Climatic Zonation Research Articles

Distribution and characteristics of mixed (transitional) mid-Permian (Late Artinskian—Ufimian) marine faunas in Asia and their palaeogeographical implications

Abstract The Permian marine biogeography of the Asian region is characterised by the development of three broad realms (Boreal, Tethyan and Gondwanan). In the early Early Permian (Asselian to Early Artinskian), there seems to have existed sharp biogeographical boundaries with no transitional zones between the realms, presumably due to the effect of Gondwanan glaciation and sharp climatic zonation. The mid-Permian (Late Artinskian to Ufimian) of the Asian region is distinguished by the rise of two broad transitional zones in which mixed marine faunas flourished. The northern transitional zone (north and northeast China, Sikhote Alin, central and northeast Japan) is characterised by an admixture of both warm-water Cathaysian and cold temperate Boreal genera. The southern transitional zone (Arabian Peninsula, Iran, Afghanistan, the Karakorum, southeast and central Pamir, Salt Range, central and northwest Tibet, Shan-Thai terrane, Timor, and western Irian Jaya), on the other hand, is distinguished by incorporating faunal elements of both Gondwanan and Cathaysian origin. The mixed faunas of both transitional zones share several antitropically distributed genera (e.g., Monodiexodina, Lytvolasma and Spiriferella ) and are succeeded by palaeotropical Tethyan faunas of Late Permian age. It has been postulated that the mixed mid-Permian fauna of the northern transitional zone was probably formed in an epicontinental sea which was connected to both the Asian Tethys and the Arctic, which facilitated the migration of Cathaysian and Boreal forms into the epicontinental sea and subsequent faunal mixing. The formation of the mixed faunas of the southern transitional zone, on the other hand, is probably related to the breaking off of the Cimmerian blocks from northern Gondwana and subsequent drifting into a lower latitudinal zone with geographical proximity to both Gondwana and Cathaysia during the mid-Permian.

Climatic Zonality of Periglacial Landforms in Mountain Areas

The alpine periglacial areas of the world can be divided into three distinctive landscape types dominated by one of the following: active rock glaciers, active block streams, or gelifluction landforms. These also correspond to distinct climates, the active rock glaciers occurring under cold, humid conditions; the active block streams in cold, dry climates; and gelifluction-dominated landforms occurring in warmer areas. These have distinct ranges of mean annual temperature and precipitation, which can be used in interpreting climatic changes based on distribution of fossil landforms. Key words: alpine permafrost, block streams, rock glaciers, gelifluction

An automated recording atmometer: 2. evaporation measurement on a high elevation transect in Hawaii

A transect of five recording atmometers was maintained over a 3-year period to monitor evaporative demand between 950 and 3000 m on the leeward slope of Haleakala Volcano, Maui, Hawaii. This elevation range traverses a portion of the slope where the persistent trade-wind inversion produces distinct vertical climate zonation, grading from a moist marine environment to extreme aridity above the inversion. Mean annual evaporation rates of 3.51 mm day −1 at both 950 and 1650 m, 3.64 mm day −1 at 2130 m, 4.82 mm day −1 at 2500 m, and 6.03 mm day −1 at 3000 m suggest a minimum between 950 and 1650 m where a cloud layer typically develops each morning. Monthly mean evaporation rates along the transect range from 2.3 mm day −1 at 950 m in December to 8.1 mm day −1 at 3000 m in August. Pronounced annual cycles are evident at the three highest stations. Midday evaporation is greatest at the upper two stations and least at 1650 and 2130 m. Differences in evaporation variability suggest that humidity changes associated with movements of the inversion are a major source of variation in the evaporation rate at high elevations.

Climate, Environmental Change, and Resources of the African Mountains from the Mediterranean to the Equator

During the last 20,000 years, the mountains of Africa between the Mediterranean and the equator have experienced significant climatic changes with important consequences for the vegetation and resource potential. At about 18,000 B. P. present altitudinal belts were depressed and the zonation of climate and vegetation was changed considerably. In the Holocene, higher temperatures led not only to more humid conditions but also to an uplifting of altitudinal belts and transformation of climatic and ecological zones and to increased natural resource potential. These changes in climate, vegetation, and altitudinal zonation are illustrated in a series of schematic diagrams. The cumulative effects of natural and anthropogenic processes and impacts within the last 2,000 years are also depicted. In particular, human impact on ecosystems formed under more favorable climatic conditions could result in irreversible degradation. The mountains of the subtropics and tropics very often have more advantageous ecological conditions than the surrounding lowlands. They are an important resource potential for the future, although they may be very sensitive to climatic and anthropogenic changes.

A review of the biogeography of cretaceous belemnites

A pattern of Boreal and Tethyan marine faunal realms was initiated in the Jurassic and continued into the Cretaceous. The belemnites first display this pattern in the Early Jurassic, and from the Middle Jurassic to earliest Cretaceous two morphologically distinct suborders, the Belemnitina and the Belemnopseina, were restricted to the boreal shelf seas and the Tethyan and Gondwanan shelf seas, respectively. An Austral marine realm was notably lacking during this interval. Significant change occurred in the late Barremian to early Aptian when the Belemnitina died out leaving the Belemnopseina, initially the Belemnopseidae, but followed by the Belemnitellidae, to invade their niches. An Austral Realm was initiated at this time, with the first appearance of a Gondwanan belemnopseine family, the Dimitobelidae. The Tethyan belemnite realm cannot be recognised after the Cenomanian, although the Belemnitellidae and Dimitobelidae defined Boreal and Austral belemnite realms throughout the Late Cretaceous. Climatic zonation remains the most often cited prime cause of provinciality in belemnites. However, examination of diversity patterns and faunal distributions reveals that palaeogeographic and palaeoceanographic factors were as important, if not more so, in determining Cretaceous provincial boundaries.

Low palaeolatitude of Late Proterozoic glaciation: early timing of remanence in haematite of the Elatina Formation, South Australia

Previous palaeomagnetic study of a ∼ 10 m thick rhythmite member of the Elatina Formation, part of the Late Proterozoic (∼ 650 Ma) Marinoan glacial succession in South Australia, argued strongly for a low palaeolatitude (∼ 5°) of deposition. However, a fold test was thwarted by the approximate alignment of the remanence with the axis of tectonic folding. Here we report results of a fold test on soft-sediment slump folds with a wavelength of 14–22 cm in the Elatina rhythmites, the axes of which are approximately perpendicular to the direction of remanence. Fifty-one standard palaeomagnetic specimens sampled across the slump structure gave α 95 = 3.7° prior to unfolding, α 95 = 1.8° with 67% unfolding, and α 95 = 2.4° with 100% unfolding. The results indicate that the remanence was acquired very soon after deposition; apparently it was acquired prior to soft-sediment slumping and then slightly sheared by the disturbance. The Elatina pole must be considered a virtual geomagnetic pole because the tidal rhythmite member studied represents only 60–70 years of deposition. However, the mean pole position is similar to other Late Proterozoic poles for South Australia, which implies that the very low inclination (< 10°) for the Elatina rhythmites does not record a geomagnetic excursion or reversal but does indeed indicate deposition in low palaeolatitudes. The similarity of many of the Late Proterozoic pole positions is evidence also that inclination error is not significant. The low palaeolatitude of Late Proterozoic glaciation is one of the major enigmas in contemporary Earth science, raising questions concerning the nature of the geomagnetic field, climatic zonation, and the Earth's rotational parameters in Late Proterozoic time.

Climatic evolution and control on carbonate deposition in northeast Australia

The characteristics of carbonate facies deposited along continental margins are directly controlled by seawater temperature. The oxygen isotopic composition of foraminifera tests reflect seawater temperature, and accordingly isotopic and age data may be combined to derive a paleotemperature record. Paleotemperature data may be used both to account for the known distribution of carbonate facies, and also to predict facies characteristics in poorly known areas. Oxygen isotope data from Deep Sea Drilling Project holes throughout the southwest Pacific have been used to compile a paleotemperature curve for offshore northeast Australia. The accuracy of paleotemperature estimates used in this compilation is dependent on the precise estimation of global ice volumes; on the estimation of surface water isotopic ratios from near-surface planktonic foraminifera; on the accuracy of biological disequilibrium isotopic fractionation constants for benthonic foraminifera; and on the identification of recrystallization, encrustation, and selective dissolution of samples. Decreasing temperatures during much of the early Cenozoic portion of the northeast Australia paleotemperature curve reflect the global high-latitude cooling trend which persisted throughout the Tertiary following the earliest Eocence temperature maximum. Warning during the middle Oligocene to Recent part of the curve reflects northeast Australia's transition from a mid-latitude situation in a world with little climatic zonation, to a low latitude situation in a world with pronounced latitudinal temperature gradients. The carbonate buildups of northeast Australia directly reflect this climatic variation. Restricted warm temperate or subtropical buildups developed during the Eocene; carbonate buildups did not develop at all during the cool Oligocene; and subtropical buildups suceeded by tropical coral reefs first developed during the latest Oligocene or Early Miocene in the northernmost part of area, and later developefurther south with continued warming in the Late Miocene and Pliocene.

Climatic evolution and control on carbonate deposition in northeast Australia

The characteristics of carbonate facies deposited along continental margins are directly controlled by seawater temperature. The oxygen isotopic composition of foraminifera tests reflect seawater temperature, and accordingly isotopic and age data may be combined to derive a paleotemperature record. Paleotemperature data may be used both to account for the known distribution of carbonate facies, and also to predict facies characteristics in poorly known areas. Oxygen isotope data from Deep Sea Drilling Project holes throughout the southwest Pacific have been used to compile a paleotemperature curve for offshore northeast Australia. The accuracy of paleotemperature estimates used in this compilation is dependent on the precise estimation of global ice volumes; on the estimation of surface water isotopic ratios from near-surface planktonic foraminifera; on the accuracy of biological disequilibrium isotopic fractionation constants for benthonic foraminifera; and on the identification of recrystallization, encrustation, and selective dissolution of samples.Decreasing temperatures during much of the early Cenozoic portion of the northeast Australia paleotemperature curve reflect the global high-latitude cooling trend which persisted throughout the Tertiary following the earliest Eocence temperature maximum. Warning during the middle Oligocene to Recent part of the curve reflects northeast Australia's transition from a mid-latitude situation in a world with little climatic zonation, to a low latitude situation in a world with pronounced latitudinal temperature gradients.The carbonate buildups of northeast Australia directly reflect this climatic variation. Restricted warm temperate or subtropical buildups developed during the Eocene; carbonate buildups did not develop at all during the cool Oligocene; and subtropical buildups suceeded by tropical coral reefs first developed during the latest Oligocene or Early Miocene in the northernmost part of area, and later developefurther south with continued warming in the Late Miocene and Pliocene.

Palaeobiogeography of Ordovician calcareous algae

From the study of Ordivician algal microfloras the following can be concluded: during the Early Ordovician, the algal microflora is scantly, but cosmopolitan, and different from that of the Upper Cambrian. Its cosmopolitan character seems to denote the absence of a climatic gradient during that time. By Middle Ordovician times, new algal taxa appear. The algal palaeographic distribution suggests a possible climatic zonation. No algae are known from Gondwana, which was located at high latitudes. For the same reason, calcaareous algae are absent (or not recorded) from South Europpe. In contrast, the occurence of calcareous algae and stromatoporoids of Middle Ordovician age provides support for inferring that the North Europe plate has reached low latitudes by Middle Ordovician times. During the Upper Ordovician, some groups of calcareous algae crossed the Proto-Atlantic or Iapetus ocean, and migrated towards North European and North American regions, according to the general pattern of oceanicsurface currents. This crossing and this migration are the result of the narrowing of the Proto-Atlantic or Iapetus ocean. At thattime, like other pelagic and benthic organisms, many groups of calcareous algae are declining. During the Middle and Late Ordovician, the migration and the distribution of some groups of calcareous algae resulted from asynchronous oceanic surface currents close to the palaeoequator, probably mainly in an eastward direction in the Late Middle Ordovician (from North America to Euroasia), and mainly in a westward direction in the Late Ordovician-Lower Silurian (from Euroasia to North America).

Palynostratigraphic zonation of Paleocene strata in the central and south-central Alberta Plains

Paleocene strata of the Scollard and Paskapoo formations in the central and south-central Alberta Plains can be subdivided into five formal biostratigraphic zones, based in part on a Momipites–Caryapollenites palynofloral lineage. A similar zonation previously identified from strata of the Wind River basin in Wyoming displays similar palynomorph occurrences. However, differences that are present are likely a result of latitudinal climatic zonation between Alberta and Wyoming during Paleocene time.Lowermost Paleocene strata of Alberta (Wodehouseia fimbriata Zone) are barren of Momipites species, which subsequently first appear in the Momipites wyomingensis Zone. These two zones include strata from the Cretaceous–Tertiary boundary (Nevis coal seam) to the top of the Scollard Formation. A diverse assemblage of Momipites spp. plus Aquilapollenites spinulosus, Caryapollenites prodromus, and Tiliaepollenites danei are present in the Aquilapollenites spinulosus Zone within the lowermost Paskapoo Formation. Two more species of Caryapollenites appear in the Caryapollenites wodehousei Zone. The Pistillipollenites mcgregorii Zone is characterized by the presence of Pistillipollenites mcgregorii, Insulapollenites rugulatus, and Caryapollenites inelegans. Momipites leffingwellii is absent from the lower portion of this zone, with Momipites waltmanensis, Momipites actinus, and Momipites triorbicularis absent from the upper portion. Lower P. mcgregorii Zone strata are the youngest strata encountered in the vicinity of the Red Deer River valley. Upper P. mcgregorii Zone strata include strata of the Obed–Marsh coal zone within the uppermost part of the Paskapoo Formation adjacent to the Alberta Foothills.

Extending the EBM: the effect of deep ocean temperature on climate with applications to the cretaceous

Three types of models are frequently applied to problems of present or past climates: (1) the energy balance model (EBM), which can be solved for the mean thermal state of the climate system based only on thermodynamical considerations, (2) the statistical dynamical model (SDM), which includes momentum considerations from which one can solve for climate statistics on a monthly or seasonal time scale including mean poloidal motions and the hydrologic cycle, and (3) the general circulation model (GCM), which can be solved for the evolving daily weather patterns that are then post-processed to yield all the climate statistics in much the same manner as synoptic data are processed. One major drawback of nearly all these models is that they typically do not consider the subsurface vertical heat fluxes (e.g., the effect of deep ocean temperatures and circulation). We present results froman SDM developed in the late 1960's that includes the parameterized effects of subsurface heat fluxes, and then use these results to demonstrate the importance that deep ocean temperatures can have in determining the climatic state. In this SDM, the ratio of the surface short wave absorption to the surface conductive capacity emerges as a quantity that competes with the subsurface (e.g., deep ocean) temperature in determining surface temperatures. For land, the conductive capacity is small and short wave absorption plays an important role; however, for the ocean the conductive capacity is large and the subsurface (deep ocean) temperature is the dominant influence on the surface temperature for the time scale over which the model is valid. This SDM also includes several of the most important features absent in an EBM, namely, an explicit dependence on the intrinsic physical nature of the earth's surface, the mean poloidal motions in the atmosphere that lead to the climate zonation, and a representation of the hydrologic cycle. When deep ocean temperatures in the model are increased to levels suggested by geologic data for the Cretaceous, surface temperatures at mid to high latitudes become much warmer and the circulation of the atmosphere becomes much subdued, especially as indicated by eddy statistics. These results hold for both present-day and Cretaceous land-ocean distributions, indicating that deep ocean temperature, not geography, is the key model boundary condition. The results also agree with interpretations of geologic data, but disagree in part with earlier interpretations of GCM studies of the Cretaceous. Removal of sea ice (with resultant change from a land-like to an ocean surface) accounts for much of the high latitude warming.

Extending the EBM: the effect of deep ocean temperature on climate with applications to the Cretaceous

Three types of models are frequently applied to problems of present or past climates: (1) the energy balance model (EBM), which can be solved for the mean thermal state of the climate system based only on thermodynamical considerations, (2) the statistical dynamical model (SDM), which includes momentum considerations from which one can solve for climate statistics on a monthly or seasonal time scale including mean poloidal motions and the hydrologic cycle, and (3) the general circulation model (GCM), which can be solved for the evolving daily weather patterns that are then post-processed to yield all the climate statistics in much the same manner as synoptic data are processed. One major drawback of nearly all these models is that they typically do not consider the subsurface vertical heat fluxes (e.g., the effect of deep ocean temperatures and circulation). We present results from an SDM developed in the late 1960's that includes the parameterized effects of subsurface heat fluxes, and then use these results to demonstrate the importance that deep ocean temperatures can have in determining the climatic state. In this SDM, the ratio of the surface short wave absorption to the surface conductive capacity emerges as a quantity that competes with the subsurface (e.g., deep ocean) temperature in determining surface temperatures. For land, the conductive capacity is small and short wave absorption plays an important role; however, for the ocean the conductive capacity is large and the subsurface (deep ocean) temperature is the dominant influence on the surface temperature for the time scale over which the model is valid. This SDM also includes several of the most important features absent in an EBM, namely, an explicit dependence on the intrinsic physical nature of the earth's surface, the mean poloidal motions in the atmosphere that lead to the climate zonation, and a representation of the hydrologic cycle. When deep ocean temperatures in the model are increased to levels suggested by geologic data for the Cretaceous, surface temperatures at mid to high latitudes become much warmer and the circulation of the atmosphere becomes much subdued, especially as indicated by eddy statistics. These results hold for both present-day and Cretaceous land-ocean distributions, indicating that deep ocean temperature, not geography, is the key model boundary condition. The results also agree with interpretations of geologic data, but disagree in part with earlier interpretations of GCM studies of the Cretaceous. Removal of sea ice (with resultant change from a land-like to an ocean surface) accounts for much of the high latitude warming.

Do fossil plants give a climatic signal?

The agreement in the pattern of major biomes with that of climatic zonation of the Earth gives a strong indication that climate is the overriding influence controlling the distribution of plant communities. Three aspects of plants which may be preserved in the fossil state, give a signal of the climatic conditions under which they grew: (1) the present climatic association of their 'nearest living relative'; (2) leaf physiognomy of arborescent plants; (3) the character of their secondary xylem ('wood' of ordinary usage) reflecting, by the presence or absence of growth rings, the seasonality (or lack of it) in their environment and the potential for tree growth that it offered. The significance and limitations of these 'palaeoclimatic signals' as they may be read from the fossil plant record are reviewed and evaluated. The recent demonstration that stomatal frequency of leaves is responsive to changes in ambient carbon dioxide partial pressure offers promise for direct palaeobotanical evidence for past changes in the level of this climatically significant atmospheric constituent.

High-paleolatitude Late Cretaceous paleotemperatures: New data from James Ross Island, Antarctica

Research Article| January 01, 1990 High-paleolatitude Late Cretaceous paleotemperatures: New data from James Ross Island, Antarctica D. Pirrie; D. Pirrie 1British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 OET, England Search for other works by this author on: GSW Google Scholar J. D. Marshall J. D. Marshall 2Department of Earth Sciences, Jane Herdmann Laboratories, University of Liverpool, Brownlow Street, P.O. Box 147, Liverpool L69 3BX, England Search for other works by this author on: GSW Google Scholar Geology (1990) 18 (1): 31–34. https://doi.org/10.1130/0091-7613(1990)018<0031:HPLCPN>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation D. Pirrie, J. D. Marshall; High-paleolatitude Late Cretaceous paleotemperatures: New data from James Ross Island, Antarctica. Geology 1990;; 18 (1): 31–34. doi: https://doi.org/10.1130/0091-7613(1990)018<0031:HPLCPN>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Oxygen-isotope analysis of well-preserved macrofossils from the Santonian-Campanian of James Ross Island and the Maastrichtian of Vega Island, Antarctica, indicates that cool high-paleolatitude temperatures prevailed during the Late Cretaceous and suggests that cooling occurred between the Santonian-Campanian and the Maastrichtian. Although more than 50% of the material showed diagenetic alteration, 52 unaltered aragonite and calcite samples were analyzed. Mean δ18O and calculated paleotemperature values were -0.23‰ and 13.6 °C, respectively, for the Santonian-Campanian, and 0.66‰ and 11.7 °C, respectively, for the Maastrichtian. In conjunction with recent Late Cretaceous paleoclimatic data from high northern paleolatitudes, these data indicate the presence of cool polar regions with broad climatic zonation during the Late Cretaceous. This may have partly controlled faunal distributions. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Distributions and extinctions of Silurian Bryozoa

Abstract Gradient and cluster analyses of bryozoan genera, from a worldwide bryozoan data base has revealed biogeographic patterns for the Silurian. In the Llandovery, three provinces can be distinguished: (1) a north American-Siberian Province; (2) a Baltic Province; and (3) a Mongolian Province, which includes localities on the Siberian and South China plates. During the Wenlock, the North American-Siberian and Baltic Provinces merged into a single province as the Iapetus Ocean continued to close, with the Mongolian Province still present. A single cosmopolitan province developed during the Ludlow, and little biogeographic differentiation can be observed among Ludlow and Pridoli faunas. Formation of the Mongolian Province may be related to latitudinal climatic zonation, as the northern portion of the Siberian plate had moved into temperate latitudes in the Early Silurian. Loss of the north temperate Mongolian Province in the Ludlow, suggests that the Siberian plate may have moved southward in the Late Silurian. Increases in extinctions of bryozoan species and genera coincided with loss of provinciality in the Silurian. Merging of the Baltic and North American-Siberian Provinces in the Wenlock coincided with large increases in extinctions in North America and Baltica. Wenlock extinctions may be related to climatic change caused by continental convergence, or competition between faunas. Loss of the Mongolian Province in the Ludlow also coincided with increases in extinctions, which may be related to southward movement of the Siberian plate into a warmer climatic zone.

Distribution and genesis of red and yellow soils in the central subtropics of southeast China

In the subtropical climatic region of southeast China, which is influenced by the monsoon climate, red soils are widespread. According to the Chinese soil classification system the main soil groups are subdivided on the base of the degree of allitic weathering. This is mainly characterized by the SiO 2:Al 2O 3 molar ratio of the clay fraction (according to the Chinese classification the fraction <1μm). The weathering stage and soil properties are determined by the horizontal and vertical climatic zonation. In basin regions and lower altitudes of the mountains up to about 600 m above sea level Red Earths (central subtropics) and Lateritic Red Earths (south subtropics) are developed on silicate rocks. In higher altitudes these soils change to Yellow Earths with goethitic B-horizons. In order to obtain information of the main soil forming processes of typical and widely distributed soils in the central subtropical region, a Red Earth from Middle Pleistocene red sediments of a basin region (Quaternary Red Clay) and two profiles of a Red Earth - Yellow Earth toposequence from granite of the neighbouring mountainous region were investigated by morphological, mineralogical and pedochemical methods. During the youngest phase of morphodynamic stability the recent soils developed on pre-weathered parent materials (basin sediments and saprolite) containing kaolinite and gibbsite formed in ancient weathering periods. In the course of soil formation weathering proceeded with the transformation of halloysite to kaolinite and mica minrals through the stages illite and vermiculite to Al-chlorite. Pedochemical characteristics are dominated by an almost complete leaching of bases and a high Al-saturation of the sorption complex. The type and intensity of soil characteristics show a marked relation to the altitude of the sites, depending on differences in humidity and intensity of leaching processes. With increasing altitude the accumulation of organic substances and the neoformation of goethite and Al-chlorite increase, while with decreasing altitude the neoformation of hematite and intensity of lessivation increases. Bt horizons, which occur only in the Red Earths show that lessivation was an important process during soil genesis, although these soils developed from pre-weathered, acid parent materials. In Yellow Earths from different parent materials no indications to clay migration were found. According to the FAO legend the Red Earths in the area investigated belong to the soil unit of Ferric Acrisols and the Yellow Earths to the soil unit of Dystric Cambisols. It appears that the soil colour and the SiO 2:Al 2O 3 molar ratio of the clay fraction used as criteria for soil systematics cannot sufficiently indicate the degree of weathering, soil genesis and site properties.

Hargreaves’ climatic classification and crop zonation in Burkina Faso

Lack of moisture in the arid and semi-arid regions of Africa is the most fundamental factor limiting crop production. Knowledge of moisture conditions will therefore go a long way to boost crop production. It is against this background that the Hargreaves monthly moisture availability index classification has been employed to identify the various moisture zones and crop zonation in Burkina Faso (formerly Upper Volta). Due to a stimulus of financial incentives, some crops are being expanded beyond their moisture availability limits.

Cenozoic evolution of continental humidity and paleoenvironment, deduced from the kaolinite content of oceanic sediments

The distribution of detrital kaolinite in Cenozoic sediments of the Atlantic and West Pacific oceans has been used to reconstruct the variations of the continental humidity and associated paleoenvironmental factors. Five stages have been recognized. 1. (1) During the Late Oligocene (Chattian, c. 30 m.y., P21 and NP24), increased kaolinite content at every site marked an increase of global humidity. 2. (2) During the Early Miocene (Aquitanian, c. 20 m.y., N5–N6 and NN2–NN3), increasing continental aridity is deduced from low kaolinite contents in the Atlantic Ocean and Philippine Sea. 3. (3) During the Middle Miocene (Langhian, c. 14 m.y., N10–N12 and NN5–NN6), increased kaolinite contents at most of the sites marked a further increase of global humidity, which was especially important at low latitudes in Africa. 4. (4) During the Late Miocene (Tortonian, c. 10 m.y., N16 and NN10–NN11), kaolinite content and inferred continental humidity increased toward high latitudes but decreased toward low latitudes, especially off tropical Africa where it marked the development of arid conditions. 5. (5) During the Late Pliocene (Piacenzian, c. 3 m.y., NN15–NN16), kaolinite content and humidity increased again toward high latitudes while these conditions decreased again toward low latitudes, emphasizing the latitudinal climatic zonation. Periods of increasing humidity show good correlation with the development of polar ice. Locally, volcanism, tectonic activity, oceanic circulation and migration of lithospheric obliterated the climatic significance of clay mineral associations, which therefore express complementary aspects of the continental and marine paleoenvironments.

Late Mesozoic bipolar bivalve faunas

AbstractBipolar bivalve genera probably existed through the greater part of late Mesozoic (i.e. late Jurassic–late Cretaceous) time. Of the various theories put forward to account for their presence, those based on some form of global climatic zonation seem most appropriate. Although equatorial–polar temperature gradients were substantially less in late Mesozoic time than at the present day, high latitude regions were subjected to temperate (or even cool-temperate) climatic regimes. Macrobenthonic marine faunas may have been more susceptible to differentiation in response to these climatic patterns than nektonic ones. This is particularly so in the late Mesozoic strata of the Southern Hemisphere.

CRITICAL AUTUMN HARVEST PERIOD FOR ALFALFA IN THE ATLANTIC REGION BASED ON GROWING DEGREE-DAYS

Air temperature normals (1951–1980 period) were analyzed for over 200 locations in the Atlantic region to estimate spatial and temporal variations in the critical autumn period during which alfalfa (Medicago sativa L.) should not be harvested to allow plants to reach adequate winter hardiness by accumulating sufficient food reserves in the roots. Data are presented which show that the starting date of the critical harvest period could be estimated from the average date when 450 growing degree-days above 5 °C remain in autumn (F450). F450 compared well with starting dates determined experimentally in 3 yr of field tests at three locations in Ontario. F450 varied from before 10 Aug. in northwestern New Brunswick and parts of Newfoundland to after 4 Sept. in southwestern Nova Scotia. Annual differences in climate cause F450 to vary with a standard deviation of about 5–6 days at a given location. A zonation map describing spatial variation in the rest period was prepared as a general guide for cutting management.Key words: Alfalfa, Medicago sativa L., cutting management, winter survival, climate zonation