Provenance in geology
, is the reconstruction of the origin of sediments
. The Earth is a dynamic planet, and all rocks are subject to transition between the three main rock types: sedimentary
, and igneous rock
s (the rock cycle
). Rocks exposed to the surface are sooner or later broken down into sediments. Sediments are expected to be able to provide evidence of the erosion
al history of their parent source rocks. The purpose of provenance study is to restore the tectonic
In the modern geological lexicon, "sediment provenance" specifically refers to the application of compositional analyses to determine the origin of sediments. This is often used in conjunction with the study of exhumation histories, interpretation of drainage networks and their evolution, and forward-modelling of paleo-earth systems. In combination, these help to characterise the "source to sink" journey of clastic sediments from hinterland
to sedimentary basin
(from the French provenir, "to come from"), is the place of origin or earliest known history of something. In geology (specifically, in sedimentary petrology
), the term provenance deals with the question where sediments originate from. The purpose of sedimentary provenance studies is to reconstruct and to interpret the history of sediment from parent rocks at a source area to detritus at a burial place.
The ultimate goal of provenance studies is to investigate the characteristics of a source area by analyzing the composition and texture of sediments. The studies of provenance involve the following aspects: "(1) the source(s) of the particles that make up the rocks, (2) the erosion and transport mechanisms that moved the particles from source areas to depositional sites, (3) the depositional setting and depositional processes responsible for sedimentation of the particles (the depositional environment), and (4) the physical and chemical conditions of the burial environment and diagenetic changes that occur in siliciclastic sediment during burial and uplift". Provenance studies are conducted to investigate many scientific questions, for example, the growth history of continental crust, collision time of Indian and Asian plates,
Asian monsoon intensity, and Himalayan exhumation
Meanwhile, the provenance methods are widely used in the oil and gas industry. "Relations between provenance and basin are important for hydrocarbon exploration because sand frameworks of contrasting detrital
compositions respond differently to diagenesis
, and thus display different trends of porosity
reduction with depth of burial."
Source of detritus
All rock exposed at the Earth's surface is subjected to physical or chemical weathering
and broken down into finer grained sediment. All three types of rocks (igneous, sedimentary and metamorphic rocks) can be the source of detritus.
Transportation of detritus
Rocks are transported downstream from higher elevation to lower elevation. Source rocks and detritus are transported by gravity, water, wind or glacial movement. The transportation process breaks rocks into smaller particles by physical abrasion, from big boulder size into sand or even clay size. At the same time minerals within the sediment can also be changed chemically. Only minerals that are more resistant to chemical weathering can survive (e.g. ultrastable minerals zircon
). During the transportation, minerals can be sorted by their density, and as a result, light minerals like quartz and mica can be moved faster and further than heavy minerals (like zircon and tourmaline).
Accumulation of detritus
After a certain distance of transportation, detritus reaches a sedimentary basin and accumulates in one place. With the accumulation of sediments, sediments are buried to a deeper level and go through diagenesis
, which turns separate sediments into sedimentary rocks (i.e. conglomerate
etc.) and some metamorphic rock
s (such as quartzite
) which were derived from sedimentary rocks. After sediments are weathered and eroded from mountain belts, they can be carried by stream and deposited along rivers as river sands. Detritus can also be transported and deposited in foreland basin
s and at offshore fans. The detrital record can be collected from all these places and can be used in provenance studies.
Reworking of detritus
After detritus are eroded from source area, they are transported and deposited in river, foreland basin or flood plain. Then the detritus can be eroded and transported again when flooding or other kinds of eroding events occur. This process is called as reworking of detritus. And this process could be problematic to provenance studies.
For example, U-Pb zircon ages
are generally considered to reflect the time of zircon crystallization at about 750° Celsius and zircon is resistant to physical abrasion and chemical weathering. So zircon grains can survive from multiple cycles of reworking. This means if the zircon grain is reworked (re-eroded) from a foreland basin (not from original mountain belt source area) it will lose information of reworking (detrital record will not indicate the foreland basin as a source area but will indicate the earlier mountain belt as a source area). To avoid this problem, samples can be collected close to the mountain front, upstream from which there is no significant sediment storage.
Development of provenance methods
The study of sedimentary provenance involves several geological disciplines, including mineralogy
, geochronology, sedimentology
, igneous and metamorphic petrology
. The development of provenance methods are heavily dependent on the development of these mainstream geological disciplines. The earliest provenance studies were primarily based on paleocurrent
analysis and petrographic
analysis (composition and texture of sandstone and conglomerate). Since the 1970s, provenance studies shifted to interpret tectonic
settings (i.e. magmatic arcs, collision orogens and continental blocks) using sandstone composition.
Similarly, bulk rock geochemistry techniques are applied to interpret provenance linking geochemical signatures to source rocks and tectonic settings. Later, with the development of chemical and isotopic micro-analysis methods and geochronological techniques(e.g. ICP-MS
), provenance researches shifted to analyze single mineral grains. The following table has examples of where provenance study samples are collected.
Generally, provenance methods can be sorted into two categories, which are petrological methods and geochemical methods. Examples of petrological methods include QFL ternary diagram, heavy mineral
index, garnet zircon
index), clay mineral
assemblages and illite crystallinity
, reworked fossils and palynomorph
s, and stock magnetic properties. Examples of geochemical methods include zircon U-Pb dating (plus Hf
isotope), zircon fission track
, apatite fission track, bulk sediment Nd and Sr isotopes, garnet chemistry, pyroxene
chemistry and so on. There is a more detailed list below with references to various types of provenance methods.
Examples of provenance methods
Sandstone composition and plate tectonics
This method is widely used in provenance studies and it has the ability to link sandstone composition to tectonic setting. This method is described in the Dickinson and Suczek 1979 paper.
Detrital framework modes of sandstone suites from different kinds of basins are a function of provenance types governed by plate tectonics. (1)Quartzose sand
s from continental cratons
are widespread within interior basins, platform successions, miogeoclinal wedges, and opening ocean basins. (2)Arkosic sand
s from uplifted basement blocks are present locally in rift trough
s and in wrench basins related to transform ruptures. (3)Volcaniclastic lithic
sand and more complex volcano-plutonic
sands derived from magmatic arc
s are present in trenches, forearc
basins and marginal sea
s. (4) Recycled orogenic
sands, rich in quartz or chert
plus other lithic fragments and derived from subduction complexe
s, collision orogens, and foreland uplifts, are present in closing ocean basins. Triangular diagrams showing framework proportions of quartz, the two feldspars, polycrystalline quartzose lithics, and unstable lithics of volcanic and sedimentary parentage successfully distinguish the key provenance types."
Resolving provenance problems by dating detrital minerals
are more and more applied to solve provenance and tectonic problems.
Detrital minerals used in this method include zircon
s, white mica
s and apatite
s. The age dated from these minerals indicate timing of crystallization
and multiple tectono-thermal events. This method is base on the following considerations: "(1) the source areas are characterized by rocks with different tectonic histories recorded by distinctive crystallization and cooling ages; (2) the source rocks contain the selected mineral;"
(3) Detrital mineral like zircon is ultra-stable which means it is capable of surviving multiple phases of physical and chemical weathering, erosion and deposition. This property make these detrital mineral ideal to record long history of crystallization of tectonically complex source area.
The figure to the right is an example of U–Pb
relative age probability diagram.
The upper plot shows foreland basin detrital zircon age distribution. The lower plot shows hinterland (source area) zircon age distribution. In the plots, n is the number of analyzed zircon grains. So for foreland basin
Amile formation, 74 grains are analyzed. For source area (divided into 3 tectonic level, Tethyan Himalaya, Greater Himalaya and Lesser Himalaya
), 962, 409 and 666 grains are analyzed respectively. To correlate hinterland
data, let's see the source area record first, Tethyan sequence have age peak at ~500 Myr, 1000 Myr and 2600 Myr, Greater Himalaya has age peaks at ~1200 Myr and 2500 Myr, and Lesser Himalaya sequence has age peaks at ~1800 Ma and 2600 Ma. By simply comparing the foreland basin record with source area record, we cam see that Amile formation resemble age distribution of Lesser Himalaya. It has about 20 grains with age ~1800 Myr (Paleoproterozoic
) and about 16 grains yield age of ~2600 Myr (Archean
). Then we can interpret that sediments of Amile formation are mainly derived from the Lesser Himalaya, and rocks yield ago of Paleoproterozoic and Archean are from the Indian craton
. So the story is: Indian plate collide with Tibet, rocks of Indian craton deformed and involved into Himalayan thrust belt (e.g. Lesser Himalaya sequence), then eroded and deposited at foreland basin.
U–Pb geochronology of zircons was conducted by laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS
Bulk sediment Nd and Sr
Depend on properties of Sm–Nd
radioactive isotope system can provide age estimation of sedimentary source rocks. It has been used in provenance studies.
Nd is produced by α decay of 147
Sm and has a half life of 1.06×1011
years. Variation of 143
Nd is caused by decay of 147
Sm. Now Sm/Nd rato of the mantle is higher than that of the crust and 143
Nd ratio is also higher than in the mantle than in the crust. 143
Nd ratio is expressed in εNd notation (DePaolo and Wasserbur 1976).