Hardgrounds, reworked concretion levels and condensed horizons in the Jurassic of western India: their significance for basin analysis

Abstract

Jurassic sediments in the shallow pericratonic basins of Kachchh and Rajasthan, western India, exhibit numerous signs of reduced sedimentation, omission, erosion and in situ reworking, in combination with synsedimentary cementation. Hardgrounds developed on carbonate shoals in the Bathonian of Rajasthan, whilst reworked concretion levels are characteristic of offshore siliciclastic sediments of the Callovian of Kachchh. A prominent marker horizon, the Oxfordian Dhosa Oolite Member, occurs throughout much of the Kachchh sub-basin and is a highly condensed unit characterized by hardgrounds, intraformational cobbles, reworked concretions, stromatolitic iron crusts, iron oncoids, and shell lags. Hardgrounds, reworked concretion levels, and condensation horizons are interpreted as the preserved relicts of transgressive pulses. Such pulses were possibly controlled by eustatic rise of sea level. Of at least equal importance, however, was a tectonic control which is demonstrated by the presence of small neptunian dykes, boulder beds derived from small submarine cliffs and rapid lateral facies and thickness changes in the Dhosa Oolite Member. These indications of extensional tectonics are thought to be connected to rifting and initial sea floor spreading between Africa and India.

Storm-influenced deposition and cyclicity in a shallow-marine mudstone succession - example from the Middle Jurassic ore-bearing clays of the Polish Jura (southern Poland)

“…Thus, it seems that the rate of sed i men ta tion was sig nif i cantly de creased only in some parts of the ba sin and, as a re sult, the ho ri zons of hi a tus con cre tions are now of a lo cal ex tent. Accord ing to Fürsich et al (1992), the for ma tion of this type of concre tions re quires si mul ta neous cur rent re work ing and re duced sed i men ta tion rate. It is likely that the hi a tus ho ri zons from the Silesian-Cra cow area could be linked with intrabasinal swells, where the sed i men ta tion rate was lower and the ero sion more in ten sive than in the in ter ven ing lows.…”

Multiscale Erosion Surfaces of the Organic-Rich Barnett Shale, Fort Worth Basin, USA

“…The dark brown color could be due to either phosphate and/or iron oxide impregnation; the latter might prevail due to the oxidation of pyrite in an oxic zone as a result of shallowing conditions. A storm event is one process that can rework concretions and is associated with a fining upward sequence afterstorm [27].…”

Lithostratigraphy and sedimentology of the latest Cretaceous-early Burdigalian Tamezzakht succession (Northern Rif, Morocco): consequences for its sequence stratigraphic interpretation

“…Lending support to this is the concomitant reworking of glaucony-bearing bioclastic material (division c.3, facies tract interval IV, Fig. 4), which is well known to be produced by healthy platforms, in which the carbonate production is commonly favoured during the transgressive regime (many authors, e.g., Swift 1968;Droxler and Schlager 1985;Nummedal and Swift 1987;Baum and Vail 1988;Plint 1988;Fürsich et al 1991Fürsich et al , 1992Glaser and Droxler 1991;Schlager 1991;El Kadiri 2002a, b). Such an assumption may also be extended to certain gravity-flows at the regional scale, since they may act as the basal conglomerate of transgressive marine formations, a phenomenon that might be interpreted in terms of the "shelf sweep" process as discussed by Carannante et al (1999) or the transgressive washing concept presented by El Kadiri et al (2003).…”