An unusual brachiopod assemblage in a Late Jurassic (Kimmeridgian) stromatactis mud-mound of the Eastern Carpathians (Hăghimaş Mountains), Romania

Abstract

An unusual fossil assemblage dominated by superabundant rhynchonellid brachiopods in a stromatactis mud-mound is recorded from the Hȃghimaş Mountains (Eastern Carpathians), Romania. The mound mainly consists of bioclastic wackestones to packstones with a very rich macrofauna including crinoids, sponges, juvenile ammonites, and echinoids. The brachiopods represent a low-diversity but high-abundance association, dominated by the rhynchonellids Lacunosella and Septaliphoria. The taphonomical features of the fossil assemblage indicate an autochthonous fauna, with successive generations of brachiopods in life position and complete well-preserved individuals in different growth stage alongside an accessory population of crinoids and sponges. Brachiopodbrachiopod endosymbiotic life strategy is documented for the first time from a post-Paleozoic brachiopod assemblage. The mound reveals abundant stromatactis, filled by radiaxial fibrous or drusy calcite cement and internal polymud sediments. This is the first Late Jurassic (Kimmeridgian) stromatactis mud-mound identified in the Eastern Carpathians.

Oxfordian neptunian dykes with brachiopods from the southern part of the Kraków-Częstochowa Upland (southern Poland) and their links to hydrothermal vents

“…Moreover, brachiopods from carbonate buildups exhibit significant diversity of morphotypes (Helm 2005). In dense populations, decreasing size, asymmetry and even deformations of shells have been observed (Asgaard 1968;Boullier 1993;Brugger 1999;Lazȃr et al 2011).…”

“…Wagenplast 1972;Nitzopoulos 1974;Gwinner 1976;Boullier 1993;Grȃdinaru and Bȃrbulescu 1994;Sulser and Meyer 1998;Brugger 1999;Helm and Schülke 1999;Helm 2005;Olóriz et al 2006;Courville et al 2007;Lazȃr et al 2011). Moreover, brachiopods from carbonate buildups exhibit significant diversity of morphotypes (Helm 2005).…”

“…In the matrix, echinoderm plates with locally growing syntaxial cement are visible. Crossed nicols L. arolica is typical of small buildups (Herrmann 1996;Lazȃr et al 2011). According to Lazȃr et al (2011), the environments particularly preferred by accumulations of L. cracoviensis are the slopes of microbial-sponge and microbial buildups, where some brachiopods might have grown in situ and others might have been relocated down the slope to those sites.…”

“…Crossed nicols L. arolica is typical of small buildups (Herrmann 1996;Lazȃr et al 2011). According to Lazȃr et al (2011), the environments particularly preferred by accumulations of L. cracoviensis are the slopes of microbial-sponge and microbial buildups, where some brachiopods might have grown in situ and others might have been relocated down the slope to those sites. L. cracoviensis is regarded as a shallowmarine form and its shells are settled by epifauna, which is related to the presence of distinct ridges (Krawczyński 2008).…”

Late Jurassic facies architecture of the Złoczew Graben: implications for evolution of the tectonic-controlled northern peri-Tethyan shelf (Upper Oxfordian–Lower Kimmeridgian, Poland)

“…The origin of stromatactis cavities, in general, is still controversial despite numerous investigations (see for review and references, e.g., Matyszkiewicz 1997a; Hladil et al 2007;Aubrecht et al 2009;Lazȃr et al 2011). Stromatactis-like cavities and stromatactoid cavities described in this paper differ from true stromatactis in terms of size, shape, and occurrence.…”