Dear all,


Many thanks to all those who have responded, to the list or me personally, and offered their opinions on these structures. As I mentioned in the first e-mail, we tried to avoid adding bias by providing a geological setting and our own ideas. But to see if I can provide some context/insights (in no particular order):


1) The study area is offshore New Zealand and the strata is predominantly mudstones (you can see a polygonal fault network adjacent to the bodies) and sandstones. There is no salt or carbonate that we are aware of...I think! There are some igneous intrusions nearby, our main reason for looking at the data, and they look very different to these struuctures.


2) The body, overall, has an elliptical(ish) geometry, ~>10 km long. Unfortunately I'm out the office for a few days so can't access more images/measurements (perhaps Chris can help...).


3) The numbers on the side of the sections are spaced every 200 ms TWT and the black/white scale bar at the bottom is 2.5 km long. I can't remember the velocity information off the top of my head, though the nearest borehole is quite far away, but from what I recall there were no weird velocity reversals or anything.


4) There is no evidence of anything being withdrawn from beneath the bodies (e.g., salt).


5) As a number have pointed out, the top (blue) reflection is a negative polarity.


6) Both the base and top reflections are transgressive in places; if you look closely (apologies for the relatively poor resolution) the strata reflections adjacent to the body can be traced through the body as well (clearest on top right). Attribute analyses reveal that the polygonal fault pattern outwith the bodies can also be seen within them.


7) The data has a slightly higher frequency within the bodies (based on spectral decomposition).


8) The seabed does indeed host a series of massive canyons but these seem spatially unrelated to these structures.


Personally, I do not think that they are salt or igneous bodies and I can see the appeal of invoking gas/fluid/hydrate. My problem with these, however, is the irregular and oft transgressive nature of the contacts. There is no apparent, pre-existing structural or stratigraphic trap for gas/fluids that I can see, so what conditions would facilitate their accumulation?


I'll stop rambling now. Once again, thanks for all the comments and insights. They have been very useful. Do keep them coming!


Kind regards,

Craig


Dr Craig Magee
Research Fellow,
Room 2.60
Basins Research Group (BRG),
Department of Earth Science & Engineering, Imperial College, LONDON,
SW7 2BP
UK
 
 
Research Group Website: http://www.basinsresearchgroup.com/
Phone: +44 (0)20 7594 6510
From: Tectonics & structural geology discussion list <[log in to unmask]> on behalf of Tiago Alves <[log in to unmask]>
Sent: 24 November 2016 09:36:15
To: [log in to unmask]
Subject: Re: Mysterious structures in seismic data...
 

Hi everyone


It might be interesting to understand where these features occur re: to present-day structure. When interpreting such features, I am all for fluid and/or diagenetic fronts of some type - especially if internal seismic reflections are dimmed, but not deformed. Not all we observed on seismic actually represents a lithological change per se.


BW, Tiago


_____________________________

Tiago M. Alves

3D Seismic Lab

School of Earth & Ocean Sciences

Cardiff University

Main Building, Room 1.57A

Park Place

Cardiff

CF10 3AT

 

Direct line: 029 208 76754

Email: [log in to unmask]



From: Tectonics & structural geology discussion list <[log in to unmask]> on behalf of Stephen Richardson <[log in to unmask]>
Sent: 24 November 2016 08:58:38
To: [log in to unmask]
Subject: Re: Mysterious structures in seismic data...
 
Hi, thanks for sharing your seismic data, really interesting!

My initial reaction was also an allochthonous body, such as a salt, injected sand, or volcanic sill, but the strata around it are not deformed; i.e where your mystery body is thickest there is no deflection of the bounding reflections around the shape; the bounding reflections tramline around it. Based on the geometry of the surrounding strata, above and below the feature, I'd be less keen on something that was laterally emplaced at depth.
It could still have been deposited at the palaeo seabed though, but it would have been very a tall blob (no visible vertical scale but a guess of 12.5 m per reflection; appx 6 - 8 reflections) was topographically positive, and was not eroded. It also appears to truncate underlying reflections in the first image.

I think it's a post depositional change in the rock's seismic properties around that region, (Someone has already sugggested gas hydrates). My suggestion, although it's not my area of expertise - and therefore almost definitely wrong(!) , is a diagenetic feature?? Some sort of concreted body perhaps?

My questions I have when seeing this, What does it look like when the reflections above it and below it are a flattened ?
And how do the uppermost, and lowermost surfaces map out in 3D? Any clues in it's orientation? and any internal seismic signal that can be teased out with an attribute extraction?
Also the reflections underneath it show a lot of irregularity. How do they map out? and if it is not noise could there be features at depth related to your mystery 'thing' (Faults, pockmarks, I'm thinking fluid conduits...). Is there also any spatial relationship with the mystery body to the deeper channels at the seabed - no causal link I can think of, but they are very deep channels.

I hope that is of any help, it was certainly interesting to see. My colleagues have suggested the following other possibilities: UFO, Dinosaur (you can see the head apparently), and what was perhaps less daft, a carbonate reef.

All the best and good luck with the mystery blob!
Steve


On Thu, Nov 24, 2016 at 8:09 AM, Patricia Ruano <[log in to unmask]> wrote:

Hi all, without any información about area (latitude) and deth of seabed, I bet to gas hydrate deposit. The seabed bathymetry could shown a podmark, join with collapse estructure and the high-amplitude reflector than could be a BSR point out to gas hydrate are messing around.
Patricia

El 24 nov. 2016 5:22 a. m., Mark Rowan <[log in to unmask]> escribió:

>

> Hi all,
>
> There have been several posts that suggest salt. In my opinion, it’s not salt. First, the stratal geometry above and below the “body” are parallel, at least in the top two images. That is not what we typically see above and below salt. Second, although it’s difficult to see on the small image with its resolution limits, it seems as though the top of the body has a negative acoustic impedance contrast (opposite to that of the seafloor and “top basement”), and vice versa for the base. If I’m right (and please correct me , Craig), it has a lower velocity than than the surrounding strata.
>
> Nobody has yet mentioned the fact that in the upper left image, the top and base of the body are mirror images of each other (also seen to some degree in the upper right image)…
>
> I’m not saying that I know what this is, but I think I know what it’s not. Isn’t that helpful??
>
> Mark
>
> ——————
> Mark G. Rowan
> Rowan Consulting, Inc.
> 850 8th St.
> Boulder, CO 80302, USA
> 1.303.545.9437
> [log in to unmask]
>
>
>

>> On Nov 23, 2016, at 3:50 PM, timothy debacker <[log in to unmask]> wrote:

>>
>> Hi Craig,
>>
>> My initial thought was salt and structures related to salt mobilisation too, with top images showing section through lateral parts. However, if so, where did the salt originate from? Is the red reflector in the bottom image truly showing top basement? Some clues may be found in lithology and stratigraphy, and tectonic evolution of the area. Without these,  also Janos's comment seems possible.
>> Also - not sure about scale here - but do you have any detailed grav data over that area?
>> cheers
>>
>> Tim
>>
>> On Wed, Nov 23, 2016 at 11:03 PM, Katie Gates <[log in to unmask]> wrote:

>>>

>>> Hi Craig-
>>>
>>>
>>>
>>> The peak or high amplitude as you call it indicates the mystery horizon has a faster velocity than the surrounding sediment. My initial interpretation was also salt but I work exclusively on seismic data in the Gulf of Mexico and may be biased!
>>>
>>>
>>> Best of luck!
>>>
>>>
>>> Katie Gates
>>> Geophysicist
>>> Schlumberger
>>> Houston, Texas
>>>
>>> On Wed, Nov 23, 2016 at 3:43 PM Dirk Nieuwland <[log in to unmask]> wrote:

>>>>

>>>> Hi Craig, 
>>>>
>>>> Interesting seismic. An interpretation is a challenge, especially because I have no idea of the stratigraphy and the geological setting, but I shall give it a go:
>>>> What strikes me about the section in the bottom left corner is, that the beds in the center of the image have dropped down a lot.
>>>> This can be the case in a pull-apart situation in s strike-slip zone, or if the deeper formation is very mobile such as for example salt.
>>>> Also the top of the deep formation is very irregular. It reminds me of a section in a salt tectonics environment.
>>>> If that is correct, then the apparently isolated bodies in the middle of the other two pictures can be explained as salt structures. They look strange in insolation, but a section across a side of a salt “mushroom” can give you the isolated geometry as seen into first picture. The second picture could be part of a salt mushroom, but now intersected closer to the central part of the mushroom.
>>>> I would like to see deeper seismic, and I wonder if on deeper sections it would be possible to see velocity effects of the salt on a yet deeper formation. All of course assuming that the salt hypothesis is correct.
>>>> On the section at the top left, it seems that a section on the right hand side of the picture  is “sagging”, this could be associated with salt withdrawal, which is supported by the congruent sagging of the deep (salt) formation. To the left of the down moving zone the beds seem to move up, which could be the result of salt flowing from the sagging area to the left were there is now more uprising of salt. Extreme uprising results in the formation of a diaper, such as I interpret on the bottom left image.
>>>>
>>>> I would love to hear your final assessment.
>>>>
>>>> Regards,   Dirk
>>>>
>>>> Dr Dirk Nieuwland
>>>> 4e Binnenvestgracht 13
>>>> 2311NT Leiden
>>>> URL: www.newtec.nl
>>>> T:  +31 (0)71 5216892
>>>> M: +31 (0)621547949
>>>> E: [log in to unmask]
>>>>
>>>>

>>>>> On 23 Nov 2016, at 17:59, Magee, Craig <[log in to unmask]> wrote:

>>>>>

>>>>> Dear all,

>>>>>  
>>>>> A slight plea for help here. For those who like a mystery…does anyone have any ideas what on Earth these features are??? These are time-migrated, seismic reflection images – the seabed is just about visible at the top and the sediment-basement interface is the high-amplitude reflection at the bottom. The top two images are of the same feature (two orthogonal sections) and the bottom left is a different structure at a slightly high stratigraphic level.
>>>>>  


>>>>>
>>>>> <image001.jpg>


>>>>>
>>>>>  
>>>>> We have been puzzling over these for a while and are keen to hear what ideas fresh sets of eyes may have! To avoid bias, that is all I’ll say. If you would like more information, better images, or a copy of a small cropped volume (the data is freely available) please do let us know.
>>>>>  
>>>>> We look forward to hearing your ideas!
>>>>>  
>>>>> Kind regards,
>>>>> Craig Magee, Jenny Reeves, and Chris Jackson
>>>>>  
>>>>>  
>>>>> Dr Craig Magee
>>>>> Research Fellow,
>>>>> Room 2.60
>>>>> Basins Research Group (BRG),
>>>>> Department of Earth Science & Engineering, Imperial College, LONDON,
>>>>> SW7 2BP
>>>>> UK
>>>>>  
>>>>> E-mail: [log in to unmask]
>>>>> Personal Website: http://www3.imperial.ac.uk/people/c.magee
>>>>> Research Group Website: http://www.basinsresearchgroup.com/
>>>>> Phone: +44 (0)20 7594 6510
>>>>> Twitter: @DrCraigMagee
>>
>>
>