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This paper looks at the organic geochemistry of the black shales deposited in the run-up to OAE 2 at Demerara Rise in the equatorial proto-Atlantic.  Using a range of biomarkers the suthors plot the increase in deoxygenation that moved in concert with increasing temperature, as documented by TEX₈₆ data.  Although association does not prove cause and effect, the paleoceanographic model they suggest makes general sense and they are careful to look also at the paleotectonic context of their section in the light of the evolving South Atlantic, which could have impacted basin geometry and watermass stratification.  An interesting highlight of the paper is the switch away from lycopane that is present in the upper Cenomanian to isorenieratane over the OAE 2 interval itself (Cenomanian–Turonian boundary), suggesting a change in the bacterioplankton consortium as photic-zone euxinic conditions took hold: presumably due to invasion by green sulfur bacteria.

Given the sampling density of this core, and the fact that the sedimentary material can move around, I wondered whether the samples giving new data could be accurately fixed in the stratigraphy and combined with pre-existing data.  Do the authors have any feeling for this?

My main grouse in the account is the mixing between rock (or sediment) and time and between rock and process.  You cannot sample an OAE or pass up into it: it is a phenomenon that leaves a distinctive record.  You cannot have a TOC value for OAE 2!  Use of the term ‘interval’, which can be applied to both sediment and time, can be helpful. 

Geological narrative should not be in the present tense.

In-text references should be preferably ordered consistently by date

Details:

Line 23:  I would hyphenate ‘water column’ where used as a compound noun–noun adjective

Line 27 and elsewhere: although the journal allows alphabetical in-text citations, I think that ordering by date is much to be preferred, as this technique indicates the academic trajectory of the point in question and gives credit where it is due.   Referencing is date ordered in some places in the manuscript . .  .  . but see below (Line 31 and 34).  Make consistent throughout the manuscript.

`line 31: references are not ordered by either alphabet or date!

Line 34: references are not ordered by either alphabet or date!

Line 41:  Avoid beginning a sentence with an unqualified ‘This’ or ‘These’, which is often ambiguous.  I suggest ‘These phenomena’

`line 76: I assume ‘sediment’ should be ‘samples’?  And change ‘was’ to ‘were’

Line 77: better would be “Cenomanian to Turonian interval’

Line 79: here you are mixing rock and time.  Unit IV is stratigraphically underlain by Albian phosphatic calcareous claystone

Line 83: there is confusion here between a phenomenon (such as an OAE) and sediment.  You cannot sample an OAE, only its sedimentary record.  Rephrase with something like ‘over the OAE 2 interval’. (‘Interval’ can be used for both rock and time and is a very useful term in this regard).  I suggest changing ‘following’ (time word) to post-dating.

Line 84: you cannot identify OAE 2 at Site 1258 (it is long gone!)  Change to ‘OAE 2 interval’

Line 101? We know that sediments can move position in a core, so conflating data sets fron samples taken years apart can be dangerous if correct stratigraphic order is not retained.  How confident are the authors that all data are in correct stratigraphic order?

Line 117: better would be ‘.  .  . serves as a proxy for water-column anoxia. .  .  .’

Line 142: ‘during’ is a time word and you are describing a geochemical characteristic of a sediment sample.  ‘  .  . in the OAE 2 interval .  .  . ‘ would be better

Line 158” change to ‘water-column’ (with a hyphen)

Line 162: change to ‘up to the OAE 2 intervaL’

Line 166: change to ‘lower Cenomanian’: this is rock not time.

Line 167: water-column

Line 177: replace ‘ “Following OAE 2’ by ‘stratigraphically higher than the OAE 2 interval’ or similar

Line 178: change to ‘Upper Cretaceous’ – you are describing a feature of the sediment

Line 182: delete hyphen after ‘long-‘

Line 183” better would be: ‘culminating in the OAE 2 interval

Line 190:: hyphenate ‘bottom water’ used as a compound adjective

Line 191: better would be ‘ just below the onset level of OAE 2’ (to avoid mixing sediment with a phenomenon)

Line 194: replace ‘sometime’ with ‘in some cases’

Line 205” ‘over the OAE 2 interval’

Line 203: but presumably impinging on the sea floor if benthic foraminifera are affected?

Line 205: change to ‘This phenomenon has also been reported. .  . .’

Line 211: change to ‘highest in the OAE 2 interval . . . ’

Line 211: change to ‘were driven’ – this is geological narrative

Line 213” ‘were replaced’

Line 218: ‘over the OAE 2 interval’ would be better

Line 219: water-column

Line 224: change ‘into’ to ‘during’

Line 225: water-column

Line 226: This process also gives rise. .  .  .

Line 230/231: change to : ‘water-column’

Line 234: change to:  ‘these metal-isotope data by confirming  .  .  .’

Line 234: water-column

Line 235: change ‘adding’ to ‘adds’

Line 235 Line 225: water-column

Line 240: delete hyphen from adverb to give ‘nearly closed’ – this is journal house style

Line 244: change to ‘This result. .  .  .

Line 245: change ‘of’ to ‘for’

Line 347: Line 225: water-column

Line 253: ‘Therefore, this result illustrates the occurrence of marine water-column anoxia  . 

Line 256: change to ‘propagated’.  .’

Line 257: should this be ‘bottom-water anoxia’?

Line 257: change to ‘was linked’

Line 258: change to ‘was overridden’

Line 259: ‘watermass’ (one word)

Line 260: change to ‘in contrast to. .  .  .’

Line 264: should this be ‘deep-water convection’?

Line 266: water-column

Line 271: change to ‘during the Cenomanian. .  .  .’

Line 273: change to ‘during this time’ (not necessary to repeat ‘Cenomanian’

Line 284: change to ‘that persisted. .  .  .’

Line 287: change ‘’is not’ to ‘was not’

Line 289: change to ‘was related’

Line 292: water-column

Line 295: not clear what ‘these’ refers to – clarify

Line 298: water-column

Line 298/299: anoxia correlates with warming but association does not prove cause and effect

Line 300: water-column

Line 305: better would be ‘albeit modulated by climatic factors

579/580” Cross-plot and water-column (add hyhens)