High‐frequency cyclicity (Milankovitch and millennial‐scale) in slope‐apron carbonates: Zechstein (Upper Permian), North‐east England

Abstract

The Upper Permian (Zechstein) slope carbonates in the Roker Formation (Zechstein 2nd-cycle Carbonate) in North-east England consist of turbidites interbedded with laminated lime-mudstone. Studies of turbidite bed thickness and relative proportion of turbidites (percentage turbidites in 20 cm of section) reveal well-developed cyclicities consisting of thinning-upward and thickening-upward packages of turbidite beds. These packages are on four scales, from less than a metre, up to 50 m in thickness. Assuming that the laminae of the hemipelagic background sediment are annual allows the durations of the cycles to be estimated. In addition, counting the number and thickness of turbidite beds in 20 cm of laminated lime-mudstone, which is approximately equivalent to 1000 years (each lamina is 200 lm), gives the frequencies of the turbidite beds, the average thicknesses and the overall sedimentation rates through the succession for 1000 year time-slots. Figures obtained are comparable with modern rates of deposition on carbonate slopes. The cyclicity present in the Roker Formation can be shown to include: Milankovitch-band ca 100 kyr short-eccentricity, ca 20 kyr precession and ca 10 kyr semi-precession cycles and sub-Milankovitch millennial-scale cycles (0AE7 to 4AE3 kyr). Eccentricity and precession-scale cycles are related to 'highstand-shedding' and relative sea-level change caused by Milankovitchband orbital forcing controlling carbonate productivity. The millennial-scale cycles, which are quasi-periodic, probably are produced by environmental changes controlled by solar forcing, i.e. variations in solar irradiance, or volcanic activity. Most probable here are fluctuations in carbonate productivity related to aridity-humidity and/or temperature changes. Precession and millennial-scale cycles are defined most strongly in early transgressive and highstand parts of the larger-scale short-eccentricity cycles. The duration of the Roker Formation as a whole can be estimated from the thickness of the laminated lithotype as ca 0AE3 Myr.

Hydrocarbon potential of the Zechstein Main Dolomite (Upper Permian) in western Poland: Relation to organic matter and facies characteristics

“…On the lower slope and on the toe-of slope apron calciturbidites and dolomudstones predominate (Type II; cf. Mawson and Tucker, 2009), as observed in the Gorz ow Wielkopolski2 well (Figs. 2 and 3A).…”

Orbital forcing in turbidite accumulation during the Eocene greenhouse interval

“…Using a similar approach, in the Eocene Ainsa basin (Spain) the accumulation of 25 turbiditic sandbodies in 10 Myr could be related to long‐period eccentricity ( ca 400 kyr) cycles (Heard et al ., ; Pickering & Bayliss, ). Finally, Mawson & Tucker () showed cyclicities in turbidite thickness and abundance in Permian carbonate slope‐apron deposits from England and suggested that they could be related to periodic fluctuations in carbonate productivity and sea‐level driven by short‐eccentricity and precession cycles.…”

Upper Permian Main Dolomite microbial carbonates as potential source rocks for hydrocarbons (W Poland)

“…Strohmenger et al (1996a) reported microbial-algal carbonates from NW Germany which were deposited in sabkha, tidal flat and reefal buildup environments. Coexisting with stromatolites, algal boundstones also occur in the Danish (Clark and (after Smith, 1980;Mawson and Tucker, 2009). BS e Bakevelia Sea.…”