AGGLUTINATED FORAMINIFERAL BIOSTRATIGRAPHY

Main Faunal Features

Agglutinated foraminifers occur in varying amounts in all the analyzed samples from 162-986D-28R-1, 30-36 cm (647.72 mbsf), through 60R-1, 29-36 cm (955.32 mbsf), as shown in Figure 5. Within this interval, four agglutinated foraminiferal assemblages (AFA) are distinguished. The preservation of the assemblages varies from dominantly porous noncompressed through mixed to dominantly silicified compressed. These preservational types occur in repeated units of changing thicknesses throughout the analyzed succession. Based on this distribution pattern, 14 preservational units (PU) are distinguished (Fig. 7).

The porous noncompressed faunal component is composed of specimens showing the original shape of the chambers (which usually are empty) and the slightly porous texture of unaltered agglutinated tests. In the silicified compressed component, the tests are flattened to disappearance of the chamber cavities. Owing to diagenetic silicification, the silt grains forming the walls are no longer discernible.

Agglutinated Assemblages

AFA1, Cyclammina pusilla assemblage

This fauna describes the lowermost part of the cored section from Sample 162-986D-60R-1, 29-36 (955.32 mbsf), through 55R-1, 24-31 cm (907.22 mbsf). It is dominated by Cyclammina pusilla, Recurvoides turbinatus, Rhizammina sp., and Thurammina papillata. Characteristic species include Rhizammina algaeformis, Verneuilinoides scitulus, Ammomarginulina foliacea, Karreriella apicularis, and Reophax mortenseni. Owing to the poor state of preservation, a large number of specimens could not be identified at the generic level and are designated as Textulariina genus indeterminate on the range chart (Fig. 5). Based on its composition and preservational features, the assemblage is interpreted to represent a bathyal in situ fauna. It is identical to the porous noncompressed interval PU1 (Fig. 7).

AFA2, Trochammina cf. nana assemblage

This assemblage comprises three intervals characterized by silicified compressed taxa or mixed faunas. It is subdivided into a lower, middle, and thick upper segment by two intervening porous noncompressed assemblages (Fig. 5). Trochammina cf. nana is dominant through each of the three segments. The undifferentiated group, Textulariina genus indeterminate, is also quantitatively important. The assemblage is interpreted to consist mainly of redeposited specimens.

The lower T. cf. nana assemblage extends from Sample 162-986D-54R-1, 29-36 cm (897.62 mbsf), through 49R-1, 29-36 cm (849.52 mbsf). Characteristic species include Ammodiscus incertus, Rhizammina sp., and Thurammina aff. albicans in addition to more sporadic occurrences of Glomospirella sp., Haplophragmoides cf. bradyi, and Verneuilinoides sp. This assemblage segment corresponds to the silicified compressed interval PU2.

The middle segment characterized by this assemblage extends from Sample 162-986D-46R-4, 29-36 cm (825.12 mbsf), to 44R-1, 29-36 cm (801.42 mbsf). Besides the dominant forms, significant taxa include A. incertus, Rhizammina sp. T. aff. albicans, Haplopragmoides sp., and Verneuilinoides sp. This segment contains the silicified compressed intervals PU4 and PU6 as well as the mixed interval PU5.

The upper part of the T. cf. nana assemblage extends from Sample 162-986D-43R-2, 29-36 cm (793.22 mbsf), through 28R-1, 30-36 cm (647.72 mbsf). Thus, it makes up almost half of the upper Pliocene part of the cored section. Characteristic, but quantitatively subordinate, species include Eggerelloides cf. scaber, A. incertus, Rhizammina sp., and T. cf. albicans. Many taxa, such as Glomospira gordialis, Repmanina charoides, C. pusilla, and Haplophragmoides sp., occur in low numbers restricted to scattered samples. Within this segment, seven preservational units are distinguished. Four of these are of the silicified compressed type (PU8, PU10, PU12, and PU14), whereas three are of mixed nature (PU9, PU11, and PU13).

AFA3, Recurvoides turbinatus assemblage

This assemblage is developed from Sample 162-986D-48R-2, 29-36 cm (841.32 mbsf), through 47R-1, 29-36 cm (830.22 mbsf). In addition to the nominate species, the unit is dominated by R. algaeformis and C. pusilla. Textulariina genus indet. is quantitatively important, whereas the frequency of C. cf. nana is strongly reduced. Characteristic species are Cyclammina trullissata, Paratrochammina cf. challengeri, Haplophragmoides bradyi, Bathysiphon hirudinea, and Reophax bilocularis. The assemblage is a porous noncompressed type, corresponding to the interval PU3.

AFA4, Ammodiscus tenuis assemblage

This is recognized only in Sample 162-986D-43R-3, 29-36 cm (794.72 mbsf), strongly dominated by C. pusilla and characterized by A. tenuis and R. algaeformis. The fauna is of porous noncompressed preservation designated as PU7.

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