A LITHOFACIES STUDY OF THE PETERBOROUGH MEMBER, OXFORD CLAY FORMATION(JURASSIC), UK - AN EXAMPLE OF SEDIMENT BYPASS IN A MUDSTONE SUCCESSION

Authors
Citation
Jhs. Macquaker, A LITHOFACIES STUDY OF THE PETERBOROUGH MEMBER, OXFORD CLAY FORMATION(JURASSIC), UK - AN EXAMPLE OF SEDIMENT BYPASS IN A MUDSTONE SUCCESSION, Journal of the Geological Society, 151, 1994, pp. 161-172
Citations number
32
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geosciences, Interdisciplinary
Journal title
ISSN journal
0016-7649
Volume
151
Year of publication
1994
Part
1
Pages
161 - 172
Database
ISI
SICI code
0016-7649(1994)151:<161:ALSOTP>2.0.ZU;2-9
Abstract
Thirteen samples from the Peterborough Member (Oxford Clay Formation, Middle Jurassic), from Quest Pit, Stewartby, central England, were exa mined in detail using a combination of optical microscopy and backscat tered electron imagery. The majority of the samples were clay-rich mud stones, two were silt-rich mudstones and one was a muddy sandstone. Th e dominant components of these samples are fine-grained clays (illite, mixed layer illite/smectite, kaolinite) and amorphous organic matter; minor components include authigenic pyrite (framboidal and euhedral), silt-sized quartz grains, calcareous nannoplankton (mainly disarticul ated coccolith plates) and a variety of early carbonate cements. Some of the mudstones were found also to contain abundant foraminifera. Tem poral trends between samples in grain size, foraminiferal abundance an d total organic carbon contents were observed. These mudstones were de posited in a shallow epeiric sea, where productivity was high and the bottom waters were oxic. Relative sea-level change, coupled to a lack of available accommodation space within the basin at low sea-level sta nds is invoked to explain the observed mudstone stacking patterns.