Mineralogical (bulk rock and clay fraction) and stable isotope composition (d13C, d18O) of Aptian deposits of the Bir Oum Ali succession, central Tunisia

Alternations between siliciclastic, carbonate and evaporitic sedimentary systems, as recorded in the Aptian mixed succession of southern Tunisia, reflect profound palaeoceanographic and palaeoclimatic changes in this area of the southern Tethyan margin. The evolution from Urgonian-type carbonates (Berrani Formation, lower Aptian) at the base of the series, to intervals dominated by gypsum or detrital deposits in the remainder of the Aptian is thought to result from the interplay between climate change and tectonic activity that affected North Africa.
Based on the evolution of clay mineral assemblages, the early Aptian is interpreted as having been dominated by slightly humid conditions, since smectitic minerals are observed. Near the early to late Aptian boundary, the onset of a gypsiferous sedimentation is associated with the appearance of palygorskite and sepiolite, which supports the installation of arid conditions in this area of the southern Tethyan margin. The evaporitic sedimentation may have also been promoted by the peculiar tectonic setting of the Bir Oum Ali area during the Aptian, where local subsidence may have been tectonically enhanced linked to the opening of northern and central Atlantic. Stress associated with the west and central African rift systems may have triggered the development of NW-SE, hemi-graben structures. Uplifted areas may have constituted potential new sources for clastic material that has been subsequently deposited during the late Aptian.
Chemostratigraphic (d13C) correlation of the Bir Oum Ali succession with other peri-Tethyan regions complements biostratigraphic findings, and indicates that a potential expression of the Oceanic Anoxic Event (OAE) 1a may be preserved in this area of Tunisia. Although the characteristic negative spike at the base of this event is not recognized in the present study, a subsequent, large positive excursion with d13C values is of similar amplitude and absolute values to that reported from other peri-Tethyan regions, thus supporting the identification of isotopic segments C4-C7 of the OAE1a. The absence of the negative spike may be linked to either non preservation or non deposition: the OAE1a occurred in a global transgressive context, and since the Bir Oum Ali region was located in the innermost part of the southern Tethyan margin during most of the Aptian, stratigraphic hiatuses may have been longer than in other regions of the Tethys. This emphasizes the importance of integrating several stratigraphic disciplines (bio-, chemo- and sequence stratigraphy) when performing long-distance correlation.

突尼斯南部阿普第阶（Aptian）混合沉积序列所记录的硅质碎屑岩、碳酸盐岩与蒸发岩沉积体系的交替变化，反映了南特提斯洋边缘该区域发生的深刻古海洋与古气候变革。研究层系底部的乌尔戈尼型碳酸盐岩（下阿普第统贝兰尼组）向上逐步过渡为阿普第阶剩余层段以石膏或碎屑沉积为主的地层，这一演化过程被认为是影响北非的气候变化与构造活动共同作用的结果。
基于黏土矿物组合的演化特征，早阿普第世以偏湿润的环境为主，这一点可由蒙脱石类矿物的产出得到佐证。在阿普第阶早-晚交界附近，石膏沉积的起始与坡缕石、海泡石的出现相伴生，这支持了南特提斯洋边缘该区域此时已进入干旱环境的认识。阿普第期比尔乌姆阿里（Bir Oum Ali）地区独特的构造背景也可能促进了蒸发岩沉积：该区域的局部沉降可能因与北大西洋、中大西洋张开相关的构造作用而加剧；西非与中非裂谷系带来的应力可能触发了北西-南东向半地堑构造的形成；抬升区则为晚阿普第世沉积的碎屑物质提供了潜在物源区。
将比尔乌姆阿里序列与其他特提斯洋周缘地区进行化学地层学（δ¹³C）对比，可补充生物地层学的研究结果，同时表明突尼斯该区域可能保存了大洋缺氧事件（OAE）1a的相关记录。尽管本研究未识别出该事件底部典型的碳同位素负异常峰值，但后续出现的大规模δ¹³C正偏移，其幅度与绝对值均与其他特提斯洋周缘地区的报道结果相似，因此可佐证OAE1a的同位素段C4-C7的识别。负异常峰值的缺失可能与沉积保存不全或未沉积有关：OAE1a发生于全球海侵背景下，而比尔乌姆阿里区域在阿普第阶大部分时期位于南特提斯洋边缘的最内侧，因此该区域的地层沉积间断可能比特提斯洋其他区域更长。这一点凸显了在开展长距离地层对比时，整合生物地层学、化学地层学与层序地层学等多学科手段的重要性。