Evaluating macrobenthic response to the Cretaceous–Palaeogene event: A high-resolution ichnological approach at the Agost section (SE Spain)

Accepted Manuscript Evaluating macrobenthic response to the Cretaceous–Palaeogene event: A highresolution ichnological approach at the Agost section (SE Spain) Weronika Łaska, Francisco J. Rodríguez-Tovar, Alfred Uchman PII:

S0195-6671(16)30254-3

DOI:

10.1016/j.cretres.2016.10.003

Reference:

YCRES 3461

To appear in:

Cretaceous Research

Received Date: 7 July 2016 Revised Date:

23 September 2016

Accepted Date: 6 October 2016

Please cite this article as: Łaska, W., Rodríguez-Tovar, F.J., Uchman, A., Evaluating macrobenthic response to the Cretaceous–Palaeogene event: A high-resolution ichnological approach at the Agost section (SE Spain), Cretaceous Research (2016), doi: 10.1016/j.cretres.2016.10.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Evaluating macrobenthic response to the Cretaceous-Palaeogene event: A high-

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resolution ichnological approach at the Agost section (SE Spain)

3 Weronika Łaska1, Francisco J. Rodríguez-Tovar2, Alfred Uchman1

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Poland; e-mail: [email protected], [email protected]

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Granada, 18002 Granada, Spain; e-mail: [email protected]

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Institute of Geological Sciences, Jagiellonian University, Oleandry 2a, 30-063 Kraków,

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Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de

Abstract

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The Agost section (Betic Cordillera, Alicante Province, south-eastern Spain) is one of only a

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few places in the world where complete sedimentary successions across the Cretaceous-

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Palaeogene (K-Pg) boundary are available. Agost enables a high-resolution ichnological

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analysis illustrating the influence of environmental perturbations on burrowing organisms

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before, during and after the K-Pg boundary event. The uppermost Maastrichtian calcareous

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marlstones and marly limestones of the Raspay Formation (Plummerita hantkeninoides

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Biozone), beside the light-filled Maastrichtian trace fossils, contain dark-coloured early

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Danian trace fossils including Chondrites targionii, Chondrites ?affinis, Chondrites isp.,

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Pilichnus isp., Planolites isp., ?Teichichnus isp., Thalassinoides isp., Trichichnus linearis,

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Trichichnus isp., and Zoophycos isp. The ichnotaxonomic composition of the late

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Maastrichtian and early Danian trace fossil association does not reveal major differences,

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indicating no significant influence on composition of their trace makers immediately after the

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K-Pg event. The main factors that most likely promoted survivorship of the trace makers were

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their feeding strategy (deposit feeders, microbe gardeners) and an increased delivery of

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organic matter to the seafloor due to the high mortality during the K-Pg boundary event.

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ACCEPTED MANUSCRIPT However, the differences in the size of trace fossils are noted: They are distinctly smaller in

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the dark boundary layer (Guembelitria cretacea Biozone) than in the underlying uppermost

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Maastrichtian calcareous marlstones. This is an example of the Lilliput Effect. The dwarfed

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ichnoassociation was produced during and shortly after sedimentation of the dark boundary

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layer pointing to a delayed reaction of the burrowing organisms to the K-Pg boundary event

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compared to other groups of organisms. The dwarfing might be caused by environmental

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stress resulting from lower food supply due to collapse of primary production in the later

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phases of the K-Pg boundary event.

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Keywords: K-Pg boundary, trace fossils, palaeoecology, Lilliput Effect, Agost, Spain.

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1. Introduction

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The Agost section (SE Spain) is one of the most important Cretaceous-Palaeogene (KPg) boundary interval sections worldwide, because of a very expanded and continuous

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sedimentary record across the boundary. This section has been profusely studied, including

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variable aspects, such as magnetostratigraphy (Groot et al., 1989), chronostratigraphy

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(MacLeod and Keller, 1991), mineralogy and geochemistry (e.g., Smit, 1990; Martínez-Ruiz,

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1994; Martínez-Ruiz et al., 1992, 1997, 1999), micropaleontology (e.g., Alegret et al., 2003;

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Arenillas et al., 2004; Canudo et al., 1991; Molina et al., 1996, 1998, 2005; Pardo et al.,

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1996). Recently, the study of trace fossils (Rodríguez-Tovar and Uchman, 2004a, b) and the

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integration of ichnological with geochemical and isotopic analyses (Rodríguez-Tovar, 2005;

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Rodríguez-Tovar et al., 2004; Sosa-Montes de Oca et al., 2013, 2016) has revealed especially

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useful in the interpretation of the K-Pg boundary in the Agost section. Since the first

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ACCEPTED MANUSCRIPT ichnological studies of the K-Pg boundary in Denmark (Ekdale and Bromley, 1984), Alabama

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(Savrda, 1993), and NE Mexico (Ekdale and Stinnesbeck, 1998), and later studies at Agost,

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Caravaca, and Sopelana in Spain (Rodríguez-Tovar and Uchman, 2006, 2008; Rodríguez-

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Tovar et al., 2010, 2011), Bidart in France (Alegret et al., 2015; Rodríguez-Tovar et al., 2010,

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2011), Gubbio in Italy (Monaco et al., 2015) and El Kef in Tunisia (Rodríguez-Tovar et al.,

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2016), new challenges have appeared, such as the selectivity of some palaeoenvironmental

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changes, the variable response of the biotic communities, or the timing of recovery after the

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K-Pg boundary event (see Labandeira et al., in press, for a recent review). Therefore, new

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high-resolution studies in the best-preserved sections worldwide must be conducted, focusing

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on the aspects that have been highlighted. The aim of this paper is a revised high-resolution

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ichnological analysis of the Agost section, in order to improve interpretation of some aspects

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of the K-Pg boundary event. For this purpose, the boundary interval has been examined

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centimetre by centimetre in order to record lithology and ichnological features, and to collect

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representative samples. As the result, the section has received a better characterization of trace

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fossils, with discoveries of new ichnotaxa, and a more precise determination of ichnological

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changes through the section, including detailed observations of the dark boundary layer.

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2. Geological setting

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The section crops out in a cut along the Agost-Castalla road (CV-827), about 1 km north of

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the town Agost in the Alicante Province, south-eastern Spain (N 38°27.147′, W 0°38.197′;

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Fig. 1). The Agost section belongs to the Prebetic, which corresponds to the outermost and

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northernmost part of the Betic Cordillera. The Prebetic is composed of Mesozoic and

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resulted from the breakup of Pangaea and divergence of Africa and Europe since the Triassic.

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The Agost section is located in the Internal Prebetic subdomain, which represents the

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relatively distal palaeogeographic part of the epicontinental shelf system developed on the

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South Iberian palaeomargin during the Mesozoic. The Agost section shows no hiatus,

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condensed interval, or erosional surface (Arenillas et al., 2004; MacLeod and Keller, 1991;

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Molina et al., 2005; Pardo et al., 1996).

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The uppermost Maastrichtian deposits belong the uppermost part of the Raspay Formation

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(Chacón and Martín-Chivelet, 2005), which consists of medium and thick beds of grey

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calcareous marlstones and marlstones (Figs. 2; 3A) containing planktic and benthic

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foraminifera, ostracods and scarce fragments of echinoderms.

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These beds are overlain by a 4–10 cm-thick layer of carbonate-poor, dark olive calcareous

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claystones (the dark boundary layer; CaCO3 content 25%) with a 2 mm-thick rusty-red layer

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(the “rusty layer”) at its base that marks the K-Pg boundary (Fig. 3A–C). The dark boundary

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layer is also called the “dark clay boundary layer”, “boundary layer” or the “K-Pg boundary

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layer” in previous papers (e.g. Alegret et al., 2015; Kędzierski et al., 2011; Rodríguez-Tovar

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et al., 2011; Sosa-Montes de Oca et al., 2016). The rusty layer contains Kfs and Fe-oxide

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sphaerules and enrichment of iridium and other platinum-group elements and it is interpreted

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as a distal ejecta layer of the Chicxulub impact (e.g., Martínez-Ruiz, 1994; Martínez-Ruiz et

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al., 1992, 1997, 1999). The carbonate content increases up the dark boundary layer, which

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passes upward into cream-coloured calcareous marlstones (CaCO3 content 70%) followed by

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rose marly limestones (CaCO3 content 85%). The rose marly limestones constitute the top of

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the studied interval. The lowermost Danian deposits belong to the lowermost part of the Agost

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Formation (Chacón and Martín-Chivelet, 2005).

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According to the benthic foraminiferal assemblages, the deposition of the sedimentary interval studied took place in middle bathyal depths (600–1000 m; Alegret et al., 2003;

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Molina et al., 2005). A detailed biostratigraphy of the Upper Cretaceous and the Lower

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Palaeogene transition in the section analyzed is based on planktic foraminifera (Alegret et al.,

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2003; Arenillas et al., 2004; Molina et al., 2005). The Plummerita hantkeninoides Subzone

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(Pardo et al., 1996) corresponds to the uppermost 3.45 m-thick portion of the Maastrichtian

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deposits. Within the lower Danian, the Guembelitria cretacea Biozone (Canudo et al., 1991;

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Molina et al., 1996, 2004), correlated with the P0 Zone (Pardo et al., 1996), is differentiated

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from the first 14 cm of the lowest Danian, including the dark boundary layer and the

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overlying ~5 cm thick layer of light calcareous marlstones. This biozone was subdivided into

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the Hedbergella holmdelensis and the Parvularugoglobigerina longiapertura subzones by

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Arenillas et al. (2004). Above the Guembelitria cretacea Biozone, the

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Parvularugoglobigerina eugubina Biozone (Molina et al., 1996), which is equivalent to the

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P1a p.p. [P1a(1)] (Pardo et al., 1996) or to the Parvularugoglobigerina longiapertura p.p.

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biozones (Canudo et al., 1991), corresponds to the 60–65 cm-thick interval above the lower

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Guembelitria cretacea Biozone.

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3. Materials and methods

The studied exposure was trenched and the continuous sampling was performed to

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provide the highest resolution studies. The overlapping samples of rocks vertical to bedding

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100 cm below the K-Pg boundary to 30 cm above the boundary were collected. In the

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laboratory samples were processed to produce above 80 slabs which were impregnated with

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improving visibility of barely noticeable bioturbation structures. The polished slabs were

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scanned using flatbed scanner Epson Perfection V 350 Photo. Digital image treatment was

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applied to enhance visibility of bioturbation structures and facilitate the ichnofabric analysis.

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Three thin sections were made to investigate Thalassinoides and Teichichnus infilling which

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were observed and photographed using a Nikon Eclipse 50i polarizing microscope equipped

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with a Nikon DS-Fi1 digital camera. A scanning electron microscope (FE-SEM, Hitachi

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S4700) with field emission and EDS analysis was used to compound and morphological

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analysis of Zoophycos ferruginous marginal tube infilling. The samples are housed at the

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Institute of Geological Science, Jagiellonian University, and at the Department of Stratigraphy

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and Palaeontology, University of Granada.

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4. Results

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4.1. Trace fossils

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Previous ichnological analyses in the Agost sections revealed a relatively abundant

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and conspicuously dark trace fossil assemblage of the Danian occurring within the light

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Maastrichtian sediments. It consists of Alcyonidiopsis longobardiae, Chondrites ?targionii,

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Diplocraterion ?parallelum, Planolites isp., Thalassinoides isp., and Zoophycos isp.

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(Rodríguez-Tovar & Uchman, 2004a, b). The high-resolution ichnological analysis herein

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confirms the presence of the previously recognized Chondrites targionii, Planolites isp.,

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Thalassinoides isp., and Zoophycos isp., but also allows recognition of new ichnotaxa

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including Chondrites ?affinis, Chondrites isp., cf. Pilichnus isp., Planolites isp. A, Planolites

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isp. B, ?Teichichnus isp., Trichichnus linearis, and cf. Trichichnus isp.

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Chondrites targionii (Brongniart, 1828) (Fig. 4A–H) is a system of tree-like branching horizontal and subhorizontal tunnels that ramify downward (1st, 2nd, and rarely 3rd order of

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branching) at acute angles (15–60°). The tunnels are elliptical cross-sections, 1–2 mm wide,

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up to 80 mm long. An alternate branching pattern is the most common; opposite branching is

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rare. The branches are straight or curved near the master tunnel. In the distal part of some

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tunnels, arched branches radiate from a single point somewhat resembling an umbel (Fig. 4C–

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G). The termination of some branches is pointed in a lanceolate (leaflike) shape (Fig. 4D).

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Cross sections of branches are visible as groups of dark, fusiform to elliptical dots. Densely

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packed tunnels of this trace fossil may occur in fillings of Thalassinoides isp. (Fig. 4E, F) (the

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Bandchondriten morphology sensu Ehrenberg, 1942; see Uchman, 2007). The preferential

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burrowing inside Thalassinoides may be caused by lower sediment consistency and higher

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organic matter content within the burrow infill than in the host sediment (Uchman and

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Wetzel, 1999).

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Chondrites ?affinis Sternberg, 1833 (Fig. 4I) consists of fragmentarily preserved,

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straight, flattened, branched tunnels at least 56 mm long and 4 mm wide. The branch runs

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under acute angle (45°) in respect to the master tunnel. The filling is darker than the host rock. Chondrites isp. (Fig. 4J) consists of straight, flattened tunnels (1 mm wide and 9–12

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mm long) with first and second-order branches that ramify at acute angles (10–45°) from the

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same points located approximately 1 mm apart and show pointed terminations. The branches

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run in opposite directions more or less perpendicularly to the master tunnel. Some of them

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gently meander in their distal part. The perpendicular arrangement of branches resembles

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Chondrites patulus Fisher-Ooster, 1858.

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Chondrites has commonly been interpreted as a fodinichnion of an unknown deposit

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feeder (e.g., Osgood, 1970), but more recently it has been considered as a chemichnion

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(Bromley, 1996) whose trace maker feeds on chemosymbiotic microbes at the aerobic-

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anaerobic interface (Seilacher, 1990). The Chondrites trace maker is not precisely identified

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but it is considered to be a low-oxygen-tolerant organism (Bromley & Ekdale, 1984).

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Cf. Pilichnus isp. (Fig. 5I) is a horizontal, straight, sinusoidal or irregularly winding, probably branched, filamentous tunnel, 0.1–0.4 mm in diameter, and filled with darker

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material than the surrounding rock. It is observed on parting surfaces. Individual cylinders

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may cross one another. The specimens differ from Pilichnus dichotomus Uchman, 1999 in the

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absence of the distinct, dichotomous branches which are diagnostic of this ichnogenus.

Pilichnus is a fodinichnion produced by vermiform organisms (Buatois and Mángano,

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2012). Recent burrows resembling Pilichnus are produced by the polychaetes Heteromastus

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filiformis (Claparède) and Capitella cf. aciculata (Hartman) in marine deposits (Hertweck et

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al., 2007).

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Planolites isp. A (Fig. 5B) is a horizontal or oblique, straight or gently curved,

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cylindrical, smooth tube, elliptical in cross-section, preserved as a full-relief exichnion with a

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fairly constant width (2–4 mm) and filled with dark clayey material.

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Planolites isp. B (Fig. 5A) is a horizontal, gently tortuous cylindrical tube, elliptical in cross-section, 3–4.5 mm wide, filled with darker material than the host rock and traced for a

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maximum distance of 56 mm. Its surface is slightly wavy, locally smooth.

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Planolites is an actively filled fodinichnion produced by eurybathic vagile “worm”like deposit-feeders (e.g., Fillion and Pickerill, 1990; Keighley and Pickerill, 1995; Osgood,

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1970; Pemberton and Frey, 1982). In contrast, Locklair and Savrda (1998) interpreted

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Planolites as a previously open burrow that was passively filled with overlying sediment.

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?Teichichnus isp. (Fig. 5C, D) was observed only on a polished surface of calcareous

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marlstone as a vertical series of parallel, retrusive, U-shaped spreite laminae, which are an

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only part of a larger structure. The spreites are 3–9 mm wide. The entire structure is 13 mm

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high. Teichichnus is an equilibrium and feeding structure (e.g., Bromley, 1996; Droser et al.,

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2002), produced by “worms” or arthropods (Pickerill et al., 1984).

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Thalassinoides isp. (Fig. 6) is a horizontal, rarely slightly oblique, mostly straight or slightly curved, occasionally strongly curved, flattened tunnel with common Y- and T-shaped

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branches. The tunnel width changes from 8 to 26 mm even within burrows. Enlargements at

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branching points are common (Fig 6C). In cross section, Thalassinoides is visible as oval or

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round spots (Fig. 6B, D). Margins of the tunnel are smooth, locally uneven and undulating

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(Fig 6B). The distance between branch points is 18–170 mm, mainly approximately 50 mm.

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The longest observed length of tunnels is 250 mm. Colour and texture of Thalassinoides differ

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from the surrounding rock, and may be rusty brown, locally beige. It is composed of a poorly

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sorted mixture of clay minerals and micrite with foraminiferal tests, ostracods, ?faecal pellets

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(<1 mm), quartz (<1 mm) and glauconite grains (<1 mm). Fairly to well-preserved tests of the

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Maastrichtian planktic foraminifera such as Rosita contusa (Cushman, 1926),

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Racemiguembelina fructicosa (Egger, 1900), Globotruncanita stuarti (de Lapparent, 1918)

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and Globigerinelloides sp. (Cushman and Ten Dam, 1948) (Fig. 6E, F) are the most abundant

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bioclasts. They may be occasionally corroded, crushed, partly micritized or ?pyritized.

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Ostracods are scarce and poorly preserved. The pellets are spherical and ovoid micritic grains.

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The bioclasts may be locally concentrated. Occasional accumulations, elliptical in cross

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section, composed of densely packed foraminiferal tests and subordinate quartz grains, could

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be bromalites (?coprolite, ?regurgitalite) (Fig. 6F). In places, the longer axes of the bioclasts,

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especially foraminiferal tests, are preferentially orientated parallel to the tunnel margins

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forming semi-circular smears (Fig. 6E).

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Thalassinoides is interpreted mostly as a fodinichnion-domichnion (e.g., Bromley, 1996) produced mainly by decapod crustaceans, especially the callianassid or thalassinidean

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shrimps (e.g., Bromley and Frey, 1974), which have a wide behavioural plasticity.

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Thalassinoides occurs in several marine facies (e.g., Monaco et al., 2007).

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Trichichnus linearis Frey, 1970 (Fig. 5F) is a straight, filamentous oblique cylinder in marlstones, 0.4 mm in diameter, up to 39 mm long, filled with material similar to the

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surrounding host sediment. The infilling material displays slight differences in grain packing

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and contains dispersed dark and rusty iron compounds.

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Cf. Trichichnus isp. (Fig. 5E, G, H) is horizontal, straight or almost straight, smooth

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cylinder, circular or elliptical in cross-section, 0.1–3 mm wide, up to 64 mm long, with rare

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Y-shaped branches. It is filled with ferruginous material with closely packed framboidal

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aggregates and surrounded by a ferruginous halo. The framboids are circular, 15–60 µm in

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diameter. In some specimens, the internal structure of the framboidal aggregates has been

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obliterated by partial recrystallization. Chemical analysis under SEM with EDS showed that

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the framboidal aggregates consist of iron oxides (?magnetite, ?hematite), which are probably

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pseudomorphoses after framboidal pyrite.

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Trichichnus occurs in both shallow- and deep-marine fine-grained deposits (Frey, 1970; Wetzel, 1983). Trichichnus is produced by opportunistics deeply burrowing organisms

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with higher tolerance for dysoxia than Chondrites (Kotlarczyk and Uchman, 2012; McBride

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and Picard, 1991; Uchman, 1995). The trace maker was originally considered as a “worm”-

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like or crustacean meiofaunal organism (Frey, 1970) and later was referred to

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chemosymbiotic feeding (Uchman, 1999), but Kędzierski et al. (2014) reinterpreted

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Trichichnus as fossilized filaments of sulphur bacteria living in the transition from anoxic to

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dysoxic sediments, closely resembling the extant Thioploca.

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Zoophycos isp. (Figs. 3D; 7) is a helicoidal spreite structure, 16–35 cm high,

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andcomposed of whorls and lobes (Fig. 7E), whose width progressively increases downward.

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Margins of the basal whorls protrude alongside as long, horizontal, or subhorizontal, tongue-

ACCEPTED MANUSCRIPT like lobes (Fig. 7A), that are 4.4–16.5 cm long, 2.2–6.2 cm wide, and 1–2 mm thick. The

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lobes are generally straight, occasionally with irregularly tortuous margins. The top of the

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whorl is prolonged in a vertical shaft, which downwardly forms a helical spiral resembling the

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Archimedes screw, whose tightly coiled, contiguous whorls screw into the host marlstones.

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The lobes show spreite structure composed of alternating light and dark lamellae, 0.25 to 1.5

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mm wide, which are less visible in the whorls. The lamellae are located 0.2–1 mm apart and

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show a crescentic course, with curvature mostly concordant to the distal part of the lobes but

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in some parts, they are slightly winding and discontinuous. The lobes are encircled by a

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marginal tunnel which is 1–6 mm wide and has a greyish-brown, clayey or ferruginous filling

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(Fig. 7A). The ferruginous filling contains densely packed microspheres that are 100–500 µm

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in diameter (Fig. 7B–D). SEM studies with EDS analysis reveal that they consist of iron

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hydroxides (?goethite). The spheres are probably pseudomorphic after framboidal pyrite.

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Pyrite framboids within the marginal tube of Zoophycos were described for the first time by

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Gong et al. (2007) and later interpreted as pyritized microorganismal colonies cultivated by

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the Zoophycos producer (Zhang et al., 2015). However, pyrite is also common in other trace

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fossils, not only within Zoophycos (Gallego-Torres et al. 2015; Reolid, 2014).

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Zoophycos displays several morphological varieties, probably constructed in different

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ways by different organisms (e.g., Monaco et al., 2016; Oliviero, 2007), which may include

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sipunculids (Wetzel and Werner, 1980), echiurans (Kotake, 1992) or polychaetes (Knaust,

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2009). Various ethologic models of Zoophycos have been proposed, including the strip-mine

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model, detritus-feeding model (Kotake, 1991), gardening model, refuse-dump model and

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cache model (Bromley, 1991). Since the Mesozoic, Zoophycos has shown a tendency to occur

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in deeper environments than in the Palaeozoic, from below the shelf to abyssal depths (Zhang

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et al., 2015).

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4.2. Distribution of trace fossils and bioturbation structures

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In the highly bioturbated (ichnofabric index 6 of Droser and Bottjer, 1986) upper Maastrichtian calcareous marlstones and marlstones belonging to the Plummerita

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hantkeninoides Biozones two trace fossil generations differing in colour of filling (light and

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overprinting dark) have been differentiated. Light-filled (grey to creamy) trace fossils and

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diffuse bioturbation structures are interpreted as Maastrichtian in age, whilst the dark (dark

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grey) trace fossil assemblage is dated as the earliest Danian (Rodríguez-Tovar et al., 2004,

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2006). The light bioturbation structures are indistinct because of their diffuse margins and

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similar colours to the host rock. The light trace fossils include Zoophycos, Chondrites,

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Thalassinoides and ?Planolites (Fig. 3M). Therefore, we focused the analysis in the dark-

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filled trace fossils.

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The dark trace fossils strongly contrast with surrounding host marlstones. They

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include all the above described ichnotaxa, such as Chondrites ?affinis, Chondrites targionii,

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Chondrites isp., cf. Pilichnus isp., Planolites isp. A, Planolites isp. B, ?Teichichnus isp.,

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Thalassinoides isp., and Zoophycos isp. (Fig. 2). The dark trace fossils crosscut the rusty layer

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(well seen in Zoophycos, Fig. 3B) and plunge below it into the Maastrichtian marlstones as

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much as 45 cm (Fig. 2); their colonization surface was above the K-Pg boundary. The dark

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infilling material derives from the dark boundary layer as evidenced by geochemical studies

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(Rodríguez-Tovar et al., 2004, 2006), as well as from the rusty layer as revealed by the

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presence of ferruginous spherules in the infilling of Thalassinoides (Rodríguez-Tovar, 2005).

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In the polished slab made through the K-Pg boundary, the rusty layer at the top of the

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Maastrichtian marlstones overlain by the dark boundary layer is disrupted by trace fossils

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whose filling definitely supports that this material comes from both the rusty layer and the

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ACCEPTED MANUSCRIPT dark boundary layer (Fig. 3C). The same material fills unidentifiable bioturbation structures

299

found just underneath the K-Pg boundary. The dark Planolites crosscuts the rusty layer,

300

occurring commonly within the uppermost centimetre of the Maastrichtian marlstones, and

301

less commonly extending downward to 14 cm (doubtful occurrences at 25 cm) below the

302

rusty layer. Well-developed, horizontal and oblique branched tunnels of dark Thalassinoides

303

(Fig. 6A), coming from the lower Danian materials, range from the rusty layer to 8 cm below

304

the boundary. The deepest tunnels were recorded 15 cm below the boundary. One specimen

305

of dark ?Teichichnus (Fig. 5C, D) and several specimens of Pilichnus (Fig. 5I) were found

306

between 3 to 4 cm below the rusty layer. The dark Zoophycos and Chondrites are abundant

307

and have the most extended record. The dark Zoophycos crosscuts the rusty layer and extends

308

downward as much as 35 cm below (Fig. 3B). Chondrites shows a continuous distribution

309

from the rusty layer as much as 40 cm below it being most abundant in the interval from 10 to

310

20 cm below the boundary. Chondrites is often present within fillings of light (Maastrichtian)

311

and dark (Danian) Thalassinoides (Fig. 3H, K–M). A crisp Trichichnus linearis is noted 35

312

cm below the boundary, while Trichichnus isp. extends downward to 45 cm below the

313

boundary, occasionally cutting dark Zoophycos and Chondrites. Therefore, it is regarded as a

314

Danian trace.

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The light Maastrichtian bioturbation structures are crosscut by dark Danian bioturbation structures (Fig. 3L, M). Within the dark (Danian) trace fossil assemblage,

317

Chondrites crosscuts Thalassinoides (Figs. 3K; 4C), Planolites and Zoophycos. Zoophycos

318

crosscuts Thalassinoides, while Trichichnus crosscuts Zoophycos and Chondrites. Any

319

crosscutting between Thalassinoides and Planolites has been observed.

320

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The dark boundary layer (Guembelitria cretacea Biozone, Agost Formation according

321

to Chacón and Martín-Chivelet, 2005) is represented by fully bioturbated, olive-grey

322

calcareous claystones (ichnofabric index 6 of Droser and Bottjer, 1986). Within the mottled

ACCEPTED MANUSCRIPT background, relatively distinct bioturbation structures with diffuse margins are marked by

324

differences in colours and colour saturation (Fig. 3F–J). Based on their colours, three

325

generations of ichnofabrics have been distinguished. The first generation consists of

326

unidentifiable bioturbation structures and Chondrites, Planolites and Thalassinoides filled

327

with olive-grey material slightly darker than the surrounding rock (Fig. 3F, H). Planolites and

328

Thalassinoides are observed mainly in cross sections, which are elliptical in outline. Their

329

fillings are often reworked with dark-grey Chondrites observed as concentrations of fusiform

330

to elliptical dots (Fig. 3H). The second generation consists of bioturbation structures filled

331

with creamy material that most probably derives from the creamy calcareous marlstones

332

overlying the dark boundary layer. These light-coloured bioturbation structures are seen as

333

dots, smears and deformed rings (Fig. 3I). Moreover, similarly filled light Zoophycos (Fig.

334

3J), and ?Planolites are recognized. The third generation consists of dark grey, unidentifiable

335

bioturbation structures and similarly filled Zoophycos, Chondrites, and ?Planolites (Fig. 3F–

336

I). Zoophycos is slightly plastically deformed (Fig. 3G), suggesting a low consistency of the

337

burrowed sediments. The layer from which the filling material derives has not been

338

recognized within the analysed section. The dark-coloured bioturbation structures crosscut the

339

preexisting olive and creamy bioturbation structures of the first and second generations (Fig.

340

3G, I).

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According to the above observations, trace fossils located in the dark boundary layer

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belong to three generations, but show a common feature: All are distinctly smaller in

343

comparison with the late Maastrichtian light trace fossils and the early Danian dark trace

344

fossils dug into the Maastrichtian calcareous marlstones (Fig. 8).

345

Above the dark boundary layer, the creamy calcareous marlstones (Guembelitria

346

cretacea Biozone) are totally bioturbated (Fig. 2). Aside from unrecognizable olive-grey

347

bioturbation structures, identifiable Chondrites, ?Planolites and Thalassinoides are present

ACCEPTED MANUSCRIPT (Fig. 3E). The overlying rose marly limestones are also totally bioturbated. In the rose mottled

349

background, bioturbation structures are visible as dots, elliptical smears, some with serrate

350

outlines. Moreover, ?Planolites shows a continuous record and Zoophycos is locally observed

351

(Fig. 3D). Both ?Planolites and Zoophycos are filled with material slightly lighter or darker

352

than the surrounding rock.

353 354

5. Discussion

355 356

5.1. The Maastrichtian ichnoassemblage

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With respect to the ichnoassemblage produced during the latest Maastrichtian, as can be

359

deduced from the crosscutting relationships, the Zoophycos and Chondrites producers

360

probably occupied the deepest tiers, whilst the Thalassinoides and ?Planolites trace makers

361

inhabited shallower tiers, similarly to trace fossil assemblages from the Upper Cretaceous

362

marls of Denmark (Ekdale and Bromley, 1991). The coexistence of ichnotaxa representing

363

different tiers at the same level suggests continuous or nearly continuous long-term

364

colonization of the substrate by the same community of bioturbators and upward shift of tiers

365

due to normal aggradation of sediment (Taylor et al., 2003). This is evidence of relatively

366

stable depositional environment during the late Maastrichtian, for at least the 50 ka calculated

367

using sedimentation rate estimated by Groot et al. (1989).

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5.2. The early Danian ichnoassemblage

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The early Danian dark trace fossils from the Agost section were previously analysed by

371

Rodríguez-Tovar and Uchman (2004a, b), focusing on the dark traces within the uppermost

372

20 cm of the Maastrichtian marlstones. Four tiers were distinguished. Now, the new high-

ACCEPTED MANUSCRIPT resolution ichnological analysis of the K-Pg boundary interval, embracing an interval 100 cm

374

below and 30 cm above the K-Pg boundary, shows the presence of dark, early Danian trace

375

fossils as low as 45 cm below the K-Pg boundary (Fig. 2). It has allowed the improvement of

376

the vertical distribution ranges of particular ichnotaxa, as well as higher detail in the structure

377

of the macrobenthic tracemaker community by the distinction of no less than five tiers

378

developed during the Danian (Fig. 9).

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The uppermost tier (A) during the earliest Danian was colonized by unknown

380

organisms responsible for intensive bioturbation of well-oxygenated poorly cohesive

381

sediments just below the seafloor. Intensive burrowing near the surface of well-oxygenated

382

sediments resulted in homogeneous background in the uppermost Maastrichtian deposits. The

383

upper tier (B) is represented by distinct, dark Thalassinoides and Planolites (the dominant

384

ichnotaxon). The colonized sediment was well-oxygenated, soft; locally very soft, as marked

385

by Thalassinoides showing uneven margins. In the intermediate tier (C), a higher diversity of

386

trace fossils is recorded from 3 to 15 cm below the K-Pg boundary. They include

387

Thalassinoides (branched burrows, most abundant from 3 to 8 cm below the boundary),

388

Planolites, and subordinate Pilichnus and ?Teichichnus. Thalassinoides is dominant.

389

Planolites and Thalassinoides are distinctly flattened, locally with their clayey infilling

390

squeezed out into surrounding marlstones (Fig. 6B). This is evidence of soft substrate at the

391

time of burrowing; the sediment was later dewatered and compacted. The presence of burrows

392

that are not permanently connected to the sea floor (Planolites) indicates high oxygenation of

393

pore waters. Chondrites and Zoophycos that crosscut other trace fossils of this tier were

394

produced probably after upward shifting of tiers caused by normal aggradation of sediment.

395

This concerns densely packed Chondrites, usually with sharp margins, in dark and light

396

Thalassinoides whose filling was already dewatered and compacted (Figs. 4C; 6E, F). The

397

deeper tier D is represented by Zoophycos and Chondrites. Chondrites crosscuts Zoophycos,

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ACCEPTED MANUSCRIPT suggesting that the Chondrites-producer burrowed in a deeper level than the Zoophycos

399

maker. This is confirmed by the deeper position of dark Chondrites (as much as 40 cm below

400

the K-Pg boundary) than Zoophycos (as much as 35 cm below). The distinct margins of the

401

marginal tube and distinct spreites in Zoophycos and distinct tunnels in Chondrites indicate

402

highly cohesive sediment during colonization (stiffground). The deepest tier E contains only

403

Trichichnus (as much as 45 cm below the boundary), which crosscuts the dark Zoophycos and

404

Chondrites. Tiers D and E evidently had pore water of low oxygen content.

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406

5.3. The dark boundary layer

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The presence of ichnofabric generations differing in colour indicates that the dark boundary layer has been reburrowed many times, confirming different phases of colonization

410

as previously interpreted (Rodríguez-Tovar et al., 2004, 2006). The order of colonization by

411

trace makers after the K-Pg boundary event is difficult to determine. Most probably, the olive-

412

grey ichnofabric generation, slightly darker than hosting claystones, is the oldest. The

413

ichnofabric generation filled with creamy material coming from the overlying creamy

414

limestones is an evidence of bioturbation just after deposition of the dark boundary layer. The

415

observed plastic deformation and the commonly diffuse margins of unidentifiable light-

416

coloured bioturbation structures suggest that the olive-grey claystones were still soft during

417

this phase of development. Judging from the crosscutting relationships, the dark-grey

418

ichnofabric generation reflects the latest phase of infaunal colonization of the dark boundary

419

layer, still in a substrate of low consistencyas inferred from the slightly plastically deformed

420

Zoophycos. No layer from which the dark grey infilling material could derive has been

421

recognized within the analysed section. The absence of such a layer may reflect a minor

422

erosion, though no discontinuity which might be evidence of this has been observed. It is

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ACCEPTED MANUSCRIPT 423

possible that this layer of dark grey sediment was completely mixed with the surrounding

424

sediment (as indicated by the biodeformational structures), and that the only evidence of its

425

original content is recorded as the infilling material of the trace fossils.

426

The lack of well-defined relationships between the analysed bioturbation structures recorded in the dark boundary layer impedes a conclusive interpretation of the tiering pattern.

428

Nevertheless, continuous colonization of the dark boundary layer, mainly by deposit-feeders,

429

is evident. The absence of primary lamination in the dark boundary layer at Agost is its

430

principal difference from the Caravaca section, the other of the best two preserved sections

431

worldwide, located in the same region, where two laminated horizons are present in the dark

432

boundary layer (Rodríguez-Tovar and Uchman, 2006). This suggests diverse colonization of

433

the dark boundary layer and its bioturbational reworking at Agost. However, we cannot

434

definitively reject the possibility of brief periods without burrowing activity in the dark

435

boundary layer in Agost that are not recorded in the ichnofabrics because of subsequent

436

bioturbation.

439 440

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5.4. The influence of the K-Pg event on the trace makers and the Lilliput Effect

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The ichnological analysis conducted by Rodríguez-Tovar and Uchman (2004a, b) revealed that after deposition of the rusty layer, in the earliest Danian, the uppermost

442

Maastrichtian marlstones were colonized by a well-developed suite of endobenthic organisms.

443

New, high-resolution ichnological analysis showed that the suite of trace makers was more

444

diverse and complex and their depth of burrowing was greater. The observed ichnotaxa may

445

be referred to different levels (tiers) occupied by deposit-feeders and trace makers of

446

chemichnia, probably sipunculid worms, crustaceans and polychaetes. The iron spherules

447

within Thalassinoides fillings in the Agost section are convincing evidence that the

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ACCEPTED MANUSCRIPT marlstones were colonized during deposition of the rusty layer, when the marlstones were

449

highly cohesive and the open tunnels of Thalassinoides were gravitationally filled

450

(Rodríguez-Tovar, 2005). A new micro- and macroscopic analysis of the dark Thalassinoides

451

fill has revealed the presence of Cretaceous foraminifera mixed with olive-grey clayey

452

material coming from the dark boundary layer. This indicates that Thalassinoides could be at

453

least partly actively filled and that the Cretaceous material was incorporated in the fill, e.g.,

454

during reburrowing of partly filled tunnels, or that the Cretaceous material was distributed on

455

the seafloor during the earliest Danian by excavation of burrows. The undulating

456

Thalassinoides tunnels with uneven margins suggest at least locally low cohesion of sediment

457

(Fig. 6B). The filling of dark Thalassinoides is the same as in the olive-grey marlstone

458

ichnofabric generations in the dark boundary layer, showing that they belong to the same

459

stage of colonization, which lasted as long as deposition of the dark boundary layer. This was

460

confirmed by the 13C/14C isotopic analysis of the dark trace fossil fillings (Rodríguez-Tovar et

461

al., 2004, 2006). The dark boundary layer, which is maximally of 10 cm, was deposited

462

during 12 ka if the accumulation rate of 0.83 cm/ka estimated for the early Danian (Groot et

463

al., 1989) is accepted.

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The dark Thalassinoides is reworked with Chondrites filled by material slightly darker

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than the Thalassinoides fill and having sharply bounded tunnels. This suggests that the trace

466

maker of Chondrites burrowed into already dewatered fill of relatively high cohesivity (Figs.

467

3K; 6C).

468

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Comprehensive studies have revealed no significant differences in composition of the

469

Maastrichtian and early Danian trace fossil assemblages. This confirms minor only impact of

470

the environmental perturbations across the K-Pg boundary on the burrowing organisms in

471

deep-marine hemipelagic settings. The persistence of the same trace fossils immediately

472

before and after the K-Pg event reflects greater adaptation or wide tolerance of the trace-

ACCEPTED MANUSCRIPT maker community (mostly of deposit feeders and chemichnia) to changing environmental

474

conditions, together with rapid reestablishment of pre-event environmental conditions.

475

Recently, ultra-high-resolution geochemical analysis in the nearby Caravaca section suggests

476

a reestablishment of oxygen conditions on the order of 104–105 years, and rapid recovery of

477

deep-sea ecosystems at the bottom and in intermediate waters, allowing the immediate

478

colonization by the macrobenthic tracemaker community (Sosa-Montes de Oca et al., 2013,

479

2016). One of the beneficial environmental factors potentially supporting their survivorship

480

was the high food concentration on the sea floor due to the increased detritus supply caused

481

by mass mortality shortly after the boundary event (Coccioni and Galeotti, 1994; Sheehan and

482

Hansen, 1986). Another important factor allowing survivorship was the feeding strategy of

483

most bioturbating organisms (see Labandeira et al., in press). According to Sheehan and

484

Hansen (1986) and several other researches (e.g., Arthur et al., 1987), marine animals within a

485

food chain starting with dead organic matter (detrital food chain), such as scavengers and

486

deposit feeders, did not experience severe extinction at the K-Pg boundary. Conversely, filter

487

and suspension feeders dependent on plankton suspended in the water column suffered more

488

significantly. Non-deposit feeders such as filter-feeding brachiopods, bryozoans and bivalves

489

and predatory ammonites experienced severe extinction across the K-Pg boundary (Arthur et

490

al., 1987). Similarly, deposit-feeding bivalves survived the K-Pg extinction event with little

491

loss, unlike suspension-feeding bivalves (Jablonski and Raup, 1995; Lockwood, 2003).

492

Decline in the number of filter- and suspension-feeding species is commonly ascribed to the

493

reduction or suppression of primary productivity after the K-Pg boundary event (e.g., Arthur

494

et al., 1987; Bernaola and Monechi, 2007; Hsü et al., 1982; Sheehan and Hansen, 1986; Zachos

495

et al., 1989). This led to reduction of food availability and caused loss of organisms strictly

496

depending on organic matter flux from the photic zone (Arthur et al., 1987).

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ACCEPTED MANUSCRIPT The absence of differences in ichnotaxonomic composition through the boundary

498

interval does not exclude an influence of the K-Pg event on the trace makers as recorded

499

different ways than a discontinuity in occurrences or extinctions. The same ichnotaxa from

500

the dark boundary layer (Guembelitria cretacea Biozone) are distinctly smaller than those in

501

underlying calcareous marlstones of the uppermost Maastrichtian (Plummerita hantkeninoides

502

Biozone). The reduction in burrow size is particularly evident for Chondrites, Planolites and

503

Thalassinoides. Burrow diameter reflects the trace-maker size and the fact that burrowing

504

organisms cannot be wider than their burrow (Twitchett and Barras, 2004). The reduction in

505

size of trace makers in the Agost section did not occur immediately after the K-Pg event,

506

when the olive-grey traces were produced in the uppermost Maastrichtian marlstones during

507

the earliest Danian, but later. Thus, the reaction of burrowing organisms to the K-Pg boundary

508

event was delayed compared to other groups of organisms. The size decrease of surviving

509

organisms within specific taxa after the extinction event is called the Lilliput Effect (Urbanek,

510

1993). This phenomenon is temporary and occurs during the so-called survival interval (sensu

511

Kauffman and Erwin, 1995).

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Dwarfism of trace makers might be caused by environmental stress conditions resulted from food shortage, dysoxia or low pH (Twitchett, 2007). Initially, no significant changes in

514

size of trace makers might be attributed to the beneficial environmental conditions following

515

the large influx of organic matter to the sea floor generated by high mortality (Coccioni and

516

Galeotti, 1994). After the initial ”food rain”, food supply to the bottom declined substantially

517

because of the collapse of primary production. It appears that one response of trace makers to

518

the chronic food shortage during the survival interval was decrease in body size. Another

519

possible cause of dwarfism among trace makers could be stress caused by the ocean

520

acidification which took place after the end-Cretaceous asteroid impact (e.g., Tyrrell et al.,

521

2015). In modern acidified shallow waters near CO2 seeps, two marine gastropod species

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ACCEPTED MANUSCRIPT 522

were smaller than the same species living in normal pH seawaters and had lower metabolic

523

demands (Garillli et al., 2015). The reported dwarfism among gastropods exposed over

524

multiple generations to higher CO2 levels was their adaptation strategy to acidic conditions

525

(Garillli et al., 2015). Burrow size is known to decrease after mass extinctions and it has been documented

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aftermath of the Late Devonian (Morrow and Hasiotis, 2007), Permian-Triassic (e.g.,

528

Twitchett, 2007) and end-Triassic extinctions (Twitchett and Barras, 2004). Burrow size

529

reduction after the K-Pg boundary event was also documented in Thalassinoides within the

530

Thalassinoides-dominated assemblage from shallow-marine siliciclastic, carbonate and

531

glauconite-dominated deposits of the Gulf Coastal Plain in Alabama and Texas and in the

532

Atlantic Coastal Plain of New Jersey, USA (Wiest et al., 2015, 2016). The data from the

533

Agost section support the response of trace makers to changing environmental conditions

534

after the K-Pg impact event. The diminishment of body size (Lilliput Effect) after the K-Pg

535

boundary event was noticed by Wiest et al. (2015, 2016) in respect to the trace makers of

536

Alabama and Texas in the USA, but the data from the Agost section shows that this

537

phenomenon concerns not only Thalassinoides but extends also to the trace makers of

538

Chondrites and Planolites.

541 542

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6. Conclusions

543

The Agost trace fossil assemblage, including Chondrites targionii, Chondrites ?affinis,

544

Chondrites isp., Pilichnus isp., Planolites isp., ?Teichichnus isp., Thalassinoides isp.,

545

Trichichnus linearis, Trichichnus isp., and Zoophycos isp., continues through the K-Pg

546

boundary interval,providing evidence of continuous habitation of the boundary interval

ACCEPTED MANUSCRIPT sediments. Detailed ichnofabric analysis, including colour infilling and diffusion of the

548

margins of the trace fossils, allows interpretation of different phases of colonization during

549

deposition of the dark boundary layer, just after the K-Pg boundary event. Size reduction of

550

some trace fossils within and just above the dark boundary illustrates the Lilliput Effect on

551

their tracemakers (e.g., Chondrites, Planolites and Thalassinoides producers) – a delayed

552

reaction of the burrowing organisms to the K-Pg boundary event resulting from lower food

553

supply due to collapse of primary production in the later phases of the event.

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554 Acknowledgements

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The authors would like to thank Andrew K. Rindsberg (University of West Alabama) and

558

Matias Reolid (Universidad de Jaén) for their constructive reviews. Research by R-T was

559

funded by Projects CGL2012-33281 and CGL2015-66835-P (Ministerio de Economía y

560

Competitividad), and Research Group RNM-178 (Junta de Andalucía). A.U. received a

561

support from the Jagiellonian University. W.Ł. was supported by the Jagiellonian University

562

(DS/MND/WBiNoZ/ING/2016).

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Fig. 1. Location of the K-Pg boundary section at Agost and main tectonic units of the south-

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eastern Spain.

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Fig. 2. The studied interval with vertical distribution of trace fossils produced after K-Pg

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boundary event.

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Fig. 3. (A) The Cretaceous-Palaeogene boundary section at Agost in general view. The red

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dash line marks the K-Pg boundary. The measurement tape is 50 cm long. (B) Detailed view

825

of the Agost section. Yellow arrows indicate Zoophycos isp. coming from the dark boundary

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layer and disturbing the rusty layer. The hammer is 23 cm long. (C) Vertical cross section of

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the K-Pg boundary with the rusty layer at the base of the dark boundary layer; a few

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millimetres below the K-Pg boundary – redistributed the rusty layer and material from the

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dark boundary layer. Polished slab. Specimen used for the thin section, INGUJ247P/Ag-K-Pg.

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(D) Rose marly limestones, lower Danian, Agost Formation, INGUJ247P/Ag+14-16(5). (E)

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Creamy calcareous marlstones overlying the dark boundary layer, lower Danian, Agost

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Formation, Ag-60. (F–J) Polished slabs of the dark boundary layer (vertical section)

833

displaying 3 different trace fossil generations differing in colour. (F) Specimen used for the

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thin section, INGUJ247P/Ag+1.1. (G) Specimen used for the thin section,

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INGUJ247P/Ag+1.2. (H) INGUJ247P/Ag+1-5(2). (I) INGUJ247P/Ag+0-6(3b). (J)

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ACCEPTED MANUSCRIPT INGUJ247P/ Ag+0-6(3c). (G) Plastically deformed Zoophycos isp. (K–M) Polished slabs of

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calcareous marlstones belonging to the Raspay Formation showing crosscutting relationships

838

between two trace fossil generations, Maastrichtian and lower Danian. Scale bar in all is 1 cm.

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(K, L) Horizontal cross section, 4 cm below the boundary. (K) Specimen used for the thin

840

section, INGUJ247P/ Ag-0-5.1. (L) INGUJ247P/Ag-10-20.1. (M) Interval from 30 to 40 cm

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below the K-Pg boundary, vertical cross section, Ag-50.

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Maastrichtian: Thalassinoides isp. (Thm), Zoophycos isp. (Zhm) Chondrites isp. (Chm);

843

Danian: Thalassinoides isp. (Thd), Zoophycos isp. (Zod), Chondrites isp. (Chd); ?Trichichnus

844

isp. (?Tr).

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Fig. 4. Early Danian trace fossils from the Agost section found within the upper Maastrichtian

847

marlstones, Raspay Formation. Scale bar in all is 1 cm. (A) Chondrites targionii and

848

Trichichnus isp. (Tr) oriented oblique to the bedding surface, INGUJ247P/Ag-20.1. (B)

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Chondrites targionii and Trichichnus isp. oriented on the parting surface, parallel to bedding

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surface, Ag-80. (C, D, G) Chondrites targionii showing well developed system of branching

851

with arched branches resembling an umbel, exichnial forms oriented on the parting surface

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parallel to the bedding surface. (C) INGUJ247P/Ag-0-20.1A (D) Ag-81. (G) Ag-84. (E, F)

853

Densely packed tunnels of Chondrites targionii within the Thalassinoides infilling,

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INGUJ247P/Ag-10-20.1. (H) Chondrites targionii with evident phobotaxis, Ag-82. (I)

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Chondrites ?affinis oriented oblique to the bedding surface, Trichichnus isp., INGUJ247P/Ag-

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25.1. (J) Oriented, exichnial Chondrites isp. resembling Chondrites patulus on a parting

857

surface parallel to the bedding, Ag-83.

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Fig. 5. Trace fossils from the K-Pg boundary interval in Agost. (A) Planolites isp. A,

860

INGUJ247P/AG-25. Scale bar is 1 cm. (B) Planolites isp. B, Ag-70. Scale bar is 1 cm. (A, B)

ACCEPTED MANUSCRIPT Exichnia observed at parting surface of the upper Maastrichtian marlstones bed. (C) Teichichnus

862

isp., exichnion visible on surface perpendicular to the bedding of the uppermost Maastrichtian

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marlstones, Raspay Formation, INGUJ247P/Ag-1.2. Scale bar is 0.5 cm. (D) U-shaped

864

laminations called spreite highlighted by difference in colour and character of bioclast packing,

865

view in optical microscope, plane polarized light, INGUJ247P/Ag-1.2. Scale bar is 1mm. (E) cf.

866

Trichichnus isp., endichnial full relief on a parting surface, Maastrichtian marlstones, Raspay

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Formation, INGUJ247P/Ag-40.1. Scale bar is 1 cm. (F) Trichichnus linearis, endichnion within

868

the marlstones bed, Raspay Formation, oriented oblique to bedding, INGUJ247P/Ag-35.1. (G, H)

869

Trichichnus isp. filled with framboidal aggregates, SEM view, INGUJ247P/Ag-24.1. (I) cf.

870

Pilichnus isp., exichnion a parting surface in a marlstone bed, INGUJ247P/Ag-0-4.1.

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Fig. 6. Thalassinoides isp. from the Agost section, exichnial forms within the upper

873

Maastrichtian marlstones, Raspay Formation. (A) Complex system of horizontal and oblique

874

tunnels exposed on bedding surface. Scale bar is 2 cm. (B) Distinctly flattened

875

Thalassinoides, evident infilling material squeezing out into the surrounding marlstones,

876

INGUJ247P/Ag-6-16.1. Scale bar is 1 cm. (C) Thalassinoides infilling reworked by

877

Chondrites targionii, INGUJ247P/Ag-3-8.1. Scale bar is 1 cm. (D) Cross section through

878

tunnel showing active infilling, scan of the thin section, INGUJ247P/Ag-1.3. Scale bar is 0.5

879

cm. (E) Fragment of active infilling of Thalassinoides isp. with preferentially orientated

880

foraminifera tests parallel to the tunnel margins (yellow, dashed line), INGUJ247P/Ag-1.3.

881

Scale bar is 0.25 cm. (F) Elliptical bioclast accumulations interpreted as possible bromalites,

882

INGUJ247P/Ag-1.4. Scale bar is 0.25 cm.

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Fig. 7. Zoophycos isp. from the Agost section, upper Maastrichtian calcareous marlstones,

885

Raspay Formation (A) Elongated tongue-like lobe surrounded by ferruginous marginal tube

ACCEPTED MANUSCRIPT fulfilled with densely packed spheres that are probably pseudomorphoses after framboidal

887

pyrite, Ag-90. Scale bar is 1 cm. (B, C) Ferruginous spheres within marginal tube, binocular

888

microscope view, INGUJ247P/Ag-0-15.1. Scale bar is 1mm. (D) SEM view of a ferruginous

889

sphere, INGUJ247P/Ag-0-15.1/SEM. (E) Distinct apex of the dark Zoophycos isp. Scale bar

890

is 10 cm.

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891

Fig. 8. Burrow diameters of Chondrites isp., Planolites isp. and Thalassinoides isp. from the

893

upper Maastrichtian to lower Danian (trace fossil generations filled with dark material coming

894

from the dark boundary layer found within upper Maastrichtian marlstones) and Danian

895

(generations measured within the dark boundary layer and overlying creamy marls) found at

896

the Agost section. Circles indicate mean values; standard deviations above and below mean

897

values are marked by vertical line; shaded region indicates range between the largest and

898

smallest recorded burrow sizes. The measurements and visual way of displaying data are

899

analogical to those of Twitchett (2007).

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Fig. 9. Tiering pattern and crosscutting relationships of the early Danian dark trace fossils

902

from the Agost section.

904 905

Appendix A. Supplementary data.

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To Castalla EUROPE

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Agost

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AGOST

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Murcia

a Beat

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K-Pg section

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Spain

CV-827

ACCEPTED MANUSCRIPT

10°W

t di

e

M

velda

o To N

To

Al

ica

0

50

100 km

Internal Prebetic

Cretaceous

Eocene

External Prebetic

Paleocene

Quaternary

nt

0

0.5

1 km

e

Chondrites isp. cf. Pilichnus isp. Planolites isp. ?Teichichnus isp. Thalassinoides isp. Trichichnus isp. Zoophycos isp.

[cm] ACCEPTED MANUSCRIPT

20

0

Abathomphalus mayaroensis

-20

dark-filled Thalassinoides

dark-filled Zoophycos

-30 dark-filled Chondrites

TE D

-40 -50

EP

light-filled Thalassinoides light-filled Zoophycos

AC C

-60

K-Pg

SC

-10

MAASTRICHTIAN

RI PT

10

M AN U

Pv. eugubina G. cretacea

DANIAN

30

-70 -80

light-filled Chondrites

-90

Lithology marly limestones calcareous marlstones calcareous marlstones and marlstones

calcareous claystones (dark boundary layer) rusty layer

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

[mm]

Chondrites isp.

burrow diameter

3

2

1 ACCEPTED MANUSCRIPT

0

n = 22

66

47 early Danian

Maastrichtian [mm]

Planolites isp.

RI PT

5

SC M AN U

3

0

EP

TE D

2

AC C

burrow diameter

4

1

Danian

n= 9

Maastrichtian

[mm]

10 early Danian

26 Danian

Thalassinoides isp.

burrow diameter

30

20

10

0

n = 20 Maastrichtian

10 early Danian

26 Danian

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT No significant mortality of macrobenthic ichnofauna after the K-Pg event but their good adaptation to environmental changes: ichnotaxa in the upper Maastrichtian and lower Danian are almost the same.

•

Chondrites, Planolites and Thalassinoides in the dark boundary layer and just above are smaller than in the older and younger sediments evidencing the Lilliput effect on their tracemakers.

•

The Lilliput effect is delayed to the K-Pg event, probably because the primary production declined after the initial increase in supply of organic matter caused by the event.

AC C

EP

TE D

M AN U

SC

RI PT

•