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This work is part of the Ph.D. Thesis of three of the authors (M.N. -geology-, R.P.F. and J.O.B. -paleobiology-), which are supported by a scholarship from the Instituto Geologic y Minero de Espana (IGME), an AVM grant of the University of Barcelona, and a FPI grant from the Spanish Ministry of Science and Technology, respectively. This study is a contribution of the IGME Project 491-CANOA 35015 "Investigacicin cientifica y tecnica de la Cueva de El Sop lao y su entomo geologico", the projects CGL2008-/01237BTE from the MICINN, CGL200800550/BTE: "Amber of the Cretaceous of Spain: A multidisciplinary study", and the ANR Project AMBRACE BLAN07-1-184190. The contribution is framed in a collaborative agreement among the Cantabrian Government (Regional Cultural, Tourism and Sports Ministry), IGME and SIEC S.A. We thank Gonzalo Nieto and the staff of the Royal Botanic Garden of Madrid for permission and assistance in the sampling of extant conifers. We also express our thanks to Francisco Javier Lopez Marcano (Regional Minister of the Cantabrian Government), Jose Pedro Ca Ivo Sorando (IGME) and Fermin Unzue (manager of the El Sop lao Cave) for their efforts and promotion of the study of the outcrop. We are grateful to Dr Daniel J. Bickel (Australian Museum, Sydney), Dr Vladimir Blagoderov (Natural History Museum, London) and an anonymous reviewer for careful reviews of the manuscript. Thanks are due to all people that participated in the paleontological excavations.

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Najarro, MariaCorresponding Author

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October 18, 2022
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Review of the El Soplao Amber Outcrop, Early Cretaceous of Cantabria, Spain

Publicated to:Acta Geol Sin-Engl. 84 (4): 959-976 - 2010-01-01 84(4), DOI: 10.1111/j.1755-6724.2010.00258.x

Authors: Najarro, Maria; Penalver, Enrique; Perez-De la Fuente, Ricardo; Ortega-Blanco, Jaime; Menor-Salvan, Cesar; Barron, Eduardo; Soriano, Carmen; Rosales, Idoia; Lopez Del Valle, Rafael; Velasco, Francisco; Tornos, Fernando; Daviero-Gomez, Veronique; Gomez, Bernard; Delclos, Xavier

Affiliations

CSIC INTA, Ctr Astrobiol, E-28850 Torrejon De Ardoz, Spain - Author
El Soplao SL, E-39553 Cantabria, Spain - Author
European Synchrotron Radiat Facil, F-38000 Grenoble, France - Author
Inst Geol & Minero Espana, E-28003 Madrid, Spain - Author
Univ Barcelona, Dept Estratig Paleontol & Geociencies Marines, Fac Geol, E-08071 Barcelona, Spain - Author
Univ Basque Country, Dpto Mineral & Petrol, E-48080 Bilbao, Spain - Author
Univ Lyon 1, CNRS, UMR 5125, PEPS, F-69622 Villeurbanne, France - Author
Univ Rennes 1, France Geosci Rennes, F-35042 Rennes, France - Author
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Abstract

El Soplao outcrop, an Early Cretaceous amber deposit recently discovered in northern Spain (Cantabria), has been shown to be the largest site of amber with arthropod inclusions that has been found in Spain so far. Relevant data provided herein for biogeochemistry of the amber, palynology, taphonomy and arthropod bioinclusions complement those previously published. This set of data suggests at least two botanical sources for the amber of El Soplao deposit. The nrst (type A amber) strongly supports a source related to Cheirolepidiaceae, and the second (type B amber) shows non-specific conifer biomarkers. Comparison of molecular composition of type A amber with Frenelopsis leaves (Cheirolepidiaceae) strongly suggests a biochemical affinity and a common botanical origin. A preliminary palynologlcal study indicates a regional high taxonomical diversity, mainly of pteridophyte spores and gymnosperm pollen grains. According to the preliminary palynologlcal data, the region was inhabited by conifer forests adapted to a dry season under a subtropical climate. The abundant charcoalified wood associated with the amber in the same beds is evidence of paleofires that most likely promoted both the resin production and an intensive erosion of the litter, and subsequent great accumulation of amber plus plant cuticles. In addition, for the first time in the fossil record, charcoalified plant fibers as bioinclusions in amber are reported. Other relevant taphonomic data are the exceptional presence of serpulids and bryozoans on the surfaces of some amber pieces indicating both a long exposure on marine or brackish-water and a mixed assemblage of amber. Lastly, new findings of insect bioinclusions, some of them uncommon in the fossil record or showing remarkable adaptations, are reported. In conclusion, a documented scenario for the origin of the El Soplao amber outcrop is provided.

Keywords

Arthropod bioinclusionsBiomarkersCharcoalChemotaxonomyConiferalesEarly albianExtensionFireFossil charcoalFossil resinGeosphereInclusionsNatural resinsNorthern spainPaleobotanyTaphonomy

Quality index

Bibliometric impact. Analysis of the contribution and dissemination channel

The work has been published in the journal Acta Geol Sin-Engl due to its progression and the good impact it has achieved in recent years, according to the agency WoS (JCR), it has become a reference in its field. In the year of publication of the work, 2010, it was in position 75/167, thus managing to position itself as a Q2 (Segundo Cuartil), in the category Geosciences, Multidisciplinary.

From a relative perspective, and based on the normalized impact indicator calculated from the Field Citation Ratio (FCR) of the Dimensions source, it yields a value of: 5.29, which indicates that, compared to works in the same discipline and in the same year of publication, it ranks as a work cited above average. (source consulted: Dimensions Jul 2025)

Specifically, and according to different indexing agencies, this work has accumulated citations as of 2025-07-06, the following number of citations:

  • WoS: 59

Impact and social visibility

From the perspective of influence or social adoption, and based on metrics associated with mentions and interactions provided by agencies specializing in calculating the so-called "Alternative or Social Metrics," we can highlight as of 2025-07-06:

  • The use, from an academic perspective evidenced by the Altmetric agency indicator referring to aggregations made by the personal bibliographic manager Mendeley, gives us a total of: 32.
  • The use of this contribution in bookmarks, code forks, additions to favorite lists for recurrent reading, as well as general views, indicates that someone is using the publication as a basis for their current work. This may be a notable indicator of future more formal and academic citations. This claim is supported by the result of the "Capture" indicator, which yields a total of: 32 (PlumX).

With a more dissemination-oriented intent and targeting more general audiences, we can observe other more global scores such as:

  • The Total Score from Altmetric: 3.
  • The number of mentions on Wikipedia: 1 (Altmetric).

Leadership analysis of institutional authors

This work has been carried out with international collaboration, specifically with researchers from: France.

There is a significant leadership presence as some of the institution’s authors appear as the first or last signer, detailed as follows: First Author (Najarro de la Parra, María) .

the author responsible for correspondence tasks has been Najarro de la Parra, María.