Data for: Oxfordian carbon-isotope stratigraphy and pelagic biofacies of the Middle–Upper Jurassic transition in the Tethys–Central Atlantic connection

A bulk carbon-isotope stratigraphy, based on high-resolution sampling of five stratigraphic ammonite-dated sections
from pelagic swells of the Subbetic basin (External Zones of the Betic Cordillera, southern Spain) is presented. The
studied sections are characterized by Callovian‒Oxfordian stratigraphic successions located in the South Iberian
palaeomargin, a key area connecting the Central Atlantic to the Tethys oceans. The rocks are mainly nodular
limestones with common extreme condensation (rosso ammonitico facies). Discontinuities with hiatuses of variable
duration, submarine “hardgrounds”, Fe-Mn ooids, limonite crusts, and neptunian dykes are observed around the
Callovian/Oxfordian boundary. The stratigraphic record, although very time-averaged, allows for a consistent and
accurate ammonite chronostratigraphy. The carbon isotopes of marine carbonates show a marked trend towards high
δ13C values from Lower Oxfordian to the Middle Oxfordian (~4.3 ‰, near the Plicatilis/Transversarium boundary). The
isotopic values stand between 2.7–3.0 ‰ at the Upper Oxfordian (Bifurcatus and Hypselum Zones) and lowermost
Kimmeridgian (Bimammatum Zone); afterward δ13C values decrease and reach a relative minimum (~2.3–2.5 ‰) in
the Lower Kimmeridgian (Bimammatum/Planula boundary). Finally, isotopic values increase again (~2.6–2.7 ‰) in the
lower Kimmeridgian (mid part of the Planula Zone). Comparison of carbon-isotope stratigraphy between Subbetic and
other Tethyan areas shows similar trends. The replacement of thin-shelled bivalves by planktonic foraminifers and
radiolarians that took place in the Callovian/Oxfordian boundary can be associated to the widening of the trans-
Pangaean seaway . This, in turn, triggered the global warming which increased nutrients concentration in upper water
column due to intensified nutrient input by river plumes. These phenomena are concomitant with the major Oxfordian
δ13C positive excursion and with a transgressive cycle.

本项研究呈现了一组基于对西班牙南部比利牛斯山外部地带（Subbetic basin）海底隆起层中五个年代学测定的有孔虫层的高分辨率采样而构建的块状碳同位素地层学。所研究的地层以位于南伊比利亚古海岸的卡尔洛夫阶至牛津阶的地层序列为特征，该区域是连接中央大西洋与泰萨海洋的关键地带。岩石主要为具极端浓缩现象的团块状灰岩（rosso ammonitico相）。在卡尔洛夫阶/牛津阶界线附近观察到的不连续层、可变持续时间的海底“硬底”、铁锰结核、褐铁矿外壳和海神岩侵入体。尽管地层记录的时间平均性很高，但仍允许进行一致且准确的有孔虫年代地层学研究。海洋碳酸盐的碳同位素显示出从下牛津阶至中牛津阶（约4.3‰，近于Plicatilis/Transversarium边界）向高δ13C值的显著趋势。同位素值在牛津阶上部（Bifurcatus和Hypselum带）和最低层的基米里阶（Bimammatum带）之间介于2.7–3.0‰；之后δ13C值下降，在基米里阶下部（Planula带中部）达到相对最低值（约2.3–2.5‰）。最后，同位素值再次上升（约2.6–2.7‰）至基米里阶下部。Subbetic与其它泰萨海洋地区之间的碳同位素地层学对比显示出相似的趋势。在卡尔洛夫阶/牛津阶界线处，薄壳双壳类生物被浮游有孔虫和放线菌所取代的现象，可以与泛大陆海域的拓宽相联系。这进而引发了全球变暖，由于河流羽流增强的营养物质输入，导致上层水柱中营养物质浓度增加。这些现象与牛津阶的主要δ13C正值异常和海侵周期相伴随。