from 11 speleothems suggest that during the warmer periods of the last 40,000 years the vegetation near Red Spider Cave was deciduous forest dominated by oak. Large percentages of herb pollen in speleothem pollen spectra for 39,000, 30,000, and before 11,000 yr. B.P. indicate that the forest at these times may have been more open and interspersed with species-rich meadows. The presence of aquatic pollen in all but mid- and late-Holocene-age speleothems implies more available moisture during interstadial, late glacial, and early Holocene times. Speleothem pollen spectra also indicate mixed mesophytic forest near Red Spider Cave at 9905 yr. B.P., 1730 yr. B.P., and prior to European settlement of the area. Pollen spectra for two active straw stalactites were entirely representative of the present oak-pine-hickory forest near the cave, indicating that valid paleovegetation data can be obtained for this site from speleothem pollen spectra.


Petrology and paleoenvironmental significance of detrital sand and silt in a stalagmite from Drotsky's Cave, Botswana

May 2013

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58 Reads

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21 Citations

Physical Geography

Analysis of a stalagmite from northwestern Botswana shows that variation in the abundance of detrital grains, which can be conveniently approximated by gray-scale measurements, provides a potentially valuable paleoclimatological record. The stalagmite, which is from near the mouth of Drotsky's Cave, is largely spelean CaCO3. It nonetheless also contains detrital grains of quartz, clays and iron oxides, carbonates, and other minerals. The abundance of those detrital materials varies along the stalagmite's growth axis. Analysis of the positions of those grains indicates that they preferentially accumulate in the dry season. Gray scale (a measure of the lightness or darkness of the cut speleothem) is inversely correlative with detrital content and thus with periods of decreased rainfall. It also correlates positively with historical records of rainfall and with rates of speleothem growth, which are controlled by rainfall. Gray-scale measurements from this speleothem can thus serve as a proxy paleoclimatological record. Similar measurement of other speleothems from similar environments, when coupled with careful analysis of the controls on gray scale, may likewise be useful in paleoclimatological studies. [Key words: Speleology, stalagmite, speleothem, sand, gray scale, paleoclimatology, Kalahari, Ngamiland, Botswana.]


Double Fourier series analysis of cockpit and doline karst near Browns Town, Jamaica

May 2013

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64 Reads

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19 Citations

Physical Geography

Double Fourier series models of two doline and two cockpit landscapes in northern Jamaica, each 2 × 2 km in area, explained 92% and 90%, and 73% and 58% of the variance in the topographic data. The ten most significant waves accounted for 74% and 76%, and 61% and 58% of the variance in each model. The greater importance of frequency pairs of longer wavelength in the doline karst models suggests that there are fewer horizontally and vertically persistent bedrock fractures controlling topographic development in the doline areas than in the cockpit terrains—a fact confirmed by fracture-trace mapping. Frequency pair orientations and powers indicate that north-west- and northeast-trending fractures exert a major influence on topographic development in the cockpit terrains and that east-trending fractures are relatively more important in the doline areas. Further studies are needed to determine if Fourier models of the doline, cockpit, and tower karst styles differ in a consistent fashion and to find out to what extent these differences are related to the bedding, fracture, and relief characteristics of the karst bedrock. [Key words: Jamaica, karst, morphometry, double Fourier series, dolines, cockpits.]


A Hydrological Budget for the Okefenokee Swamp Watershed, 1981-82

May 2013

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110 Reads

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6 Citations

Physical Geography

Previous hydrological models of the Okefenokee Swamp watershed were developed without the benefit of accurate empirical data on surface runoff into and out of the swamp, and without data on direct ground water flow into the swamp. Data from a network of ground water observation wells during 1981-82 have revealed that ground water amounted to only 1.3% of total swamp inputs. This figure is much lower than had been expected and confirms that the swamp portion of the Okefenokee watershed is predominantly a surface-water system. A simple conceptual model of the watershed hydrology with upland and swamp compartments, and upland wetland, upland terrestrial, swamp prairie-marsh, and swamp forest-shrub subcompartments, indicates that in 1981-82 actual evapotranspiration from uplands and swamp was 78% and 84% of precipitation, respectively, and that upland surface runoff contributed only 13% of swamp inputs. Significant differences between the long-term and 1981-82 hydrological budgets emphasize that the Okefenokee Swamp is a dynamic hydrological system.


Channel pattern changes along the lower Oconee River, Georgia, 1805/7 to 1949

May 2013

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161 Reads

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7 Citations

Physical Geography

Historical maps and aerial photographs of a stretch of the Oconee River channel above its junction with the Ocmulgee indicate that as erosive land use in the basin changed following European settlement so did the pattern of the river channel. Between 1805/7 and 1910, as erosive land use increased, channel sinuosity increased from 1.24 to 1.55, the number of islands in the river increased from 1 to 21, and meander wavelengths, amplitudes, and radii of curvature all decreased. The decrease in erosive land use in the period 1910 to 1949 was accompanied by a slight decrease in channel sinuosity to 1.50, a reduction in the number of islands to 9, and a slight increase in meander wavelengths and radii of curvature. The channel pattern changes may have been a response to changing river discharge and sediment transport characteristics brought about in part by land use changes in the basin. Higher peak and annual discharges in the late 1800s and early 1900s together with higher concentrations of suspended sediment because of intense soil erosion caused the river to become more sinuous between 1805/7 and 1910. Sinuosity decreased slightly in the period 1910–49 as discharge and suspended sediment concentrations dropped.


Raised marine terraces along the Gulf of Aden coast of Somalia

May 2013

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52 Reads

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7 Citations

Physical Geography

Mapping in the Galweda-Elayu area of northern Somalia has revealed depositional and erosional marine terraces at elevations of approximately 16 m, 8 m, and 2 m. These terraces vary from 0–2300 m, 200–2200 m, and 0–800 m in width, respectively. Sediments exposed in stream-valley walls demonstrate that the two higher terraces were formed by marine transgressions followed later by regressions to below present sea level. Beach ridges on the terraced alluvial fan at the mouth of togga Galweda imply that sea level and/or land elevation varied by at least 6 m during the formation of the 16-m terrace and by at least 3 m during the formation of the 8-m terrace. 230Th/234U ages of corals suggest that the 8-m terrace was formed during deep-sea isotope substage 5c (105 kyr B.P.) and the 2-m terrace during substage 5a (80 kyr B.P.). A 7-kyr-old coral from above the present storm beach on the outer flanks of the 2-m terrace suggests that sea level in the Gulf of Aden was close to its present level by the middle Holocene. No material suitable for dating was recovered from the 16-m terrace, but on morphological grounds and based on marine-terrace elevations elsewhere in the Red Sea-Gulf of Aden rift zone, we believe that the 16-m terrace was formed during isotope substage 5e (132–120 kyr B.P.), when global sea level was about 6 m above present.


A hydrologic model for lower coastal plain watersheds, southeast united states

May 2013

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8 Reads

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1 Citation

Physical Geography

A disributed, physically-based, watershed hydrologic simulation model, called COASTAL, has been specifically designed for use on watersheds of low relief where streamflow is supplied predominantly by ground water discharge. To use the model, the watershed is divided into square grid elements that are modeled by the lumped parameter approach. I nput data include daily temperature, daily precipitation, topographic elevation, soil field capacity, soil wilting point, aquifer hydraulic conductivity, aquifer thickness and land use for each grid element and a watershed stream rating curve. One or more years of daily streamflow data are needed to calibrate the model. Yearly correlation coefficients between measured and simulated daily streamflow averaged 0.85 and ranged from 0.70–0.91 in tests of the model using 1957-1964 data for the Hurricane Creek watershed, Georgia. Correlation coefficients between measured and predicted annual, monthly, and annual maximum streamflow for the eight years tested were 0.97, 0.93, and 0.82, respectively.


Cyclicity in precipitation and stream discharge in Georgia and relationships with the Southern Oscillation

May 2013

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11 Reads

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1 Citation

Physical Geography

Maximum entropy spectrum analysis of 10 stream discharge time series from four physiographic provinces in Georgia has revealed clear and statistically significant cycles in water-year discharge (October to September) over the period 1938 to 1994 at 15 to 17 and 5 to 6 years in all 10 series, and at 8 to 9 years in 9 series. Analysis of 13 precipitation records uncovered cycles at 15 to 18 years (10 stations), 8 to 10 years (8 stations), and 5 to 6 years (13 stations). The cycles are much more consistent and better defined in the stream discharge time series suggesting that large intra-annual variations in precipitation, possibly caused by spatial variations in summer convectional rainfall, are filtered in the stream records. Spectrum analysis of the Southern Oscillation (SO) for the 98-year period from 1897 to 1994 revealed water-year cycles at about 18, 10, and 6 to 7 years, which are not in phase with the stream-flow and precipitation cycles. However, a strong relationship is apparent between cool-season (December through March) precipitation and stream flow in the southern part of the state (the Coastal Plain) and the sum of SO values in the same four months. In addition, cycles in cool-season precipitation at about 19, 10, and 6 years agree well with those in the SO and appear in phase suggesting a causal relationship.




Citations (86)


... Techniques in which landscape features were used in hunting also occurred in the Upper Pleistocene. At the 77 ka open-air site #Gi in the Kalahari, MSA points are associated with significant quantities of zebra and extinct hartebeest teeth and this likely indicates an area where prey was ambushed at the margins of the lake (Robbins et al., 2023). A dense concentration of extinct wildebeest-like remains with butchery marks and lithics at Bovid Hill, Kenya, dating to around 70 ka, also suggests tactical hunting (Thompson et al., 2023a). ...

Reference:

The Upper Pleistocene (late Pleistocene) archaeology of sub-Saharan Africa (MSA and LSA)
Tsodilo Hills, NW Kalahari Desert, Botswana
  • Citing Chapter
  • August 2023

... Strong similarities are evident in the stable nitrogen isotope records (interpreted as a reflection of water availability) from middens recovered from Aba Huab/Austerlitz , Spitzkoppe (Chase et al., 2009(Chase et al., , 2019, Zizou (Chase et al., 2019), and Pella (Chase et al., 2019), indicating a generally common climate response signal across a 900-km transect of the Namib Desert (Fig. 1). Evidence of associated changes in vegetation, however, is often restricted to the Holocene (Scott et al., 1991(Scott et al., , 2022Scott, 1996;Gil-Romera et al., 2006, with the only indications of glacial-age vegetation coming from the continuous 50-kyr record from Pella (Lim et al., 2016), and shorter MIS 2-3 time slices from the Brandberg (Scott et al., 2004) and Mirabib (Scott et al., 2018). While each record expresses changes specific to its environmental context, evidence from all of these sites contrasts markedly with pollen records recovered from marine cores off the coast of Namibia (Shi et al., 2000(Shi et al., , 2001Urrego et al., 2015). ...

Holocene environmental change along the central Namib Desert escarpment derived from hyrax and owl dung
  • Citing Article
  • August 2022

Review of Palaeobotany and Palynology

... The flickering wet-dry events prior to major climate transitions, which seem to recur throughout the~620 kyr Chew Bahir record, combined with the HadCM3 modeling results presented here, confirm the existence of precursor events prior to a tipping point, previously predicted only in theory. data sets showing excursions at the termination and flickering during the AHP include a lake record from Lake Dendi 33 , a lake record from Lake Abiyata 34 , and a record from Congo stalagmites 35 . The discovery of flickering prior to and during the transition from wet to dry conditions in Africa has significant implications for interpreting the relationship between climate change, cultural developments, and human migrations in those regions. ...

Episodic deposition of stalagmites in the northeastern Democratic Republic of the Congo suggests Equatorial Humid Periods during insolation maxima
  • Citing Article
  • June 2022

Quaternary Science Reviews

... Presentan un frente casi vertical, muy cuarteado, con numerosos fragmentos de roca al pie y un faldeo que se prolonga suavemente hacia el centro del cañadón, desembocando en un pequeño arroyo. Se encuentra aproximadamente 40 km al oeste del extremo sur del Macizo del Deseado, donde se localizaron ocupaciones humanas discontinuas comprendidas entre la transición Pleistoceno-Holoceno y el Holoceno tardío (Brook et al. 2018;Franco et al. 2010Franco et al. , 2020, y a unos 45 km de los espacios al aire libre de 17 de Marzo (Fig. 1), en los que la ocupación humana ha sido datada en el Holoceno tardío . ...

Nueva información referida a la transición Pleistoceno-Holoceno y al Holoceno temprano en el extremo sur del Macizo del Deseado (Patagonia, Argentina)
  • Citing Article
  • Full-text available
  • April 2020

Revista del Museo de La Plata

... There is therefore a compelling need to understand drought, and rainfall variability in general, at the Mid-to Late-Holocene transition, along with any potential association with the 4.2 ka event and societal change. This is particularly true in the tropics and southern hemisphere where there have been only a few detailed studies (Marchant and Hooghiemstra, 2004;Railsback et al., 2018Railsback et al., , 2022. In the tropics, there may be conflation of the 4.2 ka event and what is now a widely recognised shift in tropical climate at 4.0 kyr BP (Denniston et al., 2013;Gagan et al., 2004;Giosan et al., 2018;Li et al., 2018;MacDonald, 2011;Marchant and Hooghiemstra, 2004;Toth and Aronson, 2019). ...

Additional multi-proxy stalagmite evidence from Northeast Namibia supports recent models of wetter conditions during the 4.2 ka event in the Southern Hemisphere
  • Citing Article
  • November 2021

Palaeogeography Palaeoclimatology Palaeoecology

... Outcropping salt karst has been reported from the Mt. Sedom diapir in Israel (Frumkin, 1994a(Frumkin, , 1994b(Frumkin, , 1998Frumkin and Ford, 1995), the Cordillera de la Sal Mts., Atacama, Chile (De Waele et al., 2020), the Cardona diapir in Spain (Lucha et al., 2008), and the Vrancea Hills in Romania (Giurgiu, 2005). The most extensive outcropping salt karst occurs in the Zagros Mts. and along the Persian Gulf in southern and southwestern Iran (Bruthans et al., 2010;Abirifard et al., 2017). ...

Holocene evolution of halite caves in the Cordillera de la Sal (Central Atacama, Chile) in different climate conditions
  • Citing Article
  • August 2020

Geomorphology

... ka BP (Burney, 1987a(Burney, , 1987cStraka, 1996). Similar trends have been recorded almost across the entire island, for instance in the Southwest (Razanatsoa et al., 2022), and in the Northwest suggesting climate and human activities (Railsback et al., 2020;Voarintsoa et al., 2017a) as drivers. ...

Relationships between climate change, human environmental impact, and megafaunal extinction inferred from a 4000-year multi-proxy record from a stalagmite from northwestern Madagascar
  • Citing Article
  • April 2020

Quaternary Science Reviews

... No obstante, se pueden reconocer sectores con mayor abundancia de elementos cerámicos que otros. Entre éstos, cabe señalar los espacios localizados al NE costero y NW pericordillerano de la provincia de Santa Cruz, incluyendo la porción chilena, al este de la cordillera de los Andes (Cassiodoro & Tchilinguirian, 2007;Chaile et al. 2020;Cirigliano et al. 2019 y citas allí incluidas; Mena & Jackson, 1991;Roumec et al. 2020;Zilio et al. 2018; entre otros). La frecuencia de este registro es menor en los espacios localizados al sur del río Santa Cruz (Martinic & Prieto, 1998), donde sólo se identificaron elementos cerámicos en muy pocos sectores. ...

Hallazgos cerámicos y su cronología en el área comprendida entre el extremo sur del macizo del deseado y la cuenca del Río Santa Cruz (Patagonia Sur, Argentina)

Magallania (Punta Arenas)

... Early reconstructions of palaeoclimatic conditions during the Holocene in the Namib Desert and surroundings were based on microfaunal studies, geomorphological research and radiocarbon dating of inclusions in riverine deposits and dunes (e.g., Brain and Brain, 1977;Heine, 1982;Vogel and Rust, 1987;Lancaster and Teller, 1988;Vogel, 1989), followed by studies on Atlantic Ocean pollen from marine boreholes (Fig. 1), dust geochemistry, isotopes and micropalaeontology (Scott et al., 1991;Shi et al., 1998Shi et al., , 2000Shi et al., , 2001Stuut et al., 2002;Farmer et al., 2005;Dupont et al., 2008) and terrestrial records like stalagmites, geomorphology, and archaeology (e.g., Stokes et al., 1997;Stute and Talma, 1998;Brook et al., 1999Brook et al., , 2011Brook et al., , 2015Thomas and Shaw, 2002;Eitel et al., 2005;Heine, 2005;Srivastava et al., 2005;Chase et al., 2009Chase et al., , 2011Thomas and Burrough, 2012;Sletten et al., 2013;Marais et al., 2015;Railsback et al., 2016Railsback et al., , 2018Railsback et al., , 2019Voarintsoa et al., 2017;Kinahan, 2018;Schüller et al., 2018). These studies have added critical information on past hydrological regimes of southern Africa, especially rainfall ( Fig. 1), which is one of the major shifting climate features in the subcontinent. ...

Control of insolation on stalagmite growth, rainfall, and migration of the tropical rain belt in northern Namibia over the last 100 kyr, as suggested by a rare MIS 5b-5c stalagmite from Dante Cave
  • Citing Article
  • August 2019

Palaeogeography Palaeoclimatology Palaeoecology

... Testimonian la colonización temprana por Homo sapiens en regiones de diferentes continentes, como el sudeste asiático (Aubert et al., 2017;Standish et al., 2020), el norte de Australia (David et al., 2013;Ross et al., 2016), la región Franco-Cantábrica (Quiles et al., 2016) y el cono sur de Sudamérica, (Gradin et al., 1979;Carden y Miotti 2020) 1 . En su gran mayoría, estos motivos son el producto de prácticas desarrolladas por sociedades cazadoras-recolectoras, lo cual explica su larga perduración en Australia y la región patagónica, donde este modo de vida perduró hasta momentos de contacto con los europeos (Bradley et al., 2021;Brook et al., 2018;McDonald, 2005;Morwood, 2002;Mulvaney, 1996Mulvaney, , 2013. ...

Pigments, binders, and ages of rock art at Viuda Quenzana, Santa Cruz, Patagonia (Argentina)
  • Citing Article
  • October 2018

Journal of Archaeological Science Reports