doi: 10.1111/ter.12218 Temporal and bathymetric resolution of nautiloid death assemblages in stratigraphically condensed oozes (New Caledonia) Adam Tomasovych,1 Jan Schl€ogl,2 Darrell S. Kaufman3 and Natalia Hudackova2 1Earth Science Institute, Slovak Academy of Sciences, Dubravska cesta 9, Bratislava 84005, Slovakia; 2Department of Geology and Paleontology, Comenius University, Mlynska dolina G, Bratislava 84215, Slovakia; 3School of Earth Sciences & Environmental Sustainability, Northern Arizona University, Campus Box 4099, Flagstaff, AZ 86011, USA ABSTRACT Cephalopod shells can be affected by postmortem transport at a centennial temporal resolution and with excellent and biostratigraphic condensation, but direct estimates of the bathymetric fidelity. Dead Nautilus shells exist for only a few temporal and spatial resolutions of cephalopod assemblages hundred years on the seafloor, in contrast to the biostrati- are missing. Amino acid racemisation calibrated by 14C graphically condensed mixture of extant foraminifers and demonstrates a centennial-scale time averaging (<500 years) foraminifers that went extinct during the Pleistocene. Cepha- of Nautilus macromphalus in sediment-starved, epi- and lopod shells that do not show any signs of early diagenetic mesobathyal pelagic environments. The few shells that are cementation are unlikely to be biostratigraphically thousands of years old are highly degraded. The median condensed. occurrence of dead shells is at 445 m depth, close to the 300–400 m depth where living N. macromphalus are most Terra Nova, 00: 1–8, 2016 abundant. Therefore, dead shells of this species accumulate ooze deposition in the Indo-Pacific. Introduction Methods Such environments are characterised Chambered cephalopods frequently by sediment starvation, by ferroman- Twenty-one dead shells of show rapid evolutionary turnover ganeous and glauconitic deposits that N. macromphalus were sampled with and attain broad geographic ranges, grow in the absence of sedimentation beam trawls and dredges at eleven and thus represent one of the key at millennial to million-year time- sites around the New Caledonia groups used in high-resolution strati- scales (Follmi,€ 2016), and by a co- archipelago in 1985 and 1987 graphic, biogeographic and oceano- occurrence of extant and Pleistocene (Fig. S1, Table S1, De Forges, 1990). graphic inferences of fossil foraminifers that implies significant Five additional specimens sampled assemblages (Brayard et al., 2006; stratigraphic condensation (Hayward between New Caledonia and the Dera et al., 2011; Sessa et al., 2015). and Kagawata, 2005). We suggest Chesterfield Islands in 2003 and 2005 However, chambered cephalopods that present-day sediment-starved were described by Mapes et al. can be subjected to postmortem pelagic environments can provide (2010a). Eighteen shells were col- ascent and significant drift by water taphonomic windows into processes lected between 330 and 750 m depth currents, thus confounding interpre- that generated biostratigraphically in the epibathyal zone, and eight tations of environmental conditions condensed assemblages in the past. shells were collected between 750 and and biogeographic distribution Here, we quantify the temporal 2045 m in the mesobathyal zone. (Fernandez-L opez and Melendez, and bathymetric resolutions of nau- Seawater temperature off New Cale- 1996; Chirat, 2000). Chambered tiloid death assemblages in such sedi- donia between 300 m and 600 m cephalopods are also subject to sig- ment-starved environments. First, we depth declines from 15 to 5 °C, and nificant condensation because they estimate postmortem age with 14C is 4 °C at 1000 m (Roux et al., frequently inhabited open-shelf and and amino acid racemisation in 26 1991). We split the shells into epi- pelagic-swell environments that were shells of N. macromphalus collected bathyal and mesobathyal assem- prone to sediment starvation in the in bathyal environments off New blages to reduce the effect of past (Wendt and Aigner, 1985; San- Caledonia to constrain their rate of temperature on the rate of racemisa- tantonio and Carminati, 2011; Coim- disintegration on the seafloor and tion. Fourteen shells contained ooze bra and Oloriz, 2012). Present-day thus their potential for stratigraphic sediment that was wet sieved with a species of Nautilus predominantly condensation. Second, we show that 0.071 mm mesh size. We identified inhabit bathyal environments with some calcitic foraminifers extracted 250 foraminifer specimens to species from sediment infills of Nautilus level in each of these shells, and shells went extinct during the Pleis- determined their last stratigraphic Correspondence: Adam Tomasovych, tocene, thus providing information appearance datum. Earth Science Institute, Slovak Academy on significant differences in time The ages of seven specimens dated of Sciences, Dubravska cesta 9, Bratislava with 14C at the AMS facility at the 84005, Slovakia. Tel.: +0421 904 852145; averaging between nautiloid and for- e-mail: [email protected] aminiferal assemblages. Poznan Radiocarbon Laboratory © 2016 John Wiley & Sons Ltd 1 Cephalopod time averaging in sediment-starved environments • A. Tomasovych et al. Terra Nova, Vol 0, No. 0, 1–8 ............................................................................................................................................................. were converted to calendar years time since sampling of shells on the collection, implying a decline in the using the Marine13 data and Cal- seafloor (Table S4). To quantify the rate of shell disintegration from cen- ib7.1 (Stuiver and Reimer, 1993), rate of loss of Nautilus shells from tennial- (195 years) to millennial- with a regional marine reservoir cor- the surface seafloor sediments on the scale half-lives (3013 years) while rection (ΔR) equal to 26 years basis of two depth-specific age–fre- shells are exposed in the mixed layer (SD = 23 years) (Table S2). The 14C quency distributions (AFDs), we (Table S5). The shells older than activity of one specimen (CP30/4) used a simple exponential model 1000 years are highly incomplete, was indistinguishable from back- (rate of loss is constant in time), a with relicts of walls and umbilicum ground levels, implying an age of at Weibull model (rate of loss gradually (Fig. 2); and incompleteness of least 50 000 years. declines over time, e.g. old shells dis- phragmocones correlates positively The outermost chamber whorls integrate at a slower rate than young with postmortem age (Spearman were split into external spherulitic- shells), and a two-phase exponential r = 0.77, P < 0.0001, Fig. S6). Shells prismatic and middle nacreous lay- model (rate of loss abruptly declines are frequently penetrated by micro- ers, which were analysed separately over time) (Tomasovych et al., 2014). borings (Fig. 3A,B). Some specimens for the extent of amino acid racemi- show lm-thick, yellowish to brown- sation (AAR) using reverse-phase ish aggregates of clays, goethite (de- Results high-pressure liquid chromatography termined by X-ray diffraction), and analysis (Kaufman and Manley, The AFD of N. macromphalus is coccoliths that coat empty borings 1998). We screened the data accord- strongly right-skewed, with a median and external surfaces (Fig. 3C,D). ing to Kosnik and Kaufman (2008) age of 263 years and an interquartile However, tabular aragonitic crystal- and calibrated the rate of AAR range (IQR) of 394 years (Fig. 2). lites forming the nacreous layer do according to Allen et al. (2013) with Twenty specimens are younger than not show any signs of diagenetic seven specimens (including one speci- 500 years and six specimens are older cementation (Fig. 3E,F), and the men dated by 210Pb in Mapes et al., than 1000 years (Table S1). Three internal sediment within the whorls 2010a) (Figs S2 and S3), fitting specimens older than 1000 years were is never lithified. aspartic (Asp) and glutamic (Glu) found at 1140 m depth. The AFD Of the sediment samples extracted acid D/L values separately for each from the epibathyal zone is similarly from the whorls of 14 shells, 13 con- layer (Fig. 1A,B and Table S3). characterised by centennial-scale time tained at least one foraminifer spe- Postmortem ages estimated on the averaging (median = 260 years and cies that went extinct during the basis of nacreous and prismatic lay- IQR = 220 years). The AFD from Pleistocene (Table S1). These extinct ers are similar (Fig. 1C). In addition the mesobathyal zone shows a simi- species co-occur with extant species, to the 14C and 210Pb ages of eight lar median age (363 years) but the thus showing significant million-year- shells, the AAR ages of the addi- IQR is equal to ~2000 years due to scale time averaging. They include tional 18 shells used in the analyses the presence of one very old speci- the pink Globigerinoides rubra that of temporal resolution are derived men (older than ~50 000 years). The went extinct in the Pacific 120 000 years from the nacreous layer, which mixture of frequent young shells ago (Thompson et al.,1979),the shows a larger covariation in the (younger than 500 years) and rare planktonic species Sphaeroidinellopsis extents of racemisation among amino very old shells best supports the paenedehiscens, Globigerinoides fistulosus acids and is less affected by micro- two-phase exponential and Weibull and Pulleniatina praecursor that went bioerosion than the prismatic layer models of skeletal loss in both depth- extinct during the Lower Pleistocene at (Figs S4 and S5). All ages refer to specific assemblages