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| Titel |
Multiple embryos in the Lepidocyclina pustulosa group as possible indicators of palaeoenvironmental conditions: The case of the Late Eocene Toluviejo Formation (Sinú Domain, Caribbean, Colombia |
| VerfasserIn |
Claudia Baumgartner-Mora, Peter O. Baumgartner, Daniel Rincón Martínez, Edward A. Salazar Ortiz |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250130205
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| Publikation (Nr.) |
 EGU/EGU2016-10426.pdf |
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| Zusammenfassung |
| The Middle-Late Eocene Toluviejo Formation of the Sinú-San Jacinto folded belt (Caribbean,
Colombia) contains 15-75 m thick, grey, massive limestone sequences that are interbedded
with terrigenous nearshore to offshore mudstones to quartzose sandstones and conglomerates.
The formation accumulated in a transitional continent-ocean setting, probably on
oceanic crust. We studied over 80 polished thin sections under light microscopy and
cathodoluminescence (CL) to analyse carbonate microfacies and Larger Benthic Foraminifera
(LBF). The overall facies distribution is 3-fold: (1) Facies close to the shoreline are
dominated by low diversity operculinid assemblages, rich in detrital elements. (2) Shallow
offshore facies are characterized by round lepidocyclinids, associated with, and often
encrusted by, corallinacean algae, Sporolithon and structureless microbial crusts. The matrix
is rich in carbonate/detrital mud and sand-sized detritals. (3) Distal offshore facies on
structural highs show abundance of flat, current-sorted lepidoclinids without a noticeable
detrital component. Facies 1 and 2 are clearly under the influence of suspension-
and dissolved-nutrient input, probably carried offshore by freshwater lids of river
plumes.
Facies (2) contains abundant specimens of the Lepidocyclina pustulosa group of which the
macrospheric forms show complicated embryonic apparatuses, which suppose double or
multiple embryos. Detailed observation under CL allows to count up to 6-8 embryos,
often seen aligned in the equatorial plane. The embryonic apparatus occupies often
more than half of the diameter of specimens. The tendency towards large, very
flat embryonic apparatuses (diameter measured in axial cuts up to 2,5 mm for a
thickness of 0.2-0.3 mm) is closely correlated with abundant coralgal and microbial
encrustations, oxide-stained carbonate/detrital mud and probably some preserved organic
matter.
The presence of multiple embryos has been reported by several authors and has also been
used as a morphological criterion to establish new taxa (e.g. Pliolepidina tobleri).A recent
paper has demonstrated multiple embryos of the Recent Spiroclypeus carpenteri by means of
microCT, and has discussed the possible causes of formation of tests with more than one
proloculus: During asexual reproduction a large number of individuals are released from the
mother’s test into the environment. If the daughter cells do not manage to get sufficiently
separated from each other, they may start to build several deuteroloculi around each other.
Low water energy in the habitat of Spiroclypeus has been suspected by these authors to
prevent the complete dispersion of juvenile forms and thus favouring the growth of forms
with multiple embryos.
The abundance of mud and of fragile algal and microbial mats in our facies (2) advocates for
a low bottom water hydrodynamic regime for the samples in which practically all
macrospheric forms observable in thin sections have multiple proloculi. Environmental
factors other than water energy could also play a role: Many authors have reported
teratological growth of benthic Foraminifera in hypersaline environments, or waters polluted
by heavy metals. In our case, salinity could have been below normal marine values and both
suspended and dissolved organic matter from tropical rivers could have “polluted” the
habitat of Lepidocyclina by excess nutrients and heavy metals leached from basaltic
rocks abundantly present in the Eocene drainage basin. Contemporaneous, distal
offshore, flat Lepidocyclina accumulations totally lack multiple embryos. These
facies also lack a detrital component and show current sorting/orientation of tests. |
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