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Stratigraphy, sedimentology, and paleoecology of Upper Cretaceous/Paleocene shelf-deltaic sediments of Seymour Island
Abstract
Richly fossiliferous Upper Cretaceous-Paleocene beds exposed on Seymour Island provide an excellent opportunity for a combined sedimentological- paleoecological analysis of a high-latitude shallow marine sequence. The depositional paleoenvironments of this sequence were interpreted on the basis of the stratigraphy, sedimentological analysis (including grain-size analysis) of the sediments, and auto- and synecological evaluation of the fauna present. The sequence is composed of two formations. The underlying López de Bertodano Formation (upper Campanian to Paleocene) consists of 1,190 m of gray to tan, friable, sandy, muddy siltstone, and is subdivided into 10 informal units. The lower six units (informally named the Rotularía Units) contain a depauperate macrofauna and are dominated by the annelid Rotularía. They were deposited in a shallow marine environment, near a delta or estuary. Units 7 through 10 include an abundant macrofauna (Molluscan Units). Units 7 through 9 are interpreted as progressively deeper water deposits, with Units 7 and 8 representing middle shelf facies, and Unit 9, the outer shelf facies. Macrofauna in the most offshore portion of Unit 9 is characterized by an epifaunal suspension-feeding bivalve asssemblage dominated by Pycnodonte cf. P. vesiculosa, and an increased percentage of cosmopolitan ammonites. Regressive facies appear 30 m below the inferred Cretaceous/Tertiary boundary (contact between Units 9 and 10). Unit 10 was probably deposited in a middle shelf to inner shelf environment. The overlying Sobral Formation (Paleocene) follows unconformably, and is composed of as much as 255 m of maroon, well-laminated silts at the base, followed by cleaner sandstones that become more glauconitic and crossbedded toward the top. The Sobral is not very fossiliferous and represents the filling of the basin by the progradation of a deltaic system. Units 1 and 2 are interpreted as pro-delta facies followed by clean sands of a coastal barrier (Unit 3). The uppermost Sobral (Units 4 and 5) contains the delta top facies, mostly representing the lateral accretion of distributary channels. Three unconformity-bounded depositional sequences are recognized in the studied section. The lower sequence extends from Units 1 to 9 of the López de Bertodano Formation (upper Campanian to upper Maastrichtian). The intermediate sequence is restricted to Units 9 and 10 of the same formation (upper Maastrichtian to lower Paleocene); the upper sequence is represented by the Sobral Formation (Paleocene). Uncertainties in the dating of these sequences make their comparison with worldwide sea-level fluctuations premature.
... At the top of the MG Sequence, another marked unconformity also associated with a deeply incised erosional surface separates the Danian beds of the L opez de Bertodano Formation from the Paleocene Sobral Formation (Scasso et al., 2020;Ineson et al., 2023). The L opez de Bertodano section (LBF) is constituted by c. 1000 m of marine, monotonous sandy to clayey siltstones interpreted as a transgressive shelf succession (Macellari, 1988). Macellari (1988) divided the LBF into two informal sections: the lower 'Rotularia units' section, which comprises five units, and the upper 'Molluscan units', divided into four units. ...
... The L opez de Bertodano section (LBF) is constituted by c. 1000 m of marine, monotonous sandy to clayey siltstones interpreted as a transgressive shelf succession (Macellari, 1988). Macellari (1988) divided the LBF into two informal sections: the lower 'Rotularia units' section, which comprises five units, and the upper 'Molluscan units', divided into four units. The lower section of LBF (¼ 2 to 6 Rotularia units) spans c. 600 m thick and was interpreted as deposited in shallow marine to estuarine environments (Macellari, 1988;Olivero et al., 2007Olivero et al., , 2008. ...
... Macellari (1988) divided the LBF into two informal sections: the lower 'Rotularia units' section, which comprises five units, and the upper 'Molluscan units', divided into four units. The lower section of LBF (¼ 2 to 6 Rotularia units) spans c. 600 m thick and was interpreted as deposited in shallow marine to estuarine environments (Macellari, 1988;Olivero et al., 2007Olivero et al., , 2008. The upper LBF section (¼ 7 to 10 Molluscan units) is c. 500 m thick and constitutes a monotonous succession of mudstones and glauconitic silty to very fine-grained sandstones that record an increasing abundance of molluscs, with the common occurrence of marine reptiles (Macellari, 1988;Zinsmeister & Macellari, 1988). ...
... The fine-grained Marambio Group, firstly defined by Rinaldi et al. (1978) to include the 'Older Seymour Island beds' described by Andersson (1906), has a thickness exceeding 3 km. This group comprises marine sediments that were deposited during an inversion phase of the basin and represent a prograding shelf into the Weddell Sea (Olivero 2012) and currently includes five formations: Santa Marta, Snow Hill Island, Haslum Crag, López de Bertodano, and Sobral, in successional order (Olivero et al. 1986(Olivero et al. , 2008Macellari 1988;Pirrie et al. 1997). ...
... The López de Bertodano Formation is a relatively homogeneous ~1190 m-thick unit primarily consisting of mudstones to very fine and loosely consolidated concretionary sandstones, with glauconitic layers being conspicuous in the uppermost 100 m, accumulated in a shallow transgressive shelf sequence under low-energy settings with a regressive trend recorded in the uppermost interval (Rinaldi et al. 1978;Zinsmeister 1982;Macellari 1988;Crame et al. 2004;Montes et al. 2019b;Scasso et al. 2020). It broadly crops out in the little to highly dissected wide badland which comprises the southern two-thirds of Seymour Island and also in the Spath Peninsula of the Snow Hill Island (lower part only), with minor exposures along the flanks of Sandwich Bluff at Cape Lamb, Vega Island (Macellari 1988;Crame et al. 1991;Olivero et al. 2008;Olivero 2012;Montes et al. 2019b;Roberts et al. 2022). ...
... The López de Bertodano Formation is a relatively homogeneous ~1190 m-thick unit primarily consisting of mudstones to very fine and loosely consolidated concretionary sandstones, with glauconitic layers being conspicuous in the uppermost 100 m, accumulated in a shallow transgressive shelf sequence under low-energy settings with a regressive trend recorded in the uppermost interval (Rinaldi et al. 1978;Zinsmeister 1982;Macellari 1988;Crame et al. 2004;Montes et al. 2019b;Scasso et al. 2020). It broadly crops out in the little to highly dissected wide badland which comprises the southern two-thirds of Seymour Island and also in the Spath Peninsula of the Snow Hill Island (lower part only), with minor exposures along the flanks of Sandwich Bluff at Cape Lamb, Vega Island (Macellari 1988;Crame et al. 1991;Olivero et al. 2008;Olivero 2012;Montes et al. 2019b;Roberts et al. 2022). ...
A new Xampylodon species is described based on a distinguished fossil tooth from Antarctica. The specimen comes from the uppermost level of the informal unit 9 of the Late Cretaceous (Maastrichtian) López de Bertodano Formation, 9 metres below the Cretaceous/Palaeogene boundary in Seymour Island, Antarctic Peninsula. Hexanchid sharks are relatively rare in this unit, being represented by only two species: Notidanodon pectinatus and Xampylodon dentatus. The new taxon exhibits a combination of dental features traditionally known in both Xampylodon and Notidanodon (e.g. teeth flattened labio-lingually and bearing well-developed mesial cusplets, followed by a large acrocone), but the presence of a deep root and a distally bent crown indicates a closer similarity with the former. As X. brotzeni and X. loozi, but unlike X. dentatus, the new taxon bears more than five mesial cusplets. Uniquely derived characters include the presence of a pronounced gap between mesial cusplet one and two and a pattern of non-continuous serial enlargement of the mesial cusplets. Incorporating this discovery into the spectrum of Antarctic shark diversity suggests a richness in the southern polar region at the end of the Mesozoic era that surpasses the already considerable previous assessments of diversity. ARTICLE HISTORY
... The richly fossiliferous uppermost Cretaceous -Palaeogene succession on Seymour Island, east of the Antarctic Peninsula ( Fig. 1), has long been the focus of palaeontological attention (e.g. Spath, 1953;Macellari, 1988;Zinsmeister, 1998;Stilwell et al., 2004), particularly as it represents the only exposed geological record of this important time period on the Antarctic continent. This unique situation at high southerly latitudes, and the presence of a well-exposed Cretaceous-Palaeogene (K-Pg) boundary section, have driven renewed focus on the palaeoclimatic and palaeobiological implications of this succession in the last decade (Bowman et al., 2013aKemp et al., 2014;Crame et al., 2014;Witts et al., 2015Witts et al., , 2016Whittle et al., 2019;Scasso et al., 2020;da Silva et al., 2023). ...
... The upper Snow Hill Island Formation (Haslum Crag Member of Pirrie et al., 1997, upgraded to formation status by Olivero et al., 2008) is overlain at a significant disconformity by the López de Bertodano Formation (c. 1010 m thick), a formation dominated by fine-grained, mud-rich marine shelf sediments (Macellari, 1988;Crame et al., 2004;Olivero, 2012). The latter formation is of Maastrichtianearliest Paleocene age (Macellari, 1988;Bowman et al., 2012), the Cretaceous-Palaeogene (K-Pg) boundary occurring about 50-70 m below the top of the formation within a distinctive glaucony-rich unit (Elliot et al., 1994;Bowman et al., 2012Bowman et al., , 2016. ...
... 1010 m thick), a formation dominated by fine-grained, mud-rich marine shelf sediments (Macellari, 1988;Crame et al., 2004;Olivero, 2012). The latter formation is of Maastrichtianearliest Paleocene age (Macellari, 1988;Bowman et al., 2012), the Cretaceous-Palaeogene (K-Pg) boundary occurring about 50-70 m below the top of the formation within a distinctive glaucony-rich unit (Elliot et al., 1994;Bowman et al., 2012Bowman et al., , 2016. The lower Paleocene Sobral Formation, the subject of this paper, unconformably overlies the López de Bertodano Formation (see Section 2.1) though the palynostratigraphy indicates that the erosional surface is not a significant stratigraphic hiatus on Seymour Island ). ...
... Another unconformity associated with a deeply incised erosional surface separates the uppermost Danian beds of the L opez de Bertodano Formation from the Paleocene Sobral Formation (Scasso et al. 2020). On Seymour Island, the L opez de Bertodano Formation constitutes ca 1000 m of monotonous sandy to clayey siltstones interpreted as a transgressive shelf succession (Macellari 1988). Macellari (1988) divided the L opez de Bertodano Formation into two informal units: the lower 'Rotularia units' section comprising 'unit 2' through 'unit 6'; and the upper 'Molluscan units' section divided into 'unit 7' through to 'unit 10'. ...
... On Seymour Island, the L opez de Bertodano Formation constitutes ca 1000 m of monotonous sandy to clayey siltstones interpreted as a transgressive shelf succession (Macellari 1988). Macellari (1988) divided the L opez de Bertodano Formation into two informal units: the lower 'Rotularia units' section comprising 'unit 2' through 'unit 6'; and the upper 'Molluscan units' section divided into 'unit 7' through to 'unit 10'. The lower section of the L opez de Bertodano Formation spans ca 600 m of shallow marine to estuarine deposits (Macellari 1988, Olivero et al. 2007, while the upper 500 m thick section includes concretionary mudstones and glauconitic silty to very fine-grained sandstones with abundant mollusc and marine reptile fossils (Macellari 1988, Zinsmeister & Macellari 1988. ...
... Macellari (1988) divided the L opez de Bertodano Formation into two informal units: the lower 'Rotularia units' section comprising 'unit 2' through 'unit 6'; and the upper 'Molluscan units' section divided into 'unit 7' through to 'unit 10'. The lower section of the L opez de Bertodano Formation spans ca 600 m of shallow marine to estuarine deposits (Macellari 1988, Olivero et al. 2007, while the upper 500 m thick section includes concretionary mudstones and glauconitic silty to very fine-grained sandstones with abundant mollusc and marine reptile fossils (Macellari 1988, Zinsmeister & Macellari 1988. 'Unit 7' (ca 250 m thick) and 'unit 8' (ca 100 m thick) are middle shelf facies, while the lower beds of 'unit 9' form an outer regressive shelf facies (Macellari 1988, Olivero 2012, Scasso et al. 2020. ...
... The herein-described Maorites seymourianus specimen ( Fig. 1) (Macellari, 1986(Macellari, , 1988. The Molluscan units (Units 7 to 9, Macellari, 1988;Montes et al., 2019) are a thick sequence of generally monotonous sandy siltstone that contains a rich and very abundant molluscan fauna. ...
... The herein-described Maorites seymourianus specimen ( Fig. 1) (Macellari, 1986(Macellari, , 1988. The Molluscan units (Units 7 to 9, Macellari, 1988;Montes et al., 2019) are a thick sequence of generally monotonous sandy siltstone that contains a rich and very abundant molluscan fauna. The dominant lithology is a dark, friable, bioturbated silty sandstone with minor intercalations of fine-grained glauconitic sandstone. ...
... Publicación Electrónica -2023 -Volumen 23(1): 34-48 It is inferred to have been deposited in middle-shelf to shelfslope break environments (Macellari, 1988;Olivero, 2012). ...
We report on remains of the buccal apparatus and possible associated structures for the Late Cretaceous ammonite Maorites
seymourianus from the López de Bertodano Formation (Antarctic Peninsula). This is the first description of these structures for the family
Kossmaticeratidae. Further, we discuss the most likely taphonomic processes taking place that allowed this exceptional preservation.
Reflectance Transformation Imaging (RTI) technique was employed in this work to better document the faint structures. We briefly provide a
review of this method and its potential importance for paleontological studies because it seems that this powerful technique has been largely
overlooked by paleontologists.
... Sedimentological studies have been carried out by Ineson et al. (1986), Macellari (1988), Scasso et al. (1991), Pirrie et al. (1997a), Crame et al. (2006), Olivero et al. (2008), and Olivero (2012), among others. Furthermore, there are several contributions about fossil megafauna (mainly ammonites and vertebrates, Olivero, 2012;Reguero et al., 2022 and references therein) and, to a lesser extent, micropaleontological and palynological assemblages (Dettman & Thompson, 1987;Keating, 1992;Smith, 1992;Sumner, 1992;Wood & Askin, 1992;Scasso et al., 2020;Silva et al., 2023; for further references see Amenábar et al., 2014) as well as palynofacies (Rodríguez Brizuela et al., 2007;Carvalho et al., 2013). ...
Palynological analysis of Upper Cretaceous marine rocks from the Rabot and Snow Hill Island formations, James Ross Basin, northeastern Antarctic Peninsula, has revealed the record of a previously undescribed dinoflagellate cyst species, previously assigned to Oligosphaeridium sp. A. Here, we provide a formal description of this new species, which we name Stiphrosphaeridium sobralii sp. nov. and we add some features to the description of the genus Stiphrosphaeridium. The new species is found in Campanian strata, which are calibrated with magnetostratigraphic data. It is considered an important Late Cretaceous biostratigraphic marker commonly recorded in offshore environments of Antarctica.
... (1) Materials and methods Fossil shells were collected from the shallowly buried L opez de Bertodano Formation (69-66 Ma, Seymour Island, Antarctica) (Macellari, 1988). For this study, 117 wellpreserved shells were screened for diagenetic alteration using X-ray diffraction (XRD), scanning electron microscopy (SEM), and conservative trace element thresholds [see Petersen, Dutton & Lohmann (2016) for detailed description of methodologies]. ...
Traditional bulk stable isotope (δ18O and δ13C) and clumped isotope (Δ47) records from bivalve shells provide invaluable histories of Earth's local and global climate change. However, biologically driven isotopic fractionations (BioDIFs) can overprint primary environmental signals in the shell. Here, we explore how conventional measurements of δ18O, δ13C, and Δ47 in bivalve shells can be re-interpreted to investigate these physiological processes deliberately. Using intrashell Δ47 and δ18O alignment as a proxy for equilibrium state, we separately examine fractionations and/or disequilibrium occurring in the two major stages of the biomineralisation process: the secretion of the extrapallial fluid (EPF) and the precipitation of shell material from the EPF. We measured δ18O, δ13C, and Δ47 in fossil shells representing five genera (Lahillia, Dozyia, Eselaevitrigonia, Nordenskjoldia, and Cucullaea) from the Maastrichtian age [66–69 million years ago (Ma)] López de Bertodano Formation on Seymour Island, Antarctica. Material was sampled from both the outer and inner shell layers (OSL and ISL, respectively), which precipitate from separate EPF reservoirs. We find consistent δ18O values across the five taxa, indicating that the composition of the OSL can be a reliable palaeoclimate proxy. However, relative to the OSL baseline, ISLs of all taxa show BioDIFs in one or more isotopic parameters. We discuss/hypothesise potential origins of these BioDIFs by synthesising isotope systematics with the physiological processes underlying shell biomineralisation. We propose a generalised analytical and interpretive framework that maximises the amount of palaeoenvironmental and palaeobiological information that can be derived from the isotopic composition of fossil shell material, even in the presence of previously confounding ‘vital effects’. Applying this framework in deep time can expand the utility of δ18O, δ13C, and Δ47 measurements from proxies of past environments to proxies for certain biomineralisation strategies across space, time, and phylogeny among Bivalvia and other calcifying organisms.
... The first stratigraphic studies on Seymour Island were carried out during the Swedish polar expedition [1901][1902][1903] under the command of Dr. Otto Nordenskjöld (Andersson, Publicación Electrónica -2023-Volumen 23(1): 18-33 1906. After that, various contributions to the subject completed the modern stratigraphic scheme of the outcropping sections on the island, until reaching the current model (e.g., Bibby, 1966;Elliot et al., 1975;Rinaldi et al., 1978;Feldman & Woodbume, 1988;Macellari, 1988;Sadler, 1988). In recent years there has been a constant review of the general geology of the sequences exposed on the island, with several significant contributions (e.g., Marenssi & Elliot, 1992;Marenssi & Santillana, 1994;Marenssi, 1995;Marenssi et al., 1998Olivero et al., 2008;Montes et al., 2019). ...
Trace elements, particularly rare earth elements (REE), are widely used as proxies to reconstruct paleoenvironmental and taphonomic conditions. We traced these elements in fossil penguin bones collected along the Paleogene sequence exposed in Seymour Island (=Isla Marambio) to test them as indicators of the tectonic changes to which this region was exposed. The results indicated the contents of REE in thirteen samples of the analyzed bone tissues. The negative europium anomaly in the samples from Bartonian and Priabonian beds reflects regional events. This signal coincides in time with the opening of the Drake Passage, and with the tectonic changes that occurred between the end of the Eocene and the beginning of the Oligocene, between the western margin of South America and the Antarctic Peninsula.
The Cretaceous period is particularly well represented by a thick sequence of clastic sedimentary rocks exposed in the Antarctic Peninsula region of western Antarctica. This was an active margin throughout the Late Mesozoic and in total some 7km+ of Cretaceous sedimentary rocks accumulated in a series of fore-, intra-, and back-arc basins. The Fossil Bluff Group of eastern Alexander Island can be traced from the Jurassic - Cretaceous boundary into the Upper Albian and represents a broad-scale shallowing-upwards sequence from deep marine to a prominent Upper Albian fluvial interval in which high density forests developed at a palaeolatitude of 75°S. The Cretaceous sequence exposed in the James Ross Island group continues right through the Upper Cretaceous to the K–Pg boundary. The Campanian - Maastrichtian succession in particular is over 2km in total thickness and richly fossiliferous. The improved Cretaceous stratigraphy of Antarctica is an invaluable terrestrial record of climatic change at a high palaeolatitude. This includes a gradual increase in temperature to the Cretaceous Thermal Maximum, and then a decline to the K–Pg boundary. There may be no simple link between these palaeotemperature changes and Cretaceous patterns of biotic radiation and extinction.
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