brian, Author at Geological Digressions

Negotiating a passage through remnants of sea ice, beginning the 1977 field season on Belcher Islands.

Groundwater - geofluids, How to do things, In the field, Interpreting ancient environments, Science in Context, Under the microscope

A geological life

January 20, 2023

Preview (opens in a new tab) Not really a CV, more a precis 1969 and about to begin a BSc […]

Glossary, Planetary geology

Glossary of planetary geology

December 30, 2022

Some terminology for planetary geology, the solar System, moons, asteroids, comets, meteorites, exploration, measurement, and general flotsam and jetsam. The

Talus fan colluvium sourced from bluffs of Eocene conglomerate (Buchanan Lake Fm.), Emma Fiord, Ellesmere Island. Depositional mechanisms are primarily mass wasting (rock fall and slide) and slope wash during the Arctic spring thaw. The transfer of colluvium to the shoreline will produce significant improvements in sorting and stratification.

How to do things, In the field, Interpreting ancient environments

The lithofacies of colluvium

December 10, 2022

Colluvium – the source for most of Earth’s alluvium Colluvium is a sedimentary deposit that occurs as a thin layer

The sartorial spendour of spiny Murex – the real show-offs in the world of gastropods. From the left: Chicoreus ramosus (the Ramose Murex, Philippines); Murex pecten (Venus comb Murex, Philippines); Porieria zelandica (New Zealand) – the one I stood on!.

How to do things, In the field, Interpreting ancient environments

Glossary: Paleontology

December 9, 2022

Modern and fossil critters, trace fossils, shell morphology Many, but not all the terms included here are associated with articles

How to do things, In the field, Interpreting ancient environments

The lithofacies of mountain streams

November 27, 2022

Mountain streams – the ultimate source of sediment for many fluvial systems The idea for writing this brief arose whilst

A submarine channel from thalweg to overbank pinchout margin (white arrow), incised into slope mudrocks and filled by debris flow conglomerates (about 20 m thick). Lower in the succession, a couple of overbank debris-flow lobes sourced and isolated from an older channel bankfull event (yellow arrows). Mid Jurassic Bowser Basin, northern British Columbia.

How to do things, In the field, Interpreting ancient environments

Debris flow lithofacies

November 13, 2022

A post on debris flows, mud flows, hyperconcentrated flows, mud torrents, gravel flows slurry flows, lahars. General considerations – the

Pocket beaches blanketed by pebbles, cobbles and boulders, secreted away among rocky promontories, islets, nooks and crannies. One of the many rocky coasts of north Auckland.

How to do things, In the field, Interpreting ancient environments

Beach and shoreface gravels

November 7, 2022

Pebble, cobble and boulder beaches and their shoreface equivalents. The swimmability of a beach, if it was a popularity contest,

Braided rivers are a common sight in mountainous, eastern Canadian Arctic, this one draining into Strand Fiord, Axel Heiberg Island. Flow is seasonal, and at a maximum during spring-early summer thaw. Late summer low water levels expose large mid-channel gravel bars, dissected by chutes during peak flow runoff. Partially submerged active bars are developed around more sand prone tabular bedforms during late summer low-flow conditions (this view). The floodplain has only sparse vegetation – bank collapse supplies slugs of gravel to the active channels.

How to do things, In the field, Interpreting ancient environments

Crossbedded gravel lithofacies

October 31, 2022

Featuring tabular, trough, and horizontally crossbedded gravels General occurrence Tabular and trough crossbedding in gravel and mixed sand-gravel deposits are

The beach next to the pub at New Quay, County Clare, Ireland, is composed of well-rounded pebbles, cobbles, and boulders that extend through the swash-backwash zone to a spring tide – storm ridge above the line of brown seaweed. Most of the clasts were sourced from local, Late Pleistocene glaciogenic deposits that in turn were derived from the nearby glacio-karsted Burrens, a glaciated terrain underlain by Carboniferous limestone.

How to do things, In the field, Interpreting ancient environments

Introducing coarse-grained lithofacies

October 24, 2022

Gravel, conglomerate, breccia, pebbly mudstone, diamictite, rudstone, lapilli tuff Conglomerates are eye-catching. They tend to stand out, physically in outcrop

Intertidal 2D and 3D dunes modified by the outgoing tide. Ruapuke, New Zealand.

How to do things, In the field, Interpreting ancient environments

Subaqueous dunes influenced by tides

October 15, 2022

Introducing subaqueous dunes formed or modified by tidal currents Use this link to read the introduction to the lithofacies series. A very

Author name: brian