The Monotis–Dactylioceras Bed in the Posidonienschiefer Formation (Toarcian, southern Germany): condensed section, tempestite, or tsunami-generated deposit?

Abstract

The Monotis-Dactylioceras Bed in the Toarcian Posidonienschiefer Formation is a conspicuous shell accumulation, which was used as marble in the late eighteenth century of Bavaria. The shell bed is characterized by left valves of the bivalve Meleagrinella substriata (von Münster) and local accumulations of the ammonite Dactylioceras athleticum (Simpson), and has previously been considered to reflect a regression or a storm event. Indeed, three different interpretations of the bed appear possible: (1) condensed section, (2) tempestite, or (3) tsunami deposit. New observations, specifically swaley crossstratification and sole marks, point to an event-like formation of the bed. While most of the observations are consistent with the formation by a storm event, the singular occurrence within the 4.4 Ma lasting Lower Toarcian, which spanned about 4.4 Ma, and the inverse grading of the shells point to a possible tsunami origin. The latter hypothesis is supported by contemporaneous seismites in the western Tethyan realm, and micrite injections in strata below the Monotis-Dactylioceras bed, which may reflect quake-induced sediment liquefaction.

A Dactylioceras – Meleagrinella (Clathrolima) assemblage from the Agardhbukta (eastern coast of Spitsbergen): a first in situ Toarcian molluscan occurrence from Svalbard providing interregional correlation

“…7 C-D) stored in the Munich Museum, it was established that this taxon belongs to the subgenus Meleagrinella (Clathrolima). In Europe, bivalves similar to M. (C.) substriata are typical for the Commune subzone of Germany (Riegraf et al, 1984;Arp & Gropengießer, 2016) and…”

“…-Range zone of C. substriata (Muenster) is corresponding to the lower Toarcian Bifrons ammonite zone (Lutikov & Arp, 2020a), but this species is especially common in the Commune ammonite subzone. This species is known from Spitsbergen (Agardhbukta), Northern Siberia and NE Russia (Tyung, Markha, Vilyui, Levy Kedon rivers: Lutikov & Arp, 2020b), Germany (Harries & Little, 1999;Arp & Gropengießer, 2016), the Yorkshire coast, England: (Harries & Little, 1999), Arctic Canada (Ya Ha Tinda lagerstatte: Martindale & Aberhan, 2017), Iran (Semnan area: Repin, 2000), and Japan (Okayama Prefecture: Hayami, 1961).…”

“…commune -by yellow circles). Key localities and their clusters are indicated by numerals: 1 -Astronomicheskaya river, NE Russia (this paper); 2 -Anabar Bay, Northern Siberia(Lutikov & Arp, 2020b); 3 -Tyung river, Yakutia(Lutikov & Arp, 2020b); 4 -Markha river, Yakutia(Lutikov & Arp, 2020b); 5 -Viluyi river, Yakutia(Lutikov & Arp, 2020b); 6 -Hyrnefjellet, Van Mijenfjorden(Kopik, 1968; this paper); 7 -Sørkappland (this paper); 8 -Agardhbukta, Dunérbukta(Frebold, 1929b; this paper); 9 -Yorkshire localities, England(Harries & Little, 1999); 10, 11 -German localities (Banz, Ludwigskanal, Bisinger Berg, Quarry Kromer, Dörlbach -Riegraf et al, 1984;Harries & Little, 1999;Arp & Gropengießer, 2016); 12 -Semnan province, Iran(Repin, 2000); 13 -Prince Patrick Island, Canada(Imlay, 1955); 14 -South Barrow test well 3, Alaska(Imlay, 1955); 15 -borehole Medvezh'ya-316, Western Siberia (Devyatov et al, 2006); 16 -Tsvetkov Cape, Northern Siberia(Knyazev et al, 2003).…”

Bio- and chemostratigraphy of the Posidonia Shale: a new database for the Toarcian Oceanic Anoxic Event from northern Germany

“…The "Monotis Bank" is present from 31.75 to 31.25 m in the Schandelah Core and from 15.15 m to top in the L1 Core. This regional marker bed is characterized by a peculiar wavy lamination and a conspicuous shell accumulation mainly from left valves of the bivalve Meleagrinella substriata and local accumulations of the ammonite Dactylioceras athleticum (Arp and Gropengießer 2016). An additional carbonate bed is found in both cores between 35.1 and 34.6 m in the Schandelah Core and from 18 to 17.5 m in the L1 Core.…”

Biostratigraphy and sequence stratigraphy of the Toarcian Ludwigskanal section (Franconian Alb, Southern Germany)

“…12: 3) is most abundant. Therefore, the complete event bed (Arp and Gropengießer 2016) as well as the fish-scale-rich layer below, belongs to the Commune Subzone.…”