Belemnite ecology and the environment of the Nusplingen Plattenkalk (Late Jurassic, southern Germany): evidence from stable isotope data

Abstract

The late Kimmeridgian Nusplingen Plattenkalk (palaeolatitude ~30°N) is one of the well‐known European Plattenkalk konservatlagerstätten. The laminated limestones of this lagerstätte have been deposited in a shallow lagoon, surrounded by sponge‐microbial mounds, some of which formed small islands. Plattenkalk sediments are often thought to have been deposited below a halocline, which was induced by high evaporation rates. By measuring the stable isotope composition of belemnite rostra (n = 27) of the species Hibolithes semisulcatus, the depositional environment of the Nusplingen Plattenkalk has been investigated. Cathodoluminescence‐microscopy and trace element analysis have been applied to check for diagenetic alteration of the studied rostra. The mean δ13C of the well‐preserved rostra is +0.03 ± 0.27‰, the mean δ18O −0.68 ± 0.3‰. A narrow range of stable isotope data acquired from an accumulation of rostra, regurgitated by a fish or reptile, supports the notion that belemnite calcite reflects environmental conditions. The palaeontological and sedimentological findings suggest that H. semisulcatus was autochthonous to the Nusplingen Plattenkalk. Anoxic conditions prevailed in the sediments and temporarily in the water‐column above the sediment/bottom water interface. A nektobenthic life style can be excluded for the Nusplingen belemnites; a demersal life style seems unlikely. Comparison with δ18Obel data from other latitudes indicates that a latitudinal gradient played a role in the δ18O composition of seawater. A pelagic, inner shelf setting is therefore suggested for the Plattenkalk, an interpretation that is supported by palaeontological evidence. It is here proposed that the formation of the Nusplingen Plattenkalk was not caused by salinity stratification. It is further suggested that the belemnites were not restricted to deep‐water settings, but also occurred in shallow waters and higher in the water‐column.

Diversity and morphological evolution of Jurassic belemnites from South Germany

“…According to their fossil record, these coleoids inhabited surface to deep waters of epicontinental domains, and were present at worldwide scale, both in the subtropical and polar areas (Stevens, 1963(Stevens, , 1965(Stevens, , 1971Stevens and Clayton, 1971;Christensen, 1976;Doyle, 1987Doyle, , 1994Doyle et al, 1997;Christensen, 2002). In agreement with the regional distribution and the palaeoenvironmental differences in the taxonomic composition of most belemnite communities (Mutterlose and Wiedenroth, 1998;Mariotti et al, 2012;Weis et al, 2012), recent geochemical analyses of rostra indicate that different species might have had different ecological preferences in term of life depth, seawater temperature, or salinity (Dutton et al, 2007;McArthur et al, 2007;Dera et al, 2009;Rexford and Mutterlose, 2009;Mutterlose et al, 2010;Wierzbowski and Rogov, 2011;Li et al, 2012;Harazim et al, 2013;Stevens et al, 2014;Wierzbowski, 2015). Nevertheless, some eurytopic taxa likely migrated over several hundreds of kilometers and different depths during their lifetime (Christensen, 1997;Zakharov et al, 2006;Alsen and Mutterlose, 2009;Sørensen et al, 2015).…”

“…As belemnites are often considered inhabiting deeper, hemipelagic environments (Mutterlose et al, 2010), it would be expected that higher diversity levels correspond to deep shaly facies, which favour preservation in return. However, this model is not fully coherent with data from South Germany and surrounding areas (e.g., Luxembourg, UK) because belemnite rostra are commonly found in lagoonal carbonate facies of the Late Jurassic and conglomeratic and sandy littoral facies of the Aalenian (Weis and Mariotti, 2007;Stevens et al, 2014). The reason for this occurrence in shallow seas is that numerous belemnite species could have lived the major part of their life in deeper waters, but reached shallow ecosystems for reproducing then dying (Mutterlose et al, 2010).…”

“…Recently, geochemical analyses (i.e., δ 18 O, δ 13 C, Mg/Ca) performed on belemnite rostra have highlighted singular ecological differences in term of seawater temperature or life depth according to species (McArthur et al, 2007;Wierzbowski and Joachimski, 2007;Dera et al, 2009;Wierzbowski and Joachimski, 2009;Mutterlose et al, 2010;Wierzbowski and Rogov, 2011;Li et al, 2012;Harazim et al, 2013;Stevens et al, 2014;Ullman et al, 2014;Wierzbowski, 2015). However, some geochemical analyses are not without controversy (see Mutterlose et al 2010) and might in some cases be compounded by late ontogenetic migrations (e.g., Alberti et al, 2012).…”

“…The reason for this occurrence in shallow seas is that numerous belemnite species could have lived the major part of their life in deeper waters, but reached shallow ecosystems for reproducing then dying (Mutterlose et al, 2010). At least in some cases, there is indication that they might even spent their entire life in these environments (e.g., inner shelf palaeoenvironments of the Nüsplingen Limestone; Stevens et al, 2014). In complement of the robust calcitic structure of rostra favouring their preservation (Saelen, 1989;Ullman et al, 2015), this ability to occupy a wide range of environments (and facies) is quite positive if we expect to have a continuous fossil record whatever the lithology.…”

Adaptations to squid-style high-speed swimming in Jurassic belemnitids

“…Here, we describe exceptionally preserved specimens of Acanthoteuthis, assigned by most authors to the suborder Belemnotheutina of the order Belemnitida [2,3]. Their calcitic or aragonitic rostra (bullet-shaped hard parts capping the chambered phragmocone, fin-attachment) are widely used to measure the isotopic signature of seawater [4][5][6], yielding information on palaeoclimate, habitat and the carbon cycle [7][8][9]. Although assumptions on their pelagic-nektonic (open marine, freeswimming) mode of life have been made based on comparisons with living remote relatives [10,11], the evidence was poor in spite of their great abundance.…”