Cuidados de la madre durante el puerperio

3.1. LABORATORY TECHNIQUES

A total of 364 samples from DSDP Sites 249, 256, 257, 258, 259, 260, 263 and ODP Sites 762, 763, 765 and 766 were examined. The number of samples from each site is shown below in Table 3.1.

Table 3.1. Summary of core sections studied from Indian Ocean DSDP and ODP sites.

Leg

Site

Core sections

No of samples

25 249 31R-4 to 25R-2 15 26 256 9R-1 to 8R-1 7 26 257 lOR-1 to 7R-1 12 26 258 25R-4 to 14R-1 27 27 259 33R-1 to llR-3 64 27 260 18R-1 to 6R-4 24 27 263 29R-4 to 4R-4 66 122 762C 91X-CC to 76X-4 17 122 763C 763B 46R-5 to 35R-6 54X-CC to 27X-3 40 123 765 49R-3 to 26R-CC 20 123 766 49R-4 to 16R-1 72

Sediment samples (approximately 20cc) were processed by repeated drying and washing in 1% Calgon solution. The washed residues were randomly divided into fractions with the help of a sample splitter; the fractions were then sieved (>250|im, >125|Lim and >63)Lim) and each picked for microfossils. When fossil abundance allowed, a minimum of 300 foraminifera was picked per sample as well as other microfossils (mainly ostracods, bivalve fragments, fish teeth and radiolarians). The

picked specimens were then sorted on cardboard slides for identification. These are housed in the Micropalaeontology collections of University College London.

3.2. TAXONOMIC INVESTIGATION

Taxonomic comparisons were made with type material and foraminiferal collections housed at the Senckenberg Museum in Frankfurt (Bartenstein and Brand, 1951; Bartenstein and Kaever, 1973), at the Institute for Palaeontology and Historical Geology in Munich (Weidich, 1990), at the Australian Geological Survey Organisation in Canberra (Crespin, 1953; 1963), at the South Australian Department of Mines in Adelaide (Ludbrook, 1966), at the Geological Survey of New South Wales in Sydney (Scheibnerova 1974; 1976; 1978^), at the University of Western Australia in Perth (Haig, 1992; Haig and Lynch, 1993; McLoughlin et a l, in press), at the University of Queensland in Brisbane (Playford, Haig and Dettmann, 1975; Haig and Barnbaum, 1978; Haig, 1980; 1981; 1982), at the Centre de Recherches Micropaléontologiques "Jean Cuvillier" in Nice (Moullade, 1960; 1966; Guerin, 1981) and with Lower Cretaceous foraminiferal collections from continental Europe and from Atlantic and Pacific DSDP and ODP sites, which are held at Tübingen University, Nice University and University College London. Scanning Electron micrographs were made on a Zeiss-DSM-940 SEM at the Micropalaeontology Unit of University College London.

3.3. PALAEOENVIRONMENTAL ANALYSIS

Benthic foraminiferal distribution patterns were investigated using the following parameters: species frequency, Shannon-Weaver information function, relative abundance of calcareous tests, agglutinated tests with calcareous cement and agglutinated tests with organic cement, distribution of rotaliids, lagenids and of main relevant morphogroups and relative proportion of infaunal to epifaunal/shallow infaunal foraminifera. Additional information was obtained from lithological logs, CaCOg and TOC content, associated microfossils and from published seismic and geochemical data. Backtracking calculations were applied to compute palaeodepths of sites drilled on oceanic crust. Principal Component Analysis was used to determine benthic foraminiferal biofacies trends in the Indian Ocean during the Early Cretaceous.

3.3.1. Backtracking

The initial ridge-crest depths and successive palaeoseafloor depths of sites situated on oceanic crust are determined using the empirical age/depth equation for the 70Ma to 160Ma interval (Equation 1) proposed by Parsons and Sclater (1977) and modified by Sclater et a l (1985) to allow correction for sediment accumulation (Equation 2).

d(t) = 6400-3200e(-t/62.8) m (i)

where d(t) is the depth of the seafloor in metres at time t.

dw i = dw2 + X + p m ) m (2) fpw - p m )

where /7W, p m , p s are respectively, the water, mantle and sediment densities and dw i, d w2 and x are respectively the unsedimented water depth, the sedimented water depth and sediment thickness.

3.3.2. Shannon-Weaver information function

The Shannon-Weaver information function H(S), proposed by Shannon and Weaver (1949) is a measure of heterogeneity, which is frequently used as an index of diversity. It is defined by Equation 3:

H (S ) = -Z Pilnpi (3)

i=l

where S is the number of species and pi the proportion of the ith species (p = per cent divided by 100).

3.3.3. Morphogroup analysis

From analyses of the test shape, the mode of coiling and the presence or absence of surface pores, it has been possible to classify foraminifera into morphogroups with different life positions and feeding strategies within the sediments, reflecting microhabitat preferences related to O2 and TOC contents (Severin, 1983; Corliss, 1985; Jones and Charnock, 1985; Bernhard, 1986; Corliss and Chen, 1988; Corliss and Fois, 1990; Rey et al, 1993 and Nagy et al, 1995). Infaunal morphotypes appear more tolerant of dysaerobic conditions than epifaunal ones (Kaiho, 1994; Kaminski et a l, 1995). They dominate in shallower environments, where sedimentation rates are high, whereas epifaunal taxa are more numerous in the deep sea, where sedimentation rates are low.

Recent studies have indicated that food and oxygen are the most influential factors regulating the distribution of benthic foraminifera (Jorissen, 1987, Jorissen et a l, 1992; Sjoersdma and Van der Zwaan, 1992), and it has been suggested by Tyson and Pearson (1991), Barmawidjaja et al (1992) and Jorissen et al (1992) that the depth of the redox potential discontinuity (RPD) affects the microhabitat preferences of benthic foraminifera. Linke and Lutze (1993) considered that the vertical distribution of foraminiferal morphotypes did not represent a static stratification of microhabitats within the sediments, but that it was a dynamic process, reflecting the need to optimize food acquisition. In dysaerobic environments, however, the primary control on foraminiferal distribution and the relative proportion of morphotypes is most probably oxygen availability.

For the purpose of interpreting palaeoenvironments of the Indian Ocean DSDP and ODP sites, benthic foraminifera have been combined into six agglutinated and six calcareous morphogroups, which are described below.

Agglutinated morphogroups

• T u b es comprise all tubular genera such as Rhabdammlna, Rhizammina,

Hippocrepina, Nothia and Bathysiphon, inferred to be semi-epifaunal suspension

feeders.

• Ammodiscids represent epifaunal and shallow infaunal detritus feeders mainly belonging to the genera Ammodiscus and Glomospira.

• Planispiral/streptospiral involute morphotypes consist of planispirally and streptospirally coiled forms such as Haplophragmoides, Recurvoides,

Cribrostomoides, Thalmannammina and Paratrochamminoides, which are either

epifaunal or shallow infaunal dwellers.

• Planispiral/streptospiral evolute morphotypes (Ammobaculites/Bulbobaculites)

are characterised by an initial planispiral or streptospiral coil, show a tendency to become evolute and generally share an infaunal mode of life.

• Elongate tapered forms such as Reophax, Verneuilinoides, Aaptotoichus,

Textulariopsis and Vemeuilinulla are regarded as infaunal detritivores.

• Globular forms such as Saccammina and Psammosphaera and Trochospiral

forms such as Trochammina, which are less well represented in Indian Ocean assemblages, are considered to be epifaunal or shallow infaunal dwellers.

Calcareous morphogroups

• Globular forms include Globulina, Ramulina and O olina, which are

characteristically living on or near the sediment surface.

• Planispiral involute morphotypes with a planispiral and involute mode of coiling,

such as Lenticulina, are considered to be epifaunal or shallow infaunal.

• Planispiral evolute forms, which have a tendency to become uncoiled and

elongate, such as Vaginulinopsis, Marginulinopsis, Astacolus and Saracenaria,

appear to be adapted to an infaunal mode of life.

• Trochospiral morphotypes can be divided into biconvex, plano-convex and

rounded subgroups, including Gavelinella, Berthelina, Gyroidina, Charltonina,

Scheibnerova and Quadrimorphina, which are all presumed to be epifaunal or

shallow infaunal dwellers.

• Elongate tapered forms comprise taxa with a variety of coiling modes such as

Laevidentalina, Pyramidulina, Psilocitharella, Coryphostoma and Pleurostomella,

which all share an infaunal mode of life.

3.3.4. Principal Component Analysis

Principal Component Analysis has been applied to the benthic foraminiferal data from selected DSDP and ODP sites, in order to determine main biofacies patterns in the Indian Ocean during the Early Cretaceous. The programme SPSS was used on mainframe computers at University College London. This method is discussed further in Chapter 5.