Early Jurassic foraminiferal assemblages in platform carbonates of Mt. Krim, central Slovenia

Abstract

During the Early Jurassic, the subtropical carbonate platforms of the peri-Tethys Ocean experienced significant changes in their architectures, as well as in their biota compositions. Shallow-water carbonates from the northern part of the ancient Adriatic Carbonate Platform (External Dinarides) were investigated in six sections, which taken together cover the development of the platform from deposition of the uppermost Triassic Main Dolomite to the middle Lower Jurassic, lithiotid limestone. Our aim was to establish a detailed foraminiferal biostratigraphy and to observe the changes in size, abundance and diversity of foraminifera in different types of facies. As a result, the succession was successfully divided into stage or substage levels. Foraminiferal assemblages were shown to experience a gradual change in taxonomic composition (including an increase in the proportion of complex agglutinated forms), a general increase in abundance of specimens, and greater diversity in each facies type, except in bindstone and mudstone. Notable is the difference between Hettangian assemblages, which display fairly uniform compositions in all facies types and the predominance of opportunists, and the post-Hettangian assemblages, which become progressively more species-rich and where the differences in facies are perhaps more pronounced. Changes in the size of the species Meandrovoluta asiagoensis Fugagnoli & Rettori, and of the largest specimen in the assemblages, however, are less clear, but are arguably present. Faunal changes roughly correspond to the gradual change from the flat-top platform of the upper Triassic -Hettangian, where biota would be repeatedly subjected to stressed peritidal conditions, to a platform differentiated into lagoon, sand bars and ephemeral emergent areas, offering numerous habitats and perhaps more stable living conditions for organisms. IzvlečekKarbonatne platforme območja Tetide so v času starejše jure doživljale znatne spremembe v morfologiji in sestavi biote. Plitvomorske karbonate Jadranske karbonatne platforme (Zunanji Dinaridi) smo raziskali v šestih profilih na širšem območju Krima. Profili skupaj zajemajo interval od vrhnjega dela, glavnega dolomita do litiotidnega apnenca. Naš cilj je bil identifikacija foraminifernih biocon. Poleg same taksonomske sestave smo beležili še raznolikost foraminifernih združb, pogostnost (ali gostoto) foraminifer ter spremembo v velikosti vrste Meandrovoluta asiagoensis Fugagnoli & Rettori ter v velikosti največjih primerkov v združbah. Po pričakovanjih rezultati kažejo postopne spremembe v taksonomski sestavi foraminifernih združb, vključno z naraščanjem deleža kompleksnih aglutiniranih vrst ter splošen porast gostote primerkov in raznolikosti v vseh faciesih razen v bindstone in mudstone faciesih. Zanimivo je, da hettangijske združbe izkazujejo precejšnjo podobnost v sestavi in prevlado oportunističnih vrst, medtem ko so razlike med združbami glede na facies v mlajših plasteh bolj izrazite. Sprememba v velikosti vrste M. asiagoensis je znotraj p...

Provenance analysis of Roman limestone artefacts from Colonia Iulia Emona (Marof archaeological site, Slovenia)

“…Among the unworked stone blocks, Thaumatoporella limestone (microfacies F1F) is very common. This type of microfacies was also not found in the section near Staje (Rožic ˇet al, 2018), but it is known from rocks of the same age at Preserje, 2 km west of Podpec ˇ (Gale & Kelemen, 2017;Ogorelec, 2009), and also known in abundance in the Roman quarry at Podpec ˇ (Djuri c et al, in press).…”

“…These varieties belong to the Lower Jurassic Podbukovje Fm (Dozet, 2009;Gale & Kelemen, 2017). Samples W6 (microfacies type F3A) and W7 (microfacies type F3C) also contain foraminifera Orbitopsella praecursor, which imposes a narrower constraint to the age of these samples (i.e., the Pliensbachian) and further attributes this facies to the so-called Orbitopsella beds Mb or the Lithiotid Limestone Mb (Dozet, 2009;Gale & Kelemen, 2017). The most probable source of this limestone is the Roman quarry at Podpec ˇ (Djuri c et al, 2018).…”

Multi-method study of the Roman quarry at Podpeč sedimentary succession and stone products

“…The facies dependence of Early Jurassic benthic foraminifera has been hypothesised previously by Fugagnoli (2004) and attributed to gradients in trophic resources, oxygen levels, and stability in nutrient supply. As shown by Gale and Kelemen (2017), such differences among the assemblages can be recognized from the Sinemurian onwards. Most of the taxa from the investigated assemblages are considered to be benthic opportunists (see Fugagnoli, 2004).…”

“…dolomites and predominant limestones of the Podbukovje Formation, and the Middle Jurassic oolithic limestones of the Laze Formation (Fig. 2b) (Buser et al, 1967;Buser, 1968;Ogorelec & Rothe, 1993;Miler & Pavšič, 2008;Ogorelec, 2009;Gale & Kelemen, 2017). The Podbukovje Formation is further divided into five members.…”

Sedimentary record of subsidence pulse at the Triassic/Jurassic boundary interval in the Slovenian Basin (eastern Southern Alps)

“…Meandrovoluta asiagoensis is a relatively recently described species, although it has commonly been figured under different names (Fugagnoli et al 2003). Its stratigraphic range is currently determined as Sinemurian to Toarcian (Fugagnoli et al 2003;Velić 2007), but it occurs on the Dinaric Carbonate Platform from at least the late Hettangian (Gale & Kelemen 2017). It is abundant in low-diversity assemblages, in various lagoonal environments (Fugagnoli 2004 and pers.…”