The Lower Cretaceous charophyte flora from the Cuchía section (Cantabrian Basin, North Spain): Biostratigraphy and palaeobiogeography

Abstract

The Lower Cretaceous charophyte flora from the Wealden of the Cuchía section (Barremian, North Cantabrian Basin, northern Spain) was investigated. This locality represents the northernmost charophyte flora on the Iberian microplate. Twenty-one charophyte taxa were identified and two distinct charophyte assemblages, belonging to two different biozones, were recognized. The lower part (beds 1–6) of the studied section yielded the first charophyte assemblage composed of the species Echinochara lazarii, Atopochara trivolvis var. triquetra, Globator mallardii var. trochiliscoides, Clavator grovesii var. combei, Clavator harrisii var. dongjingensis, C. harrisii var. harrisii, C. calcitrapus var. jiangluoensis, Ascidiella stellata var. lata, A. triquetra, Hemiclavator neimongolensis var. neimongolensis, H. neimongolensis var. posticecaptus, aff. Mesochara harrisii, Porochara gr. kimmeridgensis subgr. kimmeridgensis, Clavatoraxis sp., and Favargerella aquavivae. This charophyte assemblage belongs to the Eurasian “Hemiclavator neimongolensis var. neimongolensis” biozone, assigned to the upper lower Barremian–lower upper Barremian. The upper part (beds 7–12) of the studied section yielded the second charophyte assemblage composed of the species E. lazarii, A. trivolvis var. triquetra, A. trivolvis var. trivolvis, G. mallardii var. biutricularis, C. grovesii var. jiuquanensis, C. harrisii var. dongjingensis, C. harrisii var. harrisii, C. harrisii var. reyi, C. calcitrapus var. calcitrapus, H. neimongolensis var. neimongolensis, H. neimongolensis var. posticecaptus, aff. Mesochara harrisii, Munieria grambastii, Clavatoraxis sp., and Favargerella aquavivae. This charophyte assemblage is correlated to the Eurasian “Clavator grovesii var. jiuquanensis” biozone, assigned to the upper Barremian–lower Aptian. Considering that the Wealden at Cuchía section is capped by the lower Aptian calcarenites (Umbrera Formation), this series is chronostratigraphically constrained to the upper lower Barremian–upper Barremian, instead of Hauterivian–Barremian as previously thought. The Cuchía charophyte flora has some of the highest species diversity from Wealden-type facies worldwide. The charophyte hotspot of Cuchía displays a strong similarity with the previously reported contemporaneous flora diversity hotspot in the Maestrat Basin (eastern Spain), which to date shows the most diverse Barremian charophyte assemblage worldwide (33 taxa). Our results further support the significant role of the Iberian Peninsula in the evolution of Lower Cretaceous charophytes within the Central Tethyan Archipelago bioprovince.