Marcin Machalski

The Weathering-Modified Iridium Record of a New Cretaceous—Palaeogene Site at Lechówka Near Chełm, SE Poland, and Its Palaeobiologic Implications

In the light of integrated biostratigraphic and geochemical data, a complete shallow-marine succession across the Cretaceous—Palaeogene (K—Pg) boundary, with the critical boundary clay coupled with a burrowed siliceous chalk (“opoka” in Polish geological literature), possibly equivalent of the basal Danian Cerithium Limestone in Denmark, has been discovered at Lechówka near Chelm, SE Poland. An extraterrestrial signature marking the K—Pg boundary is confirmed by anomalously high amounts of iridium (up to 9.8 ppb) and other siderophile elements (especially Au and Ni), as well as by an elevated Ir/Au ratio consistent with a chondrite meteoritic composition. The major positive iridium spike surprisingly occurs in Maastrichtian marls, 10 cm below the boundary clay interval, which can be explained by diagenetic mobilisation and re-concentration of the impact-derived components. Thus, intensively infiltrating, humic acid-rich ground waters during the long-lasting Palaeogene weathering in tropical humid regimes were probably responsible not only for the large-scale decalcification of the Lechówka section, but also for both downward displaced position of the iridium enrichment, a dispersed profile of this anomaly and its significantly lessened value, but still approaching an increase by a factor of 100. This modified record of the K—Pg boundary event points to a careful reconsideration of the iridium anomaly as a trustworthy marker for studying the extinction patterns across the K—Pg boundary, as supported by the recent data from New Jersey, USA.

Ammonite extinction and nautilid survival at the end of the Cretaceous

One of the puzzles about the end-Cretaceous extinctions is why some organisms disappeared and others survived. A notable example is the differential extinction of ammonites and survival of nautilids, the two groups of co-occurring, externally shelled cephalopods at the end of the Cretaceous. To investigate the role of geographic distribution in explaining this outcome, we compiled a database of all the occurrences of ammonites and the nautilid genus Eutrephoceras in the last 0.5 m.y. of the Maastrichtian. We also included recently published data on ammonite genera that appear to have briefly survived into the Paleocene. Using two metrics to evaluate the geographic range of each genus (first, a convex hull encompassing all of the occurrences of each genus, and second, the maximum distance between occurrences for each genus), we documented that most ammonite genera at the end of the Maastrichtian were restricted in their geographic distribution, possibly making them more vulnerable to extinction. The geographic distribution of those genera that may have briefly survived into the Paleocene is significantly greater than that of non-surviving genera, implying that more broadly distributed genera were more resistant to extinction. This pattern is further emphasized by the broad distribution of Eutrephoceras , which matches that of the most widely distributed ammonites at the end of the Maastrichtian. However, even the most widely distributed ammonites eventually succumbed to extinction, whereas Eutrephoceras survived. Evidently, a broad geographic distribution may have initially protected some ammonites against extinction, but it did not guarantee their survival.

Large predatory marine reptiles from the Albian–Cenomanian of Annopol, Poland

During the Early–Late Cretaceous transition, marine ecosystems in Eurasia hosted a diverse set of large predatory reptiles that occupied various niches. However, most of our current knowledge of these animals is restricted to a small number of bonebed-like deposits. Little is known of the geographical and temporal extent of such associations. The middle Albian – middle Cenomanian phosphorite-bearing succession exposed at Annopol, Poland produces numerous ichthyosaurian and plesiosaurian fossils. These are mostly isolated skeletal elements (e.g. teeth, vertebrae), but disarticulated partial skeletons and an articulated, subvertically embedded ichthyosaur skull are also available. The following taxa are identified: ‘ Platypterygius ’ sp., cf. Ophthalmosaurinae, Ichthyosauria indet., Polyptychodon interruptus , Pliosauridae indet., Elasmosauridae indet. and Plesiosauria indet. The large-sized ichthyosaur ‘ Platypterygius ’ and the pliosaurid Polyptychodon interruptus predominate within the upper Albian – middle Cenomanian deposits. The Annopol record, combined with data from England, France and western Russia, suggests that ‘ Platypterygius ’ and Polyptychodon interruptus formed a long-term, stable ecological sympatry in marine ecosystems of the European archipelago, at least during the Albian – middle Cenomanian. In addition, the marine reptile assemblage from Annopol is distinct from other Eurasian ecosystems in containing also elasmosaurids in its Albian portion.

Ammonites on the Brink of Extinction: Diversity, Abundance, and Ecology of the Order Ammonoidea at the Cretaceous/Paleogene (K/Pg) Boundary

We examined the stratigraphic distribution of ammonites at a total of 29 sites around the world in the last 0.5 myr of the Maastrichtian. We demarcated this interval using biostratigraphy, magnetostratigraphy, cyclostratigraphy, and data on fossil occurrences in relation to the K/Pg boundary in sections without any facies change between the highest ammonites and the K/Pg boundary. The ammonites at this time represent all four Mesozoic suborders comprising six superfamilies, 31 (sub)genera, and 57 species. The distribution of ammonites is dependent on the environmental setting. Recent data suggest that ammonites persisted to the boundary and some species may have survived for several tens of thousands of years into the Paleogene. The best explanation for ammonite extinction is a brief episode of ocean acidification immediately following the Chixculub impact, which caused the decimation of the calcareous plankton including the planktic post-hatching stages of ammonites. The geographic distribution of ammonites may also have played a role in the events with more broadly distributed genera being more resistant to extinction.

Terminal Maastrichtian Ammonites from Turkmenistan, Central Asia

A complete uppermost Maastrichtian—Danian succession in the Sumbar River section, western Kopet Dagh (southwest Turkmenistan, Central Asia), constitutes one of the few instances in the world where the fossil record of the last ammonites can be directly positioned with respect to the iridium-rich, impact-related clay layer, which defines the Cretaceous—Paleogene (K—Pg) boundary. Two ammonite taxa, Baculites cf. vertebralis and Hoploscaphites constrictus johnjagti, range up to a level directly beneath the K—Pg boundary clay in the Sumbar River section. Thus, these two forms probably survived until the very end of the Maastrichtian in the western Kopet Dagh area. The terminal Maastrichtian ammonite records from the Sumbar River area represent the southeasternmost occurrences of these essentially Boreal taxa.

Foraminiferal record in a condensed marine succession: a case study from the Albian and Cenomanian (mid-Cretaceous) of Annopol, Poland

A condensed succession at Annopol is of key importance for the mid-Cretaceous palaeontology and palaeobiogeography in Poland. Here, the planktonic and benthic foraminifera from the Albian and Cenomanian intervals are studied. The local foraminiferal record is strongly influenced by burrowers. On the one hand, piping down of the foraminiferal tests through burrows disturbed the original succession, for example by introduction of the Cenomanian foraminifera into the Albian phosphorite horizon. On the other hand, the foraminifera in the burrow fills near the base of the Cenomanian provide the sole piece of evidence of a lower upper Cenomanian unit lost from the record by erosion. Changes in foraminiferal assemblages allow for the interpretation of the succession in terms of bathymetry and biological productivity. The highest rate of primary production is deduced for the Albian phosphorite horizon. Integration of foraminiferal and ammonite biostratigraphy with sedimentology allows for the comparison of a pattern of sea-level oscillations recorded at Annopol with the relevant portion of the classic graph of sea-level changes for the British Isles. It turns out that all important elements of the British curve, that is, transgressive peaks and regressive troughs or lows, left their distinctive, albeit highly residual, record in the Annopol succession. This study demonstrates that even extremely condensed marine deposits, such as those at Annopol, may provide a foraminiferal record of better quality, order and resolution than conventionally anticipated.

OYSTER–MICROBIAL ROLLING STONES FROM THE UPPER JURASSIC (KIMMERIDGIAN) OF POLAND

ABSTRACT Oyster–microbial rolling stones (ostreoliths) from the Upper Jurassic (Kimmeridgian) of Sulejów and Małogoszcz, Poland, are described and interpreted in terms of their origin and development. The ostreoliths are composed mainly of small-sized oysters (Nanogyra nana) that initially encrusted bivalve or ammonite shells. These structures were frequently overturned during their further growth by hydrodynamic agents. The oyster shells are covered by a thin crust that is suggestive in appearance of a microbial mat. We postulate that the mats not only bound the shells, but also induced early cementation of the sediment infill, thereby triggering the rapid lithification and rigidity of ostreoliths. This interpretation is supported by the presence of bivalve borings that cut the shells, microbial crust and internal sediment infill. The oyster–microbial association provided favorable conditions under which hardground biota thrived in a soft-bottom setting which was otherwise inimical to such organisms. These hardground biota are represented by a variety of encrusters (foraminifera and foraminifera-like problematica, plicatulid bivalves, cyclostome bryozoans, serpulids, and thecideid brachiopods) and borers (bivalves, bryozoans, and phoronids). Ostreoliths from Sulejów are of smaller size, and with a less-developed oyster cortex, than those from Małogoszcz. This may be due to a higher frequency of physical disturbance (storms) at Sulejów which halted ostreolith development at earlier phases than at Małogoszcz. A large oyster buildup recorded previously from Brzegi, close to Małogoszcz, suggests that, under favorable conditions, ostreoliths could eventually have transformed into stationary, patch-reef–type structures.

Late late Albian (Early Cretaceous) shark teeth from Annopol, Poland

Siversson, M. & Machalski, M., February 2017. Late late Albian (Early Cretaceous) shark teeth from Annopol, Poland. Alcheringa 41, 433–463. Screen washing of the condensed phosporite-bearing sands at the top of the Albian succession at Annopol, Poland, produced 789 selachian teeth of which 264 are determinable to at least genus level. The sediment type and methods of processing prevented recovery of small-toothed taxa, resulting in an assemblage comprising 13, mostly large-toothed taxa. Lamniformes dominates with Dwardius sp. being, by far, the most common taxon. Observations on vertical distribution and preservation of the teeth (with focus on the adhered phosphatic matrix), coupled with biostratigraphic ranges of co-occurring ammonites, indicate that the majority of the shark material is attributable to the Mortoniceras rostratum or, more probably, M. perinflatum Zone (late late Albian; mid-‘Vraconnian’). This is compatible with the composition of the shark assemblage, characterized by the co-occurrence of Paraisurus sp. aff. P. compressus, Cretoxyrhina vraconensis and Squalicorax teeth with strong serrations on the cutting edges. The tightly curved basal edge of the root in lateral teeth of C. vraconensis conforms to that of teeth from the Pawpaw Formation of Texas (M. rostratum Zone) and differs from the more divergent root lobes in younger specimens from the uppermost Albian and/or lowermost Cenomanian of Kolbay, Mangyshlak. Some specimens in the studied assemblage are probably older, within the range from the middle to earliest late late Albian. The strong numerical dominance of either Cretoxyrhina or Dwardius in late late Albian to early Cenomanian selachian faunas indicates competitive exclusion in these similar-sized, apex predatory sharks. Mikael Siversson* [mikael.siversson@museum.wa.gov.au], Department of Earth and Planetary Sciences, Western Australian Museum, 49 Kew Street, Welshpool, Western Australia 6106, Australia; Marcin Machalski [mach@twarda.pan.pl], Institute of Paleobiology, Polish Academy of Sciences, ul. Twarda 51/55, 00-818 Warszawa, Poland. *Also affiliated with: Department of Environment & Agriculture, Curtin University, Kent Street, Bentley, WA 6102, Australia.

A new hermit crab (Anomura, Paguroidea) from the upper Albian (Cretaceous) of Annopol, Poland.

A new diogenid paguroid, Paguristes liwinskii sp. nov., is described from upper Albian phosphorite-bearing deposits near Annopol, along the east bank of the River Vistula (Wisła), east-central Poland. This new species constitutes an additional example of Early-Mid-Cretaceous macrofaunal shift, from marine reefal limestone to siliciclastic facies, triggered by the worldwide radiation of planktonic organisms. The species described here is the earliest known member of the genus Paguristes, previously recorded from the upper Santonian/lower Campanian to the Recent.