Lacustrine Carbonates and Pedogenesis: Sedimentology and Origin of Palustrine Deposits from the Early Cretaceous Rupelo Formation, W Cameros Basin, N Spain

Abstract

The Berriasian Rupelo Formation of the W Cameros Basin consists of a 2-200 m thickness of marginal and open lacustrine carbonate and associated deposits. Open lacustrine facies contain a non-marine biota with abundant charophytes (both stems and gyrogonites), ostracods, gastropods and rare vertebrates Carbonate production was mainly biogenic. The associated marginal lacustrine ('palustrine') facies show strong indications of subaerial exposure and exhibit a wide variety of pedogenic fabrics. Silicified evaporites found near to the top of the sequence reflect a short hypersaline phase in the lake history. The succession was laid down in a low gradient, shallow lake complex characterized by wide fluctuations of the shoreline.Carbon and oxygen stable isotope analyses from the carbanates show non-marine values with ranges of 613C from -7 to -11%, and 6"O from -3 to -7.5%,. Differences in the isotopic composition of open lacustrine carbonates are consistent with sedimentary evidence of variation in organic productivity within the lake. Analyses from the entire sample suite plot on a linear trend; isotopic compositions become lighter with increasing evidence of pedogenic modification. This suggests progressive vadose zone diagenesis and influence of meteoric waters rich in soil-derived COz. The stable isotope data thus support evidence from petrography and facies relations that 'palustrine' limestones form through pedogenic modification of lake carbonates.

Stomatal density and stomatal index as indicators of paleoatmospheric CO2 concentration

“…The two straddling lines represent error estimates based on sensitivity analyses. Boxes in (a) represent 91 non-stomatal-based proxy estimates of varying RCO 2 resolution (data from Suchecky et al, 1988;Platt, 1989;Cerling, 1991Cerling, , 1992Freeman and Hayes, 1992;Koch et al, 1992;Muchez et al, 1993;Sinha and Stott, 1994;Andrews et al, 1995;Ghosh et al, 1995;Mora et al, 1996;Yapp and Poths, 1996;Ekart et al, 1999;Elick et al, 1999;Lee, 1999;Lee and Hisada, 1999;Pagani et al, 1999aPagani et al, , 1999bPearson and Palmer, 1999). The heavy line in (b) is a ®ve-point running average of the mean RCO 2 of every box in (a).…”

Palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record

“…The infl uence of COb derived from the soil or the atmosphere, controls the emichment of 16 0 and l2 C in shallow lakes and interstitial waters. Very commonly palustrine carbo nates show lower b 13 C and b 1S O values that non pedogenically modifi ed lacustrine carbonates (platt, 1989;Arenas et aI., 1997), and greater values than adjacent carbonate soils (Wright and Alonso-Zarza, 1992;Dunagan and Driese, 1999;Tarmer, 2000). However, evaporation processes and lakes fed by groWl dwater that have drained marine carbonates results in isotopic values greater than those expected.…”

Unusual sauropod tracks in the Jurassic-Cretaceous transition. Cameros Basin (Burgos, Spain)

“…is characterized by palustrine limestones with abundant intraclastic breccias, peloidal texture, pseudomicrokarst, root marks, and limnic fossils like charophytes, ostracods, and gastropods (Platt, 1989). The deposits are interpreted as a low gradient lake margin that exposed/inundated large areas with slight changes in water level.…”

“…In these shallow lakes, slight changes in water level associated with seasonal oscillations resulted in exposure or flooding of wide areas. During the dry season the lake water would fall to lower levels, exposing wide plains of carbonate mud affected by typical palustrine weathering (Platt, 1989;Alonso-Zarza, 2003;Huerta and Armenteros, 2005). Substrate conditions allowed the impression and preservation of tracks on these lake margins.…”

“…The tracksite together with La Pedraja tracksite is part of the Las Sereas outcrop, extending 5.6 Km from Quintanilla de las Viñas to Mambrillas de Lara villages (Torcida Fernández-Baldor et al, 2006;2012) and exposes a limestone unit known as Rupelo Fm. (Platt, 1986;Platt, 1989;Clemente, 2010). Las Sereas 7 occurs in the uppermost bed of the Rupelo Fm.…”