Meteoric-like fabrics forming in marine waters: Implications for the use of petrography to identify diagenetic environments

Interpreting carbonate and organic carbon isotope covariance in the sedimentary record

“…We suggest that these post-depositional processes may account for the low concentration of organic carbon (o0.2%), the negative d 13 C org values (Fig. 2) and the increase in the proportion of lowmagnesium calcite 40 in the section of the core affected by meteoric diagenesis.…”

“…3b) . Diagenetic zones ('meteoric', 'mixing' and 'marine burial') were defined by published interpretations of both petrographic 40 and isotopic constraints 35 . The record of percent dolomite was determined by X-ray diffractometry 39 .…”

“…Ten subaerial exposure surfaces have been identified in the top 100 m of the core, each of which is proposed to have been related to a Pleistocene glacial period 37,38 . Evidence of both meteoric and marine diagenesis has been recorded within this 5.3 Ma record of marginal and shallow marine carbonates [39][40][41] , including the development of caliche crusts, blocky spar cements, large-scale dissolution and soil development 37,38,40 . Evidence of marine burial diagenesis includes non-depositional surfaces in the core 42 , which in some cases are associated with dolomites containing negative d 13 C carb signatures 43 .…”

The calcareous nannofossil <i>Prinsiosphaera</i> achieved rock-forming abundances in the latest Triassic of western Tethys: consequences for the <i>δ</i><sup>13</sup>C of bulk carbonate

“…This process is well documented on the periplatform carbonates off the Great Bahama Bank (Lasemi and Sandberg, 1984;Melim et al, 1995;Munnecke et al, 1997;Westphal, 2006) and was then recognized in numerous Phanerozoic fine-grained limestone successions as, among others, the Silurian of Gotland (Munnecke et al, 1997), the Upper Triassic of southern Italy (Preto et al, 2009(Preto et al, , 2013, the Upper Jurassic of southern Germany (Munnecke and Westphal, 2004;Munnecke et al, 2008). In the best-studied case of the periplatform deposits of the Bahamas, aragonite derives from shallow-water environments of the Great Bahama Bank platform top, and is then exported in surrounding periplatform successions by processes such as density cascading (Wilson and Roberts, 1995).…”

“…There is evidence of nearby carbonate platforms exporting carbonate into basins, both for the Lagonegro Basin (e.g., Miconnet et al, 1983;Passeri et al, 2005;Rigo et al, 2007) and Pizzo Mondello (Rigo et al, 2012b). We thus assume that the microsparitic component associated with calcareous nannofos-sils derived, in both sections, from shallow-water aragonitic sediment, dissolved and reprecipitated in the marine burial diagenetic environment (Melim et al, 1995). It cannot be assumed that the isotopic composition of carbon in the pore water was the same of seawater (as is the case in the Bahamas, Melim et al, 2001), because organic matter has been buried along with Triassic carbonate sediments.…”