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Sedimentology and isotopic composition of Upper Palaeocene to Eocene non‐marine stromatolites, eastern Ebro Basin, NE Spain
Author(s) -
ZAMARREÑO I.,
ANADÓN P.,
UTRILLA R.
Publication year - 1997
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.1997.tb00430.x
Subject(s) - geology , sedimentology , paleontology , fluvial , facies , structural basin , mesozoic , carbonate , materials science , metallurgy
Stromatolites are abundant in Upper Palaeocene to Eocene fluvial deposits from the Eastern Ebro Basin, whereas they are scarce in the lacustrine facies. The fluvial stromatolites display a variety of growth forms: oncoids, domes, laminated crusts and locally irregular bioherms. These morphologies are related to the hydrological behaviour of the fluvial systems. Elongate domes, dome heads and ovoid to subspherical oncoids accreted in flowing water. Laminated crusts and small‐sized cylindrical to lenticular oncoids formed during low‐discharge and ponding phases. In the lacustrine environments only small‐sized ovoid oncoids occur. The main characteristics of the Ebro Basin non‐marine stromatolites are: (1) laminations and concentric banding exhibited by all morphologies; (2) the occurrence of well‐preserved cyanobacterial filaments in several laminae, suggesting that these microbiotas are the major contributors in growth; (3) the asymmetrical growth of cortices in domes and oncoids with polar thickening on the upper side suggesting in situ growth under low energy conditions. δ 13 C values of carbonate stromatolites range from ‐ 11.3%o (Late Palaeocene) to — 4.4%o (Middle‐Late Eocene). During the Late Palaeocene, under tectonically quiescent conditions, the δ 13 C values mainly reflect the influence of soil‐derived CO 2 . During the Eocene, the progressive uplift of the surrounding catchment areas led to an increase of exposures of Mesozoic rocks. Consequently, the δ 13 C values of the Eocene stromatolites reflect the influence of the CO 2 derived from the dissolution of Mesozoic marine carbonates. There is a 2.5%o shift in δ 18 O values of stromatolites from the Late Palaeocene to Middle‐Late Eocene which is consistent with the variation in δ 18 O of precipitation due to changes in altitude of the catchment area during this time. The isotopic values of all Middle‐Upper Eocene laminated crust samples show distinct covariant trends, suggesting that these stromatolites were formed either in ponding zones of fluvial channels or in disconnected pools developed during low‐discharge episodes.