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The Anisian carbonate ramp system of Central Europe (Peri-Tethys Basin): sequences and reservoir characteristics

100%

Gotz A. , Lenhardt N.

tom Vol. 61, no. 1

59-70

During Middle Triassic times, the Peri-Tethys Basin bordered the north-western Tethys shelf and was connected to the open Tethys Ocean via three seaways. Today, Lower Muschelkalk carbonates of this epeiric sea cover large parts of Central Europe, documenting the evolution of a low-relief, homoclinal, mud-dominated ramp system during the Anisian. In view of their geotectonic/climatic setting, depositional processes, facies architecture, and distribution, the rocks are considered as an outcrop analogue for layer-cake reservoirs of world-wide importance, e.g. the Permo-Triassic Khuff or Jurassic Arab carbonates in the Middle East. In general, two different reservoir types and their interplay might be considered: The proximal stacks of muddy dolostones (NW part of the basin) and the more distally developed grainy limestones (central and SE part of the basin). The rather uncommon depositional setting with minor relief and minimal accommodation contributed to both, the stratal and lateral facies development, and to unusual and possibly even "inverted" facies patterns with thick, grainy facies found in the more distal environments. Based on litho- and microfacies analyses, six main facies types are distinguished, building characteristic cyclic facies successions of different hierarchies. The stratal architecture of small-scale depositional sequ ences systematically changes in relation to their relative proximal-distal position on the Muschelkalk ramp system. Here, we present porosity and permeability data of the different facies types and within the basin-wide sequence stratigraphic framework. Dolo-wacke-/packstones and peloid grainstones attain the highest porosities of up to 24%, whereas bioclastic grainstones show porosities of up to 8%. The platy and nodular mud-/wackestone and most of the bioclastic wacke-/packstones typically show porosities below 2%. Even in the most porous strata, permeabilities do not exceed 10 mD, and only a few carbonates show higher permeabilities up to 90 mD. Within large-scale, third-order depositional sequences late highstand deposits represent the most permeable sediments.

Middle Triassic ammonoids from Silesia, Poland

70%

Kaim A. , Niedzwiedzki R.

nr 1

93-115

A description of new ammonoid specimens (Acrochordiceras aff. damesi, cf. Acrochordiceras sp. indet., Discoptychites cf. dux, ?Paraceratites sp., cf. Balatonites sp. indet., Beneckeia buchi) from the Lower Muschelkalk (Anisian, Middle Triassic) of Silesia (southern Poland) is presented. The detailed stratigraphic position of the new finds is given. The description is supplemented with a list of all species of ammonoids found hitherto in Silesia, which was a southern part of the Germanic Basin during the Anisian. Beneckeia and Noetlingites were typical of epicontinental seas and usually appeared in the early part of transgressions. Other ammonoids entered from the Tethys into the epicontinental sea of the Germanic Basin during the maxima of transgressions. Some of them (balatonitids, paraceratitids, bulogitids, Discoptychites and probably Acrochordiceras) were successful colonizers which established their own populations in the Germanic Basin and evolved towards morphologies typical of epicontinental seas. Other (Beyrichites sp., Paraceratites binodosus, and 'Trachyceras' sp.) are regarded as unsuccessful immigrants or empty shells drifted post-mortem from the Tethys.

W pracy opisano nowe okazy amonitów (Acrochordiceras aff. damesi, cf. Acrochordiceras sp. indet., Discoptychites cf. dux, ?Paraceratites sp., cf. Balatonites sp. indet., Beneckeia buchi) z dolnego wapienia muszlowego (antzyk, środkowy trias) Śląska. W stosunku do poprzednich znalezisk, nowe wyróżniają się dokładnym umiejscowieniem w profilu. Dokonano również przeglądu wszystkich dotychczas znalezionych amonitów z dolnego wapienia muszlowego na Śląsku. W anizyku rejon Śląska znajdował się w południowej części Basenu Germańskiego. Podczas transgresji Basen Germański łączył się poprzez Bramę Śląsko-Morawską z Tetydą. Beneckeia i Noetlingites są rodzajami typowymi dla mórz epikontynentalnych i pojawiają się zwykle we wczesnym etapie takich transgresji. Inne amonitowate pojawiają się w maksimach transgresji. Niektóre z nich (balatonity, paraceratyty, bulogity, Discoptychites i prawdopodobnie również Acrochordiceras) ustanowiły własne populacje w Basenie Germańskim, ewoluując w kierunku morfologii typowych dla mórz epikontynentalnych. Inne (Paraceratites binodosus i 'Trachyceras' sp.) albo nie zdołały zadomowić się w wodach morza epikontynentalnego, albo ich muszle zostały pośmiertnie przyniesione z oceanu przez prądy.