Palynofacies and paleoenvironment of the Upper Jurassic mud-supported carbonates, southern Croatia: Preliminary evaluation of the hydrocarbon source rock potential

Abstract

Despite the vast research on various aspects of its stratigraphy, relatively little is known about the source-rock potential of the Upper Jurassic Adriatic platform, southern Croatia. Here a case palynological study has been provided to determine the kerogen type, quality, and thermal maturity, and assess its relative hydrocarbon generative potential. Palynofacies characteristics indicate a low-energy, shallow-marine oxygen-depleted setting. The deposited mud-supported carbonates contain organic matter that is almost entirely composed of a fluorescent amorphous organic matter of planktonic and bacterial origin. A high phycomata/dinocyst ratio suggests relative hydrographic stability in an environment favorable for motile-stage dinoflagellate community with reduced production of dinocysts. The lack of anaerobic degradation and very good preservation of lipoid palynomorphs indicates dysoxic conditions; the latter also is suggested by a low proportion of algal-phytoplanktic carbohydrates. The lack of oxygen-deficient zone within the water column, coupled with well-preserved lipoid sediment components, suggests that the boundary between the oxygen-rich and oxygen-poor levels was likely located at/near the sediment-water interface. The palyno-organic facies analysis suggests that the organic matter corresponds to the type II (possibly I/II) kerogen (VRo ~0.3-0.4%) that was protected from degradation before, during and after sedimentation. Well-preserved lipoid components suggest a good hydrocarbon-generative potential, but the low TOC values (<0.1%) of studied outcropping Upper Jurassic carbonates prevent their designation as source rocks. Given the known sourcerock potential of the Upper Jurassic succession in the wider region, further studies of subsurface samples are needed to exclude the Oligocene-recent subaerial weathering as a culprit for the low TOC values.

Past environments of Sardinian archaeological sites (Italy, West Mediterranean Sea), based on palynofacies characterization

“…This valuable tool has been used in palaeoenvironmental, palaeoclimatological and palaeoceanographic reconstructions (e.g. van der Zwan 1990, Tyson 1995, Batten 1996, Gastaldo et al 1998, Cirilli et al 2015, Hochuli et al 2015, García Muro et al 2016, Kumar et al 2016, Okeke & Umeji 2016, Koch et al 2017) and has recently been tested in characterization of Holocene alluvial and palustrine deposits (e.g. Gastaldo & Huc 1992, Laggoun-Défarge et al 1995, Cohen et al 1999, Di Giovanni et al 1999, Bourdon et al 2000, Sebag et al 2006a, b, Serna et al 2015 through the identification and quantification of organic matter (OM) phytoclasts according to their origin, nature, formation or preservation in sedimentary processes.…”

Intelligent identification of sequence stratigraphy constrained by multipopulation genetic algorithm and dynamic time warping technique: A case study of Lower Cretaceous Qingshuihe Formation in hinterland of Junggar Basin (NW China)

“…Sediment samples of 10–30 g were treated with 10% HCl and 70% HF to remove carbonate and silica and subsequently cleaned to neutrality. Palyno‐residues were sieved using 10‐μm mesh nylon sieves (Koch et al., 2017). Finally, the kerogen residues were mounted on slides using glycerin jelly.…”

Assessing Milankovitch forcing in disconformity‐prone cyclic shallow‐water carbonates, Upper Jurassic (Kimmeridgian), Adriatic Platform, Croatia

“…The studied section makes up the highstand of JSS3, whose transgressive tract consists of poorly cyclic Oxfordian subtidal carbonates and highstand is the Kimmeridgian study interval. A major environmental change is noted in the middle Kimmeridgian, characterized by an overall shallowing‐upward associated with the establishment of more diversified and higher‐energy subtidal settings (Koch et al ., 2017).…”