Non-marine invertebrate trace fossils from the Tertiary Calatayud-Teruel basin, NE Spain

Relatively diverse trace fossils made by insects, other arthropods and oligochaete worms occur in the Miocene lacustrine and marginal lacustrine deposits of the Calatayud-Teruel basin (NE Spain). They include the ichnospecies Celliforma isp., Celliforma? isp. A and B, Celliforma? aff. habari, Rosellichnus cf. arabicus, Spongeliomorpha isp., Labyrintichnus terrerensis n. igen. et isp., Taenidium barreti, Beaconites filiformis n. isp. and Polykladichnus aragonensis n. isp. Their taxonomic and ethologic interpretations and cross-cutting relationships permit to envisage new lines of evidence for reconstructing transitions from dry-ground terrestrial to moist-ground and subaqueous environments, related to episodic floodings in lacustrine ponds. These environmental transitions (related to external controls) are characterized by benthic community replacements, evinced by vertical successions of Termitichnus, Scoyenia and Mermia-like ichnofacies.

Eocene-Oligocene terrestrial cryospheric processes: bipolar glaciation and uplifted Tibet

There is no agreement regarding the processes that have governed the birth and vanish of ice masses on Earth during Cenozoic, as well as the possible existence of unipolar vs bipolar glaciations which remain controversial. Although it is generally accepted that Cenozoic cryosphere was characterized by a unipolar Antarctic glaciation at the Eocene-Oligocene Transition (~ 34 Ma), recent investigations suggest synchronous cryospheric processes at both hemispheres at this time. Here we present the first worldwide evidence of ice-related structures in Eocene-Oligocene sediments from the mid-latitude Lunpola Basin of central Tibet. The lacustrine deposits contain two intervals dated 37.8–35.6 and 34.0-32.5 Ma, respectively, which preserve seasonal frost events, glendonites and ice-rafted debris. These cryospheric processes were synchronous with two recorded stratigraphic intervals containing ice-rafted debris along offshore Greenland and in the Arctic region. Our results provide robust continental evidence of Eocene-Oligocene bipolar glaciation and a direct evidence for an already uplifted central Tibet during late Eocene. This finding brings into debate the timing and magnitude of inherited elevation of the vast proto-Tibetan Plateau before the continental collision between India and Eurasia.

Supplemental Material: Annually resolved sediments in the classic Clarkia lacustrine deposits (Idaho, USA) during the middle Miocene Climate Optimum

Detailed methodology, supplemental figures, and separate data files containing raw U-Pb zircon data, μ-XRF elemental ratios, and color intensity variation.

Supplemental Material: Annually resolved sediments in the classic Clarkia lacustrine deposits (Idaho, USA) during the middle Miocene Climate Optimum

Detailed methodology, supplemental figures, and separate data files containing raw U-Pb zircon data, μ-XRF elemental ratios, and color intensity variation.

The mechanisms of formation of some small cones in Chryse Planitia on Mars

<p><strong>Introduction: </strong>Small cones are common on Mars. Many cones form subparallel chains several kilometers in length. Their origin is discussed in many papers, however, the mechanism of their formation is not explained [1].</p><p>In the present paper, we deal with a small region in Chryse Planitia ( ~38<sup>o</sup>13′ N and ~319<sup>o</sup>25’ E). The region is covered by lacustrine deposits.</p><p>    On Mars, chains of small cones occupy vast areas. Therefore, we try to explain the existence of the chains by specific conditions on Mars. We focus on the hypothesis connecting the formation of cones with the loss of water from the regolith due its instability. See e.g. [1], [2], [4], [5].</p><p><strong> </strong></p><p><strong>Mechanism of cones formation: </strong>We consider 3 mechanisms of cone formation: (i) a grains’ ejection, (ii) from mud or fluidized sand and (iii) explosive formation. The (iii) and (ii) are possible with additional heat sources only.</p><p>    Assuming that only heat of melting was used for vaporization, then only ~13% of liquid water will be vaporized, If the outgassing effect is to be regolith without water, then there must be also other heat sources. Therefore we consider two coexisting factors required for cones formation: (1) the presence of water in the regolith and (2) some additional heating, e.g. magma intrusion.</p><p>    The formation of a chain of cones is possible in two situations:</p><p>(a) above a linear structure containing water and areal heating. Outcrops of aquifers could serve as linear sources of volatiles.</p><p>(b) above a linear source of magmatic heat and the areal aquifer. A dike could serve as linear source of heat.</p><p><strong> </strong></p><p><strong>Conclusions and future plans;</strong></p><p>1) Considered cones could be a result of outgassing of regolith due to pressure drop.</p><p>2) Subparallel chains of cones were formed along the outcrops of volatile-rich sediments.</p><p>3) Numerical modeling indicates that small magma intrusions may not be enough for completely degassing some aquifers.</p><p><strong> </strong></p><p><strong>Acknowledgments:</strong> This study was supported by statutory project of Institute of Geophysics of University of Warsaw. We are also grateful to prof. W. Kofman and dr. J. Ciążela for their remarks.</p><p><strong> </strong></p><p><strong>References</strong></p><p>[1] Fagents, S., Thordarson, T., (2007) The Geology of Mars: Evidence from Earth-Based Analogs, ed. Mary Chapman. Cambridge Univ. Press. [2] Brož,, et al. (2019) JGR: Planets. 124, 703–720. [3] Rotto, S., Tanaka, K. L. (1995) Geologic/ geomorphologic map of the Chryse Planitia: region of Mars. USGS. [4] Barlow, N.G. (2010) GSA Bulletin (2010) 122 (5-6): 644–657. [5] Brož, P., et al. (2020) Nature Geoscience. 13, 403–407.</p>