Article: a non-technical introduction to genetics in general
The genetic history of indigenous peoples of the Americas primarily focuses on Human Y-chromosome DNA haplogroups and Human mitochondrial DNA haplogroups. Autosomal "atDNA" markers are also used, but differ from mtDNA or Y-DNA in that they overlap significantly. The genetic pattern indicates Indigenous Amerindians experienced two very distinctive genetic episodes; first with the initial peopling of the Americas, and secondly with European colonization of the Americas. The former is the determinant factor for the number of gene lineages, zygosity mutations and founding haplotypes present in today's Indigenous Amerindian populations.
Analyses of genetics among Amerindian and Siberian populations have been used to argue for early isolation of founding populations on Beringia and for later, more rapid migration from Siberia through Beringia into the New World. The microsatellite diversity and distributions of the Y lineage specific to South America indicates that certain Amerindian populations have been isolated since the initial colonization of the region. The Na-Dené, Inuit and Indigenous Alaskan populations exhibit Haplogroup Q-M242; however, they are distinct from other indigenous Amerindians with various mtDNA and atDNA mutations. This suggests that the peoples who first settled the northern extremes of North America and Greenland derived from later migrant populations than those who penetrated further south in the Americas. Linguists and biologists have reached a similar conclusion based on analysis of Amerindian language groups and ABO blood group system distributions.
__TOC__ Background
Recent African origin of modern humans
The Y chromosome is passed down directly from father to son; all male humans (Y chromosomes) today trace back to a single prehistoric father termed "Y-chromosomal Adam" originating in Africa. The Y chromosome spans about 60 million base pairs (the building blocks of DNA) and represents about 2 percent of the total DNA in all human cells. The original "Y chromosomal Adam"-DNA sequencing has mutated rarely over the 20,000 generations, but each time a new mutation occurs, there is a new branch in a haplogroup, resulting in a new subclade (single-nucleotide polymorphism (SNP)).
Both females and males inherit their Mitochondrial DNA (mtDNA) only from their mother. MtDNA mutations are also passed down relatively unchanged from generation to generation, so all humans share the same mtDNA-types. The logical extension of this is that all humans ultimately trace back to one woman, who is commonly referred to as Mitochondrial Eve. This line of biological inheritance, therefore, stops with each male. Consequently, Y-DNA is more commonly used by the general public for tracing genetic heritage of a direct male line.
An autosome (atDNA) is a chromosome that is not a sex chromosome – that is to say, there are an equal number of copies of the chromosome in males and females. Autosomal DNA testing is generally used to determine the "genetic percentages" of a person's ancestry from particular continents/regions or to identify the countries and "tribes" of origin on an overall basis. Genetic admixture tests arrive at these percentages by examining locations (SNPs) on the DNA where one nucleotide has "mutated" or "switched" to a different nucleotide. One way to examine the support for particular colonization routes within the American landmass is to determine if a closer relationship between zygosity and geography is observed when "effective" geographic distances are computed along these routes, rather than along shortest-distance paths.
There is general agreement among anthropologists that the source populations for the migration into the Americas originated from an area somewhere east of the Yenisei River. The common occurrence of the mtDNA Haplogroups A, B, C, and D among eastern Asian and Amerindian populations has long been recognized, along with the presence of Haplogroup X. As a whole, the greatest frequency of the four Amerindian associated haplogroups occurs in the Altai-Baikal region of southern Siberia. Some subclades of C and D closer to the Amerindian subclades occur among Mongolian, Amur, Japanese, Korean, and Ainu populations.
Y-DNA
individual Amerindian groups by Y-DNA Y-DNA haplogroups in indigenous peoples of the Americas
The Y chromosome consortium has established a system of defining Y-DNA haplogroups by letters A through to T, with further subdivisions using numbers and lower case letters.
Haplogroup Q
Q-M242 (mutational name) is the defining (SNP) of Haplogroup Q (Y-DNA) (phylogenetic name). Within the Q clade, there are 14 haplogroups marked by 17 SNPs.2009 In Eurasia haplogroup Q is found among indigenous Siberian populations, such as the modern Chukchi and Koryak peoples. In particular, two groups exhibit large concentrations of the Q-M242 mutation, the Ket (93.8%) and the Selkup (66.4%) peoples. The Ket are thought to be the only survivors of ancient wanderers living in Siberia. Their population size is very small; there are fewer than 1,500 Ket in Russia.2002 The Selkup have a slightly larger population size than the Ket, with approximately 4,250 individuals.
Starting the Paleo-Indians period, a migration to the Americas across the Bering Strait (Beringia) by a small population carrying the Q-M242 mutation took place. A member of this initial population underwent a mutation, which defines its descendant population, known by the Q-M3 (SNP) mutation. These descendants migrated all over the Americas.
Haplogroup Q-M3 is defined by the presence of the rs3894 (M3) (SNP). The Q-M3 mutation is roughly 15,000 years old as that is when the initial migration of Paleo-Indians into the Americas occurred. Q-M3 is the predominant haplotype in the Americas, at a rate of 83% in South American populations, 50% in the Na-Dené populations, and in North American Eskimo-Aleut populations at about 46%. With minimal back-migration of Q-M3 in Eurasia, the mutation likely evolved in east-Beringia, or more specifically the Seward Peninsula or western Alaskan interior. The Beringia land mass began submerging, cutting off land routes.
Since the discovery of Q-M3, several subclades of M3-bearing populations have been discovered. An example is in South America, where some populations have a high prevalence of (SNP) M19 which defines subclade Q-M19. M19 has been detected in (59%) of Amazonian Ticuna men and in (10%) of Wayuu men. Subclade M19 appears to be unique to South American Indigenous peoples, arising 5,000 to 10,000 years ago.
This suggests that population isolation and perhaps even the establishment of tribal groups began soon after migration into the South American areas. Other American subclades include Q-L54, Q-Z780, Q-MEH2, Q-SA01, and Q-M346 lineages. In Canada, two other lineages have been found. These are Q-P89.1 and Q-NWT01.
The principal-component analysis suggests a close genetic relatedness between some North American Amerindians (the Chipewyan and the Cheyenne) and certain populations of central/southern Siberia (particularly the Kets, Yakuts, Selkups, and Altays), at the resolution of major Y-chromosome haplogroups. This pattern agrees with the distribution of mtDNA haplogroup X, which is found in North America, is absent from eastern Siberia, but is present in the Altais of southern central Siberia. Similarly, the Asian populations closest to Native Americans are characterized by a predominance of lineage P-M45* and low frequencies of C-RPS4Y.
Haplogroup R1
Mal'ta-Buret' culture#Relationship to American Indians and Europeans
Haplogroup R1 (Y-DNA) (specially R1b) is the second most predominant Y haplotype found among indigenous Amerindians after Q (Y-DNA). The distribution of R1 is believed by some to be associated with the re-settlement of Eurasia following the last glacial maximum. One theory put forth is that R1 entered the Americas with the initial founding population, suggesting prehistoric Amerindian immigration from Asia through Beringia and correlating mostly with the frequency of haplogroups Q-M3 and P-M45*. A second theory is that it was introduced during European colonization. R1 is very common throughout all of Eurasia except East Asia and Southeast Asia. R1 (M173) is found predominantly in North American groups like the Ojibwe (50-79%), Seminole (50%), Sioux (50%), Cherokee (47%), Dogrib (40%) and Tohono O'odham (Papago) (38%).
A study of Raghavan et al. 2013 found that autosomal evidence indicates that skeletal remain of a south-central Siberian child carrying R* y-dna (Mal'ta boy-1) "is basal to modern-day western Eurasians and genetically closely related to modern-day Amerindians, with no close affinity to east Asians. This suggests that populations related to contemporary western Eurasians had a more north-easterly distribution 24,000 years ago than commonly thought." Sequencing of another south-central Siberian (Afontova Gora-2) revealed that "western Eurasian genetic signatures in modern-day Amerindians derive not only from post-Columbian admixture, as commonly thought, but also from a mixed ancestry of the First Americans." It is further theorized if "Mal'ta might be a missing link, a representative of the Asian population that admixed both into Europeans and Native Americans."
Haplogroup C-P39
Haplogroup C-M217 is mainly found in indigenous Siberians, Mongolians and Kazakhs. Haplogroup C-M217 is the most widespread and frequently occurring branch of the greater (Y-DNA) haplogroup C-M130. Haplogroup C-M217 descendant C-P39 is commonly found in today's Na-Dené speakers, with the highest frequency found among the Athabaskans at 42%. This distinct and isolated branch C-P39 includes almost all the Haplogroup C-M217 Y-chromosomes found among all indigenous peoples of the Americas. The Na-Dené groups are also unusual among indigenous peoples of the Americas in having a relatively high frequency of Q-M242 (25%).
Some researchers feel that this may indicate that the Na-Dené migration occurred from the Russian Far East after the initial Paleo-Indian colonization, but prior to modern Inuit, Inupiat and Yupik expansions.
mtDNA
Mitochondrial Eve is defined as the woman who was the matrilineal most recent common ancestor for all living humans. Mitochondrial Eve is estimated to have lived between 140,000 and 200,000 years ago, Mitochondrial Eve is the most recent common matrilineal ancestor, not the most recent common ancestor.
When studying human mitochondrial DNA (mtDNA) haplogroups, the results indicated until recently that Indigenous Amerindian haplogroups, including haplogroup X, are part of a single founding east Asian population. It also indicates that the distribution of mtDNA haplogroups and the levels of sequence divergence among linguistically similar groups were the result of multiple preceding migrations from Bering Straits populations. All Indigenous Amerindian mtDNA can be traced back to five haplogroups, A, B, C, D and X. More specifically, indigenous Amerindian mtDNA belongs to sub-haplogroups A2, B2, C1, D1, and X2a (with minor groups C4c, D2, D3, and D4h3). This suggests that 95% of Indigenous Amerindian mtDNA is descended from a minimal genetic founding female population, comprising sub-haplogroups A2, B2, C1b, C1c, C1d, and D1. The remaining 5% is composed of the X2a, D2, D3, C4, and D4h3 sub-haplogroups.
X is one of the five mtDNA haplogroups found in Indigenous Amerindian peoples. Unlike the four main American mtDNA haplogroups (A, B, C and D), X is not at all strongly associated with east Asia. Haplogroup X genetic sequences diverged about 20,000 to 30,000 years ago to give two sub-groups, X1 and X2. X2's subclade X2a occurs only at a frequency of about 3% for the total current indigenous population of the Americas. However, X2a is a major mtDNA subclade in North America; among the Algonquian peoples, it comprises up to 25% of mtDNA types. It is also present in lower percentages to the west and south of this area — among the Sioux (15%), the Nuu-chah-nulth (11%–13%), the Navajo (7%), and the Yakama (5%). Haplogroup X is more strongly present in the Near East, the Caucasus, and Mediterranean Europe. The predominant theory for sub-haplogroup X2a's appearance in North America is migration along with A, B, C, and D mtDNA groups, from a source in the Altai Mountains of central Asia.
Sequencing of the mitochondrial genome from Paleo-Eskimo remains (3,500 years old) are distinct from modern Amerindians, falling within sub-haplogroup D2a1, a group observed among today's Aleutian Islanders, the Aleut and Siberian Yupik populations. This suggests that the colonizers of the far north, and subsequently Greenland, originated from later coastal populations. Then a genetic exchange in the northern extremes introduced by the Thule people (proto-Inuit) approximately 800–1,000 years ago began. These final Pre-Columbian migrants introduced haplogroups A2a and A2b to the existing Paleo-Eskimo populations of Canada and Greenland, culminating in the modern Inuit.
A 2013 study in Nature reported that DNA found in the 24,000-year-old remains of a young boy from the archaeological Mal'ta-Buret' culture suggest that up to one-third of the indigenous Americans may have ancestry that can be traced back to western Eurasians, who may have "had a more north-easterly distribution 24,000 years ago than commonly thought" "We estimate that 14 to 38 percent of Amerindian ancestry may originate through gene flow from this ancient population," the authors wrote. Professor Kelly Graf said,
"Our findings are significant at two levels. First, it shows that Upper Paleolithic Siberians came from a cosmopolitan population of early modern humans that spread out of Africa to Europe and Central and South Asia. Second, Paleoindian skeletons like Buhl Woman with phenotypic traits atypical of modern-day indigenous Americans can be explained as having a direct historical connection to Upper Paleolithic Siberia."
A route through Beringia is seen as more likely than the Solutrean hypothesis. An abstract in a 2012 issue of the "American Journal of Physical Anthropology" states that "The similarities in ages and geographical distributions for C4c and the previously analyzed X2a lineage provide support to the scenario of a dual origin for Paleo-Indians. Taking into account that C4c is deeply rooted in the Asian portion of the mtDNA phylogeny and is indubitably of Asian origin, the finding that C4c and X2a are characterized by parallel genetic histories definitively dismisses the controversial hypothesis of an Atlantic glacial entry route into North America."
Another study, also focused on the mtDNA (that which is inherited only through the maternal line), revealed that the indigenous people of the Americas have their maternal ancestry traced back to a few founding lineages from East Asia, which would have arrived via the Bering strait. According to this study, it is probable that the ancestors of the Native Americans would have remained for a time in the region of the Bering Strait, after which there would have been a rapid movement of settling of the Americas, taking the founding lineages to South America.
According to a 2016 study, focused on mtDNA lineages, "a small population entered the Americas via a coastal route around 16.0 ka, following previous isolation in eastern Beringia for ~2.4 to 9 thousand years after separation from eastern Siberian populations. Following a rapid movement throughout the Americas, limited gene flow in South America resulted in a marked phylogeographic structure of populations, which persisted through time. All of the ancient mitochondrial lineages detected in this study were absent from modern data sets, suggesting a high extinction rate. To investigate this further, we applied a novel principal components multiple logistic regression
test to Bayesian serial coalescent simulations. The analysis supported a scenario in which European colonization caused a substantial loss of pre-Columbian lineages".
AtDNA
Genetic diversity and population structure in the American landmass is also done using autosomal (atDNA) micro-satellite markers genotyped; sampled from North, Central, and South America and analyzed against similar data available from other indigenous populations worldwide. The Amerindian populations show a lower genetic diversity than populations from other continental regions. Observed is a decreasing genetic diversity as geographic distance from the Bering Strait occurs, as well as a decreasing genetic similarity to Siberian populations from Alaska (the genetic entry point).
Also observed is evidence of a higher level of diversity and lower level of population structure in western South America compared to eastern South America. There is a relative lack of differentiation between Mesoamerican and Andean populations, a scenario that implies that coastal routes were easier for migrating peoples (more genetic contributors) to traverse in comparison with inland routes.
The over-all pattern that is emerging suggests that the Americas were colonized by a small number of individuals (effective size of about 70), which grew by a factor of 10 over 800 – 1000 years. The data also shows that there have been genetic exchanges between Asia, the Arctic, and Greenland since the initial peopling of the Americas.
In 2014, the autosomal DNA of a 12,500+-year-old infant from Montana was sequenced. The DNA was taken from a skeleton referred to as Anzick-1, found in close association with several Clovis artifacts. Comparisons showed strong affinities with DNA from Siberian sites, and virtually ruled out that particular individual had any close affinity with European sources (the "Solutrean hypothesis"). The DNA also showed strong affinities with all existing Amerindian populations, which indicated that all of them derive from an ancient population that lived in or near Siberia, the Upper Palaeolithic Mal'ta population.
According to an autosomal genetic study from 2012, Native Americans descend of at least three main migrant waves from East Asia. Most of it is traced back to a single ancestral population, called 'First Americans'. However, those who speak Inuit languages from the Arctic inherited almost half of their ancestry from a second East Asian migrant wave. And those who speak Na-dene, on the other hand, inherited a tenth of their ancestry from a third migrant wave. The initial settling of the Americas was followed by a rapid expansion southwards, by the coast, with little gene flow later, especially in South America. One exception to this are the Chibcha speakers, whose ancestry comes from both North and South America.
Linguistic studies have backed up genetic studies, with ancient patterns having been found between the languages spoken in Siberia and those spoken in the Americas.
Two 2015 autosomal DNA genetic studies confirmed the Siberian origins of the Natives of the Americas. However an ancient signal of shared ancestry with the Natives of Australia and Melanesia was detected among the Natives of the Amazon region. The migration coming out of Siberia would have happened 23000 years ago.
Overlaps between DNA types
Y-DNA haplogroups in Indigenous peoples of the Americas
Populations that have a specific combination of autosome, Y and MT-haplogroup mutations can generally be found with regional variations. Autosomes, Y mutations and mt mutations do not necessarily occur at a similar time and there are differential rates of sexual selection between the two sex chromosomes. This combined with population bottlenecks, the founder effect, mitochondrial mutations and genetic drift will alter the genetic composition of isolated populations, resulting in very distinguishable mutation patterns. (i.e. Taínos, Fuegians, Inuit, Yupik and Algonquian)
The rough overlaps between Y-DNA and mtDNA between the Americas, Circumpolar north, and Siberian indigenous populations are:
Y-DNA haplogroup(s) - mtDNA haplogroup(s) - Geographical area(s)Q-M242, R1, C-M217A, X, C, D(N types), (M types)Russian far east, Americas, Arctic
Old world genetic admixture
Miscegenation#Genetic studies of racial admixture
Interracial marriage and interracial sex and, more generally, the process of racial admixture, has its origins in prehistory. Racial mixing became widespread during European colonialism in the Age of Discovery. Genetic exchange between two populations reduces the genetic distance between the populations and is measurable in DNA patterns. During the Age of Discovery, beginning in the late 15th century, European explorers sailed the oceans, eventually reaching all the major continents. During this time Europeans contacted many populations, some of which had been relatively isolated for millennia. The genetic demographic composition of the Eastern Hemisphere has not changed significantly since the Age of Discovery. However, genetic demographics in the Western Hemisphere were radically altered by events following the voyages of Christopher Columbus. The European colonization of the Americas brought contact between peoples of Europe, Africa and Asia and the Amerindian populations. As a result, the Americas today have significant and complex multiracial populations. Many individuals who self-identify as one race exhibit genetic evidence of a multiracial ancestry.
The European conquest of Latin America beginning in the late 15th century, was initially executed by male soldiers and sailors from the Iberian Peninsula (Spain and Portugal). The new soldier-settlers fathered children with Amerindian women and later with African slaves. These mixed-race children were generally identified by the Spanish colonist and Portuguese colonist as "Castas". The subsequent North American fur trade during the 16th century brought many more European men, from France, Ireland, and Great Britain, who took North Amerindian women as wives. Their children became known as "Métis" or "Bois-Brûlés" by the French colonists and "mixed-bloods", "half-breeds" or "country-born" by the English colonists and Scottish colonists. From the second half of the 19th century to the beginning of the 20th century, new waves of immigrants from northern, eastern and southern Europe went to the Americas and consequently altered the demographics. Following World War II and subsequent worldwide migrations, the current American populations' genetic admixture can be traced to all corners of the world.
Blood groups
Prior to the 1952 confirmation of DNA as the hereditary material by Alfred Hershey and Martha Chase, scientists used blood proteins to study human genetic variation. The ABO blood group system is widely credited to have been discovered by the Austrian Karl Landsteiner, who found three different blood types in 1900. Blood groups are inherited from both parents. The ABO blood type is controlled by a single gene (the ABO gene) with three alleles: i, IA, and IB.
Research by Ludwik and Hanka Herschfeld during World War I found that the frequencies of blood groups A,B and O differed greatly from region to region. The "O" blood type (usually resulting from the absence of both A and B alleles) is very common around the world, with a rate of 63% in all human populations. Type "O" is the primary blood type among the indigenous populations of the Americas, in-particular within Central and South America populations, with a frequency of nearly 100%. In indigenous North American populations the frequency of type "A" ranges from 16% to 82%. This suggests again that the initial Amerindians evolved from an isolated population with a minimal number of individuals.
+Distribution of ABO blood types in various modern Indigenous Amerindian populationsTest results as of 2008 PEOPLE GROUP O (%) A (%) B (%) AB (%) Blackfoot Confederacy (N. American Indian) 17 82 0 1 Bororo (Brazil) 100 0 0 0 Eskimos (Alaska) 38 44 13 5 Inuit (Eastern Canada & Greenland) 54 36 23 8 Hawaiians 37 61 2 1 Indigenous North Americans (as a whole Native Nations/First Nations) 79 16 4 1 Maya (modern) 98 1 1 1 Navajo 73 27 0 0 Peru 100 0 0 0
Genealogical testing
A genealogical DNA test examines the nucleotides at specific locations on a person's DNA for genetic genealogy purposes. The test results are not meant to have any medical value; they are intended only to give genealogical information. Genealogical DNA tests generally involve comparing the results of living individuals to historic populations. The general procedure for taking a genealogical DNA test involves taking a painless cheek-scraping (also known as a buccal swab) at home and mailing the sample to a genetic genealogy laboratory for testing. Genetic testing results showing specific sub-Haplogroups of Q, R1 and C3b implies that the individuals ancestry is, in whole or in-part, indigenous to the Americas. If one's mtDNA belonged to specific sub-Haplogroups of, A, B, C, D or X2a, the implication would be that the individual's ancestry is, in whole or part, indigenous to the Americas.
See also
Indigenous peoples of North America
Archaeology of the Americas
Archaeogenetics Ancient DNA Clovis culture Early human migrations
Haplogroups of historical and famous figures
Race and genetics
Y-chromosome haplogroups by populations
Archaeogenetics of the Near East
Genetics and archaeogenetics of South Asia
Genetic history of Africa
Genetic history of Europe
Genetic history of Italy
Genetic history of North Africa
Genetic history of the British Isles
Genetic history of the Iberian Peninsula
References Further reading
American Indian mtDNA, Y chromosome genetic data, and the peopling of North America https://books.google.com/?id=FKmlyhxhw3sC&printsec=frontcover&dq=American+Indian++Genetic+Data#v=onepage&q&f=false
The first Americans: race, evolution, and the origin of Native Americans https://books.google.com/books?id=Xwx6WQaoTJkC&pg=PP1
The evolution and genetics of Latin American populations https://books.google.com/books?id=aw-jLSUlUUcC&pg=PP1
External links
Atlas of the Human Journey, Genographic Project, National Geographic
Journey of Mankind – Genetic Map – Bradshaw Foundation
An mtDNA view of the peopling of the world by Homo sapiens Cambridge DNA's
World Haplogroups Maps (2005) – University of Illinois
Learn about Y-DNA Haplogroup Q – Genebase Systems
Learn about Y-DNA Haplogroup R1 – Genebase Systems
Q yDNA Project – International society of genetic genealogy
Eastern Algonquian yDNA Project – FamilyTreeDNA
Documentaries about human migration in generalb
DNA Mysteries – The Search for Adam - by Spencer Wells - National Geographic, 2008 |
Source: Geology of India My Book Shelf Humor Maps Photomicrographs Carbonate Sedimentology Geology and Evolution
Monday, March 18, 2024
Geological Contacts: Angular Unconformity Kaladgi Basin
Remotely India Series #12
Through the Proterozoic Eon, beginning around 2 billion years ago, extensional forces acting on continental crust opened up several sedimentary basins across what is now peninsular India. Crustal blocks subsided along faults and these depressions filled in with sediments deposited in fluvial and shallow marine environments. These basins were long lived, some lasting for more than a billion years.
Sedimentation was not continuous. Pulses of sediment deposition were punctuated by long periods of non deposition. Tectonic movements deformed early deposited piles of sediment. They were uplifted and an extensive basin wide erosional surface formed.
There was then a renewed phase of basin development. Sediment of these successor basins were deposited on tilted and folded older strata. Commonly, these younger packages of sediments are relatively undeformed. They are preserved as mesas and plateaus made up of flat lying strata. This discordance in attitude between two sets of strata separated by a widespread erosion surface is known as an angular unconformity.
In this post I will highlight an angular unconformity from the Kaladgi Basin from north Karnataka, south India. I have used high resolution imagery from Indian Space Research Organization's Cartosat. Imagery is available for browsing and download from
ISRO's Bhuvan 2D web maps.
The first image shows the area around Ramdurg village. The multi-stage history of the basin is readily apparent. The light colored strata exposed along narrow ridges are folded, while the rust brown hills are made up of undeformed sediments. The light toned strata are quartzites of the Bagalkot Group. The brown sandstone which rest on the Bagalkot quartzites are the Badami Group. Standard annotations show the varying dip and strike of the folded Bagalkot sediments. The white cross in grey circle denotes horizontal Badami strata.
Kaladgi Basin history has become clearer based on
recent geochronologic work
by Shilpa Patil Pillai, Kanchan Pande, and Vivek S.Kale. They infer that basin initiation occurred around 1.4 billion years ago. Sedimentation of the Bagalkot Group terminated by 1.2 billion years ago. Movement along major WNW-ESE and tranverse NNE-SSE to NE-SW trending faults deformed the Bagalkot sediments into a series of folds around 1.1 billion years ago. This was followed by uplift and erosion of these folded sediments. Deformation was accompanied by low grade metamorphism of these rocks.
The basin floor subsided again around 900 million years ago initiating deposition of the Badami Group of sediments. The famous cave temples of Badami have been cut out from the lower part of the Badami sedimentary sequence.
The next imagery is a good example on how to recognize the relative timing of deformation events. Arrows point to fracture sets in the Bagalkot quartzites. These lineaments do not extend into the Badami sediments implying that fracturing occurred during an earlier phase of deformation.
Let's look at a location that shows the angular discordance between the Bagalkot and Badami sediments. This is near Shirur town, north of Badami. The lighter toned steeply tilted Bagalkot sediments outcrop as E-W trending narrow ribbons, north of Budanagad village. The brown colored Badami sediments form a more extensive plateau. Since these strata are horizontal, the traces of bedding planes form concentric bands mimicking contour lines.
The final location is just south of Ramdurg village. The unconformity here is a little harder to decipher, but you can make out the tilt of the light colored Bagalkot quartzites, annotated by the standard notation of strike and dip. The quartzites form triangular facets sloping eastwards. Like the previous example, the concentric bands of brown in the adjacent hill indicates that this is the overlying horizontally disposed Badami sandstone.
Many Proterozoic basins of India contain such unconformity bounded sequences. Some more classic examples come from the Chattisgarh, Cuddapah, and Vindhyan basins. These sequences from different basins were not deposited synchronously. Each basin has it own trajectory of sedimentation, deformation, and erosion.
Detailed field mapping, supplemented by absolute dating of rocks wherever possible, is elucidating the complex poly-phase history of Indian Proterozoic sedimentary basins in the context of global continental breakup and reassembly. For arm chair geologists and enthusiasts, easily available web mapping technology makes it possible to join in the excitement of teasing out these terrain's many secrets hiding in plain sight.
Posted by Suvrat Kher at 9:56 PM No comments: Labels: geology , Geology of India , Proterozoic , remote sensing , remotely india , sedimentary basins , web mapping
Monday, March 4, 2024
Links: Earthquake Detectives, Origin Of Life, India Water Act
Reading from the past few weeks-
1)
How earthquake scientists solved the mystery of the last “Big One” in the Pacific Northwest
. The American northwest is a tectonically active region. About 150 km west of the Pacific coast is the Cascadia subduction zone. Here, the Juan de Fuca, Explorer, and Gorda tectonic plates slide underneath the continental plate of North America. Large earthquakes have occurred in the past and will occur in the future.
Reporter Gregor Craige has written a book,
On Borrowed Time: North America’s Next Big Quake,
in which he explores the region's earthquake potential and the cross disciplinary studies that enable scientists to understand past earthquake history as well as the impact a big future earthquake will have.
Canadian Geographic
has shared an abstract from his book. The earthquake puzzle was solved by combining information from tree rings, Native American peoples memories of past events, and Japanese record of tsunamis. It is fascinating reading.
2)
To unravel the origin of life, treat findings as pieces of a bigger puzzle
. Was life's beginnings in a warm little pond or in a deep sea hydrothermal vent? Did lightning provide the energy, did asteroids provide the organic matter? There are many many scenarios that try to provide an explanation to this vexing question.
One of the leading researchers of this field, Nick Lane, and his colleague Joana Xavier, have summarized some of the key arguments and problems of the field in this
tour de force
of science writing. Highly recommended!
3)
Analysis: The Great Indian Water Act Of 2024
.
In more good news for industries, factories and foreign investors, yet another Indian environmental law has been diluted to facilitate “ease of business”
.
Shailendra Yashwant begins his analysis of The Water Amendment (Pollution and Prevention) Act, 2024 Bill on this depressing note. Amendments seek to "rationalize criminal provisions". Polluters can now escape jail time and get away by just paying a fine. All this when climate change and water security is one of the big challenges facing India.
Posted by Suvrat Kher at 9:42 PM No comments: Labels: chemistry , earthquakes , environment , geology , governance , groundwater , life , plate tectonics , pollution
Friday, February 16, 2024
Patterns Of Angiosperms And Insect Evolution
Charles Darwin famously called it an 'ábominable mystery'. He was referring to the sudden appearance and diversification of flowering plants in the Cretaceous fossil record. He noticed that these early fossils resembled modern flowering plants. 'Primitive' or ancestral stages were missing. Today, biologists categorize these as crown and stem representatives of a group.
The first fossil evidence of flowering plants is from 140-130 million year old sediments. These are early types of pollen grains with one aperture (uniaperturate). Triaperturate pollen is found in slightly younger 125 million year old rocks. Towards the end of the early Cretaceous, by around 100 million years ago, flowers, leaves, and other organs appear from several continents representing all the major groups of angiosperms.
The picture below is of an early Cretaceous (~100 million year old) flowering plant from the lotus family. The location is northeast Brazil. There is a remarkable preservation of the whole plant, with connected roots, rhizome, leaves, and aggregate fruit.
Source: William Vieira Gobo et.al. Nature Scientific Reports 2023-
A new remarkable Early Cretaceous nelumbonaceous fossil bridges the gap between herbaceous aquatic and woody protealeans
.
Taking a long view of their evolutionary pattern, angiosperm diversification is structured in three phases. The first phase was a steady expansion through early to late Cretaceous. There was more rapid diversification in late Cretaceous by around 70 million years ago. Enumeration of floral species through the Cretaceous indicate that angiosperms made up about 5% of species in early Cretaceous, increasing to 80% by Maastrichtian times (late Cretaceous). Despite this increase in species numbers, in terms of biomass, angiosperms were still a small component of Cretaceous floras. Their domination of floral communities, including the origin of modern wet tropical forests, began in the Paleogene (65-24 million years ago) after the end Cretaceous mass extinction. Michael J. Benton, Peter Wilf, and Herve Sauquet have provided a
good overview in New Phytologist
of this pivotal phase of ecosystem change.
These evolutionary changes did not occur in isolation. Throughout the Cretaceous, significant changes were occurring to terrestrial ecosystems, with the origination of many plant and animal groups. This extended phase of ecosystem reorganization is known as the Cretaceous Terrestrial Revolution. Angiosperm diversification is thought to have played a key role in this transformation of land biodiversity, so much so, that the phase from about 100 million years to 50 million years ago is known as the Angiosperm Terrestrial Revolution.
The Cretaceous -Paleogene mass extinction hit angiosperms hard, as well as altering the trajectory of
their evolution. For example, there was a 40% loss of diversity of
flowering plants in Colombia following the mass extinction. But certain
attributes of angiosperms, such as their partnerships with other
organisms, their ability to efficiently capture energy and enhance photosynthetic rates, and an underlying genetic propensity to speciate, resulted in them expanding rapidly in the post extinction landscape. Angiosperm evolution opened up opportunities for a variety of land creatures including insects, spiders, lizards, birds, and mammals,
eventually driving up terrestrial biodiversity to 10 times more as
marine biodiversity.
Paleobiologists are interested in understand the interaction and impact angiosperm diversification could have had on other groups of plants and animals. Of particular interest is the diversification of insects in the Cretaceous and Paleogene.
Modern insect lineages began diversifying by 245 million years ago, long before angiosperms evolved. Gymnosperm and insect communities preserved in amber and sediments show that insects had an intricate relationship with host gymnosperms like cycads, conifers and ginkgoaleans. Insect pollination of gymnosperms predated the origin of angiosperms by at least 100 million years and their fossil record show phases of diversification even when angiosperms were rare.
Did angiosperm evolution also drive a rise in insect diversity?
Pollinator insects particularly would seem to benefit from an abundance
in flowering plants, and if so, what co-evolutionary patterns are
apparent from the fossil record?
David Perise and Fabien Condamine have tackled this question in a new study in
Nature Communications
. I will share this beautifully compiled infographic from the paper that conveys so clearly the patterns of angiosperm and insect diversification through the Cretaceous and Cenozoic.
Digging into published databases, the researchers compiled data on the origination and extinction times of angiosperm and insect families. They then statistically analyzed whether angiosperm and insect origination and extinction times, and pulses of their diversification coincide. Their analysis showed that angiosperms seemed to have played a dual role in insect evolution. They mitigated insect extinction through the Cretaceous and spurred on the origination of new insect groups in the Cenozoic. Besides a broad analysis of insects, they also found that pollinator insects like bees and long proboscid butterflies show a pronounced diversification alongside angiosperm lineages.
The success of angiosperms in the late Cretaceous and Cenozoic coincided with the decline in gymnosperms. Intrinsic mechanisms of genomic rearrangements in angiosperms resulted in repeated evolution of novel traits and specializations. They competitively displaced gymnosperms. The impact on gymnosperm dependent insects was variable. Generalist insect pollinators such as several beetle lineages transitioned to angiosperms. Much of the co-diversification of angiosperm and insects can be explained by this shift of gymnosperm pollinators to angiosperm hosts. Gymnosperm specialized insect groups did not fare that well. For example, gymnosperms like Cheirolepidiaceae and Bennettitales went extinct by the latest Cretaceous. This was followed by the extinction of insect groups that were dependent on these plants such as some specialized long-proboscid flies, scorpionflies and lacewings.
Insect diversification did not depend only on angiosperms. Analysis also shows that warmer climate phases negatively impacted insect diversity and coincided with higher insect extinction rates. There seems also to be a relationship with other plant types. Spore plant and gymnosperm diversity had a positive impact on origination rates of insects. Ecosystem relationships and dependencies are multifarious and complex as this analysis between angiosperm and insect co-evolution shows.
Darwin's anxiety over flowering plants reflected his insistence that evolution is gradual. Nature does not make leaps, he stressed. He explained abruptness in the fossil record by invoking missing strata due to non deposition and erosion. Regarding flowering plants, he suggested that fossils were perhaps preceded by a period of cryptic evolution of that lineage that took place in a remote area or a lost continent, although he conceded that this was a poor explanation. However, this latter view, that a substantial lag time or a long fuse precedes the bang, continues to resonate among many biologists. Molecular methods that compares accumulated genetic difference to calculate the time of divergence of groups indicate a fairly long gap between the genetic branching of lineages and their first fossil appearance.
Most familiar is the example of the origin of animals. Molecular data indicate that animals originated by 750 million years ago, yet unequivocal animal fossils appear by 570 million years ago, close to 200 million years later. Similarly, some molecular estimates put angiosperm origins to pre-Cretaceous times, stretching back 240-200 million years ago to Triassic-Jurassic, a good 100 million to 60 million years before first appearance of fossils.
This idea of a phylogenetic fuse has been recently criticized. Published in
Systematic Biology
, Graham E. Budd and Richard P. Mann have undertaken a critical examination of molecular clock methods. Their analysis indicate that popular methods used to assign probabilities to maximum age of lineages are biased against rapid lineage radiations being true evolutionary events. In their view, the mismatch between molecular dates of lineage origin and the timing of the first appearance of their fossils is an artifact. They point out that the coincident appearance of fossils from widespread localities in a particular sequence and across different modes of preservation faithfully records evolution. The time gap between the origin and later diversification of lineages is not that deep.
The 'abominable mystery' of the sudden appearance of fossil groups may in fact be a real biological motif in earth history, signalling the rapid radiation of lineages filling ecologic spaces following an environmental crises and evolutionary innovation.
Posted by Suvrat Kher at 9:43 PM No comments: Labels: angiosperms , biology , Cenozoic , Cretaceous , Darwin , evolution , fossils , insects , palaeontology
Monday, January 29, 2024
Is It A Lava Tube?
My latest field geology video is about a small cave in the basalt lava near my house in Pune city. The location is Hanuman tekdi, also known as Fergusson College Hill. The cave is along the slope right behind IMDR canteen.
Is the cave a remnant of a lava tube, or has it formed by some other process?
Sound on. Permanent Link -
Fergusson College Hill Cave
.
You can access this cave by walking along the path starting from the main gate of Gokhale Institute of Politics and Economics. Turn left as you approach the hill and after a few steps look up to the right.
Visit quickly. As you can see from this photo, rubble from the construction works of water tanks at the top of the slope is slowly spreading and might cover up this cave. I hope not.
More geology videos soon!
Posted by Suvrat Kher at 8:42 AM No comments: Labels: deccan volcanics , geology , Pune City , science communication , science outreach
Tuesday, January 16, 2024
Deep Pacific Upside Down Waterfall
This passage from Helen Czerski's
Blue Machine: How The Ocean Shapes Our World
gives us a glimpse of the wondrous undersea universe we are just beginning to explore.
"
We see upside-down waterfalls, she says. I don't understand what she means at first, and it takes me a few seconds to process the video as Deb keep talking. In those vertical chimneys, the walls crack and hydrothermal fluids come leaking out and you get something that looks like half a toadstool growing out of a tree in an old growth forest. And suddenly I see it. This is a gigantic hydrothermal chimney looming out of the darkness, and hot water is indeed leaking out of its side. But because hot water is less dense than cold water, the hot water keeps flowing rapidly upwards. When it first hits cold water, its clearly dumped some minerals and made a ledge that sticks out- that's the toadstool shape that Deb is referring to. The water flowing upwards has had to flow outwards underneath the ledge before it can carry on upwards. But the ledge has developed a hollow on its underside like an upside-down bowl, so there is a pool of hot water there, held in the hollow as if it were filling up the inside of an umbrella. The boundary between hot and cold water shimmers like a mirror. And then the hot water is spilling out of its hollow and continuing upwards into the gloom. It really is an upside down waterfall
".
Helen Czerski is watching this footage captured by a remotely operated vehicle exploring the area around the Juan de Fuca Ridge, an undersea mountain chain a few hundred kilometers west of Seattle. Here, the Pacific and the Juan de Fuca tectonic plates diverge. Scientists are closely monitoring this ridge for seismic and volcanic activity, using a network of sensors called the Regional Cabled Array. Deb Kelly is the Director of this project. Hydrothermal chimneys are sulfide and carbonate mineral deposits that form when hot mineral saturated sea water emerges through cracks in the ocean crust. The are common near mid oceanic ridges where the interaction of sea water and rock heated up by magma generates vigorous hydrothermal systems.
I'm only a quarter into this book and am enjoying every page of it. Highly recommended!
Posted by Suvrat Kher at 10:11 PM No comments: Labels: books , geochemistry , my book shelf , oceanic crust , oceanography , volcanism Older Posts Home Subscribe to: Posts (Atom) AUTHOR CONTACT suvrat_k@yahoo.com SUBSCRIBE VIA EMAIL Follow @rapiduplift ABOUT THIS BLOG Suvrat Kher
I am a Sedimentary Geologist. On Rapid Uplift I write mostly about topics within the geosciences, but sometimes on biological evolution and environmental issues.
View my complete profile
IN YOUR LANGUAGE ARCHIVES ▼ 2024 (7) ▼ March (2)
Geological Contacts: Angular Unconformity Kaladgi ...
Links: Earthquake Detectives, Origin Of Life, Indi...
► February (1) ► January (4) ► 2023 (26) ► December (2) ► November (2) ► October (2) ► September (2) ► August (2) ► July (3) ► June (2) ► May (3) ► April (3) ► March (1) ► February (1) ► January (3) ► 2022 (25) ► December (2) ► November (2) ► October (1) ► September (1) ► August (2) ► July (2) ► June (2) ► May (3) ► April (3) ► March (2) ► February (3) ► January (2) ► 2021 (32) ► December (2) ► November (2) ► October (4) ► September (2) ► August (3) ► July (4) ► June (4) ► May (5) ► April (1) ► March (1) ► February (2) ► January (2) ► 2020 (32) ► December (2) ► November (3) ► October (4) ► September (3) ► August (3) ► July (3) ► June (3) ► May (2) ► April (1) ► March (3) ► February (4) ► January (1) ► 2019 (33) ► December (2) ► November (3) ► October (3) ► September (4) ► August (4) ► July (3) ► June (3) ► May (2) ► April (2) ► March (2) ► February (2) ► January (3) ► 2018 (35) ► December (3) ► November (3) ► October (2) ► September (3) ► August (2) ► July (4) ► June (3) ► May (3) ► April (3) ► March (3) ► February (3) ► January (3) ► 2017 (41) ► December (3) ► November (3) ► October (3) ► September (3) ► August (4) ► July (4) ► June (4) ► May (3) ► April (4) ► March (3) ► February (3) ► January (4) ► 2016 (51) ► December (3) ► November (4) ► October (4) ► September (5) ► August (6) ► July (4) ► June (4) ► May (5) ► April (4) ► March (3) ► February (4) ► January (5) ► 2015 (52) ► December (4) ► November (4) ► October (5) ► September (4) ► August (4) ► July (5) ► June (3) ► May (5) ► April (4) ► March (4) ► February (6) ► January (4) ► 2014 (38) ► December (3) ► November (2) ► October (3) ► September (4) ► August (3) ► July (3) ► May (4) ► April (4) ► March (6) ► February (1) ► January (5) ► 2013 (72) ► December (5) ► November (5) ► October (6) ► September (5) ► August (6) ► July (5) ► June (7) ► May (7) ► April (8) ► March (6) ► February (5) ► January (7) ► 2012 (85) ► December (5) ► November (5) ► October (8) ► September (7) ► August (9) ► July (6) ► June (5) ► May (8) ► April (7) ► March (7) ► February (9) ► January (9) ► 2011 (87) ► December (6) ► November (6) ► October (9) ► September (9) ► August (3) ► July (6) ► June (7) ► May (7) ► April (9) ► March (9) ► February (7) ► January (9) ► 2010 (107) ► December (8) ► November (8) ► October (6) ► September (8) ► August (5) ► July (5) ► June (9) ► May (11) ► April (14) ► March (13) ► February (8) ► January (12) ► 2009 (130) ► December (10) ► November (11) ► October (10) ► September (14) ► August (11) ► July (10) ► June (12) ► May (12) ► April (10) ► March (11) ► February (10) ► January (9) ► 2008 (97) ► December (8) ► November (10) ► October (9) ► September (9) ► August (8) ► July (8) ► June (6) ► May (8) ► April (7) ► March (8) ► February (8) ► January (8) ► 2007 (49) ► December (7) ► November (5) ► October (8) ► September (10) ► August (19)
WHAT I'M WRITING ABOUT
biodiversity books carbonates climate change creationism Darwin deccan volcanics earthquakes education environment evolution field work fossils geo-lit geochemistry geohazards
geological processes and evolution
geology geology and livelihoods GIS global warming groundwater himalayas historical events human evolution human migrations humour hydrocarbon resources mapping india maps mass extinction media metazoans mineralogy my book shelf natural gas natural selection palaeontology people and personalities plate tectonics pseudo-science public domain Pune City remote sensing research Science and Society science outreach sea-levels sedimentary basins stratigraphy water resources web mapping GEOBLOGOSPHERE FEED Loading... PAGE VISITS Powered by Blogger . |