Hirnantian (Late Ordovician) δ13C HICE excursion in a North Gondwanan (NE Spain) periglacial setting and its relationship to glacioeustatic fluctuations

摘要: Abstract In the Iberian Chains of northeastern Spain, Hirnantian Orea Shale comprises three erosive glaciogenic unconformities punctuating two transgressive glaciomarine sequences. These sequences represent ice retreat episodes grounded on a North Gondwanan region 50–60°S estimated palaeolatitude. contrast, same formation recorded in Hesperian repeated extensional tectonic activity: diamictites were associated with slope-related debris flows and slumps commonly interrupted by truncating discontinuities. An analysis δ 13 C org has revealed that lower sequence displays isotopically light baseline values (∼ −27‰) punctuated minor (2–3‰) shifts. distal parts, upper is characterised rapid rise values, which mark positive excursion, range 2.5‰ to 7‰ over 40 cm thickness. The stratigraphic gap involved intra-Orea unconformity appears be greater both proximal exposures (Hesperian) areas, where chemostratigraphic shift was not recorded. Upsection studied sections, display upsection sharp return −26‰ −28‰. strata have major correlatable events: (i) karstic surface caps Katian limestones reflects maximum glacial extension; (ii) single peak ∼6‰ recognisable ramp settings, marking beginning second episode probably representing late HICE shift; (iii) marked progradation Los Puertos shoreline complexes.