Paleocene Taxa Research Articles

Calcareous nannofossil biostratigraphy of the Late Cretaceous‒early Paleocene interval in the Zagros basin (southeastern Tethys), Iran

Calcareous nannofossil biostratigraphy reveals a continuous depositional record through the Upper Cretaceous‒Paleocene succession in the Zagros Basin; southwest Iran (southeastern part of the Neo-Tethys), especially through the Cretaceous‒Paleogene and the Danian‒Selandian boundaries. The upper part of the Gurpi Formation and the lower part of the Pabdeh Formation were investigated. Calcareous nannofossil assemblages from these formations are characterized by abundant, diverse and moderate- to well-preserved forms with Tethyan affinities. This study concentrates on two sections (the Gurpi and Kabir-Kuh sections) in the west and southwest of Iran in the Zagros Basin, which span biozones CC25c/UC20bTP to NP6/NTp10B in the Kabir-Kuh and CC25b/UC20aTP to NP5/NTp9 in the Gurpi section. Late Maastrichtian nannofossil abundance and diversity in the studied intervals is high with a sharp decrease slightly above the K/Pg boundary. The K/Pg boundary interval is marked by the FO of Biantholithus sparsus, an acme of the dinoflagellate cyst Thoracosphaera operculata, a notable decrease in Cretaceous calcareous nannofossil abundance and diversity, and the appearance of new Paleocene taxa. An increased abundance of Thoracosphaera is recorded similar to that in the El Kef (Global Stratotype Section and Point, GSSP, for the K/Pg boundary), Ellés (auxiliary section), Egypt, Atlantic Ocean and sections elsewhere in the world. Reworked Cretaceous calcareous nannofossils are recorded from the base of the Danian along with the new Paleocene species. The Danian‒Selandian boundary is marked by the appearance of Lithoptychius ulii, Lithoptychius pileatus and Lithoptychius janii at the base of NTp8C; this level is also marked by the second radiation of Fasciculithus. Azam Mahanipour [a_mahanipour@uk.ac.ir], Department of Geology, Faculty of Science, Shahid Bahonar University of Kerman, Kerman, Iran; Mohammad Parandavar [parandavar.m@gmail.com], Paleontological Research Department, Exploration Directorate of Oil and Gas, NIOC, Tehran; Mohamed Youssef [myousefgeology@gmail.com], Department of Geology, Faculty of Science, South Valley University, 83523 Qena, Egypt.

Environmental dynamics during the Paleocene–Eocene thermal maximum (PETM) in the northeastern Peri-Tethys revealed by high-resolution micropalaeontological and geochemical studies of a Caucasian key section

The sedimentary record of the Paleocene–Eocene Thermal Maximum (PETM) in the wide epeiric sea of the NE Peri-Tethys contains a sapropelitic bed (SBD) characterized by a specific microfossil assemblage and negative oxygen and carbon isotope excursions (CIE). New results obtained from a high-resolution sampling of this interval in the Kheu section, central Caucasus, allows us to explore the succession, interrelationships and consequences of global and regional palaeoenvironmental events during the PETM. The CIE apparently lasted twice as long as the SBD accumulation period; thus, the SBD represents a response to the early and most dramatic phase of the PETM related to rapid transgression and greatly enhanced eutrophication of the basin. The lithological architecture of the SBD represents four bands, each of which consists of a dark, low-calcareous TOC-rich clay and relatively paler calcareous clays. The highest TOC concentrations are found in the lower and upper bands of the SBD; however, the lower band mostly consists of basinal organic matter, while the upper band represents mixed, basinal and terrestrial, organic matter. Pre-PETM events include the initial evolution of the Rhomboaster nannofossil lineage with the early first appearance of a short-arm species, relatively reduced calcareous plankton productivity, changes in the ratios of dinocyst ecological groups, and minor fluctuations in δ13C and δ18O. The onset of the CIE corresponds to the base of the SBD, which exhibits a dramatic decrease in total nannofossil abundance and an increase in total dinoflagellate abundance, the occurrence of “excursion taxa” of nannofossils (rhomboasters, asymmetric discoasters) and dinocysts (Axiodinium augustum, Epelidinium pechoricum), and significant variations in the species ratios of both nannoplankton and dinoflagellate communities, with widespread dominance of warm-water and eutrophic species. Above the SBD but during the late phase of CIE, the nannofossil abundance and species composition show a slight recovery, but most Paleocene taxa become extinct during the CIE recovery. Apectodinium spp. significantly decrease in abundance above the SBD, but rare specimens of Ax. augustum persist higher in the section after the end of the CIE. Thus, the major extinction of the Paleocene nannofossil taxa occurs after the termination of the most critical conditions during the CIE recovery phase, while the dinocyst “excursion taxa” survive even later.

A three-dimensional morphometric analysis of the locomotory ecology of Deccanolestes, a eutherian mammal from the Late Cretaceous of India

ABSTRACT The relationships and ecology of Deccanolestes, a eutherian mammal from the Late Cretaceous of India that is known only from isolated dental, mandibular, and postcranial elements, have been a topic of considerable interest and debate. A recent comprehensive phylogenetic analysis has placed this taxon within Adapisoriculidae, a clade of otherwise Paleocene arboreal mammals, but unexpectedly resolved this expanded Adapisoriculidae near the base of the eutherian tree. Deccanolestes has been described as having an arboreal or scansorial lifestyle based on its ankle morphology. Here, we present a geometric morphometric study of the astragalus to test hypotheses pertaining to the ecomorphological affinities of Deccanolestes. Shape analyses were performed on extant eutherians and marsupials displaying a range of different lifestyles, but predominantly sampling arboreal forms, as well as relevant Cretaceous to Eocene taxa. In addition, we constructed a neighbor-joining tree based on the shape variables to identify similarities among taxa in astragalar morphology. Our results show that Cretaceous and Paleocene taxa, including Deccanolestes, cluster most closely and form a separate group distinct from extant mammal clades, including extinct Primates. Strong phylogenetic signal in astragalar morphology among extant taxa, as well as apparent phylogenetic clustering of extant and extinct taxa, complicates a straightforward interpretation of the locomotor ecology of Deccanolestes, but our results suggest that the astragalar morphology of Deccanolestes has no analogue among the sampled living species. However, this morphology appears prevalent among Cretaceous and Paleocene eutherian mammals.

Nannoplankton origination events and environmental changes in the late Paleocene and early Eocene

Abstract The origination of six nannoplankton species in the late Paleocene to middle Eocene involves significant change in the entire nannofossil assemblage. The change began at the first occurrence and accelerates at the increase in abundance of the new species. The changes in the environment generally reflect the preferred ecology of the originating species. The species that originated in the late Paleocene to early Eocene (outside of the Paleocene-Eocene thermal maximum (PETM)) are generally thought to be oligotrophic taxa adapted to warm water conditions. During this long interval, temperatures were generally increasing and nutrient availability was decreasing; conditions that would have been advantageous for the originating taxa. Conversely, the species that originated in the middle Eocene are generally thought to be mesotrophs adapted to colder water conditions. These taxa were selected for during a time of generally increasing nutrient availability and decreasing temperature. Orbital stratigraphy indicates that the first occurrences of three Paleocene taxa are time transgressive by up to 400 kyr. The only event that appears to be synchronous is the abundance increase of Zygrhablithus bijugatus during the PETM. This species is thought to be mesotrophic and replaces the genus Fasciculithus at a time when nutrient availability was likely increasing rapidly.

Metatherian petrosals from the late Paleocene of Itaboraí, Brazil, and their phylogenetic implications

ABSTRACT Four Paleocene petrosal bones from the Itaboraí fissure fillings of Brazil belong to two metatherian morphotypes. They are compared with ear regions of other fossil and recent marsupials. The results of a parsimony analysis using thirty-eight characters from the petrosal and ear region are partly congruent with recent studies and confirm that characters from the ear region are highly informative for phylogenetic reconstruction. Metatheria are diagnosed by five petrosal synapomorphies: stapedial artery absent in adults; reduced, intramural prootic canal; extrabullar internal carotid artery; inferior petrosal sinus between petrosal, basisphenoid, and basioccipital; and cava supracochleare and epiptericum completely separated. The stem group of South American and Australian metatherians is composed of the Paleocene taxa Pucadelphys, one of the oldest known metatherians from South America, and Petrosal Type II from Itaboraí. Among the South American-Australian metatherians two clades are defined here. The crown clade is composed of Australian taxa plus Dromiciops (here referred to Australidelphia sensu stricto), while they plus Caenolestes form the Australidelphia sensu lato. Petrosal Type I from Itaboraí is the most basal taxon of Australidelphia sensu lato, the latter diagnosed by three significant synapomorphies: ventral part of the mastoid rounded and bulbous owing to enlargement of the fossa subarcuata; posttemporal foramen absent; and foramen for a branch of the transverse sinus present on the posterior edge of the ventral pars canalicularis.

New coccolithophorid taxa from Geulhemmerberg airshaft, lower Paleocene, The Netherlands

A previous study on calcareous nannofossils of the K/T boundary section exposed in the Geulhemmerberg cave, The Netherlands, revealed two coccosphere-rich horizons with about 35 different coccolithophorid species. In the subsequent investigation of an airshaft section above this interval, an additional horizon with numerous intact coccospheres was discovered. Among the 32 coccolithophorid species from this upper horizon, three are new: Cruciplacolithus filigranus n. sp., Prinsius scissuratus n. sp. and Prinsius simplex n. sp. The airshaft horizon is furthermore marked by a bloom of Braarudosphaera bigelowii (Gran and Braarud) Deflandre 1947, and Cyclagelosphaera rotaclypeata Bukry 1969. Due to the presence of Futyania petalosa (Ellis and Lohmann) Varol 1989 and Prinsius dimorphosus (Perch-Nielsen) Perch-Nielsen 1971 as the youngest biostratigraphical markers, this horizon can be assigned to the lower Paleocene upper Zone NP1, Biantholithus sparsus Zone. The simultaneous occurrence of several Cretaceous and Paleocene taxa can be explained either by reworking of Cretaceous material or by survivorship of Cretaceous coccolithophorid species.

Cretaceous‐Tertiary foraminiferal succession at Flaxbourne River, Marlborough, New Zealand

The stratigraphically and biostratigraphically most complete Cretaceous‐Tertiary (K‐T) boundary succession yet identified in New Zealand occurs in bathyal limestones of the Mead Hill Formation at Flaxbourne River, coastal Marlborough. It is one of three New Zealand K‐T sections with a well‐delineated “fireball” layer, containing anomalous iridium, soot particles, and fullerenes, and it contains a highly fossiliferous latest Cretaceous marl unit, not seen in other sections, immediately underlying the K‐T boundary clay. The c. 50 m thick Flaxbourne section is the only New Zealand locality known with an essentially complete sequence of earliest Paleocene foraminiferal zones. These include (K‐T boundary is zero datum): Guembelitria cretacea Zone (P0), 0.0–0.07 m; Parvularugoglobigerina eugubina Zone (P?), 0.07–0.24 m; P. eugubina‐Subbotina triloculinoides Subzone (P1a), 0.24–0.40 m; S. trilo‐culinoides‐Globanomalina compressa/Praemurica inconstans Subzone (P1b), 0.40–0.50 m; and Globanomalina compressa/Praemurica inconstans‐Praemurica uncinata Subzone (P1c), 0.50–11.5 m. Strata from 11.5 m to the highest exposed beds at c. 38 m are classified as undifferentiated Paleocene. Cretaceous planktic “survivor taxa” occur up to 0.40 m but are replaced rapidly above Zone P0 by Paleocene taxa. Latest Cretaceous strata are dominated by Heterohelix/ Globigerinelloides planktic foraminiferal assemblages, associated with sparse (typically <5%), mainly epifaunal benthic taxa and rare radiolarians. Commencing abruptly at the base of the boundary clay, maximum size of planktic and benthic specimens decreases sharply, while abundance of both radiolarian and benthic foraminifera increase about tenfold relative to planktics, features which typify the basal 0.4 m of Paleocene strata. Heterohelix/Hedbergella associations characterise planktic assemblages initially, but give way to Eoglobigerina /Chiloguembelina planktic assemblages. Epifaunal taxa dominate benthic faunas, but mfaunal forms show minor abundance peaks. Benthic abundance remains near 45% up through c. 0.3 m but then declines sharply to c. 25% at 0.40 m (highest detailed sample). Stratigraphically higher samples were studied in less detail. From 0.5 to 11.5 m they contain poor foraminiferal assemblages similar to those described above, but these are then replaced by planktic‐poor (<5% planktics) assemblages with normal‐sized benthic taxa, including Gavelinella beccariiformis and Nuttallides cretatruempyi, which occur to the top of the exposed section.

Palaeofloristic and palaeovegetational changes across the Paleocene/Eocene boundary in northern South America

A floral change occurring in northern South America at the Paleocene/Eocene boundary is analysed using palynological data. The sequence studied is an outcrop from the Venezuelan Maracaibo basin, deposited in shallow marine to coastal environments without apparent stratigraphic breaks. Significant pollen and spore counts from 237 samples were studied stratigraphically and statistically in order to compare Paleocene and Eocene palaeofloras and palaeoecological trends. The Late Paleocene/Early Eocene transition is the boundary between two floras which differ both qualitatively and quantitatively. However, the change is not sudden but stepped and gradual. Paleocene taxa seem to be of pantropical distribution, whereas Eocene assemblages are more restricted to the Neotropics. The global warming well documented elsewhere is proposed as the major cause for these changes. Trends in sporomorph diversity in this record appear to track changes in temperature documented in isotopic records from temperate regions. The extinct parent plant of Echitriporites trianguliformis is tentatively proposed to be intolerant to high temperatures, because of its absence during the Early Eocene warm phase. Palaeoecologically, although marsh and back-mangrove swamps dominated both Late Paleocene and Early Eocene assemblages, their taxonomic compositions were different, especially in the inland marsh forests. Mangrove components are scarce or absent through the whole sequence studied, suggesting the absence of these communities during the time-interval analysed. A palaeoecological subdivision into assemblage zones was not possible; instead, a recurrent pattern suggesting palynological cycles was observed. However, palynocycles could not be studied in detail due to the lack of knowledge of botanical affinities for many of the taxa involved and the apparent absence of mangrove assemblages.