Bowland Shales – type succession

Today (15th December 2014) the exploration company reported that their exploratory well at Ellesmere Port, near the mouth of the River Mersey had struck gas, but not oil. They did not say anything beyond shales being gas-rich.  From their press release the drill had passed though some 800 ft of Coal Measures cutting through several seems and 1400ft of the magical Bowland Shales and Sabden shales, which contained quantities of gas.

As gas firms are looking for Bowland Shales thousands of feet below the surface we often don’t  see them as cores will often bring up sludge or rather cuttings! but a change of drill bit allows decent cores.  However  however there are considerable exposures of Bowland shales in the Forest of Bowland and around Pendle Hill. This Victorian geological map shows the area from the Craven fault down to the Mersey, with Ellesmere Port just south of the River Mersey. During the frist half of the Carboniferous the area from the Craven Fault to beyond the Mersey was a deepening basin, which being to deep for limestone as at Llangollen or parts of the Dales, was filled with an ooze rich in decaying life forms, which over time with the right temperature and pressure became rich in TOC (Total Organic Content) i.e. mostly Methane.

At Ellesmere Port the Bowland Shalles was 1400ft thick far thicker than the 800ft in Little Mearley Brook on the west side of Pendle Hill. The upper part of Mearley Brook is the type section of the Bowland Shales and I ascended it last September and this is a photographic record of the Brook .

Bowland geol map

The key features of the map are the type area for the Bowland Shales between the Craven Fault and the Grimsargh/Bilsborrow set of faults which run close to the M6.  This simplistically is a succession of lower Carboniferous which a mixture of  limestones and shales (Sabden) and some sandstone. Above that are the Lower and then Upper Bowland Shales capped by Pendle Grit. Below is a simplified cross-section by Chipping between the hills, Parlick and Longridge Fell. (I found oil oozing out of the UBS on Parlick.) My section on Little Mearley started at the base of the LBS and passed the Pendleside Sandstone to the UBS and the last few hundred feet of the gully was hard Pendle Grit.

geo2 - Copy

These two maps give the localities. The tower east of Blackpool marks the Cuadrilla sites near Kirkham. (1) is Pendle Hill  (2) is the gully of UBS I described in https://michaelroberts4004.wordpress.com/2014/09/15/namurian-succession-upper-bowland-shales-to-pendle-grits-forest-of-bowland/

https://michaelroberts4004.wordpress.com/2014/09/18/the-first-fracking-in-lancashire/.

(3) is Blue Scar with unusual injectites of Hind Sandstone intruding into UBS described byIan Kane in Development and flow structures of sand injectites: The Hind Sandstone Member injectite complex, Carboniferous, UK; (Marine and Petroleum Geology 27 (2010) p1200-15.

clitheroe

Here is the Cross-section of Little Mearley Brook form the BGS Memoir Geology of the country around Clitheroe and Nelson 1961 pp89-91.

Littlemearley

All my attempts to make this cross-section legible failed so I will type it out

NAMURIAN

Pendle Grit  (eqiuv to Millstone Grit)

UBS 400ft

DINANTIAN

Pendleside Sandstone  (several bands) (junction of Dinantian and Namurian)

LBS  500ft  (lower beds often calcareous)

Worsten Shale Group (often calcareous)

The Cross Section of Bowland Shales at Little Mearley Brook (GR SD7841)

x

DSCF3471

Veiw of Pendle Hill from north. Little Mearley Brook is directly below the x

Little Mearley Brook

009

View up LMB almost from junction of LBS and Worsten Shale. My route followed the stream up and round to the left

010011

012013

These four photos are 100 yards from fence i.e from Worsten Shales. Dip 32, Strike 130 , several were calcareous. Mixture of “harder” (relative) siltstones and very crumbly and fissile shales.

visiting with profs from Oxford earth science in June 2015 , we noticed some of the clays were more like a sticky clay, which would be impossible to frack!

014

Mostly shales in stream bed. Next photo just to left following stream

015017

Thin bed of sandstone  3ft finish grained , dip strike similar. similar sandstone beds cause frequent low water falls, as seen in next photo.

018019

020

A view looking back down the brook, the top of the LBS.

021022

Near the top of the LBS

023

The several beds of Pendleside Sandstone mark the transition from LBS to UBS (and Dinantian to Namurian)

024025

026027

Several photos of Pndleside Sandstone with BS between. Non-calcareous. At times both shales and sandstone were paper-thin. Bands of sandstone varied from 1 inch to 12inch. Dip and strike similar to base.

028029

Onwards and upwards through the UBS, as seen on RH bank of RH photo. The skyline is Pendle Grit and the junction is just round the corner to the left in the stream. Note the increasing of boulders of Pendle Grit.

030031

Continuing upwards with the end of the UBS in sight. To the left of each photo there are two small waterfalls in the stream. The higher one (see below) is capped with Pendle Grit.

032033

A few thin beds of sandstone. I regret I did not look closely for injectites, as this is the same horizon as the Hind Sandstone further north in the Forest of Bowland where injectites are common.

034035

Close to shale’s end; the final few sandstone bands with the final 12ft waterfall as the third and final exposure of UBS

036040

The contact of Pendle Grit and UBS. There is virtually no shale above this waterfall. Note a 3ft band of sandstone at the lip of the fall. Again I need to return to study more closely the strata below the Grit.

(I stopped for lunch here enjoyed watching and listening to the waterfall.)

043044

I continued a fair way up the stream in the Pendle Grit, but gave up as it was extremely rough going so broke out to the left and continued to the top of Pendle Hill which was shrouded in mist.

045

A final rather murky view down Little Mearley Brook. I think it qualifies as the hardest route up Pendle Hil, but very rewarding 1000ft climb through the Bowland Shales.

I hope this photogeoblog gives some idea what gas companies are looking at 8000ft below the surface in Ellesmere Port, Barton Moss and the Fylde, and shows the vertical extent of the shales.

I shall have to make another visit and discover what I missed in terms of injectites, fossils an, possibly, a little oil!

Advertisements

4 thoughts on “Bowland Shales – type succession

  1. tim

    Hi,
    Great article. Would you mind giving me the Ordnance Survey coordinates for the route you took. Just the start middle and end will be great. Many thanks,

    Tim
    bowlanwalks

    Like

    Reply

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s