Bilal U. Haq

Early Cenozoic calcareous nannoplankton biogeography of the Atlantic Ocean

Biogeographic patterns of Early Cenozoic calcareous nannoplankton assemblages are delineated for the North and South Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. Nannoplankton assemblages are defined byQ-mode Varimax Factor and Oblique Factor Analyses of census data on 44 taxa from 113 deep-sea and land-based samples. Examination of their latitudinal distribution through time allows recognition of those assemblages which can be used as environmental indicators. Comparison of the distributions of contemporaneous nannoplankton assemblages with the distribution of the appropriate environmental indicator assemblage permits their classification as either low-, mid-, or high-latitude nannoflora. Early Paleocene is characterized by a high-latitude Thoracosphaerid-Markalius astroporus Assemblage and a mid- to low-latitude Braarudosphaerid Assemblage. Eight Middle Paleocene-Early Eocene nannoplankton assemblages are identified and grouped according to their relative environmental distribution: (1) Low-latitude nannoflora: theToweius craticulus-Coccolithus pelagicus Assemblage, the Discoaster-Cyclococcolithus formosus Assemblage, theToweius craticulus-Ericsonia subpertusa-Discoaster Assemblage, and the Fasciculith-Discoaster Assemblage. (2) Mid-latitude nannoflora: theEricsonia subpertusa Assemblage and theCoccolithus pelagicus Assemblage. (3) High-latitude nannoflora: thePrinsius martinii Assemblage and theP. bisulcus Assemblage. These groupings are indicated by comparison of the distribution of our Paleocene-Early Eocene environmental indicator, the high-latitudePrinsius martinii Assemblage, with the distributions of contemporaneous assemblages. Seven Eocene nannoplankton assemblages are identified: (1) Low-latitude nannoflora: the Reticulofenestrid Assemblage and theCyclococcolithus formosus-Sphenolith Assemblage. (2) Mid-latitude nannoflora: the Discoaster Assemblage, theReticulofenestra umbilica-R. bisecta-Coccolithus pelagicus Assemblage, and theCribrocentrum reticulatum Assemblage. (3) High-latitude nannoflora: theToweius craticulus-Coccolithus pelagicus Assemblage, and theC. pelagicus-Cyclococcolithus formosus-C. aff.gammation Assemblage. Our Eocene environmental indicator is the low-latitude Reticulofenestrid Assemblage. Five Oligocene nannoplankton assemblages are identified: (1) Low-latitude nannoflora: the Sphenolith-Discoaster Assemblage. (2) Mid-latitude nannoflora: theCyclococcolithus neogammation Assemblage and theDictyococcites hesslandii Assemblage. (3) High-latitude nannoflora: the Reticulofenestrid-R. bisecta Assemblage and theCoccolithus pelagicus Assemblages. Our Oligocene environmental indicator is the low-latitude Sphenolith-Discoaster Assemblage. If it is assumed (1) that the latitudinal differentiation of calcareous nannoplankton assemblages we observe in the Early Cenozoic is related to a latitudinal temperature gradient, and (2) that the ecological preferences of these assemblages remain stable through time, then the latitudinal nannofloral migrations we recognize delineate paleotemperature changes: The maximum equatorward migration (cooling) of high- and mid-latitude nannofloras in the Paleocene occurs at about 58 m.y. B.P. This is followed by their poleward migration, the disappearance of the high-latitude nannoflora, and the appearance of a new low-latitude nannoflora. A major poleward migration (warming) occurs at about 49 m.y. B.P. The Middle Eocene is characterized by the return of high-latitude nannofloras into mid-latitudes, with the maximum equatorward migration (cooling) occurring at 48-43 m.y. B.P. Low-latitude nannoflora again gradually invade high latitudes through the Late Eocene, indicating a second major Eocene warming by at least 38 m.y. B.P. There is a well-defined migration of high-latitude nannoflora into the mid-latitudes during the Middle Oligocene, with the maximum indicated cooling between 32 and 27 m.y. B.P.; an earlier, though minor, Oligocene cooling may have occurred at about 36 m.y. B.P. During the Late Oligocene, low-latitude nannoflora migrate into high latitudes, indicating a warming by 26 m.y. B.P. These inferred paleotemperature changes are similar to those delineated by some workers on the basis of terrestrial flora. Nannoflora characterized by the cool-water coccolithCoccolithus pelagicus predominate at the equator throughout most of the Paleocene, are confined mostly to high latitudes in the Eocene, and generally remain above mid-latitudes during the Oligocene. Although this migration could indicate that the Paleocene was the coolest epoch in the Early Cenozoic, and the Oligocene the warmest, we suggest instead that this shift ofC. pelagicus to higher latitudes is a result of evolution in its ecology. The implications of paleobiogeography to high-latitude biostratigraphy are discussed and theacme horizon as a time-stratigraphic concept is informally introduced. The following new taxa are described:Fasciculithus rotundus, Neochiastozygus imbriei andThoracosphaera atlantica. The following taxa are recombined:Cyclococcolithus protoannulus, Cyclolithella bramlettei Dictyococcites hesslandii, andNannotetrina alata.

Introduction to marine micropaleontology

Marine micropaleontology: an introduction (W.A. Berggren). Calcareous Microfossils. Foraminifera (A. Boersma). Calcareous nannoplankton (B.U. Haq). Ostracodes (V. Pokomy). Pteropods (Y. Herman). Calpionellids (J. Remane). Calcareous algae (J.L. Wray). Bryozoa (K. Brood). Siliceous Microfossils. Radiolaria (S.A. Kling). Marine diatoms (L.H. Burckle). Silicoflagellates and ebridians (B.U. Haq). Phosphatic Microfossils. Conodonts and other phosphatic microfossils (K.J. Muller). Organic-Walled Microfossils. Dinoflagellates, acritarchs and tasmanitids (G.L. Williams). Spores and pollen in the marine realm (L. Heusser). Chitinozoa (A. Jansonius, W.A.M. Jenkins).

Biogeographic history of Miocene calcareous nannoplankton and paleoceanography of the Atlantic Ocean

Biogeographic patterns of Miocene calcareous nannoplankton in the North and South Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico are apparent from a Q-mode factor analysis of census data from 49 DSDP sites. In a total of 444 relatively well-preserved Miocene samples, 5 major and 1 minor (but relatively important) assemblages were recognized, most of which show distinct spatial and temporal distribution patterns. The major assemblages (identified by the dominant taxa) are the Dictyococcites minutus, Cyclicargolithus floridanus, Coccolithus pelagicus, Reticulofenestra pseudoumbilica-R. haqii, and Discoaster-Sphenolithus assemblages. Four of the major assemblages show distinct shifts through latitudes that are interpreted as a response to changing climate. Four warming and cooling cycles of 4 to 4.5 m.y. duration are identified in the Miocene. Both the paleobiogeographic and available isotopic data show the warming episode between 17 and 15.5 Ma and the cooling trend that followed, as well as the warming episode between 9 and 7 Ma, to have been particularly extreme in both Hemispheres, and probably of global extent. The sharp cooling centered at 1 5 Ma and the biogeographic changes at this time suggest this event to have been associated with the development of an extensive ice-cap on Antarctica. Biogeographic history of Miocene calcareous nannoplankton and paleoceanography of the Atlantic Ocean

Assessment of quantitative techniques in paleobiogeography

Abstract A series of multivariate methods has been compared to assess their effectiveness in extracting essential information out of a complex micropaleontological data-set. The data-set used for this experiment consists of relative frequencies (percentages) of Miocene coccolith taxa or groups of taxa in cores of the Deep Sea Drilling Project (DSDP) from the Atlantic Ocean. All methods tested are varieties of principal components analysis in R - and Q -mode, and “true” factor analysis. Various secondary rotational procedures ancillary to some of these methods are also tested. A test, denoted Δ-Test, is developed, which assesses how well principal components or factors reproduce the data-set. Δ-Test may be used for determining the optimum number of principal components or factors, the most relevant rotational procedure, and thus the most suitable analytical technique. The Δ-Test does not rely on mathematical testing, but on simple inspection of the compositions of the principal components or factors, and their relations to correlations existing in the data-set. Our experiment reveals that the most efficient methods are the maximum-likelihood factor analysis and the R -mode principal components analysis, within which the varimax (orthogonal) rotations best reproduce correlations. Of these methods, maximum-likelihood factor analysis is considered the optimum method, because of the greater simplicity of compositions. In addition to these methods, Kaisers second generation “Little Jiffy” factor analysis was also found to be efficient. Three methods provide less sensitive reduction of the data: the “true” R -mode principal components analysis (without secondary rotations), the Q -mode principal components analysis, and the correspondence analysis.

Transgressions, climatic change and the diversity of calcareous nannoplankton

Abstract Plankton-diversity models of various authors are examined in the light of available diversity data on calcareous nannoplankton. To account for the diversity peaks during times of widespread epicontinental seas in the Mesozoic and Tertiary, a new explanation is given.

The El Cuervo section (Andalusia, Spain): Micropaleontologic anatomy of an early Late Miocene lower bathyal deposit

Abstract An examination of its calcareous and siliceous microfauna and microflora indicates that the El Cuervo section (Andalusia, Spain) is a lower bathyal deposit (formed between 1000 and 1500 m in a zone of near-coastal upwelling) of early Late Miocene age, penecontemporaneous with the lower part of the stratotype Andalusian Stage and equivalent to, at least, a part of Magnetic Epochs 10 and/or 11. The bottom depths where the benthonic fauna (foraminifera and ostracodes) lived at the time of deposition were well beneath the boundary between the upper warm mixing zone (thermosphere) of the Atlantic and Tethys and the lower permanently cold layers (psychrosphere) originating only in the Atlantic. Mixing of the deep faunas of Tethys and the Atlantic is indicated. The El Cuervo fauna is part of an important sequence of sections in which the benthonic fauna indicates a deep passage (Iberian Portal) from the Atlantic into Tethys in southern Spain. The significance of this section on the Late Miocene closure of the Iberian Portal is discussed.