Cretaceous Oceanic Anoxic Event 2 in eastern England: further palynological and geochemical data from Melton Ross
Version 3 2020-06-25, 12:58
Version 2 2020-05-27, 10:52
Version 1 2020-05-21, 08:53
Posted on 2020-06-25 - 12:58
The lowermost 1.45 m of the Welton Chalk Formation, including the regional sedimentary record of Oceanic
Anoxic Event 2 (OAE-2), has been sampled at Melton Ross Quarry in eastern England, UK. The section is investigated for
organic geochemistry and stable isotopes for the first time, while a detailed palynological study follows previously published
preliminary results. It comprises a condensed interval that spans the Cenomanian–Turonian Stage boundary. A locally
preserved, lower ‘anomalous’ succession (Beds I–VII) and a ‘Central Limestone’ (Bed A) are shown to correlate respectively
with the pre-Plenus sequence and Plenus Bed at Misburg and Wunstorf in the Lower Saxony Basin (LSB),NWGermany. They
are overlain by a succession of variegated marls (Bed B to Bed H), including the Black Band (Beds C–E), that can be correlated
across eastern England. Based on a carbon isotope (δ13C) profile and dinoflagellate cyst and acritarch bio-event correlation,
Beds B–H appear to be a highly attenuated post-Plenus equivalent of the LSB succession, including part of the ‘Fish Shale’.
The δ13C profile shows possible ‘precursor’/‘build-up’ events in the lower succession at Melton Ross, with the main OAE-2
δ13C excursion occurring in the Central Limestone and overlying Beds B–H. The darker coloured marls from the Black Band
and Bed G contain 1.43–3.47% total organic carbon (TOC), hydrogen index values of 78–203 mg HC/g TOC and oxygen
index values of 15–26 mg CO2/g TOC, indicating type III and type II–III organic matter, of mixed terrigenous and marine algal
sources. The corresponding palynological assemblages are dominated by marine dinoflagellate cysts, comprising mainly
gonyaulacoid taxa, with subordinate terrigenous miospores, mainly gymnosperm bisaccate pollen, consistent with a distal
marine setting. The interbedded lighter-coloured marls contain less than 0.4% TOC and lower proportions of miospores and
peridinioid dinoflagellate cysts compared with the darker layers. This is suggestive of moderately raised levels of productivity
during deposition of the darker layers, possibly related to greater nutrient availability from land-derived sources. The
occurrence of the peridinioid taxa Eurydinium saxoniense and Bosedinia spp., together with higher proportions of prasinophyte
phycomata in the darker layers, may also point to stimulation of organic-walled phytoplankton productivity by reduced nitrogen
chemo-species encroaching the photic zone, possibly by expansion of an oxygen-minimum zone. Exceptionally high
concentrations of palynomorphs (in the tens of thousands to lower hundreds of thousands per gramme range) in the darker
layers at Melton Ross and eight other eastern England localities is consistent with increased quality of seafloor preservation in a
low oxygen environment, coupled with a high degree of stratigraphic condensation. Two new dinoflagellate cyst species are
described from Melton Ross, Canninginopsis? lindseyensis sp. nov. and Trithyrodinium maculatum sp. nov., along with two
taxa described in open nomenclature.
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Dodsworth, Paul; Eldrett, James S.; Hart, Malcom B. (2020). Cretaceous Oceanic Anoxic Event 2 in eastern England: further palynological and geochemical data from Melton Ross. Geological Society of London. Collection. https://doi.org/10.6084/m9.figshare.c.4987205.v3
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AUTHORS (3)
PD
Paul Dodsworth
JE
James S. Eldrett
MH
Malcom B. Hart
CATEGORIES
KEYWORDS
OAE -2 δ13 C excursionδ13 C profileTrithyrodinium maculatum spinterbedded lighter-coloured marlsCOgymnosperm bisaccate pollenperidinioid taxa Eurydinium saxonienseBlack Bandmarine algal sourcesEnglandOceanic Anoxic Event 2successionperidinioid dinoflagellate cystsHCMelton RossLSBmarine dinoflagellate cystsattenuated post-Plenus equivalentWelton Chalk FormationUKCretaceous Oceanic Anoxic Event 2dinoflagellate cyst speciesorganic-walled phytoplankton productivityoxygen index valuesTOCMelton Ross Quarryacritarch bio-event correlationIIIIIlowermost 1.45 mGeology