The bulk sediment δ13Ccarb record on the Ainsa slope shows a remarkable degree of correlation (R = 0.81) with the eustatic curve of Miller et al. (2005) from the New Jersey margin (Fig. 2.3), and weaker correlation with other sea-level curves (R < 0.5). This correlation allows a comparison of local and global δ13C, and interpretation of patterns of transgression and regressions with respect to global sea-level changes. The average bulk δ13Ccarb of -1.21 h ± 0.62 h is consistent with values from large benthic foraminifera of the same succession (Das Gupta (2008); meanδ13C = -1.05 h ± 1.36h), indicating dominant contribution of in situ foraminiferal content. The studied slope section is 1.96h more negative than the contemporaneous deep-sea global average of +0.75h, and 3.5 ×more variable (1σ = 0.62 h compared with 1σ = 0.17 h). The δ13Ccarb variations commonly reflect a combination of diagenesis, mineralogical variability, and vital effects of calcifying organisms, but the negative shift and signal amplification observed here are consistent with the restricted physiography and proximal position of the Ainsa Basin. Such physiography prevents rapid exchange with the ocean and can lead to larger amplitude and higher frequency in δ13C variability than the global ocean reservoir (Saltzman and Thomas (2012)). Moreover, lower isotopic values are imposed upon proximal environments by oxidation of organic carbon brought by rivers (Kroopnick (1985), Jenkyns (1996)). Both the correlation with eustasy and similarity of shape between several segments of the global and local δ13C records (e.g., excursions a, b, c in Fig. 2.3) support a primary component in the bulk sediment δ13Ccarb signal. In addition, the lack of statistically significant positive correlation between δ13Ccarb and δ18Ocarb values (R = 0.35) and the narrower range of the δ18Ocarb compared to that of the δ13Ccarb values (2.6 h and 3.5h, respectively) indicate very low or no diagenetic resetting of the primary isotopic
δ13C & sea level in the Ainsa Basin 29 compositions (Fig. A.2; Table B.1). TOC is overall low (∼0.34 wt%), with mature to overmature Tmax indices (Fig. A.3) and no major variations or systematic link with δ13Ccarb, but shows significant pulses of preservation during the highstand of sequence E4 of Miller et al. (2005). Positive excursions of HI/OI (indicative of material derived from marine and/or lacustrine algae and plankton and in situ bacterial reworking; McCarthy et al. (2011)) mostly take place at times of interpreted maximum flooding surface and sea-level highstands (Fig. 2.2). The Fosado, Gerbe I, Gerbe II, and Banaston sand systems were active during sea-level lowstands of sequences E4, E6, E6a, and E7 (Miller et al. (2005)). Progradation of the shelfal Perrarua Formation (Mutti et al. (1988), Payros et al. (2009)) took place during the lowstand of sequence E5 (Fig. 2.3). Deposition during highstands of E4, E5, E6, and E6a was dominated by distal slope hemipelagic sedimentation.
The Arro SGF deposition took place ca. 50 Ma, during rising relative sea level (positive δ13Ccarb excursion) and a plateau highstand of sequence E4.
2.4 Discussion: eustatic, tectonic, and climatic controls on clastic deposition
At periodicities of 1 m.y., both climate and solid Earth processes control eustasy (Cloetingh and Haq (2015)). Similarly, landscape response times are
compati-ble with climate-controlled sediment supply variations over time scales of 1 m.y.
(Castelltort and Van Den Driessche (2003)). It is challenging to distinguish between a purely eustatic and a coupled climate-eustatic origin for the observed strati-graphic cycles. Therefore, the correlations between Ainsa stratistrati-graphic cycles, bulk sediment δ13Ccarb, and the eustatic curve of Miller et al. (2005) reflect a eustatic (tectonic or climatic) control on SGF deposition possibly (but not necessarily) coupled with a climatic control on sediment supply, and rule out a Pyrenean tectonic control. Specifically, the Fosado, Perrarua, Gerbe I and II, and Banaston SGF deposits were emplaced during global lowstands, implying eustatic forcing of sediment transfer to deep-water.
In contrast, the occurrence of the Arro SGF deposit ca. 50 Ma during rising and highstand sea levels of sequence E4 suggests a pulse of sediment supply of sufficient magnitude to have induced deltaic progradation to the shelf edge and subsequent deep-marine deposition (Burgess and Hovius (1998)). This is
Pedraforca nappes Vallfogona thrust Sierras Marginales / Montsec / Boixols Morerres thrust and Axial Zone Exhumation ~50 Ma
16001400120010008006004000
meters
Kominz et al. (2008) Eastern Pyrenees South-Central Pyrenees
464748 4950C22rC21rC20C21nC22n
100
Figure 2.3: Theδ13Ccarb record in the Ainsa Basin (Pyrenees, Spain) versus Pyrenean tectonics, global sea level, and isotopic records. SGF-sediment gravity flow; C-chron.
White stars 1–4 are biostratigraphic anchors in the depth domain placed with age uncertainty in the time domain. δ13Ccarb maxima are aligned with highstands (white dots) on the New Jersey (USA) eustatic curve (Miller et al. (2005)). Resulting correlation yields R = 0.81. E3-E6a-Miller et al. (2005) sequences. Eustatic and deep-sea benthic isotope records (Cramer et al. (2009)) calibrated to The Geologic Time Scale 2012 (GTS;
Gradstein et al. (2012)) are shown for comparison. Tectonic events are derived from Whitchurch et al. (2011). Positive excursions a, b, and c of Cramer et al.’s (2009) global
synthesis show similarity with carbon isotope record of the Pueyo section.
supported by anomalous progradation of the Arro-equivalent Castissent fluvio-deltaic formation (Fig. A.1), reaching the break-in-slope of the coeval delta-front
δ13C & sea level in the Ainsa Basin 31 platform (Marzo et al. (1988)). In the absence of notable global climatic events at that time (Zachos et al. (2001)), a tectonic origin is suggested by stratigraphic evidence of basin-axis shift toward the foreland at Arro time (Marzo et al. (1988), Nijman (1998)) linked with renewal of thrust activity and a pulse of exhumation in the hinterland at 50 Ma (Whitchurch et al. (2011)). We speculate that tectonic uplift induced a transient pulse of sediment supply during landscape readjustment, trigger- ing progradation of the Castissent fluvio-deltaic system and deposition of the Arro highstand SGF. During subsequent deposition above the Arro SGF, it appears that landscape conditions closer to equilibrium were responsible for more constant sediment supply, and stratigraphic cyclicity could have been modulated by eustasy, coupled or not with climate, despite the active tectonic context of the Pyrenees and the narrow shelf prone to deep-marine coarse-clastic deposition during highstands (Covault et al. (2007)).
Carbon isotope studies of paleoclimate and oceanographic evolution have proposed a relationship between eustatic changes and carbon isotopic profiles primarily based on deep-sea pelagic sections of fine-grained carbonate-rich lithologies, generally away from clastic influx of active continental margins (Woodruff and Savin (1985), Arthur et al. (1987), Weissert (1989), Jenkyns (1996), Zachos et al. (2001)).
However, such distal carbonate records have poor physical relationships with thick clastic stratigraphic sequences of continental margins. High-resolution carbon isotopes in clastic slope systems provide a potentially sensitive proxy of global sea-level changes, amplified with respect to coeval deep-sea records as a result of the restricted nature of the margin setting (Saltzman and Thomas (2012)). Collection of such an independent continuous sea-level proxy between sequence stratigraphic surfaces provides a more robust means to assess relationships between stratigraphy and possible driving signals than widely used approaches of matching sequence boundaries with global charts (Miall (1992)).
Other key slope outcrops such as the Karoo (Flint et al. (2011)), Tres Pasos (Romans et al. (2011)), or Spitsbergen (Crabaugh and Steel (2004)) could constitute interesting tests of the approach presented here, provided adequate preservation of primary signals.