Charophyte biostratigraphy of the Lower Cretaceous (Wealden) Cuchia section, Basque-Cantabrian Chain, North Spain: Interest for regional stratigraphic correlation
Authors: Trabelsi Khaled , Mai Anna Tamara , Sames Benjamin , Herrle Jens O. , Wiese Frank 
Published: March 2022

&lt;p&gt;A 55 meters thick section at Cuchia, Basque-Cantabrian Chain, North Spain, mainly formed by Lower Cretaceous Wealden facies, has been intensively investigated from the micropalaeontological viewpoint. The carbonate beds intercalated within this series yield a rich and diverse charophyte assemblages of high biostratigraphic interest, which could be studied for the first time after successful preparation following the acetolysis method.&lt;/p&gt;&lt;p&gt;Twenty-two charophyte taxa were identified forming two distinct charophyte assemblages belonging to two successive charophyte biozones. The first charophyte assemblage, from the lower part of the studied section, is composed of &lt;em&gt;Echinochara &lt;/em&gt;&lt;em&gt;lazarii&lt;/em&gt;, &lt;em&gt;Atopochara trivolvis&lt;/em&gt; var. &lt;em&gt;triquetra&lt;/em&gt;, &lt;em&gt;Globator mallardii&lt;/em&gt; var. &lt;em&gt;trochiliscoides&lt;/em&gt;, &lt;em&gt;Clavator grovesii&lt;/em&gt; var. &lt;em&gt;gautieri&lt;/em&gt;, &lt;em&gt;Clavator harrisii&lt;/em&gt; var. &lt;em&gt;dongjingensis&lt;/em&gt;, &lt;em&gt;C&lt;/em&gt;. &lt;em&gt;harrisii&lt;/em&gt; var. &lt;em&gt;harrisii&lt;/em&gt;, &lt;em&gt;C&lt;/em&gt;. &lt;em&gt;calcitrapus&lt;/em&gt; var. &lt;em&gt;jiangluoensis&lt;/em&gt;, &lt;em&gt;C&lt;/em&gt;. &lt;em&gt;calcitrapus&lt;/em&gt; var. &lt;em&gt;calcitrapus&lt;/em&gt;, &lt;em&gt;Ascidiella stellata&lt;/em&gt; var. &lt;em&gt;stellata&lt;/em&gt;, &lt;em&gt;A&lt;/em&gt;. &lt;em&gt;triquetra&lt;/em&gt;, &lt;em&gt;Hemiclavator neimongolensis&lt;/em&gt; var. &lt;em&gt;neimongolensis&lt;/em&gt;, &lt;em&gt;H&lt;/em&gt;. &lt;em&gt;neimongolensis&lt;/em&gt; var. &lt;em&gt;posticecaptus&lt;/em&gt;, &lt;em&gt;Mesochara&lt;/em&gt; &lt;em&gt;voluta&lt;/em&gt; gr. &lt;em&gt;voluta&lt;/em&gt; and &lt;em&gt;Favargella&lt;/em&gt; sp. According to P&amp;#233;rez-Cano et al. (2021), such a charophyte assemblage belongs to the new Eurasian &amp;#8220;Hemiclavator neimongolensis var. neimongolensis&amp;#8221; biozone, late early Barremian&amp;#8211;early late Barremian in age as calibrated by Sr isotope stratigraphy and by correlation with marine biostratigraphy.&lt;/p&gt;&lt;p&gt;The second charophyte assemblage, which occurs in the upper part of the studied section is composed of the species &lt;em&gt;E&lt;/em&gt;.&lt;em&gt; &lt;/em&gt;&lt;em&gt;lazarii&lt;/em&gt;, &lt;em&gt;A&lt;/em&gt;. &lt;em&gt;trivolvis&lt;/em&gt; var. &lt;em&gt;triquetra&lt;/em&gt;, &lt;em&gt;A&lt;/em&gt;.&lt;em&gt; trivolvis&lt;/em&gt; var. &lt;em&gt;trivolvis&lt;/em&gt;, &lt;em&gt;C&lt;/em&gt;.&lt;em&gt; grovesii&lt;/em&gt; var. &lt;em&gt;jiuquanensis&lt;/em&gt;, &lt;em&gt;C&lt;/em&gt;.&lt;em&gt; harrisii&lt;/em&gt; var. &lt;em&gt;dongjingensis&lt;/em&gt;, &lt;em&gt;C&lt;/em&gt;. &lt;em&gt;harrisii&lt;/em&gt; var. &lt;em&gt;harrisii&lt;/em&gt;, &lt;em&gt;C&lt;/em&gt;. &lt;em&gt;harrisii&lt;/em&gt; var. &lt;em&gt;reyi&lt;/em&gt;, &lt;em&gt;Ascidiella cruciata&lt;/em&gt;, &lt;em&gt;H&lt;/em&gt;.&lt;em&gt; neimongolensis&lt;/em&gt; var. &lt;em&gt;neimongolensis&lt;/em&gt;, &lt;em&gt;H&lt;/em&gt;. &lt;em&gt;neimongolensis&lt;/em&gt; var. &lt;em&gt;posticecaptus&lt;/em&gt;, &lt;em&gt;Mesochara&lt;/em&gt; &lt;em&gt;voluta&lt;/em&gt; gr. &lt;em&gt;voluta&lt;/em&gt;,&lt;em&gt; Munieria&lt;/em&gt; &lt;em&gt;grambastii&lt;/em&gt;, &lt;em&gt;Clavatoraxis&lt;/em&gt; sp., &lt;em&gt;Charaxis&lt;/em&gt; sp. &amp;#160;and &lt;em&gt;Tolypella&lt;/em&gt; sp. vel. &lt;em&gt;Mesochara&lt;/em&gt; sp. According to P&amp;#233;rez-Cano et al. (2021), such a charophyte assemblage belongs to the new Eurasian &amp;#8220;Clavator grovesii var. jiuquanensis&amp;#8221; biozone, late Barremian&amp;#8211;early Aptian in age as calibrated by Sr isotope stratigraphy and by correlation with marine biostratigraphy.&lt;/p&gt;&lt;p&gt;As the overlaying succeeding limestones is early Aptian in age, our results allow constraining the chronostratigraphy of the Wealden series at Cuchia section to the late early Barremian&amp;#8211; late Barremian, instead of Hauterivian&amp;#8211;Barremian (Najarro et al., 2011) as previously thought, leading for a more detailed stratigraphic correlation of the Cuchia section to equivalent units of the Iberian plate, especially from the Iberian Chain and the Pyrenees.&lt;/p&gt;&lt;p&gt;References.&lt;/p&gt;&lt;p&gt;Najarro, M., Rosales, I., Martin-Chivelet, J. (2011). Major palaeoenvironmental perturbation in an Early Aptian carbonate platform: Prelude of the Oceanic Anoxic Event 1a. Sedimentary Geology 235, 50&amp;#8211;71. https://doi.org/10.1016/j.cretres.2021.104934&lt;/p&gt;&lt;p&gt;P&amp;#233;rez-Cano, J., Bover-Arnal, T., Mart&amp;#237;n-Closas, C. (2021). Barremian&amp;#8211;early Aptian charophyte biostratigraphy revisited. Newsletters on Stratigraphy (&lt;em&gt;in press&lt;/em&gt;). DOI: 10.1127/nos/2021/0662&lt;/p&gt;