Evolution of pelagic swells from hardground analysis (Bathonian–Oxfordian, Eastern External Subbetic, southern Spain)

Abstract

The Middle Bathonian to Middle Oxfordian interval in the Eastern External Subbetic (Betic Cordillera, SE Spain) is characterized by Ammonitico Rosso facies including various stratigraphic breaks. Five hardgroundbounded units are recognized in relation to hiatuses in the ammonite record at the following stratigraphic boundaries: Hg1 (Lower-Middle Bathonian), Hg2 (Middle-Upper Bathonian), Hg3 (Lower-Middle Callovian), Hg4 (MiddleUpper Callovian), and Hg5 (Callovian-Oxfordian). Interesting features of these hardgrounds include their microfacies, ferruginous crusts and macro-oncoids, taphonomy of macroinvertebrates, trace fossils, neptunian dykes, and the hiatuses associated with each of them. The main hardgrounds (Hg1, Hg2, and Hg5) contain trace fossils of the Cruziana and Trypanites ichnofacies as well as abundant fossil macroinvertebrates with taphonomic features evidencing corrasion, early diagenesis, and reworking, indicating substrate evolution from softground to hardground. Neptunian dykes aVected the trace fossils and ammonoid moulds, and their walls and the hardground surfaces were colonized by ferruginous microbial crusts. These features are characteristic of the External Subbetic pelagic swells, where the absence of sedimentation, sediment bypassing and erosion, and early diagenesis during relative sea-level falls produced hardgrounds. The neptunian dykes are indicative of tectonic activity in the areas of pelagic swells.Ferruginous crusts and macro-oncoids developed only on hardground surfaces and neptunian dykes walls prior to deposition of condensed bioclastic beds, which are interpreted as the Wrst deposits after hardground development and are related to the onset of transgression. The varying ranges of the gaps as well as lateral facies changes are related to diVerent local paleobathymetry controlled by the activity of listric faults.

The oldest stage of the Outer Carpathian evolution in the light of Oxfordian–Kimmeridgian exotic clast studies (southern Poland)

“…Synsedimentary tectonics periodically active in the northern Tethyan shelf was related to the opening of the North Atlantic and Tethys oceans. It resulted in the Late Jurassic stress-field reorganization, which also included the passive northern margin of the Tethys (e.g., Allenbach 2002;Nieto et al 2012).…”

Jurassic Non-Carbonate Microbialites from the Betic-Rifian Cordillera (Tethys Western End): Textures, Mineralogy, and Environmental Reconstruction

“…In the Eastern External Subbetic, three hardgrounds were identified, usually overimposed [118,119]: The Lower-Middle Bathonian hardground, the Middle-Upper Bathonian hardground, and the Callovian-Oxfordian hardground. The Fe crusts and macro-oncoids from these discontinuities are composed by Fe-Mn oxyhydroxides [51,120].…”

“…In this sense, the Ce enrichment resulting in a positive anomaly might be adequately explained by oxidative scavenging of Ce 4+ from normal seawater by Fe-Mn oxyhydroxides formed by BMC [11]. The hemipelagic swells of the External Subbetic were favorable settings for microbially mediated authigenesis due to the sediment-starved conditions [97,118].…”