A depositional model for spherulitic carbonates associated with alkaline, volcanic lakes

Ramon Mercedes-Martín, Alexander T Brasier, Mike Rogerson, John J. G. Reijmer, Hubert Vonhof, Martyn Pedley

Research output: Contribution to journalArticle

11 Citations (Scopus)
9 Downloads (Pure)

Abstract

The South Atlantic Aptian 'Pre-salt' reservoirs are formed by a combination of spherulitic carbonates and Mg-rich clays accumulated in volcanic alkaline lake settings with exotic chemistries. So far, outcropanalogues characterised by metre-thick successions deposited in lacustrine scenarios are elusive so disentangling the genesis of spherulitic carbonates represents a major scientific challenge with business impact. In particular the controls on spatial distribution and the environment of spherulitic facies formation remain poorly constrained, little studied, and hotly debated. To shed light on this conundrum, a spherulitic carbonate-rich, alkaline volcanic lacustrine succession has been analysed at outcrop scale: the Carboniferous East Kirkton Limestone (Scotland). Despite clays being very scarce and limited to layers of amorphous Mg-Si minerals, a diverse array of components were formed, including coated grains, crusts, and build-ups with spherulitic calcitic morphologies. This setting enables the mechanisms of spherulitic calcite development and the patterns of sediment accumulation to be explored in a geobiological and hydrochemical scenario similar to the 'Pre-Salt' subsurface occurrences but divorced from clay influence. The integration of logs, borehole data, outcrop photomosaics and petrographic observations collectively allowed the reconstruction of a depositional model for the East Kirkton lacustrine succession. In this model, calcite spherule nucleation took place at the sediment-water interface in the littoral zone, driven by the co-occurrence of 1) high alkalinity, 2) CaMg rich hydrochemistry, and 3) microbial-derived colloidal exopolymeric substances. These environmental conditions permitted the coeval development of spherulitic cementstone build-ups and spherulitic
grainstone-packstone within the wave-agitated zone, and the accumulation of floatstones and laminites of spherulitic grains in deeper lake regions by means of downslope reworking. This model is consistent with the previously documented microbial bloom occurrences and highlights the need to better understand the complex 'microbe-solution' interactions before any reliable facies model is envisaged.
Original languageEnglish
Pages (from-to)168-191
Number of pages26
JournalMarine and Petroleum Geology
Volume86
Early online date25 May 2017
DOIs
Publication statusPublished - Sep 2017

Fingerprint

lakes
volcanology
carbonates
clays
carbonate
outcrops
lake
occurrences
calcite
clay
sediments
outcrop
spherules
salts
salt
alkalinity
Scotland
spherule
hydrochemistry
limestone

Keywords

  • spherule
  • spherulitic
  • calcite
  • alkaline
  • lacustrine
  • volcanic
  • carboniferous
  • pre-salt

Cite this

A depositional model for spherulitic carbonates associated with alkaline, volcanic lakes. / Mercedes-Martín, Ramon ; Brasier, Alexander T; Rogerson, Mike ; Reijmer, John J. G. ; Vonhof, Hubert ; Pedley, Martyn .

In: Marine and Petroleum Geology, Vol. 86, 09.2017, p. 168-191.

Research output: Contribution to journalArticle

Mercedes-Martín, Ramon ; Brasier, Alexander T ; Rogerson, Mike ; Reijmer, John J. G. ; Vonhof, Hubert ; Pedley, Martyn . / A depositional model for spherulitic carbonates associated with alkaline, volcanic lakes. In: Marine and Petroleum Geology. 2017 ; Vol. 86. pp. 168-191.
@article{f162b739bace44a19233db6b8fe57afc,
title = "A depositional model for spherulitic carbonates associated with alkaline, volcanic lakes",
abstract = "The South Atlantic Aptian 'Pre-salt' reservoirs are formed by a combination of spherulitic carbonates and Mg-rich clays accumulated in volcanic alkaline lake settings with exotic chemistries. So far, outcropanalogues characterised by metre-thick successions deposited in lacustrine scenarios are elusive so disentangling the genesis of spherulitic carbonates represents a major scientific challenge with business impact. In particular the controls on spatial distribution and the environment of spherulitic facies formation remain poorly constrained, little studied, and hotly debated. To shed light on this conundrum, a spherulitic carbonate-rich, alkaline volcanic lacustrine succession has been analysed at outcrop scale: the Carboniferous East Kirkton Limestone (Scotland). Despite clays being very scarce and limited to layers of amorphous Mg-Si minerals, a diverse array of components were formed, including coated grains, crusts, and build-ups with spherulitic calcitic morphologies. This setting enables the mechanisms of spherulitic calcite development and the patterns of sediment accumulation to be explored in a geobiological and hydrochemical scenario similar to the 'Pre-Salt' subsurface occurrences but divorced from clay influence. The integration of logs, borehole data, outcrop photomosaics and petrographic observations collectively allowed the reconstruction of a depositional model for the East Kirkton lacustrine succession. In this model, calcite spherule nucleation took place at the sediment-water interface in the littoral zone, driven by the co-occurrence of 1) high alkalinity, 2) CaMg rich hydrochemistry, and 3) microbial-derived colloidal exopolymeric substances. These environmental conditions permitted the coeval development of spherulitic cementstone build-ups and spheruliticgrainstone-packstone within the wave-agitated zone, and the accumulation of floatstones and laminites of spherulitic grains in deeper lake regions by means of downslope reworking. This model is consistent with the previously documented microbial bloom occurrences and highlights the need to better understand the complex 'microbe-solution' interactions before any reliable facies model is envisaged.",
keywords = "spherule, spherulitic, calcite, alkaline, lacustrine, volcanic, carboniferous, pre-salt",
author = "Ramon Mercedes-Mart{\'i}n and Brasier, {Alexander T} and Mike Rogerson and Reijmer, {John J. G.} and Hubert Vonhof and Martyn Pedley",
note = "BP Exploration Co. is thanked for funding, and particularly the Carbonate Team for supporting this research and for fruitful discussions. West Lothian Council and Scottish Natural Heritage are thanked for allowing access and permission for sampling the site. Graham Tulloch (BGS Edinburgh), Nick Fraser (NMS), Tracey Gallagher and the Core Store Team at BGS Keyworth are particularly acknowledged for their assistance. Rona McGill is kindly thanked for provide the photomosaic in Figure 3. Tony Sinclair, Mark Anderson (University of Hull), and Bouk Lacet (VU University Amsterdam) are thanked for sample preparation. Reviewers are warmly thanked for their detailed and valuable comments which help to sharpen the manuscript. Peir Pufahl is acknowledged for his constructive advice on an earlier draft, and Nereo Preto for his editorial assistance.",
year = "2017",
month = "9",
doi = "10.1016/j.marpetgeo.2017.05.032",
language = "English",
volume = "86",
pages = "168--191",
journal = "Marine and Petroleum Geology",
issn = "0264-8172",
publisher = "Elsevier",

}

TY - JOUR

T1 - A depositional model for spherulitic carbonates associated with alkaline, volcanic lakes

AU - Mercedes-Martín, Ramon

AU - Brasier, Alexander T

AU - Rogerson, Mike

AU - Reijmer, John J. G.

AU - Vonhof, Hubert

AU - Pedley, Martyn

N1 - BP Exploration Co. is thanked for funding, and particularly the Carbonate Team for supporting this research and for fruitful discussions. West Lothian Council and Scottish Natural Heritage are thanked for allowing access and permission for sampling the site. Graham Tulloch (BGS Edinburgh), Nick Fraser (NMS), Tracey Gallagher and the Core Store Team at BGS Keyworth are particularly acknowledged for their assistance. Rona McGill is kindly thanked for provide the photomosaic in Figure 3. Tony Sinclair, Mark Anderson (University of Hull), and Bouk Lacet (VU University Amsterdam) are thanked for sample preparation. Reviewers are warmly thanked for their detailed and valuable comments which help to sharpen the manuscript. Peir Pufahl is acknowledged for his constructive advice on an earlier draft, and Nereo Preto for his editorial assistance.

PY - 2017/9

Y1 - 2017/9

N2 - The South Atlantic Aptian 'Pre-salt' reservoirs are formed by a combination of spherulitic carbonates and Mg-rich clays accumulated in volcanic alkaline lake settings with exotic chemistries. So far, outcropanalogues characterised by metre-thick successions deposited in lacustrine scenarios are elusive so disentangling the genesis of spherulitic carbonates represents a major scientific challenge with business impact. In particular the controls on spatial distribution and the environment of spherulitic facies formation remain poorly constrained, little studied, and hotly debated. To shed light on this conundrum, a spherulitic carbonate-rich, alkaline volcanic lacustrine succession has been analysed at outcrop scale: the Carboniferous East Kirkton Limestone (Scotland). Despite clays being very scarce and limited to layers of amorphous Mg-Si minerals, a diverse array of components were formed, including coated grains, crusts, and build-ups with spherulitic calcitic morphologies. This setting enables the mechanisms of spherulitic calcite development and the patterns of sediment accumulation to be explored in a geobiological and hydrochemical scenario similar to the 'Pre-Salt' subsurface occurrences but divorced from clay influence. The integration of logs, borehole data, outcrop photomosaics and petrographic observations collectively allowed the reconstruction of a depositional model for the East Kirkton lacustrine succession. In this model, calcite spherule nucleation took place at the sediment-water interface in the littoral zone, driven by the co-occurrence of 1) high alkalinity, 2) CaMg rich hydrochemistry, and 3) microbial-derived colloidal exopolymeric substances. These environmental conditions permitted the coeval development of spherulitic cementstone build-ups and spheruliticgrainstone-packstone within the wave-agitated zone, and the accumulation of floatstones and laminites of spherulitic grains in deeper lake regions by means of downslope reworking. This model is consistent with the previously documented microbial bloom occurrences and highlights the need to better understand the complex 'microbe-solution' interactions before any reliable facies model is envisaged.

AB - The South Atlantic Aptian 'Pre-salt' reservoirs are formed by a combination of spherulitic carbonates and Mg-rich clays accumulated in volcanic alkaline lake settings with exotic chemistries. So far, outcropanalogues characterised by metre-thick successions deposited in lacustrine scenarios are elusive so disentangling the genesis of spherulitic carbonates represents a major scientific challenge with business impact. In particular the controls on spatial distribution and the environment of spherulitic facies formation remain poorly constrained, little studied, and hotly debated. To shed light on this conundrum, a spherulitic carbonate-rich, alkaline volcanic lacustrine succession has been analysed at outcrop scale: the Carboniferous East Kirkton Limestone (Scotland). Despite clays being very scarce and limited to layers of amorphous Mg-Si minerals, a diverse array of components were formed, including coated grains, crusts, and build-ups with spherulitic calcitic morphologies. This setting enables the mechanisms of spherulitic calcite development and the patterns of sediment accumulation to be explored in a geobiological and hydrochemical scenario similar to the 'Pre-Salt' subsurface occurrences but divorced from clay influence. The integration of logs, borehole data, outcrop photomosaics and petrographic observations collectively allowed the reconstruction of a depositional model for the East Kirkton lacustrine succession. In this model, calcite spherule nucleation took place at the sediment-water interface in the littoral zone, driven by the co-occurrence of 1) high alkalinity, 2) CaMg rich hydrochemistry, and 3) microbial-derived colloidal exopolymeric substances. These environmental conditions permitted the coeval development of spherulitic cementstone build-ups and spheruliticgrainstone-packstone within the wave-agitated zone, and the accumulation of floatstones and laminites of spherulitic grains in deeper lake regions by means of downslope reworking. This model is consistent with the previously documented microbial bloom occurrences and highlights the need to better understand the complex 'microbe-solution' interactions before any reliable facies model is envisaged.

KW - spherule

KW - spherulitic

KW - calcite

KW - alkaline

KW - lacustrine

KW - volcanic

KW - carboniferous

KW - pre-salt

U2 - 10.1016/j.marpetgeo.2017.05.032

DO - 10.1016/j.marpetgeo.2017.05.032

M3 - Article

VL - 86

SP - 168

EP - 191

JO - Marine and Petroleum Geology

JF - Marine and Petroleum Geology

SN - 0264-8172

ER -