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Timing and duration of the early Hettangian marine inundation in the Polish Basin: organic carbon isotopes and astronomical calibration of the Triassic-Jurassic transition of the Niekłań PIG core (Holy Cross Mountains, SE Poland)

Lodowski Damian G., Martinez Mathieu, Hesselbo Stephen P., Hodbod Marta, Leng M., Pieńkowski Grzegorz, Brański Paweł, Pointer Robyn

Volumina Jurassica

2024

Vol. 22

87--116

Stratigraphy of non-marine sections and dynamics of marine transgressions in the deep geological past are important, yet challenging issues. Here we discuss results obtained from the Triassic–Jurassic (T–J) boundary interval of the Niekłań PIG drillcore section (Holy Cross Mountains or HCM, SE Poland). The core represents an expanded record of continental to marginal-marine facies, deposited within the axial part of the Polish Basin. The section is dated based on an integrated approach, utilizing palynologic proxies, stable carbon isotope correlations, and astronomical tuning of the section. Palaeoenvironment and its evolution is established by means of high-resolution sedimentology, clay mineral assemblages, and geochemical weathering indices (chemical index of alteration, CIA). The early to mid-Rhaetian was seasonal and progressively warmer and more humid, culminating with a hot and humid climate in the late Rhaetian; the earliest Jurassic was slightly cooler, yet still warm and humid, with year-round rainfall. Characteristic for the T/J boundary is the occurrence of two fern spikes (uppermost Rhaetian and lowermost Hettangian), which are associated with vegetation crises; this interval is also marked by wildfire indicators. Recognition of short eccentricity (~100 kyr) cycles enables calculation of sedimentation rates as well as temporal interpretation of the early Rhaetian marine inundation onto coastal plains of the Polish Basin. To begin with, over a period of ~200 kyr, a base-level rise led in the HCM region to a shift from fluvial to lacustrine depositional systems, while the final flooding marked by the onset of marine facies took another ~350 kyr. Additionally, observations allow inference of the magnitude of the early Hettangian relative sea-level rise, estimated herein to have been about 55 m.

A Callovian-Kimmeridgian stable isotope record from Staffin Bay, Isle of Skye, UK: implications for the ocean-atmosphere system

Nunn E., Price G., Hart M., Page K., Leng M.

Volumina Jurassica

2006

Vol. 4, no. 1

198-198

The Staffin Bay section in the Isle of Skye, UK is one of the most stratigraphically complete Oxfordian sections in Europe. This contribution presents the first high-resolution stable isotope record of this Middle Callovian to Early Kimmeridgian succession. The isotope record includes both terrestrial and marine data that were obtained from microscopic wood debris and belemnites respectively. The organic carbon-isotope record was derived from organic rich sediment samples taken almost entirely from the Staffin Shale Formation. This formation is largely represented by a series of isolated foreshore exposures dominated by mudrocks that were deposited in a predominantly offshore marine environment. Over 200 sediment samples were analysed from the 150 m section. The concurrent ä13C marine carbonate curve was produced using belemnites collected from the same formation. Approximately 200 belemnite horizons were sampled. The organic carbon-isotope data show a broad Lower to Middle Oxfordian positive carbon isotope excursion from the Mariae to Tenuiserratum Zone, with maximum values occurring in the Cordatum Zone. This is followed by a return to pre-excursion values continuing into the Early Kimmeridgian Cymodoce Zone. A brief negative excursion (of ~2‰) is also identified near the Densiplicatum-Tenuiserratum zones boundary. Rock-eval analysis confirms that the organic matter is predominantly terrestrial in origin. The concurrent ä13C marine carbonate curve derived from belemnites shows a broadly similar trend. This suggests that the positive carbon-isotope excursion recorded here may have affected the global carbon reservoir (i.e. the whole ocean-atmosphere system). The carbon-isotope record derived from this section appears to be generally consistent with Oxfordian Tethyan records (e.g. Wierzbowski 2002, 2004) and a preliminary study of the Staffin Bay area by Pearce et al. (2005).