Monthly Archives: June 2018

Martian organics; one more step in the right direction

Facebooktwitterlinkedininstagram

Organic compounds (i.e. molecules that contain carbon bonded to hydrogen) are not the prerogative of earth.  They have been identified (remotely) in interstellar space, stellar gas clouds, and measured directly on comets and meteorites. And now Mars.

We tend to associate earth-bound organic compounds with life forms and processes, past and present. So, any discovery of organics elsewhere – the solar system and beyond – always begs the question; were these too associated in some way with extra-terrestrial life?  The answer is usually ‘No’, although media outlets, frequently prone to exaggeration, tend to stretch the answer beyond credulity. In fact we know that most of the organic molecules identified in deep space and on comets probably had an abiotic-non-biological origin.

One of the technical hurdles when working with Martian or comet samples, is the analysis of small volumes of rock and soil, that might, if we’re lucky, contain organic compounds in even smaller amounts. Curiosity Rover has, among its sophisticated array of instruments, a small electrically heated furnace that basically cooks the samples.  The method, called analytical pyrolysis, is used to identify complex organic compounds of unknown composition. Samples are placed in the furnace and heated gradually through temperatures up to 900oC. As temperature increases, small molecular fragments are thermally severed, or broken from the unknown compound.  Heating is usually done in an inert atmosphere (like Helium), that acts as a carrier for the smaller fragments, so they can be identified by gas chromatogram.  The molecular fragments, once identified, help to fingerprint the unknown organic compound.

Two back-to-back papers in the June 2018 issue of Science, provide grist for the ‘Life on Mars’ mill.  The new data do not show definitively that there was/is Martian life, but it does point to some intriguing possibilities.

Soil samples collected by Curiosity Rover from an ancient lake bed in Gale Crater (3 billion years old) are responsible for the current burst of extra-terrestrial excitement. The samples were heated incrementally to 860oC, releasing a range of organic fragments including aromatic organic compounds containing benzene rings (hexagon-shaped molecules), and sulphur-bearing molecular fragments belonging to chemical groups called thiols and thiophenes.

These discoveries are exciting in themselves, but they do not point definitively to any particular origin – whether biological, geological, or derived from meteorites. One reason for this ambiguity is the potential for organic molecules to be altered over time. Note that the Martian organics have been sitting around for about 3000 million years. Organic molecules are susceptible to chemical change if they come into contact with groundwater, hydrothermal-geothermal fluids (fluids at elevated temperatures), and importantly, ionizing solar radiation that on Mars’ surface is intense because of the thin atmosphere (compare this to the strong filtering attributes of earth’s atmosphere).  In fact, the sulphur-bearing compounds are thought to be alteration products that may have enhanced the overall preservation of Martian organic matter.  The current analyses show that complex organic molecules do exist on Mars, although they were not able to identify any clear biological signals.  Buried organic matter, that is shielded from ionizing radiation, may offer the best opportunity to identify fossil biological molecules

Our current preoccupation with methane is linked to its important role as a greenhouse gas. Methane, like other organic compounds on earth, is largely a by-product of biological processes.  It’s only natural then, to entertain the idea that methane in the Martian atmosphere might also be linked to past life forms.  Such flights of scientific imagination are brought to an abrupt halt, when we are reminded that methane can also be produced by geological processes, such as the chemical alteration of certain igneous rocks, or from melting clathrates – indeed, subsea methane bursts are well documented in polar regions.

The amount of methane in the Martian atmosphere is really tiny – measured in parts per billion. The concentration is also known to vary over time and geographically, but until Curiosity rover began its adventures in 2012, the data was too sparse to identify any kind of regularity or pattern of variation.  Regular atmospheric gas measurements by Curiosity over the last 3 years, have begun to fill this data gap.

The gas measurements were taken during Curiosity’s residence in Gale Crater, where there is a strong signal of seasonal variation, from 0.24 to 0.65 parts per billion methane by volume (yes, the amounts are tiny). The magnitude of the variation is larger than that expected from ultra violet light degradation of organic compounds delivered by meteorites, or the expected seasonal changes in atmospheric pressures. The authors conclude that the variation is caused by seasonal changes in methane released from local reservoirs at or buried beneath the Martian surface.  One intriguing possibility is methane release from clathrates, analogous to those commonly found at shallow depths beneath earthly sea floors (a clathrate is water ice that contains weakly bound methane molecules). Surface heating during the Martian summer would lead to increased methane release through permeable soils, or via open fractures and faults.

As so often happens in science, the new data provoke more questions about the nature of the original organic matter, than providing definitive answers. But this is a positive outcome. We now know there are diverse, complex organic compounds preserved in Martian mudrocks like those deposited in ancient lakes. Continued exploration will no doubt lead to the discovery of other complex organic molecules, some of which may be the fingerprints of ancient life.

There is reasonable confirmation that atmospheric methane varies with the Martian seasons. The cause of these variations is unknown, but if it is from buried reservoirs like clathrates, then the next question is ‘where did that methane come from?’.

None of the data so far indicate past or present biogenic influences. The data do suggest directions for future exploration, such as a focus on buried lake sediments, or geological structures that provide potential pathways for migrating methane gas.  New data is always exciting, but so too is the next generation of questions.

Facebooktwitterredditlinkedin
Facebooktwitterlinkedininstagram

Atlas of volcanoes and volcanic rocks

Facebooktwitterlinkedininstagram

Volcanoes and the products of volcanism

The Atlas, as are all blogs, is a publication. If you use the images, please acknowledge their source as indicated below (it is the polite, and professional thing to do).  I retain copyright of all images presented herein

Brian Ricketts –  www.geological-digressions.com

Volcanoes shape our earth: landscapes, the air we breathe, the oceans.  From day one they have had a direct influence and impact on life itself.  They still occupy a central place in our daily lives. Recent events in Hawaii (fissure eruptions, May-June 2018) and the explosive eruption of Fuego with its destructive pyroclastic flows (Guatemala, June 2018), have killed local inhabitants and destroyed property. Social media makes sure that we are kept up to date with these events; the fourth estate makes sure we are regaled with the death and mayhem.

I have never seen an actual eruption; the inquisitive, scientific part of me would love to witness one (at a safe distance). On my doorstep are three extinct stratovolcanoes 2-3 million years old. An hour and a half drive south puts me smack in the middle of the Taupo Volcanic Zone that, historically and prehistorically, is prone to cataclysmic, explosive fits. The same travel time north and I’m in the Auckland volcanic field, the most recent eruption of which was about 600 years ago. But I have seen the products of volcanism – the quiet effusive type, explosive and cataclysmic events; some as old as 2 billion years, others much more recent.

The collection of images here is a sample of these events. Some I have published, others just visited. I include this category in the Atlas because volcanic edifices and eruption products have a significant impact on sedimentary basins, and provide large volumes of sediment that ultimately are distributed throughout terrestrial drainages systems and marine environments; volcanoes contribute to sediments and sedimentary environments.

There are lots of good sites detailing volcanoes and eruptions. One of my favourite sites for volcano updates is Voices of Volcanology – Facebook @VoicesofVolcanology

Its contributors also provide a rational response to some of the silly, sometimes dangerous media hyperbole.

The USGS also provides media, scientific, and activity alert updates for many volcanoes around the world. One that I keep tabs on (for obvious reasons) is the NZ volcano scene

Click on the image for an expanded view, then ‘back page’ arrow to return to the Atlas. Use the following links to jump to specific image sets:  Precambrian  Arctic

New Zealand  Hawaii  Haleakala

This link will take you to an explanation of the Atlas series, the ownership, use and acknowledgment of images.  There, you will also find links to the other Atlas categories.

 

The images:

Paku Rhyolite dome

Paku rhyolite dome, guards the entrance to Tairua Harbour and estuary, east Coromandel Peninsula, New Zealand. The Paku eruptive center was part of widespread rhyolitic and dacitic volcanism from Late Miocene to Early Pleistocene in the Coromandel Volcanic Zone. They are part of the Minden Rhyolite Group. Paku is about 7-8 million years old (Pliocene). The Paku hypersthene-hornblende-biotite rhyolites here are beautifully flow banded and spherulitic,

             

 

             

 

            

 

Garibaldi Volcanic Field

The Garibaldi and Garibaldi Lake volcanic fields contain some of the youngest eruption products in Canada; most of the activity is about mid-Pleistocene through Holocene.  Most common are calc-alkaline andesites and dacites, with some basaltic rocks, associated with subduction of the Juan de Fuca Plate. They are located 60-70 km north of Vancouver. Mt. Garibaldi is a stratovolcano, with foundations as old as 1.3 Ma; Black Tusk also has old volcanic foundations, but its present form is due to much younger activity.  Late Pleistocene activity took place beneath the western segment of the Laurentide-Cordilleran Ice Sheet.

Herein are a few images of Garibaldi, Tusk, and Garibaldi Lake (the latter is a really nice hike).  Images of lava flows are from exposures along Highway 99 between Squamish and Pemberton.

                 

Lake Garibaldi. Sub-glacial andesite flows in the foreground

 

             

Black Tusk is the remains of an eroded stratovolcano whose foundations erupted about 1.3Ma. Rocks forming the present pinnacle were erupted about 200,000 years ago. This dome was subsequently eroded by the Cordilleran Ice sheet.  Left: from the Callaghan River access road. Right: From Brandywine Falls lookout.

 

          

A tiered, columnar jointed flows overlying Coast Mountain granodiorite. About 10 km north of Squamish, on Highway 99

 

          

Jointed andesitic-dacitic overlying pre-existing, sub-glacial topography on eroded Coast Mountains granodiorite and metamorphic rocks. The contact is shown in red on the left image. Right image: detail of the bedrock, that here contains structurally interleaved and sheared granodiorite and amphibolite. About 10km north of Squamish, Highway 99.

 

                       

 

About 15 km north of Squamish on Highway 99; this jointed lava flow has over-ridden dacitic agglomerate. The flow base is lined with abundant vesicles, most of which have been stretched approximately parallel to the basal flow contact.  The flow base is highly irregular, possibly following sub-glacial erosional topography.

 

                           

Same lication as above. The basal agglomerate here appears to be part of the original flow unit, where the lower cooled lava has been fragmented by the moving flow. Some fragments have been reincorporated into the base of the solid flow.

Precambrian volcanics

This set of images is from the Proterozoic Flaherty Formation, Belcher Islands. A small number of Rb/Sr and Pb-Pb ages indicate between 2.0-1.9 billion years. The Flaherty succession consists of interleaved tholeiitic to subalkaline basalt flows, pillowed lavas, pyroclastic and/or density current ash flows, and interflow turbidites, that accumulated mostly in a marine environment, although edifices may have extended above sea level. Metamorphism is prehnite-pumpellyite grade, and preservation of primary volcanic and volcaniclastic structures is excellent.  The volcanics were extruded on Proterozoic continental crust. However it is still uncertain whether they represent some kind of mantle plume, or formed during extension associated with crustal flexure, or are a hybrid of continental arcs.

              

Jointed lava flows and wrap-around piles of pillow lavas on Flaherty Island. Outcrops often permit the 3-dimensional geometry of flows and pillows to be mapped.

An interpretation of interleaving flows and pillowed lavas, and associated volcaniclastics. The figure is from a 1982 paper: Volcaniclastic rocks and volcaniclalstic facies in the Middle Precambrian (Aphebian) Belcher Group, Northwest Territories, Canada. Canadian Journal of Earth Sciences, v. 19, p. 1275-1294. 

 

 

              

Spheroidal, lobate, and lozenge-like pillow lavas. Left: the main pile is overlain and partly amalgamated with a second pile (top to the right), separated by a layer of glassy fragments formed by thermal shock. West Flaherty Island. Right: Oblique section through pillows, shows chilled margins with small vesicle traces (formerly gas bubbles).

 

                

Surface structures on pillows. Left: small ropy festoons. Right: crudely polygonal crusts formed by rapid cooling in the Precambrian ocean.

 

              

Left: Lozenge-shaped pillows with central flat-bottomed gas cavities, now filled with coarse calcite and prehnite crystals. Right: Filling of a pillow interstice with a layer of shards formed by thermal shock, overlain by coarse calcite. Look closely and you will see the first generation calcite grew in radial clusters on the pillow margin.  Both structures (also called geopetal structures) are useful for determining stratigraphic way-up (top).

 

             

Small lava tube that acted as a feeder to the pillow lavas. Lava in the tube must have drained, leaving an open tube that subsequently was filled by very coarse calcite crystals.

 

A recent lava tube breakout on Kamokuna lava delta, November 2017, Hawaii. This example is on land, but serves as a useful analogy to the submarine lava tube in the image immediately above.

 

 

 

              

Two perspectives of the tops of lava flows. Left: A bedding view (looking down on the flow top) of brecciated, folded and generally squished basalt fragments that formed as the flow cooled, and were carried along the top of the flow. The oblique grooves across the rock face were formed by glacial scouring.  Right: Cross-section through a lava flow; the upper part is completely broken up by movement as the lava solidified. More coherent, less fragmented rock occurs below this (lower right), was deeper in the flow and cooled more slowly.

 

More fluid lava flows formed ropy festoons. Here, flow direction was approximately to the lower right.

 

 

 

              

The base of a lava flow will also cool more quickly, especially if sediment or rock beneath is wet. Cooling here has resulted in rapid expansion of gas bubbles, (probably steam) that have risen into the flow forming elongated, sub-vertical, worm-like cavities, or spiracles. On the right, a larger gas bubble has risen above the flow, and subsquently evolved gas into small cavities in a crude radial pattern (arrow).

 

Larger gas cavities (vesicles) also form within the flow masses, as volcanic gas (water, CO2, SO2) separates from the melt. Here, the cavities are surrounded by much smaller vesicles.

 

 

 

Upper contact of a massive sediment gravity flow. Framework clasts up to a metre are mostly volcanic, but there are a few ripped up sandstone and dolomitic sandstone clasts, presumably from units underlying the Flaherty Formation. Maximum thickness is 85m; the unit covers and area greater than 3000 sq km. There are no obvious depositional or erosional breaks within the unit; there are parallel laminae, and rare crossbeds. The framework is mainly pumice fragments, shards with bubble-wall texture, and lapilli (see photomicrographs below). Pumice generally increases towards the top – density grading, but no obvious size grading. It is not welded.  It is sandwiched between pillowed and jointed lava flows.  It was most likely deposited subaqueously, although it is also possible that the flow originated on a subaerial edifice. Parallel laminae may indicate a degree of surging.  The irregular surface patterns are due to late diagenetic silica replacement of the original volcanic glass.

 

                               

 

Photomicrographs from the massive volcaniclastic flow. From the Left: 1. pumice with elongate gas pores, and various shards (glass replaced by silica). Field of view 8 mm.  2 Shards and lapilli. Both cements are coarse calcite, that has also replaced some matrix. Field of view 8 mm.  3. Bubble-wall ash shards, pumice and matrix in finer-grained part of the flow unit. Field of view 3 mm. 4 Fine, distal flow unit, predominantly bubble-wall shards, some pumice, and basalt fragments.  Field of view 8 mm.

 

              

Inter-flow volcaniclastic turbidites, layers of air-borne ash into water, and hemipelagic mudrock and ash. Right: detail of thin graded volcaniclastic turbidite Tb-d beds, hemipelagic ash, and highly calcareous mudstone – the latter indicating periods of very slow clastic deposition.

 

              

Left: Laminated and rippled volcaniclastic sandstone-siltstone. The middle bed has several load casts. Right: Volcaniclastic sandstone with ripples and climbing ripples. Bedforms in the upper orange-brown layer resemble antidunes.

 

              

Left: Graded volcaniclastic turbidite (Tb-d divisions), in erosional contact with a (steel grey), muddy limestone calcareous mudstone. Right:Laminated and convoluted volcaniclastic Tc-d turbidite intervals. The middle graded bed truncates  the convolutions below.

 

              

Left: Photomicrograph of turbidite volcaniclastic sandstone. Clear bubble-wall textures, some pumice, and crude alignment of shard long directions. Field of view 3 mm. Right: Prehnite in very fine-grained basalt. Field of view 3 mm.

 

Arctic

              

Strand Fiord volcanics, an Upper Cretaceous unit on Axel Heiberg Island, Canadian Arctic. Here an ‘organ-pipe’ array of columnar joints (4m high) have perforated the basalt during cooling. On the right, a bird’s-eye view of 4, 5 and 6-sided columns.

 

              

Curved and radiating entablature joints in Strand Fiord basalt flows, Axel Heiberg Island. Structural dip here is about 60 degrees. Flow thickness is about 35m. The entablature on the left is underlain by bed-normal jointed basalt.

 

              

Left: Cow pat ballistics in bedded lapilli and reworked basalt gravel, attests to eruption material mixing directly with fluvial reworked debris. The right image shows a coalified tree fragment caught up in a lahar. Strand Fiord volcanics, Axel Heiberg Island.

 

              

The Mount Edziza volcanic field in Stikine, northern British Columbia began 7.5 million years ago, and continued into the Pleistocene. It features large stratovolcanoes, calderas and cinder cones. Featured here is a stairway of jointed basalts, and a well preserved cinder cone.

 

New Zealand

                            

 

Upper Miocene Coroglen volcanics north of Whiritoa,  east coast of Coromandel, New Zealand. From the left: 1. Cooling joints in ignimbrite. 2. Detail of ignimbrite fragmental pumice and rhyolite, and fiamme (dark fragments stretched during hot emplacement of the pyroclastic flow).  3. Flow banded rhyolite. Outcrop is about 5m high.  4. A lahar with fragments of rhyolite, ignimbrite and possible andesite, over-ridden by a flow-banded rhyolite.

 

              

Late Pliocene flow-banded rhyolite at Mount Maunganui, New Zealand.

 

                              

 

Karioi volcano, Raglan New Zealand.  A Late Pliocene stratovolcano that during eruptions and later formation of lahars, dipped its toes in Tasman Sea. Three images from the left show an upper andesite flow, over airfall lapilli tuffs, and at base a laharic breccia.  On the right, detail of lapilli tuffs with a larger ballistic clast (20cm long).

 

                            

 

Stream reworking and lahars from the flanks of an active Karioi volcano, delivered pebble to boulder sized debris to the Late Pliocene coast. Evidence for this is seen in pockets of fossil molluscs (mostly bivalves) – modern bivalves commonly are wedged between clasts – these are not fossils. Rounding of clasts probably took place in streams and during coastal reworking. A few large boulder rafts are 3-4m across.

 

Auckland volcanic field contains about 50 known eruptive centres; scoria cones, lava flows,  and craters formed by highly explosive, phreatomagmatic eruptions, concentrated in an area of metropolitan Auckland, about 360 sq km. Activity began about 250,000 years ago; the youngest is Rangitoto which erupted 600 years ago, and was witnessed by Auckland Maori.

             

Eruption of Rangitoto in Auckland Harbour produced a circular island. The central scoria cone is flanked by aa basalt flows, air-fall scoria and lapilli. In the left image, In the left image (viewd from Musik Pt.), Motukorea (also known as Brown’s Island) is a small cone, thought to have erupted 7000-9000 years ago. Right image from Motuihi Island.

 

                           

 

Rangitoto features: From the left: Blocky and rubbly aa flows; a lava cave, and a profile of weathered lapilli.

 

                          

Explosion craters, or maars. Lake Pupuke, now filled with a fresh water lake is more than 45,000 years old. Orakei Basin (centre) is tidal – more than 83,000 years, and Panmure Basin (right), also tidal, is older than 17,000 years. The crater entrance is a narrow rocky channel, connected to Tamaki estuary – this is the Pacific Ocean side of Auckland. The stretch of water in the distance is part of Manukau Harbour – the Tasman Sea side of Auckland. A narrow isthmus separates the two ocean water bodies.  All three craters are rimmed by tephras. Lake and tidal basin sediment fill can also be used to date the events, using pollen and ash layers derived from more distant eruptions in Rotorua-Taupo.

 

                          

 

           

This group of images shows well bedded air-fall tephra layering near the outer rim of Maungataketake maar volcano, bordering Manukau Harbour, west Auckland. It is close to Auckland International Airport. Age is uncertain but could be as old as 177,000 years. Layers were also disrupted by ballistics (bomb sag, 3rd from left).  The eruption apparently obliterated a nearby forest – ash layers drape a stump (4th from left), and in the modern shore platform, large tree trunks were flattened.

 

                         

 

Mt Taranaki (Egmont), is an andesitic stratovolcano that began erupting 130,000 years ago. It is  regarded as active. The edifice is surrounded by a spectacular ring plain, dotted with lahar mounds, testament to the destructive nature of volcanoes even when not erupting. The lahars were generated on the volcano flanks during large landslides, including possible sector collapse; loose rock, mud and water form fluid, fast-moving flows. They can travel many kilometres from their source.  Conical lahar mounds commonly form around very large rafts of rock (sometimes many metres across), once the flow has come to rest.  Images on the right show typical, poorly sorted lahar textures.

 

                           

West of Auckland city, Waitakere hills are underlain by Early Miocene andesitic and basaltic flows, pillows, and debris flows, derived from volcanic centres off the west coast of New Zealand. Marine fossils are commonly caught up in the lahars and debris flows. Typical debris flow textures shown on the left; centre cliff with many stacked debris flows) boulders up to 1.5m wide), intruded by a dyke – Karekare Beach. Right image shows two, very large lava tubes, filled with radially jointed andesite (Maori Bay), feeders from nearby Waitakere Volcano.

 

                           

Conical mounds on Mamaku Plateau, north of Rotorua, look superficially like lahar mounds. However, in this case the mounds formed from a hot ignimbrite (240,000 years ago) with preferential cementation and welding by hot gases.  Subsequent erosion has left the harder zones upstanding (also called Tors).  The image on the right shows this hard, central zone. (located on State Hwy 5)

 

                         

A Mamaku Plateau mound with central cemented, resistant hard core (a remnant of the Mamaku Plateau Ignimbrite), draped by air-fall tephra.

 

             

Mt Ngauruhoe (aka Mt Doom) is a stratovolcano, and the youngest component of the Tongariro volcanic complex. It may be as old as 7000 years. It is made up of andesite flows, scoria and ash. Several young lava flows extend into adjacent Mangatepopo Valley.

 

             

Left: Typical scoriaceous aa flow in Mangatepopo Valley. Right: Looking down the path of a pyroclastic flow generated during the 1975 eruption. The flow contains a chaotic jumble of scoria and ash, with blocks up to 2m across. In place there are distinct rubbly levees. The flow rode over part of an older lava flow – the darker grey area, upper middle of image.

 

Hawaii

              

Halemaumau crater, Kilauea as it was in 1983. It looks very different now!

 

             

Left: Lava tree, cast during a 1790 eruption. Right: A nice sea arch eroded into layered flows.

 

             

Left: Spatter on a small lava tube vent, Kilauea. Right: Pelee’s Hair – volcanic glass that has been stretched while molten.  The preservation potential of such structures is very low.

A small flow with ropy central portion and raised levees of fragmented basalt.

 

                          

 

Ropy lavas, festooned, twisted, knot-like, and folded. Kilauea

 

Haleakala crater, Maui

A large stratovolcano that last erupted about 500 years ago

                          

From the summit (a little over 3000m) climb down to the crater floor to a parched landscape of cinder cones, crunchy lapilli underfoot, and a myriad ballistics. The crater walls (centre) exposes multiple episodes of dyke intrusion that fed the overlapping scoria mound conduits.

 

                          

Ballistics: left is a flattened cow pat splatter. Centre a spindle bomb, twisted in flight. Right bread-crust cooling pattern on a flattened bomb.

 

Hardy Silver Swords. Spikey

 

             

Oxidised air-fall lapilli and ash layers on older flanks of the Haleakala Volcano

 

 

 

Facebooktwitterredditlinkedin
Facebooktwitterlinkedininstagram

Atlas of Sequence stratigraphy

Facebooktwitterlinkedininstagram

The Atlas, as are all blogs, is a publication. If you use the images, please acknowledge their source as indicated below (it is the polite, and professional thing to do).  I retain copyright of all images presented herein

Brian Ricketts –  www.geological-digressions.com

This category of Atlas images, is not intended as a comprehensive outline or set of definitions of sequence stratigraphy, but rather field examples of strata, stratigraphic trends (an essential component of systems tracts), and stratigraphic surfaces.  There are many excellent journal papers, text books, and conference short courses devoted to sequence stratigraphy, so consult them if needs be.  SEPMStrata is a good place to start.

Some key sequence stratigraphic components illustrated here include (abbreviations on the images):

HST        Highstand Systems Tract (progradational-aggradational) overlies the MFS and underlies the erosion surface formed during the FSST)

FSST       Falling Stage Systems Tract (forced regression and progradation during relative sea-level fall)

LST         Lowstand systems tract (now restricted to end of relative sea-level fall and beginning of sea-level rise)

TST        Transgressive Systems Tract (above the transgressive surface; Retrogradational onlapping during rising relative sea-level and low sedimentation rates. Condensed stratigraphy).

MSF        Maximum Flood Surface (at the transition to sedimentation rates greater than creation of accommodation space. Also the base of the HST).

Each example has a pair of images, one annotated, the other without annotation.

This link will take you to an explanation of the Atlas series, the ownership, use and acknowledgment of images.  There, you will also find links to the other categories.

Click on the image for an expanded view, then ‘back page’ arrow to return to the Atlas.

 

The images:

Late Cretaceous to Middle Eocene 3rd-order stratigraphic sequences in the Eureka Sound Group, Canadian Arctic Islands (mostly Ellesmere and Axel Heiberg islands). Sequences 1 and 2, mainly wave-dominated deltas, and along the eastern basin margin, estuarine – shelf. Sequences 3 and 4: river-dominated deltas, sandy inner shelf, muddy outer shelf; Sequence 5 basin inversion and fragmentation into small, thrust-related, syntectonic basins. Sequence 5 represents the acme of the Eurekan Orogeny.

 

Sequence 1, wave-dominated delta parasequences, Strand Fiord, Axel Heiberg Island. There is about 150m of stratigraphy in this view.

 

Detail of Sequence 1 coarsening upward, wave-dominated delta parasequence and MFS. Axel Heiberg Island.

 

Sequence 1, Major unconformity between Ordovician limestone and onlapping Lower Paleocene estuarine, sandy shelf-bar-sand spit. Combined  karstification and erosion produced significant paleotopgraphy. Mount Moore, eastern Ellesmere Island.

 

Sequence 1 estuarine, sand spit, and shallow shelf bars, onlapping karsted Ordovian limestones, Mount Moore, eastern Ellesmere Island. In the foreground, crossbedded sandstone is in direct contact with paleotopography.

Reconstructed Early Paleocene paleotopography and Sequence 1 facies.  For details see: Ricketts, B.D.  1991: Lower Paleocene drowned valley and barred estuaries, Canadian Arctic Islands: aspects of their geomorphological and sedimentological evolution; in Clastic Tidal Sedimentology, Rahmani, R.A., Smith, D.G., Reinson, G.E., and Zaitlin, B.A. (ed.); Canadian Society of Petroleum Geologists, Memoir 16, p. 91-106.

 

 

Sequence 3. River-dominated prodelta – delta front parasequences.  About 300m of stratigraphy here. Abrupt, mappable parasequence tops coincide with the MFS. Axel Heiberg Island.

 

Sequence 3: FSST with forced regressive wedge – sharp-based shoreline sandstones formed by wave erosion as sea-level falls.  The subsequent TST and HST extends to the right of the image. Axel Heiberg Island.

 

Sequence 3, as in the above image pair, focusing on the FSST. Axel Heiberg Island.

 

The basal part of the FSST in Sequence 3 (as above), featuring a sharp-based forced regressive shoreline wedge.

Sequence 3. Downlap surface with basinward progradation of mudstone fine-grained sandtone.

 

Sequence 3: Strongly aggradational HST, shelf parasequences, South Bay, Ellesmere Island.

 

Sequence 3: Shelf parasequences, mostly HST, thin TST, and MFS that corresponds with the resistant top of each cycle. For an overview see the next images above. South Bay

 

Sequence 3: A great example of a higher-order subaerial sequence boundary (SB) (top of coal seam), thin TST muddy sandstone, MFS, and HST. The orange blobs are mineralized tree roots. It’s also a much younger me. Strathcona Fiord, Ellesmere Island.

Sequence 3, a different perspective, as immediately above.

 

 

 

 

Jurassic mid-outer shelf parasequence, Bowser Basin. The MFS immediately overlies the resistant ledge, above which is a thick coarsening  upward HST. Tsatia Mountain, northern British Columbia.

 

 

Mid-shelf parasequences with well defined MFS, transgressive surfaces, and TSTs. Tsatia Mountain, Bowser Basin.

 

Closer view of a mid-inner shelf parasequence, Tsatia Mountain, Bowser Basin. The coarsening upward HST is capped by a pebbly, fossiliferous TST and MSF. The transgressive surface is one of marine erosion during changing wave-base.

 

Detail of the top HST, transgressive surface (of erosion), the fossiliferous, pebbly TST (ammonites and bivalves), a calcareous mudstone that is part of the condensed TST stratigraphy when terrigenous sediment input was at its lowest, the MFS, and succeeding HST. Tsatia Mountain, Bowser Basin.

 

The Tsatia Mountain section contains some shelf parasequences that are truncated by lowstand, channelized fluvial sandstone – the LST. The TST is a thin, pebbly mudstone similar to that in the image immediately above. Bowser Basin.

 

The abrupt contact between the erosional base of the TST fluvial channel, and the preceding shelf parasequence. Tsatia Mountain, Bowser Basin.

Facebooktwitterredditlinkedin
Facebooktwitterlinkedininstagram

Bishop James Ussher, and the beginning of everything

Facebooktwitterlinkedininstagram

In 1650 AD/CE, James Ussher, Bishop of Amargh and Primate of all Ireland, published the scholarly “Annals of the Old Testament, deduced from the first origins of the world” where he concluded that the universe, and everything in it, began at noon, October 23, 4004 BC. To many modern scholars of the earth, this seems outlandish, even ridiculous. Creationists though still attest to its veracity.

It is easy to fall into the trap of judging old ideas with modern concepts and proofs, rather than judging them according to the precepts and traditions of their day; of course, the real kicker here is that one needs to have some knowledge of those cultural contexts and traditions. I was reminded of this during a re-read of Stephen J. Gould’s Fall in the House of Ussher (Natural History, 1991). In an early paragraph Gould writes “To this day, one can scarcely find a textbook in introductory geology that does not take a swipe at Ussher’s date as the opening comment in an obligatory page or two on older concepts of the earth’s age (before radioactive dating allowed us to get it right). Other worthies are praised for good tries in a scientific spirit (even if their ages are way off), but Ussher is excoriated for biblical idolatry and just plain foolishness. How could anyone look at a hill, a lake, or a rock pile and not know that the earth must be ancient?” (Gould often used diverse ‘lead-ins’ to his essays, the pithy import of which don’t become apparent until one is well into the reading).  It is basically a statement about making judgements.

Confronted by a “hill, lake, or rock pile”, you try to imagine how long it took to get there. Your cogitation will go no further, from the point of view of actual explanation or some empirical value, unless you also happen to know about geological and geomorphic processes, their short-livedness or longevity. Without this knowledge, a priori, the longevity of this pile of rock will remain a mystery. For Ussher, this kind of knowledge was not part of his paradigm, his view of the universe.  Quite the opposite; his view was imbued with a theological tradition that was still trying to deal with the monstrous notion that man and earth were not the centre of the universe. Galileo’s excommunication had taken place a mere 17 years earlier.

Ussher lived and rationalised the universe in a tradition of theological doctrine, a tradition imbued with a belief in divine intervention. He was admired at the time as a scholar, who impressed the nobility so much that on his death in 1656, Oliver Cromwell ordered him buried at Westminster. The starting point for Ussher’s Old Testament genealogy was the death of King Nebuchadnezzar II (634-562 BC/BCE) of Babylon; from there he worked back through the generations to Adam, using a combination of biblical patriarchy and secular history.

Ussher was by no means the first to calculate a creation time-line. Luminaries like the Venerable Bede (672-735), who counted all the begets and begots in Genesis, traced creation to 3952 BC. Even Isaac Newton and Johannes Kepler, two giants in the history of science who we tend to associate with the rise of empiricism, concurred that 4000 BC was not just a nice round number but had meaning as the beginning of everything, based on biblical and secular histories. However, it was Dr. John Lightfoot, Chancellor of the University of Cambridge no less, who in 1642 used biblical genealogies and classical history to calculate the beginning at 9am, October 23, 4004 BC. October the 23rd was a Sunday (appropriate) and close to the autumnal equinox. Ussher must have been aware of Lightfoot’s work, and some historians have suggested that there was a degree of one-upmanship between the two academics. One historical footnote has even suggested that Lightfoot’s addition of “9 am” to the October 23rd date, was inserted after Ussher’s 1650 publication in a fit of academic pique (I guess some things haven’t changed).    Lightfoot’s work is now little more than a historical footnote to Ussher’s opus.

Following Ussher’s publication, The King James Bible (first completed in 1611) added dates to the margins of Old Testament scripture. Thus, “In the beginning…” (Genesis 1:1) has the margin note ‘4004 BC’, and the date Noah’s ark became stranded on Mt Ararat “May 5, 1491 BC. The annotations have been attributed to Ussher rather than Lightfoot, perhaps because he was in court-favour at the time. Use of Ussher’s dates in marginal notation continued in some published Bibles into the 20th century.  Perhaps the whole idea of a creation time-line needed a personality, and James Ussher was it.  Ussher’s legacy is that he still bears the brunt of the creationist claims of a ‘young’ earth, and a tendency to denigration from the scientific community who know how old earth really is.

And this is the central theme of Stephen Gould’s complaint. We now know earth is about 4.6 billion years old; this knowledge derives from radiometric dating of the most ancient earth rock, meteorites, and moon rocks.  But this knowledge was established only in the last half of the 20th century. Earlier estimates of the age of the earth (and solar system) through the 19th century, ranged from a few 100,000 to 300 million years (e.g. Charles Darwin, Charles Lyell, Lord Kelvin). All these early calculations by learned folk are taken (as they should) to be the best estimates at that time, given what was known about earth processes. The calculations were scholarly, and for the most part, well considered. We don’t ridicule them, simply because we now know them to be incorrect (radiometric dating methods were not part of the geologists’ toolbox until the early 1900s).

Likewise, Ussher and Lightfoot used, in a considered fashion, the information available at that juncture of the 17th century – the genealogies in biblical scripture and classical history. Galileo and Copernicus had certainly rocked the boat in terms of humanity’s place in the universe, but not its longevity. In the 17th century, the only way to decipher time past was through written history, or a vivid imagination.

According to the Old Testament, there were 75 generations between Adam and Jesus, and if we assume that each lived 50 years (with overlap of first-born sons – sorry, but it was all about the patriarchy back then), some quick, back-of-the-envelope arithmetic gives us about 3000-4000 years from creation. And again, if we treat the 6 days of creation as a kind of metaphor, where ” For a thousand years in thy sight are but as yesterday when it is past, and as a watch in the night” (Psalm 90, King James Bible), then 6000 years gives an upper limit for Day 1. These dates became ingrained in Renaissance and Enlightenment Christian views of the universe. For some in the 21st century they are still ingrained.

By all accounts, neither Ussher or Lightfoot were charlatans; they did not take all those BC genealogies through arcane twists and turns to prove a point (something modern Creationists are quite good at).  They were not trying to disprove science. No doubt there were errors of interpretation, and perhaps errors of omission.  There were certainly difficulties in aligning events according to the Julian, Gregorian, and Hebrew calendars, as Gould and other scholars have pointed out.

We often think of the Enlightenment as the beginning of modern science, but in the 17th century it was still nascent, and in a state of almost continuous tension with approved church doctrine. Ussher and Lightfoot may have been sympathetic with the emerging science (I’m not sure historians really know this), but they were also immersed in theological tradition. They took the information that was available and used it in a scholarly fashion.

So, next time you hear someone disparage Ussher and his colleagues, remind them that cultural, philosophical, political, and religious contexts are important when judging historical events. It is also worth keeping in mind that, 100 years hence, theories and hypotheses that today have scientific value, may send future generations into paroxysms of laughter.

Footnote: The historical annotations CE (Common Era) and AD (Ano Domini) refer to dates since the first year of the Gregorian calendar. Thus, BCE is before the common era, and refers to the same dates as BC (before Christ). The difference between the older BC/AD and recent BCE/CE notations is that the latter has no Christian connotations.

Facebooktwitterredditlinkedin
Facebooktwitterlinkedininstagram