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Algal and invertebrate microfossil assemblages from lake sediments in the reconstruction of past community dynamics - preliminary information

Antipushina Z, Szeroczyńska K, Zawisza E.

Studia Quaternaria

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2012

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Vol. 29

53--58

EN

This paper focuses on the usefulness of a palaeolimnological method called the joint algological and zoological analysis. The joint algo-zoological analysis involves counting all identifiable remains of the main algae groups (Bacillario- phyta, Cyanophyta, Desmidiales, other Chlorophyta, Trachelomonas sp.) and invertebrate groups (Cladocera, Ostra- coda, Chironomidae, Chaoborus sp., and other insects, Turbellaria, Bryozoa, Spongia and Testacida) in volumetric samples. We present results from recent sediments of Lake Glubokoe (Moscow region, Russia) as an example of the application of this method. We reconstruct the structure of phytoplankton, zooplankton and zoobenthos communities and their dynamics over the last 25 years. Our results support the validity of this method in the reconstruction of the structure of phyto- and zooplankton communities and their dynamics, information that may be lost when carrying out separate analyses for individual groups. Simplicity is another advantage of this methodology.

2

The facies and biota of the oldest exposed strata of the Eocene La Meseta Formation (Seymour Island, Antarctica)

Tatur A. E., Krajewski K. P., lvalle de R. A.

Geological Quarterly

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2011

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Vol. 55, No. 4

345-360

EN

La Meseta Formation is made up of estuarine and shallow marine, fossiliferous clastic deposits 720 m thick that provides a unique record of marine and terrestrial biota of Antarctic ecosystems preceding continental glaciation in the Oligocene. The lower limit of this formation has been poorly known, and therefore it has been carefully investigated. The lowest part of the La Meseta Formation, at the southern bank of a palaeodelta, is represented by relics of a prograding sequence of sediments deposited in the wave-dominated part of a deltaic system in the offshore and lower and upper shoreface environments. The sequence is completed landwards by younger tidal plain sediments deposited at 40 m lower altitude in a relatively protected, central estuarine basin, which was dominated by tidal activity and influenced by periodic fluvial inflow. These strata were deposited during a late Paleocene or Ypresian/Lutetian lowstand of sea level, which might reflect a glaciation event or glacioisostatic rebound of land following deglaciation of hypothetic Antarctic inland glaciers. Forced regression of sea level and seaward expansion of a deltaic freshwater environment, led to local extinction of a unique assemblage of marine echinoderms, bryozoans, corals and brachiopods. These marine fossils, representing a thanatocoenosis, are perfectly preserved due to syngenetic goethite permineralisation. This process owed its origin to excess reactive iron coming from sulphide-rich bedrock through weathering processes and acid sulphate drainage of the neighbouring land area.

3

Zespół skamieniałości a biocenoza - reprezentatywność zapisu paleontologicznego

Niedźwiedzki R.

Przegląd Geologiczny

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2002

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Vol. 50, nr 10/1

899-904

PL

Podczas przeobrażania się biocenozy w oryktocenozę największe znaczenie mają czynniki oddziaływujące na nekrocenozę, zwłaszcza rozkład organizmów bezszkieletowych, w rezultacie którego w tafocenozie nie zachowuje się przeciętnie od ok. 70% gatunków (w środowiskach morskich) do ponad 90% gatunków (w środowiskach lądowych) występujących w biocenozie. Wśród zwierząt szkieletowych podstawowymi czynnikami działającymi na etapie nekrocenozy jest dysartykulacja i fizyczne, chemiczne lub biologiczne niszczenie szkieletów. Procesy te działają często selektywnie w zależności od przynależności taksonomicznej, a także od wielkości okazów i niekiedy uniemożliwiają odtworzenie liczebności taksonów. Bardzo istotne jest uśrednianie czasowe, które zachodzi zarówno w obrębie nekrocenozy, jak i tafocenozy. Zjawisko to powoduje nadreprezentację wielu taksonów oraz niemożność obserwowania krótkoterminowych zmian biocenozy. Po utworzeniu się tafocenozy zachodzą dalsze zmiany zespołu skamieniałości, m.in. w wyniku rozpuszczania szkieletów aragonitowych oraz pokryw chitynowych. Dlatego w artykule używam terminu "oryktocenoza" dla zespołów skamieniałości zachowanych do czasów współczesnych.

EN

Most important for post-mortem modification of biocoenosis structure are processes which influenced the necrocoenosis, especially nonpreservation of soft-bodied organisms. This factor alone may eliminate from about 70% species in marine environments to more than 90% species in terrestrial environments. Shelly communities are changed post-mortem mainly by disarticulation and by physical, chemical or biological destruction. These factors are strongly selective and their importance depend on taxonomic position and size of specimens. Such processes can seriously hamper the recognition of abundance of specimens and proportions of taxa. Time-averaging is very important for modification both the necrocoenosis and the taphocoenosis. The consequences of this phenomenon are preservational bias favouring some taxa of the taphocoenosis and the fact, that short-term biologic phenomena are extremely rarely observed in the fossil assemblages. Many kind of taphocoenosis modifications are documented, e.g., dissolution of aragonite shells or chitinous integuments. Therefore, I use the term " orictocoenosis "for assemblages of fossil remains preserved to our times.