Origin, sequence stratigraphy and depositional environment of an Upper Ordovician (Hirnantian) deglacial black shale, Jordan - discussion

Following the Latest Ordovician glaciation, black, graptolitic, organic-rich shales were deposited in many places across northern Gondwana that form important hydrocarbon source rocks in the region. Armstrong et al. (2005) presented a study of black shales of this episode from southern Jordan and propose biostratigraphic, sequence stratigraphic and black shale depositional models which differ markedly from ours (Lüning et al., 2000). Two of us (S.L., D.K.L.) have recently had the opportunity to study the same black shales in Jordan that Armstrong et al. (2005) investigated. The database of both study teams appears to overlap significantly; in particular, we also studied the shallow borehole core BG-14 and two outcrop sections in the southern Jordanian Desert. The results of our study can be found in Lüning et al. (2005). We comment here on the models proposed by Armstrong et al. (2005), in order to stimulate an open, scientific discussion that may help to identify the most likely depositional scenario for these black shales.